Lake Biwa Survey

Abstract

AbstractThe purpose of this study was to survey the distribution and habitat of submerged macrophytes in the Seta River outflow from Lake Biwa, Shiga Prefecture, Japan. To accomplish this, a field survey with sampling was conducted in January 2009. Nine submerged macrophyte species were collected during the diving operation. The sample collection showed that submerged macrophytes flourished on both sides of the river but did not flourish in the central portion of the river. Alien species (Egeria densa and Elodea nuttallii) were collected on all survey lines, while domestic species (Ceratophyllum demersum, Myriophyllum spicatum, Hydrilla verticillata, Vallisneria biwaensis, Vallisneria denseserrulata, Potamogeton maackianus and Potamogeton malaianus) were collected in large amounts on the survey lines near Lake Biwa. The dominant species in cohesive soil or fine soil was Egeria densa, while the dominant species in sand gravel was Potamogeton maackianus. Although Egeria densa was also collected in sand gravel, Potamogeton maackianus was not collected in cohesive soil or fine soil, which indicates that Egeria densa has high fertility and can survive in an oxygen-poor environment, while Potamogeton maackianus cannot survive in an oxygen-poor environment. A great amount of sunlight travels to the bottom of the lake because of artificial water-level manipulation in early summer. As a result, submerged macrophytes prosper in the summer. It is desirable to change the artificial water-level manipulation to control the extensive amount submerged macrophytes. For example, postponing the time for drawdown from 15 June to 15 July is preferable for not only controlling overgrowth of submerged macrophytes but also conserving fish spawning.KeywordsAlien speciesDomestic species Egeria densa Lake Biwa Potamogeton maackianus Submerged macrophyteWater-level manipulation