Catchment Studies in Kajikawa Study Site and Lake Ijira Monitoring Site (2002- )

A small catchment plot (Kajikawa study site), which is facing to the Sea of Japan, was established in a Japanese cedar forest of Shibata City (former Kajikawa Village), Niigata Prefecture and effects of transboundary air pollution on forest ecosystems have been studied since 2002 in cooperation with Niigata University and Niigata Prefecture, as one of the EANET Network Center research activities.
Lake Ijira catchment in Yamagata City, Gifu Prefecture, has been monitored the catchment monitoring site based on the Long-term Monitoring Plan on Transboundary Air Pollution and Acid Deposition, the Ministry of the Environment, Japan, and also registered as the EANET site. Including assessment of the monitoring data, effects of air pollution on forest ecosystems in the inland area of the Pacific Ocean side have also been studied there.

Response of river water chemistry to changing the atmospheric environment and sulfur dynamics in a forested catchment in central Japan

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 SO₄^2- 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:

Sase H et al. 2019. Response of river water chemistry to changing atmospheric environment and sulfur dynamics in a forested catchment in central Japan.
Biogeochemistry, 142, 357–374.
https://doi.org/10.1007/s10533-019-00540-1