Salt pollution in a Japanese stream and its effects on water chemistry andepilithic algal chlorophyll-a

Concentrations of major ions, total phosphorus, dissolved organic carbon, b iological oxygen demand and chlorophyll-a of epilithic algae were determine d weekly at nine sites in a Japanese stream receiving effluent from a groun dwater treatment plant. The concentrations of four major cations (Na, K, Ca and Mg) and chloride ion increased significantly immediately at downstream sites of the effluent outfall. The ionic concentrations decreased with inc reasing dilution from merging tributaries but never reached the original co ncentrations and relative composition of stream water within a 10.7 km stre am distance from the outfall. The changes in total ionic concentration and relative ionic proportion also changed the chlorophyll-a content of epilith ic algae. The results also showed significantly higher chlorophyll-a conten t in epilithic algae under moderate salinity.