DIURNAL, RAINFALL RESPONSE, AND LONGER PERIOD TEMPERATURE VARIABILITY IN TWO WATERSHEDS IN WESTERN MICHIGAN

Temperatures in river and stream systems affect wildlife, riparian vegetation, and aquatic ecosystems. Continuous water temperature data was collected during the summer of 2006 for Sand Creek, a large watershed of 14,245 hectares; and Little Mac Ravine, a small watershed of approximately 53 hectares. Little Mac Ravine watershed is heavily impacted by urbanization, while Sand Creek watershed is relatively unimpacted. Sand Creek sediment is primarily coarse sand with interbeds of gravel while Little Mac ravine sediment is comprised of clay with interbeds of medium to fine sand and abundant organic matter.

Temperature data exhibit diurnal, rainfall response, and longer period changes in stream temperature. These changes are a function of several variables including: 1) sediment substrate composition and thickness; 2) groundwater input and hyporheic flow; 3) urbanization/land usage in the watershed; 4) discharge volume and variability; 5) ambient air temperature and solar insolation; 5) the amount of vegetation and cover; and 6) the amount of suspended particulate matter.

Water table data, collected at monitoring wells adjacent to temperature gages, was used to evaluate the amount of groundwater input to each stream. Preliminary groundwater data suggest that both streams are gaining streams. Hourly air temperature data, solar insolation, and solar energy input were compared with stream temperatures to evaluate the contribution of ambient air temperature and solar insolation.

Comparing these two very different watersheds gives us a better understanding of the relative contribution of the factors that affect stream temperature. This may provide valuable insight into methods to restore impacted streams to a more natural temperature regime.