26. Nutrient Inputs Through Submarine Groundwater Discharge to Ariake Bay, Kyushu Island, Japan

Submarine groundwater discharge (SGD) is now recognized as an important pathway between land and sea. This study attempts to estimate the nutrient inputs through SGD to Ariake Bay. SGD rates and its quality along the coast of Ariake Bay in the Oura Region, Japan, were investigated. It was shown that the on-site SGD rate ranges from 0.01 to 20.52 μm/s, and SGD flows through the shallow confined aquifers, which consist of two kinds of rocks: basalt and pyroclastic rocks. The reduction reaction for SGD proceeded just up to denitrification. SGD associated with nutrient loads of N, P and SiO2 were estimated to be 1.40, 0.07 and 52.78 g m⁻² d⁻¹, respectively. This study demonstrates that SGD must be considered as a significant source of nutrient input to the coastal sea area in Ariake Bay.