Study of seasonal manganese anomalies in Tingxia reservoir of Ningbo City

In general, natural manganese in water bodies is harmless to human health, however, it is severe threats to human body when drinking higher-level-manganese water for a long period. Seasonal manganese content in Ningbo City has been higher than the standard permitted since 2011. In this paper, the seasonal manganese abnormal in the Tingxia reservoir of Ningbo City is studied using GPS technology. The results show that there was a high concentration of active manganese above the sediment range from 5 to10 meters, and the average concentration was 0.66mg/L； Stratification was existed in the vertical direction in the reservoir；The content of manganese increased as the depth increase under the surface of water by 30 meters. There was an obvious seasonal variation of manganese in the vertical direction, which turned to lower in the summer and autumn, higher in the spring and winter. The study also reveals that the seasonal "turnover" of reservoir caused by temperature change was a trigger to the rise of manganese. In addition, the water disturbance by heavy rainfall also had a certain effect on increasing content of manganese in the reservoir.