Biological manipulation of eutrophication in West Yangchen Lake

Abstract

This paper aims to share findings on nonclassical biomanipulation from a field study on eutrophic West Yangcheng (WY) Lake. In the forty years before 2009, cyanobacteria frequently bloomed in WY Lake, an event which has not occurred since 2009. The stocking density of filter-feeding carp was estimated to be more than 50 g/m3 in July after 2009, approximately double the amount observed before 2009, and the ratio of silver carp to bighead carp (SBR) increased from 0.8 to more than 1.6. Compared with the water quality between 2004 and 2007, the total nitrogen (TN) and the chlorophyll-a (Chl-a) concentration decreased while total phosphorus (TP) and transparency (SD) increased significantly after 2009 (P < 0.05). The decreasing Chl-a concentration was observed in Jul, Jun, May, Jul, and Mar in 2009, 2010, 2011, 2016, and 2017, respectively. The Chl-a concentration was significantly negatively correlated with TP (P < 0.05), and no significant correlation with TN was observed (P > 0.05). A significant negative correlation was observed between fish yield and SD (P < 0.05). The results also showed that filter-feeding carp more effectively restrained algae growth when SD was low. These results indicated that a high density of filter-feeding fish with increased SBR interfered with the driving effects of nutrients and temperature on the growth of algal biomass and then restrained bloom of algae. It may be necessary to take SD into consideration for determining the appropriate fish stocking density for the biomanipulation of algae.