A Framework for Trading Phosphorus Credits in the Lake Allatoona Watershed

Abstract

Lake Allatoona is a large reservoir northeast of Metropolitan Atlanta threatened by excessive algal growth. Rapid population growth has occurred in the southern part of the watershed and poultry combined with beef cattle production is an important activity in the more rural northern part of the watershed. This paper presents preliminary results from a project, that integrates research, education and extension activities to develop a framework for trading phosphorus (P) credits between point and non-point sources in the Lake Allatoona watershed. It shall describe the process being used to monitor 12 first order streams in forested and poultry watersheds to determine P loading based on land use and to model the entire watershed. Calibrated SWAT modelswere used to estimate of the annual P load to Lake Allatoona in 1992 and in 2001 after significant changes occurred in land use. Land cover data from 1992 and 2001 showed that forest land use decreased during this period by about 20% and urban and pasture land uses increased by about 225% and 50%, respectively. Our simulation results showed that the P load to Lake Allatoona increased from 174 Mg to 239 Mg, which were 87% and 118% of the total P annual cap (201 Mg) set by the GA Environmental Protection Division for discharge into Lake Allatoona. In 1992, pasture was the largest source, contributing about 36% of the total P load to Lake Allatoona, followed by forest, point sources, and urban land uses, which contributed 26%, 23%, and 12%, respectively. A decade later, the largest P source was still pasture which contributed 47% of the total P loading to Lake Allatoona. Point source P dropped to 10% while the contribution from urban land use increased to 27%. Permit limits on poultry processing plants reduced the point source P loads but increasing urban land use increased non-point sources of P. After presenting some results from these efforts, it will briefly discuss planned efforts to establish a trading program in the watershed.