Lotic environment and biota in a stream having inflow of treatment water from a constructed wetland in northern Hokkaido

Abstract

In 2006, the secondary reed bed treatment system has been constructed to treat sewage from milking parlor in the northern Hokkaido. This system which efficiently uses natural purification abilities has got much attention as a waste treatment facility. However, there are only a few studies about the effects of the treated effluent having high environment loads from the system on surrounding lotic environments and their biota. Therefore, we investigate the effects on stream environments and biotic communities having the effluent through biota studies and survival experiments. These experiments were done by using three representative species, that is, oriental weather fish Misgurnus anguillicaudatus, lake prawn Palaemon paucidens, and Jesogammarus jesoensis. The biota of the study area was poor, and a species of the family Chironomidae was dominant, and no fish species was found. The survival rates of experimental animals were higher in the two upstream sections than those of the two downstream sections in which the effluent flow. The survival rates of experimental animals significantly correlated with concentrations of DO and NH₄⁺ , and COD. Moreover, concentrations of DO were lower, and NH₄⁺ and COD were higher in the two downstream sections than those of the two upstream sections. As a result, it appears that the poverty of biota in the two downstream sections has been caused by anoxic conditions and ammonia toxicity due to the effluent of the waste treatment system.