7/1/2014 - 6/30/2016
- Steven Loheide, UW-Madison
Understanding surface water –groundwater (SW-GW) interactions at large scales is critical for effective, conjunctive management of these waters as a single resource and understanding SW-GW interactions at a local scale, including the process of hyporheic exchange, is essential for predicting biogeochemical and ecosystem processes including nutrient processing, contaminant attenuation, and thermal buffering. Stream ice formation is a rarely recognized driver of stream-aquifer interactions, though it may affect these interactions across a range of spatial scales. When ice forms on a channel, additional resistance to flow is created beneath the ice layer causing an abrupt increase in stage during stream freeze and a drop in stage during thaw. This fluctuation in stream stage changes the hydraulic gradients between the channel and the groundwater system, altering SW-GW interactions. This project will use a three-pronged approach to investigate the hydrologic impacts of less harsh winters on SW-GW interactions in Wisconsin by addressing the following three research questions: I) How do ice cover regimes vary across stream types (order/size), and how have these regimes changed over the period of historic observations? II) What effects do ice cover regimes have on SW-GW interactions across a range of stream types and field conditions? III) What is the magnitude of ice formation-induced changes to SW-GW interactions and how has observed climate change altered SW-GW exchange? First, we will address question I using an observational approach by analyzing historical USGS stream stage records. Secondly, this research will address research question II using a field campaign to directly monitor the effect of ice formation on surface water and groundwater levels at a suite of field sites. Third, we will use a modeling framework to simulate and quantify SW-GW exchange across a gradient of stream types and through time to address research question III.