EPA
United States
Environmental Protection
Agency
EPA/600/R-08/131 | January 2010 | www.epa.gov/ncea
Stressor Identification in an
Agricultural Watershed:
Little Floyd River, Iowa
National Center for Environmental Assessment
Office of Research and Development, Washington, DC 20460
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EPA/600/R-08/131
January 2010
Stressor Identification in an
Agricultural Watershed:
Little Floyd River, Iowa
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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NOTICE
The Iowa Department of Natural Resources and the U.S. Environmental
Protection Agency through its Office of Research jointly prepared this report. It has
been subjected to the Agency's peer and administrative review and has been approved
for publication as an EPA document. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
ABSTRACT
In Iowa, the use of the stressor identification (SI) protocol was prompted by
stream impairments of the fish and benthic macroinvertebrate communities. The Little
Floyd River was included on the 1998 303(d) list of impaired waterbodies based on a
1990 stream-use assessment. At that time, no fish were observed and only
pollution-tolerant benthic macroinvertebrate species were present. Fish have since
recolonized the stream.
The Little Floyd River is a third-order, warm-water stream located in the
Northwest Iowa Loess Prairies Ecoregion. Land use in the watershed is dominated by
row-crop agriculture and livestock production. Candidate causes for this biological
impairment included flow alteration, substrate alteration, turbidity, altered basal food
source, low dissolved oxygen concentrations, high temperature, and high ammonia
concentrations.
The Iowa Department of Natural Resources (IDNR) characterized the impairment
of the stream using chemical and biological samples, as well as observations of the
physical habitat collected at four sites over the course of four years. The evidence was
reanalyzed by comparing data among the four sites using a less impaired comparator
site within the Little Floyd to determine the co-occurrence of stressors with benthic
macroinvertebrates and fish. Other types of evidence used in the case were complete
causal pathway, stressor response from other field studies, and stressor-response
studies from laboratory data and other studies. IDNR identified the primary probable
causes of biological impairment as deposited sediment and low dissolved oxygen.
Based on the original SI completed by the IDNR, total maximum daily load (TMDL) for
sediment and dissolved oxygen were submitted to and approved by the U.S.
Environmental Protection Agency in 2005.
Preferred citation:
Haake, D.T. Wilton; K. Krier, T. Isenhart, J. Paul, A. Stewart, and S. M.Cormier. 2010. Stressor
Identification in an Agricultural Watershed: Little Floyd River, Iowa. U.S. Environmental Protection Agency,
National Center for Environmental Assessment, Cincinnati, OH. EPA/600/R-08/131.
Cover photo:
Photo taken by IDNR in 2001 at Floyd River at station 3.
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TABLE OF CONTENTS
Page
NOTICE ii
ABSTRACT ii
LIST OF TABLES v
LIST OF FIGURES vi
LIST OF ABBREVIATIONS vii
PREFACE viii
AUTHORS, CONTRIBUTORS AND REVIEWERS x
ACKNOWLEDGMENTS xii
1. DEFINITION OF THE CASE 1
1.1. REGULATORY CONTEXT FOR THE CASE 1
1.2. DESCRIPTION OF THE RIVER AND WATERSHED 2
1.3. SPECIFIC BIOLOGICAL IMPAIRMENT 5
1.4. SELECTION OF COMPARATOR SITE 7
2. LIST THE CANDIDATE CAUSES 11
2.1. IOWA STANDARDIZED LIST OF CANDIDATE CAUSES 11
2.1.1. Candidate Causes Deferred 11
2.1.2. Candidate Causes Analyzed 12
3. EVALUATE DATA FROM THE CASE 20
3.1. SOURCES OF DATA FROM THE CASE 20
3.2. EVALUATION OF DATA FROM THE CASE 20
3.2.1. Spatial/Temporal Cooccurrence 20
3.2.2. Causal Pathway 21
4. EVALUATE DATA FROM ELSEWHERE 26
4.1. SOURCES OF DATA FROM OUTSIDE THE CASE 26
4.2. EVALUATION OF DATA FROM OUTSIDE THE CASE 26
4.2.1. Stressor-Response Relationships from Other Field Studies 26
4.2.2. Stressor-Response from Laboratory and Other Studies 27
4.2.2.1. Dissolved Oxygen (+) 27
4.2.2.2. Temperature (+) 33
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TABLE OF CONTENTS cont.
4.2.2.3. Ammonia (+) 34
5. IDENTIFY THE PROBABLE CAUSES 35
5.1. PROBABLE PRIMARY CAUSES 37
5.1.1. Deposited Sediment 37
5.1.2. Low DO 38
5.2. PROBABLE SECONDARY CAUSES 39
5.2.1. High Temperature/Temperature Flux 39
5.2.2. Ammonia 40
5.3. UNSUPPORTED CAUSES 41
5.3.1. Altered Flow Regime 41
5.3.2. Suspended Sediment 41
5.3.3. Altered Basal Food Source 42
6. DISCUSSION AND HIGHLIGHTS 43
6.1. FROM SITOTMDL 43
6.2. UNCERTAINTIES 43
6.3. FUTURE PROJECTS 44
6.4. CONCLUSION 45
7. REFERENCES 46
APPENDIX A STATE OF IOWA METHODOLOGY 48
APPENDIX B DATA SUMMARY 54
APPENDIX C ANALYSIS OF EVIDENCE TABLES 69
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LIST OF TABLES
No. Title Page
1 Metrics Used for Iowa's Fish and Benthic Macroinvertebrate Indices.
Macroinvertebrate metrics are based on either multihabitat samples (MH)
or standard-habitat samples (SH) 6
2 Index of Biotic Integrity Scores for Fish (FIBI) and Benthic
Macroinvertebrates (BMIBI) in the Little Floyd River. Highlighted cells
meet state biological criteria, others do not 7
3 Evidence of Spatial/Temporal Co-occurrence in the Little Floyd River,
Iowa 22
4 Stressor-response from Other Field Studies for Candidate Causes in the
Little Floyd River, Iowa 28
5 Summary of Violations of Iowa's Water Quality Standard for DO in the
Little Floyd River 33
6 Strength of Evidence Tables for Little Floyd River 36
7 Details of Several Habitat Metrics for Deposited Fine Sediment 37
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LIST OF FIGURES
No. Title Page
1 The Watershed of the Little Floyd River, Showing the Locations of the
Impaired Segment, Bioassessment Sites, Livestock Operations, and
Urban Areas 3
2 Land Uses in the Little Floyd River Watershed Based on 2002 Satellite
Imagery 4
3 Discharge Measured in the Little Floyd River at Site 4 in 2001 5
4 Invertebrate metrics at four sites along the Little Floyd River 8
5 Fish Metrics at Four Sites Along the Little Floyd River (CPUE—Catch per
Unit Effort) 10
6 Conceptual Model for Altered Flow Regime Showing Evidence for and
Against the Stressors and Steps in the Pathway 14
7 Conceptual Model for Increased Sediment Showing Evidence for and
Against the Stressors and Steps in the Pathway 15
8 Conceptual Model for Altered Basal Food Source Showing Evidence for
and Against the Stressors and Steps in the Pathway 16
9 Conceptual Model for Decreased Dissolved Oxygen Showing Evidence for
and Against the Stressors and Steps in the Pathway 17
10 Conceptual Model for Increased Temperature Showing Evidence for and
Against the Stressors and Steps in the Pathway 18
11 Conceptual Model for Increased Ammonia Showing Evidence for and
Against the Stressors and Steps in the Pathway 19
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BMIBI
CBOD
CPUE
DELT
DO
EPT
FFG
FIBI
GPP
IAC
IDNR
P:R
REMAP
SI
TDS
TMDL
TSS
UHL
U.S. EPA
WQC
VWVTP
LIST OF ABBREVIATIONS
Benthic Macroinvertebrate Index of Biotic Integrity
carbonaceous biochemical oxygen demand
catch per unit effort
deformities, eroded fins, lesions, and tumors
dissolved oxygen
phylogenetic Orders Ephemeroptera, Plecoptera and Trichoptera
functional feeding group
Fish Index of Biotic Integrity
gross primary production
Iowa Administrative Code
Iowa Department of Natural Resources
production-to-respiration ratio
Regional Environmental Monitoring and Assessment Program
stressor identification
total dissolved solids
total maximum daily load
total suspended solids
University of Iowa Hygienic Laboratory
U.S. Environmental Protection Agency
water quality criteria
wastewater treatment plant
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PREFACE
This is a screening causal assessment of a biologically impaired stream in the
state of Iowa. The case was investigated by the Iowa Department of Natural Resources
(IDNR) after the Little Floyd River was listed as impaired on 303d lists and identified as
requiring a determination of the total maximum daily load (TMDL) of the unknown
pollutants causing the biological impairment. For this document, the causal analysis
was restructured from the original TMDL (IDNR, 2005c) during a workshop at Canaan
Valley, West Virginia in May of 2005 and in subsequent discussions. One difference
from the original TMDL assessment is that comparisons are made within the Little Floyd
River to a "less impaired" comparator site. The sampling, analysis, and conclusions are
those of researchers who were employed by the IDNR. Comments appearing in text
boxes were prepared by NCEA except where noted. NCEA provided editorial and
formatting assistance to make the original IDNR report similar to four other case studies
that were solicited as examples for practitioners of causal assessment. The reports and
methods are posted on the Causal Analysis and Diagnosis Decision Information System
EPA Website (www.epa.gov/caddis).
The Floyd River case study is one of five causal analyses that were completed
prior to 2005 by states. These cases were used to support state programs that required
that the probable cause of a biological impairment be determined. Data for these cases
were not collected as a part of an investigation. Rather, most data were collected
during routine monitoring done by the state or by other agencies for other purposes. It
is common that these are the type of data upon which state agencies base their
determinations. Resources for additional sampling are often unavailable. In fact, some
reviewers commented that the data for the Little Floyd River case study was greater
than what is typically available in many other situations. And yet, IDNR developed
evidence to show that some causes co-occurred with the biological impairment, were a
part of a larger causal chain of events, occurred at sufficient levels known to cause the
observed effects, and were due to physical interactions that occurred after the
introduction of stressors associated with land cover/land use changes following
settlement. Although the amount and quality available evidence was not equivalent in
for all candidate causes, it was enough to identify some probable causes and to suggest
what additional, targeted data might greatly improve the confidence in the
determination.
These cases, as all cases, could be improved but represent the state of the
capability and analysis that was available in 2005. Since then, additional analytical
tools and databases have become more readily available; and states, tribes and
territories continue to reduce the uncertainty of the analysis. All of these case studies
from the Canaan Valley Workshop defined the impairment based on a biological index
rather than more specific impairments. This practice diminishes the ability to detect
associations because summing the metrics dampens the overall signal from individual
metrics and species that are responding differently to environmental conditions or
stressors.
viii
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To address these and other issues, comment boxes have been inserted
throughout the Little Floyd River case study to supply commentary or to suggest other
approaches that could strengthen the case. The analyses in the cases cannot be
modified as they are already a part of the Iowa's public record. It is our intention to link
the case studies to relevant tools and guidance on the EPA website:
www.epa.gov/caddis.
Overall, the case study of the Little Floyd presents a very realistic example of the
difficulties of assigning specific cause to biological impairment. The Little Floyd Case
Study is a good example of several strategic techniques to use when data are collected
in different years, when the discrimination between acceptable streams and impaired
streams is small, and when multiple stressors affect a stream's biological condition.
Highlights include:
1. Defining the scope of the study based on different types of biological impairment
(fish kill versus low biological index score).
2. Rationales for differentiating between deferred causes due to insufficient data or
practical consideration and elimination of causes on the bases of logical
implausibility.
3. Using limited data and data collected in different years.
4. Using encountered data that were developed for purposes other than causal
analysis.
5. Using intermediate stressors to evaluate the causal pathways leading to the
proximate causes.
6. Differential comparisons of sections of river using an internal comparator site and
to regional reference sites. However, proper classification to account for natural
variation needs to be an integral part of this process.
7. Assessment of a highly modified river in the agricultural Midwest.
Editor: Susan M. Cormier January 2010
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
AUTHORS
Danelle Haake
Iowa Department of Natural Resources
Des Moines, IA 50319
Current Affiliation:
Litzsinger Road Ecology Center;
9711 Litzsinger Road Ladue, MO 63I24, USA.
314-961-4410 (phone); 314-961-6825 (fax)
danelle.haalie@mobot.org
Tom Wilton
Water Monitoring and Assessment Section; Iowa Department of Natural Resources
502 East 9th Street; Des Moines, IA 50319-0034
515-281-8867(phone); 515-281-8895 (fax)
tom.wilton@dnr.iowa.gov;
Ken Krier
Water Monitoring and Assessment Section; Iowa Department of Natural Resources
502 East 9th Street; Des Moines, IA 50319-0034
3515-242-5184(phone); 515-281-8895 (fax)
ken.krier@dnr.state.ia.us
U.S. EPA EDITOR
Susan M. Cormier, Ph.D.
U.S. EPA, Office of Research and Development
Cincinnati, OH 45268
CONTRIBUTORS
Tom Isenhart
Iowa State University
Ames, IA 50011
John Paul
U.S. EPA, Office of Research and Development
Research Triangle Park, NC 27709
Athur J. Stewart
Oak Ridge Associated Universities
Oak Ridge, TN 37830
(865) 576-2312 (phone); (865) 574-4528 (fax)
arthur.stewart@orau.org
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AUTHORS, CONTRIBUTORS AND REVIEWERS cont.
REVIEWERS
Don A. Essig, M.S.
Idaho Department of Environmental Quality
Boise, ID 83706
Marian Maas, Ph.D.
Private Consultant
Bellevue, NE 68123
Patrick A. O'Brien
Nebraska Department of Environmental Quality
Lincoln, NE 60509
EPA Reviewers
Evan Hornig
U.S. Environmental Protection Agency
Office of Water
Office of Science and Technology
Washington, DC 20460
Robert Spehar
U.S. Environmental Protection Agency
Office of Research and Development
National Health and Environmental Effects Research Laboratory
Mid-Continent effects Research Laboratory
6201 Congdon Blvd.
Duluth, MN 55804
Glenn Suter II
U.S. Environmental Protection Agency
Office of Research and Development
National Center for Environmental Assessment
Cincinnati, OH 45268
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ACKNOWLEDGMENTS
We wish to thank Marian Maas for her support of the use of the stressor
identification (SI) protocol in Iowa; Jerry Neppel, Jennifer Ender, and Jamie Mootz for
their contributions in the collection and processing of data for IDNR's original SI; and the
crew from the University of Iowa Hygienic Laboratory who continue to spend countless
hours collecting data, analyzing samples, and identifying aquatic organisms for IDNR.
xii
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1. DEFINITION OF THE CASE
1.1. REGULATORY CONTEXT FOR THE CASE
In Iowa, the 1998 303(d) list identified impaired water bodies that were required
to have a total maximum daily load (TMDL) report completed by a specified time, as
stipulated in a U.S. Environmental Protection Agency (U.S. EPA) consent decree.
Several of the waterbodies on the 1998 list were included based on biological
impairments due to "unknown causes" or "unknown toxicity." The Little Floyd River was
among those.
The impairment of the Little Floyd River was identified during a 1990 stream-use
assessment conducted by the Iowa Department of Natural Resources (IDNR). No fish
were observed during that assessment and only pollution-tolerant benthic
macroinvertebrate species were found. At that time, the cause of the biological
impairment was reported as unknown. Follow-up monitoring was conducted in 1999,
2001, and 2002 to quantify the impairment; both fish and benthic macroinvertebrates
were observed in these studies. (See Appendix A for methodology.)
In 2002 and 2004, the IDNR
classified the designated use (Class B
aquatic life) for the stream as "partially
supporting." These 305(b) water quality
assessments were based on low scores
on the Fish Index of Biotic Integrity
(FIBI) and Benthic Macroinvertebrate
Index of Biotic Integrity (BMIBI) (Wilton,
2004) from biological monitoring at
multiple sites in the watershed over the
course of several years. Methods for
305(b) assessments for the State of
Iowa may be found on-line (IDNR,
2005a).
In 2004, the IDNR completed a
stressor identification (SI) for biological
impairments of the Little Floyd River to
identify the causal agents that would
require a TMDL. The IDNR completed
the TMDL report in 2005. One of the
IDNR's major goals was to determine
whether the biological impairment was caused by a pollutant requiring a TMDL or due to
causes that do not require a TMDL, such as physical habitat alteration. Whether or not
pollutant load reductions could correct impairment, IDNR expected that a complete SI
would identify the key causal agents and pathways that would need to be addressed in
Comment 1. What are These Boxes For?
At various points in this document, comments have
been inserted by the U.S. EPA editor and the authors.
These comments are not meant to indicate that the
IDNR causal analysis is in error. The Stressor
Identification (SI) process does not address every
possible option, nor does it provide details on
implementation, so there are many opportunities for
interpretation (U.S. EPA, 2000). The U.S. EPA
encourages states and tribes to improve and interpret
the methodology in ways that are appropriate to their
circumstances. Hence, the comments are meant to
assist other SI users by suggesting alternative
approaches that may be applied to their cases.
By using the SI process, the IDNR sought to
determine the cause of the biological impairment,
which they did without involvement from the U.S.
EPA, and U.S. EPA editor is grateful the IDNR is
willing to share its experience from this case.
Some of the analyses and terminology have been
reformatted to be consistent with the revised U.S.
EPA guidance (2006). The final determination of the
probable cause was unchanged from those found
using the original process as applied by IDNR.
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order to allow the aquatic community to recover to a condition that supports the
designated aquatic life use.
1.2. DESCRIPTION OF THE RIVER AND WATERSHED
The Little Floyd River watershed is located in the Northwest Iowa Loess Prairies
(Ecoregion 47a), a gently undulating plain with a moderate to thick layer of fine loess
soil (Griffith et al., 1994). The Loess Prairie is the highest, driest region of the Western
Corn Belt Plains as it rises to meet the Northern Glaciated Plains of the Dakotas.
Although loess covers most of the broad upland flats, ridges, and slopes, minor glacial
till outcrops occur near the base of some of the side slopes. Silty clay loam soils have
developed on the loess under native tall-grass prairie vegetation.
The Little Floyd River is a warm-water stream with little groundwater contribution.
The water chemistry is typical of other streams within the Western Corn Belt Region: the
water contains relatively high concentrations of dissolved solids, has a slightly alkaline
pH, and has high concentrations of nitrate (see Appendix B, Tables B-1 and B-2).
Located in northwest O'Brien County, the Little Floyd River is a wadeable stream
with a watershed area of 15,780 hectares (39,700 acres) (see Figure 1). The river flows
southwest before joining the Floyd River 3 kilometers (km) southwest of the city of
Sheldon. Annual row-crop agriculture, in a corn-soybean rotation, dominates current
land use in the watershed (see Figure 2). Pastures are located predominantly in
streamside areas that allow livestock direct access to water. In 2004, livestock in the
watershed included approximately 7100 hogs, 2900 cattle, 630 turkeys, and 250
chickens.
Streamflow in the Little Floyd River is very responsive to rainfall and snowmelt;
discharge can fluctuate by one order of magnitude within a few days of storms or
snowmelt (see Figure 3). Annual stream low flows are less than 0.05 m3/s. Extensive
subsurface drainage tile within the watershed exacerbates flow variability. Portions of
the river and tributary streams have been straightened, and almost all of the ephemeral
watercourses have been converted into grass waterways or straightened into open
drainage ditches to facilitate agricultural production.
The only permitted point source in the watershed is the city of Sanborn's
wastewater treatment plant (WWTP). In addition to serving a population of 1350, the
WWTP treats wastewater from a local dairy. The WWTP uses a conventional
activated-sludge treatment process. Following sludge treatment, the effluent moves
through several storage and treatment lagoon cells before discharge. Due to the
storage capacity of these cells, discharge occurs only two or three times per year. The
amount of wastewater was judged to be small compared to hog farm waste applied to
fields adjacent to the river.
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® Bioassessment Sites /\/ Impaired River | | Watershed
a City of Sanborn WWTP /\J Rivers j | County Line
Confinement/Feediot Roads Incorporated City
FIGURE 1
The Watershed of the Little Floyd River, Showing the Locations of the Impaired
Segment, Bioassessment Sites, Livestock Operations, and Urban Areas
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LAND USES
| Rowcrop (88.3%)
Grass/CRP/Hay (8.2%)
Urban/Residential (1.9%)
Pasture (0.9%)
Forest (0.2%)
FIGURE 2
Land Uses in the Little Floyd River Watershed Based on 2002 Satellite Imagery
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TABLE 1
Metrics Used for Iowa's Fish and Benthic Macroinvertebrate Indices. Macroinvertebrate
metrics are based on either multihabitat samples (MH) or standard-habitat samples (SH).
Benthic Macroinvertebrate Index of Biotic Integrity
(BMIBI)
Fish Index of Biotic Integrity (FIBI)
1. Taxa Richness (MH)
1. # Native Fish Species
2. Taxa Richness (SH)
2. # Sucker Species
3. EPT Richness (MH)
3. # Sensitive Species
4. EPT Richness (SH)
4. # Benthic Invertivore Species
5. Sensitive Taxa (MH)
5. % 3 Dominant Fish Species
6. % 3 Dominant Taxa (SH)
6. % Benthic Invertivores
7. Biotic Index (SH)
7. % Omnivores
8. % EPTa (SH)
8. % Top Carnivores
9. % Chironomidae (SH)
9. % Simple Lithophil Spawners
10. % Ephemeroptera (SH)
10. Fish Assemblage Tolerance Index
11.% Scrapers (SH)
11. Adjusted Catch Per Unit Effort
12. % Dominant Functional Feeding Group (SH)
12. % Fish with DELTb
aEPT = Ephemeroptera, Plecoptera, Trichoptera.
bDELT = deformities, eroded fins, lesions, tumors.
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macroinvertebrates in Iowa have been
determined for each level IV ecoregion.
For the Northwest Iowa Loess Prairies
Ecoregion (47a), a FIBI score of less than
40 or a BMIBI score of less than
53 indicates impairment of the aquatic
ecosystem. A site is considered impaired
if the criteria are not met for either the FIBI
or BMIBI. Further details may be found in
Appendix A and in Biological Assessment
of Iowa's Wadeable Streams (Wilton, 2004) (
In the impaired segment of the Little Floyd River, the IDNR conducted biological
assessments at four sites over a 4-year period. Each site was sampled only once.
Table 2 summarizes the resulting FIBI and BMIBI scores. Figure 1 shows the locations
of the assessment sites.
TABLE 2
Index of Biotic Integrity Scores for Fish (FIBI) and Benthic Macroinvertebrates (BMIBI)
in the Little Floyd River. Highlighted cells meet state biological criteria, others do not.
Site
Year
BMIBI
FIBI
Reference Criteria3
53
40
Site 1 (Upstream of Bridge)
1999
41
28
Site 2 (Downstream of Bridge)b
2001
65
39
Site 3 (REMAP Site)
2002
52
33
Site 4 (Downstream Site)
2001
34
41
aCriteria for the Northwest Iowa Loess Prairies ecoregion from Table 6-1 of Biological Assessment of
Iowa's Wadeable Streams (Wilton. 2004).
bBased on the relatively high FIBI and BMIBI scores, Site 2 was selected as representative of
less impaired conditions in the Little Floyd River for fish and macroinvertebrates.
REMAP = Regional Environmental Monitoring and Assessment Program.
1.4. SELECTION OF COMPARATOR SITE
The development of evidence depends on comparisons of the conditions at
impaired locations with conditions at unimpaired or impaired laboratory, field, or
modeled data. Comparisons within the same stream or watershed, from the case,
Comment 3. New Standards.
In 2006, the IDNR updated Iowa's water
quality standards regarding warm-water stream
aquatic life uses. When/if the U.S. EPA
approves these changes, aquatic life use
designations and water quality criteria protection
will expand to a substantially greater number of
stream miles within the Little Floyd River
watershed.
see Comment 3).
7
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provide a different and sometimes strong form of evidence. In this assessment, an
internal comparator site was selected based
on the year of collection, IBI scores, and the
relative location along the stream reach.
Site 2 (a "less-impaired" site) was selected
as a comparator to assess causes of
impairments of the benthic
macro invertebrate and fish assemblages.
Site 2 was sampled in the same year as
Site 4, reducing some year-to-year variation,
Comment 4. The Use of Metrics.
In the initial case, the IDNR selected the
metrics believed to be most representative of
the impairment based on which metrics scored
the lowest at all sites. In future cases, the IDNR
may compare individual metrics at sites in the
impaired segment to the metrics at reference
sites or compare metrics among sites in the
watershed as described here.
and is upstream of Sites 3 and 4 (see Comment 4).
The BMIBI score at Site 2 met Iowa's state biocriterion and was the greatest
score among the four sites sampled in the Little Floyd River. Several invertebrate
metrics within the BMIBI scored higher at Site 2 than at the other three sites (see
Appendix B; Table B-3). These metrics provide insight into the aspects of the
invertebrate community that need improvement. Site 2 has greater total taxa and
Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa in both the multihabitat and
standard-habitat samples than any of the other sample sites (see Figure 4).
Additionally, Site 2 has the greatest metric scores for percent chironomids and percent
scrapers, and the greatest metrics for the percent of individuals from both the top three
dominant taxa and the dominant functional feeding group (FFG). Therefore, Site 2 was
selected to compare to the other three sites on the Little Floyd River that were in poorer
condition based on the BMIBI scores.
~ Site 1
Site 2
g Site 3
~ Site 4
SH EPT taxa
SH %
SH % scraper
chironomid
SH total taxa MH EPT taxa
SH % top 3
dominant
SH %
dominant FFG
FIGURE 4
Invertebrate metrics at four sites along the Little Floyd River. (SH—standard habitat;
MH —multihabitat; EPT—ephemeroptera, plecoptera, trichoptera; FFG—functional
feeding group.)
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Site selection for a fish assemblage comparator was less clear. While Site 4 had
the only FIBI score that met the state biocriterion, Site 2 was selected as a better
internal comparator for two reasons. First, the number of native species and sensitive
species of fish, benthic invertivores, the percent of omnivores and tolerance values all
had the highest scores at Site 2. Second, the remaining fish metrics for Site 2 were
similar to or slightly higher than those for Site 4 with one exception: the adjusted catch
per unit effort (CPUE) at Site 4 was greater than at Site 2 (see Figure 5). This
difference in CPUE is attributed to the proximity of Site 4 to the confluence with the
larger Floyd River and therefore not characteristic of the Little Floyd fish populations
(see Comment 5).
The causal assessment, therefore, is limited to
differential levels of stressors at Site 2 compared to the
other three sites. Since fish metrics were qualitatively
different among all four sites, a second assessment
using metrics to describe the impairment would be
needed to refine the assessment. Also, although a
cause of stress was attributed to both the fish and
benthic macroinvertebrate communities, the mechanism
of action may be different.
Comment 5. Comparator Site.
Clearly identifiable internal
comparator sites and references
sites are not always available.
Some options are to use sites in
nearby tributaries (see
Willimantic Case) or regional
sites (see Touchet and Bogue
Homo Cases). Another novel
approach is to use a site that is
worse, a type of positive
reference, sometime referred to
as a "dirty reference" (see Clear
Fork Case).
9
-------
V
i-
o
o
CO
o
0)
~Site 1
Site 2
Site 3
~Site 4
Native species Sensitive Benthic % top 3
species invertivores abundant
% omnivore Tolerance Adjusted CPUE
index
FIGURE 5
Fish Metrics at Four Sites Along the Little Floyd River (CPUE—Catch per Unit Effort). Note, there were no sensitive
species at Site 1 or Site 3 (see Table B-3).
-------
2. LIST THE CANDIDATE CAUSES
2.1. IOWA STANDARDIZED LIST OF CANDIDATE CAUSES
The candidate causes analyzed for this SI case were selected from a standard
list of causes developed by the IDNR (2004) (see Comment 6). Because the SI process
in Iowa is triggered by listings for biological impairments with unknown causes in the
303(d) list of impaired waters, the causes for the SI are linked to candidate cause
possibilities for the 303(d) list as
described in ADB+, Iowa's 305(b)
assessment database (IDNR, 2005a).
The IDNR standard list is
generalized, but it does identify
subcauses for most of the following
parameters (e.g., arsenic [As] is included
under metals):
• Metals
• Pesticide
• Ammonia
• Salinity
• Other nonmetal toxicant or biological
toxin
• Basal food source alteration
• Exotic/introduced species
• Flow alteration
Comment 6. Nutrients as Intermediate
Stressors.
Nutrients are a contributing cause of algal
growth leading to low dissolved oxygen.
Phosphorous and nitrogen rarely act directly as
toxicants. So, although nutrients are not
identified as a proximate cause, they are part of
the causal pathways for low dissolved oxygen,
ammonia toxicity, and altered basal food source.
Temperature
Dissolved oxygen (DO)
pH
Conductivity/total dissolved
solids (TDS)
Turbidity/total suspended solids
(TSS)
Substrate alteration/increased
sediment
Habitat alteration
2.2. PRELIMINARY EVALUATION PROCESS
Using IDNR's standardized list, each candidate cause was either deferred or
included for in-depth causal analysis (see Comment 7). Some candidate causes were
deferred because preliminary analysis suggested that the exposures were within
acceptable or expected ranges; others were deferred because there was not enough
data to permit a more thorough analysis. By deferring, the IDNR ensured that if the SI
did not determine the stressor or stressors with some certainty, the deferred candidate
causes could be analyzed in greater detail at a later time. Causes were broken down
into subcauses as needed.
2.1.1. Candidate Causes Deferred
Based on a preliminary analysis of Regional Environmental Monitoring and
Assessment Program (REMAP) data from Site 3 (see Appendix B, Table B-4), the IDNR
11
-------
deferred metals as a candidate cause. Of the 10 metals sampled, all were below
detection limits in the water samples and were well below levels of concern in the
sediment. For example, concentrations of arsenic (As) and zinc (Zn) in the sediment
were 2.2 and 38 mg/kg dry weight, respectively. Concentrations in sediment that may
cause concern are 17 mg/kg dry weight for As and 270 mg/kg dry weight for Zn
(Ingersoll et al., 2000).
The IDNR deferred pH as a
candidate cause because the measured
values were consistently between 7.5 and
8.7 (see Appendix B, Table B-1) similar to
pH measured at ecoregion reference sites.
Similarly, conductivity and TDS were
deferred at a screening level because
values for these parameters in the Little
Floyd River were similar to or lower than
those in the ecoregion reference dataset.
The IDNR deferred
exotic/introduced species as a candidate
cause because limited numbers of
common carp (Cyprinus carpio) were the
only nonindigenous aquatic species
collected at any of the sites, and there was
no known mechanism for carp to cause
changes in the aquatic community
observed in the Little Floyd River.
Comment 7. Elimination Versus Deferment.
Many states have found it useful to use an
iterative approach in which the most suspicious
and very uncertain candidate causes are
evaluated first. Other candidate causes are
deferred until such time that the case is
unresolved or that influential causes remain
unidentified.
In the original study of the Little Floyd River,
IDNR "eliminated" rather than "deferred"
candidate causes as described in the U.S. EPA
Stressor Identification Guidance of 2000.
However, the U.S. EPA intended elimination to
be used for only those candidate causes with
irrefutable evidence of impossible exposure, for
example, the effect was present before the
candidate cause. In reality, such strong
evidence is rarely available. Recognizing the
benefits of an iterative analysis and retaining the
distinction of very strong evidence, the U.S. EPA
has clarified its guidance so that elimination of
causes can be used as well as a "softer"
exclusion in which the assessment of the
candidate cause is "deferred." See Finalize List
on the bottom Step 2.2 on the CADDIS website.
The U.S. EPA editor has substituted the term
deferred for the original 2005 IDNR's elimination
when the intention was a postponement of
analysis until new evidence indicates that
additional investigation is warranted.
The IDNR deferred pesticides as a
candidate cause because data for the
Little Floyd River were limited to a single
sample collected in August 2002. The
rnnrpntratinns nf npstirirlps in this samnlp
were below the detection limit for all parameters measured (see Appendix B,
Table B-5). However, insecticides were not among the measured pesticides.
The IDNR deferred the other nonmetal toxics and salinity because there was not
enough data to consider. At the completion of the SI, if probable causes of the
biological impairment were not identified, additional data would need to be gathered to
resolve the case.
2.1.2. Candidate Causes Analyzed
Candidate causes for the case are those that remain after the screening
assessment. From the list of candidate causes, flow alteration, substrate
12
-------
alteration/increased sediment (including turbidity/TSS), altered basal food source, DO,
temperature, and ammonia were evaluated by a formal weight-of-evidence analysis.
2.3. CONCEPTUAL MODELS
The IDNR developed conceptual
models for each candidate cause to
reflect known current and historical land
uses, expected pathways of causation,
and observed impacts to the ecological
community. Figures 6-11 depict the
models for this case (see Comment 8).
Comment 8. Generic Conceptual Models.
Generic conceptual models and narrative text
describing them can be easily downloaded from
the conceptual model library or select databases
from the left navigation bar anywhere in CADDIS
then choose conceptual models.
13
-------
I Riparian
Vegetation
Channelization
Row Crop
Agriculture
I Large Woody Debris
I Sinuosity
t Velocity
I Infiltration/
t Runoff
I
i Flow
Heterogeneity
i 1 Deposited Fine Sediment i
T i (see Fig 7) ;
1 Max Flow
(Seasonal and Stormflow)
1 Frequency
of Low Flows
| Stream
Power (see
Fig 7)
t Temperature
(see Fig 10)
KEY
^ourc^
Additional Step in
Causal Pathway
Related
Conceptual
Model
Evidence
Against Step
Proximate
Stressor
Evidence
for Step
Reduced FIBI and
BMIBI Scores
FIGURE 6
Conceptual Model for Altered Flow Regime Showing Evidence for and Against the Stressors and Steps in the Pathway
-------
Row Crop
Agriculture
I Riparian
Vegetation
Grazing
f Velocity
(see Fig 6)
f Stream
Power
I Bank Stability
f 1° Producers
(see Fig 8)
f Channel and
Bank Erosion
f Soil Erosion
f Input of Fine Particles
I Flow
Heterogeneity
(see Fig 6)
f Suspended Sediment
f Deposited Fine Sediment
I Light
I Water Depth
I Aeration
(see Fig 9)
f Burial of
Organisms
Embedded
Riffles
I Algae
I Clarity
I Pools
f Temperature
(see Fig 10)
KEY
Related
Conceptual
Model
Additional Step in
Causal Pathway
Reduced FIBI and
BMIBI Scores
Source
Evidence
Against Step
Proximate
Stressor
Evidence
for Step
Response
FIGURE 7
Conceptual Model for Increased Sediment Showing Evidence for and Against the Stressors and Steps in the Pathway
-------
Wastewater
T reatment Plants
I Riparian
Vegetation
Row Crop
Agriculture
Animal Feeding
Operations
Septic
Systems
Urban
Runoff
Grazing
1 Nutrients
T Light
i Leaf
Litter
I Large Woody Debris
11 ° Producers/
A 1° Producer
Composition
(Algae & Macrophytes)
11nput of Fine
Particles
(see Fig 7)
TPH
(see Fig 11)
1 Organic Matter
(see Fig 9)
I Allochthonous
Food Resources
KEY
Related
Conceptual
Model
Additional Step in
Causal Pathway
Source
Reduced FIBI and
BMIBI Scores
Evidence
Against Step
Proximate
Stressor
Evidence
for Step
Response
FIGURE 8
Conceptual Model for Altered Basal Food Source Showing Evidence for and Against the Stressors and Steps in the
Pathway
-------
Row Crop
Agriculture
Grazing
Channelization
I Riparian
Vegetation
T
| Organic Matter
>
>
r
f 1° Producers
(see Fig 8)
I
I
Riffles
f Heterotrophs
J
I Large Woody Debris
I Turbulence
f Temperature ¦
(see Fig 10) j
f Respiration
I Photosynthesis/
Respiration Ratio
I Aeration
J Embedded Riffles
"J (see Fig 7)
I
! Dissolved Oxygen
(Water Column and/or Interstitial)
KEY
^ourc^
Additional Step in
Causal Pathway
Related
Conceptual
Model
Evidence
Against Step
Proximate
Stressor
Evidence
for Step
Reduced FIBI and
BMIBI Scores
FIGURE 9
Conceptual Model for Decreased Dissolved Oxygen Showing Evidence for and Against the Stressors and Steps in the
Pathway
-------
I Riparian
Vegetation
t Light
J, Water Depth
(see Fig 7)
f Temperature
J, Dissolved Oxygen
(see Fig 7)
Reduced FIBI and
BMIBI Scores
! f Frequency of Low
J Flows (see Fig 6)
f Ammonia
(see Fig 11)
KEY
Related
Conceptual
Model
Evidence
^ourc^
Additional Step in
Causal Pathway
Against Step
Proximate
Stressor
^^espons^^
Evidence
for Step
FIGURE 10
Conceptual Model for Increased Temperature Showing Evidence for and Against the Stressors and Steps in the Pathway
-------
Wastewater j \ ^ ( Animal Feeding i \ Row Crop
Treatment Plants I I Septic Systems I I operations \ I Agriculture
1
f 1° Producers i ^ t pH
(see Fig 8) i *
T NH4+
1 | Temperature
>
r
[ (see Fig 10)
T NH3
I
Reduced FIBI and
BMIBI Scores
KEY
Related
Conceptual
Model
Additional Step in
Causal Pathway
Source
Evidence
Against Step
Proximate
Stressor
Evidence
for Step
Response
FIGURE 11
Conceptual Model for Increased Ammonia Showing Evidence for and Against the Stressors and Steps in the Pathway
-------
3. EVALUATE DATA FROM THE CASE
3.1. SOURCES OF DATA FROM THE CASE
In the impaired segment of the Little Floyd River, the IDNR contracted the
University of Iowa Hygienic Laboratory (UHL) to conduct biological assessments at four
sites over a 4-year period. Each site was sampled only once. Despite the spatial and
temporal variation in the samples, each assessment showed similar weaknesses in the
biological assemblage as noted previously and in Table B-3.
Water chemistry data were collected at three of the biological assessment sites
over the course of three years (see Appendix B, Tables B-1 and B-2). Because
ecoregion reference data were collected only between midJuly and midOctober, data
from the Little Floyd River outside this time-frame were excluded when comparing
conditions in the Little Floyd to conditions at ecoregion reference sites. Mean values for
chemical parameters for each site are used in the causal analysis (see Appendix C).
Diurnal variations of temperature and DO were measured at two of the sites (see
Appendix B; Figure B-1). These data were used to determine if violations of the DO
standard had occurred and to evaluate diurnal range in concentration. They were also
used to evaluate temperature as a candidate cause in the Little Floyd River.
For the majority of the parameters described above, sites within the Little Floyd
River were compared using the internal comparator (Site 2) as described in Section 1.3.
For others, such as the analysis for co-occurrence, values for the four Little Floyd River
sites were compared to the interquartile range (25th to 75th percentile) of values for
reference sites within the Northwest Iowa Loess Prairies ecoregion.
It was possible that multiple stressors were acting independently upon the fish
and invertebrates. However, although the calculated metrics listed in Table B-3 were
separately maintained and analyzed, there were no pieces of evidence that were
applied differently to fish and invertebrates. Thus, the same causes were likely to be
identified for fish and invertebrates at the level of the index. The results may have been
different if the analysis used individual fish or invertebrate metrics; however, this was
not done during IDNR's study submitted for their TMDL report or in this edited version.
3.2. EVALUATION OF DATA FROM THE CASE
Two types of evidence were evaluated using data from the case: (1) spatial
co-occurrence and (2) complete causal pathway.
3.2.1. Spatial/Temporal Co-occurrence
The analysis of associations began with the determination of the presence or
absence of the proximate stressor. For both the fish and benthic macroinvertebrate
20
-------
communities, the levels of the stressors at Site 2 (internal comparator) were compared
to levels at the other three sites in the watershed.
• If the stressor levels were greater at the comparator (Site 2) than at the other
three, more-impaired sites (Sites 1, 3, and 4), this is evidence of co-occurrence.
The strength is low because the association could be coincidental and was
scored with a plus sign (+).
• If the relationship was reversed, then the evidence against the cause was strong
because causes must co-occur with their effects and was therefore scored with
three minus signs (—).
• If the relationship was supported at some sites but not at other sites, the
evidence was uncertain and was scored zero (0).
• When data were not available for a measure at the less-impaired comparator
site, there was no evidence (NE).
Table 3 provides a summary of the measures for which data were available at
the comparator site. Table C-1 of Appendix C contains the complete analysis of
co-occurrence.
3.2.2. Causal Pathway
The second type of evidence, complete causal pathway, used observations from
the case to link potential source(s) to the proximate candidate cause(s). The first step
in this process was to analyze evidence for each step in each of the causal pathways,
similar to the examination of co-occurrence in Section 3.2.1.
For the Little Floyd River, to determine if each linkage in the causal pathway was
present, the values at the impaired sites (Sites 1, 3, and 4) were compared to the levels
of the intermediate stressors at the comparator site (Site 2) and the interquartile range
(25th to 75th percentile) of values for reference sites within the Northwest Iowa Loess
Prairies ecoregion (see Comment 9). For algal parameters, the mean from random
statewide sites was used to represent the unimpaired condition. Table C-2 of
Appendix C includes this analysis; Figures 6-11 graphically represent the causal
pathways using conceptual models. When evidence weakens a pathway, that measure
is depicted with hatch marks. When evidence strengthens a pathway, the measure is
shaded a solid grey.
The second step was to determine the completeness of the pathways from
watershed sources to each proximate stressor. All of the sources shown in the
conceptual models were known to occur within the watershed (see Figures 1 and 2).
Contributions of both point and nonpoint sources from the watershed (as described in
Section 1.2) are roughly equivalent at all sites. However, data to evaluate all pathways
was not available. Only a very few steps in the causal pathways presented in the
conceptual models could be eliminated, such as a decrease in the amount of large
21
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TABLE 3
Evidence of Spatial/Temporal Co-occurrence in the Little Floyd River, Iowa
Spatial/Temporal Co-occurrence
Proximate
Stressor
Measure of
Exposure
Measurement
at Internal
Comparator
(Site 2)
Measurements
at Sites 1, 3,
and 4,
Respectively
Evidence of
Co-occurrence
Score
Increased Sediment (see Figure 7) Summary Score: Suspended: 0 Deposited: +
Increased
Suspended
Sediment
TSS
(mg/L)
38.8
M; 45.0; 33.3
NE; yes; no
0
Increased
Deposited
Fine
Sediment
% total
fines
75
95; 80; 85
yes; yes; yes
+
% silt
32
58; 29; 42
yes; no; yes
0
% sand
40
31; 47; 41
no; yes; yes
0
% total
coarse
25
5; 19; 15
yes; yes; yes
+
% total
gravel
19
3; 19; 11
yes; no; yes
0
Loss of Pool
Depth
% reach as
pool
habitat
54
48; 50; 23
yes; yes; yes
+
maximum
depth (cm)
91
55; 73; 37
yes; yes; yes
+
Embedded
Riffle
% riffles
11
0; 0; 5
yes; yes; yes
+
22
-------
TABLE 3. cont.
Decreased DO (see Figure 9)
Summary Score
: +
Decreased
DO
lowest
observed
summer
DO (mg/L)
(daytime
grab
samples)
6.2
15.3; 6.2; 4.6
no; no; yes
0
average
summer
DO (mg/L)
before
10 am
(daytime
grab
samples)
7.8
M; M; 8.1
NE; NE; no
0
minimum
DO (mg/L)
(daytime
grab
samples)
6.2
15.3; 6.2; 3.3
no; no; yes
0
ratio of
highest to
lowest
summer
DO
1.6
M; 1.8; 2.9
NE; yes; yes
+
Increased Temperature (see Figure 10)
Summary Score: +
Increased
Temperature
mean °C
(summer
grab
samples)
17.5
18; 24; 21
yes; yes; yes
+
maximum
°C
(summer
grab
samples)
25.7
18; 25.7; 27.6
no; no; yes
0
23
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TABLE 3. cont.
Increased Ammonia (see Figure 11 )
Summary Score: +
Increased
mean
0.07
M; 0.19; 0.08
NE; yes; yes
+
Ammonia
ammonia
(mg/L)
(grab
samples)
maximum
0.12
M; 0.32; 0.18
NE; yes; yes
+
ammonia
(mg/L)
(grab
samples)
M = missing.
NE = no evidence.
24
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Comment 9. Quartiles Used for Stressor-Response.
The use of quartiles to evaluate exposure-response relationships from field data and relate them to
site data is similar to the use of box plots. Both methods presume a monotonically increasing or
decreasing relationship. If conditions are optimal at an intermediate level of the causal agent and
suboptimal at both extremes, the technique is not appropriate. Further, comparison of site data to
regional quartile ranges can support a candidate cause if the following are true:
1. Quartile ranges do not overlap between reference sites and a known population of impaired sites.
If they do overlap, the reference sites may be affected by the stressor. Alternately, overlap may
indicate that the stressor is not a significant cause in the region because the levels of response
do not greatly differ between extremely high and low levels of the candidate cause.
2. Quartile ranges are small. If the cause is important, there should be a relatively consistent
response. This criterion is weaker than Criterion 1, above.
3. The response at the impaired site falls within the quartile for the extreme level predicted by the
causal hypothesis. This criterion was not evaluated in the Floyd River case except that the
values for the index scores were below the reference criteria at some sites (see Table 2).
4. The level of the candidate cause at the impaired site falls within the appropriate regional extreme
range. That is, if the biological response at the impaired site corresponds to the levels seen at an
extreme level of the candidate cause (i.e., Criterion 3 is met), then the level of the candidate
cause should be extreme at the impaired site. For example, the mean percent silt was 40, well
outside the interquartile range for regional reference sites (6-20% silt).
5. Criteria 1-4 are true for most, if not all, of the response metrics that define the impairment. That
is, if the candidate cause is responsible for the impairment, it should be associated with most or
all of its component biological effects. The Floyd case did not examine metrics or other individual
assessment endpoints.
woody debris. Conversely, few of the proximate stressors could be linked to sources by
an entirely complete pathway.
Candidate causes were scored for complete causal pathway as follows:
• Evidence linking sources by at least one complete pathway (from source to
proximate stressor) was scored with two plus signs (++).
• Evidence of at least some supported steps in the pathway was scored with a
single plus sign (+).
• No evidence of an intermediate stressor for or against any part of the pathway
was scored with a zero (0).
• Evidence that at least one step was missing in every causal pathways was
scored with a minus sign (-).
• When data were not available to evaluate a candidate cause, no evidence (NE)
was indicated and no evaluation was made.
Section 5 provides the scores for completeness of the causal pathway for the
proximate stressors in this case.
25
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4. EVALUATE DATA FROM ELSEWHERE
4.1. SOURCES OF DATA FROM OUTSIDE THE CASE
This case study included information from statewide water quality monitoring
programs and from the scientific literature; that is, data from outside the Little Floyd
River. The statewide monitoring data used in this case were from the Biological
Assessment of Iowa's Wadeable Streams project, which monitored ecoregion reference
sites (Wilton, 2004), and the REMAP (IDNR 2001c, 2002) data collected from random
sites throughout the state.
It is important to note that most Iowa streams, both impaired and unimpaired,
have been affected to some degree by anthropogenic changes in drainage patterns
and/or channel morphology. Conditions in the Little Floyd River were compared to sites
in the ecoregion and across the state that had similar land-use patterns.
4.2. EVALUATION OF DATA FROM OUTSIDE THE CASE
Two types of evidence were used to evaluate data from outside the case:
stressor-response relationships from other field studies and stressor-response
relationships from laboratory studies (referred to as stressor-response [other]). These
types of evidence were used to establish whether the stressors are present in the Little
Floyd River at levels that may be expected to elicit a biological response.
4.2.1. Stressor-Response Relationships from Other Field Studies
Data from field studies were used to develop stressor-response associations and
then the measured levels of exposure in the Little Floyd River were evaluated to
determine if they were sufficient to cause the observed biological effect. The
interquartile range of values for the various stressors from ecoregion reference sites
were compared to the values observed for the Little Floyd River. The mean value at
statewide random sites was compared to the values in the Little Floyd River except
where noted. Table B-6 of Appendix B contains data from ecoregion reference sites.
Values for the Little Floyd River were compared to the interquartile range of
values for reference sites within the Northwest Iowa Loess Prairies ecoregion. In a few
cases, such as measures of extreme temperature or DO, the maximum or minimum
ecoregion reference value was used as a comparative value. For measures of algae
and diurnal variations, the mean from random statewide sites were considered
representative of the unimpaired condition because these parameters were not
measured at the ecoregion reference sites.
Scoring for stressor-response from other field studies was based on a
comparison between the mean or range of statewide or regional reference sites to the
26
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within-site means in the Little Floyd River for chemical parameters, or to the mean for all
four Little Floyd River sites for habitat parameters (exceptions are noted in Table C-3):
• If exposure to the candidate cause was greater in the Little Floyd River than at
the reference sites, the evidence for a plausible stressor-response was
considered strengthened and scored with a plus sign (+).
• If the exposure levels in the Little Floyd River were less than or equal to the
exposure at the reference sites, the evidence weakened that candidate cause
and was scored with a minus sign (-).
• If the relationship was ambiguous, it received a zero (0).
• If data were not available to evaluate a candidate cause, then there was no
evidence (NE) and no impact on the case.
Table 4 provides a summary of the measures for which data were available. The
detailed analysis is available in Appendix C (see Table C-3). Section 5 gives the final
score for the stressor-response for each proximate stressor.
4.2.2. Stressor-Response from Laboratory and Other Studies
Data from laboratory studies are
the basis for stressor-response
relationships that are used to derive most
ambient water quality criteria (WQC) for
chemicals (see Comment 10). Ambient
WQC were used to judge if the DO levels
or ammonia levels were sufficiently
altered to cause the types of impairments
observed in the Little Floyd. The Little
Floyd River SI, as developed for the
TMDL, relied in part on best professional
judgment and Iowa water quality
standards. The evidence from criteria
documents for DO levels and ammonia
levels strengthened these candidate
causes because values at the impaired
sites exceeded the criteria. For other
stressors, such as pH, values at the site
did not exceed the criteria, the evidence
weakened that candidate cause and it was deferred (see Section 2.2.1).
4.2.2.1. Dissolved Oxygen (+)
Although DO concentrations measured in daytime sampling from the Little Floyd
River are similar to those measured at the ecoregion reference sites, nighttime DO
concentrations fall below the Iowa WQC for DO, which requires:
Comment 10. Cautious Use of Water Quality
Criteria.
In some cases, the IDNR uses water quality
criteria (WQC) in lieu of a stressor-response curve
to evaluate if exposures to a candidate cause were
sufficient to cause the effects observed in the Little
Floyd River. However, the SI process
recommends great caution with this approach
because the WQC were not developed to estimate
likely effects for different intensities of stressors.
The WQCs provide a single-point comparison
rather than characterizing the stressor-response
curve. Used individually, the WQC do not account
for the combined exposures from multiple
chemicals or factors in the field that increase or
decrease their effects and they are not protective
of all species in all situations. See Ambient Water
Quality Criteria Documents as Literature Reviews
and various sections on interpreting
stressor-response information in the Analytical
Tools section of the CADDIS Web site.)
27
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TABLE 4
Stressor-Response from Other Field Studies for Candidate Causes in the Little Floyd River, Iowa
Stressor Response Relationship from Other Field Studies
Proximate
Stressor
Exposure
Measurement at Regional
Reference Sites (n = 8) or
Statewide Random Sites
(¦n = 72)
Measurements in the Little
Floyd River
Evidence of
Score
Increased Sediment (see Figure 7) Summary Score: Deposited: + Suspended: 0
Increased
Suspended
Sediment
TSS (mg/L)
10-37 interquartile range
Site 4 (mean baseflow and
storm event; n = 10)
no; yes; no
0
Decreased
Water Clarity
turbidity (NTU)
8-24 interquartile range
22 at Site 3 (mean; n = 3); 14
at Site 4 (mean; n = 5)
no; no
-
Decrease in
Algal Growth
seston
chlorophyll a
(Mg/L)
32 mean (n = 72)
at Site 4 (mean; n = 5)
yes; yes
+
periphyton
chlorophyll a
(Mg/cm2)
32 mean (n = 72)
38-45 (range; n - 2)
no
-
-------
TABLE 4. cont.
Stressor Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement at Regional
Reference Sites (n = 8) or
Statewide Random Sites
(n = 72)
Measurements in the Little
Floyd River
Evidence of
Stressor
Response
Score
Decrease in
Algal Growth
cont.
sediment
chlorophyll a
(|jg/cm2)
27 mean (n = 72)
21-22 (range; n = 2)
yes
+
gross primary
production (GPP)
and production-
to-respiration
ratio (P:R)
4.8, 0.68 (GPP, P:R),
mean (n = 72)
10.9, 0.82 (GPP, P:R) at Site
3, (mean; n = 12 days); 4.4,
0.37 (GPP, P:R) at Site 4
(mean; n = 19 days)
no; yes
0
Increased
Deposited
Fine
Sediment
% total fines
46-86 interquartile range
(/7 = 8)
84 mean of all 4 sites (n = 4)
no
0
% silt
6-20 interquartile range
(/7 = 8)
40 mean of all 4 sites (n = 4)
yes
+
Loss of Pool
Depth
% reach area as
pool habitat
645 interquartile range
(/7 = 8)
44 mean of all 4 sites (n = 4)
no
-
maximum depth
(cm)
76-88 interquartile range
(n = 8)
64 mean of all 4 sites (n = 4)
yes
+
-------
TABLE 4.
cont.
Stressor Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement at Regional
Reference Sites (n = 8) or
Statewide Random Sites
(n = 72)
Measurements in the Little
Floyd River
Evidence of
Stressor
Response
Score
Altered Basal Food Source (see Figure 8)
Summary Score: 0
Increased/
Altered
Primary
Producers
seston
chlorophyll a
(MQ/L)
32 mean (n = 72)
20 at Site 3 (mean; n = 3); 9.7
at Site 4 (mean; n = 5)
no; no
-
periphyton
chlorophyll a
(|jg/cm2)
32 mean (n = 72)
38-45 (range; n = 2)
yes
+
sediment
chlorophyll a
(|jg/cm2)
27 mean (n = 72)
21-22 (range; n = 2)
no
-
(GPP; g 02/m2/d)
4.8 mean (n = 72)
10.9 at Site 3, (mean; n = 12
days); 4.4 at Site 4 (mean;
n = 19 days)
yes; no
0
Decreased DO (see Figure 9)
Summary Score: 0
Decreased
DO
mean DO (mg/L)
(daytime grab
samples)
6.9-9.4 interquartile range
(/7 = 8)
8.3 at Site 2 (mean; n = 7);
8.5 at Site 3 (mean; n = 3);
8.8 at Site 4 (mean baseflow
and storm event; n = 10)
no; no; no
-------
TABLE 4.
cont.
Stressor Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement at Regional
Reference Sites (n = 8) or
Statewide Random Sites
(n = 72)
Measurements in the Little
Floyd River
Evidence of
Stressor
Response
Score
Decreased
DO cont.
minimum DO
(mg/L) (daytime
grab samples)
5.4 minimum (n = 8)
6.2 at Site 2 (/? = 7); 6.2 at
Site 3 (/? = 3); 4.6 at Site 4 (n
= 10)
no;no;yes
0
Increased Temperature (see Figure 10)
Summary Score: +
Increased
temperature
mean
temperature (°C)
(grab samples)
15.1-19.8 interquartile
range n = 8)
17.5 at Site 2 (mean; n = 7);
24 at Site 3 (mean; n = 3); 21
at Site 4 (mean baseflow and
storm event; n = 10)
no; yes; yes
0
maximum
temperature (°C)
(grab samples)
24.9 maximum (n = 8)
25.7 at Site 2 (n = 7); 25.7 at
Site 3 (n = 3); 27.6 at Site 4
(n = 10)
yes; yes; yes
+
mean
temperature (°C)
19.8 mean (n = 72)
26.2 at Site 3; 23.2 at Site 4
yes; yes
+
diurnal maximum
temperature (°C)
26.2 mean (n = 72)
33.4 at Site 3; 30.4 at Site 4
yes; yes
+
-------
TABLE 4.
cont.
Stressor Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement at Regional
Reference Sites (n = 8) or
Statewide Random Sites
(n = 72)
Measurements in the Little
Floyd River
Evidence of
Stressor
Response
Score
Increased Ammonia (see Figure 11)
Summary Score: +
Increased
ammonia
ammonia
nitrogen as N
(mg/L)
0.085-0.10 interquartile
range (n = 3)
0.06 at Site 2 (/? = 7); 0.19 at
Site 3 (n = 3); 0.08 at Site 4
(n = 10)
no; yes; no
0
Maximum
ammonia
nitrogen as N
(mg/L) (grab
samples)
0.10 maximum sites (n = 3)
0.87 at Site 2 (n = 7); 0.32 at
Site 3 (/? = 3); 0.18 at Site 4
(n = 10)
yes; yes; yes
+
-------
• A minimum DO of 5.0 mg/L for at least 16 hours of every 24-hour period; and
• A minimum DO of 4.0 mg/L at any time during every 24-hour period (IAC, 2004).
The U.S. EPA designed this standard as a protective measure for aquatic life and it
reflects the levels of protection suggested in U.S. EPA's Ambient Water Quality Criteria
for Dissolved Oxygen (1986). Table 5 summarizes the violations of these limits.
TABLE 5
Summary of Violations of Iowa's Water Quality Standard for DO in the Little Floyd River
Date(s)
Description of Violation
3/11/03
DO measurement of 3.3 mg/L at Site 4 (grab sample)
7/27/02, 7/28/02, 7/29/02,
7/30/02, 7/31/02, 8/1/02,
8/4/02, 8/5/02, 8/6/02
DO measurements below 5 mg/L for more than 8 hours at Site 3
(diurnal measurements 7/24/02 to 8/6/02; 13 d)
7/31/02, 8/1/02, 8/4/02
DO measurements below 4 mg/L at Site 3 (diurnal
measurements 7/24/02 to 8/6/02; 13 d)
8/16/03, 8/17/03, 8/18/03,
8/19/03, 8/20/03, 8/21/03,
8/22/03, 8/24/03, 8/25/03,
8/26/03
DO measurements below 5 mg/L for more than 8 hours at Site 4
(diurnal measurements 6/24/03 to 7/1/03 and 8/12/03 to 8/26/03;
21 d)
8/16/03, 8/17/03, 8/18/03,
8/19/03, 8/20/03, 8/21/03,
8/25/03, 8/26/03
DO measurements below 4 mg/L at Site 4 (diurnal
measurements 6/24/03 to 7/1/03 and 8/12/03 to 8/26/03; 21 d)
4.2.2.2. Temperature (+)
In the Little Floyd River, water temperatures changed more rapidly than 1 °C per
hour for some portions of all three diurnal sampling events in 2002 and 2003 (see
Figure B 1). At Site 3, for example, the rate of temperature increase exceeded 8°C over
a 4 hour period on both August 2 and 3, 2002. The IDNR judged thermal changes of
1 °C per hour to be excessive. These rapid thermal fluctuations create highly stressful
conditions for fish and macroinvertebrates and could be expected to negatively affect
aquatic communities. In addition the Little Floyd River also had daily high temperatures
that exceeded 32°C during one of the three diurnal sampling events; the maximum
water temperature during this time was 33.4°C (see Comment 11).
Unfortunately, much of the literature dealing with fish thermal limitations focuses
on cold-water species. This is especially true of the literature dealing with temperature
fluctuations. However, in a study of the potential effects of climate change, Eaton and
Scheller (1996) provide estimates of the maximum weekly average temperature
33
-------
tolerance of several fish species that inhabit
the Little Floyd River. The maximum weekly
average temperature measured in the Little
Floyd River during diurnal sampling was
27.4°C. This is greater than or equal to the
published tolerance levels for 4 of 11 fish
species on their list found in the Little Floyd
River.
4.2.2.3. Ammonia (+)
Iowa water quality standards include
a specific numeric limit on ammonia in
classified rivers and streams.
Concentrations of ammonia in stream
samples must be interpreted with respect to pH
and temperature in order to determine if the
concentrations violate Iowa water quality
standards for aquatic life use (IAC, 2004). Iowa's
water quality standards are based on the criteria
developed by the U.S. EPA (1999).
During a rainstorm in November of 2003,
ammonia concentrations exceeded the acute
toxicity standard for ammonia. Concentrations of
ammonia were measured at 4.9 mg/l and
6.5 mg/L under prepeak and postpeak flow
conditions, respectively, with a temperature of
4.1 °C and a pH of 8.2. These concentrations
were the result of the over application of hog
manure on a soybean field the day before the
storm and caused a fish kill over a 6.6 km reach
of the Little Floyd River (IDNR, 2005b) (see
Comment 12).
Comment 11. Changes to State Limits.
When the original SI was completed, the Iowa
Administrative Code (IAC) did not include
specific limits on maximum temperature or the
rate of temperature change. This standard was
under development at that time. Recent
revisions to the IAC, which apply to the Little
Floyd River, include the following:
No heat shall be added to interior streams or
the Big Sioux River that would cause an
increase of more than 3°C. The rate of
temperature change shall not exceed 1 °C per
hour. In no case shall heat be added in
excess of that amount that would raise the
stream temperature above 32°C (IAC, 2006).
Effect levels that were the basis for this
decision were not used to evaluate this case.
Comment 12. Assessing Different
Impairments.
Biological impairments can be due to
different mechanisms and causes.
IDNR strategically chose to investigate
the cause of massive kills to wildlife
separately from pervasive, chronic
causes. The cause of the fish kill was
identified as ammonia toxicity that
resulted from a spill from a hog farm.
This impairment was not the focus of
this study.
Ammonia was also a candidate cause
for the chronic impairment and
implicated in the Little Floyd River. In
addition to toxicity due to water column
levels of ammonia, other causes that
might be considered are: ammonia
toxicity associated with deposited
sediment, episodic formation of
ammonia due to high levels of nitrate in
reducing environments at high pH, and
unreported, repeated episodic spills of
waste.
34
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5. IDENTIFY THE PROBABLE CAUSES
Four types of evidence are included in the SI for the Little Floyd River: (1) spatial
co-occurrence, (2) complete causal pathway, (3) stressor-response relationships from
other field studies, and (4) stressor-response from laboratory studies. Once a score
was assigned for each candidate cause, an overall score for each type of evidence was
determined for each candidate cause. Section 5 contains these final scores. See the
CADDIS website (http://epa.gov/caddis/) for scoring protocols.
Since some types of evidence were composed of more than one piece of
evidence, these were synthesized into a single score before comparing among different
candidate causes. For example, co-occurrence for increased temperature includes four
pieces of evidence that scored +, 0, and NE (see Table C-1). These four pieces of
evidence were synthesized into a score of"+". Then the four types of evidence for each
candidate cause were scored for consistency. Rules for scoring consistency among the
different types of evidence for a candidate cause were as follows (U.S. EPA, 2007):
• A positive response in at least three types with no negative responses received
two pluses (+ +).
• A positive response in two types with no negative responses scored one plus (+).
• The presence of both positive and negative responses received a minus (-).
• Two or more negative responses with no positive responses received two
minuses (- -).
• Any other combination scored zero (0).
Table 6 shows the strength of evidence for each of these considerations across the
proximate stressors defined in the conceptual models.
The IDNR examined evidence for each candidate cause in order to determine
which of the causes were likely to have the greatest affect on the aquatic community.
As shown in Table 6, of the seven candidate causes, the four most likely candidate
causes are deposited sediment, decreased DO, increased temperature, and increased
ammonia (shaded solid grey). These four candidate causes were then divided into
primary causes for which IDNR developed TMDLs and secondary causes that were due
to pollution, which would not require TMDLs. IDNR included both in their remediation
plans.
35
-------
9e
Consistency
Stressor-Response
(Other)
Stressor-Response
(Field)
Complete Pathway
Co-occurrence
TABLE 6
Strength of Evidence Tables for Little Floyd River
o
:z:
m
:z:
m
o
:z:
m
Decreased Flow Heterogeneity
Altered Flow
Regime
o
:z:
m
:z:
m
¦
:z:
m
Increased Maximum Flow
o
:z:
m
:z:
m
o
:z:
m
Increased Frequency of Low Flows
o
:z:
m
o
+
o
Increased Suspended Sediment
Suspended
Sediment
¦
:z:
m
¦
+
:z:
m
Decreased Clarity
o
:z:
m
o
+
z
m
Decreased Algal Growth
+
+
:z:
m
+
+
+
Increased Deposited Fine Sediment
Deposited Sediment
+
:z:
m
o
+
+
Loss of Pool Depth
+
:z:
m
:z:
m
+
+
Embedded Riffles
o
:z:
m
:z:
m
+
:z:
m
Burial of Organisms
o
:z:
m
:z:
m
o
z
m
Decreased Allochthonous Food
Resources
Basal Food
Source
o
:z:
m
o
+
+
z
m
Change in Primary Production
+
+
+
o
+
+
Decreased DO
+
+
+
+
+
+
+
Increased Temperature
+
+
+
+
+
+
Increased Ammonia
-------
5.1. PROBABLE PRIMARY CAUSES
5.1.1. Deposited Sediment
IDNR identified excessive silt and sediment deposition in the Little Floyd River as
a cause of the reduction in the FIBI and BMIBI scores. The levels of deposited
sediment that were observed could limit the assemblages of benthic macroinvertebrates
that require gravel substrates found in riffles for refugia and reproduction. Sediments
could decrease habitat available to pool-dwelling fish and organisms that prefer coarse
substrates.
IDNR determined that siltation and sedimentation was a problem based on
habitat data collected by the IDNR/UHL biological assessment team (see Table 7).
Total fine sediment was at the extreme end of the range for the regional reference sites
at all four sites in the Little Floyd River. The percent silt is far greater than expected
based on reference sites. The percent sand was within the expected range based on
ecoregion reference data, but this is partially explained by the dominance of silt in the
Little Floyd River. While the percentage of the Little Floyd River with pool habitats was
greater than expected, the maximum depth in these pools was generally less than those
at the ecoregion reference sites. Although embedded riffles were observed at seven of
the ecoregion reference sites, riffles were generally lacking in the Floyd River and may
be indicative of sedimentation problems beyond mere embeddedness. The lack of
riffles limits the diversity of habitats available to aquatic organisms and thereby limits the
diversity of the aquatic community.
TABLE 7
Details of Several Habitat Metrics for Deposited Fine Sediment
Parameter
9/14/99
Site 1
9/12/01
Site 2
8/22/02
Site 3
9/11/01
Site 4
Ecoregion 47a
Reference
% total fines
95
75
80
85
46-86, 62, 59
% silt
58
32
29
42
6-20, 13, 13
% sand
31
40
47
41
29-59, 47, 44
% riffle
0
11
0
5
5-18, 13, 15
% pool
48
54
50
23
6-45, 24, 21.5
maximum depth (m)
1.8
3
2.4
1.2
2.5-2.9, 2.7, 2.7
37
-------
Table 6 contains three measures under the umbrella of increased deposited
sediment. This table documents the variety of evidence that pointed to the impacts of
sediment in the Little Floyd River. The most convincing evidence for sediment as a
proximate stressor was from the measurements of increased deposited fine sediment
(see Table 6). Co-occurrence was supported, largely based on the lesser percent total
fines and greater percent riffle and maximum depth at the internal comparator, Site 2,
relative to the other three sites. The verified steps in causal pathway and
stressor-response from the field further strengthened increased deposited fine sediment
as a primary cause of biological impairment in the Floyd River. These findings resulted
in a high level of consistency among both types and pieces of evidence.
Reduced pool depth and increased riffle embeddedness also lend support to
deposited sediment as a probable cause of biological impairment. Co-occurrence was
demonstrated and there was supporting evidence for steps in the causal pathway.
5.1.2. Low DO
Low levels of and fluctuations in concentrations of DO likely contribute to low FIBI
and BMIBI scores in Iowa. DO measurements taken in the Little Floyd River over two
separate 2-week periods in August of 2002 and 2003 using continuous dataloggers
show that levels fluctuate by 7 mg/L or more over 24-hour periods (see Appendix B,
Figure B-1). These extreme rates of change suggest that DO production during the day
causes supersaturation while algal and bacterial respiration depletes DO when
photosynthesis ceases at night.
In addition to diel fluctuations, the August data showed that DO levels fell below
4 mg/L for several hours each night for several nights each summer. Monthly grab
samples collected by UHL showed that DO concentrations were within acceptable limits
except for a measurement of 3.3 mg/L at Site 4 on March 11, 2003. On this day, DO at
the Site 3 upstream site was 6.7 mg/L and the temperature was 0°C at both sites.
These DO concentrations are equivalent to less than 50% saturation at Site 3 and less
than 25% saturation at Site 4.
Concentrations of DO in August 2002 and 2003, particularly during the night and
in the early morning, were at levels known to stress the species in the Little Floyd River.
While the diel cycling of DO concentrations demonstrate that algae contribute to the DO
stress, the evidence does not suggest that the Little Floyd River has higher than normal
algal productivity for this ecoregion. For this reason, high summer temperatures may
cause an increase in respiration rates or there may be additional sources of oxygen
demand. Also, DO measurements in the water column may not adequately
characterize DO concentrations on and near the Little Floyd River's stream bed. The
amount of deposited sediment could restrict aeration of substrates.
Three types of evidence strengthen DO as a probable cause of biological
impairment in the Floyd River: (1) co-occurrence was demonstrated using the internal
comparator; (2) steps in the causal pathway were supported; and (3) DO levels were
38
-------
likely to cause detrimental effects based on a plausible relationship between the
stressor (DO) and the response (impaired biological assemblages) based on state
standards. This resulted in a high degree of consistency for DO as a stressor in the
Little Floyd River.
Iowa water quality standards (IAC, 2004) define the minimum level of DO allowed
in Class B (LR) streams as 4.0 mg/L and that DO levels must be at least 5.0 mg/L for
16 hours of every 24-hour period. Independent of biological impairments and their
causes, the documented violations of the DO standard are sufficient to include the Little
Floyd River on Iowa's 303(d) list of impaired waterbodies. The Little Floyd River is in
violation of these standards thus SI was not needed for regulatory action. However, the
causal assessment confirmed that low DO was one among several probable causes.
Therefore, remediation of low DO alone may not achieve the desired aquatic life uses.
5.2. PROBABLE SECONDARY CAUSES
5.2.1. High Temperature/Temperature Flux
The thermal conditions of the Little Floyd River include high temperatures and
rapid, daily temperature fluctuations. These conditions contribute to the low FIBI and
BMIBI scores for the River. Both monthly sampling and the diurnal samples from
dataloggers deployed in the summers of 2002 and 2003 showed that daytime water
temperatures exceeded 30°C. The summer measurements in both years also revealed
temperature fluctuations that exceed 2°C per hour. Both of these conditions can be
stressful to aquatic organisms.
There is evidence of increased heat in the Little Floyd River. The mean
temperature of available measurements is higher at Sites 3 and 4 than Site 2 and the
interquartile range for ecoregion reference sites. In addition, the maximum
temperatures were greater at all three measured Little Floyd River sites compared to
the maximum for ecoregion reference sites. Only one reference site had a water
temperature greater than 20°C (observed in early August). At sites in the Little Floyd,
temperatures above 20°C were recorded into September.
Co-occurrence was demonstrated with the benthic macroinvertebrate and fish
community and a complete causal pathway was documented. A field stressor-response
was verified using ecoregion data and statewide data. This allows a high level of
consistency for the identification of water temperature as a stressor in the Little Floyd
River.
Since there are no industrial thermal discharges in the watershed, causal
pathways to increased temperature in the Little Floyd River result from poor riparian
conditions and possibly reduced ground water base flow.
39
-------
5.2.2. Ammonia
The Little Floyd River watershed supports a large number of livestock. This
livestock produces a large quantity of manure that is applied to fields each year.
Periodic leaks, spills, over-application, and lagoon failures throughout the watershed will
have adverse effects on the biological community in the river.
High concentrations of ammonia have been detected infrequently in the Little
Floyd River. Over-application of hog manure on October 31, 2003, caused a fish kill
over a 6.6-km reach of the river. Following the application of manure, a storm and
subsequent increased flow triggered the UHL event sampler on November 1. The
pre- and postpeak samples registered ammonia concentrations of 4.9 and 6.5 mg/L.
These concentrations, respectively, violate the chronic and acute limits in Iowa water
quality standards and are associated with a known fish kill that included the three
upstream sampling sites.
Minor manure releases and small fish kills may occur without notification being
sent to IDNR. Without this notification, it is impossible to quantify the effects of
ammonia and other manure-related parameters on the fish and benthic
macroinvertebrate communities in the Little Floyd River. Smaller repeated exposures
remain a potential cause.
Four types of evidence strengthen ammonia as a candidate cause:
(1) co-occurrence, (2) steps in the causal pathway, (3) field stressor response, and
(4) stressor-response based on Iowa's state standards. The evidence is consistent for
ammonia in the water column as a probable chronic cause. Ammonia is sediment was
not measured.
However, while the evidence supported ammonia as a candidate cause, the
evidence was relatively weak and somewhat circumstantial. The concentrations of
ammonia in the Little Floyd River were below the detection limit on most occasions,
(see Appendix B; Table B-1). In fact, other than the high concentrations measured in
association with the known fish kill, the highest concentration of ammonia measured in
the Little Floyd was 0.32 mg/L, well below concentrations expected to cause
impairments of the aquatic community. The evidence for increased sediment deposition
and low DO were more compelling than the evidence for ammonia as a probable cause
of biological impairment as measured by fish and benthic macro-invertebrate indices.
Whereas, episodic fish kills were attributed to ammonia toxicity in a separate
assessment.
40
-------
5.3. UNSUPPORTED CAUSES
5.3.1. Altered Flow Regime
Data for the analysis of alteration of
the flow regime in the Little Floyd River
are limited (see Comment 13). A lack of
historical flow data for both the impaired
stream segment and the ecoregion
reference sites prevented an analysis of
co-occurrence and stressor response.
There was evidence for several steps in
the causal pathways, but without evidence
for the proximate stressors, it is
impossible to draw any conclusions about
the relationship of the existing flow
conditions to the impairment.
Comment 13. Data Limitations.
Several of the potential stressors in the Little
Floyd River case are reported as unsupported, that
is, lacking evidence as the cause for the more
severe impairment at other sites compared to
Site 2. This is not to say that these causes are not
affecting the stream community in a detrimental
way. These stressors were not eliminated (i.e.,
refuted). Although the evidence suggests that they
are not probable causes for the differences
observed between Site 2 and the other three sites
in the Little Floyd River, these causes may be
responsible for other characteristics of the fish and
invertebrate communities that were not evaluated
in this assessment.
Also, had there been a weaker case for
deposited sediment, DO, temperature, and
ammonia as proximate stressors, the IDNR would
have needed to collect additional data to allow a
more thorough examination of co-occurrence and
stressor response for altered flow regime and
altered basal food source and suspended
sediment in the Little Floyd River.
Despite this lack of data, altered
flow regime is categorized as
unsupported. This decision is based in
oart on the characteristics of the
watershed. The land-use patterns and tile drainage systems in the Little Floyd River
watershed and the channel alteration in the river itself are characteristic of the
conditions of streams throughout the region which are not biologically impaired based
on IDNR biological criteria. Furthermore, there are no impoundments or water
withdrawals and flow is expected to be similar to other locations on the Little Floyd
River. However, flow may affect other candidate causes.
5.3.2. Suspended Sediment
Suspended sediment is considered an improbable cause for the biological
impairment of the Little Floyd River. While the evidence within the causal pathway
strengthened suspended sediment as a possible stressor, the data and evidence for
co-occurrence and stressor response were unavailable, inconclusive, or contradicted
suspended sediment as a stressor.
TSS and turbidity were evaluated to determine co-occurrence and stressor
response for increased suspended sediment. TSS as measured at the less-impaired
comparator site, (38.8 mg/L) was between the values for the more impaired sites (33.3
and 45.0 mg/L), therefore TSS evidence was scored as inconsistent. When comparing
the Little Floyd River sites to reference sites within the ecoregion, the mean TSS
concentration was outside the interquartile range at only one of the Little Floyd River
sites. This evidence also is considered inconsistent. The measurements of turbidity
from the Little Floyd River were all within the interquartile range of the ecoregion
reference sites, contradicting the mechanism involving a decrease of water clarity.
41
-------
Although the evidence from the
Little Floyd River do not specifically point
to problems of suspended sediment, the
biological sampling period occurred
during a limited time frame. Ecoregion
reference values were collected only
from July 15 to October 15 in order to
have a consistent monitoring period
during relatively low-flow periods.
However, the higher concentrations of
TSS that may be caused by spring storm events are not taken into account within the
existing sampling regime (see Comment 14). Therefore, despite the classification of
this stressor as unsupported, the available evidence was inadequate to fully eliminate
increased suspended sediment as a potential seasonal stressor.
Comment 14. From a Reviewer.
Effects of TSS are concentration and duration
dependent (see Newcombe and Jensen, 1996).
Persistent levels of low TSS may be more
important to aquatic life than the spikes in TSS
due to spring freshets.
Nevertheless, in the Little Floyd River, TSS
levels were similar to regional reference sites
where no impairments were observed (U.S. EPA
editor.)
5.3.3. Altered Basal Food Source
Data limitations for the altered basal food source allowed for the examination of
only two types of evidence: causal pathway and stressor-response. While the relatively
high phosphorus concentrations and decreased stream shading (see Table C-2)
allowed a strong causal pathway for increased primary production, the inconsistent
evidence of a plausible stressor-response relationship from the field from ecoregion
data weakens altered basal food source as a likely cause of the described impairments
(see Comment 9.
Seston and sediment chlorophyll measurements in the Little Floyd River were
less than the mean values reported for statewide sites. However, the periphyton
measurements were greater than the statewide mean. Changes in the basal food
source seem to be due to the presence of increased periphytic algae. This change
could influence the composition of the benthic macroinvertebrate and fish communities
in the Little Floyd River. However, due to the small differences between the Little Floyd
River sites and the statewide averages, an altered food resource is a weaker probable
cause than low DO or increased temperature.
42
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6. DISCUSSION AND HIGHLIGHTS
6.1. FROM SI TO TMDL
IDNR used the SI process to identify the probable causes for impairments in the
Little Floyd River in order to fulfill their 303(d) reporting requirements. The probable
causes determined in the SI were increased deposited sediment (particularly increased
fine sediment, increased embeddedness of riffles, and reduced pool depth) and
decreased concentrations of DO. Elevated temperature was designated as a
secondary cause because it was not due to regulated pollutant sources in Iowa.
Ammonia was not considered as the cause in this particular case, but was a pollutant of
concern in the river and was treated separately as described below. For TMDL
purposes, the terminology for these causes is siltation, organic enrichment/low DO,
thermal modification, and un-ionized ammonia. However, the 303(d) listing and the
TMDL for the Little Floyd River did not include all of these causes.
Based on the recommendations of the original SI, IDNR submitted a TMDL for
Sediment and DO on April 25, 2005; it was approved by the U.S. EPA on June 6, 2005.
The IDNR also listed un-ionized ammonia as a stressor in the SI primarily due to high
concentrations associated with a known fish kill that occurred in the Little Floyd River in
October 2003. Based on 305(b) assessment and 303(d) listing methodology (found in
IDNR, 2005a), ammonia would not be included as a cause for an impaired waters listing
but would be added to the 305(b)
assessment. IDNR identified the source
of the ammonia leading to this fish kill and
took appropriate action independently
from the TMDL process.
The thermal modification of the
stream is strongly related to habitat
alterations that have widened the channel
and increased exposure of the water and
stream sediments to sunlight. Although
not included in the TMDL as a cause, the
TMDL's implementation plan includes
remediation components to address
thermal stress, such as increasing
riparian vegetation, that IDNR expects will
improve the thermal regime of the Little
Floyd River (see Comment 15).
6.2. UNCERTAINTIES
The IDNR identified three uncertainties in the Little Floyd River case,
predominantly related to the timing of data collection and the overall quantity of data:
Comment 15. Some Regulatory Approaches
for Addressing Causes of Biological
Impairments.
Some states do not have biological criteria.
They rely on water quality criteria to protect
aquatic resources through TMDL
implementation. Some states do not have
criteria for thermal inputs. They may rely on
biological criteria to detect problems and then
use a TMDL to address thermal stress along with
other parameters. For example, High
temperatures in the Little Floyd River were
caused by nonpoint source changes in land uses
due to removal and alteration of vegetation. At
the time of the study, IDNR did not have state
temperature criteria, but has since implemented
them (see Comment 11). Therefore, the state
chose to recommend actions in the TMDL that
would lower temperature and thereby also
increase DO and reduce sediment loading.
43
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(1) ecoregion reference data were collected only during summer periods, when low-flow
conditions prevailed, (2) few data were available for ecoregion reference sites and for
several parameters within the Little Floyd River and its watershed, (3) historical data on
stream conditions is lacking both at ecoregion reference sites and in the Little Floyd
River. At each ecoregion reference site, the IDNR measures biological, chemical,
physical, and habitat parameters during each visit. The operating procedure dictates
that these samples be collected between July 15 and October 15 each year. However,
limiting sampling to this time period for developing stressor response relationships has
the disadvantage of not capturing the full range of physical and chemical parameters
that the resident community experiences over the course of a year. For example,
high-flow conditions associated with snowmelt and spring rains may cause pulses of
sediment, fertilizers, and pesticides—stressors that may have significant episodic
effects on the biological assemblages.
An added degree of uncertainty in the SI for the Little Floyd River lies in the
limited amount of ecoregion reference data. For the larger ecoregions across the state,
the IDNR collected 20 to 40 reference samples. In the Northwest Iowa Loess Prairies
ecoregion, the IDNR has collected only eight reference samples from six different sites.
This limitation in reference data further increases the uncertainty of the values used for
comparisons.
Within the dataset for the Little Floyd River itself, four very short reaches of
stream were sampled and these were not necessarily sampled in the same year. The
total evaluated length for habitat considerations was approximately 760 m. As shown in
Figure 1, the impaired segment is nearly 5.5 km long and the waterways above this
reach are extensive. This situation makes it difficult to assess the true condition of the
stream and watershed as a whole. For example, data from the impaired segment
indicate that stream bank erosion is minimal. However, general knowledge of the soils
and topography of this region suggests the possibility that bank erosion may be
occurring in the upper reaches of the watershed.
The limited historical dataset available for Iowa streams in general is problematic.
Changes in stream channel sinuosity, stream gradient, and channel morphology are
largely undocumented. The U.S. Geological Survey surface water gauges provide an
extensive flow record for many larger streams and rivers. However, the lack of records
for flow and other parameters in smaller streams like the Little Floyd River hinders
causal analysis.
6.3. FUTURE PROJECTS
The IDNR has continued to use the SI approach to determine the causes of
biological impairments in streams across the state. The results of this case are being
used to better design future sampling in order to acquire sufficient data to assess the
causal pathways in other impaired Iowa streams. Synoptic assessments are being
used to supplement the data collected in the typical sampling regime. These
assessments include full bioassessments used to determine FIBI and BMIBI scores,
44
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supplemented by several rapid bioassessments on both the mainstem and tributaries of
the streams. For example, more recent biological sampling on a biologically impaired
stream in eastern Iowa included three full bioassessments and 15 rapid
bioassessments. IDNR expects that synoptic sampling will provide paired data and thus
stronger evidence for co-occurrence in future SI efforts.
To improve the usability of the data from the rapid bioassessments, the IDNR
has developed a supplemental datasheet for the rapid bioassessment sites. The new
datasheet should provide valuable information about the condition of the stream as a
whole. Some of the additional information collected for future Sis will fill gaps in the
characterization of the causal pathways that increased uncertainty in the Little Floyd
River case (for example, qualitative determinations of floodplain connectivity and leaf
litter abundance). A portion of the new datasheet will provide supplemental
measurements of parameters that are measured at full bioassessment sites but which
are not normally captured in a rapid bioassessment (for example, stream shading,
embeddedness, and abundance of woody debris).
In future SI cases, the IDNR also hopes to make more extensive use of the data
available using Geographic Information Systems. Estimates of watershed soil loss (via
the revised universal soil loss equation), land cover, livestock abundance, and other
basin and subbasin statistics would compliment the SI process. Further, the
comparison of geo-referenced aerial photographs and topographic maps generated
over the years may provide insights into recent physical changes in the watershed.
6.4. CONCLUSION
The SI process as used by the IDNR has been a successful endeavor. This
process made it possible for the IDNR to complete several TMDLs. These TMDLs
include a rational and scientifically sound basis for improving the biological condition of
impaired waterways. The SI and TMDL are the initial steps toward improving the
conditions in the Little Floyd River and other streams. Implementation and continued
monitoring are vital to the restoration of a sustainable community to biologically
impaired waters such as the Little Floyd River.
45
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7. REFERENCES
Eaton, J.G., Scheller, R.M. 1996. Effects of climate warming on fish thermal habitat in
streams of the United States. Am. Soc. Limnol. Oceanogr. 41 (5): 1109—1115.
Griffith, G.E., Omernik, J.M., Wilton, T.F., et al. 1994. Ecoregions and subecoregions
of Iowa: a framework for water quality assessment and management. J. Iowa Acad.
Sci. 10(1 ):5—13.
IAC (Iowa Administrative Code). 2004. Chapter 567-61: water quality standards,
[effective date 6/16/04],
IAC (Iowa Administrative Code). 2006. Chapter 567-61: water quality standards,
[effective date 2/15/06],
IDNR (Iowa Department of Natural Resources). 2004. Draft protocol for stressor
identification. Environmental Protection Division, TMDL and Water Quality Assessment
Section; Des Moines, Iowa.
IDNR (Iowa Department of Natural Resources). 2005a. Methodology for Iowa's 2004
water quality assessment, listing, and reporting pursuant to Sections 305(b) and 303(d)
of the federal Clean Water Act. Environmental Protection Division; Des Moines, Iowa.
Available online at:
http://wqm.igsb.uiowa.edu/WQA/303d/2004/2004FinalMethodology.pdf.
IDNR (Iowa Department of Natural Resources). 2005b. Fish kill data available online.
Environmental Protection Division; Des Moines, Iowa. Available online at:
http://wqm.igsb.uiowa.edu/wqa/fishkill.html.
IDNR (Iowa Department of Natural Resources). 2005c. Iowa Department of Natural
Resources TMDL & Water Quality Assessment Section. Total Maximum Daily Load For
Sediment and Dissolved Oxygen, Little Floyd River, Sioux and O'Brien Counties, Iowa.
Available at:
http://www.epa.gov/Region7/water/pdf/littlefloyd_riv_sediment_do_final060605.pdf.
Ingersoll, C.G., MacDonald, D.D., Wang, N.,etal. 2000. Prediction of sediment toxicity
using consensus-based freshwater sediment quality guidelines. U.S. Geological Survey
final report for the U.S. Environmental Protection Agency. EPA 905/R-00/007.
Available online at: http://www.cerc.usgs.gov/pubs/center/pdfdocs/91126.pdf.
Newcombe, C.P., and J.O.T. Jensen. 1996. Channel suspended sediment and
fisheries: a synthesis for quantitative assessment of risk and impact. N. Am. J. Fish.
Man. 16:693-727.
46
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U.S. EPA (Environmental Protection Agency). 1986. Ambient water quality criteria for
dissolved oxygen. Office of Water Regulations and Standards; EPA/440/5-86/003.
Available online at
http://www.sjrdotmdl.Org/concept_model/bio-effects_model/documents/Chapman1986.p
df.
U.S. EPA (Environmental Protection Agency). 1999. 1999 Update of ambient water
quality criteria for ammonia. Office of Water; EPA/822/R-99/014. Available online at
http://www.fs.fed.us/fire/retardant/references/US_EPA_1999.pdf.
U.S. EPA (Environmental Protection Agency). 2000. Stressor identification guidance
document. Office of Water; EPA/822/B-00/025. Available online at
http://www.epa.gov/waterscience/biocriteria/stressors/stressorid.pdf.
U.S. EPA (Environmental Protection Agency). 2006. Causal Analysis/Diagnosis
Decision Information System, www.epa.gov/caddis.
Wlton,T.F. 2004. Biological assessment of Iowa's wadeable streams. Project Report.
Iowa Department of Natural Resources, Environmental Protection Division, TMDLand
Water Quality Assessment Section. Des Moines, Iowa. Available at:
http://wqm.igsb.uiowa.edu/wqa/streambio/index.html.
47
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APPENDIX A
STATE OF IOWA METHODOLOGY
A.1. ECOREGION REFERENCE SITES
In Iowa, ecoregion reference sites represent contemporary stream conditions that
are minimally disturbed by human activities. As they are used in bioassessment,
reference sites define biological conditions against which other streams are compared.
Therefore, they should not represent stream conditions that are anomalous or
unattainable within the ecoregion.
Reference sites represent desirable, natural qualities that are attainable by other
streams within the same ecoregion. IDNR evaluated a number of important watershed,
riparian, and in-stream characteristics as part of the reference site selection process
(Griffith et al., 1994; Wilton, 2004). Currently, there are 96 ecoregion reference sites
used by IDNR for stream biological assessment purposes (see Figure A-1). Reference
condition is the subject of a significant amount of research and development throughout
the United States. The IDNR will continue to refine Iowa's reference condition
framework as new methods and technologies become available.
A.2. SAMPLING PROCEDURES
A.2.1. Biological and Habitat Parameters
The IDNR uses standard procedures for sampling stream benthic
macroinvertebrates and fish assemblages to ensure data consistency between
sampling sites and sampling years (IDNR, 2001 a,b). Routinely, sampling is conducted
during a 3-month index period (July 15-October 15) in which stream conditions and
aquatic communities are relatively stable. A representative reach of stream ranging
from 150-350 m is defined as the sampling area.
Two types of benthic macroinvertebrate samples are collected at each site:
(1) Standard-Habitat samples are collected from rock or wood substrates in flowing
water and (2) Multihabitat samples are collected by handpicking organisms from all
identifiable and accessible types of benthic habitat in the sampling area. The
multihabitat sample data improve the estimate oftaxa richness for the entire sample
reach. Benthic macroinvertebrates are identified in the laboratory to the lowest practical
taxonomic endpoint.
IDNR samples fish using direct current (DC) electrofishing gear. In shallow
streams, one or more battery-powered backpack shockers are used. A tote barge,
generator-powered shocker is used in deeper, wadeable streams. Fish are collected in
one pass through the sampling reach proceeding downstream to upstream. The
number of individuals of each species is recorded, and individual fish are examined for
48
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Eco regions: \J,\
40(a) - Central Irregular Plains (Loess Flats and Till Plains)
47(a) - Western Corn Belt Plains (Northwest I owa Loess Prairies) 47(b) - WCBP (Des Moines Lobe)
47(c) - WCBP (lowan Surface) 47(d) - WCBP (Missouri Alluvial Plain) 47(e) - WCBP (Steeply Rolling Loess Prairies)
47(f) - WCBP (Rolling Loess Prairies) 47(m) - WCBP (Western Loess Hills)
52(b) - Driftless Area (Paleozoic Plateau) 72(d) - Central Interior Lowland (Upper Mississippi Alluvial Plain)
FIGURE A-1
Iowa Ecoregions and Wadeable Stream Reference Sites: 1994-2000. Little Floyd River
is in Ecoregion 47a.
49
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external abnormalities, such as deformities, eroded fins, lesions, and tumors (DELT).
Most fish are identified to species in the field; however, small or difficult fish to identify
are examined under a dissecting microscope in the laboratory.
IDNR evaluates physical habitat systematically at each stream sampling site.
Different in-stream and riparian habitat variables are estimated or measured at
10 stream channel transects that are evenly spaced throughout the sampling reach.
Summary statistics are calculated for a variety of physical habitat characteristics, and
these data are used to describe the stream environment and provide a context for the
interpretation of biological sampling results.
A.2.2. Physical and Chemical Parameters
Grab samples are collected and analyzed for a number of chemical parameters,
including concentrations of ammonia nitrogen (as N), nitrate + nitrite nitrogen (as N),
total Kjeldahl nitrogen (as N), 5-day carbonaceous biochemical oxygen demand
(CBOD), total phosphate (as P), and TSS. Standard U.S. EPA-approved procedures
are used in the analysis of all chemical constituents. Field measurements are recorded
for flow, pH, DO, and water temperature.
Event monitoring involves the use of ISCO samplers equipped to determine
stream stage. Composite samples are tested in the laboratory in the same way as grab
samples. Field parameters are recorded when the samples are retrieved from the ISCO
sampler.
Samples tested for pesticides and metals are collected and analyzed following
REMAP protocols (IDNR, 2001 c; IDNR 2002).
A.2.3. Biological Indices
Biological sampling data from ecoregion reference sites were used to develop a
Fish Index of Biotic Integrity (FIBI) and a Benthic Macroinvertebrate Index of Biotic
Integrity (BMIBI) (Wilton, 2004). The FIBI and BMIBI are described as multimetric or
composite indices because they combine several individual measures or metrics. A
metric is an ecologically relevant and quantifiable attribute of the aquatic biological
community. A useful metric can be measured cost-effectively and reliably and responds
predictably to specific environmental disturbances.
The FIBI and BMIBI indices each contain 12 metrics that reflect a broad range of
aquatic community attributes (see Table A-1). Metric scoring criteria are used to
convert raw metric data to normalized scores ranging from 0 (poor) to 10 (optimum).
The normalized metric scores, which are weighted equally, are then combined to obtain
the FIBI and BMIBI scores, which both have a possible scoring range from 0 (worst) to
100 (best). Table A-2 lists qualitative categories for FIBI and BMIBI scores. A detailed
description of the FIBI and BMIBI development and calibration process is available on
the IDNR Web page (http://wqm.igsb.uiowa.edu/wqa/streambio/index.html) (Wlton,
2004).
50
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TABLE A-1
Data Metrics of the Benthic Macroinvertebrate Index of Biotic Integrity (BMIBI)
and the Fish Index of Biotic Integrity (FIBI)
(BMIBI)
(FIBI)
1. MH-Taxa Richness
1. # Native Fish Species
2. SH-Taxa Richness
2.# Sucker Species
3. MH-EPT Richness
3.# Sensitive Species
4. SH-EPT Richness
4.# Benthic Invertivore Species
5. MH-Sensitive Taxa
5. % 3-Dominant Fish Species
6. % 3-Dominant Taxa (SH)
6. % Benthic Invertivores
7. Biotic Index (SH)
7. % Omnivores
8.% EPT (SH)
8. % Top Carnivores
9. % Chironomidae (SH)
9. % Simple Lithophil Spawners
10.% Ephemeroptera (SH)
10. Fish Assemblage Tolerance Index
11.% Scrapers (SH)
11. Adjusted Catch Per Unit Effort
12.% Dominant Functional
Feeding Group (SH)
12.% Fish with DELTs
MH = Multihabitat sample.
SH = Standard-habitat sample.
51
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TABLE A-2
Qualitative Scoring Guidelines for the BMIBI and FIBI
Biological Condition Rating
BMIBI
FIBI
Poor
0-30
0-25
Fair
31-55
26-50
Good
56-75
51-70
BMIBI = Benthic Macroinvertebrate Index of Biotic Integrity.
FIBI = Fish Index of Biotic Integrity.
52
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A.3. REFERENCES
Griffith, G.E., Omernik, J.M., Wilton, T.F., et al. 1994. Ecoregions and subecoregions
of Iowa: a framework for water quality assessment and management. J. Iowa Acad.
Sci. 10(1 ):5—13.
IDNR (Iowa Department of Natural Resources). 2001a. Biological sampling procedures
for wadeable streams and rivers in Iowa. June 30, 1994 revised May 3, 2001.
Environmental Protection Division, Water Resources Section; Des Moines, Iowa; 15 p. +
appendices.
IDNR (Iowa Department of Natural Resources). 2001 b. Habitat evaluation procedures
for wadeable streams and rivers in Iowa. June 30, 1994 revised May 3, 2001.
Environmental Protection Division, Water Resources Section; Des Moines, Iowa: 17 p. +
appendices.
IDNR (Iowa Department of Natural Resources). 2001c. A probabilistic survey of Iowa's
stream resources: R-EMAP project proposal. July 9, 2001. Environmental Protection
Division, Water Resources Section; Des Moines, Iowa: 13 p. + appendices.
IDNR (Iowa Department of Natural Resources). 2002. Quality assurance project plan
for a Region 7 REMAP project: a probabilistic survey of Iowa's wadeable streams.
October 28, 2002. Environmental Protection Division, Water Resources Section; Des
Moines, Iowa: 17 p. and appendices.
Wlton,T.F. 2004. Biological assessment of Iowa's wadeable streams. Project Report.
Iowa Department of Natural Resources, Environmental Protection Division, TMDLand
Water Quality Assessment Section; Des Moines, Iowa. Available at:
http://wqm.igsb.uiowa.edu/wqa/streambio/index.html.
53
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APPENDIX B
DATA SUMMARY
TABLE B-1
Monthly Monitoring Results for the Little Floyd River at Sites 2, 3, and 4
Collection
Date
Flow
Rate
(cfs)
DO
(mg/L)
Temp
(°C)
PH
Ammonia
Nitrogen
as N
(mg/L)
TKN as
N (mg/L)
no3 +
N02 as
N
(mg/L)
CBOD
(20-d)
(mg/L)
CBOD
(5-d)
(mg/L)
Site 2
4/10/2001
34.5
10.2
6.8
8
<0.1
0.6
13
--
<2
5/8/2001
100
10.7
9.6
8
<0.1
<0.1
18
--
<2
6/12/2001
30
9.5
15.9
8
<0.1
<0.1
17
--
<2
7/17/2001
7
10
25.7
8.2
<0.1
0.5
10
--
<2
8/14/2001
3.7
7.5
17.9
8.1
<0.1
0.9
9.1
--
<2
9/12/2001
1.6
6.2
16
8.3
0.03
0.56
5
--
<2
10/9/2001
3.3
8.6
11.9
8.3
<0.05
1.1
4.7
--
2
11/13/2001
2.2
9.3
10.2
8.4
<0.05
0.67
4.4
--
<2
3/11/2003
0.6
6.7
0
7.8
0.12
0.44
5
3
--
4/8/2003
1.7
15.3
2.1
8.4
<0.05
0.68
4.5
8
--
5/13/2003
32.6
9.9
10.6
8.2
<0.05
0.62
13
6
--
6/10/2003
24
12.3
16.3
8.2
<0.05
0.7
13
35
--
7/8/2003
108.8
6.9
16.8
7.6
<0.05
1.7
7.6
20
--
8/12/2003
2.5
7
22.6
8.1
<0.05
0.74
4.8
5
--
9/9/2003
1.2
10
19.4
8.2
0.05
1.1
3
9
--
10/14/2003
1.9
9
8.8
8.1
<0.05
0.65
3.1
4
--
54
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TABLE B-1. cont.
Site 3
7/24/2002
2
10.9
25
8.1
<0.05
1
3
--
--
8/6/2002
2
8.5
25.7
8.3
0.32
1.6
1.6
--
--
8/22/2002
5.6
6.2
21.3
8.1
0.21
11
1.6
--
--
Site 4
3/13/2001
1.2
9.9
0
7.8
<0.1
0.2
6.5
--
3
4/10/2001
33.5
10.6
8.1
8.1
<0.1
0.7
13
--
<2
5/8/2001
107
10.5
10.9
8
<0.1
0.1
18
--
<2
6/12/2001
35
9.5
16.6
7.9
<0.1
<0.1
17
--
<2
7/17/2001
9
13.4
27.6
8.5
<0.1
<0.1
10
--
<2
8/14/2001
4.9
8.6
18.3
8.2
<0.1
0.7
9.2
--
<2
9/11/2001
1.9
12.2
22.1
8.5
0.04
0.87
3.8
--
3
10/9/2001
3.5
8.6
12.9
8.4
<0.05
0.9
4.9
--
2
11/13/2001
9
10.3
10.1
8.7
<0.05
0.6
3.9
--
<2
3/11/2003
0.6
3.3
0
7.7
0.18
1.2
5.9
4
--
4/8/2003
2
16
0.9
8.3
<0.05
0.4
4.6
7
--
5/13/2003
31.6
9.1
11.1
8.2
<0.05
0.63
13
5
--
6/10/2003
18
10.1
17.4
7.9
<0.05
0.83
13
30
--
7/8/2003
118.5
7
17.2
7.8
0.15
3
8.8
24
--
8/12/2003
7.3
9.9
25.8
8.2
0.06
0.9
4.3
4
--
9/9/2003
0.9
7.3
20.2
8.2
<0.05
0.69
2
7
--
10/14/2003
1.7
10.5
9.6
8.2
0.06
0.6
2.2
6
--
55
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TABLE B-1. cont.
Collection
Date
Total
Phosphorus
as P (mg/L)
Orthophosphate
as P (mg/L)
TSS
(mg/L)
TVSS
(mg/L)
Silica as
Si02
(mg/L)
Specific
Conduct-
ance
(|jS/cm)
Site 2
4/10/2001
0.1
<0.1
37
--
--
740
5/8/2001
0.1
0.14
18
--
--
780
6/12/2001
<0.1
0.03
6
--
--
760
7/17/2001
<0.1
0.07
6
--
--
730
8/14/2001
0.15
0.07
29
--
--
790
9/12/2001
0.16
0.05
15
--
--
700
10/9/2001
0.61
0.49
70
--
--
1300
11/13/2001
0.47
<0.05
28
--
--
1200
3/11/2003
0.06
0.06
2
<1
19
750
4/8/2003
0.12
<0.05
24
5
--
720
5/13/2003
0.09
0.06
13
3
--
820
6/10/2003
0.07
0.04
22
4
--
860
7/8/2003
0.87
0.54
220
37
--
440
8/12/2003
0.23
0.21
10
1
--
750
9/9/2003
0.28
0.12
97
13
--
700
10/14/2003
0.11
0.08
24
4
--
750
Site 3
7/24/2002
0.23
0.14
16
3
22
--
8/6/2002
0.31
0.26
57
6
25
--
8/22/2002
0.28
0.12
62
8
21
--
56
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TABLE B-1. cont.
Site 4
3/13/2001
0.3
0.2
6
--
--
760
4/10/2001
0.2
0.1
24
--
--
740
5/8/2001
0.1
0.12
21
--
--
770
6/12/2001
1.2
0.03
9
--
--
750
7/17/2001
<0.1
0.05
5
--
--
700
8/14/2001
0.22
0.03
14
--
--
820
9/11/2001
0.16
0.02
4
--
--
620
10/9/2001
0.41
0.37
28
--
--
1300
11/13/2001
0.49
0.53
8
--
--
1300
3/11/2003
0.12
0.06
37
5
18
810
4/8/2003
0.07
<0.05
11
2
--
700
5/13/2003
0.08
<0.05
25
4
--
820
6/10/2003
0.1
0.05
33
5
--
840
7/8/2003
0.84
0.44
260
46
--
540
8/12/2003
0.22
0.17
16
2
--
740
9/9/2003
0.15
0.08
41
7
--
690
10/14/2003
0.1
0.05
34
4
--
710
TKN = total Kjeldahl nitrogen.
TVSS = total volatile suspended solids.
57
-------
TABLE B-2
Event Sampling Results at Site 4 in the Little Floyd River
Collection
Date
Flow
Rate
(cfs)
DO
(mg/L)
Temp
(°C)
PH
Ammonia
Nitrogen
as N
(mg/L)
TKN as
N (mg/L)
no3 +
N02 as
N (mg/L)
CBOD
(20-d)
(mg/L)
CBOD
(5-d)
(mg/L)
3/28/2001
116.4
11.7
0.4
7.5
0.3
1.5
6.9
—
<2
7/25/2001
113
7.8
21.8
7.9
<0.1
1.6
13
—
2
4/9/2003
5.3
16.9
4.4
8.4
<0.05
0.48
3.9
2
—
11/1/2003
(grab)
1.6
10
4.1
8.2
—
—
--
--
—
11/1/2003
(prepeak)
—
—
—
—
4.9
5.6
4.7
26
--
11/1/2003
(postpeak)
—
—
—
—
6.5
9
4.7
40
--
Collection
Date
Total
Phosphorus
as P (mg/L)
Orthophospha
te as P (mg/L)
TSS
(mg/L)
TVSS
(mg/L)
Specific Conductance
(pS/cm)
3/28/2001
0.6
0.5
38
—
430
7/25/2001
0.6
0.5
81
—
490
4/9/2003
0.06
<0.05
18
3
640
11/1/2003
(grab)
—
—
—
—
—
11/1/2003
(prepeak)
0.34
0.1
38
10
760
11/1/2003
(postpeak)
0.61
0.2
66
18
810
58
-------
TABLE B-3
Metrics Calculated from the Biological Samples Collected from the Little Floyd
River, 1999-2002
Metrics
9/14/1999
Site 1
9/12/2001
Site 2
8/22/2002
Site 3
9/11/2001
Site 4
Drainage Area (km2)
109
119
142
154
Reach Length (m)
174
202
183
191
FIBI
Total Fish (#)
1063
875
1068
2025
Total Species (#)
10
14
14
14
Native Species
5.1
6.8
6.3
6.2
Sucker Species
3.0
3.1
2.9
2.8
Sensitive Species
0
4.3
0
3.9
Benthic Invertivores
3.9
4.0
3.7
3.6
% Top 3 Abundant
4.4
5.1
3.3
5.4
% Benthic Invertivores
0.7
0.9
0.7
0.9
% Omnivore
6.4
8.5
7.1
8.4
% Top Carnivore
0
0
0
0
% Lithophilic Spawners
0
0
0
0
Tolerance Index
2.2
3.9
3.8
3.4
Adjusted CPUE
5.2
6.5
8.5
10
% DELT
0
0
0
0
BMIBI
MH Total Taxa
4.0
6.1
4.8
5.6
59
-------
TABLE B-3 cont.
Metrics
9/14/1999
Site 1
9/12/2001
Site 2
8/22/2002
Site 3
9/11/2001
Site 4
SH Total Taxa
6.6
10
7.2
6.0
MH EPT Taxa
2.7
6.3
4.7
3.4
SH EPT Taxa
5.9
9.2
5.9
6.1
Metrics
9/14/1999
Site 1
9/12/2001
Site 2
8/22/2002
Site 3
9/11/2001
Site 4
MH Sensitive Taxa
0
1
2.9
1.9
SH Ephemeroptera %
3.6
5.0
5.6
2.7
SH EPT %
4.3
6.3
5.6
2.6
SH Chironomid %
5.0
8.2
6.9
3.1
SH Scraper %
2.5
3.9
2.5
0.6
SH Top 3 Dominant %
4.7
9.3
6.2
2.4
SH Dominant FFG %
4.5
8.4
5.3
2.0
Mod. Hilsenhoff Index
5
4.6
4.7
4.4
CPUE = catch per unit effort.
DELT = deformities, eroded fins, lesions, tumors.
EPT = Ephemeroptera, Plecoptera, and Trichoptera.
FFG = Functional feeding group.
MH = Multihabitat.
SH = Standard habitat.
60
-------
TABLE B-4
Concentrations of Metals Found in Water and Sediment in the Little Floyd River at
Site 3 on 8/22/2002. Probable effect concentrations for these substances are also
given for comparison.
Parameter
Concentration
in Water (mg/L)
Concentration in
Sediment (mg/kg dry wt)
Probable Effect Concentration
(mg/kg dry wt)*
Total Arsenic
<0.01
2.2
33
Total
Cadmium
<0.001
<2
4.98
Total
Chromium
<0.02
12
111
Total Copper
<0.01
8.8
149
Total Lead
<0.01
10
128
Total Mercury
<0.00005
<1
1.06
Total Nickel
<0.05
17
48.6
Total
Selenium
<0.01
1.1
—
Total Silver
<0.01
<1
—
Total Zinc
<0.02
38
459
Source: Ingersoll, C.G., MacDonald, D.D., Wang, N., et al. 2000. Prediction of sediment toxicity using
consensus-based freshwater sediment quality guidelines. U.S. Geological Survey final report for the
U.S. Environmental Protection Agency. EPA 905/R-00/007. Available online at:
http://www.cerc.usgs.gov/pubs/center/pdfdocs/91126.pdf.
61
-------
TABLE B-5
Concentrations of Common Pesticides and Pesticide Residue as Measured on
8/22/2002 at Site 3 in Sediments of the Little Floyd River.
Parameter
Concentration in
Sediment (mg/kg)
Parameter
Concentration in
Sediment
(mg/kg)
Aldrin
<0.01
Endosulfan I
<0.01
alpha-BHC
<0.01
Endosulfan II
<0.01
alpha-Chlordane
<0.01
Endosulfan sulfate
<0.01
Aroclor 1016
<0.05
Endrin
<0.01
Aroclor 1221
<0.05
Endrin aldehyde
<0.01
Aroclor 1232
<0.05
Endrin ketone
<0.01
Aroclor 1242
<0.05
gamma-Chlordane
<0.01
Aroclor 1248
<0.05
Heptachlor
<0.01
Aroclor 1254
<0.05
Heptachlor epoxide
<0.01
Aroclor 1260
<0.05
Hexachlorobenzene
<0.01
beta-BHC
<0.01
Lindane
(gamma-BHC)
<0.01
cis-Nonachlor
<0.01
Methoxychlor
<0.01
DDD
<0.01
Mirex
<0.01
DDE
<0.01
Pentachloroanisole
<0.01
DDT
<0.01
Propachlor
<0.01
delta-BHC
<0.01
Toxaphene
<0.1
Dieldrin
<0.01
trans-Nonachlor
<0.01
62
-------
TABLE B-6
Habitat and Water Quality Measurements in the Little Floyd River and in the Ecoregion 47a (Northwest Iowa Loess Prairies)
Reference Sites (Reference Samples 73 and 78 Represent a Single Site Sampled Twice [8/27/2002 and 7/9/1996] and 75 and 79
Represent a Single Site Sampled Twice [8/14/2001 and 8/3/1995])
Site
#
Date
Stream
Width
(m)
Width:
Depth
Std Dev
Depth
(cm)
Avg
Thalweg
Depth
(cm)
Avg
Depth
(cm)
Max
Depth
(cm)
Riffle
%
Pool
%
Run
%
Avg
Embedd-
edness
%
Embedd-
edness
LF1
9/14/1999
4.8
25
7
19
12.
55
0
48
52
NA
NA
LF2
9/12/2001
3.6
7.96
21
45
24
91
11
54
36
0
NA
LF3
8/22/2002
5.9
13.15
14
44
28
73
0
50
50
2
21-40
LF4
9/11/2001
5.2
22.99
7
23
12
37
5
23
71
0
NA
73
8/27/2002
2.7
8.33
11
33
23
82
9
62
29
2.5
41-60
74
9/14/2001
7.6
18.15
16
42
23
113
16
52
32
2
21-40
75
8/14/2001
5.2
13.98
11
37
21
82
14
23
62
2.5
41-60
76
10/7/1998
21.5
49.72
12
43
20
76
4
5
91
0
41-60
77
9/5/1996
9.4
41.62
6
23
11
46
4
0
96
0
NA
78
7/9/1996
4.2
11.60
13
36
24
79
18
23
59
0
41-60
79
8/3/1995
6.9
14.01
13
49.
26
107
28
20
52
0
41-60
80
8/2/1995
11.4
30.99
12
37
19
76
18
7
75
0
41-60
-------
TABLE B-6. cont.
Site
#
% Horizontal +
%Vertical
% Moderate
+ %
Undercut
Left
Horiz.
%
Left
Moderate
%
Left
Vert.%
Left
Undercut
%
Right
Horiz.%
Right
Moderate
%
Right
Vert.%
Right
Under-
cut%
LF1
40
50
20
20
30
10
20
70
10
0
LF2
35
50
30
30
10
0
30
70
0
0
LF3
15
35
0
0
0
0
0
70
30
0
LF4
25
50
20
20
10
0
20
80
0
0
73
10
40
10
70
20
0
10
90
0
0
74
35
15
60
40
0
0
70
20
10
0
75
12.5
37.5
10
90
0
0
40
60
0
0
76
22.5
27.5
30
60
10
0
30
40
20
10
77
0
0
0
0
0
0
0
0
0
0
78
0
0
0
0
0
0
0
0
0
0
79
0
0
0
0
0
0
0
0
0
0
80
0
0
0
0
0
0
0
0
0
0
-------
5
25
19
15
56
38
43
7
4
66
36
32
TABLE B-6. cont.
Total
Fines
95
75
80
85
43
62
55
93
94
28
56
66
Clay
%
Silt
%
58
32
29
42
26
13
22
13
Sand
%
31
14
40
47
41
17
43
31
80
90
22
44
52
Soil
%
Gravel
%
19
19
11
31
32
20
52
26
Cobble
%
17
21
10
28
Boulder
%
Rip
Rap
%
Detritus/
Muck %
Wood
%
Bed-
rock
%
-------
TABLE B-6. cont.
Site
#
Lt Bare
Bank (%)
Rt
Bare
Bank
(%)
Lt
Buffer
Width
Lt Buffer
Avg
Rt
Buffer
Width
Rt
Buffer
Avg
Instream
Cover(%)
Woody
Debris
(%)
Avg
Canopy
Shade
Canopy
Std Dev
Canopy
Max
Shade
Canopy Min
Shade
LF1
48
36
--
100
--
52
1
0
5
12
60
0
LF2
49
64
--
8
--
8
12
0
15
22
41
5
LF3
11
22
--
42
--
22
8
0
12
21
32
2
LF4
41
42
--
33
--
33
2
4
6
12
15
0
73
7
5
--
100
--
100
28
0
5
8
18
0
74
53
90
--
93
--
100
2
29
27
23
53
0
75
17
24
--
100
--
100
2
0
13
24
32
0
76
60
63
40-
100+
0
50-
100+
0
2
18
29
34
52
6
77
73
88
100+
0
100+
0
0
18
6
11
16
0
78
24
36
100+
0
100+
0
6
0
24
35
48
0
79
29
31
80-
100
0
50-100
0
7
7
17
20
23
1
80
53
42
100+
0
<10
0
1
4
6
17
26
0
-------
TABLE B-6. cont.
Site
#
Ammonia
Nitrogen
as N
(mg/L)
Atrazine
Screen
(Mg/L)
DO
(mg/L)
Field
pH
Field
Temp
(°C)
Flow
Rate
(cfs)
no2
+
no3
as N
(mg/
L)
Specific
Conduct-
ance
(pS/cm)
TKN
(mg/
L)
TDS
(mg/
L)
TSS
(mg/
L)
Total
Hardness
(mg/L as
CaC03)
Total
Phos-
phorus
as P
(mg/L)
Turbidity
(NTU)
LF1
--
--
15.3
8.1
18
0.7
--
--
--
--
--
-
-
LF2
0.03
--
6.2
8.3
16
1.6
5
700
0.56
--
15
--
0.16
-
LF3
0.21
--
6.2
8.1
21.3
5.6
1.6
--
11
350
62
--
0.28
33
LF4
0.04
--
12.2
8.5
22.1
1.9
3.8
620
0.87
4
--
0.16
-
73
M
0.14
9.50
7.3
18.5
27.0
9.40
770
0.40
410
11
375
0.10
10
74
M
0.12
8.90
7.1
17.5
19.0
12.00
880
0.60
480
56
430
0.10
31
75
M
0.28
8.70
7.9
14.3
5.0
9.90
730
0.40
410
38
400
0.10
26
76
M
0.14
7.30
7.4
20.0
8.0
0.50
870
0.90
490
33
410
0.10
18
77
M
0.10
10.20
8.3
12.7
38.5
7.40
720
0.80
490
14
370
0.10
8
78
0.10
0.14
9.20
8.3
19.0
5.5
9.00
850
0.65
520
7
420
0.02
4
79
0.10
0.11
6.80
8.1
18.3
11.8
5.10
680
1.20
420
23
330
0.02
18
80
0.07
0.09
5.40
7.9
24.9
1.6
5.90
760
0.90
450
9
400
0.05
9
NTU = Nephelometric Turbidity Units.
-------
40
• Temperature (C)
* D.O. (mg/L)
7/24/02
7/26/02
7/28/02
7/30/02
8/1/02
8/3/02
8/5/02
8/7/02
30
• Temperature (C)
* D.O. (mg/l)
25
20
15
10
5
0 -I 1
6/24/03 6/25/03
6/26/03 6/27/03
6/28/03 6/29/03 6/30/03
7/1/03
7/2/03
35
• Temperature (C)
® D.O. (mg/l)
30
25
20
15
10
5
0
8/12/03
8/14/03
8/16/03
8/18/03
FIGURE B-1
8/20/03
8/22/03
8/24/03
8/26/03
Diurnal Temperature and Dissolved Oxygen Measurements in the Little Floyd River (a)
at Site 3 from July 24 to August 6, 2002; (b) at Site 4 from June 24 to July 2, 2003; and
(c) at Site 4 from August 12 to August 27, 2003
68
-------
APPENDIX C
ANALYSIS OF EVIDENCE TABLES
TABLE C-1
Evidence of Spatial/temporal Co-occurrence in the Little Floyd River, Iowa
Spatial/Temporal Co-occurrence
Proximate
Stressor
Measure of
Exposure
Measurement
at Internal
Comparator
(Site 2)
Measurements
at Sites 1, 3,
and 4,
Respectively
Evidence of
Co-occurrence
Score
Altered Flow Regime (see Figure 6)
NE
Decreased
Flow
Heterogeneity
NE
NE
Increased
Maximum
Flow
NE
NE
Increased
Frequency of
Low Flows
NE
NE
Increased Sediment (see Figure 7)
Suspended: 0 Deposited: +
Increased
Suspended
Sediment
TSS (mg/L)
38.8
Missing (M);
45.0; 33.3
NE; yes; no
0
Decreased
Clarity
turbidity
(NTU)
M
M; 21.6; 12.7
NE
NE
Decreased
Algal Growth
seston
chlorophyll a
(Mg/L)
M
M; 19.7; 7.4
NE
NE
periphyton
chlorophyll a
(Mg/cm2)
M
M; 42; M
NE
NE
69
-------
TABLE C-1. cont.
Spatial/Temporal Co-occurrence
Proximate
Stressor
Measure of
Exposure
Measurement
at Internal
Comparator
(Site 2)
Measurements
at Sites 1, 3,
and 4,
Respectively
Evidence of
Co-occurrence
Score
sediment
chlorophyll a
(|jg/cm2)
M
M; 22; M
NE
NE
gross primary
production
(GPP)
M
M; 11; 4.4
NE
NE
production to
respiration ratio
(P:R)
M
M; 0.82; 0.37
NE
NE
Increased
Deposited
Fine
Sediment
% total fines
75
95; 80; 85
yes; yes; yes
+
% silt
32
58; 29; 42
yes; no; yes
0
% sand
40
31; 47; 41
no; yes; no
0
% total coarse
25
5; 19; 15
yes; yes; yes
+
% total gravel
19
3; 19; 11
yes; no; yes
0
Loss of Pool
Depth
% reach as
pool habitat
54
48; 50; 23
yes; yes; yes
+
maximum
depth (cm)
91
55; 73; 37
yes; yes; yes
+
Embedded
Riffle
% riffles
11
0; 0; 5
yes; yes; yes
+
embeddedness
rating
M
M; 21-40%; M
NE
NE
Burial of
Organisms
NE
NE
70
-------
TABLE C-1
. cont.
Spatial/Temporal Co-occurrence
Proximate
Stressor
Measure of
Exposure
Measurement
at Internal
Comparator
(Site 2)
Measurements
at Sites 1, 3,
and 4,
Respectively
Evidence of
Co-occurrence
Score
Altered Basal Food Source (see Figure 8)
NE
Increased/
Altered
Primary
Producers
seston
chlorophyll a
(MQ/L)
M
M; 19.7; 7.4
NE
NE
periphyton
chlorophyll a
(|jg/cm2)
M
M; 42; M
NE
NE
sediment
chlorophyll a
(Mg/cm2)
M
M; 22; M
NE
NE
GPP
M
M; 11; 4.4
NE
NE
P:R
M
M; 0.82; 0.37
NE
NE
Decreased
Allochthon-
ous
Resources
NE
NE
Decreased DO (see Figure 9)
+
Decreased
DO
lowest
observed
summer DO
(mg/L) -
daytime grab
samples
6.2
15.3; 6.2; 4.6
no;no;yes
0
71
-------
TABLE C-1
. cont.
Spatial/Temporal Co-occurrence
Proximate
Stressor
Measure of
Exposure
Measurement
at Internal
Comparator
(Site 2)
Measurements
at Sites 1, 3,
and 4,
Respectively
Evidence of
Co-occurrence
Score
average
summer DO
(mg/L) before
10 am —
daytime grab
samples
7.8
M; M; 8.1
NE; NE; no
0
lowest
observed
summer DO
(mg/L) -
continuous
monitoring
M
M; 4.5; 3.5
NE
NE
minimum DO
(mg/L) daytime
grab samples
6.2
15.3; 6.2; 3.3
no;no;yes
0
ratio, highest to
lowest summer
DO
1.6
M; 1.8; 2.9
NE; yes; yes
+
Increased Temperature (see Figure 10)
+
Increased
Temperature
mean °C from
summer grab
samples
17.5
18; 24; 21
yes; yes; yes
+
maximum °C
from summer
grab samples
25.7
18; 25.7; 27.6
no;no;yes
0
diurnal mean
(°C)
M
M; 26.2, 25.7
NE
NE
diurnal
maximum (°C)
M
M; 33.4; 30.4
NE
NE
72
-------
TABLE C-1
. cont.
Spatial/Temporal Co-occurrence
Proximate
Stressor
Measure of
Exposure
Measurement
at Internal
Comparator
(Site 2)
Measurements
at Sites 1, 3,
and 4,
Respectively
Evidence of
Co-occurrence
Score
Increased Ammonia (see Figure 11 )
+
Increased
Ammonia
mean ammonia
(mg/L) from
grab samples
0.07
M; 0.19; 0.08
NE; yes; yes
+
maximum
ammonia
(mg/L) from
grab samples
0.12
M; 0.32; 0.18
NE; yes; yes
+
NE = indicates no evidence.
73
-------
TABLE C-2
Evidence Used to Assess Complete Causal Pathway for Candidate Causes in the Little Floyd River,
Iowa
Complete Causal Pathway
Step in
Pathway
Measure of
Exposure
Measurement at
Comparator and
Ecoregion
Reference Sites
Measurements at the
More-impaired Sites (1, 3, and
4) or Overall in the Little Floyd
River
Score for
Pathway/
Step
Altered Flow Regime (see Figure 6)
0
Decrease in
Large Woody
Debris
% woody debris
S2: 0
S1,3,4: 0; 0; 4
-
IR: 0-18 (n = 8)
1.0 mean of all 4 sites
0
% wood
substrate
S2: 0
S1,3,4: 0; 0; 0
0
IR: 0-0.25 (n = 8)
0 at all 4 sites
0
Increased
Deposited
Fine
Sediment
See spatial/temporal co-occurrence for increased sediment.
+
Decreased
Infiltration,
Increased
Runoff
% annual row
crop
NE
% perennial
vegetation
% urban
74
-------
TABLE C-2. cont.
Complete Causal Pathway
Step in
Pathway
Measure of
Exposure
Measurement at
Comparator and
Ecoregion
Reference Sites
Measurements at the
More-impaired Sites (1, 3, and
4) or Overall in the Little Floyd
River
Score for
Pathway/
Step
Decreased
Sinuosity
sinuosity
(stream
length/straight
line)
IR: 1.3-2.4 (n = 5)
Avg. approx. 1.5 (3 of 4 sites
channelized); 49% (Site 3) and
9% (Sites 1&2) decrease in
sinuosity ca. 1970s; no change
from 1992 to 2002.
0
Increased
Velocity
stream gradient
(ft/mi)
IR: 5-20 (n = 5)
Sample site avg. approx. 5;
However, 17% overall main
channel slope increase since
1964.
Increased Sediment (see Figure 7) Suspended: + Deposited: +
Decreased
Bank Stability
% vertical bank
S2: 5
S1,3,4: 20; 15; 5
+
IR: 0-6.3 (n = 8)
11.3 mean of all 4 sites
+
Increased
Velocity
See causal pathway for altered flow regime.
+
Increased
Stream Power
NE
Increased
Channel and
Bank Erosion
% horizontal +
% vertical bank
S2: 35
S1,3,4: 40; 15; 25
0
IR: 0-20 (n = 8)
14.4 mean of all 4 sites
-
% bare bank
S2: 56
S1,3,4: 42; 16; 41
-
IR: 28-64 (n = 8)
40 mean of all 4 sites
-
Increased
Primary
Producers
See spatial/temporal co-occurrence for altered basal food source.
NE
Increased Soil
Erosion
revised
universal soil
loss equation
measurements
16,300 tons/year
(2 tons/acre/year)
NE
75
-------
TABLE C-2. cont.
Complete Causal Pathway
Step in
Pathway
Measure of
Exposure
Measurement at
Comparator and
Ecoregion
Reference Sites
Measurements at the
More-impaired Sites (1, 3, and
4) or Overall in the Little Floyd
River
Score for
Pathway/
Step
Increased
Input of Fine
Particles
NE
Decreased
Light
NE
Decreased
Water Depth
average depth
(cm)
S2: 24
S1,3,4: 12; 28; 12
0
IR: 20-23 (n = 8)
19 mean of all 4 sites
+
average thalweg
depth (cm)
S2: 45
S1,3,4: 19; 44; 23
+
IR: 35-42 (n = 8)
33 mean of all 4 sites
+
standard
deviation of
depth (cm)
S2: 21
S1,3,4: 7; 14; 7
+
IR: 11-13 (/7 = 8)
12 mean of all 4 sites
-
Altered Basal Food Source (see Figure 8)
++
Increased
Nutrients
nitrate + nitrite
(mg/L)
IR: 5.3-9.8 (n = 8)
5.7 at Site 2 (mean; n = 7); 2.1
at Site 3 (mean; n = 3); 5.5 at
Site 4 (mean baseflow and
storm event; n = 10)
total
phosphorus
(mg/L)
IR: 0.03-0.10
(n = 8)
0.23 at Site 2 (mean;n=7);
0.27 at Site 3 (mean; n = 3);
0.26 at Site 4 (mean baseflow
and storm event; n = 10)
+
Increased
Light
% shade
S2: 15
S1,3,4: 5; 12; 6
+
IR: 6-25 (n = 8)
9.5 mean all 4 sites
0
standard
deviation of %
shade
S2: 22
S1,3,4: 12; 21; 12
+
IR: 15.5-26.3
(n = 8)
16.8 mean of all 4 sites
0
76
-------
TABLE C-2. cont.
Complete Causal Pathway
Step in
Pathway
Measure of
Exposure
Measurement at
Comparator and
Ecoregion
Reference Sites
Measurements at the
More-impaired Sites (1, 3, and
4) or Overall in the Little Floyd
River
Score for
Pathway/
Step
Decrease in
Large Woody
Debris
See causal pathway for altered flow regime.
-
0
0
0
Decreased
Leaf Litter
NE
Decreased DO (see Figure 9)
+
Increased
Primary
Producers
See spatial/temporal co-occurrence for altered basal food source.
NE
Increased
Organic
Matter
NE
Increased
Heterotrophs
NE
Increased
Temperature
See spatial/temporal co-occurrence for increased temperature.
+
Increased
Respiration
community
respiration
7.8 mean from
statewide random
sites (n = 72)
13.3 at Site 3, (mean;
n= 12 d); 11.1 at Site 4
(mean; n = 19 d)
+
Decreased
Production:
Respiration
Ratio
production-to-
respiration ratio
(P:R)
0.68 mean from
statewide random
sites (n = 72)
0.82 at Site 3, (mean;
n = 12 days); 0.37 at Site 4
(mean; n = 19 d)
0
77
-------
TABLE C-2. cont.
Complete Causal Pathway
Step in
Pathway
Measure of
Exposure
Measurement at
Comparator and
Ecoregion
Reference Sites
Measurements at the
More-impaired Sites (1, 3, and
4) or Overall in the Little Floyd
River
Score for
Pathway/
Step
Decrease in
Large Woody
Debris
See causal pathway for altered flow regime.
-
0
0
0
Decreased
Riffles
% riffle
S2: 11
S1,3,4: 0; 0; 5
+
IR: 5-18 (n = 8)
4.0 mean of all 4 sites
+
Decreased
Turbulence
NE
Embedded
Riffles
See spatial/temporal co-occurrence for increased sediment.
+
Decreased
Aeration
reaeration
coefficient
NE
Increased Temperature (see Figure 10) ++
Increased
Light
See causal pathway for altered basal food source.
+
0
+
0
Decreased
Water Depth
See causal pathway for increased sediment.
0
+
+
+
+
78
-------
TABLE C-2. cont.
Complete Causal Pathway
Step in
Pathway
Measure of
Exposure
Measurement at
Comparator and
Ecoregion
Reference Sites
Measurements at the
More-impaired Sites (1, 3, and
4) or Overall in the Little Floyd
River
Score for
Pathway/
Step
-
Increased
Frequency of
Low Flows
See spatial/temporal co-occurrence for altered flow regime.
NE
Increased Ammonia (see Figure 11) +
Increased
Primary
Producers
See spatial/temporal co-occurrence for altered basal food source.
0
Increased pH
mean pH from
grab samples
IR: 7.3-8.3 (n = 8)
8.2 at Site 2 (mean; n = 7);
8.2 at Site 3 (mean; n = 3);
8.2 at Site 4 (mean baseflow
and storm event; n = 10)
pH range from
grab samples
IR: 7.1-8.3 (n = 8)
8.1-8.3 at Site 2 (n= 7);
8.1-8.3 at Site 3 (n = 3);
7.8-8.5 at Site 4 (n= 10)
-
Increased
nh4+
NH4+ (mg/L)
NE
Increased
Temperature
See spatial/temporal co-occurrence for increased temperature.
+
S2 = Site 2 Less-Impaired Comparator.
S1, 3, 4 = Sites 1, 3, and 4.
IR = Interquartile Range for Regional Reference Sites.
NE = No evidence.
79
-------
TABLE C-3
Stressor-Response from Other Field Studies for Candidate Causes in the Little Floyd
River, Iowa
Stressor-Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement
at Regional
Reference
Sites (n = 8) or
Statewide
Random Sites
(n = 72)
Measurements in the
Little Floyd River
Evidence
of
Stressor
Response
Score
Altered Flow Regime (see Figure 6)
NE
Decreased
Flow
Hetero-
geneity
NE
NE
Increased
Maximum
Flow
NE
NE
Increased
Frequency
of Low
Flows
NE
NE
Increased Sediment (see Figure 7) Suspended: 0 Deposited: +
Increased
Suspended
Sediment
TSS (mg/L)
10-37
interquartile
range (n = 8)
36 at Site 2 (mean;
n = 7); 45 at Site 3
(mean; n = 3); 29 at
Site 4 (mean baseflow
and storm event;
n = 10)
no; yes;
no
0
Decreased
Clarity
turbidity
(NTU)
8-24
interquartile
range (n = 8)
22 at Site 3 (mean;
n = 3); 14 at Site 4
(mean; n = 5)
no; no
-
80
-------
TABLE C-3. cont.
Stressor-Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement
at Regional
Reference
Sites (n = 8) or
Statewide
Random Sites
(n = 72)
Measurements in the
Little Floyd River
Evidence
of
Stressor
Response
Score
Decrease in
Algal Growth
seston
chlorophyll
a (|jg/L)
32 mean
(n = 72)
20 at Site 3 (mean;
n = 3); 9.7 at Site 4
(mean; n = 5)
yes; yes
+
periphyton
chlorophyll
a (pg/cm )
32 mean
(n = 72)
38-45 (range; n = 2)
no
-
sediment
chlorophyll
a (pg/cm )
27 mean
(n = 72)
21-22 (range; n = 2)
yes
+
gross
primary
production
(GPP) and
production
to
respiration
ratio (P:R)
4.8, 0.68
(GPP, P:R),
mean (n = 72)
10.9, 0.82 (GPP, P:R)
at Site 3, (mean;
n = 12 days); 4.4,
0.37 (GPP, P:R) at
Site 4 (mean; n = 19
days)
no;yes
0
Increased
Deposited
Fine
Sediment
% total
fines
46-86
interquartile
range (n = 8)
84 mean of all 4 sites
(/7 = 4)
no
0
% silt
6-20
interquartile
range (n = 8)
40 mean of all 4 sites
(n = 4)
yes
+
Loss of Pool
Depth
% reach
area as
pool
habitat
6-45
interquartile
range (n = 8)
44 mean of all 4 sites
(/7 = 4)
no
81
-------
TABLE C-3. cont.
Stressor-Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement
at Regional
Reference
Sites (n = 8) or
Statewide
Random Sites
(n = 72)
Measurements in the
Little Floyd River
Evidence
of
Stressor
Response
Score
maximum
depth (cm)
76-88
interquartile
range (n = 8)
64 mean of all 4 sites
(/7 = 4)
yes
+
Embedded
Riffles
embedded
-ness
rating
41-60% at 6
of the 8 sites
not available (possibly
could not be
determined due to
lack of gravel)
NE
NE
Burial of
Organisms
NE
NE
Altered Basal Food Source (see Figure 8)
0
Increased/
Altered
Primary
Producers
seston
chloro-
phyll a
(MQ/L)
32 mean
(n = 72)
20 at Site 3 (mean;
n = 3); 9.7 at Site 4
(mean; n = 5)
no; no
periphyton
chloro-
phyll a
(|jg/cm2)
32 mean
(n = 72)
38-45 (range; n = 2)
yes
+
sediment
chloro-
phyll a
(Mg/cm2)
27 mean
(n = 72)
21-22 (range; n = 2)
no
(GPP)
(g 02/m2/d)
4.8 mean
(n = 72)
10.9 at Site 3, (mean;
n = 12 days); 4.4 at
Site 4 (mean;
n = 19 days)
yes; no
0
82
-------
TABLE C-3. cont.
Stressor-Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement
at Regional
Reference
Sites (n = 8) or
Statewide
Random Sites
(n = 72)
Measurements in the
Little Floyd River
Evidence
of
Stressor
Response
Score
Decreased
Allochthon-
ous Food
Resources
NE
NE
Decreased DO (see Figure 9)
0
Decreased
DO
mean DO
(mg/L)
from
daytime
grab
samples
6.9-9.4
interquartile
range (n = 8)
8.3 at Site 2 (mean;
n = 7); 8.5 at Site 3
(mean; n = 3); 8.8 at
Site 4 (mean baseflow
and storm event;
n = 10)
no; no; no
minimum
DO (mg/L)
from
daytime
grab
samples
5.4 minimum
from ecoregion
reference sites
(n = 8)
6.2 at Site 2 (n = 7);
6.2 at Site 3 (n = 3);
4.6 at Site 4 (n = 10)
no; no;
yes
0
diurnal
mean DO
(mg/l)
7.2 at Site 3; 7.9, 6.2
at Site 4
NE
NE
diurnal
minimum
DO (mg/l)
4.5 at Site 3; 5.3, 3.5
at Site 4
NE
NE
83
-------
TABLE C-3. cont.
Stressor-Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement
at Regional
Reference
Sites (n = 8) or
Statewide
Random Sites
(n = 72)
Measurements in the
Little Floyd River
Evidence
of
Stressor
Response
Score
Increased Temperature (see Figure 10)
+
Increased
Temperature
mean
temp. (°C)
from grab
samples
15.1-19.8
interquartile
range (n = 8)
17.5 at Site 2 (mean;
n = 7); 24 at Site 3
(mean; n = 3); 21 at
Site 4 (mean baseflow
and storm event; n =
10)
no; yes;
yes
0
maximum
temp. (°C)
from grab
samples
24.9 maximum
(/7 = 8)
25.7 at Site 2 (n = 7);
25.7 at Site 3 (n = 3);
27.6 at Site 4 (/? = 10)
yes; yes;
yes
+
diurnal
mean
temp. (°C)
19.8 mean
(n = 72)
26.2 at Site 3; 23.2 at
Site 4
yes; yes
+
diurnal
maximum
temp. (°C)
26.2 mean
(n = 72)
33.4 at Site 3; 30.4 at
Site 4
yes; yes
+
Increased Ammonia (see Figure 11)
+
Increased
Ammonia
ammonia
nitrogen as
N (mg/L)
0.085-0.10
interquartile
range (n = 3)
0.06 at Site 2 (n = 7);
0.19 at Site 3 (/? = 3);
0.08 at Site 4 (n = 10)
no; yes;
no
0
84
-------
TABLE C-3. cont.
Stressor-Response Relationship from Other Field Studies
Proximate
Stressor
Measure of
Exposure
Measurement
at Regional
Reference
Sites (n = 8) or
Statewide
Random Sites
(n = 72)
Measurements in the
Little Floyd River
Evidence
of
Stressor
Response
Score
max
ammonia
nitrogen as
N (mg/L)
from grab
samples
0.10 maximum
for regional
reference sites
(/7 = 3)
0.12 at Site 2 (/? = 7);
0.32 at Site 3 (n = 3);
0.18 at Site 4 (/? = 10)
yes; yes;
yes
+
NE = No evidence.
85
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