SUBTERRANEAN ESTUARIES ARE DYNAMIC SYSTEMS: WHAT DOES THIS MEAN FOR POLLUTANT INPUTS TO COASTAL WATERS? (Invited Presentation)

Predicting pollutant inputs from groundwater to coastal waters is complex as the magnitude and timing of these inputs are controlled by the specific pollutant sources, groundwater flow paths, and by biogeochemical processes occurring along these flow paths including within subterranean estuaries. Subterranean estuaries are spatially heterogeneous and dynamic systems with multiple hydrologic forces acting on the systems across a wide spectrum of timescales from decadal and seasonal time-scales to high frequency sub-second wave and current action. Further the physical interface between the ocean and aquifer is continuously evolving due to short- and long-term coastal erosion and accretion. This presentation will examine recent advances in our understanding of subterranean estuaries as dynamic systems and what this means for the way in which we conceptualize these systems, conduct field investigations, interpret field data, and quantify and predict pollutant inputs to coastal waters via submarine groundwater discharge. The presentation will focus on three examples: i) impact of tides and waves on flows and salt transport in subterranean estuaries and submarine groundwater discharge; ii) impact of tides and waves on terrestrial nitrogen inputs to coastal waters; and iii) impacts of coastal shoreline change on the timing of groundwater nutrient inputs to coastal waters. While the presentation will cover examples that focus on the impacts of tides, waves and shoreline change, the findings will be generalized for application in understanding and evaluating the impacts of other forces acting on subterranean estuary systems.