Citation:

Mayer, P., C. Cooper, K. Forshay, S. Kaushal, M. Langland, D. Low, D. Merritts, G. Sivirichi, AND R. Walter. Approaches to characterizing biogeochemistry effects of groundwater and surface water interaction at the riparian interface. Presented at AWRA's 2012 Summer Specialty Conference - Riparian Ecosystems IV: Advancing Science, Economics, and Policy, June 27 - 29, 2012.

Impact/Purpose:

Presentation for the American Water Resources Association's 2012 Summer Specialty Conference - Riparian Ecosystems IV: Advancing Science, Economics, and Policy, Denver, CO, June 27-29, 2012

Description:

Groundwater-surface water interaction (GSI) in riparian ecosystems strongly influences biological activity that controls nutrient flux and processes. Shallow groundwater in riparian zones is a hot spot for nitrogen removal processes, a storage zone for solutes, and a target for restoration activities. However, characterizing GSI and, in turn, nitrogen transformation, is difficult because of physical obstacles to sampling. We present results from sampling at various spatial and temporal scales including high spatial-resolution surface water nutrient sampling (“sampling slam”) that revealed GSI and biochemical patterns in streams of the Chesapeake Bay watershed. Despite considerable reach-scale variability, we observed consistent longitudinal patterns in biogeochemistry along streams such as chloride from road salts. Groundwater was a reservoir for chloride, leading to chronically elevated surface water concentrations. High temporal resolution sampling 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. Water table fluctuations in the riparian zone controlled subsurface redox conditions which dictated nitrogen dynamics. Microbial activity confirmed that subsurface sediments were actively removing nitrate nitrogen, especially when more organic carbon was available for microbial respiration. Relatively small inputs of organic carbon corresponded to large reductions in ground water nitrate, especially where agricultural inputs of nitrogen were high. Prehistoric wetland sediments were significantly better able to support denitrification than so-called “legacy sediments” deposited in fl

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