Seasonal changes in species composition and production of periphyton in an urban river running through an abandoned copper mining region.

Abstract

Seasonal changes in species composition and photosynthesis of the periphyton community were investigated in a copper (0.07-0.22 mg·l-1) -and zinc (0.13-0.55 mg·l-1) -polluted urban river (River Miyata, Japan). The pH, water temperature, concentrations of dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), total copper and total zinc were measured. SRP was mostly below 0.01 mg·l-1, whereas ammonium- and nitrate-nitrogen were high ranging from 0.1-2.0 mg·l-1 and 0.9-4.0 mg·l-1, respectively. The number of species in this river was restricted (only 7-10). The dominant species were Chamaesiphon subglobosus, Phormidium foveolarum, P. uncinatum, Achnanthes minutissima, Nitzschia palea, Stigeoclonium aestivale and Oocystis lacustris. The diatoms tended to be abundant with a lower temperature and Stigeoclonium tended to be dominant in a better illuminated condition in this river. The maximum photosynthetic rates were related closely to water temperature, and the values (0.0025-0.217 gC·gC-1·hr-1) were lower than those for unpolluted rivers in the literature. However, chlorophyll a in the periphyton was high, ranging from 31 to 1, 162 mg·m-2. Therefore the primary production in this river was not low as compared with the reported unpolluted rivers. The unbalanced high algal biomass in contrast to low SRP concentrations may be due to low grazing pressure by the poorly developed aquatic insect community (HATAKEYAMA and SUGAYA unpublished).