7/1/2001 - 6/30/2003
- Stephen Gaffield, WGNHS
One of the most difficult challenges in managing coldwater stream fisheries is understanding the controls of summer water temperature, which typically limits the distribution of brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta). It is widely recognized that Midwestern streams are cooled by groundwater; however, stream-channel shape and shade from riparian vegetation also have an important impact. Human activities in the riparian zone and throughout a watershed can impact stream temperature by altering shade from vegetation, increasing stormwater runoff and channel erosion, and reducing groundwater recharge and stream baseflow. A lack of detailed understanding of these interactions and the tools to evaluate them makes habitat-management decisions difficult. The objective of this study was to develop decision-making tools for watershed managers by combining field monitoring during the summer of 2001 with two mathematical modeling exercises. First, we tested the model developed for the Driftless Ecoregion of Wisconsin, based on a stream-temperature modeling technique developed for the other three major ecoregions in Wisconsin. This model predicts stream temperature as a function of groundwater inflow, channel shape, weather conditions, and shade from riparian vegetation. The five streams tested are in the Northern Lakes and Forests, the North-Central Hardwood Forest, and the Southeast Wisconsin Till Plain Ecoregions. Second, we linked this stream-temperature model to two additional models of groundwater recharge and groundwater flow for the Rowan Creek watershed in Columbia County. Groundwater recharge is affected by human land uses (such as the addition of paved surfaces) that change the ability of the soil to absorb precipitation and snowmelt. Changes in recharge to the groundwater flow system can affect the groundwater discharge that maintains stream baseflow in dry weather. We tested these linked models as a decision-making tool for watershed managers to predict the impact of future land-use changes on stream temperature.