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Nutrient Cycling and Water Quality
in an Urban Drinking Water Reservoir
I. The
Challenge: Compromised Water Quality
Drinking water reservoir eutrophication burdens a municipal economy
in the short term, as costly algicide treatments are applied to
control productivity, and possibly the long term as well, as
chemical treatments have to be carefully balanced with ecosystem
health. Discovering the sources of excess nutrients driving
eutrophication, either external via watershed runoff, and/or
internal to the reservoir via bottom sediment reflux, then
controlling these sources is a nationwide objective.
With water quality, odor, and taste issues as top priorities for the
Indianapolis water supply, a research and development partnership
spanning twenty years, known as the Central Indiana Water Resources
Partnership (CIWRP), was established to conduct detailed analysis of
the three water supply reservoirs, including Eagle Creek.
Figure 1. Construction of Eagle Creek Reservoir (ECR),
located in the Eagle Creek Watershed, was completed in 1967 to
provide downstream flood control for the cities of Indianapolis and
Speedway, Indiana (red outline). The reservoir is home to Cagle
Creek Park, providing recreational activities such as swimming,
boating, fishing, and sporting events. An abandoned quarry adjacent
to, but separated from the ECR, serves as a bird sanctuary.
The reservoir became a public drinking water source
in 1976 when the T.W. Moses water treatment facility was
constructed, using water directly from the reservoir. However, the
treatment facility can not effectively remove the high levels of
taste and odor compounds that periodically occur in the reservoir as
a result of blooms of blue green algae.
The area emptying into ECR is 162 mi2 /419.58 km2, about half of
which is used for corn and soybean crops; the reservoir has a water
surface area of 1350 acres/5460 m2, and a maximum depth of 54
ft/16.46 m, allowing some regions to become thermally stratified
during summer and winter, creating the potential for anoxic bottom
waters.
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II. Algal Blooms
in ECR
The reservoir experiences periodic algal blooms that can directly
affect the taste and odor of the drinking water produced by the T.W.
Moses treatment facility. Customer complaints have increased in
recent years, and have been attributed to the growth of undesirable
algal species, such as the blue green algae Pseudanabaena. Increased
nutrient levels in the reservoir are expected to be directly related
to the algal blooms.
Figure 2. Dissolved Oxygen (DO) measured between 1976-1996 at
T.W. Moses Water Treatment Facility raw water intake from ECR.
Strict state regulations allow copper treatments to occur only when
morning DO is > 8. ECR has routinely low DO in mid-summer to early
fall, hindering the use of algicides, which would further stress
fish populations.
It is widely held that agricultural and urban runoff are primary
nonpoint sources of pollution, and may contribute to the degradation
of water quality via nutrient loading, specifically phosphorus (P),
commonly the growth limiting nutrient in aqueous systems. This
increase in external P loading can drive enhanced productivity in a
reservoir, leading to lower oxygen contents of deeper waters and
thus higher internal P recycling.
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III. The Phosphorus Cycle
In natural waters, the exchange of P between sediments and the
overlying water column is a major component of the P cycle.
Biologically reactive P is incorporated into terrestrial systems via
mineral weathering. After release from minerals, P is often
transformed via a series of natural soil-forming processes. Upon
erosion from a landscape, the total load of potentially
biologically-available P includes dissolved inorganic P, dissolved
organic P, and weakly surface-bound P associated with particulates.
Upon entering a reservoir, biologically-available P can be rapidly
incorporated into photosynthetic biomass as a limiting nutrient.
This P is transformed into an organically-bound fraction, and will
be transported to the reservoir sediments upon organism death or
consumption via zooplankton.
Another significant component of P for biomass productivity can be
introduced to a reservoir internally. In this process, P is
regenerated from bottom sediments either by the degradation of
organic matter (and thus release of organic P) or by desorption
and/or dissolution from mineral surfaces. In low oxygen conditions,
this dissolution process can be a substantial contributor of P, due
to the dissolution of iron oxyhydroxides, which are typically
extremely P-rich.
Figure 3. A conceptual diagram of P geochemistry in oceanic
sediments (from Filippelli and Delaney, 1996).
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III. Hypothesis: Examine the Potential of Internal P Recycling
In several anthropogenically influenced setting like that
encountered in the Eagle Creek watershed, the net external input of
P to the reservoir can be enhanced by loading from human and
industrial waste (sewage is high in reactive P, as are the
detergents and surfactants used in industrial processes), from
excess fertilizer application in agricultural areas, and from
increased weathering of organic-rich surface soils during land use
change.
This increase in external P loading can drive enhanced productivity
in a reservoir, leading to lower oxygen contents of deeper waters
and thus higher internal P recycling. Finally, as the load of
external P to reservoir sediments hits a certain threshold,
regardless of reducing external inputs, internal recycling of P from
P-rich reservoir sediments can drive eutrophication of a reservoir
system.
This objective of this research is to investigate the internal P
cycling of ECR by analyzing the geochemistry of sediments from the
ECR. This is occurring as a two step process,
1. spatial distributions of surficial P within the ECR have been
studied
2. detailed analysis of P in its different fractions down four
sediment cores is to be undertaken.
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IV. Phase One: Organic Matter Content and Surficial Phosphorus
Concentration
Using this sedimentation rate, plus the dry bulk density of the
sediment and the average content of P in the reservoir sediments, we
obtain a P accumulation rate of about 50 µmol P/cm2/yr. This rate is
about 10 to 100 times higher than what is found in lake sediments
unaffected by urbanization, revealing the extent of P loading in the
ECR.
Figure 4. P concentrations in ECR surficial sediments are
high compared to background values (soil usually contains 0.5-2
mg/g). The high P contents of ECR sediments reflect the history of P
loading and high organic matter productivity. Apparent varves are
observed in sediments from the deep hole of the south reservoir,
which yield an approximate sedimentation rate here of 1 cm/yr.
Figure 5. The relationship between P and organic matter is
relatively strong, supporting the assertion that in situ organic
matter productivity is strongly affecting the distribution of both
of these components. Organic matter determinations were done on a
Loss on Ignition (LOI) basis. The regression line is for all
samples.
Figure 6. A correlation exists between P and grain size, with
finer mean grain sizes correlating with high P contents. Since the
grain size analysis was performed on an organic-free basis, the
correlation indicates that finer sediments are responsible for
retaining a significant portion of the total P signal. The
regression line is for all samples.
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V. Phase Two: Figure 8 A-D. Geochemical results of gravity cores
A. Phosphorus
P concentrations cycle from 1.0 mg/g [P] to 2.5 mg/g [P]. Both
sections of the reservoir behave in much the same manner.
B. Organic Matter
Organic matter stays constant in the North core, and varies from 6-7
wt. % to 12-14 wt. % in the South. Organic matter does not correlate
with P down-core. The lack of correlation between organic matter and
P suggests that the P is found in different fractions down-core from
the predominantly in situ fraction at the sediment surface.
C & D. Lead and Copper
Lead (fig. 8C) decreases in concentration through time, especially
in the upper 20 cm of the cores. The high correlation between P and
Pb suggest that they are related to fine particles, as they both
show high affinity to particle size below that of 64um in surficial
sediments.
After 10-15 cm copper (fig. 8D) concentrations return to those of
background levels, as indicated in the core data. The copper spike
in the top cm of core represents recent Cutrine Plus applications.
Down-core migration of copper is attributed to bioturbation.
 
V. Phase Two: Continuing Research on Detailed Record of Phosphorus
and Metals
 Figure
7. Two gravity cores were taken from ECR ( ), one from the
northern and southern portions of the reservoir, corresponding to
high surficial organic and P concentrations in the deeper regions.
Bioturbation was evident within the top 10 cm of each core.
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VI. Continuing Research
The two preliminary cores have added to our understanding of the
internal cycling of P, and have also shed light on further core
sampling. Geochemical analysis on future cores will include
sequential extraction of P in order to pinpoint the amounts of
bioavailable fractions within the sediments of ECR.
Detailed grain size analysis, along with historical data from the
reservoir, such as flooding events, will be compiled to create a
complete history of reservoir through the past 36 years.
This investigation will show how the internal P load is possibly
affecting algal blooms within the water column, as related to the
physical factors known to occur at the sediment-water interface,
including that of hypolimnial anoxia.
Acknowledgements
Generous funding is provided by USFilter, Indianapolis Water LLC.
The assistance of all those working on the project is gratefully
acknowledged. Technical support provided by Bob E. Hall, Vince
Hernly, and Jeremy Webber.
References
-
Filippelli, G.M. and Delaney, M.L., 1995, Phosphorus geochemistry
and accumulation rates in the eastern Equatorial Pacific Ocean:
Results from Leg 138: Proceedings of the Ocean Drilling Program,
Scientific Results, v. 138, p. 757-767.
-
Kleeberg, A., and Kozerski, P., 1997, Phosphorus Release in Labe
Grober Muggelsee and its implications for lake restoration,
Hydrobiologia, 342/343, 9-26.
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Schauser, I., Lewandowske, J., Hupfer, M., 2003, Decision support
for the selection of a appropriate in-lake measure to influence the
phosphorus retention in sediments, Wat. Res., 37, 801-812.
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Schlesinger, W.H., 1997, Biogeochemistry an analysis of global
change: San Diego, Academic Press, 588 p.
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Tedesco, L.P., Atekwana, E.A., Filippelli, G.M., Licht, K., Shrake,
L., Hall, B.E., Pascual, D.L., Latimer, J., Raftis, R., Sapp, D.,
Lindsey, G., Maness, R., Pershing, D., Peterson, D., Ozekin, K.,
Mysore, C., and Prevost, M., 2003. Water Quality and Nutrient
Cycling in Three Indiana Watersheds and Their Reservoirs: Eagle
Creek/Eagle Creek Reservoir, Fall Creek/Geist Reservoir and Cicero
Creek/Morse Reservoir. Central Indiana Water Resources Partnership,
CEES Publication 2003-01, IUPUI, Indianpolis, IN, 163 p.
-
Wetzel, Robert G., 1983, Limnology (2d ed): Orlando, Harcourt Brace
Jovanovich, p. 255-297, chap. 13.
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Publications\2003-GSA_Raftis.ppt
Raftis, R., Filippelli, G., Tedesco,
L., Atekwana, E., Latimer, J., Pascual, D.L., and Shrake, L., 2003.
Nutrient Cycling and Water Quality in an Urban Drinking Water
Reservoir. Geological Society of America Abstracts with Programs.
35(6): 145.
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