The Lake Ijira catchment (IJR) is located in the downwind region of the Chukyo Industrial Area in central Japan and has historically experienced large-scale deposition of S and nitrogen (N) from the atmosphere. Previous studies have suggested that IJR was acidified and N-saturated, which was triggered by climatic anomalies (cold summer and drought summer) in the mid-1990s. Long-term monitoring data on the river water (RW) chemistry since 1988 were assessed with intensive survey datasets on the input–output material budgets and S isotopic analysis (δ34S).
With a decline in NO3- concentrations, RW pH recovered to its original level, around 7.0, in the early 2000s. Reductions in atmospheric deposition, diminished effects of climatic anomalies, and forest management practices (such as thinning), have all contributed to RW chemistry recovery.
Although the SO42- output significantly exceeded the input, the δ34S analysis showed that geological (rock) S largely contributed (estimated as 75-91%) to the discrepancy of the input–output budget. On the other hand, atmospheric S appeared to accumulate in the soil as organic S. The tree-ring δ34S profile recorded historical changes in the atmospheric inputs in the Chukyo region.
RW chemistry has sensitively responded to changes in the atmospheric environment, including the atmospheric deposition of S and N and climatic anomalies, and as future changes are likely, long-term monitoring is essential.
This study was conducted using monitoring data obtained from the MOEJ and the related research outputs. Sulfur isotopic analysis of tree disks was conducted with the support of the Joint Research Grant for the Environmental Isotope Study of Research Institute for Humanity and Nature.
The paper on this study is as follows: