1. URBANIZATION IMPACTS ON STREAM NUTRIENT
CONCENTRATIONS IN THE SEATTLE REGION
Michael T. Brett,1 Sara E. Stanley,1 Giorgios Arhonditsis,1
David M. Hartley,2 Jonathan D. Frodge,2 & David E. Funke2
1Department of Civil & Environmental Engineering,
Box , University of Washington,
Seattle, WA
2King County Water & Land Resources,
201 South Jackson St #600,
Seattle, WA

2. Land Cover

3. King County Data
10 years, 17 streams, sampled monthly • Non-storm and storm samples
7 variables analyzed

4. Land Cover Versus Stream Nutrients: Normal Flows20 40 60 80
100
Geomean TP (µg/l) 0%
20%
40%
60%
80%
100%
Percent Urban Land Cover r 2
= 0.58
Total Phosphorus 10 30 50
Geomean SRP (µg/l)
= 0.56
Soluble Reactive Phosphorus 4 6 8
Geomean TSS (mg/l)
Percent Urban
Land Cover
= 0.03
Total suspended solids 1 3 5
Geomean turbidity (NTUs)
= 0.33
Turbidity
Tibbets
Geomean NH
(µg/l)
= 0.36
Ammonium
250
500
750
1000
1250
1500
Geomean NO
= 0.16
Nitrate

5. Change in Concentration: Storm/Normal Flow
Total Phosphorus
Nitrate
Turbidity
3.0
2.0 8 r 2
= 0.03 r 2
= 0.67 r 2
= 0.11
2.5
Coal
Coal
1.6 6
184 ± 83%
2.0
1.2
(Storm/Normal Flow)
TP (Storm/Normal Flow)
1.5 4
Turbidity (Storm/Normal Flow)
0.8
1.0 2
55 ± 45%
0.4
0.5 3 NO
0.0
0.0 0%
20%
40%
60%
80%
100% 0%
20%
40%
60%
80%
100% 0%
20%
40%
60%
80%
100%
Precent Urban Land Cover
Percent Urban Land Cover
Percent Urban Land Cover
Soluble Reactive Phosphorus
Ammonium
Total Suspended Solids
1.6
2.5 14 r 2
= 0.51 r 2
= 0.18 r 2
= 0.09 12
2.0
Coal
1.2 10
1.5
244 ± 116%
(Storm/Normal Flow) 8
SRP (Storm/Normal Flow)
0.8
TSS (Storm/Normal Flow) 6
1.0 4
0.4
0.5
67 ± 36% 4 2 NH
0.0
0.0 0%
20%
40%
60%
80%
100% 0%
20%
40%
60%
80%
100% 0%
20%
40%
60%
80%
100%
Percent Urban Land Cover
Percent Urban Land Cover
Percent Urban Land Cover

6. Seasonal Fluctuations in Stream Constituent Concentrations
1.0
seasonal mean/yearly mean
Summer
Fall
Winter
Spring
Nitrate & Ammonium NH 4 NO 3
Total & Soluble Reactive Phosphorus
SRP TP
TSS and Turbidity
Turbidity
TSS
2.0
0.5

7. Percent Urban Enrichment
Average
Percent
Constituent
Units
Forested
Urban
Enrichment
Total Phosphorus
µg/l
32.3
67.8
109%
Soluble Reactive P
13.1
33.4
154%
Total Nitrogen
1065
1412
33%
Nitrate
840
1088
29%
Ammonium
13.7
24.8
81%
Turbidity
NTUs
1.71
3.01
77%
Total Susp. Solids
mg/l
4.33
5.90
36%

8. Agricultural vs. Urban Enrichment
Seattle streams
Omernik (1976)
Seattle For./
Seattle Urban/
Constituent
Forested
Urban
Agri.
Omernik's For.
Omernik's Ag.
Total Phosphorus 32 70 35
135
0.92
0.52
Soluble Reactive Phosphorus 13 14 58
0.94
0.61
Total Nitrogen
1065
1404
885
4170
1.20
0.34
Dissolved Inorganic Nitrogen
862
1107
347
3190
2.48
0.35

9. Averaged Overall Change in Urban Stream SRP Concentrations
Urban stream nitrate concentrations 60
1300
y = x
y = -9x r 2 55
= 0.42 r 2
= 0.31
1200 50
1100 45
Mean Annual SRP conc. (µg/l)
Mean annual nitrate conc. (µg/l) 40
1000 35
900 30
800 25
1980
1985
1990
1995
2000
1980
1985
1990
1995
2000

10. Conclusions:
Urban streams are enriched with Phosphorus by about % and with Nitrogen by about 30-70%.
Stream TSS concentrations and Turbidity are more closely related to short term flow fluctuations than to land cover.
Forested streams export inorganic nitrogen and phosphorus during storms.
Stream phosphorus concentrations peak during the summer, and nitrogen and sediment concentrations peak during the winter.
The most urbanized streams have had a 36% decline in SRP and a 15% decline in nitrate concentrations during the last 20 years.

11. 2.0 1.5 Signal/Noise 1.0 0.5 0.0 Constituent TP SRP NO3 NH4 Turbid TSS
Log 10 A
rithmetic