Abstract. The stable isotopic compositions of nitrate in precipitation (wet deposition) and groundwater (spring, lake, and stream water) were determined for the island of Rishiri, Japan, so as to use the 17 O anomalies ( 17 O) to trace the fate of atmospheric nitrate that had deposited onto the island ecosystem, which is a representative background forest ecosystem for eastern Asia. The deposited nitrate had large 17 O anomalies with 17 O values ranging from +20.8‰ to +34.5‰ (n = 32) with +26.2‰ being the annual average. The maximum 17 O value of +34.5‰, obtained for precipitation on the 23rd to 24th of February 2007, was an extraordinarily large value among values for all samples of precipitation in Rishiri. Most nitrate in the sample might have been produced via NO 3 radical in a highly polluted air mass that had been supplied from megacities on the eastern coast of the Asian continent. On the other hand, nitrate in groundwater had small 17 O values ranging from +0.9‰ to 3.2‰ (n = 19), which corresponds to an mixing ratio of atmospheric nitrate to total nitrate of (7.4±2.6)%. Comparing the inflow and outflow of atmospheric nitrate in groundwater within the island, we estimated that the direct drainage accounts for (8.8±4.6)% of atmospheric nitrate that has deposited on the island and that the residual portion has undergone biological processing before being exported from the forest ecosystem.

No abstract

Abstract. Fresh submarine groundwater discharge (SGD) is the key pathway of flux and nutrients for the groundwater from land to the ocean. SGD flux is a current issue of discussion and a means to clarify the coastal marine system under climate change. SGD flux accounts for about one-quarter of the river runoff in the Katakai alluvial fan in Uozu, Toyama, Japan, which is an ideal area to study SGD flux considering the need for a rapid response to climate change and the prior research on SGD there. In this paper, the monthly groundwater table's condition over 30 years is analyzed using monthly rainfall, snowfall, and the climate change index. Rainfall has been on an upward trend, but the snowfall has decreased over 40 years. Furthermore, the groundwater table at monitoring wells in the coastal area increased, as a result of the increased rainfall. However, the relationship between snowfall and groundwater is negative. As expected by Darcy's law, SGD flux was controlled by the hydraulic gradient of the coastal groundwater. The estimated historic SGD flux by groundwater table variation shows an upward trend of SGD. Considering the increase in precipitation and the groundwater table, SGD flux may increase under climate change.

We have investigated the effectiveness of using the Micropterus salmoides largemouth bass, which is a top predator found throughout the world, as the index of a hydrosphere environment and its food chain. To this end, we used stable carbon and nitrogen isotope analysis (SIA). Largemouth bass were collected from eight dam reservoirs and two ponds in Toyama Prefecture, Japan. Toyama is located in central Japan and features a variety of distinct geographical environments, a result of the 3000-m elevation that changes over short distances, and abundant water systems. The mean δ(13)C and δ(15)N values for the lipid-extracted muscle of largemouth bass from all sampling locations showed large variability, but there were only small standard deviations at each sampling location. The isotope ratios for largemouth bass express the characteristics of each investigated hydrosphere environment and food chain. A very high correlation (δ(13)C: Y(scale) = 0.96 X(muscle) + 1.58, R(2) = 0.98, δ(15)N: Y(scale) = 0.92 X(muscle) - 1.15, R(2) = 0.95) of SIA values was found between largemouth bass scales and lipid-extracted muscles, which suggests that the more easily analyzed scales are useful as SIA samples for the monitoring and comparison of hydrosphere environments throughout the world.

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