Subterranean Groundwater Discharge and Marine Ecosystems
The discharge of subterranean groundwater serves as a geochemical conduit from freshwater aquifers to coastal waters. In arid regions, such as the Dalmatian coast, input via submarine groundwater discharge (SGD) frequently exceeds riverine inputs creating pockets of elevated primary productivity and coastal nursery habitat for many marine species. SGD into coastal waters is important for the maintenance of coastal productivity and support of nearshore ecosystems. Anthropogenic impacts upon on aquifers can destabilize coastal ecosystems two ways: via reduction in SGD and the influx of contaminants. With coastal development, there is an associated increase in water usage. As water is withdrawn from the aquifer, there is a corresponding inland increase in saltwater intrusion, reducing subterranean groundwater flows and indirectly reducing primary productivity. Ecosystems can also be destabilized through the discharge of contaminated water, either in the form of excessive nutrients or as heavy metals, into coastal habitats. Continued residential and agricultural development of near-shore areas worldwide leads to increased inputs of nitrogen and phosphorus into groundwater. Trace metals can be influenced by human activity and are toxic to aquatic organisms. Overlooking the contribution of groundwater to the productivity of coastal ecosystems could lead to serious misinterpretation of ecological data. Due to the long residence time of water in the subterranean environment, abatement would take decades. Therefore, determination of flow rates and the quantitative assessment of the impact subterranean groundwater discharge has upon organisms and ecosystems are the first steps toward understanding the subterranean environment that connects the land and sea.