| Due to the limited capacity of self-purification of water in ponds,accumulation of feed residue and metabolites lead to endogenous,exogenous pollution,and eutrophication.Currently,physical,chemical and biological methods are used to purify aquaculture wastewater.Meanwhile,aquatic plants,aquatic animals and microorganism were used to purify water quality.Chinese mitten crab(Eriocheir sinensis)is an important economic aquatic crustacean in China,customarily,aquatic plants are often used to purify water quality during the breeding process of high-density cultured young crab.Alternanthera philoxeroides were planted in the pond,which could not only provide a habitat for shelter and molt for crab,but also could purify the water quality.However,considering the low economic value of Alternanthera philoxeroides,some aquatic plants attracted attention of researchers,which can produce high economic value and purify water quality.Meanwhile,reed type rice is lodging-resistant,which has tall stems,developed root system and suitable for planting in crab pond.In freshwater ecosystems,phytoplankton represents their primary productivity of water bodies,and metazoan zooplankton includes Rotifers,Cladocera,and Copepods.The Plankton is an important component of material transformation,energy flow and information transmission in freshwater ecosystem,and closely related to water environment.Simultaneously,The community structure and dynamic changes of Plankton could indicate the change of water environment quickly and accurately.On the other hand,Changes of water environment also change the community structure of Plankton.Because of the community structure of Plankton can react to the water environment,so,the temporal and spatial variation of the community structure and species diversity of them are often used as indicators of water quality and freshwater ecosystem assessment.So,Four treatments,including control(group A),and three reed type rice planted with 10%(group B),20%(group C),30%(group D)were set to the present study,and every treatment has three replicates.In this study,the water quality,phytoplankton and metazoan zooplankton in the young crab pond of different reed type rice acreage were studied.Aim to explore the effect of reasonable reed type rice acreage on the purification of cultured pond culture water and reveal the change of water quality;to analysis the characteristics of phytoplankton functional group and metazoan zooplankton community,and their relationship with environmental factors;to assessment the water environment ecosystem of planting different areas reed rice crab pond scientifically.Simultaneously,provide reference for the related research on purification of aquatic pond water quality,reed rice purification aquaculture water and pond water environment ecosystem.1.Preliminary study on the effects of different areas of reed type rice on the water purification in young crab pond.From July 2015 to October 2015,the water quality indicators including temperature,dissolved oxygen,pH,total hardness,permanganate index,total nitrogen,ammonia nitrogen,nitrite nitrogen,nitrate nitrogen,total phosphorus,phosphate phosphorus,chlorophyll a of the young crab pond were monitored.The results indicated that pH of water in pond was in line with the fisheries water quality and surface water environmental standards,while permanganate index,total phosphorus,ammonia nitrogen,total nitrogen,reached class I,II,III,IV of surface water environmental standards,respectively.Simultaneously,during the feeding period,temperature,dissolved oxygen,total hardness,nitrite,nitrate,phosphate phosphorus,and Chlorophyll a of water were 18.77-29.53 ?,0.86-5.01 mg/L,0.088-0.756 mg/L,0.011-0.015 mg/L,0-0.006 mg/L,0.004-0.057 mg/L,and 0.008-0.440 × 103?g/L,respectively.But,the content of chlorophyll a in the young crab pond was higher than the crab cultured pond and river.In conclusion,reed type rice could purify the water quality in crab-cultured pond,and the water quality was the best when 50% Alternanthera philoxeroides and 20% reed type rice were planted in young crab pond,respectively.2.Structure of phytoplankton functional groups in the young crab pond water of different reed type rice acreageInvestigations were conducted from July to October,2015 to evaluate the characteristics of phytoplankton community structure and its relationship to water environmental factors of different rice acreage(0%,10%,20% and 30%),and to explore how much area of reed rice is appropriate in the young crab pond.The species composition,biological density,biomass,Shannon-Wiener diversity index,Pielou evenness index,and Margalef Richness index of phytoplankton and their relationship to environmental factors were analyzed.As the results showed that a total of 126 phytoplankton species were identified,most of them belonged to Bacillariophyta,Chlorophyta and Cyanobacteria,belonging to 71 genera and 8 phyla.Simultaneously,16 dominant species were classed and the phytoplankton functional groups of them were R,S1,G,J,B,D,P,LO,WO,X2,X1 and MP.Whlie,the range of average biological density,average biomass,Shannon-Wiener diversity index,Pielou evenness index and Margalef Richness index were 0-8.135±4.794×107cell/L,1.079±0.454-38.162±13.414mg/L,1.301±0.072-2.387±0.368,0.346±0.006-0.843±0.125,1.038±0.183-1.852±0.131 respectively.Simultaneously,the RDA(redundancy analysis)result showed that the most important factor affecting the phytoplankton functional groups' s community structure were nitrate nitrogen,total nitrogen,temperature,total phosphorus,chlorophyll a and nitrite nitrogen.In conclusion,planting 10% and 20% of the reed type rice enriched the young crab pond ecosystem diversity,while the 30% area reduced its diversity.Therefore,the crab pond planting 20% area reed type rice is more appropriate.3.The metazoan zooplankton community structure and its relationship with environmental factors in the young crab pond water of different reed type rice rcreageInvestigations were conducted from July to October,2015 to evaluate the characteristics of metazoan zooplankton community(including Rotifera,Cladocera and Copepoda)and its relationship to environmental factors,and to explore how much area of reed rice is appropriate in the young crab pond water of different rice acreage.The species composition,biological density,biomass,biodiversity of metazoan zooplankton and its relationship to environmental factors was analyzed.The results indicated that 42 metazoan zooplankton species,including 20 Rotifera,10 Cladocera and 12 Copepoda were identified in the young crab pond water of different rice acreage,and the number of dominant species of them was 8,6,8 respectively.Simultaneously,the range of average biological density of Rotifera,Cladocera and Copepoda were 1.40±0.17-370.00±8.50 ind/L,1.50±0.00-391.88±8.88 ind/L,11.25±0.75-873.00±16.17 ind/L respectively.While,the range of average biomass of them were 0-0.711±0.004 mg/L,0.090±0.084-94.500±4.025 mg/L,0.098±0.005-56.140± 0.703 mg/L respectively.Simultaneously,the range of Shannon-Wiener diversity index of them were 0.111±0.096-1.792±0.410,0-1.688±0.013,0-1.783±0.077 respectively.Seasonally,the biological density and biomass of Rotifera and Cladocera in autumn was higher than that in summer.While the biomass density and biomass of Copepoda reached their maximum in July and October respectively.The Shannon-Wiener diversity index of Rotifera,Cladocera and Copepoda in summer was higher than that in autumn.Simultaneously,the results of RDA(redundancy analysis)showed that the main driving factors of the dominant species of zooplankton were p H,total phosphorus,potassium permanganate index,dissolved oxygen,Chlorophyll a and ammonia nitrogen.In conclusion,crab pond planted 20% reed rice was more appropriate and the pond ecosystem was the best when 20% reed type rice was planted in it. |
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