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The Confounding Effect of River Discharge on Estuarine Response to Nutrient Loading
Borsuk, M. E., C. A. Stow, and K. H. Reckhow. 2004. Confounding effect of flow on estuarine response to nitrogen loading. Journal of Environmental Engineering, 130: 605-614.
Craig A. StowNOAA Great Lakes Environmental Research Laboratory
Ann Arbor, MI
Additional Insights and Inputs provided by Conrad Lamon and Song Qian
The Neuse River Basin
Courtesy USGS
Vollenweider Cross-Sectional Lake Nutrient Loading Model
Brazenly stolen from:Vollenweider, R.A. 1976. Advances in defining critical loading levels for phosphorus in lake eutrophication. Mem. Ist. Ital. Idrobiol., 33:53-83.
Single Lake Relationship:
Positive
Negative
Nonlinear
River Flow
Nutrient Loading
Nutrient Concentration Eutrophication
EstimatedNutrient Loading
EstimatedConcentration=
f(Flow)
Residence TimeTurbiditySalinity
Temperature
River discharge highly variable – even on relatively long time-scales
Drives Nutrient Load Variability at this scale
Concentration:Flow relationships idiosyncratic: positive, negative, or non-monotonic
In the Neuse the relationship was negative
-9
-8
-7
-6
-5
12 13 14 15 16 17 18
Log flow
Log
conc
entra
tion
Data Provided by:NC DENR DWQ – nutrient concentrationsUSGS – daily flow
High load = low concentrations
New New BernBern
10 miles
10 kilometers
10
20
30
40
50
0
6070
8090
100110
120 130140
150160
170
180
N
Water Quality StationWater Quality Station
Hydrographic StationHydrographic Station
River
Upper
Middle
BendLower
Upper
Middle
Bend
Model SectionsModel Sections
chlTNT
wey
TNTflowIflow
flowIflowchl
)()20(}){ln(}){ln(
}){ln(}){ln()ln(
sec,secsecsec,2
secsecsec,1sec,0
Chlorophyll a Model(Bayesian multilevel piecewise lognormal model)
Med
ian
Ann
ual T
otal
N (m
g/L)
0.25
0.50
0.75
1.00
1.25
1.50
1.75
Fort Barnwell Total N Load (tonnes)
2000 3000 4000 5000 6000 7000
Ft. BarnwellSwift CreekNew BernBroad CreekOrientalPamlico
Estuarine N Concentrations vs. Annual N Load
Med
ian
Ann
ual T
otal
P (m
g/L)
0.02
0.12
0.22
0.32
0.42
Fort Barnwell Total P Load (tonnes)
300 400 500 600 700 800 900 1000 1100 1200 1300
Ft. BarnwellSwift CreekNew BernBroad CreekOrientalPamlico
Estuarine P Concentrations vs. Annual P Load
Summary
Nonlinear chlorophyll, flow (~ load) relationship on short time-scales
Relationship differs systematically along spatial gradient
Maximum differs systematically along spatial gradient
No relationship between nutrient load, concentration on medium time-scales
This may differ among systems
Nutrient Loading
Eutrophication
Hypoxia
Nutrient Loading
TMDLs
Eutrophication
Hypoxia
Nutrient load targets appropriate on longer (multi-year) time scales
Short-term (yearly or less) misleading
Assuming stationary flow (long-term)
Year
Log
Flow
1980 2000
-0.3-0.2-0.10.00.10.2
Jan
1980 2000
Feb
1980 2000
Mar
1980 2000
Apr
1980 2000
May
1980 2000
Jun
1980 2000
Jul
1980 2000
Aug
1980 2000
Sep
1980 2000
Oct
1980 2000
Nov
1980 2000
Dec
1980 1985 1990 1995 2000 2005
5.5
5.65.75.8
Log
Flow
1980 1990 2000
-0.2
0.0
0.2
Trend
1980 1990 2000
Seasonality
1980 1990 2000
Residuals
Mississippi River Flow – Seasonal Trend Decomposition Using Loess
April 2006 - U.S. Court of Appeals District of Columbia Circuit ruled that EPA-approved plan to limit pollution into Anacostia River contrary to Clean Water Act requirements to set "total maximum daily loads" of pollutants.
January 2007 -- United States Supreme Court let stand lower court ruling requiring limits on pollution allowed in Anacostia River each day.
Anacostia River in Washington, DC
Photo by City of Washington DC
River Flow
Nutrient Loading
Nutrient Concentration Eutrophication
Upper Trophic LevelEffects
Hypoxia?
The End
River Flow
Nutrient Loading
Hypoxia
EstimatedNutrient Loading