Season Effects on a Macroinvertebrate Index Developed for Puerto Rico Streams
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Report prepared by: James Kurtenbach, Aquatic Biologist
Monitoring Operations Section
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Approved by: Randy^&raun, Acting Chief '
Monitoring and Assessment Branch
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TABLE OF CONTENTS
List of Figures ii
List of Acronyms iii
Executive Summary iv
Introduction 1
Methods 1
Results 3
Discussion 7
Conclusions 8
Literature Cited 8
i
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LIST OF FIGURES
1. Map of stream sites in Puerto Rico 2
2. Mean average (n=6) Mil scores for Puerto Rico stream sites during the
study period 3
3. Change in Mil scores at six Puerto Rico stream sites during the study period 3
4. Mean average (n=6) dissolved oxygen values for Puerto Rico stream sites
during the study period 4
5. Mean average (n=6) total phosphorus values for Puerto Rico stream sites
during the study period 4
6. Mean average (n=6) total nitrogen values for Puerto Rico stream sites
during the study period 5
7. Mean average (n=6) chloride values for Puerto Rico stream sites during
the study period 5
8. Habitat scores at six Puerto Rico stream sites during the study period 6
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LIST OF ACRONYMS
DOC
dissolved organic carbon
EPA
Environmental Protection Agency
GIS
Geographical Information System
Mil
Macro invertebrate Integrity Index
PREQB
Puerto Rico Environmental Quality Board
TOC
total organic carbon
TSS
total suspended solids
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EXECUTIVE SUMMARY
Few examples of studies from the neotropics exist in the documented literature on the effects
season change has on the composition of benthic macro invertebrates, and this information is
particularly nonexistent for Puerto Rico. The primary objectives of this study were to assess
potential season effects on the community structure of benthic macroinvertebrates in Puerto Rico
streams and to determine if the macroinvertebrate integrity index (Mil) is applicable outside the
March-April index period for which it was developed.
This report describes the results of season effects on the application of the Mil on streams in ,
Puerto Rico.
In 2012, sampling was conducted at six stream sites during three discrete season periods, spring
(March-April), summer (June-August), and fall (October-December). The study area
encompassed three geographical regions, humid east central, rainy west central, and rainy eastern
Luquillo Mountains, all characterized by relatively heavy rainfall and steep topography.
Results of the study showed an increasing trend of the Mil scores from spring to fall, although
individual sites had changes that varied differently with season. None of the results is believed
to be significantly influenced by human activities. Water chemistry and habitat conditions were
fairly consistent across seasons and did not exceed levels that would suggest anthropogenic
degradation. Variation of the Mil scores across seasons in this study is within the variation seen
from samples collected over shorter time periods.
Results of this study will be used to make recommendations to the Puerto Rico Environmental
Quality Board (PREQB) for their stream monitoring and assessment program. Expanding the
sampling window for Mil use would provide field staff and program managers with more
flexibility on the timing and number of macroinvertebrate samples that could be collected
annually. It is recommended here the index period can be expanded, but sampling should still be
avoided during seasonal periods of intense rainfall.
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Introduction
Few examples of studies from the neotropics exist in the documented literature on the effects
season change has on the composition of benthic macro invertebrates. Unlike temperate North
America where stream temperature and inputs of organic matter (e.g., leaves) respond abruptly to
seasonal change, in Puerto Rico stream temperatures and inputs of organic matter are relatively
uniform throughout the year. Bioassessment programs in temperate North America target a
specific index period to avoid the intra annual variability known to occur with seasonal
recruitment cycles of invertebrates. In Puerto Rico the climate is humid subtropical, with rainfall
weakly related to season and amounts generally greater with tropical disturbances September
through November.
The primary objectives of this study were to assess potential seasonal effects on the community
structure of benthic macro invertebrates in Puerto Rico streams and to determine if the
macro invertebrate integrity index (Mil) is applicable outside the March-April index period for
which it was developed. This was tested by collecting samples from six least disturbed
(reference) streams located in the eastern, central, and western regions of the island. These six
sites are part of several sites used to establish reference thresholds for the development of the
Mil (Kurtenbach 2011) and interpretation of water chemistry and physical habitat data collected
from the 2009 and 2013 probabilistic streams surveys (Kurtenbach 2012 and 2014).
Results of this study will be used to make recommendations to the Puerto Rico Environmental
Quality Board (PREQB) for their stream monitoring and assessment program. The Mil was
developed to provide the PREQB with an assessment tool to implement biological criteria in
their water quality program, more accurately determine aquatic life use support, and prioritize
streams for protection and restoration. Expanding the sampling window would provide field
staff and program managers with more flexibility on the timing and number of samples that
could be collected annually.
Methods
In 2012, sampling was conducted at six stream sites during three discrete season index periods,
spring (March-April), summer (June-August), and fall (October-December). Sites were selected
to ensure they represented reference condition. For a site to qualify as meeting reference
condition, stream watersheds were required to have a minimum 85% forest cover since the
period of the 1950's until present. This information was obtained from historical forest maps
and current GIS land cover data. The area of study (figure 1) included three geographical
regions, humid east central, rainy west central, and rainy eastern Luquillo Mountains, all
characterized by relatively heavy rainfall and steep topography. The islands climate is humid
subtropical, with rainfall weakly related to season and amounts generally greater with tropical
disturbances September through November. Stream size was small first and second order
headwaters, exclusively high and moderate in gradient and dominated by riffle-run-pool habitat.
Each streams bottom substrate consisted of boulders (large, medium, small), cobble, and varied
amounts of gravel, sand, and silt. 1
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Figure 1. Map of stream sites in Puerto Rico.
At each stream location a single riffle area was chosen closest to a predetermined x-site for
collection of a benthic macro invertebrate sample. Macro invertebrates were collected from rock
substrates (cobble and small boulder) using a large frame rectangular kick net, constructed with
800 x 900 um mesh net (Bode 1991). Sample collection was accomplished by placing the kick
net on the stream bottom, mid-stream in the riffle, while gradually working the net downstream
and laterally (approximately two net widths) for 5 minutes. The bottom substrate was vigorously
disturbed by foot so that sufficient organisms would be dislodged and swept into the net.
After a sample was collected, large debris were removed from the net, inspected for organisms
and discarded. Macroinvertebrates retained in the net were placed in a one liter container and
preserved with 10% buffered formalin. Sample containers were labeled with the appropriate site
information and delivered to the EPA Edison laboratory. The kick net was thoroughly rinsed and
cleaned between stream sites.
In situ measures of water temperature, specific conductance, pH, and dissolved oxygen were
taken at each site. Water chemistry samples were collected and analyzed for 18 parameters (e.g.,
major anions/cations, nutrients, DOC, TOC, TSS, turbidity). Measurements of habitat quality
were performed using EPA's visual habitat assessment method (Barbour et al. 1999). All these
attributes combined may be directly or indirectly altered by human activities in watersheds.
Water quality, physical habitat, and land use information were used to ensure that study results
represent seasonal effects and not some unknown water quality or habitat degradation caused by
human disturbance.
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Results
Mean average (n=6) Mil scores showed an increase over the spring, summer, and fall seasons
(Figure 2). Individual sites displayed fluxuation in the Mil scores between seasons (Figure 3).
Only sites 17, 6, and 1152 had a consistent increase in Mil scores over each season.
Seasonality Study Average Mil Score
100.00
90.00 t
80.00
70.00
60.00
o
£ 5000
5
40.00
30.00
20.00
10.00
50,86
55:91
52.14
0.00
Spring
Summer
Figure 2. Mean average (n=6) Mil scores for Puerto Rico stream sites during the study period.
Seasonality Study Mil Scores
100.00
90.00
80.00
70,00
60.00
50.00
40.00
30.00
2000
10.00
0.00
-47
•17
- 7
•6
- 1152
1
Spring
Fall
Figure 3. Change in Mil scores at six Puerto Rico stream sites during the study period.
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Water chemistry mean average (n=6) values were fairly consistent across seasons and did not
exceed levels that would suggest anthropogenic degradation of water quality over the study
period (Figures 4-7). Total phosphorus levels showed a spike during the summer season but the
mean value was still representative of reference condition for Puerto Rico streams.
Dissolved Oxygen
10
3
E 5
o
Q
5 mg/L WQS
I Dissolved Oxygen
Spring
Summer
Fill
Figure 4. Mean average (n=6) dissolved oxygen values for Puerto Rico stream sites during the
study period.
Phosphorus
0 Orf
0.035
Medium
0.036 mg/L
0.03
0.025
0.02
0 015
001
0.00S
I Phosphorus
Spring
Summer
Figure 5. Mean average (n=6) total phosphorus values for Puerto Rico stream sites during the
study period. 4
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Nitrogen
0.3
0.2S
Medium
- 0.25 mg/L
0,2
0.15
0.1
0.0S
IN i trogcn
Spring
Figure 6. Mean average (n=6) total nitrogen values for Puerto Rico stream sites during the study
period.
Chloride
Medium
11 mg/L
10
£
± 6
Spnn
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Habitat scores were high for each site ranking them in the optimal condition category with the
exception of site 6 (Figure 8). Lower habitat score at site 6 probably reflects the occurrence of
some residential and commercial development in the watershed adjacent to the sampling
location. However, upper reaches of the watershed are highly forested. Overall, physical habitat
condition would not suggest significant human activity at the study sites.
Habitat Score
200
47 17 7 6 IIS2 1
Figure 8. Habitat scores at six Puerto Rico stream sites during the study period.
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Discussion
The current index period for use of the Mil in Puerto Rico is March-April. For multimetric
indexes like the Mil to be applied throughout the calendar year, the index must exhibit minimal
season variation, otherwise, an index window for sampling must be established.
Our study showed a slight increasing trend of Mil scores from spring to fall. One question to ask
is whether this is a significant seasonal effect or within the natural variability of the Mil.
Significant anthropogenic stressors were absent from the study sites, so this probably is not a
confounding factor.
Development of macro invertebrate indices are lacking throughout the neotropics and studies on
seasonal variation are virtually nonexistent. However, some studies from the neotropics exist in
the documented literature on the effects season change has on the structure, composition and
functional feeding groups of aquatic macroinvertebrate assemblages. Mathuriau et al (2008) in a
one year study of an Andean stream located in Columbia, found macroinvertebrate density and
taxa richness was bimodal with peaks in January to mid-March and July to mid-October. Their
study concluded this was controlled by stream discharge. In another stream study from Brazil
(Marden et al. 2013), environmental factors (conductivity, pH, dissolved oxygen, alkalinity, etc)
were determined to show significant variation between an annual wet and dry season and
macroinvertebrate measures were found to be correlated with this seasonal variation of
environmental variables. Palaemonidae and chironomidae were the dominant taxa during the
rainy and dry season, respectively. Neither of these study findings matched the results of the
Puerto Rico stream survey. Probably not surprising given the variation of important
environmental determinants found across streams in the neotropics. Nonetheless, other studies
from tropical regions have shown macroinvertebrate community structure to correspond with
stream discharge as an indirect measure of rainfall (Dudgeon 1993, Flecker and Feifarek 1994,
Rincon Hernandez 1996, Cressa 1998, Ramirez and Pringle 1998, and Jacobsen and Encalada
1998). In Puerto Rico rainfall amounts are generally greater with tropical disturbances
September through November.
Results of two probabilistic stream surveys conducted in Puerto Rico in which 10 sites had
repeat sampling of macro invertebrates the mean variation was a Mil score of 6.9 (unpublished
data). This is within the range of variation seen in the current study which showed a Mil
increase of 7.7 from the spring through fall period (Figure 2). These results suggest that the
variation across seasons is not any greater than samples collected within a short time frame of
two weeks. Unexplained factors likely result in some variability that cannot be controlled by the
sampling protocol.
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Conclusions
Concrete conclusions on season dynamics of Puerto Rico stream macro invertebrate communities
should be tempered because of the limited number of sites sampled in the study. Future studies
with additional data may reveal more consistent seasonal patterns which can be taken into
account when considering index periods for application of macroinvertebrate indices on Puerto
Rico streams. In addition, other studies from tropical regions have indicated correspondence of
macroinvertebrate communities to wet and dry seasons. However, variation in the Mil scores
associated with season were not significantly greater than what occurs at a shorter temporal
scale, thus suggesting the application of the Mil in Puerto Rico could be extended beyond the
current index period of March-April. It is recommended here that the index period can be
expanded, but sampling should still be avoided during seasonal periods of intense rainfall.
Literature Cited
Barbour, M. T, J. Gerritsen, B. D. Snyder, and J. B. Stribling. 1999. Rapid bioassessment
protocols for use in streams and wadeable rivers: periphyton, benthic macro invertebrates and
fish. Second edition. EPA/841 -B-99-002. U. S. Environmental Protection Agency, Office of
Water, Washington, DC.
Bode, R.W., M. A. Novak, and L.E. Able. 1991. Methods for rapid bioassessment of streams.
New York State Department of Environmental Conservation, Division of Water, Albany, NY.
Cressa, C. 1998. Community composition and structure of macroinvertebrates of the river
Camuri Grande, Venezuela. Verh. Internat. Verein. Limnol. 26: 1008-1011.
Dungeon, D. 1993. The effect of spate-induced disturbance, predation and environmental
complexity on macroinvertebrates in a tropical stream. Freshwater Biology 30: 189-198.
Flecker, A. S. and Feifarek, B. 1994. Disturbance and the temporal variability of invertebrate
assemblages in two Andean streams. Freshwater Biology 31: 131 -142.
Jacobsen, D. and Encalada, A. 1998. The macroinvertebrate fauna of Ecuadorian high-land
streams in the wet and dry season. Arch. Hydrobiol. 142: 53-70.
Kurtenbach, J. K. 2011. Macroinvertebrate protocol and development of the Puerto Rico high
gradient streams benthic index. U. S. Environmental Protection Agency, Region 2, Edison, NJ.
Kurtenbach, J. K. 2012. 2009 Probabilistic streams survey in Puerto Rico. U. S. Environmental
Protection Agency, Region 2, Edison, NJ.
Kurtenbach, J. K. 2014. 2013 Probabilistic streams survey in Puerto Rico. U. S. Environmental
Protection Agency, Region 2, Edison, NJ.
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Marden, S. L., Gregorio, G. F., and Liriane, M. F. 2013. Benthie macro invertebrate community
structure and seasonal variation in a neotropical stream in the State of Alagoas, Brazil. Biota
Neotropical 13:
Mathuriau, C., Thomas Alain G. B., and Chauvet, E. 2008. Seasonal dynamics of benthie
detritus and associated macro invertebrate communities in a neotropical stream. Fundamental
and Applied Limnology 171: 323-333.
Ramirez, A. and Pringle, C. M. 1998. Structure and production of a benthie insect assemblage
in a neotropical stream. Journal of the North American Bentho logical Society 17: 443-463.
Rincon Hernandez, M. E. 1996. Aspectos bioecologicos de los tricopteros de la quebrada
Carrizal (Boyaca, Columbia). Rev. Col. Ent. 22: 53-60.
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