PS 44-187 - Projecting the consequences of future forest loss to urbanization on water quality across the Savannah River basin

Abstract: More than any other land cover, forests provide the greatest benefits for stable, high-quality water resources, but the ecosystem services forest provide for water are threatened by land cover change. Growing, urbanizing populations are creating landscape mosaics with increasing urban land cover. In the Southeast US, expanding urban development most frequently occurs on previously forested land. Such conversions can increase nutrient and sediment loads, degrading water quality and aquatic ecosystem health, while increasing water treatment costs. Understanding these potential consequences is important for the development of mitigation strategies including forest conservation. With this motivation, we quantified the role of forest land cover in supporting water quality in the approximately 7.2 million ha Savannah River Basin, USA under current and potential future conditions in 2070 using the Soil and Water Assessment Tool (SWAT) hydrologic model with scenarios of future climate and land cover.



The Savannah River basin is approximately 70% forest, 4% other natural (wetland, water, shrub, grassland), 10% agriculture (pasture and crop), and 9% developed. Within the basin, catchments with the greatest extent of forest cover generally had the lowest yields of sediment and nutrients (total phosphorus, total nitrogen). Nutrient yields are greatest in the upper portion of the watershed (ie) Broad River subbasin) as well as near population centers, including Athens, GA and Greenville, SC. Downstream, nutrients are concentrated near the cities of Augusta and Savannah. Sediment yield is greatest upstream of Augusta, GA. An envelope of future scenarios suggests a loss of between 3-4% forest (81,759- 109,012 ha) and 2% agriculture (54,506 ha) for a 4-6% gain in developed land cover (109,012- 163,518 ha) basin wide. Projected loss of forest occurred in population centers but also in rural areas, suggesting potential impacts to water quality throughout the watershed. Forecasts of future water quality will be used to identify particularly vulnerable areas of aquatic habitat and drinking water intakes where forest conservation might be prioritized.