REGION III
ANNAPOLIS FIELD OFFICE
Thomas H. Phe";f~er
Annapolis Field Office
Region 111
U. S, Environmental F'rotection Agency
[MENT
•r?r-5
U.S. EPA ANNAPOLI
, Annapolis, Md. 21401
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ABSTRACT
In order to assess the current nutrient impact on the upper
Potomac Estuary, 1973-74 data from major wastewater sources were com-
pared to previous data to note possible trends. A comparison of
recent water quality data with 1969-70 data at three control sampling
stations shows reductions of inorganic phosphate in the upper estuary,
particularly at the historical bloom area for blue-green algae. The
absence of massive algal blooms since 1972 is noted, together with
a discussion of the framework necessary to develop the predictive
capability to quantitatively identify the cause-effect relationships
in the estuary.
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Types of Nutrients
Plant growth requires nutrients. Plant physiologists classify
nutrients into two categories. Macro-nutrients are those chemical
elements required by plants in large amounts. The macro-nutrients are
carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulphur,
calcium, iron, and magnesium. Micro-nutrients include molybdenum,
boron, manganese, zinc, and sometimes, even iodine and chlorine.
They are just as essential to plant growth as the macro-nutrients, but,
as their name implies, they are required by plants in minute quantities,
Their abundance in nature relative to plant needs is evidenced by the
lack of case histories on micro-nutrients as rate limiting growth
factors.
Of the various nutrients, carbon, nitrogen, and phosphorus have
received more attention in the field of water pollution biology.
These three elements have life cycles in which they undergo changes
in chemical composition as they interact with various components of
their immediate environment. Concerning the life cycles, only the
phosphorus is not open to the atmosphere for replenishment purposes.
In the case of carbon, a constant diffusion rate from the atmosphere
into the water column exists at normal pH and temperature ranges. In
fact, the oceanic carbonate system is, in most cases, in equilibrium
with the atmospheric C02. Changes in the partial pressure of C02 in
the atmosphere or changes in the aquatic carbonate cycle can effect
changes in the rate of COo dissolution into water bodies.
As with carbon, there exist natural source factors which influence
the abundance of nitrogen in the aquatic environment. The atmosphere
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is composed of approximately 80 percent nitrogen, which is roughly the
equivalent of 148,000 tons of nitrogen in the atmosphere for every acre
of land area []]. Literature values show nitrogen from rain water and
o
airborne particulate matter contribute 480 Ibs/mi per year [2]. In
addition, atmospheric nitrogen being so inert in the free state allows
certain groups of soil bacteria and blue-green algae to fix nitrogen.
The literature pretty much establishes the fact that certain groups
of blue-green algae can fix nitrogen directly from the atmosphere.
The literature, however, is split on the ability of Microcystis sp. and
Anacy_s_ti_s_ sp. (blue-green algae) to fix nitrogen [2,3]. These are the
pollution tolerant phytoplankton identified as being prevalent during
massive blooms in the freshwater portion of the Potomac Estuary. The
basic point to be made, is that it is imperative to establish as soon
as possible the nitrogen fixation abilities of Microcystis sp. and
Anacystis sp. in the freshwater estuarine environment of the Potomac.
Phosphorus enters the aquatic environment from the erosion of soils
and from man induced inputs such as human and industrial wastes.
Because of the nature of its sources, it makes sense that phosphorus
can be controlled to the extent that it could be made the rate limiting
nutrient to curb and hopefully reverse an accelerated eutrophic
condition.
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Impact of Nutrients
Let us turn our attention to the impact of nutrients. We can
probably say, in general, that nutrients are present in sufficient
concentration in most water bodies to provide for the needs of aquatic
organisms. In the presence of light, photosynthesis occurs and plant
biomass is created. In a healthy environment the plant biomass is
grazed on by zooplankton, which is followed by an ordered series of
events to complete the food chain.
When there exists an overabundance of nutrients in a system,
massive algal blooms of an undesirable nature can occur. This con-
dition first presented itself in August-September 1959, when blooms of
the nuisance blue-green algae Anacystis sp. were reported in the
Anacostia and Potomac Rivers near Washington. Chlorophyll a_ at Indian
Head and Smith Point for 1965-66 and 1969-70, as shown in Figures 1
and 2, indicate that algae had not only increased in density but became
more persistent over the annual cycle. The figures also show a decrease
in chlorophyll ^concentrations during the 1973-74 sampling cruises.
The exact nature of this decrease has yet to be determined.
When algae is not consumed by higher trophic forms, which is the
apparent case with the blue-greens in the Potomac Estuary, the effects
of massive blooms can be quite devastating. Jaworski, et al. [4],
estimated that the combined ultimate oxygen demand of nitrogen and
carbon resulting from the death of algal cells during intense summer
bloom conditions in the estuary is approximately 490,000 Ibs/day, if
exerted. For comparison purposes, this load would be greater than the
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MAINS POINT
MILES BELOW CHAN BRIDGE - 7.60
CHLOROPHYLL a
POTOMAC ESTUARY
JUL AUG SEP
r-T-^r
i9 " I ' 1970
FEB MAfi APR
PISCATAWAY CREEK
MILES BELOW CHAIN BRIDGE = 18 35
FIGURE - I
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SMITH POMT
MIES KUMT CHAM MDOC • 4&W
CHUOROPHYLL a
POTOMAC ESTUARY
MDOLE «*4 LOWER REACH
jut. JUL
ttf. OCT
NOV. DEC I JAN.
«M »-!-» m
MM. tff.
301 BRIDGE
ML£S BELOW CHAM tKXXX. m 87.4O
HW JUN.
OCT. NOV.
n» MML
ML- «ja.
PtCY PONT
MLES (EUOW CHAM BROGC > M2O
OCT. NOV. OK. I JAN
FIGURE -2
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total oxygen demand by all wastewater discharges into the upper estuary.
Other undesirable effects of accelerated eutrophication include decreases
in the dissolved oxygen budget caused by algal respiration, creation of
nuisance and aesthetically objectionable conditions, and possible toxic
effects on other aquatic organisms.
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Major Sources of Nutrients
The major sources of nutrients to the upper Potomac Estuary can
be categorized as follows: wastewater treatment plants within the
Washington Metropolitan Area, contributions from the upper freshwater
basin, and stormwater runoff from the highly urbanized area of
Washington, D.C.
Figures 3 and 4 present wastewater nutrient enrichment trends
and ecological effects on the upper Potomac Estuary. The loadings
represent the major wastewater treatment plant sources within the
Washington Metropolitan Area. With respect to Figure 3, Jaworski,
et^ al_. [4], hypothesized that the nuisance plant conditions did not
develop linearly with an increase in nutrients. Instead, the increase
in nutrients appeared to favor the growth and thus the domination by
a given species. As nutrients increased further, the species in turn
was rapidly replaced by another dominant form. For example, water
chestnut was replaced by water milfoil which in turn was replaced by
blue-green algae.
Figure 4 is a presentation of the current wastewater treatment
plant loadings to the upper estuary. The loadings show a gradual
decrease in total phosphorus (as P) from 24,000 Ibs/day at the end of
1969 to 16,310 Ibs/day as an average for 1974. BOD5 loadings have
shown a downward trend from a high of 154,000 Ibs/day in 1971 to the
current rate of 119,870 Ibs/day (1974). Total nitrogen loadings were
also lower in 1972 and 1973, but showed a slight increase during 1974,
the average being 59,710 Ibs/day.
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Since 1972 there has been a noticeable absence of dense blue-green
algal blooms of any duration in the upper estuary. In the historical
bloom area near Indian Head (30.6 miles below Chain Bridge), chloro-
phyll a^ levels were observed in range of 25-70 yg/1 and 40-78 yg/1
during the 1973 and 1974 summer seasons, respectively. (See Figure 1.)
In contrast, during the 1969 and 1970 summer months, chlorophyll a^
approached and on two observed occasions, in .July and August 1970,
exceeded 200 yg/1.
It is premature to hypothesize that the absence of massive blooms
is a direct result of reduced wastewater loadings in the Washington
Metropolitan Area. If there are no massive blooms this summer and
in subsequent years, and if wastewater loadings continue to decline,
a more definitive cause-effect relationship would be established between
nutrient concentrations and algal populations. Also, the relative
merit of Hurricane Agnes as a cleansing mechanism must be viewed as a
transient phenomenon. After all, Hurricane Camille provided a flushing
of the estuary in August 1969 which did not appear to significantly
reduce the algal populations. The essence of this brief discussion is,
at this time, we do not know all the causitive agent or agents that
trigger massive blue-green algal blooms in the Potomac Estuary. This
point will be developed later in this paper.
The relative contribution of nutrients to the Potomac Estuary
from its upper basin has been documented by the Annapolis Field Office,
EPA, in Technical Report Nos. 15 and 35 [4,5], In summary, this
previous work established that during a selected low-flow of 1200 cubic feet
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per second (cfs), at which the loadings will be equaled or exceeded
95 percent of the time, the total phosphorus contribution from the
upper basin is 3.7 percent of the total phosphorus load to the estuary.
In contrast, the load from the wastewater treatment plants in the
Washington Metropolitan Area constitutes 96 percent of the total phos-
phorus load. The disparity in loadings is similar for total nitrogen.
With regard to the upper basin nutrient contributions, Technical
Report 35 [4] concluded that a 50 percent reduction in the phosphorus
load from the upper Potomac River, together with the recommended
phosphorus reductions in the Washington Metropolitan Area, is required
if the recommended phosphorus criteria are to be achieved in the upper
estuary. In order to realize the 50 percent reduction, it was con-
cluded that the wastewater contribution from point sources of 6,100
Ibs/day must be reduced to 700 Ibs/day. Should this recommendation be
implemented, point sources of phosphorus would have to be reduced by
90 percent.
During August 1973, and again on three separate occasions during
the summer of 1974, the Annapolis Field Office carried out intensive
surveys in the upstream reach from Chain Bridge to just above the
confluence of the Monocacy River with the Potomac, a distance of ap-
proximately 38 miles. The purpose of these studies was to assess
current water quality conditions. The revealing finding of the surveys
was the significant biological activity taking place in the reach.
Chlorophyll a^ had not been measured previous to the surveys. During
August 6-9, 1973, chlorophyll a^ levels of 150 yg/1 were observed
between river miles 17 and 26, or the area from Seneca Creek upstream
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to the mouth of Goose Creek. From June 18-20, 1974, chlorophyll averaged
about 60 yg/1 in the same reach, while during the period July 16-18, 1974,
the levels averaged about 40yg/l. On September 3, 1974, a chlorophyll
concentration of 310 yg/1 was observed about one mile above Seneca Creek.
During this observation dramatic decreases in nitrate nitrogen and
inorganic phosphorus were noted suggesting that these compounds were
being utilized by the algae.
A review of earlier chlorophyll a^ data (1966-70) indicates that
upstream algal activity was not occurring to the extent recently ob-
served. For example, just below the fall line at Key Bridge, chlorophyll
levels in 80-90 yg/1 range were recorded in July-August 1973, with a
historically high value of 171 yg/1 observed on September 5, 1974. The
previous levels in this vicinity were around 30 yg/1. This indicates a
carry over or upstream contribution of chlorophyll a^ or algal biomass to
the upper estuary. But, this condition does not persist down the estuary.
The impact of the freshwater algae on estuarine biological communities
has not been evaluated. Extensive analyses of all available upstream
water quality data will be carried out by the Annapolis Field Office in
order to establish any significant changes in upstream loadings as well
as the species identification and significance of the recently observed
algal blooms.
With respect to the impact of nutrients from stormwater runoff
on water quality of the estuary, a few general conclusions can be drawn
at this time. The significance of stormwater nutrients on the eutro-
phication process will depend on the magnitude, intensity, and duration
of the storm event, the time of occurrence of the storm, and whether
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or not the nutrients reach the critical growth zone in a readily
available form. To date, the actual impact of stormwater on water quality
in the estuary has not been evaluated. As part of its NPDES permit for
Blue Plains, the D. C. Department of Environmental Services is required
to monitor stormwater loadings.
Based on earlier work of Roy Weston Associates and Philip Graham,
Council of Governments, on water quality aspects of stormwater, the
Annapolis Field Office has, based on rainfall records of 1973-74, cal-
culated the relative pollutant loadings from combined and separate
storm sewers within the Washington, D.C., Beltway for different
rainfalls, including the frequency of the rainfalls. These estimates,
with appropriate updating to reflect forthcoming monitoring data, will
be useful in future modelling efforts where the ability to predict
diurnal fluctuations on a real time basis will be developed.
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Water Quality Data Trends
Data presented earlier in this paper showed marked reductions in
wastewater loadings from the major sources in the Washington Metro-
politan Area. In order to evaluate the effects of the reduced loadings,
a comparison is made of the 1973-74 and 1969-70 nutrient data from
three representative sampling stations in the upper estuary.
The Mains Point sampling station is located 7.6 miles below Chain
Bridge, the fall line. Hains Point can be considered the control point,
i.e., the area located above the influence of the Blue Plains Waste-
water Treatment Plant. The inorganic phosphorus (as PCty) concentrations
(Figure 5) show a general decrease over those of 1969-70, while nitrate
nitrogen concentrations (Figure 6) between the periods of 1969-70 and
1973-74 appear to have remained unchanged. Ammonia nitrogen (Figure 7)
did not exhibit the high peaks shown in 1969, yet the recent data show
no dramatic decline over 1970 concentrations.
The Woodrow Wilson Bridge sampling station is expected to show the
effects of the major wastewater discharges. A comparison of the ammonia
and nitrate nitrogen data show no significant changes for the periods of
comparison. The inorganic phosphorus appears to have dramatically
declined. On close examination, however, the high peak in May-July 1969
could be due to the low flow conditions (3000 cfs) and the buildup of
phosphorus from the discharges. During August 1969 Hurricane Camille
and higher flows (8000 cfs) flushed the estuary, as can be seen by the
sharp drop in phosphorus concentrations. Likewise, the high peak of
3.4 mg/1 inorganic phosphorus (as PO^) in September 1970 is associated
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INORGANIC PHOSPHATE
POTOMAC eSTUARV
4 M9-V7D
1973-1974
P04
HAMS POMT
HUES KLCW CHUN MIOGC • 7.60
WOODR0M WILSON BfitOGE
MIES 6O.OW CHAM BRIOGt > 12.10
Ftfc. HA*. A». r MAV JUK JUL iNJG. SOI OCT NW OCC.
FO. UAH. JMt
a?-
a*-
M. I .
JAM. nm.
WTO
OJ-
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(XI-
P1NEV POJNT
MLCS
CHAN 6MDGE *
ret. UAA.
MAY JLM.
— ' -. ' ^ ' JUU '
FIGURE - 5
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-i
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01 -
NITRATE and NITRITE NITROGEN as N
POTOMAC ESTUARY
MAINS POINT
MUS KLOW 'CHAN SROGE > 7.60
MAX JUN. JUL. AUG SCP OCT NOV OCC I JAN FEB.
APR MAY JUN JUL AUG SCP
01-
O4-
02-
WOOOfiOW WILSON BRtOGC
'
1,5-
14 -
L3-
L2 -
I I -
^
sr «..
04-
O4-
03-
01-
01-
MAM. AM MAY
INDIAN HEAD
MILES ftELOW CHAIN BRIDGE > 30.60
JUL. AUG- SCP. OCT NOV. OCC
FT*. ' MA*
MAY JLK
AUk SEP
APK MAY JUN
AUO SCP
ac-
05-
o*-
01-
oz-
01-
SMfTH PCXNT
NMLES BELOW CHAM BRIDGE * 46.60
u-
u-
03-
02-
01-
301 BRIDGE
MILES BELOW CHAIN BROGE > 67.40
FfB MM APR, MAY JUN. JUL AUG SCP
FEB. MAR
JUN JUL
as-
f «.
+ | 03-
cf1" a?-
01-
PINEY POINT
MLCS BELOW CHAIN BRIDGE =9020
FEB. MAM
MAY JUN JUL AUG. SEP OCT
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AMMONIA NITKOGtN as N
POTOMAC ESTUARY
ft-
MAINS POINT
MLES BELOW CHAIN BRIDGE » 7.60
1969-WTO
1973 -1974
MAY JIM JUL. MJG SEP OCT. NOV DEC. I JAN FEB.
MAV JUN JUL
WOODROW WILSON BRIDGE
MLES BELOW CHAIN BRDGE = 12.10
AUG. SEP OCT. NOV.
MAY JUN. JUL AUO. SEP.
INDIAN HEAD
MILES BELOW CHAIN BRIDGE * 30.60
AUG. SEP. OCT. NOV. DEC f JAM
SMITH PONT
MLES BELOW CHAIN BRIDGE - 4«.«0
MAY JUN JUL AUG. SEP OCT. NOV. DEC JAN. FTB.
JUN ' JUL. AUG. SEP.
301 BRIDGE
MLES BELOW CHAIN BRIDGE = 67.40
JUN JUL AUG SEP OCT NOV
JUN. ' JUL ' AUG. SEP
PINEY POINT
MLES BELOW CHAM BRIDGE * 90.20
JUN JUL AUG SEP OCT NOV DEC JAN FEB
MAY JUN. JUL. AUO. SEP.
FIGURE - 7
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with the low flow condition (1600 cfs). It was during this period of
low flow and high temperatures that algal mats encroached into the
Tidal Basin.
The Indian Head sampling station, 30.6 miles below the fall line,
is located in the historical bloom area of the blue-green algae. The
nitrate and ammonia nitrogen have remained fairly constant as was
noted at the two upstream stations. The 1973-74 inorganic phosphorus
(as PC>4) concentrations were consistently lower at Indian Head when
compared to the 1969-70 concentrations. While 1969 was a low-flow year,
the freshwater inflows for 1970 (10,500 cfs) and 1974 (11,500 cfs) were
similar. This would infer that the differences in comparative phos-
phorus levels for 1970 and 1974 were not greatly effected by freshwater
f1ows.
The literature states that an average N/P ratio, by atoms, is
about 15 or 20 to 1. In general, if the ratio is less than 10:1 the
system can be considered nitrogen deficient. If it is greater than
25:1 the system may be phosphorus deficient. At the Indian Head sampling
station the N/P ratios for inorganic nitrogen versus inorganic phos-
phorus on a yearly average basis for the comparative study periods are
as follows: 14.0:1, 1969; 16.9:1, 1970; 32.3:1, 1973; and 31.4:1, 1974.
In the same order the ratios for the summer seasons (May-September)
were: 21.4:1, 15.9:1, 31.3:1, and 28.0:1. (It should be noted that the
data sets for 1973 and 1974 summer seasons were limited to 6 and 7,
respectively.)
It is quite evident that in this particular area of the estuary
the system has switched from nitrogen deficient to nitrogen abundant.
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It should be stated that atomic ratios cannot be taken as an absolute,
but they can serve as a useful tool to evaluate the respective relative
shifts in the abundance of nutrients.
It is most important to point out that while intense algal popu-
lations were not observed in the last couple of years in the upper
estuary, there were sufficient concentrations of nutrients to support
algal growth. According to the literature, 10 ug/1 (.01 mg/1) of
inorganic phosphorus can stimulate an algal bloom [5], During the critical
summer months of 1973 and 1974, at Indian Head, concentrations of in-
organic phosphate were measured at .35 and .27 mg/1, respectively. Why
there were no major blooms is not fully understood.
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Water Quality Predictions
Finally, because of current economic considerations, the role of
nitrogen in the eutrophication process of the Potomac Estuary has to
be defined. The Dynamic Estuary Model of the Potomac Estuary has been
modified by the Annapolis Field Office so that the yield of algae is
determined either by phosphorus or nitrogen; the nutrient that produces
the least growth in any given time or place is the controlling factor.
Model runs have been made using the nitrogen and phosphorus limi-
tations set forth in the Blue Plains NPDES permit, as well as nutrient
limitations recommended for the other major discharges to the estuary,
and freshwater inflows to the estuary of 9000, 3000, and 1000 cfs.
Preliminary results show that chlorophyll production is fairly
uniform with both N and P control and P control only, at the higher
flow (9000 cfs). At the 1000 and 3000 cfs flows the reduction of chloro-
phyll with N and P control is in the range of 10-20 yg/1. It could be
expected that at high flow conditions an ample supply of nutrients from
sources other than treatment plants would be available for algal growth.
In order to answer the phenomena of why blooms occur and why
blooms do not occur, the Annapolis Field Office has begun to lay out
the framework of a new model that represents the state-of-the-art
in the area of eutrophication dynamics. The model should have the
predictive capability to assess the function of light, temperature, and
nutrients as rate limiting factors in the eutrophication process in
the Potomac Estuary.
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Coupled with the modelling effort, an extensive monitoring effort
is being planned. The purposes of the monitoring program are:
1. To provide data for model calibration and verification.
2. To perform specialized field and lab studies (e.g., algal
bioassays) to assist in identifying limiting nutrients
and algal growth characteristics.
3. To assess both the seasonal and long term water quality
trends in the estuary.
The combined information from the modelling and monitoring
programs should provide the information necessary to quantitatively
identify the cause-effect relationships in the estuary.
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REFERENCES
1. Millar, C. E., L. M. Turk, and H. D. Foth. 1962. Fundamentals of
Soil Science (3rd Ed.)- John Wiley and Sons, New York.
2. "Scientific Fundamentals of the Eutrophication of Lakes and
Flowing Waters, With Particular Reference to Nitrogen and Phosphorus
as Factors in Eutrophication," Environment Directorate, Organi-
sation for Economic Co-Operation and Development, Paris, 1971.
3. Fog, G. E., W. D. P. Stewart, P. Fay, and A. E. Walsby. 1973.
The Blue-Green Algae. Academic Press, incorporated, New York.
4. Jaworski, N. A., L. 0. Clark, and K. D. Feigner. "A Water Resource-
Water Supply Study of the Potomac Estuary," CTSL, MAR, WQO, U.S.
Environmental Protection Agency, Technical Report No. 35, April 1971.
5. Jaworski, N. A. "Nutrients in the Upper Potomac River Basin,"
CTSL, MAR, FWPCA, U. S. Department of the Interior, Technical
Report No. 15, August 1969.
6. Allen, H. E. and J. R. Kramer. 1972. Nutrients in Natural
Waters. John Wiley and Sons, New York.
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