Freshwater ecosystems play an important role in the quality of life in urban areas by providing a variety of ecosystem services including recreation, water supply, flood damage reduction and wildlife habitats. Most of these ecosystem goods and services are water-quality related and are negatively impacted by many anthropogenic actions. The overall focus of this study is to assess how land use changes can impact water quality and ecosystem services of a major urban freshwater system in a rapidly urbanizing basin. Understanding the consequences of future watershed development on water quality and habitats can inform management and restoration efforts. Central Puget Sound and Lake Sammamish were selected as study systems. Central Puget Sound is the anchor of the Pacific Northwest and one of the fastest growing regions of the United States. Lake Sammamish is a major recreational destination and a valuable natural resource as urban wildlife refuge and habitat for the native kokanee salmon. The Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) freshwater models are applied to different land use scenarios that illustrate increasing gradients of urbanization for the 2005-2060 time-period and alternative land development under both permissive and more constraint environmental policies. Values of phosphorus export (Kg/ha) generated by the InVEST models serve as inputs to a dynamic, deterministic total phosphorus simulation model developed and applied to Lake Sammamish.
Results/Conclusions
Preliminary results revealed that by 2050 urbanized areas will cover about 25% of the Central Puget Sound region. Urban expansion will occur at the expense of agricultural and forested regions that are projected to decline about 3% and 12%. Developed land areas have a higher nutrient export coefficient compared to forested land and will likely be a principal source of excess loads of nitrogen and phosphorus runoff across the watershed. As a result, the increased level of external nutrient loading could be an important factor leading to higher productivity and water quality impairment in Lake Sammamish. Under these scenarios, strict implementation of nutrient management practices will be necessary to offset the negative impact of urbanization on water quality and related ecosystem services. Estimating changes in productivity and freshwater ecosystem service provisions under different gradients of urbanization can be valuable to develop sustainable watershed land-use planning.