Seasonal and longitudinal changes in copper and iron in surface water of shallow eutrophic Lake Kasumigaura, Japan

The concentrations of copper and iron in surface water of the eutrophic Lake Kasumigaura, the second largest lake in Japan, have been monitored at three sites monthly from April 1989 until March 1994. The metals were analyzed by a graphite furnace AAS after filtration with a 0.45-μm membrane filter. The concentrations of copper in the water were in the range 10−9 to 5 × 10−8 M and showed clear seasonal changes, being higher in summer and lower in winter. The concentrations of copper did not decrease on passage through the lake. The values of dissolved chemical oxygen demand (CODMn) showed a similar behavior, an interaction of copper in the lake water with organic matter was estimated. The concentration of copper in the lake became sometimes higher than the value of EC50 for Microcystis, however, the metal forms stable complex species with organic matter and the toxic effect may be reduced. The concentrations of iron, on the other hand, showed wide variation, but no obvious seasonal change. The concentrations of iron decreased very markedly during flow of water through the lake.