Primary Productivity of Epiphytic and Planktonic Algae and Biogeochemical Characteristics in Reed Zones of Lake Biwa.

Abstract

Primary productivity of epiphytic and planktonic algae and their biogeochemical characteristics in five shallow littoral reed zones showing a different trophic character in Lake Biwa were investigated. Concentrations of nutrients and dissolved organic matter varied widely horizontally, locally and seasonally in the reed zones. It seems that the reed zone has a heterogeneous environment. The photosynthetic rates of epiphytic and planktonic algae were, respectively, 0.2 to 5.7 mg C surface shoot area m-2 hr-1 and 4 to 70 mg C m-3 hr-1. The areal primary productivity of epiphytic algae was estimated as 0.3 to 9.7 mg C m-2 hr-1 in summer and 0.4 to 3.1 mg C m-2 hr-1 in winter from the shoot density of Phragmites and the water depth in each reed zone. The productivity of phytoplankton, on the other hand, was 3 to 56 mgC m-2 hr-1 in summer and 1 to 12 mgC m-2 hr-1 in winter. The contribution of epiphytic algae to total primary productivity averaged 15 %, although the assimilation number was much lower than that of phytoplankton. The present study indicates that epiphytic algae are one of the significant primary producers in reed zone.