Evaluation of Nutrient and Heavy Metal Elution Flux from Lake Biwa Sediment through Elution Tests

Abstract

In Lake Biwa, annual vertical mixing of the water column is becoming less likely to occur, and there is concern about a steady state of anoxia in the bottom layer and the associated elution of nutrients and heavy metals. In this study, a 15-day elution test was conducted to estimate the differences in elution fluxes of organic matter, nutrients and heavy metals under aerobic and hypoxic conditions from the undisturbed sediments collected from southern Lake Biwa. Under hypoxic conditions, the elution fluxes of dissolved total phosphorus, total iron and manganese were estimated to be 3.05, 21.3 and 10.5 ㎎/㎡/day, respectively, higher than those under aerobic conditions. The elution flux of sulfate ions was higher under aerobic conditions than under hypoxic conditions. In addition, the dissolved total nitrogen and silica did not differ with the dissolved oxygen concentration. This study provides basic and quantitative data on the organic matter, nutrients and heavy metals that could be eluted from the sediment under hypoxic conditions in Lake Biwa.