The Research Of Water Purification And Dissolved Oxygen Change Rule Of Crab Eco-culture Ponds

Crab, Chinese mitten crab, Eriocheir sinensis Milne-Edwards, is place in Decapoda, Grapsidae, Eriocheir, commonly known as the hairy crab.Because of crabs’unique flavor, nutrition and economic value, more and more aquatic farmers favor to breed them. The breeding scale expands gradually, the breeding area rose to about930000hectares, the production is about640000tons in2009. Along with the development of aquaculture, aquatic breeding eutrophication become more and more serious, lead to water quality deterioration, the environmental problems trigger by breeding gradually serious. Aquatic breeding, whether certain pollute environment? There are many controversy about it. Traditional breeding mode can cause nitrogen and phosphorus content of crabs pond increased, But reasonable pond farming mode can ensure there is no effect in ecological environment. Although the area of Lakes fence crabs breeding reduce, but the water quality is no be better; However the area of ecological farming pond increase, the water quality is better than the traditional farming pond.The area of Datong Lake in Hunan province is more than8000hm2, because of more than20years traditional farming mode and breeding grass carp since1980s, Datong Lake’s self-purification serious fall and become eutrophication. We committed to monitoring the effect of purifying waste water, which breeding in high density of crab ecological aquaculture mode, and preliminary study on the dissolved oxygen distribution of ecological aquaculture ponds.We research investigated and detected water acuity of Datong Lake in Hunan province at April to September in2011, the main growth period of crabs. Attributed to the eutrophication of the water source area, many indexes had exceed, such as TN, NH3-N, TP, DO and CODMn. Compare With the surface water environment standard III, the most exceeding range of them were311.0%,35.0%,242.0%,48.0%�'�86.5%respectively. The crab eco-culture ponds exceeding indexes were pH and CODMn, the most exceeding range were30.5%and217.5%respectively. In the end of the breeding period, crab eco-culture ponds physical and chemical water quality indexes: CODMn、TN, NH3-N, NO2--N had descend about56.5%,72.9%,66.6%,79.5%, while TP increased about83.3%, compare With the headwaters. The reasons of increasing indexes of TP are most about water source quality, increasing feed quantity of exogenous vegetal and creatural fodder and the decay of Elodea canadensis. Based on the all, the water quality of crab eco-culture ponds is better than the water source area, basically achieve fishery water quality standards requirements. There were no harmful effects wound be taken to outside water environment by crab eco-culture in Datong pond in Hunan province.We monitoring dissolved oxygen in different deep of ponds, according to the distribution of the aquatic in pond in high temperature season. The result show that while a sunny day no wind, large temperature difference in the water up and down and heat resistance phenomenon, fluctuation water dissolved oxygen content showed extremely significant difference, and the dissolved oxygen concentration in aquatic plants is significantly higher than aquatic sparse area; while windy weather, wind promoting the water mix, the dissolved oxygen concentration in upper water simile with the middle; while rain, the dissolved oxygen concentration in all the ponds is low, the dissolved oxygen concentration in aquatic plants is slightly higher than aquatic sparse area, and at night, the aquatic sparse area slightly higher than aquatic plants area. Due to the higher plants biomass, smaller phytoplankton biomass, wind directi on the dissolved oxygen distribution has little influence.We preliminary study on the bottom PVC micro porous aerator effect of increasing oxygen ecological aquaculture ponds in high temperature season, the result show that starting up at12:00-14:00at noon about2hours tile6:00next day, the dissolved oxygen was67.1%higher than the control group;0:00～6in the night for increasing oxygen, the dissolved oxygen in pond is108.7%higher than the control group. And according to the result, we must starting up1hour at least at noon to break up the water heat resistance within10m, make water mix and at least2hours at night. In short, ecological aquaculture pond bottom crabs PVC aerator rule is:sunny noon open, before sunrise frequently open; rain night always open; Hot weather extended open, windy weather may be less open.