Rice floating bed with substrated ceramsite improving bacterial activity and diversity under condition of coexistence of fish and rice

Abstract: The planted floating bed is an innovative technology which consists of aquatic or terrestrial plants growing in a hydroponic manner with buoyant frames floating on the surface of waters. It is regarded as a low-cost, solar-energy-based and eco-friendly technology for in situ purification of surface water, and has been used all over the world as an important ecological remediation to control water eutrophication. At present, the conventional planted ecological floating bed body is generally made of natural materials and artificially synthesized materials. However, natural materials such as natural wood and bamboo are easy to rot and artificially synthesized materials such as synthetic polystyrene foam may easily cause secondary contamination if being long-term immersed in water. Porous ceramsite has high porosity and specific surface area which is in favor of absorbing microorganisms and is an ideal filtration material widely used in wastewater treatment. Biolog-ECO method has advantages over both classic cell culture techniques and molecular-level RNA (ribonucleic acid) amplification which has been widely used and shown to be a useful tool to detect differences in functional diversity of microbial populations in aquatic environments. In the present study, a novel type of floating bed carrier, which was mainly made of ceramsite functioned as a medium for biofilm growth and buoyant frames, was developed to remedy the water environment in the fishpond. Rice was planted on the floating bed functioned as nutrients assimilation species because it has strong anti-pollution and fast-growing abilities. The objective of the present study was to combine the rice hydroponic planting floating bed system and new floating bed carrier to develop an appropriate approach for the recycling of nitrogen and phosphate in the fishpond, and use it for eutrophic water remediation by studying the water quality purification efficacy and its effect on the metabolic activity and diversity of bacterioplankton in fishpond. The field experiments were carried out in 6 intensive fishponds in Jingzhou City, Hubei Province, China during the growing season in 2014. The results showed that the concentrations of total nitrogen (TN), total phosphorus (TP) and nitrite nitrogen (NO2--N) in the ponds employing the novel floating bed were significantly lower than that in the control ponds in August, and the permanganate index (IMn) was significantly lower in August and October. The metabolic pattern and diversity of bacterioplankton in the fishpond were analyzed by Biolog-ECO technique. The metabolic activity, which was indicated by average well color development (AWCD), Shannon diversity index and richness index in August and Shannon evenness diversity index in October, was significantly higher in the test ponds applying floating bed than that in the control ponds. The results indicated that the application of the novel floating bed changed the carbon source utilization pattern of the bacterioplankton communities in the intensive culture pond, and increased the metabolic activity and functional diversity of the bacterioplankton while controlled nitrogen and phosphorus nutrition level in the pond water. In addition, the rice absorbed nutrition directly from the fishpond water and formed biomass and gained a yield of 5 900 kg/hm2, which could provide extra profit. The results can provide a new approach for the regulation of water environment in aquaculture ponds, and provide valuable insight and theoretical guidance for controlling and optimizing the structure of bacterioplankton by applying the ecological engineering measures such as floating bed.