903R82003
WATER-QUALITY OF THREE MAJOR TRIBUTARIES
TO THE CHESAPEAKE BAY, THE SUSQUEHANNA
POTOMAC, AND JAMES RIVERS,
JANUARY 1979-APRIL 1981
U.S. GEOLOGICAL SURVEY
Ruionffl Library
Water-Resources Investigations 82-32 Environuwntal Protection
I' xx ,--t-7<
l.l pared in cooperation with the
j r
. ENVIROMENTAL PROTECTION AGENCY
SAPEAKE BAY PROGRAM
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50272-101
REPORT DOCUMENTATION
PAGE
1. REPORT NO.
2.
4. Title and Subtitle
Water Quality of the Three Major Tributaries to the
Chesapeake Bay, the Susquehanna, Potomac, and James Rivers,
January 1979 - April 1981
7. Author(s)
David J. Lang
9. Performing Organization Name and Address
U.S. Geological Survey, Water Resources Division
208 Carroll Building
8600 La Salle Road
Towson, Maryland 21204
12. Sponsoring Organization Name and Address
U.S. Geological Survey, Water Resources Division
208 Carroll Building
8600 La Salle Road
Towson, Maryland 21204
3.
5.
6.
8.
10.
11.
(0
(G)
13.
Recipient's Accession No.
Report Date
May 1982
Performing Organization Rept. No.
USGS/WR1-82-32
Project/Task/Work Unit No.
Contract(C) or Grant(G) No.
Type of Report & Period Covered
Final
14.
IS. Supplementary Notes
Prepared in cooperation with the U.S. Environmental Protection Agency, Chesapeake Bay
Program
16. Abstract (Limit: 200 words)
Water-quality constituent loads at the Fall Line stations of the Susquehanna,
Potomac, and James Rivers, the three major tributaries to the Chesapeake Bay, can be
estimated with reasonable accuracy by regression techniques, especially for wet periods
of 1 year or more. Net transport of all nutrient species and most other constituents is
dominated by a few spring and storm-related, high-flow events. Atrazine and 2,4-D are
the two herbicide residues most consistently detected at the Fall Line of the Susquehanna
and Potomac Rivers. Concentrations of total residual chlorine and low-molecular-weight
halogenated hydrocarbons at selected sites in estuaries to the upper Bay are generally at
or below detection limits. Ammonia concentrations and loads are decreasing at all three
Fall Line stations, as is orthophosphate in the Susquehanna and Potomac Rivers. The
James River has the lowest average concentrations of total nitrogen and nitrite plus
nitrate. Slight increases in total nitrogen and nitrite plus nitrate in the Susquehanna
River from 1969 to 1980 may warrant continued monitoring.
When water discharge of the Susquehanna River is below about 400,000 cubic feet per
second at Conowingo, Maryland, sediments are deposited behind the three hydroelectric
dams located between Harrisburg, Pennsylvania and its mouth. Peak discharges above
400,000 cubic feet per second resuspend the sediments and their sorbed chemical constitu-
ents, carrying them to the Bay.
17. Document Analysis a. Descriptors
*Water Quality, *Nutrients, *Sediment transport, *Sediments, Pesticides, Trace metals,
Stream discharge, Storms, Chlorine
b. Identifiers/Open-Ended Terms
*Chesapeake Bay, *Susquehanna River, *Potomac River, *James River, Conowingo Dam,
Fall Line
c. COSATI Field/Group
18. Availability Statement
No restriction on distribution.
19. Security Class (This Report)
20. Security Class (This Page)
21. No. of Pages
72
22. Price
(See ANSI-Z39.18)
See Instructions on Reverse
OPTIONAL FORM 272 (4-7
(Formerly NTIS-35)
Department of Commerce
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t
I
WATER QUALITY OF THE THREE MAJOR TRIBUTARIES
TO THE CHESAPEAKE BAY, THE SUSQUEHANNA,
POTOMAC, AND JAMES RIVERS,
JANUARY 1979 - APRIL 1981
By David J. Lang
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations 82-32
Prepared in cooperation with the
U.S.ENVIRONMENTAL PROTECTION AGENCY
CHESAPEAKE BAY PROGRAM
May 1982
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UNITED STATES DEPARTMENT OF THE INTERIOR
JAMES G. WATT, Secretary
GEOLOGICAL SURVEY
Dallas L. Peck, Director
For additional information write to:
U.S. Geological Survey
208 Carroll Building
8600 La Salle Road
Towson, Maryland 21204
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CONTENTS
Page
Abstract 1
Introduction 2
Data collection 4
Basin land use and its effect on water quality 4
Hydrologic conditions 5
Methods of collection and laboratory analysis 5
Constituent loads 8
Load estimation techniques—nutrients and metals 8
Load estimation techniques—major cations and anions 16
Evaluation and limitation of the load estimates 18
Examination of selected water-quality constituents 20
Seasonal characterization of pesticides 20
Seasonal characterization of chlorophyll a 23
Chlorine 23
Total recoverable aluminum, iron, and manganese 27
Sulfate 27
Nutrients and their relationships to suspended
sediment and discharge 31
Seasonal variability of nutrient transport 36
Comparison of nutrient data among the three
Fall Line stations 42
Comparison of nutrient data with previous studies 46
Comparison of nutrient data at the Susquehanna River
stations at Harrisburg, Pa., and Conowingo, Md 51
Sediment transport characteristics 54
Susquehanna River 54
Potomac River 58
James River 58
Summary and conclusions 61
References 63
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ILLUSTRATIONS
Page
Figure 1. Map of study area showing location of drainage
basins and sampling sites 3
2. Hydrograph showing mean monthly and long-term
average monthly discharge for the three Fall
Line stations 7
3. Hydrograph showing seasonal fluctuations in
concentrations of 2,4-D at the Susquehanna
and Potomac Fall Line stations 21
4. Hydrograph showing seasonal fluctuations in concen-
trations of atrazine at the Susquehanna and
Potomac Fall Line stations 22
5. Hydrograph showing seasonal fluctuations of concen-
trations of chlorophyll a at the three Fall Line
stations 24
6. Map showing location of chlorine-monitoring stations
on selected tributaries to Chesapeake Bay 25
7. Hydrograph showing aluminum, iron, and manganese
concentrations during February 20-26, 1981, at
the Susquehanna River Fall Line station 28
8. Hydrograph showing aluminum, iron, and manganese
concentrations during September 5-8, 1979, and
March 21-24, 1980, at the Potomac River Fall
Line station 29
9. Hydrograph showing aluminum, iron, and manganese
concentrations during April 15-17, 1980, at the
James River Fall Line station 30
10. Hydrograph showing nutrient concentrations
during February 20-27, 1981, at the
Susquehanna River Fall Line station 33
11. Hydrograph showing nutrient concentrations
during September 5-8, 1979, and
March 21-24, 1980, at the Potomac River Fall
Line station 34
12. Hydrograph showing nutrient concentrations
during April 15-17, 1980, at the James
River Fall Line station 35
13. Hydrograph showing nutrient concentrations
during February 25 - March 1, 1979, at
the Potomac River Fall Line station 37
IV
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ILLUSTRATIONS-Continued
Figure 14. Bar graph showing monthly loads of nitrogen at the
three Fall Line stations
Bar graph showing monthly loads of phosphorous
at the three Fall Line stations
16.
Hydrographs showing suspended-sediment transport
for three high flows at the Susquehanna River
at Harrisburg, Pa., and Conowingo, Md.
17. Hydrographs showing suspended-sediment transport
for three high flows at the Potomac River
at Chain Bridge at Washington, D.C. .
Page
43
44
56
59
TABLES
Table 1. Average discharge for study period and long-term
average discharges for the three Fall Line stations
Page
2.
5.
6.
7.
Least squares regression equations for load calculations
of selected nutrients and metals with standard
deviation (s2) and coefficients of determination (r2)
Monthly load estimates (in hundreds of thousands of
pounds) for the Susquehanna River at Conowingo, Md.
Monthly load estimates (in hundreds of thousands of
pounds) for the Potomac River at Chain Bridge at
Washington, D.C
Monthly load estimates (in hundreds of thousands of
pounds) for the 3ames River at Cartersville, Va.
Least squares regression equations for load calculations
of selected cations and anions with standard deviation
(s2) and the coefficients of determination (r2) -
Nutrient loads (in millions of pounds) for the Potomac
River at Chain Bridge at Washington, D.C., computed
from the Potomac estuary and Fall Line monitoring
study data
Schedule of low-molecular-weight, halogenated organic
compounds analyzed in selected tributaries to the
Chesapeake Bay
9
10
12
14
17
19
26
v
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TABLES—Continued
Page
Table 9. Sulfate loads in the Susquehanna, Potomac, and James
Rivers from May 1980 to April 1981 32
10. Annual loads of selected nutrients (in millions of pounds)
at the three Fall Line stations for calendar years
1979 and 1980 38
11. Seasonal fluctuations of selected nutrients for the
three Fall Line stations 39
12. Total nutrient loads and discharge-weighted average
nutrient concentrations for the period January 1979
to December 1980 at the three Fall Line stations 45
13. Average daily loads (in Ibs/d) of selected nutrient
species for the three Fall Line stations derived
from different hydrologic investigations 47
14. Discharge-weighted average concentrations (in mg/L)
of selected nutrient species for the three Fall Line
stations derived from different hydrologic
investigations 48
15. Estimates of nutrient loads (in Ibs/d) at three
different discharges for 1969-72 and 1979-81
data sets for the Susquehanna River at
Conowingo, Md 50
16. Water-quality constituent loads (in millions of
pounds) for stations on the Susquehanna River
at Harrisburg, Pa., and Conowingo, Md., from
April 1980 through March 1981 52
17. Relative proportions of orthophosphate, nitrite +
nitrate, and ammonia + organic nitrogen to
total phosphorous and nitrogen loads at the
Susquehanna River at Harrisburg, Pa.,
and Conowingo, Md., from April 1980 to
March 1981 53
18. Discharge-weighted average concentrations (in mg/L)
of water-quality constituents for stations on the
Susquehanna River at Harrisburg, Pa., and
Conowingo, Md., from April 1980 through
March 1981 55
19. Suspended-sediment loads (in tons) at the Harrisburg, Pa.,
and Conowingo, Md., stations on the Susquehanna
River for three high-flow periods 57
20. Unit discharge sediment yields for the Potomac River
at Chain Bridge at Washington, D.C., for three
high-flow periods 60
VI
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CONVERSION OF MEASUREMENT UNITS
The following factors may be used to convert the inch-pound units published in
this report to International System (SI) metric units.
Multiply inch-pound unit
inch (in.)
foot (ft)
mile (mi)
square inch (in2)
square mile (mi2)
gallon (gal)
cubic foot (ft3)
cubic foot per second
(ft3/s)
gallon per minute (gal/min)
it By To obtain metric unit
Length
25.40
2.54
.3048
1.609
Area
6.452
2.590
Volume
3.785
.003785
.02832
Flow
millimeter (mm)
centimeter (cm)
meter (m)
kilometer (km)
square centimeter (cm2)
square kilometer (km2)
liter (L)
cubic meter (m3)
cubic meter (m3)
degree Fahrenheit (°F)
pound per cubic foot
pound per day (Ib/d)
28.32
.02832
.06309
.00006309
Temperature
-32 x 0.555
Concentration
16055
Mass
0.454
liter per second (L/s)
cubic meter per second
(m 3/s)
liter per second (L/s)
cubic meter per second
(m 3/s)
degree Celsius (°C)
milligram per liter (mg/L)
kilogram per day (kg/d)
vn
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WATER QUALITY OF THE THREE MAJOR TRIBUTARIES TO THE CHESAPEAKE BAY,
THE SUSQUEHANNA, POTOMAC, AND 3AMES RIVERS,
JANUARY 1979 - APRIL 1981
By David 3. Lang
ABSTRACT
Water-quality constituent loads at the Fall Line stations of the Susquehanna,
Potomac, and James Rivers, the three major tributaries to the Chesapeake Bay,
can be estimated with reasonable accuracy by regression techniques, especially for
wet periods of 1 year or more. Net transport of all nutrient species and most other
constituents, especially those found in greatest concentrations associated with
suspended material, is dominated by a few spring and storm-related high-flow
events. Atrazine and 2,4-D are the two herbicides most consistently detected at
the Fall Line of the Susquehanna and Potomac Rivers. Concentrations of total
residual chlorine and low-molecular-weight, halogenated hydrocarbons at selected
sites in estuaries to the upper Bay are generally at or below detection limits. When
compared to the two other major tributaries, the James River has the lowest
discharge-weighted-sulfate concentrations, presumably because of the lack of coal
mining activity in this basin. This river also has lower total nitrogen concen-
trations. Ammonia concentrations and loads are decreasing at all three Fall Line
stations, as is orthophosphate in the Susquehanna and Potomac Rivers. Slight
increases in total nitrogen and nitrite plus nitrate concentrations in the
Susquehanna River from 1969 to 1980 may warrant continued monitoring.
Analyses of data for this report confirm the previous suggestion that when
water discharge of the Susquehanna River at Conowingo, Maryland, is below about
400,000 cubic feet per second, sediment, with sorbed nutrients and other constitu-
ents, is deposited behind the three hydroelectric dams on this river between
Harrisburg, Pennsylvania, and its mouth. Discharges above 400,000 cubic feet per
second resuspend these sediments and transport constituent loads to the Bay well in
excess of loads transported by the Susquehanna River at Harrisburg. In addition to
precipitation quantity and intensity, antecedent conditions and season of the year
play a major role in the transport of sediments and their associated chemical
constituents at all three stations.
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INTRODUCTION
The Chesapeake Bay is the largest estuary in the United States: 200 mi long;
8,000 mi of shoreline; and 4,400 mi2 of water surface. It has a drainage area of
64,000 mi2 and is fed by more than 150 tributaries (U.S. Dept. of the Army, Corps
of Engineers, 1973). The three major tributaries of the Bay (Susquehanna,
Potomac, and James Rivers) drain about 85 percent of the total Chesapeake Bay
drainage basin.
The Bay supports substantial commercial and sport fishing and recreational
industries. Its water also provides access to two major shipping ports—Baltimore,
Md., and Hampton Roads, Va. Ship traffic on the Chesapeake Bay is increasing and
is expected to continue growing as more coal is exported from Eastern United
States.
In order to protect and preserve this valuable natural resource, the U.S.
Environmental Protection Agency (EPA), under Congressional directive (Senate
Report No. 94-326), conducted an in-depth study of the environmental quality of
the Chesapeake Bay. As part of that study, the U.S. Geological Survey (USGS)
assessed the water quality of the three major tributaries to the Bay [the
Susquehanna, Potomac, and James Rivers (fig. 1)] at the Fall Line from January
1979 to April 1981. (The Fall Line is the boundary between the Coastal Plain and
Piedmont physiographic provinces.)
This report presents the following water-quality information for the
Susquehanna, Potomac, and James Rivers:
1. Estimated loads of major ions, suspended sediment, selected nutrient species,
and selected trace metals for the 2-year, data-collection period.
2. An assessment of accuracy and limitations inherent in these estimates.
3. Seasonal characterization of nutrients, pesticides, and chlorophyll a collected
during the study.
4. Relationships between discharge, specific conductance, and suspended sediment
and selected nutrient and trace metal concentrations.
5. Comparisons of nutrient loads with other studies and the detection of trend in
these loads.
The cooperation and assistance received from Mr. Howard Jarmon and staff
of the Susquehanna Electric Company at Conowingo Dam are gratefully acknowl-
edged.
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EXPLANTION
Drainage Basin boundary
A Surface-Water station
T Water-Quality station
| Surface-Water and Water-
Quality station
50 0 50 MILES
I ' I I I I ;
A-
K
i,
£A^-
75°
^
^A ,
/^-•/r
v L >/'
) ,—^\—\ r /
r*- -•*- j ^- ^ r V-^N f ~ 42°
; / Susquehanna
River
Basin
^lver'fe/
Basin
/ i.jii
Cham Bridge
39
37'
Figure 1.—Study area showing location of drainage basins and sampling sites,
3
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DATA COLLECTION
Figure 1 shows the location of the water-quality monitoring stations used in
the study. The Susquehanna River station is at Conowingo Dam, Conowingo, Md.
From January 1979 to April 1981, if flow conditions permitted, base-flow water
quality was measured every 2 weeks. The James River station is at Cartersville,
Va., and the Potomac River site is at Chain Bridge at Washington, D.C.; during the
study, both were sampled monthly. Water samples analyzed for both sediment and
chemical quality were collected frequently during high flows at all three sites to
better understand the mechanisms that affect the water quality during these
critical periods of high mass transport.
The USGS continuously monitors stage and flow at the Cartersville and
Conowingo sites. Potomac River flow is monitored at Little Falls, Md., half a mile
upstream from Chain Bridge.
The Susquehanna River contributes almost half of the fresh-water inflow to
the Bay. It is important to understand the net effects on water quality of the three
hydroelectric dams located in the Susquehanna River between Harrisburg, Pa., and
Conowingo, Md. This report presents only comparisons of selected constituent
loads for these two stations. A more detailed analysis of the Harrisburg station
data was made in another Geological Survey report, now in preparation.
Because the monitoring sites on the Potomac and James Rivers are not
located at the mouths of these rivers, actual loads to the Chesapeake Bay were not
measured. However, the samples collected at these stations are representative of
constituents available to the Bay.
BASIN LAND USE AND ITS EFFECT ON WATER QUALITY
The following table indicates the percentages of each land-use category in
the Susquehanna, Potomac, and James River basins. Land use in the Susquehanna
and Potomac basins is similar with slightly more than half the area covered by
forest. The James River basin contains 75-percent forest cover.
Land
use
Susquehanna River at
Conowingo, Md.
drainage area -
27,100 mi2
Potomac River at
Chain Bridge at
Washington, D.C.
drainage area =
11,360 mi2
James River at
Cartersville, Va.
drainage area =
6,257 mi2
Agriculture and
pastureland
Forest
Urban
35%
60%
55%
22%
75%
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Land use has a significant effect on the water quality of any river. Areas
with large forest cover normally have lower nutrient concentrations than agricul-
tural areas. A study of 473 non-point source drainage areas in Eastern United
States showed that nutrient concentrations are generally proportional to the
percentage of agricultural land in the watershed (Omerik, 1976). In general,
inorganic nitrogen makes up a larger percentage of total nitrogen concentration in
streams with larger percentages of agricultural land. In that study, inorganic
nitrogen was found to be 27 percent of the total nitrogen in streams which drained
forested watersheds and over 75 percent in streams draining agricultural areas.
Orthophosphate portion of total phosphorous remained unchanged at approximately
40 percent, regardless of land-use type. These observations are fairly consistent
with the results of this report.
Coal mining along the tributaries to the Susquehanna and Potomac Rivers
influences water quality at the Fall Line. Major coal fields are found in the Tioga,
Juniata (both in the Susquehanna watershed), and North Branch Potomac River
basins. Mining exposes pyritic rock surfaces to weathering and oxidation processes,
which can cause a decrease in pH and elevate concentrations of iron, manganese,
and sulfate in water emanating from these areas. Mine drainage with low pH
characteristically contains iron and manganese in solution. When this water is
diluted by inflow and the acids are neutralized, and if oxidizing conditions exist,
these metals will precipitate and sorb onto sediment particles to be transported
downstream. Iron and manganese are carried in this fashion from the mining areas
into the Susquehanna and Potomac Rivers.
HYDROLOGIC CONDITIONS
Average discharge at each of the Fall Line sites for the study period was
about 20 percent greater than the long-term averages for the Potomac and James
Rivers, but 4 percent less than the long-term averages for the Susquehanna River
(table 1). Streamflow was unevenly distributed over the 28-month study period,
with discharge generally well above normal during the winter and fail of 1979 (fig.
2). However, from summer of 1980 to the end of the data-collection period in
April 1981, flow at all three stations was well below the long-term averages, with
the exception of a brief period in February 1981.
METHODS OF COLLECTION AND LABORATORY ANALYSIS
All water-quality and suspended-sediment samples were collected by USGS
personnel using depth-integrating methods described by Guy and Norman (1970).
All water-quality samples were preserved in the field according to methods
described in the National Handbook of Recommended Methods for Water Data
Acquisition (U.S.Geological Survey, 1977) and analyzed at the USGS Central
Laboratory in Doraville, Ga. Pesticide residues, low-molecular-weight halo-
genated hydrocarbons, and organic carbon were determined according to methods
described by Goerlitz and Brown (1972), and inorganic constituents were analyzed
according to procedures cited by Skougstad and others (1979). Samples for analysis
of chlorine were collected and analyzed using methods described in another section
of this report. Sediment samples were analyzed in the USGS sediment laboratory
in Harrisburg, Pa., by methods described by Guy (1969).
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Table 1.—Average discharge for study period and long-term average
discharges for the three Fall Line stations
Period
of
average
Average
discharge
for study
period
Long-term
average
discharge
(ftJ/s)
Percent
difference
from long-
term average
SUSQUEHANNA RIVER AT CONOWINGO, MD.
Jan.-Dec. 1979
Jan.-Dec. 1980
Jan.-Apr. 1981
Jan. 1979-Apr. 1981
52,300
28,400
45,900
41,100
'38,900
'38,900
^6,700
L42,900
+ 34
- 27
- 19
- 4
POTOMAC RIVER AT CHAIN BRIDGE AT WASHINGTON, D.C.
Jan.-Dec. 1979
Jan.-Dec. 1980
Jan.-Apr. 1981
Jan. 1979-Apr. 1981
20,400
11,000
9,060
14,800
11,500
11,500
15,300
12,000
+ 79
- 3
- 41
+ 23
JAMES RIVER AT CARTERSVILLE, VA.
Jan.-Dec. 1979
Jan.-Dec. 1980
Jan.-Apr. 1981
Jan. 1979-Apr. 1981
12,000
7,790
3,180
8,950
7,050
7,050
10,000
7,470
+ 70
+ 11
- 68
+ 20
Based on long-term discharge record for the Susquehanna River at
Harrisburg, Pa., and drainage area relationships.
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SUSQUEHANA RIVER AT CONOWINGO
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200
100
80
60
40
20
10
8
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2
1
60
MEAN MONTHLY DISCHARGE
LONG-TERM AVERAGE MONTHLY DISCHARGE
IFMAMIJASOND
1979
JFMAMIJASONDJFMA
1980
1981
POTOMAC RIVER AT CHAIN BRIDGE, WASHINGTON D.C.
2 -
JFMAMJJASONOj FMAMJjASONDJFMA
1979 1980 1981
JAMES RIVER AT CARTERSVILLE , VA
IFMAMI JASOND I FMAMIJASONDJ FMA
Figure 2.—Mean monthly and long-term average monthly discharge for the three
Fall Line stations.
7
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CONSTITUENT LOADS
Load Estimation Techniques—Nutrients and Metals
Bivariate linear regression equations were used to estimate all loads in this
study. Instantaneous constituent concentrations and discharges were used to
formulate the equations, which were then used with either mean daily discharges or
daily sediment loads to obtain daily constituent loads.
Instantaneous constituent loads were computed for each sample collected
using the following equation:
L = C x Q x 5.38
where
L = nutrient or metal load at time of sample,
in Ibs/d;
C = nutrient or metal concentration at time of sample,
in mg/L;
Q = instantaneous discharge at the time of sample, in ft3/s; and
5.38 = conversion factor.
The log of this instantaneous load was regressed against the log of the instan-
taneous discharge and the log of the instantaneous suspended-sediment load at the
time of sampling. Regression equations were fitted analytically by the method of
least squares.
Three criteria were then used for selecting either the discharge or sediment
regression to calculate loads: (1) The chosen equation should have a low standard
deviation. (2) A large percentage of the variance in the dependent variable (loads)
should be explained or accounted for by the regression. The coefficient of
determination (r2) is a measure of this. The greater r2 is, the better the regression
line fits the observed data points, and the more highly correlated one variable is to
another. (3) The signs of all significant regression coefficients should agree with
accepted chemical and physical principles.
Table 2 presents the regression equations and related statistics derived from
the above regression analysis and used to calculate constituent loads. Both
equations, using either discharge or suspended sediment as the independent
variable, are shown. An asterisk notes the equation selected for determination of
constituent loads found in tables 3, 4, and 5. The selected equation is in the form:
Log1Q L - a + b(log10 Q)
or
Log]0 L = a + b (log1Q SS)
where
_L_ = daily nutrient or metal load, in Ibs/d;
Q = mean daily discharge, in ft3/s;
SS = daily sediment load, in Ibs;
a = constant defining y intercept; and
b = constant defining slope of regression.
The mean daily discharge or suspended-sediment load is then substituted to
obtain daily constituent load. These daily loads are then summed to obtain the
monthly totals found in tables 3, 4, and 5.
-------
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— v co -^ co -^ co /-^ co ^ co X-N to *— - co ^ tn *~. to -*^ en
Cxco CXco O*co cxco Cx co cxtn CXto Cxto CXto CXtn
OC bO OCOC 60 60 60 60 bCbO bCOO 60 60 00 60 60 60 OObO
OO OO OO OO OO OO OO OO OO OO
J HH J _J ,J ,J ,J^I HH _J -H ,J _4 -J -H ,-H- ^J ,J J _J
-H — i com co r- m OO
+ + II II 1+ 1+ II 1+ 1+ ++ 1 +
os os r- oo coos r-. r-- oo os coos osco osos r-oo coos
osin rocs sjoco oos co i— t c^ro in co ro — -* coos CNCO
—I-H in»J rOCM <)-CO CMCM CNCM -HCM — I CN fOCN COCN
****** *
— v co ^tn /^co x-.co /^to x^co -—.to /-^tn /-.co ^^to
ex c/j cxto cxco cxco cxco cxtn cxco cxco cxco ex tn
bCOC 60 60 bOOC 60 60 60 bC 60 60 60 60 OCbC 60 M 00 60
oo oo oo oo oo oo oo oo oo oo
rovD osc^ co CO roin ro\c ^XiD -nm CNtn CMin inr--
— < O -HO -HO -HO -HO — *O -HO — < O -HO -HO
OO-H or*. VOCN -J--J- coo •«d-'-i -HOS min o "- ' CMOS
-H^D coo\ ooso O\CN oin ro-jr O^D -nin -HCN CN«J
+ 4- II II II 1+ 1+ + + 1+ II II
osco r^oo coco r-sc cor- r-r- osvD osr- vcm coco
OCN CN^ r-00 CNvO CN\C vOOs co
CXto O*co O*cn Cxco O*co Cxto cxco cxco cxco CXtn
60 60 0000 OOOC 6000 60 60 6060 bOOO 0000 60 60 bOOO
oo oo oo oo oo oo oo oo oo oo
^J^H _J,J hJ^J -JJ JJ J-J nJ-J J iJ PKJ .JJ
CO--H co^- m*o \oco OCM roro r-ro ooco \or^ coo
CN\O \ooo co^O — H in — H in — H to o^o O>3" O«ff *dr f*--
COF — OSON min m— H Oin •d'sD m — H mm oo-d" com
O-H CNO -HO -HO O-H O-H OO OCM O -H CMO
+ + II 1+ i + 1 + 1+ +4- + + 1+ 1 +
eu
-H o cy *~
-D •— 1 4J a;
CO C CO 4-1
(H I-H CO — H p to
(L CD « 60 CO 4_) X
— H — H > iJ l-i 4_| «H O,
RJJLOOOOC w^-
4-) CO U 4-> 4J O *
OtnO) +/-^ +'^ .CO
4->oitH- ss» z O.PX
> to CO O CD O •—"
•> O t-l •-! *H CO *H 4JtD X05^
U U « C C«C .HCO-H 4JCOAJ/^
•H 0) r^ 4J /•*. O O CO )_i CO IH O-a
c^- tntu oc E'^ EtJ °°'~v *J »J *j '^ o^J wo
COCJ [*H 4J£ GEE E^- InZ — l-^- O2 ^- CM
00 — < ai CObOO C 60 J-J - 60 *•
IH W (TJ 05 ^07 (C £ 10 E (0 toE «>CO
On) 4-1 (0 0)CO *-tO o-^x •- tO •-N-' r> CO 3 vw' 3 to
O « C C C C C t- tJ
»-J 4-icJ (U i-J O iJ QJ<-H CphJ O>-H QJ >-2 O*-1 O i-J
§"*- ^-- C **- bO~^ 00 tO 00*--. 00 to OC^-- JZ CO X *--
00 »-OO CflbO OOO O4J ObC O4J OOO G.W &.00
j=>E C3. ooa uiE no nE no nE too wE
Jj^^ O^-' C'-' 4-)'^^ 4JJJ 4J *— ' 4JJ-* J-Ji-x OJ-J O1*-'
a: n co -H -H -H -H -in .c js
O»-(j:2r;Z22 StXiCn
-------
Table 3.—Monthly load estimates (in hundreds of thousands of pounds) for the
Susquehanna River at Conowingo, Md.
[ Dashes indicate missing data ]
Month
Mean
discharge
(ft3/s)
Aluminum,
total
recoverable
as Al
Calcium,
dissolved
as Ca
Carbon,
organic,
total
as C
Chloride,
dissolved
as Cl
Iron,
total
recoverable
as Fe
Magnesium,
dissolved
as Mg
Manganese,
total
recoverable
as Mn
January 1979
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1980
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1981
February
March
April
101,200
47,600
143,000
65,200
43,900
26,900
13,000
16,140
28,000
48,900
48,300
44,200
52,300
27,200
13,100
70,400
108,000
46,500
17,500
12,300
8,450
4,740
6,270
9,800
16,800
28,400
7,170
104,000
35,500
36,800
57.0
34.5
15.7
4.7
6.7
16.3
45.6
35.9
42.7
-
10.9
2.8
119.3
126.7
44.9
13.5
4.3
3.1
1.8
4.3
5.2
5.3
342
5.1
221.5
20.0
~
-
-
624
688
1,060
1,780
1,710
1,490
-
1,009
614
2,170
2,650
1,480
700
593
438
278
397
685
793
11,800
395
2,800
1,220
~
636
245
969
342
224
120
50.2
65.2
125
256
248
225
3,510
122
47.2
426
648
235
69.5
46.9
29.8
14.5
21.3
35.9
69.4
1,770
24,6
622
174
171
-
-
309
340
530
893
858
748
—
504
304
1,093
1,350
743
349
294
217
137
196
336
393
5,920
195
1,420
615
—
90.0
54.4
24.6
7.4
10.3
25.6
77.0
61.0
72.3
-
18.0
4.4
209.2
219.5
75.7
22.1
6.8
4.9
2.9
6.9
8.4
8.5
587
8.3
394.2
33.2
~
-
-
192
212
317
519
499
426
—
294
188
610
700
420
210
180
135
87
125
219
241
3,410
123
779
352
~"
21.7
13.8
7.0
2.7
3.5
7.3
19.6
15.0
18.0
-
5.9
2.0
38.4
44.3
19.5
7.3
3.0
2.3
1.5
2.9
3.3
3.5
134
3.3
63.0
10.0
~"
Total January 1979
to April 1981
6,260
10
-------
Table 3.—Monthly load estimates (in hundreds of thousands of pounds) for the
Susquehanna River at Conowingo, Md.—Continued
Month
Nitrogen,
ammonia,
total
as N
Nitrogen,
organic,
total
as N
Nitrogen,
ammonia
+ organic,
total as N
Nitrogen,
nitrite
+ nitrate,
total as N
Nitrogen,
total
as N
Phosphorous,
ortho-
phosphate ,
total as POU
Phosphorous ,
total
as PO^
Sodium,
dissolved
as Na
Sulfate,
dissolved
as SO,,
January 1979
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1980
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1981
February
March
April
18.4
7.3
27.4
10.4
6.9
3.8
1.7
2.2
4.0
7.8
7.6
6.9
104
3.9
1.6
12.4
18.8
7.3
2.3
1.6
1.0
.52
.74
1.2
2.3
53.7
0.9
17.7
5.4
5.4
63.9
25.7
94.0
36.8
24.7
13.9
6.3
8.0
14.5
28.0
26.9
24.9
368
14.3
5.9
43.5
65.6
26.1
8.5
6.0
4.0
2.0
2.8
4.5
8.4
192
3.3
61.0
19.6
19.4
80.7
32.8
117.8
47.3
32.0
18.2
8.4
10.6
18.9
36.1
34.7
32.2
470
18.8
7.9
55.2
83.0
33.8
11.3
7.9
5.3
2.7
3.8
6.0
11.2
247
4.4
76.6
25.5
25.3
201
82.8
291
120
82
47.1
22.3
28.1
49.1
92.1
88.3
83.0
1,190
48.9
21.0
138.0
207
86.7
29.6
21.1
14.1
7.4
10.3
15.9
29.4
629
11.9
189.7
65.5
65.3
285.0
116.8
413.0
169.0
115.0
65.8
31.0
39.0
68.6
129.4
124.1
115.8
1,670
68.3
29.0
195.5
293.5
121.6
41.2
29.2
19.5
10.1
14.3
22.0
40.9
885
16.4
269.3
91.8
91.5
13.2
5.5
19.1
8.0
5.5
3.1
1.5
1.9
3.3
6.1
5.9
5.5
78.6
3.3
1.4
9.1
13.7
5.8
2.0
1.4
1.0
.5
.7
1.0
2.0
41.8
0.8
12.5
4.4
4.4
42.0
15.3
68.7
19.7
12.3
6.1
2.2
2.9
6.3
14.5
14.2
12.4
217
6.0
2.0
27.3
41.9
12.8
3.1
2.0
1.2
.53
.82
1.6
3.2
102
1.0
43.1
9.4
8.9
-
-
-
-
-
-
210
233
350
570
549
470
-
324
206
670
780
460
230
198
148
95
137
239
264
3,751
134
862
388
-
-
-
-
-
-
-
1,210
1,340
2,000
3,280
3,160
2,700
-
1,863
1,190
3,860
4,490
2,650
1,320
1,140
849
549
786
1,370
1,520
21,600
770
4,950
2,230
-
Total January 1979
to April 1981 188
663
848
2,150
3,030
143
381
11
-------
Table 4.—Monthly load estimates (in hundreds of thousands of pounds) for the
Potomac River at Chain Bridge at Washington, D.C.
[Dashes indicate missing data ]
Month
Mean
discharge
(ft3/s)
Aluminum,
total
recoverable
as Al
Calcium,
dissolved
as Ca
Carbon,
organic,
total
as C
Chloride,
dissolved
as Cl
Iron,
total
recoverable
as Fe
Magnesium,
dissolved
as Mg
Manganese,
total
recoverable
as Mn
January 1979
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1980
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1981
February
March
April
31,100
30,600
38,300
18,900
17,400
14,600
5,960
5,940
21,900
33,700
18,300
13,200
20,400
18,400
8,050
23,300
31,000
25,300
7,910
4,280
3,400
1,670
1,700
3,710
3,550
11,000
1,680
13,700
7,550
13,100
133
138
80.9
24.9
24.6
31.6 -
3.8
7.7
99.8
103
30.8
10.0
689
14.7
4.0
49.7
63.2
63.2
6.2
3.6
2.0
.44
.50
2.7
1.1
211
0.41
42.3
3.8
~
1,045
-
-
-
729
561
317
-
791
1,084
318
604
-
609
341
-
-
65.1
368
259
222
112
138
264
215
-
108
583
359
352
341
255
271
111
114
133
35.6
56.2
274
310
119
56
2,080
76.6
30.3
170
236
217
48
33
20.4
7.6
7.9
21.1
14.3
882
7.3
153
33.3
~
352
-
-
-
277
208
133
-
284
285
126
235
-
227
137
-
-
25.0
149
110
96.2
49.0
62.7
117
91.5
~
49.5
229
141
131
216
237
126
37.2
36.4
47.5
5.1
10.6
161
164
47.2
14.5
1,100
21.4
5.5
77.8
96.4
98.2
8.4
4.7
2.6
.53
.61
3.7
1.4
321
0.49
65.2
5.0
~
219
-
-
-
161
123
73.6
-
170
233
72.0
135
-
133
77.5
-
-
14.5
83.9
60.4
52.3
26.5
33.4
63.0
50.3
~
26.2
131
80.7
77.0
15.9
16.2
9.9
3.1
3.1
3.9
.51
1.0
12.0
12.6
3.8
1.3
83.3
1.9
.52
6.1
7.8
7.8
.81
.47
.27
.06
.07
.35
.15
26.3
0.06
5.2
.50
"
Total January 1979
to April 1981
947
3,150
1,490
115
12
-------
Table 4.—Monthly load estimates (in hundreds of thousands of pounds) for the
Potomac River at Chain Bridge at Washington, B.C.—Continued
Month
Nitrogen,
ammonia,
total
as N
Nitrogen,
organic,
total
as N
Nitrogen,
ammonia
+ organic,
total as N
Nitrogen,
nitrite
+ nitrate,
total as N
Nitrogen,
total
as N
Phosphorous,
ortho-
phosphate ,
total as POi,
Phosphorous ,
total
as PO,,
Sodium,
dissolved
as Na
Sulfate,
dissolved
as SO,,
January 1979
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1980
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1981
February
March
April
4.56
5.53
5.80
2.04
1.87
1.49
.40
.40
2.80
5.00
2.06
1.35
33.3
2.16
.63
3.06
4.12
3.39
.65
.29
.21
.08
.08
.26
.23
15.2
0.09
1.43
.63
1.46
44.2
34.8
33.9
13.3
13.5
16.0
3.8
6.3
35.1
39.4
14.5
6.5
261
8.9
3.3
21.0
29.1
27.0
5.3
3.6
2.1
.74
.78
2.3
1.5
106
0.71
18.8
3.6
11.8
54.3
42.8
41.6
16.3
16.7
19.7
4.7
7.7
43.2
48.5
17.8
7.9
321
11.0
4.1
25.9
35.8
33.2
6.5
4.4
2.6
.91
.96
2.8
1.8
130
0.87
23.2
4.4
-
65.8
68.0
82.9
33.5
31.3
25.1
8.2
8.2
42.3
72.6
33.6
23.4
495
35.1
12.1
47.1
62.1
51.6
12.4
6.2
4.7
1.9
2.1
5.3
5.0
247
2.2
23.3
12.1
24.0
125.0
140.9
158.5
59.3
54.9
43.8
12.8
12.9
78.3
137.5
59.7
40.2
924
62.6
19.7
86.4
115.3
95.2
20.1
9.5
7.1
2.7
2.9
8.4
7.5
438
3.1
41.4
19.6
42.4
6.96
7.20
8.82
3.48
3.24
2.58
.81
.81
4.47
7.68
3.48
2.40
51.9
3.60
1.20
4.95
6.60
5.43
1.23
.60
.45
.18
.21
.54
.48
25.5
0.21
2.40
1.20
2.49
34.2
30.7
23.8
8.3
8.4
10.3
1.82
3.3
26.5
28.9
9.6
3.7
190
5.3
1.7
14.6
19.6
18.7
2.7
1.7
.98
.28
.30
1.2
.61
67.8
0.26
12.8
1.7
—
251
-
-
-
232
170
125
-
221
296
112
202
~
186
123
-
-
21.3
134
104
93.0
47.8
63.1
116
86.8
-
50.1
200
124
107
1,024
-
-
-
1,517
1,219
650
-
1,744
2,403
672
1,289
~
679
-
-
-
1,064
770
528
448
224
198
368
284
-
156
697
430
391
Total January 1979
to April 1981
52.1
402
480
804
1,470
83.7
273
13
-------
Table 5.—Monthly load estimates (in hundreds of thousands of pounds) for the
James River at Cartersville, Va.
[Dashes indicate missing data]
Month
Mean
discharge
(ftVs)
Aluminum,
total
recoverable
as Al
Calcium,
dissolved
as Ca
Carbon,
organic ,
total
as C
Chloride,
dissolved
as Cl
Iron,
total
recoverable
as Fe
Magnesium,
dissolved
as Mg
Manganese,
total
recoverable
as Mn
January 1979
February
March
April
May
June
July
Augu st
September
October
November
December
Calendar year
total
January 1980
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1981
February
March
April
16,400
18,200
20,100
9,690
9,190
13,800
3,580
3,000
16,100
16,000
11,900
7,110
12,000
14,600
6,540
17,900
21,500
8,040
3,590
2,350
1,820
1,420
1,410
2,020
1,860
7,790
1,680
4,760
2,650
3,640
46
115
64.4
12.6
12.1
51.4
1.9
1.5
60.0
40.0
20.0
7.4
432
35.1
5.5
46.6
67.3
9.1
2.0
.9
.5
.3
.3
.7
.6
169
0.51
3.6
1.1
1.9
393.7
-
463.5
264.6
261.4
316.1
122.8
106.4
353.2
391.5
307.0
213.5
~
364.6
188.5
431.3
264.6
236.2
118.3
86.2
69.8
53.5
56.2
73.3
71.0
2,010
65.3
137.1
95.3
120.6
179
207
225
90.1
87.7
149
28.8
23.8
176
171
115
65
1,520
155
54.6
194
234
74.7
28.3
17.7
13.1
9.1
9.7
14.4
13.4
819
11.9
37.2
20.4
28.3
164.5
-
172.4
-
155.7
-
93.3
828
-
172.5
164.0
137.8
~
167.6
126.0
182.2
155.5
147.6
89.0
69.8
58.8
46.7
48.8
60.6
59.6
1,210
55.6
95.8
75.8
91.3
93
261
132
23.1
22.3
110
3.1
2.4
127
79.4
37.6
13.1
904
69.6
9.6
93
138
164
3.4
1.4
.8
.5
.5
1.1
.9
483
0.7
6.2
1.8
3.1
80.6
-
93.7
56.5
55.9
64.4
27.3
23.7
71.1
80.6
64.7
46.1
~
75.4
41.0
88.4
56.4
50.8
26.2
19.3
15.8
12.2
12.8
16.5
16.0
431
14.8
30.0
21.4
26.8
3.5
7.9
4.9
1.1
1.0
3.7
.18
.14
4.4
3.1
1.6
.64
32.2
2.8
.49
3.6
5.1
.78
.19
.09
.05
.03
.03
.07
.06
13.4
0.05
.32
.10
.18
Total January 1979
to April 1981
608
2,430
1,400
46.3
14
-------
Table 5.—Monthly load estimates (in hundreds of thousands of pounds) for the
James River at Cartersville, Va.—Continued
Month
Nitrogen,
ammonia,
total
as N
Nitrogen,
organic,
total
as N
Nitrogen,
ammonia
+ organic,
total as N
Nitrogen,
nitrite
+ nitrate,
total as N
Nitrogen,
total
as N
Phosphorous,
ortho-
phosphate,
total as P0<,
Phosphorous,
total
as PO,,
Sodium,
dissolved
as Na
Sulfate,
dissolved
as SO,,
January 1979
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1980
February
March
April
May
June
July
August
September
October
November
December
Calendar year
total
January 1981
February
March
April
1.1
1.1
1.4
.61
.59
.90
.22
.18
1.1
1.1
.75
.45
9.5
0.97
.39
1.2
1.4
.52
.21
.14
.11
.08
.08
.12
.11
5.3
0.10
.27
.16
.21
18.0
27.1
23.4
7.3
7.0
16.1
1.8
1.4
19.4
16.7
10.0
4.9
153
14.9
3.9
19.1
24.5
5.8
1.8
.98
.67
.43
.47
.78
.70
74.0
0.60
2.6
1.2
1.8
18.9
28.5
24.7
7.7
7.4
16.9
1.9
1.5
20.3
17.6
10.6
5.2
161
15.7
4.2
20.1
25.8
6.1
1.9
1.0
.7
.5
.5
.8
.7
78
0.6
2.8
1.2
1.9
8.7
9.3
10.8
4.7
4.6
7.2
1.7
1.4
8.4
8.5
5.9
3.5
74.7
7.7
3.0
9.5
11.3
4.0
1.6
1.1
.8
.6
.6
.9
.8
41.9
0.7
2.1
1.2
1.6
29.6
39.3
38.0
13.3
13.0
25.5
3.7
3.0
30.6
28.0
17.8
9.2
251
25.1
7.6
31.9
39.7
10.8
3.7
2.1
1.5
1.0
1.0
1.7
1.6
128
1.4
5.1
2.5
3.7
3.2
2.7
3.7
2.3
2.2
2.6
1.2
1.1
2.9
3.2
2.6
1.9
29.6
3.0
1.7
3.5
3.8
2.1
1.1
.89
.75
.60
.63
.77
.76
19.5
0.71
1.3
.97
1.2
12.4
14.5
15.7
6.2
6.1
10.4
2.0
1.6
12.3
11.9
8.0
4.5
106
10.7
3.8
13.5
16.3
5.2
1.9
1.2
.89
.6
.7
1.0
.9
56.7
0.8
2.6
1.4
1.9
115.4
-
123.9
-
102.6
-
59.5
52.6
-
119.7
110.0
89.8
-
115.4
81.6
127.5
102.7
96.6
56.8
44.2
37.0
29.3
30.7
38.2
37.5
798
35.0
61.7
48.1
58.2
240.0
-
277.3
172.1
170.6
191.3
85.0
74.1
209.8
240.8
195.7
141.8
-
226.0
126.2
263.4
172.1
155.8
81.7
60.7
49.7
38.5
40.4
51.9
50.5
1,320
46.6
92.8
66.8
83.4
Total January 1979
to April 1981
15.6
233
246
122
391
53.3
169
15
-------
Load Estimation Techniques—Major Cations and Anions
Because specific conductance is directly related to the number of dissolved
ions in water, it is appropriate to use this parameter to predict loads of major
cations and anions in the three rivers. The James River specific conductance data
were not sufficient, thus log Q was substituted as the independent variable. The
relationships used were:
C = a + b (SC)
or
C = a + b (log Q)
where
C = major ion concentration at the time of sample, in mg/L;
SC = specific conductance at the time of sample, in ^jmhos/cm2;
Q = instantaneous discharge at the time of sample, in ft3/s;
a = constant defining y intercept; and
b = constant defining slope of regression.
Instantaneous constituent concentrations were regressed against the daily
specific conductance or the log of the instantaneous discharge and the above
equations fitted analytically by the method of least squares. By substituting the
daily specific conductance or log of the mean daily discharge into the equations
instead of the value at the time of sample, an average daily concentration C was
calculated:
C = a + b (SCd)
or _ _
C = a + b (log Q).
Then, the daily load was computed by:
L = C x Q x 5.3S,
where _
C = average daily ion concentration, in mg/L;
SCjj = daily specific conductance value, in umhos/cm;
Q = mean daily discharge, in ft3/s;
L = daily load in Ibs/d;
a = constant defining y intercept;
b = constant defining slope of regression; and
.5.38 = conversion factor.
Daily major cation and anion loads are summed to obtain monthly loads and
are tabulated in tables 3, 4, and 5. The regression equations used to estimate them
are presented in table 6.
16
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-------
Evaluation and Limitation of the Load Estimates
In tables 3, 4, and 5, and in subsequent listings, all constituent loads are
calculated independently from their regression equations, regardless of the rela-
tionships that are known to exist among the parameters. For example, total
nitrogen concentration equals the sum of nitrite + nitrate and ammonia + organic
nitrogen concentrations for each individual sample. If the load estimation
techniques are accurate, the sums of monthly or yearly loads of nitrite + nitrate,
and ammonia + organic nitrogen should be nearly the same as loads for total
nitrogen for the same periods. Also, the summed loads of ammonia nitrogen and
organic nitrogen should be the same as ammonia + organic nitrogen. The
agreement or disagreement of the constituent loads and the sums of their
component species is an indication of the ability of the regression technique to
accurately estimate those constituent loads for the specific period.
To test further the accuracy of this technique, yearly constituent loads
calculated by this regression method were compared to those obtained by a totally
different method for Potomac River at Chain Bridge (table 7). The USGS's
Potomac Estuary Project personnel independently collected data on selected
nutrient species at this site through calendar years 1979 and 1980. For their load
computations, they had access to a large data base of which only part was used in
this report to obtain regression equations and to compute constituent loads. The
Estuary Project group calculated their loads using the hydrograph method
(Porterfield, 1972). In this technique, enough data must be available to estimate a
continuous plot of constituent concentrations. This, along with a continuous plot of
discharge, is used to obtain a continuous measure of constituent loads, subdividing
days as necessary. This is a more direct and, hence, accurate method of load
computation.
The comparisons in table 7 show relatively small differences in annual total
loads. Month-by-month comparisons do not compare as well because the regression
technique does not allow for seasonal- and antecedent-flow variations, which are
accounted for in the hydrograph technique. Similar results can be expected from
the Susquehanna and James Rivers.
The regression load-estimation technique requires intensive sampling of high
discharges, which carry the majority of most constituent loads. An inconsistent or
incomplete, high-flow sampling program will not cover the full range of hydrologic
events and may incorrectly bias the regression equations to only those high-flow
events that are sampled.
The regression load-estimation technique is most accurate in wet years
having a wide range of flow. Factors not taken into account in the regression
technique, such as season and time since the previous flow peak, have a greater
relative effect on constituent loads during sustained low-flow periods. Based only
on low-flow constituent loads, the regression line has higher standard deviation,
which leads to a lower coefficient of determination.
The basic data used in calculating loads for the Susquehanna and Potomac
Rivers are available in USGS annual reports titled "Water Resources Data for
Maryland and Delaware;" the James River data is found in the USGS publication
titled "Water Resources Data for Virginia."
18
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19
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EXAMINATION OF SELECTED WATER-QUALITY CONSTITUENTS
Seasonal Characterization of Pesticides
Pesticide residue data (organochlorine and organophosphorous insecticides
and chlorophenoxy acid herbicides) were collected monthly and during high flows at
each of the Fall Line stations. Only 2, 4 dichlorophenoxyacetic acid (2,4-D) and
atrazine were consistently detected at the Conowingo and Chain Bridge stations.
Pesticide concentrations at the Chain Bridge site were generally less than at
Conowingo. Maximum concentrations detected at Conowingo were 0.30 and 1.2
ug/L for 2,4-D and atrazine, respectively. At Chain Bridge, maximum concen-
trations were 0.14 and 0.4 ug/L for 2,4-D and atrazine, respectively. Atrazine,
2,4-D, and silvex were detected at James River at Cartersville several times, but
concentrations were at the lower limit of detection.
Both 2,4-D and atrazine concentrations show strong seasonal patterns in the
Susquehanna and Potomac Rivers (figs. 3 and 4). Both rivers have 2,4-D and
atrazine concentration peaks in late spring and summer. This is reasonable because
herbicides are usually applied just before and during spring planting, and both 2,4-D
and atrazine are readily soluble in water. Therefore, runoff from cropland and
residential areas in late spring and summer usually carries higher than normal
concentrations of these herbicides in solution to nearby tributaries and streams.
These streams, in turn, carry the herbicides into the estuaries of the Chesapeake
Bay.
The highest concentrations of 2,4-D in the Susquehanna River occurred during
low-flow periods in fall 1980 and spring 1981. As streamflow decreased, the
concentration of 2,4-D in the Susquehanna River increased. This trend continued
until high flows in February diluted the concentration to much lower levels.
Following this high-flow event, 2,4-D concentrations again increased in March
1981. This type of concentration-discharge relationship is typical of a constant,
continual input of a constituent into a variable flow system; runoff during high
flows dilutes the constituent to low concentrations, but concentrations begin to
rise during base flow. Considering 2,4-D is a widely-used domestic herbicide, it is
possible that input of 2,4-D to the Susquehanna River could be from shallow
ground-water sources or point discharges. However, more data are needed to
determine the source of 2,4-D in the Susquehanna River which keeps concentra-
tions high (0.20-0.30 ug/L) even during winter months when herbicide applications
are at a minimum. In contrast, the Potomac basin, which has similar land-use
practices as the Susquehanna, had very small concentations (<0.05 pg/L) during the
same low-flow periods in fall 1980 and spring 1981.
20
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SUSOUEHANNA RIVER AT CONOWINGO . MD.
0.35 |—i 1—i—i—r
0.30 -
0.25 -
0.20 -
0.15
0.10 -
0.05 -
0.00 -•
T—(—,140,000
- 120,000
- 100,000
— 80,000
60,000
i— 40 000
- 20,000
IFMAMJJASOND JFMAMJJASONOJFMA
1979
1980
1981
POTOMAC RIVER AT CHAIN BRIDGE , WASHINGTON D.C.
DISCHARGE
2, 4-D CONCENTRATION
IFMAMJJASOND
0.25 -
0.20 -
0.15
0.10
0.05 -
48,000
- 40,000
- 32,000
- 24.000
- 16,000
8,000
0.00 -
Q
Z
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IFMAMJJASOND
1979
1980
J F M A
1981
Figure 3.—Seasonal fluctuations in concentrations of 2,4-D at the Susquehanna
and Potomac Fall Line stations.
21
-------
SUSQUEHANNA RIVER AT CONOWINGO, MD.
Ot
HI
1-
cc
LU
a
cc
O
O
cc
O
0.0 -
0.8 -
0.6
0.4 -
0.2 -
140,000
- 120,000
- 100,000
- 80,000
— 60,000
- 40,000
0.0
JfMAMJIASONDJFMAMJJASOND
1979
1980
I F M A
1981
a
z
o
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UJ
cc
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- 20,000 ,_
LU
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13
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POTOMAC RIVER AT CHAIN BRIDGE , WASHINGTON D.C
0.0
JFMAMJJASONDJFMAMJJASONDJFMA
1979 1980 1981
Figure 4.—Seasonal fluctuations in concentrations of atrazine at the Susquehanna
and Potomac Fall Line stations.
22
-------
Seasonal Characterization of Chlorophyll A
Chlorophyll a is the primary pigment of all oxygen-evolving photosynthetic
organisms and is present in all algae and photosynthetic organisms, except some
photosynthetic bacteria (Wetzel, 1975). Figure 5 presents the chlorophyll a
concentrations for each of the Fall Line stations. Maximum chlorophyll a
concentrations at all three sites occur during spring runoff. Increased spring
concentrations may be caused by high-velocity runoff carrying with it fragments of
underdeveloped and emerging plankton or a spring accumulation of periphytic
chlorophyll. Concentration peaks of lesser magnitude occur during the late spring
and summer months, but these are generally not related to discharge. The summer
peaks may be related to increased biological activity which accompanies warmer
temperatures, increased daylight, and rapid nutrient recycling.
Chlorine
Because of recent interest in the effects of chlorine on marine life, water
samples were collected and field-analyzed for total residual chlorine at five sites
on tributaries to the Chesapeake Bay (fig. 6). At the same time, additional samples
were collected and sent to the laboratory for analysis of low-molecular-weight
halogenated hydrocarbons listed in table 8. The sites are: (1) Susquehanna River
at Conowingo, Md.; (2) Potomac River at Chain Bridge at Washington, D.C.; (3)
Potomac River at Woodrow Wilson Bridge at Alexandria, Va.; CO Patuxent River
near Bowie, Md.; and (5) Back River at Edgemere, Md.
The total residual (free residual and combined) chlorine analysis employed
(American Public Health Association, 1976) was an amperometric titration tech-
nique which measures the total oxidants in the water. Therefore, significant
concentrations of constituents such as bromine, iodine, chlorine dioxide, or
permanganate in the sample may produce erroneously high values for total residual
chlorine.
The five stations shown in figure 6 were each sampled in December 1980 or
January 1981 and again in June or July 1981. All samples had total residual
chlorine concentrations of less than or equal to the lower limit of detection for the
technique, 0.01 mg/L. In three instances the chemicals listed in table 8 were
detected. Trichloroethylene (TCE) concentrations of 0.005 and 0.009 mg/L were
reported for the Back and Patuxent River sites, respectively, on July 1, 1981. On
June 26, 1981, a benzene concentration of 0.002 mg/L was detected for the
Potomac River at Alexandria, Va. The limits of detection for both TCE and
benzene are 0.001 mg/L.
23
-------
SUSQUEHANNA RIVER AT CONOWINGO . MD
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J FMAMI JASON 01 J F' M A M I I A S 0 N D| J F M A M
1979 1980 1981
POTOMAC RIVER AT CHAIN BRIDGE. WASHINGTON DC
90
80
70
60
50
40
30
20
10
0
CHLOROPHVLL A
--J I I ' 'J 'v-s^r-vy
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J FMAMJIASOND|JFMAMIIASOND|JFMAM
56,000
48,000
40,000
32,000
24,000
16,000
8,000
0
1979 1980
JAMES RIVER AT CARTERSVILLE , VA
1981
O
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N Oil F M A M I ] A S 0 H Oil F M A
1979 1980 1981
Figure 5.--Seasonal fluctuations of concentrations ol chlorophyll a at the
three Fall Line stations.
-------
EXPLANATION
Drainage Basin boundary
S7 Chlorine- Monitoring station
> NY._., l_^T
;J Susquehanna
River
Basin
Figure 6.—Location of chlorine-monitoring stations on selected tributaries
to Chesapeake Bay.
25
-------
Table 8.—Schedule of low-molecular-weight, halogenated organic compounds
analyzed from selected tributaries to Chesapeake Bay. All
samples were collected at base flow and performed on unfiltered,
water-sediment mixtures.
Benzene
Bromoform
Carbon tetrachloride
Chlorobenzene
Chlorodibromomethane
Chloroethane
2-Chloroethyl vinyl ether
Chloroform
Dichlorobromoethane
Dichlorodifuloromethane
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Di chloroethylene
1,2-trans-Dichloroethyiene
1,2-Dichloropropane
1,3-Dichloropropene
j'jthylbenzene
Methylbromide
1,1,2,2-Tetrachlorethane
Tetrachloroethylene
Toluene
1,1,1-Trichloroethane
1,1,2-Trichloroethane
Trichloroethylene
Trichlorofluoromethane
Vinyl chloride
26
-------
Total Recoverable Aluminum, Iron, and Manganese
The term "total recoverable" refers to the amount of a particular constituent
that is in solution after a water/suspended-sediment mixture sample has been
digested by dilute acid. Complete dissolution of all particulate matter by this
method is not achieved or desirable. The purpose of the digestion is to remove
those constituents readily recoverable from the surfaces of the sediment particles
without breaking down the crystalline structure of the sediments. Minerals within
this crystalline structure are considered essentially unavailable for biological
uptake under normal conditions existing in the estuaries of the Chesapeake Bay.
Computed loads for total recoverable aluminum, iron, and manganese are
presented in tables 3, k, and 5. The greatest loads for each constituent were
carried in the Susquehanna River basin, whereas the smallest loads were found in
the James River basin. Figures 7, 8, and 9 show aluminum, iron, manganese, and
suspended-sediment concentrations, and discharge at the three Fall Line stations
for selected high-flow periods. Regression data from table 2 for the Susquehanna
River show higher correlations of aluminum, iron, and manganese with suspended
sediment than with discharge. Because of the three dams in the lower Susquehanna
River, this correlation is not evident in figure 7.
Aluminum, iron, and manganese correlated very well with suspended sediment
in the Potomac River at Chain Bridge (table 2 and fig. 8). As suspended-sediment
concentrations increased, so did concentrations of aluminum, iron, and manganese.
All three metals had peak concentrations that were greater during the high flow in
March than in September.
Figure 9 shows slightly different relations at the James River. Although
manganese and suspended-sediment concentrations increased proportionally with
discharge, aluminum and iron decreased at the peak of both suspended sediment
and discharge. This sag may be caused by different quality and arrival times of
water coming from upstream tributaries. No other storms were intensively
sampled to verify whether this phenomenom occurs frequently.
Sulfate
Sulfate is not a major constituent in the earth's outer crust (Hem, 1970). It is
commonly derived from metallic sulfides which occur in both igneous and sedi-
mentary rocks. As these sulfides come into contact with aerated water, they are
oxidized to sulfates. The oxidation of sulfur-containing minerals, such as pyrite, is
especially common in coal areas.
Sulfate concentrations generally are inversely related to discharge. Because
rainwater contains very small concentrations of sulfate as compared to streams,
sulfate concentrations drop sharply during runoff events. During low-flow periods,
streams are fed principally from ground-water sources, which have relatively high
concentrations of sulfate due to prolong and intimate contact with sulfate-yielding
minerals.
27
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SUSPENDED SEDIMENT
DISCHARGE
O WATER SAMPLE
TOTAL Hi-L'JVERABLE ALUMINUM
TOTAL RECOVERABLE MANGANESE
Figure 7.—Aluminum, iron, and manganese concentrations during
February 20-26, 1981, at the Susquehanna River
Fall Line station.
28
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SEPTEMBER 1979
220,000-
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MARCH 1980
TOTAL RECOVERABLE IRON
TOTAL RECOVERABLE ALUMINUM
TOTAL RECOVERABLE MANGANESE
Figure 8.--Aluminum, iron, and manganese concentrations during
September 5-8, 1979, and March 21-24, 1980, at the
Potomac River Fall Line station.
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Q 20,000 3.0
SUSPENDED SEDIMENT
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•12.0
TOTAL
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TOTAL
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600
400
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15
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APRIL 1980
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Figure 9.—Aluminum, iron, and manganese concentrations during April 15-17, 1980,
at the James River Fall Line station.
30
-------
Table 9 compares sulfate loads for the three Fall Line stations for the period
May 1980 to April 1981. This period was chosen because it contained the most
complete set of data for each of the stations, primarily during ba. 3-flow periods.
The James River site carried 8.3 percent of the water discharge for the three
stations but only 3.2 percent of the sulfate load. Both the Susquehanna and
Potomac Rivers carried slightly more than their share of sulfate loads, when
compared to their flow contributions for the same period. The discharge-weighted
average concentrations of sulfate also point out that the Susquehanna and Potomac
Rivers carry greater amounts per unit discharge of sulfate than the James River.
The increased sulfate concentrations may be the result of drainage from coal areas
in the Susquehanna and Potomac River basins. Very little coal is mined in the
James River basin.
Nutrients and Their Relationships to
Suspended Sediment and Discharge
Nutrients, chemical species of phosphorous, nitrogen, and carbon necessary
for the growth of plant life, are found in water in the dissolved form associated
with clay particles and as suspended organic matter. Certain nutrient species, such
as orthophosphate, nitrite, and nitrate, are usually found dissolved in water. Most
of the organic phosphorous and organic nitrogen is usually suspended. Ammonia
and carbon can be found in the dissolved or suspended phase.
Generally, the highest concentrations of all nutrients occur during storms
when water discharge and suspended-sediment concentrations are highest (figs. 10,
11, and 12). Nitrite + nitrate and orthophosphate loads correlate closely with
discharge at all three Fall Line stations (table 2). All of the nutrient species data
for the Susquehanna River at Conowingo correlate more closely with discharge;
whereas, for the Potomac River at Chain Bridge, some parameters correlate better
with suspended sediment while others correlate better with discharge. In general,
nutrient parameters known to associate with suspended material relate better to
suspended sediment, and constituents with greater solubility relate better to
discharge.
For the Susquehanna River site, the hydroelectric dams between Harrisburg
and Conowingo alter the natural riverine, sediment-flow patterns. During most
years, suspended sediment becomes trapped behind these dams (Williams and Reed,
1972). The effect that the dams between Harrisburg and Conowingo have on the
sediment transport of the lower Susquehanna River is discussed in more detail in a
later section. However, those nutrients normally in suspension obviously have their
transport regulated by the dams on the lower Susquehanna. Figure 10 shows the
nutrient and suspended-sediment concentrations at Conowingo for the largest
storm during the 1981 water year. None of the water-quality parameters show
clear relationships with either suspended sediment or discharge, although both
nitrite-nitrate and ammonia + organic nitrogen both have their highest concen-
trations occurring at the discharge and suspended-sediment peak.
31
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MARCH 1980
24
— — — — TOTAL AMMONIA + ORGANIC NITROGEN as N
TOTAL NITRITE + NITRATE as N
TOTAL PHOSPHOROUS as P
Figure 11.—Nutrient concentrations during September 5-8, 1979, and
March 21-24, 1980, at the Potomac River Fall Line station.
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Figure 12.—Nutrient concentrations during April 15-17, 1980, at the
James River Fall Line station.
35
-------
In figures 11 and 12, ammonia + organic nitrogen is clearly related to the
suspended-sediment hydrograph at both the Chain Bridge and Cartersville sites.
Nitrite-nitrate nitrogen relates better to discharge at these two sites. Total
phosphorous shows good correlation with suspended sediment at the Chain Bridge
station and less correlation with suspended sediment at the Cartersvilie site.
During the high-flow events, it is critical to sample intensively before,
during, and after both the discharge and suspended-sediment peaks to provide data
sufficient for accurate nutrient load estimates. At the Chain Bridge and
Cartersville stations, suspended-sediment concentration peak precedes the dis-
charge peak by 8 to 40 hours (figs. 11 and 12). If samples are collected only
between the peaks, one might wrongly conclude that certain nutrient parameters,
such as total phosphorous and organic nitrogen, are inversely related to discharge
during storm periods; the loads of these constituents would then be underestimated.
In only one instance in the 2-year data-collection period did nutrient concen-
trations decrease significantly during a high-flow event. For the Potomac River at
Chain Bridge in February 1979 (fig. 13), the rise of nutrient concentrations at the
beginning of the flow peak was reversed, probably because of a dilution effect from
snowmelt (fig. 13). However, when the snow cover had been melted and the rain
came in contact with the land surface, the concentrations of nitrite + nitrate,
ammonia + organic nitrogen, and total phosphorous again increased.
Table 10 presents annual loads of selected nutrient species and annual mean
discharges at the three Fall Line stations for 1979 and 1980. This table shows that
at each of the stations, mean streamflow during 1980 was approximately one-half
that of 1979; likewise, all listed nutrient loads are reduced by about half. This
suggests the possibility of using annual mean discharges to approximate annual
nutrient loads for past and future years.
Seasonal Variability of Nutrient Transport
Table 11 lists the transported loads of selected nutrients at the three Fall
Line stations for 2 complete calendar years. The period of data collection is
divided into 4-month intervals: (1) January-April, which represents the late winter
and early spring high-flow period; (2) May-August, the most intense part of the
growing season when flows are low, except during hurricane-related storms; and (3)
September-December, when flows are low to moderate (except during hurricane-
related storms) and biological activity for the year is declining. Data from January
to April 1981 are not included in order to limit this analysis to two complete yearly
cycles.
The data in table 11 show that for all three stations, the January-through-
April period transports most of the loads of these nutrient species. Sixty-one per-
cent of the total nitrogen and about two-thirds of the total phosphorous and
organic carbon loads at the Susquehanna River at Conowingo accompany the high
runoff occurring in late winter and early spring. At the Potomac and James River
Fall Line stations, the January-through-April period contributes 50 to 61 percent of
the loads for these three constituents.
36
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Figure 13.--Nutrient concentrations during February 25 - March 1, 1979,
at the Potomac River Fall Line station.
37
-------
Table 10.—Annual loads of selected nutrients (in millions of pounds) at the
three Fall Line stations for calendar years 1979 and 1980
Constituent
Susquehanna
at Conowingo
1979 ]
River
, Md.
1980
Potomac River
at Chain Bridge
at feshington, D.C.
1979
1980
James River at
Cartersville, Va.
1979
1980
Nitrogen, nitrite +
nitrate, total as N
119
62.9
49.5
24.7
7.47
4.19
Nitrogen, ammonia,
total as N
Nitrogen, ammonia +
organic, total as N
Nitrogen, organic,
total as N
10.4
47.0
5.37
24.7
36.8 19.2
3.33
32.1
26.1
1.52
13.0
10.6
0.95
16.1
15.3
0.53
7.80
7.40
Nitrogen, total
as N
167
88.5
92.4
43.8
25.1
12.8
Phosphorus ,
orthophosphate,
total as PO
7.86 4.18
5.19
2.55
2.96
1.95
Phosphorous,
total as PO
21.7 10.2
19.0
6.78 10.6
5.67
Carbon, organic,
total as C
351
177
208
1.2 152
81.9
Mean discharge
(ft3/s)
52,300 28,400 20,400 11,000 12,000
7,790
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During the May-through-August period, transport of nitrogen, phosphorous,
and organic carbon is at a minimum. StreamfJow is normally low and biological
uptake of nutrients is high. During the September-through-December period, while
evapotranspiration, temperature, and biological uptake of nutrients decline,
stream flow and nutrient concentrations show marked increases.
Figures 14 and 15 graphically present monthly nitrogen and phosphorous
species loads from the three Fall Line stations. As shown in table 11, much of the
load is delivered during the first few months of each year when streamflow is
above average. Also worth noting are the very small loads which were carried by
the three rivers during the summer and fall of 1980 when streamflow was below
normal. Nitrogen and phosphorous loads are not evenly distributed throughout the
year, but are delivered mainly during high-flow periods.
Comparison of Nutrient Data Among the
Three Fall Line Stations
Of the three stations, the Potomac River at Chain Bridge had the highest
discharge-weighted averge concentration of total nitrogen, 2.20 mg/L (table 12);
the Susquehanna value had 1.61 mg/L, followed by the James River average
concentration of 0.96 mg/L.
Most of the total nitrogen load transported by the Susquehanna and Potomac
Rivers at their Fail Line is in the nitrite + nitrate form (table 12 and fig. 1^).
Nitrite + nitrate comprised 71 and 55 percent of the total nitrogen at the
Conowingo and Chain Bridge sites, respectively. On the other hand, at the James
River at Cartersville, nitrite + nitrate comprised only 31 percent of the total
nitrogen load, with the remainder being mostly in the form of organic nitrogen.
Since a much larger portion of the Susquehanna and Potomac River basins is
involved in agriculture, this agrees with the results of Omerik (1976) mentioned
previously.
The Susquehanna River at Conowingo has discharge-weighted average con-
centrations of both total phosphorous and orthophosphate notably lower than the
other two rivers (table 12).
Orthophosphate comprises 38, 31, and 32 percent of the total phosphorous
load at the Susquehanna, Potomac, and James River stations, respectively. The
remainder is in the form of organic or acid hydrolyzable phosphorous. Figure 15
breaks down the transport loads of each of the phosphorous species for the 28-
month data-collection period.
42
-------
SUSQUEHANNA RIVER AT CONOWINGO . MD.
as.o-
40.0-
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1980 198
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(/) 180-
O 16.0-
^ 140-
1 120 -
10.0-
- 80-
Q' 6.0 _
-------
SUSQUEHANNA RIVER AT CONOWINCO. MD
8 0-
6.0-
4.0-
I
I
Q Orthophosphate as PO4
O Acid Hydrolizable + Organic
Phosphorous as PC>4
JFMAMJJASONDJFMAMJIASOND[JFMA
1979 1980 1981
ID|7
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Comparison of Nutrient Data with Previous Studies
Tables 13 and 14 compare average nutrient loads and concentrations obtained
from different hydrologic studies conducted at the Fall Line stations since 1966.
At the Chain Bridge station, the period of the Jaworski (1969) report (January
through December, 1966) was the driest in over 50 years of record. The loads and
concentrations of Guide and Villa (1972) were computed for a period (June 1969 to
May 1970) when Potomac River flow was 4 percent below normal. The Fall Line
monitoring comparisons were made during a period (January 1979 to December
1980) when streamfiow was 38 percent above average. However, even with these
differences in flow, conclusions can be drawn from the data in tables 13 and 14.
From 1969 to 1980, average concentrations and loads of ammonia decreased
at all three Fall Line stations; this is true even though the mean discharges for the
sampling periods increased in all cases. The average concentrations and loads of
orthophosphate at the Susquehanna and Potomac River sites also declined. The
average concentration of nitrite + nitrate decreased slightly at the Potomac River
from 1966 to 1980. At Conowingo, an increase in nitrate + nitrate concentrations
was noted.
As another basis for evaluating trends in nutrient loads, the regression equa-
tions for the Susquehanna, Potomac, and James Rivers used by Guide and Villa
(1972) were applied to the mean daily discharge data from January 1979 to
December 1981. These hypothetical loads and average concentrations better
reflect a true trend in nutrient loads because the same flow regime is utilized in
each comparison (Hirsch-1 , oral commun., 1982). Tables 13 and 14 show hypo-
thetical loads and average concentrations which would have occurred if the 1972
regressions were valid during 1979 and 1980.
In most cases, the hypothetical average concentrations for the Susquehanna
and Potomac Rivers are nearly the same as those derived by Guide and Villa (1972).
In table 14, these data support the previous conclusion that ammonia and
orthophosphate concentrations have decreased. The James River results are
inconclusive. Examination of the data used to calculate the 1972 regressions show
that there were a significant number of high-flow samples collected at the
Susquehanna and Potomac River stations. This is not true for the James River. In
order to properly predict loads over a wide range of stages by regression, samples
should be collected over this wide range. It is extremely difficult to accurately
extrapolate high-flow loads from low-flow data. The only trend in James River
water quality apparent from the data in tables 13 and 14 is a decrease in the
ammonia loads and average concentrations.
Analysis of covariance was applied to the Guide and Villa (1972) and the Fall
Line data for the nutrients found in tables 13 and 14. Results indicate a significant
difference in all population means at a 5-percent significance level. There were no
analytical changes in procedure for determining nitrite + nitrate, orthophosphate,
_i/ Hirsch, R. M., Chief, U.S. Geological Survey Systems Analysis Group,
Reston, Va.
46
-------
Table 13.—Average daily loads (in Ibs/d) of selected nutrient species for the three Fall Line stations
derived from different hydrologic investigations
Investigation
and period
of coverage
Average daily
discharge for
sampling period
(fWs)
Phosphorous,
total as POi.
Phosphorous,
ortho-
phosphate ,
total as PCK
Nitrogen,
nitrite +
nitrate ,
total as N
Nitrogen,
ammonia +
organic ,
total as N
Nitrogen,
ammonia,
total as N
Carbon,
organic,
total as C
SUSQu'EHANNA RIVER AT COWOWINGO, MD
Guide & Villa (1972);
June 1969 - May 1970
Fall Line Monitoring
Study; January 1979 -
December 1980
Hypothetical loads2
'36,000
'40,300
'40,300
POTOMAC
37,800
43,600
46,600
RIVER AT CHAIN
23,300
16,400
30,300
BRIDGE AT
174,000 101,000
249,000 98,600
203,000 110,000
WASHINGTON, B.C.
30,800 568,000
21,600 722,000
32,200 633,000
Jaworski (1969);
January 1966-December 1966
Guide and Villa (1972);
June 1969 - May 1970
Fall Line Monitoring
Study; January 1979 -
December 1980
Hypothetical loads 2
Guide 4 Villa (1972) "
June 1969 - May 1970
Fall Line Monitoring
Study; January 1979 -
December 1980
Hypothetical loads
310,500
15,900
15,900
56,880
24,800
35,300
38,400
11,000
65,600 37,400
10,600 102,000 61,700
18,200 144,000 52,800
JAMES RIVER AT CARTERSVILLE, VA.
8,670 5,100 18,200
9,910 22,300 6,700 16,000
69,910 23,700 13,100 33,900
21,600
32,700
48,600
6,700 285,000
6,600 405,000
9,670 377,000
5,130 159,000
2,000 320,000
18,300 229,000
' Mean annual discharge for this station is 38,900 ft3/s, based on records at Hamsburg, Pa.
2 Based on regressions from Guide and Villa (1972) and streamflow from Fall Line study.
3 Mean annual discharge for this station is 11,500 ft3/s.
* Station is located at Huguenot Bridge in Richmond, Va., about 40 miles downstream.
5 Mean annual discharge for this station is 7,610 ftVs.
6 Mean annual discharge for this station is 7,110 ftVs.
47
-------
Table 14.—Discharge-weighted average concentrations (in mg/L) of selected nutrient species for the
three Fall Line stations derived from different hydrologic investigations
Investigation
and period
of coverage
Average daily
discharge for
sampling period Phosphorous
(ftVs) total as PO
SUSQUEHANNA
i»
Pho
P
tot
RIVER
sph
ort
hos
al
AT
orous, Nitrogen, Nitrogen,
ho- nitrite + ammonia •*•
as POk total as N total as N
CONOWINGO ,
MD
Nitrogen, Carbon,
ammonia, organic,
total as N total as C
Guide 8, Villa (1972);
June 1969 - May 1970
Fall Line Monitoring
Study; January 1979
December 1980
Hypothetical concen-
trations 2
'40,300
'40,300
.20
.21
.08
.14
1.14
.94
0.52
.45
.51
0.16
.10
.15
2.92
3.32
2.92
Jaworski (1969);
January 1966-December 1966
Guide and Villa (1972);
June 1969 - May 1970
Fall Line Monitoring
Study; January 1979 -
December 1980
Hypothetical concen-
trations 2
POTOMAC RIVER AT CHAIN BRIDGE AT WASHINGTON, D.C.
36,740 0.47 - 1.35 0.16
310,500
315,900
'15,900
.44
.42
.45
.20
.13
.21
1.16
1.20
1.69
.66
.72
.62
.12
.08
.11
5.06
4.79
4.42
Guide S, Villa (1972)"
June 1969 - May 1970
JAMES RIVER AT CARTERSVILLE, VA.
0.23 0.14 0.49
0.58
1 Mean annual discharge for this station is 38,900 ftVs, based on records at Harrisburg, Pa.
2 Based on regressions from Guide and Villa (1972) and streamflow from Fall Line study.
3 Mean annual discharge for this station is 11,500 ftVs.
** Station is located at Huguenot Bridge in Richmond, Va. , about 40 miles downstream.
5 Mean annual discharge for this station is 7,610 ft3/s.
6 Mean annual discharge for this station is 7,110 ft3/s.
0.14
4.30
Fall Line Monitoring
Study; January 1979 - 9,910 .41
December 1980
Hypothetical concen- 9,910 .44
trations 2
.12 .30 .61 .04 5.95
.24 .64 .91 .34 4.29
48
-------
and total phosphorous that would influence the results of comparisons between the
two studies (Erdmann- , written commun., 1981; and Villa- , written commun.,
1981). Because of a more thorough digestion process, ammonia concentration
values recorded during the Fall Line study may actually be higher than during the
1972 study by Guide and Villa. It has been noted previously that ammonia
concentrations apparently decreased during the Fall Line study. This is the
opposite of what would be expected if the more thorough digestion influenced the
results.
Table 15 compares nutrient loads for the Susquehanna River at Conowingo
computed by Clark, Donnelly, and Villa (1973) to loads calculated for the period of
this report. Both studies use the same load versus discharge regression technique
to compute loads, although each uses a different regression equation. Therefore,
load estimates can be made for any chosen discharge. In the table, loads are listed
for three discharges (10,000, 50,000, and 100,000 ft 3/s), which represent low,
medium, and high flows at this station. Because the comparisons of estimated
loads are made at the same discharges for the two data periods, differences in the
loads may represent trends in water-quality characteristics rather than reflect the
combined effects of varying amounts of rainfall, runoff, or ground-water infiltra-
tion.
The comparisons in table 15 verify the apparent reductions in loads of
ammonia and orthophosphate at this site, as previously noted. They also reinforce
the suggestion of an increase in nitrite + nitrate. If nitrogen is the limiting
nutrient for algal growth in the upper Chesapeake Bay, as reported by Clark,
Donnelly, and Villa (1973). this trend in particular warrants continued monitoring.
With mixed results, previous investigations have attempted to correlate
discharge with nutrient concentrations. In most instances, there was either no
correlation or discharge directly related to nutrient concentration. However, in
several instances, investigators detected an inverse correlation of discharge with
concentrations of certain nutrient species. Guide and Villa (1972) noted this
inverse correlation for ammonia + organic nitrogen at the Susquehanna River at
Conowingo; for total phosphorous at the Potomac River at Great Falls (about 8 mi
upstream from Chain Bridge); and for nitrite + nitrate at the James River at
Cartersville. Clark, Guide, and Pheiffer (197^) also noted an inverse relationship
between concentrations of total phosphorous or ammonia + organic nitrogen and
discharge at the Susquehanna River at Conowingo site. Jaworski (1969) noted a
similar correlation for total phosphorous and discharge at the Potomac River Fall
Line site.
_2/ Erdmann, D. E., Chief, U.S. Geological Survey National Water-Quality
Laboratory, Alanta, Ga., June 1981.
j/ Villa, Orterio, Chief, U.S. Environmental Protection Agency, Region III
Laboratory, Annapolis, Md., May 1981.
49
-------
Table 15.—Estimates of nutrient loads (in Ib/d) at three
different discharges for 1969-72 and 1979-81 data
sets for the Susquehanna River at Conowingo, Md.
Constituent
Discharge of Estimate (ft-Vs)
10,000
Data Set
1969-721 1 1979-81
50,000
Data Set
1969-721 1 1979-81
100,
Data
1969-721
000
Set
1979-81
Phosphorus, total
as PO/,
7,500
4,370 50,000 43,800 120,000 117,000
Phosphorus,
orthophosphate,
total as PO,
3,500
3,360 30,000 20,000 75,000 41,700
Nitrogen, organic, 2
total as N
14,700 2100,000 90,300 2200,000 197,000
Nitrogen,
inorganic,
total as N
58,000
359,700 300,000 3330,000 600,000 3694,000
Nitrogen,
nitrite +
nitrate, as N
40,000 53,700 250,000 301,000 530,000 631,000
Nitrogen,
ammonia +
organic,
total as N
'40,000
20,000 4150,000 117,000 4270,000 251,000
Nitrogen,
ammonia,
total as N
'18,000
3,900 550,000 25,200 570,000 56,200
Nitrogen,
total as N
80,000 74,100 400,000 423,000 800,000 891,000
'1969-72 data from Clark, Donnelly, and Villa (1973).
Calculated by (Total nitrogen) - (Total inorganic nitrogen).
Calculated by (Total nitrogen) - (Total organic nitrogen).
^Calculated by (Total nitrogen) - (Nitrite + Nitrate nitrogen).
Calculated by (Total inorganic nitrogen) - (Nitrite + nitrate nitrogen).
50
-------
Concentrations of all nutrient parameters analyzed for this report correlate
directly with discharge including data for total phosphorous, ammonia + organic
nitrogen, and nitrite + nitrate. Figures 10, 11, and 12 present typical relationships
between discharge, suspended sediment, and nutrient species for the three Fall
Line stations during storms. The direct relationships between discharge or sus-
pended sediment and nutrient parameters are clearly apparent for the Potomac and
James River stations. Regulation of the lower Susquehanna River obscures these
relationships somewhat at the Conowingo station.
Clark, Donnelly, and Villa (1973) stated that inorganic nitrogen and the total
nitrogen loads in the upper Chesapeake Bay were generally constant regardless of
the Susquehanna River flow. The previous discussion has shown that in the
Susquehanna, for calendar years 1979 and 1980, nitrite + nitrate (which is the
majority of inorganic nitrogen) and total nitrogen transport are dependent on river
discharge; more than half of their total load is transported by spring high flows
(table 10). The fate of these nutrients in the water of the upper Bay is crucial to
the development of control strategy and requires further study.
Comparison of Nutrient Data at the Susquehanna River Stations
at Harrisburg, Pa., and Conowingo, Md.
From April 1980 to March 1981, the water quality of the Susquehanna River
was intensively monitored at both Conowingo, Md., and Harrisburg, Pa. The results
of sampling at these two stations are presented in tables 16 and 17 where water-
quality constituent loads for the period are compared. All load computations were
by methods previously described in an earlier section.
The three hydroelectric dams on the Susquehanna River between Harrisburg
and Conowingo influence the transport of many water-quality constituents. For
the period of concurrent sampling, the suspended-sediment load at the Conowingo
site is 45 percent lower than the Harrisburg site, even though the drainage area at
the downstream site is 13 percent greater. It is reasonable to assume then that
those constituents which are mainly sorbed to suspended-sediment particles or are
contained in suspended material should also have smaller loads at Conowingo. The
data in table 16 show that this is indeed true for total phosphorous, organic and
ammonia + organic nitrogen, organic carbon, aluminum, iron, and manganese. A
more thorough analysis of the reductions of the suspended-sediment loads between
the two stations on the Susquehanna River is presented in a subsequent section.
The data in table 17 point out that orthophosphate and nitrite + nitrate make
up a greater percentage of the total phosphorous and nitrogen loads at the
Conowingo station than at the Harrisburg site. This is also reasonable since these
constituents are usually dissolved in streams, and their concentrations are not
diminished by the settling of suspended sediment behind the dams. There is also a
large percentage of agriculture in the area between the two stations. As
previously noted, agricultural areas normally have higher nitrite + nitrate concen-
trations because of the use of nitrogen based fertilizers.
51
-------
Table 16.—Water-quality constituent loads (in millions of pounds) for
stations on the Susquehanna River at Harrisburg, Pa., and
Conowingo, Md., from April 1980 through March 1981
Constituent
Susquehanna River at
Harrisburg, Pa.1
Susquehanna River at
Conowingo, Md.2
Phosphorous,
total as PO,
18.3
12.1
Phosphorous,
orthophosphate,
total as PO,
3.14
4.58
Nitrogen, organic,
total as N
28.2
21.2
Nitrogen, nitrite
+ nitrate, total as N
Nitrogen, ammonia
+ organic, total as N
Nitrogen, ammonia,
as N
53.4
33.6
4.23
68.9
27.2
6.00
Nitrogen,
total as N
90.8
97.0
Carbon, organic,
total as C
237
199
Manganese, total
recoverable as Mn
20.4
16.6
Aluminum, total
recoverable as Al
50.5
46.0
Iron, total
recoverable as Fe
Solids, dissolved
Sediment, suspended
162
5,550
4,600
78.8
7,200
2,540
JMean daily discharge for the period is 26,500 ft3/s.
2Mean daily discharge for the period is 31,400 ft3/s.
52
-------
Table 17.—Relative proportions of orthophosphate, nitrite 4- nitrate, and ammonia
+ organic nitrogen to total phosphorous and nitrogen loads at the
Susquehanna River at Harrisburg, Pa., and Conowingo, Md. , from
April 1980 to March 1981
Constituent
Susquehanna River at
Harrisburg, Pa.1
Load
(in millions of pounds)
Percent of
total PO,
or N
Susquehanna River at
Conowingo , Md . 2
Load
(in millions of pounds)
Percent of
total PO,
or N
Phosphorous, total
as PO.
4
Phosphorous,
orthophosphate,
total as PO,
4
Nitrogen, total
as N
Nitrogen, nitrite
+ nitrate,
total as N
Nitrogen, ammonia
+ organic,
total as N
18.3
3.5
534
336
100
17
100
61
39
12.1
4.56
J961
689
272
100
38
100
72
28
*Mean daily discharge for the period 26,500 ft /s.
2Mean daily discharge for the period 31,400 ft~Ys.
3Total nitrogen load is the sum of this station's nitrite + nitrate and ammonia + organic
nitrogen loads (as N) for the period.
53
-------
Table 18 presents the discharge-weighted average concentrations for water-
quality constituents sampled at both Susquehanna River stations. Reductions in a
downstream direction are again noted in the concentration of those parameters
generally associated with suspended sediment. The largest reductions are noted in
total phosphorous, organic nitrogen, and organic carbon. Orthophosphate and
nitrite + nitrate concentrations show slight increases at the Conowingo site when
compared to the Susquehanna River at Harrisburg. Some of these differences are
probably attributed to the large amount of agriculture present between the two
stations.
Sediment Transport Characteristics
Susquehanna River
In an average year, the Susquehanna River transports 1.8 million tons of
sediment to the Chesapeake Bay (Williams and Reed, 1972). Most of the load is
carried to the Bay during spring high flows or hurricane-related storms.
According to Williams and Reed (1972), dams on the lower Susquehanna con-
structed before 1931 reduce the natural suspended-sediment load by 40 percent.
Between April 1980 and March 1981, 2.3 million tons of suspended sediment were
measured at the Susquehanna River at Harrisburg, and 1.3 million tons at
Conowingo—a 56-percent reduction even though the drainage area at Conowingo is
13 percent greater. The pools behind the dams on the lower Susquehanna River act
as sediment traps during low and medium flows.
However, at high flow, the dams are suspended-sediment sources. Ritter
(1974) reports that 7.5 million tons of suspended sediment were measured at the
Harrisburg site during Hurricane Agnes in June 1972. Gross and others (1978)
estimate that for the same period, the river at Conowingo transported 27 million
tons to the Bay, or about a 360-percent increase. They suggest that during major
floods (discharges greater than about 400,000 ft3/s), previously deposited sediment
is eroded from behind the dams and transported downstream. This discharge has a
recurrence interval of approximately 4 years at Conowingo based on 110 years of
streamflow data at Harrisburg and adjusted for drainage-area difference between
Harrisburg and Conowingo.
A comparison of recent suspended-sediment transport data for the
Susquehanna River at the Harrisburg and Conowingo stations supports the sugges-
tion that above a discharge of 400,000 ft3/s, sediment is scoured from behind the
dams. Suspended-sediment concentrations at the Harrisburg and Conowingo sites
during the three highest discharge peaks from March 1979 to April 1981 are shown
in figure 16. The March 5-11, 1979 storm, which had a peak discharge of about
500,000 ft 3/s, transported 67 percent more sediment at Conowingo than at
Harrisburg (table 19). The other storms in figure 16 had peak discharges of 240,000
and 353,000 ft 3/s. During these storms, the suspended-sediment transport at
Conowingo was about 50 percent less than that of Harrisburg. The only time in this
data-collection period when suspended-sediment transport on the Susquehanna
River at Conowingo exceeded that of the Harrisburg station was during the March
5-11, 1979 storm.
54
-------
Table 18.—Discharge-weighted average concentrations (in mg/L) of water-
quality constituents for stations on the Susquehanna River at
Harrisburg, Pa., and Conowingo, Md., from April 1980 through
March 1981
Constituent
Susquehanna River at
Harrisburg, Pa.
Susquehanna River at
n
Conowingo, Md.
Phosphorous, total
as PO,
4
Phosphorous,
orthophosphate,
total as PO,
4
Nitrogen, organic,
total as N
Nitrogen, inorganic,
total as N
Nitrogen, nitrite +
nitrate, total as N
Nitrogen, ammonia +
organic, total as N
Nitrogen, ammonia,
total as N
Nitrogen, total as N
Carbon, organic,
total as C
Manganese, total
recoverable as Mn
Aluminum, total
recoverable as Al
Iron, total
recoverable as Fe
Solids, dissolved
Sediment, suspended
0.35
0.06
0.54
1.20
1.03
0.65
0.08
1.74
4.54
0.39
0.97
3. 12
107
0.20
0.07
0.34
1.22
1.11
0.44
0.10
1.57
3.27
0.27
0.75
1.28
117
41
Mean daily discharge for the period is 26,500 ft /s.
2Mean daily discharge for the period is 31,400 ft Vs.
55
-------
500,000
300,000
100,000
H £ H
H 7^—I-
500
400
300
200
100
5^6' 7 8 9 10 11
MARCH 1979
cc
LU
a.
en
5
<
cc
O
o
o
Ul
03
CC
UJ
Q.
UJ
LL
O
m
z>
o
HI
I
o
C/3
500,000
300,000
100,000 -'
500
400
300
200
100
22 ' 23 24 ' 25 ' 26
MARCH 1980
27
28
500,000
300,000 -
100,000 -
500
- 400
- 300
- 200
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FEBRUARY 1981
26
27
DISCHARGE FOR SUSQUEHANNA RIVER AT CONOWINGO MO
— SUSPENDED SEDIMENT FOR SUSOUEHANNA RIVER AT HARRISBURG PA
SUSPENDED SEDIMENT FOR SUSOUEHANNA RIVER AT CONOWINGO MD
Figure 16.—Suspended-sediment transport for three high flows at the
Susquehanna River at Harrisburg, Pa., and Conowingo, Md.
56
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Table 19.--Suspended-sediment loads (in tons) at the Harrisburg, Pa., and
Conowingo, Md., stations on the Susquehanna River for three
high-flow periods
Date
March 5, 1979
March 6
March 7
March 8
March 9
March 10
March 11
Total load for
high-flow period
March 21, 1980
March 22
March 23
March 24
y.irch 25
March 26
Total load for
high-flow period
February 21, 1981
February 22
February 23
February 24
February 25
February 26
February 27
Susquehanna River at
Harrisburg, Pa.
(Drainage area is 24,100 mi )
32,300
284,000
316,000
149,000
90,100
69,700
30,000
971,100
33,200
152,000
132,000
116,000
55,200
31,600
520,000
196,000
183,000
127,000
199,000
142,000
78,400
30,200
Susquehanna River at
Conowingo , Md .
(Drainage area is 27,100 mi 2)
15,300
] 84, 000
568,000
412,000
236,000
136,000
67,800
1,619,100
13,500
28,000
57,500
63,300
46,900
34,700
243,900
31,600
78,200
76,600
90,800
137,000
70,500
36,200
Total load for
high-flow period
955,600
520,900
57
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Potomac River
During the 1979 water year (Oct. 1978 to Sept. 1979), the suspended-sediment
load at the Potomac River at Chain Bridge at Washington, D.C., was 2.64 million
tons (Lang and Grason, 1980). Water year 1979 had the second highest annual mean
discharge in this station's 86-year period. Periods of exceptionally intense runoff
in January, February, March, and September 1979 were the principal causes of the
high yearly discharge and sediment load (fig. 17). Feltz (1976) estimated the
average annual suspended-sediment load to be 1.5 million tons from 1964 to 1975 at
the Potomac River at Great Falls, 8 mi (and 99 percent of the drainage area)
upstream from Chain Bridge.
Figure 17 shows the importance of antecedent conditions to sediment trans-
port at the Chain Bridge station. Depicted in this figure are the three highest
discharge peaks occurring during the study period. Even though the peak and total
discharges for the January 22-21, 1979 storm are very much less than the February
25 -March 1, 1979 storm, suspended sediment reaches higher concentrations during
the January storm. The most readily available sediments were probably trans-
ported in the January storm, and the February storm occurred less than 1 month
later before much more material was available for transport. The snow cover
during February also dampened any effect the precipitation had impacting the land
surface and loosening soil particles. This would also reduce the sediment erosion
rate.
The September 6-8, 1979 discharge peak, which occurred as a result of
Tropical Storm David, is only 51 percent that of the February 25 - March 1 peak,
but it has a peak suspended-sediment concentration of 1,140 mg/L, nearly twice as
high as that in February. The intensity of the rainfall from the tropical storm and
the relatively dry period preceding it greatly increased the unit discharge yields of
suspended sediment during this high-flow event (table 20).
The hydrograph and suspended-sediment plots resulting from Tropical Storm
David both show a double peak (fig. 17). Other storm hydrographs for this station
do not show this double-peak pattern. Its cause during the September 5-8, 1979
high flow may be related to the timing of tributary inflow or may have resulted
from two separate periods of intense precipitation during this storm.
James River
Because of problems in establishing and maintaining a daily sediment station
for the James River at Cartersville, suspended-sediment data were incomplete and
no storm comparisons or annual totals were available.
58
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180,000
140,000
too,ooo
60,000
20,000-
„ SUSPENDED SEDIMENT
:V
DISCHARGE
24
25 26
JAN. 1979
800
600
400
200
27
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100,000
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800
600
400
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25 ' 26 27 28
FEB -MAR 1979
220,000
180,000
140.OOO
100,000
60.000
20 000
/ I SUSPENDED SEDIMENT
/ M
I I
- / / DISCHARGE
i
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SEP. 1979
Figure 17.—Suspended-sediment transport for three high flows at the
Potomac River at Chain Bridge at Washington, D.C.
59
-------
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SUMMARY AND CONCLUSIONS
1. Loads of water-quality constituents estimated in this report were using linear
regression relations and daily values of either streamflow, suspended-sedi-
ment concentration, or specific conductance. Comparison of these estimates
to loads calculated by a more data-intensive and accurate technique
(Porterfield, 1972) for selected constituents at the Potomac River Fall Line
station showed good agreement (within 10.5 percent), when considering the 2-
year data set as a whole. The regression technique is more accurate for
years when precipitation and streamflow are above average.
2. The only two pesticide residues consistently detected at the Susquehanna and
Potomac River Fall Line stations were 2,4-D and atrazine. The concen-
trations of both generally peak at these stations in the late spring and
summer, although 2,4-D concentrations at the Susquehanna River site re-
mained high during the fall and winter of 1980-81. In this case, 2,4-D may
have entered the stream in ground-water inflow.
3. Generally, the highest concentrations of chlorophyll a occurred at the three
Fall Line stations during spring high flows. These peak concentrations may
have been caused by high velocity runoff carrying fragments of under-
developed and emerging plankton or spring accumulation of periphytic
chlorophyll.
4. Samples collected at five sites in tributaries to the northern part of
Chesapeake Bay were analyzed for total residual chlorine and selected low-
molecular-weight hydrocarbons. The results of all the chlorine analyses were
less than or equal to the detection limit of 0.01 mg/L. There were three
instances when those organic compounds listed in table 8 were detected.
Trichloroethylene (TCE) was detected at low levels at Back and Patuxent
River sites on 3uly 1, 1981; a 0.002 mg/L concentration of benzene was
found in the Potomac River at Alexandria, Va., on June 26, 1981.
5. For the Susquehanna and Potomac River Fall Line stations, concentrations of
total recoverable aluminum, iron, and manganese correlated closely with
suspended sediment. However, the character of this correlation differs for
the two sites and from one storm to the next at each site. For the James
River at Cartersville, there was lesser correlation between suspended sedi-
ment and these metals.
6. When measured at their Fall Line stations, the Susquehanna and Potomac
Rivers had significantly greater discharge-weighted-average sulfate concen-
trations than the James River. Significant areas of active coal mining in the
Susquehanna and Potomac basins may account for this.
7. Concentrations and loads of all nutrient species were highest during spring
and storm-related high flows for the three Fall Line stations.
8. At each of the Fall Line stations, there was a close correlation between mean
annual water discharge and the corresponding annual nutrient loads. This
relationship may provide a basis for estimating specific nutrient loads in
years for which load estimates are not now available.
61
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9. Of the three Fall Line stations, the Potomac River at Chain Bridge had the
highest discharge-weighted average concentration of total nitrogen, 2.20
mg/L, and the James River station had the lowest, 0.96 mg/L. Most of the
total nitrogen load at the Susquehanna (71 percent) and Potomac River (5.5
percent) sites was in the form of nitrite and nitrate. However, 69 percent of
the total nitrogen at the James River station was ammonia + organic
nitrogen, and only 31 percent is nitrite + nitrate nitrogen.
10. Of the three rivers sampled, the Susquehanna River had the lowest discharge-
weighted average concentrations of total phosphorous and orthophosphate,
0.20 and 0.08 mg/L, respectively.
11. Based on comparisons with previous studies, ammonia concentrations and
loads decreased at all three Fall Line stations from 1969 to 1981. Ortho-
phosphate concentrations and loads in the Susquehanna and Potomac Rivers
also declined.
12. If nitrogen is the limiting nutrient for algal growth in the upper Chesapeake
Bay, as suggested by Clark, Donnelly, and Villa (1973), the slight increases in
total nitrogen, principally as nitrite + nitrate, at the Susquehanna River at
Conowingo may signal the need for further monitoring.
13. Generally, nutrient concentrations were proportional to streamflow. The
data in this report do not support suggestions from some previous investi-
gations that certain nutrient species are inversely proportional to stream-
flow. The majority of the nutrient loads transported by the three rivers
occurred during spring storm events. This is particularly significant in light
of the conclusions of Clark, Donnelly, and Villa (1973), who suggested that
total and inorganic nitrogen loads in the upper Chesapeake Bay are generally
constant regardless of Susquehanna River flow.
14. Comparison of data for the Susquehanna River at Harrisburg and Conowingo
indicated that loads of dissolved constituents such as orthophosphate and
nitrite + nitrate, increased in the downstream direction. Both orthophosphate
and nitrite + nitrate comprised a larger fraction of the total phosphorous and
nitrogen loads at Conowingo than at Harrisburg.
15. The data in this report support the suggestion by Gross and others (1978) that
at discharges below about 400,000 ft 3/s at the Susquehanna River at
Conowingo, sediment accumulates behind the three hydroelectric dams
between Harrisburg and the mouth. Above that peak discharge, sediment is
scoured and resuspended for transport to the Bay. The recurrence interval
for this flow is approximately 4 years.
16. Sediment transported by the Potomac River at Chain Bridge is heavily
influenced by seasonal variations, type of precipitation, rainfall intensity, and
antecedent conditions. Peak concentrations of suspended sediment for a
late-winter flow peak were half that of a late-summer high flow, although
the winter storm peak discharge was twice that of the summer storm.
62
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REFERENCES
American Public Health Association, 1976, Standard methods for the examination
of water and wastewater, Part 409 C., Amperometric Titration Method,
fourtheenth edition, p. 322-325.
Clark, L. J., Donnelly, D. K., and Villa, Orterio, 1973, Nutrient enrichment and
control requirements in the upper Chesapeake Bay: Environmental Pro-
tection Agency, Region III, Annapolis Field Office, Technical Report 56, 58 p.
Clark, L. J., Guide, Victor, and Pheiffer, I. H., 1974, Summary and conclusion-
nutrient transport and accountability in the lower Susquehanna River basin:
U.S. Environmental Protection Agency, Region III, Annapolis Field Office,
Technical Report 60, 97 p.
Feltz, H. R., 1976, Sedimentation in the Potomac River basin: Presented before
Subcommittee on the Bicentennial, the Environment and the International
Community, House Committee on the District of Columbia, June 17, 1976,
28 p.
Gross, M. G., Kariverit, M., Cronin, W. B., and Schubel, 3. R., 1978, Suspended-
sediment discharge of the Susquehanna River to northern Chesapeake Bay,
1966 to 1976: Estuaries, v. 1, no. 2, p. 106-110, June 1978.
Goerlitz, D. F., and Brown, Eugene, 1972, Methods for analysis of organic
substances in water: U.S. Geological Survey Techniques of Water-Resources
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Guide, Victor, and Villa, Orterio, 1972, Chesapeake Bay nutrient input study: U.S.
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Guy, H. P., 1969, Laboratory theory and methods for sediment analysis: U.S.
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Guy, H. P., and Norman, U. W., 1970, Field methods for measurement of fluvial
sediment: U.S. Geological Survey Techniques of Water-Resources Investi-
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Hem, J. D., 1970, Study and interpretation of the chemical characteristics of
natural waters, U.S. Geological Survey Water-Supply Paper 1473, 363 p.
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Pollution Control Administration, U.S. Department of the Interior, Technical
Report No. 15, 98 p.
Lang, D. J., and Grason, David, 1980, Water-quality monitoring of three tributaries
to the Chesapeake Bay—interim data report: U.S. Geological Survey Water-
Resources Investigations 80-78, 66 p.
63
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Omerik, 3. M., 1976, Influence of land use on stream nutrient levels: U.S.
Environmental Protection Agency Office of Research and Development,
Corvallis, Oregon, EPA-600/3-76-014, 106 p.
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study: U.S. Environmental Protection Agency Office of Research and
Development, Corvallis, Oregon, EPA-600/3-77-105, 151 p.
Porterfield, George, 1972, Computation of fluvial-sediment discharge, Book 3,
Chapter C3: U.S. Geological Survey Techniques of Water-Resources Investi-
gations, 66 p.
Ritter, 1. R., 1974, The effects of the Hurricane Agnes Flood on channel geometry
and sediment discharge of selected streams in the Susquehanna River basin:
Pennsylvania Journal Research, U.S. Geological Survey, v. 2, p. 753-761.
Skougstad, M. W., Fishman, M. 3., Friedman, L. C., Erdmann, D. E., and Duncan, S.
S., 1979, Methods for determination of inorganic substances in water and
fluvial sediments: U.S. Geological Survey Techniques of Water-Resources
Investigations, Book 5, Chapter Al, 626 p.
U.S. Department of the Army, Corps of Engineers, 1973, Chesapeake Bay—existing
conditions report, summary: U.S. Department of the Army, Corps of
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U.S. Geological Survey, 1977, National handbook of recommended methods for
water-data acquisition, Chapter 5, Chemical and physical quality of water
and sediment: U.S. Geological Survey, Office of Water-Data Coordination,
196 p.
Wetzel, R. G., 1975, Limnology: New York, W. B. Saunders, 743 p.
Williams, K. F., and Reed, L. A., 1972, Appraisal of stream sedimentation in the
Susquehanna River basin: U.S. Geological Survey Water-Supply Paper 1532F,
24 p.
64
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