A Study On The Water Environmental Profits And Water Quality Control Technology Of The Organic Crab Farming

China has the lagest quantity of the aquiculture products in the world.But water pollution problem made by the intensive cultivation is even worse, especially the problem of water eutrophication. Hence, the environment pollution problem has already aroused wide atterntion from all walks of people. This study take Shi shu Aquatic product project fishery in Yangjiang town of Gaochun county as typical proving ground, which cultivate Eriocheir Sinensis H.milne-Edwards in organic way and in conventional way. A field work and in-lab work was integrated in the study, to compare the differences of the environmental impact of the organic and conventional aquiculture, and probe into the technique of controlling water quality, so as to maxmize both the benefit of environment and economic. Accordingly, a better outline can be made for the aquiculture industry, less water pollution will be made by the aquiculture industry. So, it is of great importance to prevent and control the problem of water eutrophication and to keep good water quality.Several main aspects was included in this study:(1) Investigate and valuation of the crab culture site status in quo was made.(2) A study on the relation between the sediment and water N and P content variation was made.(3) A quantificationally study was made to probe into the technique of controlling water quality, including the a laboratory simulation of the dissolution characteristics of nitrogen and phosphorus from sediments in organic and conventional crab pond farming system, and a field work to compare the water quality improving effect of the Photosynthetic Bacteria-organic farming and organic farming system.Investigate and valuation of the crab culture site status in quo showed that, the water environmental quality of organic farming system is better than the conventional one. Organic farming system can control the concentration of TN and TP in the water better, and concentration of DO is usually higher than the conventional counterpart, hereby, the organic way showed better environment benefit. During May to July of2008, the concentration of TP of conventional farming system is triple to quintuple than the organic counterpart, besides, it can not be reduced distinctly only by changing aquiculture water. Different contaminations behave different variation disciplinary, but the same contamination in different farming system behaves almost the same. During May to December of2008, the concentration of TP was always in high level, the concentration of NH/-N was climbing slowly since March of2008. The aquiculture drainage in September of2008has coused greatest negtive impact to the GuCheng Lake. The main contamination load are TP and TN, with comparativly high temperature, it will be very easy to trigger water eutrophication. Besides, the water quality of GuCheng Lake in the end of December of2007was also not satisfied, the conventional farming system discharge larger quantity than the organic counterpart.The study of the relation between the sediment and water N and P content variation indicated that, N and P index concentration cooperate very well with the their enrichment in the sediment, but their enrichment behave lag behinde the variation in water. In the same farming system, the content TN, easy-hydrolize-N, rapidly-available-P and organic matter in the pond bottem sediment are more than those in the pond canal sediment. A large part of the bait has sinked in the pond canal sediment but not ate by the crab. No matter the pond bottem sediment and the pond canal sediment, the content of TN, TP, easy-hydrolize-N, rapidly-available-P and organic matter in the conventional farming system is higher than its organic counterpart, so the conventional farming system behave higher risk of water eutrophication, on the contrary, the pond sediment of organic farming system is much more better.A laboratory simulation was used to compare the dissolution characteristics of nitrogen and phosphorus from sediments in organic and conventional crab farming system. The results showed that the total dissolution quantity of NH4+-N from the sediment of organic crab farming system was distinctively larger than the conventional one. In the early part of the experimentation, the organic group with sediment thickness of10cm demostrate larger NH4+-N dissolution potential than the conventional group with sediment thickness of5cm. But later,the sediment type became the major influencing factor.With the same sediment thickness, the organic farming system demonstrated smaller NO3--N pollution capacity than the conventional one. No matter what thickness of the sediment (5cm or10cm), NO3-N and NO2--N from the sediment of conventional farming systemn was dissolved easier than the organic one in a short period of time. But it is reverse for total phosphorus, with sediment thickness of5cm. And during the beginning simulation4days, the total phosphorus dissolution rate of the organic farming sediment was lower than the conventional one.The water quality improving effect of the Photo synthetic Bacteria in the aquiculture water is very distinctive, it can not only distinctivly reduce the organic contamination concentration in the water, but also show great effect to reduce the concentration of NO3-N, NH4+-N and TN. The Photosynthetic Bacteria can steadily reduce CODMn, with very little influence with pH value and water temperature. The highest reduction percentage climb to30%for the concentration of N03-N, NH4+-N and TN, but with much influence with pH value and water temperature, lower pH value will be better for its reduction, which is the same for reduction of TP concentration. Differing from that, the reduction effect of P043is not distinctive at all. Besides, Photosynthetic Bacteria boost the concentration of DO in the water, which is better for the growth and active of the crab.