Effects of macrophyte harvesting on the water quality and bottom environment of Lake Biwa, Japan

Appropriate management of macrophyte biomass via harvesting is crucial for maintaining eutrophic inland waters. However, information on the effects of macrophyte harvesting on the quality and bottom environment of these waters is limited. For our project on Lake Biwa in Japan, we focused on the pore water quality of the surface sediment as a reliable tool for estimating the effects of macrophyte harvesting. We compared the release of heavy metals and nutrients from the sediment based on the pore water quality of harvesting and non-harvesting sites. Our results suggested that macrophyte harvesting affected the water quality poorly in terms of sediment resuspension, but effectively reduced the amount of macrophyte litter on the lake bottom. Different methods of macrophyte harvesting are discussed, and cutting away only the upper section of macrophytes to avoid sediment resuspension instead of pulling up the macrophytes by the root was found to be the ideal harvesting method. In addition, sustainable harvesting to reduce the macrophyte litter on the lake bottom would be required to conserve the lake environment.