Modern lake ecosystem management by sustainable harvesting and effective utilization of aquatic macrophytes

There are many problems related to overgrowth of aquatic macrophytes in many lakes and rivers throughout the world; for instance, the harvesting costs in Lake Biwa have been increasing by 200 million Japanese yen a year (equivalent to 1.8 million USD). Historically, aquatic macrophytes were harvested for use as fertilizer in agriculture in Japan, but are no longer in use because chemical fertilizers promote plant growth more effectively and are easier and cheaper to use. Thus, developing effective ways to utilize aquatic macrophytes is important to resolve this issue. In addition, sustainably harvesting macrophytes is also important for aquatic ecosystem management because macrophytes play a key role in aquatic ecosystems as nursery grounds and refuges for other small organisms living in the littoral area. Therefore, management and effective utilization of macrophytes through sustainable harvesting may play an important role in the conservation of lake ecosystems. In this short review, a recycling system using anaerobic digestion (AD) of submerged macrophytes, which were sustainably harvested from lakes, and microalgal mass culturing with AD effluent were introduced as a new technique for the conservation of lake ecosystems.