Water Temperature Controls in the Sheepscot River, Maine
The Sheepscot River watershed is 590 km2 located in mid-coast Maine. Two branches comprise the river: the main stem and the West Branch, which merge in North Whitefield before flowing into the Gulf of Maine. The Sheepscot River has an imposed form that is strongly influenced by the Norumberga Fault Zone and it flows through glacial deposits. The watershed has a temperate climate because of its location in mid-latitudes in the northern hemisphere. Water temperatures vary in the Sheepscot River over time and along the length of the river. The temporal and spatial variability of the river is due to air temperature, precipitation, discharge from the Palermo Fish Rearing Station, Long Pond, tree shade, confluence, and drainage area. Analysis of these hypothesized controls revolves around field water temperature measurements made between August 2005 and January 2006 and data collected from the North Whitefield gauging station. Supplementary digital spatial data from the Maine Geographic Information Systems data set were also used. Field measurements were taken at seven sites directly upstream and downstream of assumed controls. Climactic features of the watershed exert the main control over the entire river. Air temperature is the first order controls on water temperatures. Precipitation has some effect on water temperature but of less significance than air temperature. The river system has three areas that are affected by different combinations of the other controls: the upper main stem, the West Branch, and the lower main stem. Discharge from the Palermo Fish Rearing Station is the second major controlling factor of water temperature in the upper main stem. Its buffering effect is diluted downstream. Long Pond also affects the upper main stem by warming the water in the summer and cooling it in the winter. Drainage area explains variability in the West Branch and lower main stem. As drainage area increases downstream, water temperatures are controlled by more integrated factors. As a result of this the West Branch fluctuates more than the main stem because it has a smaller drainage area. Temperatures in the downstream reaches are less sensitive to any single control. Confluence and tree cover exert less influence over the system than other controls.