Spatial distribution of submerged macrophytes in the south basin of Lake Biwa in the summer of 2012, compared with 2002 and 2007.

Abstract

The spatial distribution of submerged macrophytes, in terms of biomass and species composition, was surveyed in the south basin of Lake Biwa in September, 2012 using scuba. Submerged macrophytes were observed in 48 out of 52 sampling stations, and 12 species were found in this study. The number of species of submerged macrophytes per site was 4 . 6 ± 2 . 0 . The area with vegetation cover and the total biomass ( dry weight ) during the study period were estimated to be 47 . 6 km 2 and 3264 ± 1445 t, respectively. Although the area with vegetation cover was only 1 km 2 less than in 2007 , total biomass of submerged macrophytes declined by 6360 t during the same period. Biomass of Potamogeton maackianus , Egeria densa , and Ceratophyllum demersum decreased signifi cantly between 2007 and 2012 ( paired Student 2007 and 2012 ( paired Students t -test, P < 0 . 05 , n = 52 ) , 4107 t, 879 t, and 804 t, respectively. Biomass reduction in these three species accounted for 91 % of the entire reduction. The biomasses of the other species also declined, with excepthion of two, Potamogeton malaianus and P. anguillanus