Promoting effect and mechanism of residual feed organic matter on the formation of cyanobacterial blooms in aquaculture waters

Cyanobacterial blooms and eutrophication often occur in aquaculture waters where feeds are used. We hypothesize that residual feed organic matter (RFOM) can contribute to increased dissolved reactive phosphorus (SRP) concentrations in the water column by altering sediment phosphorus release characteristics (PRCS), including phosphorus fractions (i.e., Fe–P) and phosphorus adsorption (i.e., Qmax, EPC0), which is ultimately conducive to the formation of cyanobacteria blooms. Three types of aquaculture waters that were never feeding (NF), long-term feeding (LF), and stopped feeding (SF) for several years were studied to verify the above hypothesis. The results showed that the concentrations of SRP and chlorophyll-a in LF were significantly higher than those in SF and NF (P < 0.05). RFOM significantly affects PRCS with a power function relationship with EPC0 and a linear relationship with Qmax. Similarly, SRP in the water column was positively correlated with PRCS (i.e., Fe–P, EPC0), cyanobacterial biomass, and trophic state index (P < 0.01). This suggested that SRP may be an essential link between sediment and algal community structure. Simulation experiments further confirmed the above hypothesis, With the increase in RFOM (94.36 g/kg), PRCS (i.e., Fe–P, EPC0, and Qmax) increased significantly, which were 6.60, 282.36, and 2.47 times that of the control group, respectively. The sediment bacterial community and the partial least squares path model indicated that RFOM could regulate the SRP concentration in the water body and promote the formation of cyanobacterial blooms through PRCS, in which Firmicutes played an important role. This study revealed the driving process and mechanism of feeding behavior on the formation of cyanobacterial blooms and eutrophication in aquaculture waters, which provided a basis for the health management and cleaning strategy of aquaculture waters.