Effects of integrated lotus-fish farming systems on macrozoobenthosin lotus field

Integrated Agri-Aquaculture Systems (IAAS) such as rice-fish farming have been practiced for centuries in China. In these systems, on-farm wastes and by-products are recycled in relatively closed nutrient cycles. IAAS also utilizes resource efficiently and provides additional food and income to local farmers. Thus these systems are more sustainable compared with other food production systems such as monoculture systems. In the north of Jiaxing City, Zhejiang Province, a wide area of low-lying wetlands exists because of land subsidence. The permanently flooded field is not suitable for grain and oilseed rape production and thus agricultural economy development in the area is seriously restricted. As an innovation of IAAS, the trapa-fish (e.g. trapa-loach, trapa-Chinese snakehead fish and trapa-Chinese soft-shelled turtle), lotus-fish (e.g. lotus-loach, lotus-Chinese soft-shelled turtle and lotus-Chinese snakehead fish) and water bamboo-fish (e.g. water bamboo-loach) integrated patterns were being gradually developed in recent years. As an important ecological group in freshwater ecosystems, macrozoobenthos are important in material cycling and energy flow, and are widely used in environmental monitoring. In order to determine the response of macrozoobenthos diversity to lotus-fish farming, field experiments were conducted in Zhejiang Northbay Wetland Eco-agricultural Science and Technology Ltd. Co. Three typical integrated lotus-fish farming systems (including integrated lotus-soft-shelled turtle system, integrated lotus-Oujiang color common carp system and integrated lotus-loach system) along with one monoculture system (soft-shelled turtle monoculture system) were selected in the study. Ecological surveys of each system were carried out at three periods — before lotus-fish co-culture period (late March 2013), after lotus-fish co-culture and the lotus in vigorous growth period (mid-August 2013) and after fish harvesting period (early January 2014). The species composition, standing crops and diversity of samples were analyzed. Altogether, 13 macrozoobenthos taxa belonging to 6 families and 12 genera were identified from all the qualitative and quantitative samples. Results showed that there was no significant difference in the macrozoobenthos species after the adoption of integrated lotus-fish farming system. However, macrozoobenthos biodiversity decreased because of sediment disturbance caused by aquatic animals after fish stocking. The density and biomass of aquatic insects and macrozoobenthos in the integrated lotus-fish farming systems all increased after fish stocking. The average density and biomass of aquatic insects, total density and biomass of macrozoobenthos increased by 12 times and 336 times, 11 times and 273 times, respectively. However, in the soft-shelled turtle monoculture system, macrozoobenthos biomass decreased after soft-shelled turtle stocking. Meanwhile, the integrated lotus-soft-shelled turtle system had higher density and biomass of aquatic insects and macrozoobenthos compared with soft-shelled turtle monoculture system. Conversely, the density and biomass of oligochaetes in integrated lotus-soft- shelled turtle system were lower than those in monoculture system. Results of bioassessment using Hilsenhoff biotic index indicated that water quality under lotus-Oujiang color common carp system was better than that under lotus-loach system and lotus-soft-shelled turtle system.