Print PageThe groundwater–surface water interface, consisting of shallow groundwater adjacent to stream channels, is a hot spot for nitrogen removal processes, a storage zone for other solutes, and a target for restoration activities. Characterizing groundwater-surface water interaction is difficult because of physical obstacles to sampling. We present results from high spatial-resolution surface water nutrient sampling (“sampling slam”) that revealed groundwater-surface water interactions and biochemical patterns at two streams in the Chesapeake Bay watershed.
Results/Conclusions
Despite considerable reach-scale variability, we observed consistent longitudinal patterns in biogeochemistry. For example, specific conductivity and chloride clearly showed the effects of road salts at storm-water outfall pipes and where the stream flowed under a major freeway. Groundwater was a reservoir for chloride, leading to chronically elevated surface water concentrations. Our sampling slam approach also revealed strong, consistent relationships among dissolved organic carbon, nitrate nitrogen and sulfate that were driven by both biological transformations (e.g. denitrification) and by hydrologic connectivity between groundwater and surface water. Therefore, nitrogen transformations that occur in groundwater could be reflected in surface water chemistry patterns when streams are at base flow. Our results demonstrated the importance of understanding groundwater ecology in order to interpret stream chemistry patterns and subsequently apply best management practices. Monitoring at high spatial resolution and beyond the stream-reach scale is recommended for evaluation of biogeochemical function in streams, especially in urban ecosystems and where there are various point and non-point sources of nutrients.
