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Study focus: There have been far more studies on how the variability in surface water discharge affects production of animal communities in aquatic ecosystems while less information has been accumulated on the mechanisms of how the groundwater supply works. Study region: Physical and biological surveys were conducted to test the hypothesis that high level of submarine ground water discharge enhances species richness, abundance and biomass of fishes and invertebrates in coastal waters of Obama Bay, Japan, where a high contribution of nutrients (ca. 65% of phosphorus) to total provided through all freshwater has been reported. Survey for horizontal distribution of radon-222 (222Rn) concentration showed high levels of submarine groundwater discharge in the west part of survey area. Fish and invertebrate communities were compared within a relatively small spatial scale (ca. 100 m) in relation to level of submarine groundwater discharge. New hydrological insights: Species richness, abundance and biomass of fishes and abundance and biomass of turban snail and hermit crab were significantly higher in the area with high 222Rn concentration. Abundance of gammarids, the most major prey item of the fishes, was 18 times higher in the area with high 222Rn concentration. Since the turban snail, hermit crab and gammarids feed on producers (phytoplankton and benthic microalgae), submarine groundwater are concluded to increase species richness and production of fishes and invertebrates through providing nutrients and enhancing primary production.

Study region: Kita and Minami River basins in Japan. Study focus: The coastal watershed in central Japan along the Sea of Japan has suffered large amounts of atmospheric nitrogen (N) deposition from northeastern Asia. However, the quantitative influences of atmospheric N deposition onto forested watersheds in the two basins and riverine N export into coasts remain unclear. To evaluate the current contribution of atmospheric N deposition, N deposition rates from the atmosphere to both basins, and N export rates from the rivers to the sea were quantified. New hydrological insight for the region: Deposition rates of bulk N in each basin exceeded 1000 mg m−2 year−1, more than 60% of which was supplied from winter to early spring by westerly winds. Annual deposition rates in the two basins did not differ, but annual export rates of inorganic N from the Kita River were significantly higher than those from the Minami River. These results suggest that symptoms of N saturation in the Kita River forested watershed are more serious. Furthermore, recent increasing trends of riverine N concentrations may have caused shifts in the limiting nutrient for coastal primary production from N to phosphorous. We suggest reductions in nitrate exports from forests as a strategy to improve nitrate pollution to both downstream waters and coastal ecosystems; however such efforts would involve intercontinental-scale actions in reducing N emissions.