| The environmental concern and safety of pond aquaculture has become an important factor restricting the development of freshwater aquaculture in china.Research and development of efficient,ecological,safe and healthy culture technology and model has become an important development direction of domestic and foreign fishery production.By the ecological engineering of paddy fields,the integrated paddy-pond recirculating ecological system was constructed.In the system,the paddy field acted as the production unit,as well as water and nutrient recycling purification unit.The water quality parameters and bacterioplankton community structure and metabolic function characteristics in the integrated system were investigated to analysis the regulation mechanism of the integrated system.The comprehensive benefit of the integrated system were evaluated and the utilization efficiency of nitrogen was simulated by the IAA mode,and in order to provide the basis for promotion and the application of the culture mode for standardization transformation of China's traditional culture pond upgrade.The main results and conclusions are as follows:1.The construction and optimization of the operation of the integrated system.The integrated paddy-pond recirculating ecological system was constructed by purificating and reusing the tail pond water by the engineered paddy field according to the waterlogged land drainage method for ecological engineering.The results showed that under the water flow rate of 7 m3.h-1 and surface flow operation mode,the DO was significantly higher in the outflow of the paddy,the removal efficiency of the paddy on the NH4+-N,NO2--N,TN,TP and CODMn were 37.04%,39.39%,31.01%,27.74% and22.28% respectively.When the water flow rate increases to 12 m3.h-1,under the surface flow and subsurface flow combining operation,the DO concentration significantly increased in the outflow,the removal efficiency of the paddy on NH4+-N,NO2--N,TN,TP and CODMn nutrients were 30.8% 34.5% 20%,18.7% 19.2%,23.4% 25% and35.5% 36.7% respectively in 2014 and 2015.In general,the DO concentrations in the outflow of the paddy field were higher than 9 mg.L-1,and the NH4+-N and NO2--N content were lower than 0.8 mg.L-1 and 0.1 mg.L-1.The nitrogen and phosphorus retained in paddy field can be 6.24 kg 15.66 kg and 2.16 2.5 kg during the experiment period.The surface flow and subsurface flow combining operation strategy is more appropriate.2.Regulating effect on the water quality.In 2013,The pH value in the experimental pond water was significantly lower in July,and the content of NH4+-N and TN in experimental ponds were significantly lower in August and the CODMn content was significantly lower in July and in August.In 2014,the pH value in the experimental pond water was significantly lower in June and August,and the NH4+-N content was significantly lower from August to October,and the NO2--N content was significantly lower in August,and the TN content was significantly lower in October.In 2015,the DO in experimental pond water was significantly higher in August and October,and the contents of Chl-a and TN were significantly lower in September and October.The content of CODMn was significantly lower in September.The results indicated that the NH4+-N and NO2--N in the pond water were significantly lower than that of the controlpond during the middle and later stage of culture.The regulation effect on the NH4+-N and NO2--N in aquaculture ponds seemed be better under the surface flow and subsurface flow combining operation.The eutrophication status of the pond water was evaluated by the calculation of trophic status index?TSI?.The results showed that the increase of the trophic status index in the control ponds and experimental ponds in 2013 was 5.21% and 11.92%,4.98% and 10.61% in 2014,18.38% and 25.12% in 2015.The results indicatd that the trophic status increased in experimental ponds was lower than that of the control pond.Therefore,the integrated system effectively controled the trophic status in the pond through the recycling of nutrients by the paddy field.3.Regulation effect on the structure of the bacterioplankton.The structure and diversity of bacterioplankton communities in the inflow and outflow of the engineered paddy field were analyzed and compared based on the Illumina MiSeq second generation high-throughput sequencing technology to characterize the effect of ecological engineed paddy field recycling the tail water from fishpond on the bacterioplankton communities.The results showed that the bacterioplankton community composition at phylum level in the inflow and outflow of the engineered paddy field was similar and the dorminatnt phylums were Cyanobacteria,Proteobacteria,Actinobacteria,Planctomycetes and Bacteroidetes.However,their relative abundances were different.The relative abundance of Cyanobacteria was significantly decreased while the Actinobacteria significantly increased in the surface outflow and subsurface outflow.The bacterioplankton community composition at genus level was also similar.The species richness index?Chao?of bacterioplankton communities significantly increased in the surface outflow.The Shannon diversity index significantly increased and the Simpon index significantly decreased in the subsurface outflow.The results indicated that the structure and diversity of bacterioplankton communities was significantly changed in the outflow of the paddy and the purification effect of the paddy could influence the the structure and diversity of bacterioplankton communities directively.The dorminatnt phylums in the experiment pond and the control pond were similar while their relative abundances were different.The results of cluster and PLS-DA analysis showed that there were differences in the community structure of bacterioplankton community composition between the control ponds and experimental ponds.The relative abundance of Chlorobi was significantly lower,and the relative abundance of TM6,Spirochaetae and Gracilibacteria was significantly higher than that of the control ponds.At the genus level,the relative abundance of the dominant genera hgcIclade was significantly higher than that of the control pond,and the relative abundance of norankf<sub>OPB56 was significantly lower.In addition,the relative abundance of 27 species of low abundance bacterioplankton was significantly different from that of the control pond.The Sobs richness index of the bacterioplankton community in the experiment pond was higher than that of the control pond.The results showed that the structure of the bacterioplankton in the experiment pond were changed through the recirculating in the system.The pH,TP,EC,NH4+-N,Chla,T,CODMn,SD,and DO were related to the community structure of bacterioplankton in the culture pond.The grass carp yield was positively related to Ace index of bacterioplankton community in Juneand the total yield was positively related to sobs index of bacterioplankton community in August.The improvement of richness of bacterioplankton community in the integrated system may contributed to higer culture yield of pond culture.4.Regulation effect on the metabolic patterns and functional diversity of the bacterioplankton community.A comparative analysis on the metabolic patterns and functional diversity of the bacterioplankton community by the integrated aquaculture system was conducted.The results showed that the metabolism of AWCD were significantly higher in the outflow than that in the inflow of water under the two kinds of different operation modes,.The number of available carbon source of S in the effluent was significantly higher than that of influent.The carbon source including D-Glucosaminic Acid,a-D-Lactose,a-Cyclodextrin and Phenylethyl-amine were used only in the outflow.The utilization rate of 4-Hydroxy Benzoic Acid and Tween 40 by bacterioplankton community was significantly improved in the effluent under both operating mode.In July and August,the diversity index of inflow was significantly lower than that of the outflow.The diversity and activity of the bacterioplankton community in the outflow of the paddy was significantly improved.The AWCD value and the Shannon index of the bacterioplankton community in the experiment pond was significantly higher than that of the control group in August,and the Shannon evenness index was significantly higher in October,the number of available carbon sources S was significantly higher in July and August.The carbon sources such as 4-Hydroxy Benzoic Acid,a-D-Lactose,D-Malic Acid and D-Glucosaminic Acid were exclusively used in the experimental ponds.The utilization rate of a-Ketobutyric was significantly higher,while the utilization rate of D-Galacturonic Acid,D-Cellobiose,N-Acetyl-D-Glucosamine and D-Galactonic Acid y-Lactone by the bacterioplankton community in the experimental pond were significantly lower in July or August.The correlation between the metabolic patterns and functional diversity of the bacterioplankton and culture yield showed that the ultilization of Pyruvic AcidMethyl,4-Hydroxy Benzoic Acid and Glucose-1-Phosphate were higher,and the ultilization of D-Mannitol,a-Ketobutyric Acid,D,L-a-Glycerol were lower in the pond with high yield.The Grass carp yield and McIntosh index were positively correlated.The increase in the ultilization of 4-Hydroxy Benzoic Acid and McIntosh index may contribute to the high culture yield.5.Comprehensive evaluation of the integrated paddy-fishpond system for recirculating aquaculture.The model of integrated agriculture-aquaculture system was optimized,and the ecological process of the interaction between paddy field and culture pond was simulated.The muscle hardness,crude protein content and blood sugar content of Carassius auratus were significantly higher than those in control ponds,and the moisture,total protein?TP?and cholesterol?TCHO?were lower than those in the control ponds?P <0.05?.The quality of nutrition,tenderness and flavor were improved in the experiment pond.The ecological footprint analysis results showed that theecological footprint per unit profit in the traditional pond aquaculture was 16.75 gha per million yuan,while 7.10 gha per million yuan in the integrated system which indicated that the integrated paddy-pond recirculating ecological system is a kind of sustainable aquaculture model from an environmental and economic point of view.6.Comprehensive regulation mechanism of the integrated paddy-fishpond system.The nitrogen and phosphorus from the pond tail water were recycled and DO increased from the paddy field in the integrated system thus the content of NH4+-N and NO2--N and eutrophication status decreased,and DO were improved in the experiment pond.In addition,by direct screening of paddy field on bacterioplankton species and indirect effect through the regulation of water quality,the structure and functional diversity of the bacterioplankton communities in the experiment pond were increased.Therefore,the integrated system regulated the micro-ecological environment of ponds by controlling the water quality and optimizing the structure and function of bacterioplankton communities. |
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