Phosphorus Mobilization from Lake Sediments Driven by Silver Carp Fecal Inputs: A Microcosm Study

Harmful cyanobacterial blooms pose significant threats to lake ecosystems, and the stocking of filter-feeding fish has often been used for their control. However, filter-feeding fish like silver carp excrete feces that not only retain viable cyanobacterial cells but also increase nutrient loading to the sediment. Furthermore, the quantity and frequency of fecal input vary depending on the biomass of algae and fish and the stocking strategy. In this study, a two-by-two factorial microcosm experiment was carried out to investigate the effects of silver carp feces on P release in shallow lakes. Results showed that fecal input quantity was the key determinant of P release. The peak flux reached 8.82 mg m−2 d−1 in high input treatments, compared to 1.01 mg m−2 d−1 in low input treatments. Phased-input exacerbated these effects compared to single-input. The dominant mechanisms of sediment P release varied with input levels. Microbial reduction was strongly associated with P release at low fecal input, while high-input scenarios showed concurrent hypoxia, an increase in sediment pH (from 7.28 to 7.46), and competition for adsorption sites by dissolved organic matter (DOM up to 38.57 mg L−1). These results indicate that stocking of filter-feeding fish for cyanobacterial bloom control substantially altered P flux dynamics, with high input treatments exhibiting fluxes from −6.02 to 8.82 mg m−2 d−1 compared to −0.007 to 0.33 mg m−2 d−1 in controls, depending on the patterns of fecal input. For the prevention and control of cyanobacterial blooms and to ensure the sustainability of lakes, the stocking of filter-feeding fish should be carried out before the outbreak of blooms to avoid the impact of large amounts of fish feces input on P release and water quality during the blooms.