POTENTIAL CAUSES FOR MARKED WATER TEMPERATURE DIFFERENCES IN TWO ADJACENT STREAMS

A wide range of factors are known to affect the mean and variability of water temperature in headwater streams. Among these are surface topography, bedrock type, soil type and depth, vegetative cover, and local variations in groundwater contribution. We would expect most of these factors to be similar in two spatially adjacent, headwater streams, resulting in similar stream water temperatures. However, we measured persistent differences exceeding 3℃ in two headwater streams at their junction. In this study, we investigated the differences of several known stream temperature-control factors to determine if they could explain the observed temperature differences. To do this, we measured water temperature every 10 minutes for six months at several locations throughout a 2.14 km headwater stream network in a 50 ha watershed in southwest Virginia. We then compared the observed temperatures with other attributes of the surface and subsurface. We examined vegetation, topography, soil depth and drainage class, stream substrate, and bedrock geology. We then compared these data from the two watersheds in an effort to explain the variations in temperature of water in the two streams. Preliminary analysis suggests differences in aspect, channel length, and bedrock orientation may explain the differences in temperatures. Determining the causes of these large differences in stream temperature may help us better understand controls on stream water temperature.