Growing Environment of Vallisneria asiatica Miki, a Freshwater Plant in Brackish Lake Togo-ike

Abstract

We investigated the growth potential of the freshwater plant Vallisneria asiatica Miki in Lake Togo-ike, a brackish lake that was shown to have reduced biodiversity in a study focusing on salinity and light, which are important aspects of the growing environment for aquatic plants. Based on the results of a one-year salinity study that began in April 2016, it was revealed that growth was possible at 6.98 PSU, which exceeds the previously reported upper limit of salinity. Furthermore, based on the average annual transparency in Lake Togo-ike in 2016, it was estimated that Vallisneria asiatica Miki can grow at water depths of up to 1.5 m. With these conditions, areas of Lake Togo-ike that are suitable for the growth of Vallisneria asiatica Miki were extracted from a salinity distribution map and a topographic map of the lake bottom. The northeastern and western inlets, which satisfied both conditions, were selected as areas with high growth potential. It was suggested that these areas, which have both low salinity and a shallow water depth throughout the year, would be important sites for the conservation of this species.