| | | 5.1 Introduction |
Non-point source nutrient fluxes are a growing issue in the assessment of coastal ocean and estuarine biogeochemistry. Surface water discharge has long been recognized as an important source of dissolved compounds, including nutrients, to the coastal zone and the transport of river-borne dissolved constituents continues to be a well-studied realm of environmental science [312][42]. River discharge has been gauged for centuries and long-term studies have been performed to assess the chemistry of fluvial discharge and its biogeochemical impact on estuarine and coastal ocean waters (e.g., [312][421][369][92][284]). More recently, environmental regulators and researchers have come to recognize the importance of non-point source discharges, including land surface runoff and atmospheric deposition of dissolved and aerosol compounds [362]. As has been discussed elsewhere in this text, both fluvial discharge and non-point source discharges play an important role in nutrient fluxes to the coastal zone.
In recent decades, researchers have begun to turn attention to an underground path to the coastal oceans: submarine groundwater discharge. Submarine freshwater springs in the coastal ocean were used as sources of potable water for sailors and coastal residents alike for at least 2,000 years [268]. Originally considered a novel process, limited to the existence of occasional springs, it has taken some time for the true extent of coastal groundwater discharge to be recognized. In research initiated over the past 25 years, we are becoming aware of the fact that groundwater inputs account for a significant portion of the water and chemical flux to the coastal zone.
The role of groundwater transport has gained increasing attention in both marine [113] and freshwater [91] aquatic research, particularly in light of research showing considerable groundwater fluxes directly to estuaries and the coastal ocean (e.g., [64][317]). The use of new groundwater tracers and the expansion of the scope of submarine groundwater discharge research has led to the still-growing realization that the direct discharge of groundwater to coastal zones is not a novel process, but, does indeed occur "anywhere that an aquifer ...is connected hydraulically with the sea through permeable bottom sediments and the [potentiometric] head is above sea level" [251].
| | | 5.1 Introduction |