One-quarter of the global population lives in coastal regions; these people subside onless than 10% of the global renewable water supply. Coastal populationsare expanding rapidly, while potable coastal water supplies are decreasing due to over-pumping and sea water intrusion into coastal aquifers. This is a global problem that affects almost all coastlines of the world.
This talk is not about potable water supplies. Instead I will focus on some biogeochemical consequences of sea water intrusion into coastal aquifers. First I will demonstrate that sea water intrusion has affected coastal aquifers worldwide and that these changes will likely become greater as coastal populations and sea level increase. Next I will discuss how replacing fresh water with sea water in coastal aquifers changes the biogeochemical reactions that occur within these systems. Finally I will show that these aquifers, which we call subterranean estuaries, exchange reaction products with the coastal ocean. The flow into the ocean is called submarine groundwater discharge (SGD).
Continued over utilization of fresh water in coastal aquifers and other anthropogenic changes will lead to inland expansions of subterranean estuaries. This expansion may lead to greater total SGD fluxes of nutrients, carbon, and metals because the biogeochemical reactions that affect their concentrations may operate over larger spatial scales and affect aquifers that have not been in contact with seawater for thousands of years.
