Evaluation of benthic nutrient fluxes and their importance in the pelagic nutrient cycles in Suo Nada, Japan

The benthic nutrient fluxes in Suo Nada, in the western part of Seto Inland Sea, Japan were estimated seasonally in 2002, and their contribution to the pelagic nutrient cycle was evaluated. The horizontal distributions of inorganic phosphorus (DIP), ammonia and dissolved silica (DSi) concentrations in the pore water of the surface (0-3 cm) sediments were high in the western part, indicating a eutrophic condition relative to the other parts. Seasonally, the highest nutrient concentration in the pore water was observed In summer, as reflected by the increasing decomposition rate of organic matter. Multiple regression analyses revealed significant positive effects of add volatile sulfide (AVS) and temperature on the DIP flux and also significant positive effects of ignition loss (IL) along with these two parameters on the dissolved inorganic nitrogen (DIN) flux. Temperature, IL and redox potential (Eh) were effective on DSi. The estimated DIP, DIN and DSi fluxes from the sediments were relatively high or equivalent to the total inputs from rains and rivers in annual average, with high values in summer of 2-3-fold higher than the other sources (rain plus rivers). Thus, it is concluded that the benthic nutrient fluxes play an important role in the pelagic nutrient cycle of the Suo Nada ecosystem.