Abstract
Calculating the change of stock of each month of the nitrogen in Lake Shinji, a brackish lagoon in Japan, it is assumed that TN is released from the sediment. This relationship has not been observed for the mean water temperature and TN release from the sediment. With respect to TN in Lake Shinji, a significant release from the sediment was not seen in the summer, which was observed for TP, but the effect of the TN concentration in River Hii was large as compared to the TN concentration of Lake Shinji. As for TN content in Lake Shinji, a correlation between the TN concentration of River Hii of the same month was observed (r = 0.57, p<0.001).
Nitrogen mass balance for 19 years was calculated. The percentage of annual deposition of TN to the TN inflow was in the range of -4.2 to 38.4%, and 19.8% on average.
We calculated the average annual value balance of TN and TP for 19 years. For TN, 1480 t flowed in, 1170 t flowed out, and 310 t settled in the Lake Shinji, and for TP, 134 t flowed in, 106 t flowed out, and 28 t had settled in Lake Shinji. Settling TN/TP ratio was 10.7, which was 11.4 for an annual average TN/TP ratio of Lake Shinji.
