Biodiversity and sustainability of the integrated rice-fish system in Hani terraces, Yunnan province, China

Agricultural nonpoint source pollution is a critical issue that causes eutrophication in water bodies, due to the application of fertilizers. The traditional rice-fish coculture systems may develop a novel sustainable agriculture. The present study was undertaken to understand the ecological mechanisms of integrated fish farming especially water chemistry, dynamics of plankton, and benthic populations and their community compositions. In the rice-fish coculture system (RF), the total nitrogen in the water was higher compared to the rice monoculture system (RM), but significantly lower than in conventional fertilized rice farming. Dissolved oxygen (DO) presented a significant "Month x Treatment" interaction (p < 0.05) with differences across sampling period (p < 0.05). Higher DO concentrations and lower ammonium nitrogen levels suggested better water quality. The dominant zoobenthos were Chironomus spp. and oligochaetes worms in RF, which indicated the mesotrophic water levels. The plankton biodiversity and soil benthic fauna were dynamic in the integrated farming. More plankton species in RF were discovered and could serve as natural feeds for fish. A complementary use of nitrogen (N) between rice and fish in RF results in low N fertilizer application and low N release into the environment. These findings provide unique insights into how water environment could be improved and how the integrated farming practice could balance the production and environmental contamination.