1. URBAN NON-POINT SOURCE NUTRIENT IMPACTS
ON SEATTLE AREA STREAM CHEMISTRY
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. phosphorus and sediment transport differ in Seattle area
How much does nitrogen,
phosphorus and sediment
transport differ in Seattle area
urban and forest streams?
SCALES: Long term
(decadal), seasonal (monthly),
inter-annual (daily), and
event based (hourly).

3. Initial objective: to determine how land use impacts the pathways and
nutrient load of water as is falls as rain, is transported as surface runoff,
subsurface flow, or groundwater.
Ultimate objective: to develop a mechanistic model
of land use impacts on stream nutrient transport.

4. Lake Washington in the Past
© World Watch Magazine
Lake Washington in the Past
(and the Future?)
SWAMP
&
Water-reuse

5. Land Cover

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

7. 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

8. 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

9. 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
Seasonal Fluctuations in Stream Constituent Concentrations

10. 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%

11. Seattle forest streams have 150% more DIN than typical forest streams25 50 75
100
125
Phosphorus concentration (µg/l)
Seattle For.
Seattle Urb.
Omernik For.
Omernik Ag.
SRP TP
1000
2000
3000
4000
Nitrogen concentration (µg/l)
DIN TN
Seattle forest streams have 150%
more DIN than typical forest streams
Seattle urban streams have about 50%
as much phosphorus as typical
agricultural streams
Seattle urban streams have about 35%
as much nitrogen as typical

12. Averaged Change in SRP Concentrations for the most urban Seattle
area streams (Thornton, Juanita, McAleer, Lyon, Forbes, Kelsey) 25 30 35 40 45 50 55 60
Mean Annual SRP conc. (µg/l)
1980
1985
1990
1995
2000
y = x r 2
= 0.42
Urban stream SRP concentrations
800
900
1000
1100
1200
1300
Mean annual nitrate conc. (µg/l)
y = -9x
= 0.31
Urban stream nitrate concentrations
36% decline in SRP
15% decline in NO3
WHY: BMPs, human behavior, catchment surface disturbance?

13. Long Term Conclusions:
Urban streams are enriched relative to forest streams with Phosphorus by % and with Nitrogen by 33%.
Stream TSS concentrations and Turbidity are more closely related to short term flow fluctuations than to land cover.
Inorganic nitrogen and phosphorus concentrations increase in forest streams and decrease in urban streams during storms.
Stream phosphorus concentrations peak during the summer, and nitrogen and sediment concentrations peak during the winter.
The most urbanized streams have had declines in SRP and nitrate concentrations during the last 20 years.

14. An Annual Time Series of Stream Phosphorus Transport
Issaquah - Forest
North - Mixed
Swamp - Mixed
Thornton - Urban
Daily TP
Weekly SRP
Daily TSS

15. Objective: to collect a high resolution stream phosphorus
concentration database in order to develop statistical time
series models of stream phosphorus transport.
Model structure:
Seasonal term
Spikeness term
Antecedent term
Rainfall term

16. SRP was on average 48% of TP
North Creek
250 TP
200
SRP
Overall TP varied by
± 50% from week to week
150
Phosphorus (µg/L)
100 50
2001/2000 A S J M F D N O
SRP varied by ± 20%
from week to week
SRP was on average 48% of TP

17. Soluble reactive phosphorus times series
North Creek 10 20 30 40 50 60
Soluble Reactive P (µg*L -1 )
Issaquah Creek
Predicted
Observed
Thornton Creek
Soluble Reactive P
(µg*L
Swamp Creek r 2
= 0.25
= 0.79
= 0.85
= 0.63
2001/2000 A S J M F D N O
Soluble reactive phosphorus times series

18. Stream flow times series
Issaquah Creek
North Creek
100 )
(cfs
Streamflow 10
Observed
Predicted 1
Swamp Creek
Thornton Creek
100 )
(cfs
Streamflow 10 1
2001/2000 A S J M F D N O
2001/2000 A S J M F D N O

19. SRP conc. = 18.1 - 16.3*(seasonal) + 0.961*(mean stream conc.),
where the seasonal term = monthly median flow/overall median flow,
and mean conc. = the respective stream flow weighted concentration. 10 20 30 40 50 60
Observed SRP (µg/L)
Predicted SRP (µg/L) r 2
= 0.84
Overall model
-20
-10 10 20
Stream Residual SRP (µg/L)
0.4
0.7
1.0
1.3
1.6
Normalized Seasonal Baseflow r 2
= 0.62
Seasonal baseflow submodel
-30
-20
-10 10 20
Seasonal Residual SRP (µg/L) 15 25 30 35 40 45
Vol. Wt. SRP (µg/L) r 2
= 0.77
Stream conc. submodel

20. Total phosphorus times series)
200
Issaquah Creek
North Creek -1
Observed r 2
= 0.49 r 2
= 0.55
Predicted
150
Total Phosphorus (µg*L
100 50
Swamp Creek
Thornton Creek
200 r 2
= 0.38 r 2
= 0.53
150
Total Phosphorus (µg*L-1)
100 50
2001/2000 A S J M F D N O
2001/2000 A S J M F D N O

21. Observed TP (µg/L) 100 10 Predicted TP (µg/L) 0.0 0.1 0.2 0.3 0.4
Partial r 2
Flow Wt conc.
Seasonal
Spikeness
Antecedent
Rainfall
Term 10
100
Observed TP (µg/L)
Predicted TP (µg/L)
y = 1.631x
0.878 r 2
= 0.71
0.6
0.5
0.4 2
Overall Model
Overall r
0.3
Individual Model
0.2
0.1
0.0
Issaquah
Swamp
North
Thornton

22. Inter-annual Conclusions:
Stream SRP concentrations are much less variable than TP concentrations, and SRP constitutes about 48% of TP.
Stream SRP concentrations follow a simple sine-wave annual cycle that is probably due to the relative contributions of groundwater and subsurface flows to stream flow.
Stream TP concentrations are highly variable and are strongly influenced by short term flow fluctuations.
Individual times series models for SRP were able to predict about 75% of the overall variability in the annual cycle, while individual TP models explained about 50% of the annual cycle.
Overall models for SRP and TP were able to explain 84% and 71% of the variability for these variables, respectively.

23. Still needed: Estimates of hydrologic pathways
Rainwater nutrient determinations
Surface flow and ground water nutrient determinations
Event based nutrient responses
A MECHANISTIC NUTRIENT TRANSPORT MODEL!