Landscape Predictors of Groundwater Influence on Stream Temperature in Forested Headwater Catchments

Abstract:

Understanding groundwater contribution to stream temperature is critical for predicting climate effects on thermal habitat in streams. Recent studies suggest that in forested watersheds, groundwater influences on water temperature can be inferred by air-water temperature regression models. The goal of this research is to identify landscape attributes that predict groundwater influence at the stream reach spatial scale. We examined estimates of groundwater influence at 81 sites within nine watersheds in Shenandoah National Park, Virginia, USA, over two summers (2012-2013) and determined effects of varying groundwater contribution on thermal sensitivity (extent to which stream temperature changes with unit change in air temperature). We used a GIS to derive a series of landscape factors based upon gradients in geomorphic, geological, and network topology parameters to predict the spatial distribution of groundwater influence on thermal sensitivity during baseflow summer months. We found that groundwater thermal influence was patchy, varying as much within as among watersheds, and that spatial variation in groundwater contribution is influenced by complex interactions among landscape attributes. Moreover, although groundwater influence was relatively consistent among summers at most sites, it changed dramatically at others. There are indications that recent (within one year) precipitation patterns are strongly influencing these transient groundwater sites.