Influence Of Submarine Groundwater Discharge On Nutrients Balance In Coastal Waters

Submarine Groundwater Discharge (SGD) is now recognized as an important process of Land-Ocean Interactions in the Coastal Zone(LOICZ),which acts as a significant pathway for the transport of water and dissolved constituents from land to sea,and plays an important role on coastal ecosystem that can not be ignored.China has long shoreline,and coastal zones are most polluted by nutrients like nitrogen and phosphorus and so on. Unfortunately, SGD is often ignored as pollutant source, and is still not clear about the mechanism that how SGD works on nutrient balance of coastal waters, which has significance for coastal environment management. In this paper, experiments (laboratory simulation and field investigation) were carried out on SGD, and detailed study on water quality, especially form and spatial and temporal distribution nutrient distribution of nutrients in groundwater and seawater was made, also isotope 226Ra was measured and water balance method was used to obtain the flux of SGD.Results which we got are as follows:1.Simulation experiments indicated that during the mixing of groundwater and seawater, there are three areas temporally and spatially with different physical and chemical properties if without any disturbance:homo-groundwater area, groundwater-seawater equivalence mixing area, homo-seawater area. Content and relative components of nutrient are extremely influenced by changing of pH value and temperature, directly and indirectly.2.Site investigation was carried out at Aiwan Bay and Zhujiajian Island of Zhejiang province.Through analysis of the shallow groundwater and seawater, it indicated that SGD indeed exists, which is supported by evidence from isotopic trace. This phenomenon can also be proved by the Characteristic of spatial distribution of salinity, pH and nutrients.3.The quality of coastal water suffered significant changes from SGD, including pH, salinity and other basic water quality parameters.In particular, the relative content of nutrients and their spatial distribution are subjected to large difference both in the horizontal direction and depth.4.Site investigation also showed that contents of carbon, nitrogen and phosphorus in groundwater are much higher than those in seawater, and the corresponding ratio of them has consistent performance.SGD had changed the nutrients structure of coastal water, and living environment of aquatic organisms was influenced severely.5.The SGD fluxes at Dongsha Bay of Zhujiajian were estimated from isotope 226Ra and water balance method. Results showed the big differences between the two fluxes. According to the estimation of net groundwater flux by water balance modle, fluxes of nutrients inputting to Dongsha Bay were calculated. Nitrogen, phosphorus and silicon derived from land-based sources of groundwater were 3.02,0.033 and 22.50 tons/year, respectively.