Vertical-flow constructed wetlands applied in a recirculating aquaculture system for channel catfish culture: effects on water quality and zooplankton

In recent decades, considerable attention has been paid to the serious water pollution caused by the fastgrowing aquaculture industry. On the other side, water quality determines to a great extent the success or failure of an aquaculture operation. So highlighted is the need for sustainable development of aquaculture. In the present work, we established a recirculating aquaculture system (RAS) by vertical-flow constructed wetlands (CWs) for channel catfish (Ictalurus punctatus) culture, and assessed its effects on water quality improvement. The results indicated that the CWs applied in the RAS showed relatively higher removal efficiency for particulate matter (more than 55%) and lower, uneven removal efficiency for nutrients and organic matter (from -34.1% to 48.7%). Paired t-tests showed that only parameters of NH4 +-N, TN, COD, BOD5, TSS, and Chl-a were significantly (p<0.05) lowered after wetland treatment. Despite this, nutrients (but NH4 +-N, NO2--N, and NO3--N), organic matter, and suspended solids (including plankton) in the recirculating ponds were significantly lowered compared to the control, indicating a decline in trophic status. Multivariate analyses revealed strong relationships between zooplankton community structure and the measured environment in the culture ponds. Cyanobacterial blooms that occurred heavily in the control were strongly restrained in the recirculating ponds. This led to water quality that was suitable for fish culture. Hereby, conclusions could be reached that the recirlulating treatment by the CWs achieved its aim of sustaining or extending water quality improvement in the RAS.