Estimation of submarine groundwater discharge and its impact on the nutrient environment at Kamaiso beach, Yamagata, Japan

Submarine groundwater discharge (SGD) was estimated on the Kamaiso Coast, a coastal zone at the base of Mt. Chokai, Yamagata, using a continuous heat-type automated seepage meter and Lee-type seepage meter. Significant SGD was observed and it changed with tidal cycle; the SGD flux reached a maximum value of 200 cm/day. The contribution of fresh groundwater reached 20%. The concentrations of nitrate and phosphate at the SGD point were several times larger than those at observation points some distance from the SGD point. The nitrogen stable isotope ratios of nitrate at the points that were significantly influenced by SGD were lower than those at the points without SGD. The results of this study indicate that SGD quantitatively impacts the nutrient environment in the coastal zone and that nitrate contained in submarine groundwater is taken up by seaweed, one of the major primary producers.