Evaluation of Submarine Groundwater Discharge(SGD) effects on the fisheries resources based on stable & radio isotopes techniques

陆地淡水和相关的养分通量影响沿海地区的初级生产。然而，与Chikugo河等河流水不同，有明湾地下水排放对沿海生态系统的贡献尚未得到很好的评价。在本研究中，^<222> Rn被认为是地下水的一个很好的指标，因为有明湾西海岸地下水中^<222> Rn浓度比河水中高一到三个数量级。^<222>基于采样点累积降雨量和水深标准化的Rn分布成功地反映了地下水流量的空间变化。此外，由于^<222> Rn的空间分布与5个不同地点测量的实际地下水通量相关，因此可以通过^<222> Rn的分布来评估地下水总通量。地下水径流中的养分通量也存在空间差异；7. 8 ~ 510 kg-N天^ DIN（溶解无机氮）<-1>。5比3。溶解无机磷（DIP）为9 kg-P天^<-1>，最大值在岛原地区，那里的地下水通量和地下水中的营养物浓度都最高。另一方面，利用硝酸盐中δ^<15> N和有机质中δ^<13> C和δ^<15> N的研究未观察到地下水养分对近海海洋生态系统的影响。在无大河的有明湾西海岸，地下水是提高初级生产的重要营养来源，为双壳类提供了良好的食物来源，并形成了绿色大型藻类的大量繁殖。但是，地下水营养物的影响范围仅限于浅海沿岸地区。

Terrestrial freshwater and associated nutrient fluxes affect primary production at coastal areas. Differently from river water like Chikugo River, however, the contribution of groundwater discharge to coastal ecosystem has not been well evaluated in Ariake Bay. In this study,^<222> Rn was considered as a good indicator of groundwater, because^<222> Rn concentrations in groundwater along the west coast of Ariake Bay were one or three orders of magnitude higher than those in river waters.^<222> Rn distribution standardized based on the accumulated rainfall and water depth at the sampling location successfully indicated a spatial variation of groundwater discharge. Furthermore, total groundwater fluxes were evaluated from the^<222> Rn distributions, because spatial distributions of^<222> Rn were correlated with actual groundwater fluxes measured at 5 different locations. Nutrient fluxes through the groundwater discharge had also spatial variation ; 7. 8 to 510 kg-N day^<-1> for DIN(dissolved inorganic nitrogen), and 0. 5 to 3. 9 kg-P day^<-1> for DIP(dissolved inorganic phosphorus), with the maximum values at Shimabara area, where both groundwater fluxes and nutrient concentrations in groundwater were highest. On the other hand, the impact of groundwater-derived nutrients on marine ecosystem at offshore area was not observed from the researches usingδ^<15> N in nitrate andδ^<13> C andδ^<15> N in organic matter. Along the west coast of Ariake Bay, where there are no big rivers, groundwater can be important nutrient sources to enhance primary production, resulting in good food sources for bivalves and blooming of green macroalgae. However, the influential areas of groundwater-derived nutrients would be limited in shallow coastal areas.