Non-point-source impacts on stream nutrient concentrations along a forest to urban gradient.

Area of Science:

• Environmental Science
• Water Quality Research
• Urban Hydrology

Background:

• Urban non-point-source pollution poses a significant threat to regional water quality.
• Understanding the impact of land cover on stream ecosystems is crucial for effective environmental management.

Purpose of the Study:

• To determine the impact of urban non-point-source pollutants on stream water quality in the greater Seattle region.
• To analyze the relationship between land cover type and nutrient/sediment concentrations in streams.

Main Methods:

• Statistical analysis of a 10-year dataset of stream nutrient and sediment concentrations.
• Comparison of water quality parameters across streams with varying percentages of urban and forest land cover.

Main Results:

• Stream phosphorus concentrations showed a moderate correlation (r2=0.58) with catchment land cover.
• Urban streams exhibited significantly higher total phosphorus (95%) and soluble reactive phosphorus (122%) compared to forested streams.
• Nitrogen concentrations showed a weak correlation (r2=0.19) with land cover, and nitrate, ammonium, and total suspended solids did not vary significantly.

Conclusions:

• Urbanization markedly increases stream phosphorus concentrations and modestly increases nitrogen concentrations.
• Despite increases, nutrient concentrations in Seattle urban streams are lower than those reported for agricultural streams.
• Land cover is a key factor influencing phosphorus levels in urbanizing watersheds.