Effects Of Fertilization On Water Quality And Plankton Of Young Chinese Mitten Crab Ponds

As a well-known breeding organism in the field of aquatic products in China,in recent years,with the expansion of the scale of the industry,environmental problems have also become apparent.The ponds of juvenile crab cultures are poor in fluidity of small water bodies and lack of purification ability.The need for feeding,fertilization and accumulation of its own metabolites,As well as the pond itself leaching,seepage and so on function,has caused the severe environment question.The current environment advocates the concept of clean water fishery,and whether some feeding operations（fertilization）are scientific needs to be solved urgently.Through reviewing previous research data,it is found that the research direction mainly focuses on the type and mode of fertilization and the frequency of fertilization.It does not involve the rationality of fertilization,or it is only a single study of water quality indicators or changes in floating organisms.Comprehensive research and evaluation of a water ecosystem.Therefore,I hope that through the exploration of the impact of fertilization on the water quality index of the pond process,and further statistical evaluation of the community structure changes of pond plankton,understand the community succession and the composition process of its dominant species,and contact the water quality indicators and juvenile crabs.A comprehensive assessment of the plankton in the pond was carried out to obtain a comprehensive systematic assessment of the ecological environment of the pond.Through the maintenance period of 6 months and comprehensive monitoring of 12indicators such as water temperature（T）,it is concluded that the water quality of the crab crab pond has obvious seasonal characteristics.The water quality factors were comparatively steady in June and September.COD_Mn and Chl.a increased significantly in July and August,while the DO decreased markedly.In the end of experiment,most of the water quality factors increased significantly in two groups,but the total hardness and DO decreased greatly.Experiments show that there is no significant difference in T and pH between source water and pond water（p>0.05）.The value of DO and NO₃^--N were higher than the two groups of juvenile crab ponds（p<0.05）.TP,PO43--P,Chl.a and total hardness of non-fertilized ponds were significantly lower than those of fertilization ponds（p<0.05）.The juvenile crab ponds after fertilizing would involve contemporary increase of Short increases of TN、NH₄⁺-N、NO₂^--N、NO₃^--N and COD _Mn were appeared after fertilization.The pond will cause excessive accumulation of phosphorus and organic matter due to fertilization.From June 2016 to October 2016,a total of 48 species of zooplankton were identified in the ponds of the two groups of crabs,belonging to 18 families.Among them,there were 21,15 and 12 species of rotifers,branching horns and copepods,and 21 species of dominant species of zooplankton.There are 8 species of rotifers,7 species of cladocerans and 6 species of copepods.In addition,there are 12 dominant species in the F1 group and18 dominant species in the F2 group.The dominant species in the F1 group were significantly less than those in the F2 group.The study found that after fertilization,the density and biomass of zooplankton increased significantly（P<0.05）,while the diversity index was significantly lower than that of non-fertilized ponds（P<0.05）.According to the redundancy analysis（RDA）,the main water quality indicators affecting the changes of zooplankton community structure in juvenile crab culture ponds were COD_Mn,pH,Chl.a,TN,T,DO and TP.A total of 6 pond phytoplankton were collected from the two groups through 9experiments.The results identified that there were 117 species of phytoplankton in the pond of young crabs,belonging to 8 genus 68.Among them,Chlorophyta（47 species）,Diatoms（26 species）and Cyanophyta（21 species）,Euglena（13 species）,Yellow algae（2 species）,Gold algae（1 species）,A Algae（4 species）,cryptophyta（2 species）.The composition of phytoplankton in young crab ponds is mainly green algae,diatoms and cyanobacteria,and has seasonal succession characteristics.Green-cyanobacteria in summer and green-diatom in autumn.A total of 15 phytoplankton dominant species were identified in the experiment,including green algae（6 species）,cyanobacteria（4 species）,diatoms（4 species）and cryptophytes（1 species）.The main dominant species are Oscillatoria chalybea var,Pediastrum duplex,Ankistrodesmus falcatus,Dactylococcopsis acicularis,and Cyclotella.Stelligera),A.granulate,Chroomonas acuta Uterm.The experimental results show that there are 11 dominant species in the F1 group and15 species in the F2 group.The average density of phytoplankton in F1 and F2 groups was 1.005×107⁴.723×107cell/L and 1.035×107⁴.935×107 cell/L biomass were2.634²0.63 mg/L and 2.995²5.706 mg/L,respectively.The diversity index ranges from2.53 to 3.137 and 2.288 to 3.066.The study found that the young crab pond is mainly composed of silicon-green algae,and the water body is at the middle nutrient level.After fertilization,not only the average abundance and biomass of phytoplankton increased significantly（P<0.05）,but also destroyed the diversity of phytoplankton community,resulting in the pollution-tolerant population becoming the dominant species,which adversely affected the pond.According to the above studies,fertilization in pond water would cause the decrease of dissolved oxygen in water,the accumulation of phosphorus and chlorophyll a,and then promote the increase of cell density and biomass of phytoplankton in pond,and cause the decrease of community diversity index.Water fertilization can also promote the growth of zooplankton,promote the increase of its average density and biomass,increase the biological carrying capacity of the pond water environment,and have adverse effects on cultured organisms.A comprehensive evaluation of various indicators such as water quality indicators and planktonic plants and plants has been found.The water environment of the young crab pond is a medium nutrient level,and then the fertilization operation will cause the risk of eutrophication of the water body.Therefore,the strategy of not applying fertilizer is more in line with the concept of ecological farming.