Chesapeake Technical Support Laboratory
Middle Atlantic Region
Federal Water Quality Administration
U. S. Department of the Interior
CURRENT WATER QUALITY CONDITIONS
AND INVESTIGATIONS IN THE
UPPER POTOMAC RIVER TIDAL SYSTEM
Technical Report No. hi
Johan A. Aalto, Chief, CTSL
Norbert A. Jaworski, Ph.D.
Donald W. Lear, Jr., Ph.D.
May 1970
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TABLE OF CONTENTS
Page
LIST OF FIGURES iv
LIST OF TABLES v
Chapter
I INTRODUCTION I- 1
II SUMMARY II- 1
III DESCRIPTION AND LOCATION INDEX OF THE
POTOMAC RIVER TIDAL SYSTEM Ill- 1
A. General Description Ill- 1
B. Location Indexes Ill- 1
1. Reaches of Potomac River Tidal System . . Ill- 3
2. Zones of Upper Potomac Tidal System . . . Ill- 3
IV WATER QUALITY CONDITIONS IV- 1
A. Upper Potomac River Tidal System IV- 1
B. Potomac Tributaries IV- 5
V CURRENT ACTIVITIES V- 1
A. Wastewater Composition V- 3
1. Historical Trends V- 3
2. Evaluation of Sources V- 3
B. Nutrient Response Studies V- 7
1. Biological Discontinuity Studies V- 7
2. Ecological Trends as Related to
Nutrient Loadings V- 9
ii
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TABLE OF CONTENTS (Continued)
Chapter
V CURRENT ACTIVITIES (Cont.)
C. Nutrient Transport V-14
D. Dissolved Oxygen Budget V-18
E. Embayment Studies V-19
REFERENCES
ill
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LIST OF FIGURES
Number
I Wastewater Discharge Zones in
Upper Potomac Estuary Ill- 2
II Potomac River Tidal System Ill- k
III Nutrient Enrichment Trends and
Ecological Effects in the Upper
Potomac Tidal River System V-10
IV Total P as P0« Isopleth V-15
iv
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LIST OF TABLES
Number
I Zones of Upper Potomac Estuary Ill- 5
II Fecal Coliform Densities - Upper
Potomac River Tidal System IV- 3
III Fecal Coliform Summary -
Potomac Tributaries IV- 6
IV Wastewater Loading Trends - Washington
Metropolitan Area V- 5
V BOD, Carbon, Nitrogen and Phosphorus -
Summary of Contributions V- 6
VI River Discharge and Phosphorus Loading . . . V-16
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I- 1
CHAPTER I
INTRODUCTION
During the November 1969 progress meeting of the Potomac Washington
Metropolitan Area Enforcement Conference, information was presented on
water quality conditions and wastewater loadings in the upper Potomac
tidal system during 1969- At the spring meeting of the Interstate
Commission on the Potomac River Basin (iCPRB) at Indian Head, Maryland,
April 16-17, 1970, a summary statement was presented giving data on
waste loadings, water quality, and studies by the Chesapeake Technical
Support Laboratory on the middle and lower Potomac estuaries as part
of the joint study proposed in Recommendation Ik of the conference. A
detailed oral presentation was also given by Dr. Lear on the "Ecology
of a Eutrophic Estuarine Discontinuity."
Since there were no significant changes in water quality conditions
and wastewater loadings as of November 1969; this report will concentrate
on the status of investigations currently being conducted by the Chesa-
peake Technical Support Laboratory. Specific references will be made to
the Potomac-Piscataway and the Anacostia wastewater assimilation and
transport studies. Separate reports on both of these studies have been
prepared and are available.
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II- 1
CHAPTER II
SUMMARY
Based on data obtained "by personnel of the U. S. Geological Survey,
Dalecarlia Filtration Plant, U. S. Army Corps of Engineers, D. C. Depart-
ment of Sanitary Engineering (DCDSE), D. C. Department of Public Health
(DCDPH), Chesapeake Technical Support Laboratory (CTSL) of the Federal
Water Quality Administration (FWQA) and the several wastewater treatment
agencies in the Washington metropolitan area, a statement on current
water conditions and investigations of the upper Potomac River tidal
system was prepared and is summarized below:
1. Fecal coliform densities in the area of Woodrow Wilson Bridge
continue to be significantly lower as a result of the increased chlori-
nation of treated waste discharges initiated in June-September 1969
For example, during the months of June, July, and August 1965, the median
density was about 90,000 MPW/100 ml, while from September 1969 to April
1970^ over 50 percent of the samples had fecal coliform densities less
than 1000.
2. High fecal coliform densities were prevalent at times of high
stream flow in the portion of the Potomac from Chain Bridge to Memorial
Bridge, which is above the major wastewater discharges. These high
densities can be attributed to a combination of land runoff from the
upper Potomac basin, urban runoff, storm sewers and combined sewer
overflows.
3. Tributaries of the Potomac in the Washington metropolitan area
also contained very high fecal coliform densities at times. Cabin John
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II- 2
Creek had consistently high counts in 1969 with 25 out of 28 samples
showing fecal coliform densities over 10,000.
k. A Potomac Estuary Technical Committee was formed to provide
guidance and coordination in the study of water quality problems of
the upper Potomac Paver tidal system.
5- Studies by CTSL are continuing in three major areas: (l)
nutrient ecological responses, (2) nutrient transport, and (3) oxygen
budget resources.
6. During February and March in 1969 and again in 1970, extensive
phytoplankton blooms were detected in the Potomac from Smith Point to
Gunston Cove.
7. Under summer conditions massive blooms of blue-green algae were
prevalent from Fort Washington to Maryland Point. The densities of
these blooms were about 5 to 10 times that reported in most other
eutrophic waters.
8. Preliminary results of ecological studies of the Potomac estuary
in the area immediately above the Route 301 Potomac River Bridge indicate
that the decrease in the massive blue-green algae, Anacystis, is inter-
related to (l) the increase of salinity from about 2,000 to 10,000 ppm,
(2) the decline in nutrients, mainly phosphorus and nitrogen, and (3) the
competition for available nutrients by the dominant marine communities
in the area below the Route 301 Bridge.
9. Since the late 1930's the amount of phosphorus entering the
Potomac from wastewater discharges in the Washington metropolitan area
has increased about tenfold and nitrogen increased about fivefold.
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II-3
The amount of BOD (carbon) since then, although increasing to about
200,000 Ibs/day in 1957, has decreased to about 129,000 Ibs/day in 1969.
10. The major shift from the balanced ecological communities in
the Potomac toward nuisance blue-green algal growths appears to be
related to increases in nitrogen and phosphorus, and not BOD (carbon).
This shift in ecological communities has also been simulated in controlled
studies.
11. Nutrient data from March 1967 suggest that while large phosphorus
loadings enter the Potomac estuary during extremely high discharge from
the river upstream, the effect appears to be a decrease rather than an
increase in concentration in the upper Potomac tidal system. Most of
the phosphorus which entered the tidal system from the upper basin, plus
some in the system from the wastewater discharges, was adsorbed and depos-
ited in the bottom sediments of the estuary.
12. Studies of nitrification rates suggest that the oxidation of
ammonia nitrogen is not a significant factor in the oxygen budget when
the water temperature is below 10° C. Studies are continuing to determine
the effects of nitrogen on the eutrophication aspects.
13- Dye and mathematical model investigations of the Piscataway
embayments and the Anacostia tidal system indicate that wastewater assimi-
lation and transport rates are very low. Wastewater discharges into the
embayments of the Potomac may require higher removal rates than those
required by the enforcement conference.
lh. An analysis of each individual embayment will be required before
wastewater treatment levels can be determined.
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Ill- 1
CHAPTER III
DESCRIPTION AND LOCATION INDEX
OF THE POTOMAC RIVER TIDAL SYSTEM
A. GENERAL DESCRIPTION
The Potomac River Basin is the second largest watershed in the
Middle Atlantic States. Its tidal portion begins at Little Falls in
the Washington metropolitan area and extends 11^ miles southeastward
to the Chesapeake Bay.
The tidal system is several hundred feet in width at its head near
Washington and broadens to nearly six miles at its mouth. A shipping
channel with a minimum depth of 2k feet is maintained upstream to
Washington. Except for the channel and a few short reaches where depths
up to 100 feet are found, the tidal system is relatively shallow with
an average depth of about 18 feet.
Effluents from twelve major wastewater treatment plants, with a
thirteenth under construction, serving a population of about 2,500,000
people, are discharged into the upper tidal system. The locations of
the discharges from these treatment facilities are shown in Figure I.
B. LOCATION INDEXES
To achieve uniformity in locating water quality sampling stations,
wastewater effluents and related activities, a detailed location index
was developed for the entire Potomac River tidal system. A starting point
at the confluence of the Potomac with the Chesapeake Bay was established.
Uniform river mile locations using statute miles have been developed for
the primary sampling stations, landmarks, navigation buoys, etc. The
data will be published by the CTSL in the near future.
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Ill- 2
R:VER MILES FROM CHAIN BRIDGE - 0
(STRICT OF COLUMBIA
ALEXANDRIA
WESTGATE
r?IVER MILES FROM CHAIN BRIDGE - 15
LITTLE HUNTING Ck.
ANDREWS A.F. B.
FORT BELVOIR
PISCATAWAY Ck
ZONE II
RIVER MILES FROM CHAIN BRIDGE - 30
WASTEWATER DISCHARGE ZONES
' in UPPER POTOMAC ESTUARY
ZONE III
R' .'ER MILES FROM CHAIN BRIDGE = 45
FIGURE -I
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Ill- 3
1. Reaches of Potomac River Tidal System
For discussion and investigative purposes, the tidal portion of
the Potomac River has been divided into three reaches as shown in
Figure II and described below:
Reach Description River Miles Volume n
cu. ft. x 10
Upper From Chain Br. to 114.4 to 73-8 93-50
Indian Head
Middle From Indian Head to 73-8 to kj.0 362.28
Rt. 301 Bridge
Lower From Rt. 301 Bridge 47-0 to 00.0 1754.74
to Chesapeake Bay
The upper reach, although tidal, contains fresh water. The middle
reach is normally the transition zone from fresh to brackish water. In
the lower reach, chloride concentrations near the Chesapeake Bay range
from about 7,000 to 11,000 rag/1.
2. Zones of Upper Potomac Tidal System
To facilitate determination of water quality control requirements,
the upper estuary was segmented by the CTSL into 15 mile zones beginning
at Chain Bridge. Establishment of zones similar in physical character-
istics allows flexibility in developing control needs. This zone concept
was adopted by the conferees of the Potomac Enforcement Conference on
May 8, 1969.
River mile distances from both the Chesapeake Bay and Chain Bridge
for the upper three zones are given in Table I as well as in Figure II.
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Ill- k
CHAIN BRIDGE
N
CHfSAPfAKf
POTOMAC RIVER TIDAL SYSTEM
FIGURE -H
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IV- 1
CHAPTER IV
WATER QUALITY CONDITIONS
A. UPPER POTOMAC RIVER TIDAL SYSTEM
During the November 1969 progress meeting, it was reported, that
there had been a significant reduction in the fecal coliform densities
in the area of Woodrow Wilson Bridge [l]. This was a result of the
installation of effluent chlorination facilities at all major wastewater
treatment plants during June-September 1969-
Fecal coliform records at four stations in the Washington metro-
politan area of the Potomac River, as summarized in Table II, support
this November conclusion. Fecal coliform densities continued to be high
during periods of considerable runoff in the area from Chain Bridge to
Hains Point. These high counts can be attributed to (l) land runoff
from above and below Chain Bridge, (2) storm sewer discharge, and (3)
malfunctioning sanitary sewer systems.
Nevertheless, there continues to be a significant reduction in fecal
coliforms from previous years in the treatment plant discharge area. As
an example, in 1965 the median fecal coliform counts near Woodrow Wilson
Bridge was about 90,000 MPN/100 ml for the months of June, July and August.
Since September 1969> over 50 percent of the samples had fecal coliform
counts of less than 1000.
There has been no significant change in dissolved oxygen readings in
the Potomac estuary since November 1969- During the winter and spring
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IV- 2
months, freshwater flows were near or above normal with the April flows
at about twice the median flow. As a result of the higher flows and low
winter and spring temperatures, the dissolved oxygen (DO) concentrations
were above 8,0 mg/1.
DO concentrations were about 5-0 mg/1 for the first week of May 1970
with a river discharge of 15,000-20,000 cfs. This can be compared to
DO concentrations of less than 1.0 mg/1 at the Woodrow Wilson Bridge in
early May 1969 when a fish kill occurred.
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IV- 3
TABLE II
FECAL COLIFORM DENSITIES MEN/100 ml
Upper Potomac River Tidal System
D.C. Water Pollution Control Division Data
April 1969 - April 1970
Date
4- 7
4-21
5- 5
5-12
6- 2
6-18
6-23
6-30
7- 7
7-14
7-28
8-11
8-18
8-25
9- 1*
9- 8
9-15
9-25
9-29
10- 6
Chain Bridge
--
--
--
--
--
--
--
--
--
23
4,300
4,300
1,100
1,500
230
2,400
15,000
150
360
730
Memorial Bridge
930
210
150
150
240, 000
9,300
2,400
750
11,000
36
240, 000
4,300
3,000
360
230
93,000
4,300
230
23
110
Opposite
Blue Plains
910
93,000
2,300
73,000
4,300
9,300
230
360
2,300
230
93,000
7,300
1,500
910
360
7,200
9,300
2,100
230
730
W.Wilson
Bridge
9,100
360
3,600
--
2,300
3,600
2,300
3,600
4,300
1,500
24, 000
11,000
360
230
230
9,300
9,300
360
230
360
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TV- 4
TABLE II (continued)
Date
10-20
10-29
11- 3
11-11
11-17
11-24
12- 1
12- 8
12-15
2- 2
2- 9
2-16
2-23
3- 2
3-16
3-23
3-30
4- 6
4-13
Chain Bridge
23
23
43
93
930
4,300
23
2,400
1,200
24,000
4,300
2,400
2,400
150
73
930
4,300
--
2,400
Memorial Bridge
23
36
930
93
430
4,300
73
24, 000
1,500
110, 000
2,400
15,000
2,400
230
430
930
2,400
430
430
Opposite
Blue Plains
9,300
230
930
1,500
4,300
930
910
36
2,400
110, 000
4,300
46,ooo
9,300
240
1,500
230
9,300
430
36
W.Wilson
Bridge
360
23
910
36
23
150
150
43
11,000
110, 000
9,300
92,000
2,400
23
1,500
4,300
15,000
430
430
* By September 1969, all effluents from the wastewater treatment
facilities were continuously chlorinated.
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IV-5
B. POTOMAC TRIBUTARIES
In the previous section, fecal coliform counts were shown to be
high during times of high runoff. Sampling data for tributaries of
the Potomac taken by the D. C. Department of Public Health in 1969
also show high counts as given in Table III. The locations of the
six stations in the table are:
Tributary Sampling Point Miles from Potomac
Cabin John (Md.) G. Washington Parkway 0.3
Rock Run (Md.) David Taylor Model Basin 0.7
Seneca Creek (Md.) River Road 0.7
Broad Run (Va.) Leesburg Turnpike 2.0
Sugarland Run (Va.) Leesburg Turnpike 0.5
Difficult Run (Va.) Old Georgetown Road 1.0
For the months of June, July, August, and September, high fecal
coliform densities were observed for all six stations. The data for the
Cabin John station show high densities the year round, suggesting a
periodically overloaded sanitary sewerage system in this watershed.
Data for other urban streams in the Washington metropolitan area,
such as Rock Creek as reported by Aalto, et al [2], and Anacostia River
by Jaworski et al [3]; also indicated high fecal coliform densities.
While increases in fecal coliforms occur during periods of high flow,
the large increases were usually associated with either combined sewer
overflows or defective sewerage systems.
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IV- 6
TABLE III
EECAL COLIFORM SUMMARY - MPH/100 ml
Potomac Tributaries
B.C. Department of Public Health Data
1969
Date
01-08
01-15
02-05
02-12
02-19
04-09
04-16
04-23
04-30
05-07
05-14
05-21
06-04
06-11
06-18
07-09
07-23
08-13
08-27
Cabin John
250,000 +
250,000+
250,000 +
400, 000
25, ooo
25, ooo
250, ooo
25, ooo
250, ooo
250, ooo
25,000
200, 000
250, ooo
6,000
25,000
25,000
25,000
170, ooo
120, 000
Rock Run
25, ooo
6,000
1,200
4oo, ooo
2,500
250
1,200
7,000
4,000
12, 000
500
250
30,000
600
2,500
6,000
30,000
25,000
60, 000
Seneca Sugar land Difficult
Greek Broad Run Run Run
~_
5,000
400
400, 000
1,200
250
1,200
2,500
500
6,000
1,700
200, 000
250, ooo
4, ooo
2,500
1,700
250, 000+
6,000
25, 000+
600
4,000
500
250
600
400
250
2,500
400
1,300
1,200
60, 000
600
4,000
25,000+
60, 000
2,500
4,000
4,000
17, ooo
10, 000
__
2,500
4,000
2,500
3,000
--
6,000
6,000
5,000
120, 000
25, ooo
4,000
4o, ooo
250, 000+
25,000
120, 000
250
6,000
4oo
400
600
4oo
600
7,000
600
1,200
6,000
60, 090
120, 000
4,000
4,000
1, 700
250, 000+
4,000
12, 000
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IV- 7
TABLE III (Continued)
Seneca Sugar-land Difficult
Date
09-03
09-10
09-24
10-01
10-08
10-22
n-o4
12-09
12-16
Cabin John
4, 000,, 000+
4, 000, 000
120, 000
12, 000
25, ooo
12,000
12, 000
1,600
4,000
Rock Run
400, 000+
6,000
6,000
40, 000
6,000
4,000
0
2,500
60
Creek Broad Run
250, 000+
25, 000+
3,500
1,700
4,000
6,000
200
T,ooo
4oo
7,000
4,000
1,100
2,900
1,700
4,000
50
1,200
1,700
Run
250, 000+
6,000
12, 000
25, ooo
60, 000
250, 000+
4,000
40, 000
4,000
Run
250, 000+
12, 000
1,700
2,500
7,000
4,000
2,500
1,700
1,700
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V- 1
CHAPTER V
CURRENT ACTIVITIES
Studies to investigate the nutrients that stimulate algal
growth and to determine the major driving forces producing dissolved
oxygen stresses are continuing. The objectives of the ecological,
nutrient transport, and dissolved oxygen budget studies are to:
(l) determine the extent of present water quality degradation, (2)
develop predictive capabilities for stresses from projected loadings,
(3) determine the corrective actions required, and (4) evaluate the
detailed ecological pattern during changes resulting from selective
nutrient reductions.
Other tidal waters of the Chesapeake Bay are also currently being
monitored to provide a basis for comparison. These waters include
the Patuxent, Rappahannock, Chester, and Severn Rivers, and the upper
Chesapeake Bay itself.
To provide input and guidance for the CTSL program in studying
the Potomac, a Potomac Estuary Technical Coordination Committee (PETCC)
was formed, with the first meeting held in November 1969- Members of
PETCC include individuals from Maryland Department of Water Resources,
Maryland State Department of Health, ICPRB, Maryland-National Capital
Parks and Planning Commission, Virginia Water Control Board, Virginia
Department of Economic Development, DCDPH, DCDSE, U.S. Army Corps of
Engineers, and FWQA.
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V- 2
This chapter presents specific areas currently being investigated.
Included are recent findings within each of five study areas: wastewater
composition, nutrient response, nutrient transport, dissolved oxygen
budget, and discharges into embayments.
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V- 3
A. WASTEWATER COMPOSITION
1. Historical Trends
While the population in the Washington metropolitan area increased
eightfold from 1913 to 1969 as shown in Table TV", the phosphorus content
in the waste discharges increased almost twentyfold. For the same time
period the nitrogen loadings have increased about ninefold, from 6,^-00
to 52,000 Ibs/day, while the BOD's have increased from 58,000 to over
200,000 Ibs/day in the late 1950's. Since I960 the BOD loading has been
reduced to 129,000 Ibs/day.
The twentyfold increase is a result of the rapid increase in use
of detergents high in phosphorus content since the 19^-0's in place of
the soap products formerly used in household cleaning usage. At the
present time approximately 50 to 70 percent of all phosphorus in
municipal waste discharges can "be attributed to the use of detergents
2. Evaluation of Sources
As previously reported [l] CTSL conducted a nutrient survey of the
upper estuary during 1969 to determine the relative contributions of
critical water quality parameters from the upstream freshwater inflow
and wastewater discharges in the metropolitan area. The loadings for the
first eight months are given in Table V and a summary of the relative
percentages follows:
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V- k
Parameter Freshwater Inflow Wastewater Discharge
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V- 5
TABLE IV
Wastewater Loading Trends*
Discharge to Potomac
Washington Metropolitan Area
Year
1913
1932
1944
195^
1957
I960
1965
1968
1969
Population
of
Service
Area
320, ooo
575,000
1,149,000
1,590,000
1,680,000
1,860,000
2,100,000
2,415,000
2,480,000
Wastewater
Flow
(mgd)
42
75
167
195
210
222
285
334
348
BOD
(Its/day)
58,000
103,000
i4i,ooo
200, 000
204, 000
110,000
125,000
130, ooo
129,000
T. Nitrogen
as W
(Its/day)
6,400
11,500
22,980
31,800
33,600
37,200
42,000
53,000
52,000
T . Phosphorus
as PO.
(Its/day)
3,300
6,000
12,000
16,700
26,000
30, ooo
57,000
61, ooo
64, ooo
In estimating phosphorus, allowances were made to reflect
the effect of detergents.
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V- 6
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V- 7
B. NUTRIENT RESPONSE STUDIES
During 1969^ field investigations were continued to further define
the nutrient requirements (carbon, nitrogen and phosphorus) for producing
nuisance algal growths. Considerable efforts were spent in defining
eutrophic conditions in the salinity transition zone.
In the freshwater portions of the tidal system, large blooms of
phytoplankton were observed in February and March of 1969 and again in
19TO. Water temperatures at the beginning of these blooms were about
4° C. These blooms were primarily in areas between Smith Point and
Gunston Cove.
Under 1969 summer and fall conditions as in previous years, large
populations of blue-green algae, primarily Anacystis sp., were prevalent.
An important aspect of these algal growths was that the "standing crop"
as measured by chlorophyll a had concentrations ranging from approxi-
mately 75 to over 200 ,ug/l. This is about five to ten times that
reportedly observed in most other eutrophic waters [15] [16]-
The algal populations in the saline water areas were not as dense
as those in the fresh water areas. Nevertheless in summer large popu-
lations of the dinoflagellates Gymnodinium sp. and Amphidinium sp.
occurred producing the phenomenon known as "red tides."
1. Biological Discontinuity Studies
During the summer of 1969, a special ecological study was under-
taken in a 20-mile portion of the Potomac estuary just upstream from
the Potomac River Bridge at Morgantown. This area has been observed
for several years [10] to be the lower limit in terms of distance from
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V- 8
TJhain Bridge of massive blue-green algal blooms. The major purpose of
this intensive study was to determine why algal blooms apparently
decreased at this location.
The area of investigation was found to be a reach of rapidly
increasing salinity downstream, the "salt wedge". An obvious bio-
logical discontinuity was found in this reach with marine organisms
dominant at the lower end.
Tentative conclusions from this study indicate:
1. The massive blooms of the blue-green alga Anacystis currently
terminate in this reach for three interrelated reasons: (l) the increase
of salinity from approximately 2 to 12 parts per thousand, (2) a decline
in nutrients, especially nitrogen and phosphorus, and (3) the competition
for available nutrients by the essentially marine dominated biological
community in the lower reach is apparently successful under present
conditions.
2. These observations may be useful for predicting the time,
duration and extent of a possible similar invasion of blue-green algae
in other fresh water tributaries at the head of the Chesapeake Bay,
especially the Sassafras, Bohemia, Elk, and Northeast Rivers.
3- When firmer conclusions can be drawn from continued obser-
vations, the effects of disposal of nutrients from treated sewage into
saline waters as compared to fresh waters may assist in optimizing the
increase in estuarine water productivity by controlled addition of
nutrients, or at least minimize any stress to the estuarine system
caused by these additions.
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V- 9
5- Single sets of daily observations were difficult to interpret,
but the aggregate of 15 cruises over a six weeks period showed some
statistically significant patterns.
2. Ecological Trends as Related to Nutrient Loadings
A review of past eutrophic trends with estimated nutrient loadings
from wastewater discharges into the Potomac was made. In Table IV it
can readily be seen that while the present BOD (carbon) loading is the
same as in the late 1930's, there is about ten times as much phosphorus
and five times as much nitrogen now being discharged.
The effect of these increased nutrient loadings can be seen in
Figure III. The change in the ecology from 1913 has been dramatic.
Several nutrients and growth stimulants have been implicated as causes
of this accelerated eutrophication with nitrogen and phosphorus showing
promise of being the most manageable.
The historical plant life cycles in the upper Potomac estuary can
be inferred from several studies. Gumming [4] surveyed the estuary in
1913-191^-; and noted the absence of plant life near the major waste
outfalls with "normal" amounts of rooted aquatic plants on the flats
or shoal areas below the urban area, No nuisance levels of rooted
aquatic plants or phytoplankton blooms were noted.
In the 1920's an infestation of water chestnut appeared. This was
controlled by mechanical removal [5]
In September and October of 1952, another survey of the reaches
near the metropolitan area, made by Bartsch [6], revealed that vegetation
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(T/Ste)
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FIGURE -
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V-ll
in the area was virtually nonexistent. Wo dense phytoplankton blooms
were reported, although the study did not include the areas downstream
where they were subsequently found.
In August and September of 1959; a survey of the area was made
by Stotts and Longwell [?] Blooms of the nuisance blue-green alga
Anacystis were reported in the Anacostia and Potomac Rivers near
Washington, D. C.
In 1958; nuisance conditions of the rooted aquatic plant water
milfoil developed in the Potomac estuary. The growth increased to
major proportions by 1963^ especially in the embayments from Indian
Head downstream [8].
These dense stands of rooted aquatic plants which rapidly invaded
the system also dramatically disappeared in 1965 and 1966. The decrease
was presumably due to a natural virus [9]-
Subsequent and continuing observations by the CTSL have confirmed
persistent massive summer blooms of the blue-green alga Anacystis at
nuisance concentrations from the metropolitan area downstream at least
as far as Maryland Point [10].
Data as presented below for comparable flow and temperature
conditions for September-October 1965 and October 1969 indicate that
algal populations have not only increased in density but have become
more widespread.
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18.35
30.60
^5.80
Sept. 15,
1965
49
36
6l
Oct. 19,
1965*
90
75
56
Oct. 14-16,
1969**
74
120
70
V-12
Potomac Estuary River Miles from Chlorophyll a - jug/1
Location Chain Bridge
Piscataway
Indian Head
Smith Point
* Single sample
** Average of a minimum of 5 samples
While data are limited for 1965; based upon these data and field obser-
vations the increase in nuisance algae appears to be significant. Sampling
difficulty makes it impossible to quantify the increase at the present time,
These biological observations can be interpreted as an ecological
succession. The initial response to a relatively light over-enrichment
was the growth of water chestnut,, which when removed allowed the increas-
ing nutrient load to be incorporated into the rooted aquatic plant water
milfoil (Myriophyllum spicatum). The water milfoil dieoff allowed the
nutrients to be competitively selected by the blue-green alga Anacystis.
Since Anacystis is apparently not utilized in the normal food chain,
huge mats and masses accumulate and decay.
From these considerations it would appear that nuisance conditions
did not increase directly with an increase in nutrients as indicated by
the concentrations of phosphorus and nitrogen. Instead, the nutrient
increase encouraged a given species to dominate the plant life in the
aquatic environment. With a further increase in nutrients this species
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V-13
was rather rapidly replaced in turn by another dominating nuisance form.
This is indicated in Figure III where the massive persistent blue-green
algal blooms were associated with large increases in phosphorus and
nitrogen enrichment in the upper reaches of the Potomac River tidal
system. The persistent massive algal blooms have been occurring since
the early 1960's even though the amount of carbon (BOD) has been reduced
by almost 50 percent.
Laboratory and controlled field pond studies by Mulligan [11] have
indicated similar results. Ponds receiving low nutrient additions
(phosphorus and nitrogen) had submerged aquatic weeds. Continuous
blooms of algae occurred in the ponds having high nitrogen and phosphorus
concentrations. An important aspect of Mulligan's studies is that when
the aquatic resources were returned to their natural state, the eco-
system returned to its natural state. This is also supported by studies
of Edmondson [12] on Lake Washington and Hasler on the Madison,, Wisconsin
lakes
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V-lU
C. NUTRIENT TRANSPORT
A one-year cooperative sampling program with Steuart Petroleum
Company has been completed. The survey was designed to determine the
nutrient movement throughout the entire tidal system. Since 19^9
was a nontypical stream flow year, the study was extended into 1970.
Nutrient data from 1969 taken at Great Falls, Maryland, indicated
that large quantities of nutrients enter the tidal system during
periods of high stream flow. A study of a high runoff period in 1967
revealed a significant phenomenon. Figure TV shows that the total
phosphorus concentration on the early days of March was about 0.150 mg/1
at Chain Bridge increasing to over 1.0 mg/1 at Woodrow Wilson Bridge
as result of wastewater discharges. At the same time the concentrations
at Piscataway and Indian Head were 1.4 and 1.0 mg/1, respectively.
On March 7 and 8, the river discharge increased rapidly to about
139,000 cfs (Table VI). This resulted in a discharge on March 8 of
over 1,208,000 Ibs/day of phosphorus into the tidal system.
However, when the concentrations in the entire upper tidal sjs tern
are compared to early March, a general overall decrease in phosphorus
can be observed. Phosphorus concentrations during high flows are accom-
panied by high sediment loads and when they enter the slow moving tidal
system, much of phosphorus was adsorbed onto the sediment particles and
was removed from water as the sediment settled. CTSL conducted labora-
tory studies using Potomac River samples to confirm this removal of
phosphorus by adsorption.
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55-i
ct
CD
o
50-
i 20-
TOTAL P o« P04 ISOPLETH
(mg/l)
POTOMAC TIDAL RIVER SYSTEM
WOODROW WILSON BRIDGE
MARCH 1967
FIGURE -
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V-16
TABLE VI
RIVER DISCHARGE AND PHOSPHORUS LOADING
Potomac River at Washington, D. C.
March 1 to 14, 196?
Date River discharge T. Phosphorus T. Phosphorus
3- 1
3- 2
3- 3
3- 4
3- 5
3- 6
3- 7
3- 8
3- 9
3-10
3-11
3-12
3-13
3-14
(cfs)
7,690
7,010
7,230
7,270
7,620
8,590
63,100
133,000
139, 000
76,400
46,700
36,500
29,500
25,100
as PO,
(mg/lj
0.153
--
0.155
0.132
0.225
0.177
1.316
1.701
0.936
0.717
0.578
0.355
0.26U
--
as PO,
(Ibs/day)
6,280
--
5,990
5,130
9,150
8,120
44,800
1,208,000
694,800
292,500
144,200
69,200
41,588
--
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V-IT
A more sophisticated mathematical model has been recently adapted
to the Potomac Estuary to increase sensitivity in simulating the move-
ment of nutrients and other pollutants. Once this capability has been
developed and verified, technical areas to be investigated will include:
1. Sensitivity of nutrient concentrations in the upper, middle,
and lower reaches to loadings in the upper reach, including contributions
from land runoff,
2. The flow probability to be used in determining maximum permissible
nutrient levels, including transport, such as seven-day-ten-year flow or
the mean monthly flow,
3- Ecological,nutrient transport and nutrient response studies will
be necessary to determine whether or not the same nitrogen, phosphorus
and carbon removal levels are required during twelve months of the year
in order to enhance the water quality in the upper, middle, and lower
reaches.
4. Effects of withdrawal of water from the upper portion of Zone I
as a supplemental water supply for the Washington metropolitan area on
the allowable nitrogen, phosphorus, and carbon loadings from wastewater
discharges, and
5. Development of seasonal nutrient loadings for Zones II and III
of the upper reach and for the middle and lower reaches of the tidal
system.
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V-18
D. DISSOLVED OXYGEN BUDGET
Investigations of the oxygen budget are in three areas: (l)
carbonaceous and nitrogenous oxygen demand from wastewater discharges,
(2) oxygen production by phytoplankton, and (3) increased organic
carbon and nitrogen loadings from phytoplankton, primarily in the
middle and lower reaches. During 19^9, preliminary CTSL studies
were in the first two areas.
Preliminary analyses of nitrogen data from the past five years
indicate that nitrification (the oxidation of NIL to NO ) becomes a
minor factor in the oxygen budget at water temperatures below 10°C.
This observation would suggest that nitrogen removal from wastewater
for the maintenance of oxygen standards would not be required at
temperatures below 10°C. The need for nitrogen removal for the control
of eutrophication is still being investigated as previously reported.
Effects of organic loadings on the dissolved oxygen budget in the
middle and lower reaches is being intensively studied during 1970.
During the summer months, dissolved oxygen in the lower reach is often
depressed at greater depths, attributed partially to the decay of
organic matter, mainly phyfcoplankton. Salinity differences between
surface and bottom waters cause stratification resulting in poor mixing
and consequently restrict aeration.
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V-19
E, EMBAYMEWT STUDIES
Except for the Blue Plains facility of the District of Columbia,,
all major wastewater discharges are into embayments of the Potomac
River tidal system. As an interim measure to protect the embayments,
the conferees at the Potomac Enforcement Conference applied the Zone I
removal percentages to wastewater discharges in Zone II.
A study of the wastewater assimilation and transport capacity
of the Piscataway embayment was recently completed [13] One of the
findings of the study was that this embayment has little capacity to
assimilate and transport treated wastewater. The study further indicated
if the same nutrient levels were to be maintained in the embayments as
in the Potomac, only a limited poundage of the waste constituents could
be discharged into the embayment if low nutrient levels are to be
maintained. Moreover, if the plant were to be expanded to 30 mgd, a
higher degree of removal than that currently agreed upon (9o% for BOD,-,
for phosphorus, and 85/£ for nitrogen) would be required if the lower
nutrient levels are to be maintained.
Preliminary analysis of the Anacostia River tidal system also
indicates a limited assimilation and transport capability [31 In this
embayment, complete renovation or ultimate wastewater treatment (UWT) will
be required if there are to be any large discharges in the upper portion
of the Anacostia tidal system.
Based on the Piscataway and Anacostia studies, a re-examination of
the removal requirements for embayment discharges is required. The
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V-20
"real time" mathematical model previously mentioned includes all the
major embayments. To complete the analysis, a dye release in each
embayment will be required to verify predictive coefficients.
Nutrient response characteristics of the waters of the various
embayments are currently being investigated by CTSL. Limited data
attained in 1968 and 1969 indicate greater standing crops of algal
populations in the embayment for given nutrient levels than in the
main stem of the tidal river. The sampling program for the embay-
ments, especially Piscataway, Dogue, Gunston Cove, Occoquan-Belmont,
and Mattawoman was initiated in February 1970 to further explore
these observations.
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REFERENCES
1. Jaworski, N.A., Aalto, J.A., Lear, D.W., and Marks , J.W.,
"Water Quality and Wastewater Loadings Upper Potomac Estuary
Daring 1969 , " Technical Report Wo. 27, CTSL, FWPCA, MAR,
November 1969.
2. Aalto, J.A., Jaworski, N.A., and Schremp, W.H., "A Water
Quality Study of the Rock Creek Watershed; " CB-SRBP Working
Document No. 30, FWPCA, MAR, March 1969.
3. Jaworski, U.K., Clark, L.J., Feigner, K.D., "Preliminary
Analyses of the Wastewater and Assimilation Capacities of
the Anacostia Tidal River System," Technical Report No. 39,
CTSL, FWQA, MAR, April 1970.
k. Gumming, H.S., "Investigation of the Pollution and Sanitary
Conditions of the Potomac Watershed, " USPHS Hygiene Laboratory
Bulletin 104, 1916.
5- Livermore, D.F. and Wunderlich, W.E., "Mechanical Removal of
Organic Production from Waterways," Eutrophi cation; Causes,
Consequences, Correctives, National Academy of Sciences,
Washington, B.C., ~
6. Bartsch, A.F., "Bottom and Plankton Conditions in the Potomac
River in the Washington Metropoli can Area, " Appendix A, A
report on water pollutioE in the Washington metropolitan area,
Interstate Commission on the Potomac River Basin,
7. Stotts, V.D. and Longwell, -J.R,, "Potomac River Biological
Investigation 1959," Supplement to technical appendix to part
VII of the report on the Potomac River Basin studies, U. S.
Dept. of KrtW, 1962.
8. Elser, H.J., "Status of Aquatic Weed Problems in Tidewater
Maryland, Spring 1965, " Maryland Department of Chesapeake Bay
Affairs, 8 pp mimeo, 1965.
9- Bayley, S., Rabin,, H., and Soutliwlek, C.H., "Recent Decline
in the Distribution and Abundance of Eurasian Watermilfoil in
Chesapeake Bay/' Chesapeake Science 9(3): 173-l8l, 1968.
10. Jaworski, N.A., Lear, D.W., and Aalto, J.A., "A Technical
Assessment of Current Water Quality Conditions and Factors
Affecting Water Quality in the Upper Potomac Estuary, "
Technical Report No. 5, CTSL, FWPCA, MAR, 1969.
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11. Mulligan, H.T., "Effects of Nutrient Enrichment on Aquatic Weeds
and Algae/' The Relationship of Agriculture to Soil and Water
Pollution Conference Proceedings, Cornell University, New York,
January 19-21, 1970.
12. Edmondson, W.T., "The Response of Lake Washington to Large
Changes in its Nutrient Income," International Botanical Congress,
Seattle, Washington, 1969.
13. Jaworski, N.A., Johnson, James H., "Potomac-Piscataway Dye
Releases and Wastewater Assimilation Studies," Technical Report
No. 19, CTSL, FWPCA, MAR, December 1969.
Ik. Easier, A.D., "Culture Eutrophication is Reversible," BioScience,
Vol. 19, No. 5, May 1969.
15. Brezanik, W.H., Morgan, W.H., Shannon, E.E., and Putnam, H.D.,
"Eutrophication Factors in North Central Florida Lakes," Florida
Engineering and Industrial Experiment Station, Bulletin Series
No. l^k, Gainesville, Florida, August, 1969.
16. Welch, E.B., "Phytoplankton and Related Water Quality Conditions
in an Enriched Estuary," JWPCF, Vol.40, pp 1711-1727, October 1968.
17- Task Group Report on Nitrogen and Phosphorus in Water Supplies,
JAWWA, Vol. 59, No. 3, PP 3kk-366, March 1967.
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