Water quality improvement through the interaction of biotic and abiotic variables within the rhizospheric zone of an artificial floating vegetation Island

Abstract

Demands for water quality improvement and reduction of harmful algal blooms in Korean lakes and rivers due to eutrophication and climate change have been increasing. As an environmentally friendly measure to mitigate the eutrophication and phytoplankton growth, a full-scale artificial floating vegetation island (AFVI) was installed in Lake Paldang, a large on-river reservoir. This study investigated the detailed mechanisms for improving water quality and reducing the phytoplankton growth of the AFVI by comparing the biotic and abiotic environmental factors between the AFVI and the adjacent pelagic part of the lake. Much lower chlorophyll a concentration, much higher zooplankton biomass, especially large crustacean zooplankton, and a higher proportion of active bacteria in total bacteria in the AFVI indicate an effective reduction of phytoplankton growth and vigorous decomposition of organic matter. The major mechanisms for improving water quality of the AFVI are shown to be inhibition of phytoplankton growth by attenuating light and topdown control by zooplankton grazing. Active microbial decomposition of organic matters and nitrate reduction in the hypoxic rhizospheric zone also would be a major mechanism for improving water quality, even though it is difficult to quantify in the open water system.