Oral Abstract Details

Author(s):
Emile Elias, Dr. Mark Dougherty

Affiliation:
Auburn University

Presentation Type:
Oral

Topic Area:
Monitoring and predicting human influences on landscapes and ecosystems

Abstract Text:
For two decades high total organic carbon (TOC) levels in Converse Reservoir, a water source for Mobile, Alabama, have concerned water treatment officials due to the potential for disinfection byproduct formation. TOC reacts with chlorine during the drinking water treatment to form disinfection byproducts, some of which are carcinogenic and regulated under the Safe Drinking Water Act. This study evaluates how urbanization will alter watershed derived total nitrogen, total phosphorus and TOC inputs to a source water reservoir. Converse watershed, on the urban fringe of Mobile, is projected to undergo considerable urbanization by 2020. Base scenarios using 1992 and 2001 land cover are coupled with 2020 projections of land use and applied to 62 subwatersheds within the greater 267 km2 watershed. The Loading Simulation Program C++ watershed model is used to evaluate changes in nutrient concentrations (mg L-1) and loads (kg) to Converse Reservoir. From 1992 to 2020 simulated urban and suburban growth of 52 km2, which is an increase in urban area of 19% to a total of 22%, resulted in more than doubling TN and TP total loads and median monthly loads (kg) to Converse Reservoir. TN and TP loads increased by 114 and 120%, respectively. From 2001 to 2020 simulated urban and suburban growth of 32 km2, which is an increase in urban area of 12% to a total of 21%, resulted in an increase of 51 and 54% in TN and TP loads (kg), respectively. Results indicate total streamflow increased by 13 to 22% due to urbanization. Urban growth generally increased monthly flows, but led to lower flows in drought months. Results indicate future median TN and TP concentrations (mg L-1) are 37 and 75% greater than 1992 concentrations, but TOC concentrations are 10% lower in future urban scenarios. An increase in urban flow caused TOC loads (kg) to increase by 14 to 28%, despite lower future TOC concentrations (mg L-1). The largest average increase in monthly watershed-derived TOC concentrations from TOC loading occurs in July, ranging from 0.20 to 0.42 mg L-1. This increase may necessitate additional drinking water treatment due to watershed urbanization, depending upon existing reservoir TOC concentrations. Post-urbanization source water TOC concentrations will likely increase more than predicted by the watershed model, which simulates only watershed-derived increases in TOC. The larger TP loads following urbanization will likely support increased algae growth, thereby increasing internally generated and overall TOC. Expected urbanization by 2020 increased TN and TP loads by at least 50% and TOC load by at least 14% to a drinking water supply reservoir. Unless additional drinking water treatment is implemented to remove increased TOC, the result of urbanization in this source watershed is increased carcinogenic disinfection byproducts in drinking water.