STREAM TEMPERATURE DYNAMICS AND INFLUENCES IN URBAN HEADWATER STREAMS, GREENVILLE, SOUTH CAROLINA

Stream water temperature governs many in-stream physical and chemical processes that affect overall water quality and stream ecosystem health. Urbanization can impact stream water temperature through a myriad of activities including runoff from impervious surfaces, industrial dumping, and loss of riparian cover, among others. Headwater stream temperatures are particularly sensitive to these activities given their limited discharge.

The purpose of this study was to examine the temperature dynamics and to identify the impacts of suburban/urban development on stream temperatures along two urban headwater stream reaches in Greenville, South Carolina. In each reach, five temperature loggers were evenly deployed along a 650 meter transect that began at the headwater source. Stream stage was monitored along each reach using a pressure transducer. Stream temperature and stage height were recorded at synchronous five minute intervals from June through October 2009.

Stream temperatures were influenced by a combination of natural drivers and anthropogenic influences. Water temperatures fluctuated daily in response to the diurnal increase and decrease in air temperatures. The size of the diurnal variability varied based on distance downstream, relative proportions of groundwater to surface water contributions, and the extent of riparian cover. Temperature sensors farther downstream generally showed larger temperature variability and warmer temperatures overall. In addition to these natural drivers, anthropogenic influences including industrial dumping, residential irrigation, and urban runoff had measurable, and in some cases significant, impacts on stream temperature. Industrial wastewater release from a poultry processing plant at one site resulted in daily temperature spikes of as much as + 1.1C or - 3.88C downstream of the suspected discharge point. Urban runoff from summer storms consistently caused essentially instantaneous (< 15 minutes) temperature increases up to 5.6C at both sites. Even lawn irrigation from an abutting property owner resulted in a daily 0.5C spike in temperature at one site. The ecological significance of these anthropogenic impacts is unknown, but given the magnitude and often abrupt nature of the observed changes could be consequential, and is an area for future study.