EVALUATION OF LAND-USE CHANGE IN RELATION TO P LOADING IN TWO SMALL WATERSHEDS, MONROE COUNTY, NY

Water quality of streams and the coastal zone of Lake Ontario have received increased attention in the past several decades. It is considered that phosphorus loading plays a significant role in the degradation of water quality in this area, and results from land-use changes. Unfortunately, attempts to quantify the impacts of land-use practices on the export of P from small watersheds are few. This ongoing investigation uses a stressed stream segment analysis approach to evaluate relationships between recent land-use change and phosphorus export for two small watersheds of the Lake Ontario lake plain region near Rochester, NY. A survey of the watersheds has identified three segments for continued long-term monitoring of both base flow and storm event conditions. Total phosphorus (TP), soluble reactive phosphorus (SRP) and turbidity are the key parameters indicating impact. TP concentrations, representative of other monitored parameters, are found to range from a low of 8.1 ug/L during base flow to as much as 1144.5 ug/L during storm flow events. Evaluating TP concentration data spatially identifies stream segments where TP loading is increases downstream by as much as one order of magnitude. The three segments identified are currently mixed land-use, but have been under significant development pressure in recent years. Analysis of land-use has shown that in two of the three segments, land-use change is significantly greater within the segment as compared to the entire watershed. The analysis was completed within a GIS, and compared land-use categories designated for the watershed by the USGS in 2001 with current land-use identified using 2005 orthophotography. Using the change in the sum of low, medium and high density development from 2001 to 2005 as a measure of land-use change shows higher rates of change within two of the identified segments. For example, within the Northrup Creek watershed, developed land-use increased from 13.9% developed in 2001 to 19.2% developed in 2005. Within one of the identified segments in this watershed, developed land-use increased from 4.9% in 2001 to 34% in 2005. Although the segment represents only a small portion of the watershed, land-use change appears to be a critical factor within this segment related to P loading.