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 352700, University of Washington, Seattle, WA 98195. 2King County Water & Land Resources, 201 South Jackson St #600, Seattle, WA 98104-3854.

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).

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.

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

Land Cover

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

Land Cover Versus Stream Nutrients: Normal Flows 20 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

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

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

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%

Seattle forest streams have 150% more DIN than typical forest streams 25 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

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 = -0.86x + 1747 r 2 = 0.42 Urban stream SRP concentrations 800 900 1000 1100 1200 1300 Mean annual nitrate conc. (µg/l) y = -9x + 18950 = 0.31 Urban stream nitrate concentrations 36% decline in SRP 15% decline in NO3 WHY: BMPs, human behavior, catchment surface disturbance?

Long Term Conclusions: Urban streams are enriched relative to forest streams with Phosphorus by 100-150% 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.

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

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

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

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

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

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

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

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

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.

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!