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

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

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%

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

Averaged Overall Change in Urban Stream SRP Concentrations Urban stream nitrate concentrations 60 1300 y = -0.86x + 1747 y = -9x + 18950 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

Conclusions: Urban streams are enriched with Phosphorus by about 100-150% 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.

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