On the nutrient concentration and primary productivity in Ohnuma Lake, Hokkaido [Japan]

An investigation in the lake was made from June 1977 to May 1978. The average value of primary production was below 0.2 g C/m2 day from April to October. The concentrations of nitrate and phosphate were almost zero in summer, and phosphate in particular showed a value of almost zero throughout the year. Transparency was below 2m in all stations throughout the year. From the measurement of C/N ratio of suspended matter in lake and river waters, it was suggested that much of the suspended matter in the lake derived from the river flowing into and this had caused a decrease in transparency. The suspended matter scarcely settled because of the active vertical and horizontal movement of the lake water. The nutrient supply from waste water was less than 10 % of the total nutrient supply.