Search

Since 1983, the Ministry of the Environment of Japan has conducted nation-wide acid deposition surveys. To investigate the effects of acid deposition on surface water, we used the nonparametric Mann–Kendall test to find temporal trends in pH, alkalinity, and electrical conductivity (EC) in more than 10 years of data collected from five lakes and their catchments (Lake Kuttara: northernmost; Lake Kamakita: near Tokyo; Lake Ijira: central; Lake Banryu: western; and Lake Unagiike: southernmost). The pH of Lake Ijira water has declined slightly since the mid-1990s, corresponding with the downward trends seen in the pH and alkalinity of the river water flowing into the lake. There were significant upward trends in the EC of both the lake and stream water; the same trends were also found for $$ {\text{NO}}^{ - }_{3} $$ concentrations. These trends show evidence of acidification due to atmospheric deposition, and this is the first such finding in Japan based on significant long-term trends. Lake Ijira is located about 40 km north of the Chukyo industrial area near Nagoya. The annual depositions of H+, nss- $$ {\text{SO}}^{{2 - }}_{4} $$ , and $$ {\text{NO}}^{ - }_{3} $$ in Lake Ijira were among the highest of all deposition monitoring sites, suggesting that this is the main cause of the significant acidification observed in Lake Ijira. No significant trends suggesting acidification were observed in any of the other lake catchments in spite of the significant upward trends in EC. Upward trends in pH and alkalinity at Lake Banryu and upward trends in alkalinity at Lake Kamakita were detected, but no change in pH or alkalinity at Lake Kuttara and Lake Unagiike was observed. [ABSTRACT FROM AUTHOR]

Major conclusions from our two projects focussing on carbon cycling in terrestrial ecosystems are as follows: 1) A rural system or a farmland system tends to be a source of carbon dioxide. However, it was possible to increase carbon dioxide sequestration in soil by changing soil or paddy/upland-field management systems. 2) A model simulation showed that a carbon budget in a natural forest was balanced before cutting but the large minus (source) was observed just after cutting. But the balance changed from minus to plus (sink) in 10 years after cutting. Nearly the same amounts of carbon as that stocked in the timbers before harvesting accumulated in 70-80 years after the cutting. 3) These results indicate the possibility of soils in terrestrial ecosystems as the major sink of atmospheric carbon dioxide. [ABSTRACT FROM AUTHOR]