Impact of Direct Nutrient Inputs via Groundwater on Near-shore Zones of Large Water Bodies: Regional Scale Approaches

English Abstract:

Direct groundwater discharge to near-shore zones of large water bodies (lakes and oceans) is a pathway for freshwater and associated dissolved nutrients. However, it is hard to quantify, especially at regional to continental scales. Some coastal ecosystems are at particular risk through eutrophication, hypoxia, or harmful algal blooms, and while local field methods or models are available, targeted research at larger scales is scarce. Here, we review available assessments of direct groundwater discharge and solute transport, using examples from large inland water bodies (here, the Laurentian Great Lakes), as well as coastal areas surrounding tropical islands. We demonstrate example approaches, reaching from the use of the ratio of coastline length to hinterland area as first-order approach to estimate the importance of direct groundwater discharge compared to rivers (Moosdorf et al. 2015), to the use of large-scale hydrological and hydrogeological models. Information on near-shore groundwater quantity and/or baseflow, combined with assessments of nutrient concentrations in groundwater bodies, can set an upper boundary for the potential contribution, and identify likely hotspots of nutrient delivery via this discharge pathway.

Moosdorf N., Stieglitz T., Waska H., Dürr H.H., Hartmann J., (2015). Submarine groundwater discharge from tropical islands: a review. Grundwasser, doi:10.1007/s00767-014-0275-3.