Long term trend in dissolved iron concentration in the Amur River basin: Observation and modeling, possible causes of abrupt increase in the late 1990s’

Recent studies revealed that significant part of iron which limits primary production of the Sea of Okhotsk is delivered from the Amur River basin with the form of dissolved iron. Thus, it is very important to understand dissolved iron producion mechanism of the basin. With long term trend analysis in dissolved iron concentration, we found that abrupt increase in the late 1990s’ was observed at the Khabarovsk station. Abrupt increases were also recorded at many observation stations, and are spreading over wide range of the basin. Potential drivers of these increases are considered, including temperature, rainfall, and land cover change. It was suggested that both temperature and land cover change may have significant effect on increasing dissolved iron concentration. Especially, drastic increase in groundwater pumping wells for paddy water irrigation which contains high concentrated dissolved iron has a significant impact on dissolved iron concentration of the basin. However, modeling study which considers possible mechanism of dissolved iron increase indicates that temperature change and land cover change can not fully reproduce the increase amount. In the presentation, several new possibilities of increase will also be discussed.