Changes in particulate organic matters and plankton populations in nature-like fishways: role of nature-like fish ways in water treatment

Nature-like fishways, designed to mimic a small natural stream, have been widely used in river restoration projects as well as in rivers with dams and weirs. Because they are built with diverse natural materials similar to those in natural streams, we aimed to estimate the self-purification ability of nature-like fishways. Monthly sampling was conducted at inlet and outlet points of two nature-like fishways in Korea: the Baekjae and Sejong fishways. Two artificial fishways and main river channels were also evaluated to be used as references. Suspended solids (SS), chlorophyll a (Chl. a), and plankton abundances were measured. A significant reduction in plankton abundances and decrease in SS and Chl. a were observed in nature-like fishways, and no significant changes were observed in concrete artificial fishways and main river channels. In Baekjae and Sejong fishways, average 28.2% and 14.9% of the SS concentrations were reduced, respectively. The Chl. a concentration also significantly decreased (44.8% and 29.8% in Baekjae and Sejong fishways, respectively). A decreasing pattern was more apparent in the Baekjae fishway, which is longer and has a slower water velocity. The rate of decrease was higher when SS and Chl. a concentrations were high at the inlet points. Thus, we confirmed that particulate organic matters could be reduced in nature-like fishways. However, the direct cause and purification process mechanisms in them could not be clearly identified. Further studies should examine the biological and chemical mechanisms in fishways, allowing us to estimate their capacity for self-purification.