| Pond aquaculture is the main mode of fishery production in China,which plays an important role in fishery economy.However,in the process of fishery production,farmers often use high-density stocking and large-scale fertilization and feeding to obtain higher fishery production and economic benefits,resulting in increasingly serious ecological problems such as water environment pollution.How to reduce the level of eutrophication and improve the aquaculture environment has become a research hotspot.In order to promote the green development of aquaculture industry and practice the new concept of developing resource-saving and environment-friendly aquaculture,this study carried out experiments on the sedimentation of nutrients in freshwater ponds under different aquaculture modes,the migration of nutrients in different aquaculture water bodies and sedimentary environments,and the purification of biological floating bed in freshwater fish aquaculture ponds.The source and destination of nutrients in freshwater pond aquaculture system,the migration law of nutrients between water body and sediment in pond system,and the ecological regulation technical measures for the enrichment of nutrients in aquaculture environment were explored and analyzed.This study intends to select the biological floating bed control measures to optimize the freshwater pond aquaculture environment,so as to obtain the greatest economic and social benefits as much as possible with the smallest resource consumption and environmental costs,and realize the green and sustainable development of freshwater pond aquaculture.Through the monitoring and analysis of water quality indicators such as ammonia nitrogen(NH4+-N),nitrite nitrogen(NO2-N),total nitrogen(TN),total phosphorus(TP)and permanganate index(CODMn)in the aquaculture environment,combined with the tracking and monitoring of aquatic organisms,especially plankton in the water body,so as to provide information reference and technical support for solving the potential environmental pollution problems in the current freshwater pond aquaculture process.The main results are as follows :(1)Study on the characteristics of nutrient deposition in freshwater ponds under different culture modes.Based on the differences in the ecological habits,feeding methods and environmental control measures of aquaculture animals in the main freshwater ponds in Shandong Province,four kinds of freshwater aquaculture ponds were selected for the main culture of perch,carp,mandarin fish and silver carp and bighead carp.The silver carp and bighead carp model did not obtain sedimentation particles during the test period,but the water,sediment environment and sedimentation particle quality of the three models of perch,carp and mandarin fish were investigated and monitored.The contents of ammonia nitrogen,nitrite nitrogen,TN and TP in the aquaculture water were 0.744 ± 0.045 mg/L,0.147 ± 0.014 mg/L,5.12 ± 0.18 mg/L and 0.26 ± 0.02 mg/L,respectively.The order of ammonia nitrogen,nitrite nitrogen,TN and TP in different aquaculture modes was Micropterus salmoides > Carp > Mandarin fish.The average settling amount of settling particles in aquaculture ponds was 71.29 ± 13.29 g/(m2·d),and the settling amount of settling particles in Siniperca chuatsi ponds was significantly higher than that in Perch ponds and Carp ponds.The average deposition fluxes of TN,TP and TOM were 0.32 ± 0.04 g/(m2·d),0.31 ± 0.04 g/(m2·d)and 7.19 ± 1.32 g/(m2·d),respectively.The deposition fluxes of various nutrients in carp ponds were the lowest,and the deposition fluxes of TN,TP and TOM in California perch ponds were the highest.The contents of TN,TP and TOM in the surface sediments were 0.35%,0.33% and 8.24%,respectively.Under different aquaculture modes,the contents of TN,TP and TOM were California bass > Carp>Mandarin fish.Therefore,in the environmental regulation of aquaculture ponds,it is advisable to formulate targeted sedimentary environment regulation measures according to different aquaculture varieties.(2)Study on the migration of nutrients in different aquaculture waters and sedimentary environments.In this study,the method of simulated culture in the laboratory was used to monitor the migration characteristics of nutrients at the sediment-water interface by selecting the surface sediments of three kinds of fish culture ponds with long-term main culture of Micropterus salmoides,Cyprinus carpio and Hypophthalmichthys molitrix and Aristichthys nobilis,and three kinds of pond culture water and sand-filtered source water with main culture of Micropterus salmoides,Hypophthalmichthys molitrix and Aristichthys nobilis,in order to explore the potential impact of the differences in the sediment and water quality of the pond culture system on the regulation of the aquaculture environment.The results showed that there were significant differences in the environmental conditions of water and sediment in different aquaculture systems.The TN contents of sediments in the culture ponds of Micropterus salmoides,Cyprinus carpio and Hypophthalmichthys molitrix were 0.328%,0.230% and 0.204%,respectively.The TP contents were 0.551%,0.261% and 0.260%,respectively.The TOM contents were 9.05%,7.69% and 7.82%,respectively.The ammonia nitrogen contents in the source water of Micropterus salmoides,Hypophthalmichthys molitrix and Hypophthalmichthys molitrix were 0.9822 mg/L,0.3521 mg/L and 0.0152 mg/L,respectively.Nitrite nitrogen content was 0.0210 mg/L,0.0189 mg/L and 0.0248 mg/L,TP content was 0.3196 mg/L,0.1465 mg/L and 0.0823 mg/L,and CODMn concentration was 17.33 mg/L,11.16 mg/L and 7.92 mg/L.Under different overlying water and sediment conditions,there were some differences in the influencing factors of nutrient migration between sediment-water interface.Ammonia nitrogen was released from sediment to overlying water as a whole and the migration flux was 0.1282 ± 0.0237 g /(m2·d),which was affected by the content of nitrogen nutrients in sediment and the content of ammonia nitrogen in water.The overall migration flux of NO2-N was-(0.001 ± 0.0002)g/(m2·d),which was affected by the content of nitrogen nutrients in sediments.Although TP migration is affected by sediments,the migration flux is low [0.0015±0.0009 g/(m2·d)],and its influence mechanism may be more complicated.Organic matter mainly deposited from water to sediment [-(0.76±0.05)g/(m2·d)],and the deposition flux was mainly affected by the adsorption of sediments with higher organic matter content.In addition,through the influence of water and sediment environments with different nutritional status,the nutrient content of surface sediments in the aquaculture system is more susceptible to the quality of overlying water.It can be seen that although the sedimentary environment and aquaculture system have certain potential buffering effects,it is more direct and important to take measures to create a good water quality environment to maintain the pond aquaculture environment.(3)Analysis of typical biological floating bed plant growth and water quality control effect.In this study,the combination of indoor aquarium system simulation culture and pond culture system application was used.On the one hand,the growth of typical ecological floating bed plant-water hyacinth in pond culture water was tracked and monitored.Water hyacinth with different coverage rates(5%,10% and 20%)and microecological preparations with different application amounts(recommended amount and double amount)were applied in the experimental system.The effects of different ecological control measures on the changes of ammonia nitrogen,nitrite nitrogen,TN,TP and CODMn in aquaculture water were analyzed.The results showed that the weight gain rate,specific growth rate and net yield of high and low density water hyacinth were 472.89% and 239.01%,8.73% and 6.10%,13.43 kg and 3.37 kg,respectively.The water hyacinth with dense planting had better growth effect.In the water quality control experiment under different measures,the maximum removal rates of ammonia nitrogen in B,HL,HM,HH,PL and PH treatments were 91.53%,89.87%,91.97%,91.71%,89.72% and 83.50%,respectively.The maximum removal rates of nitrite nitrogen were 17.02%,29.86%,49.27%,53.57%,29.44% and 29.10%,and the maximum removal rates of total nitrogen were 54.40%,50.41%,50.43%,51.00%,46.50% and 53.73%.The maximum removal rates of total phosphorus were 48.25%,49.87%,54.28%,67.96%,44.15% and 50.75%,and the maximum removal rates of CODMn were 22.35%,23.67%,22.62%,22.88%,25.84% and 21.27%,respectively.Water hyacinth,especially at higher densities,showed good removal effects on the nutrient contents of aquaculture water,but management should be strengthened to prevent secondary pollution after decay.Microecological agents showed better removal effects on total phosphorus and nitrite nitrogen,and their application may require auxiliary measures to transfer substances out of the water body.Through the analysis of the good regulation effect of biological floating bed on the aquaculture environment under different environmental nutrient migration conditions,and considering the ecological and economic benefits of bioremediation technology,the use of biological floating bed to regulate the ecological restoration technology of freshwater pond aquaculture environment has a positive effect on the transformation and upgrading of freshwater pond aquaculture technology.It has realized the simultaneous development of environmental benefits,economic benefits and social benefits,and can achieve the purpose of purifying the water body of aquaculture ponds and developing new fisheries for energy conservation and emission reduction.It has important application value and good development prospects. |
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