Effect Of Eriocheir Sinensis Eco-culture On Water Quality

We usually call crab,its scientific name is Eriocheir sinensis, it is a freshwater aquaculture specie with high economic value, large-scale culture. Eriocheir sinensis meat is lush and has a high nutritional value, it is recognized by consumers, so market demand is increasing year by year. Enclosure culture in lakes and pond culture are two main models in artificial breeding, the former requires a specific geographical environment, the latter only mechanical excavation ponds for breeding. Now, the most Eriocheir sinensis culture models are eco-culture, which is that the Eriocheir sinensis can growth in high quality water by using ecological farming technology. So, it can produce green organic food.The most important method of Eriocheir sinensis eco-culture is planting grass in pond, the method is simple and effective. The nitrogen and phosphorus produced by Eriocheir sinensis excretion and daily feeding can be absorbed by plants,which can reduce the impact on the water environment. At the same time, the plants can be habitat and plant food for Eriocheir sinensis, so the farming system can be a "mutually beneficial symbiosis" ecosystem. Eriocheir sinensis life cycle including 5 periods, this paper studies the effects of button crab-mature crab stage and plants decomposing on water quality.Eriocheir sinensis eco-culture model was used in actual production and achieved fruitful results. The studies on water quality are more in the pattern of Eriocheir sinensis eco-culture,but the variation of the water quality in differen layers and effect of water plants decomposition on water quality are less. The variation of different layer was more accurately grasp the changes of water quality. The study on the impacts degree of decomposing of plants on water quality has an important on planted area, balance of the ecosystem,daily management of plants and salvage plants. In order to explore the changes of different layers water quality in Eriocheir sinensis pond and effects of decomposing plants on water quality,we monitored different layers water factors and the changes of water quality factors during plants decomposition. We monitored the changed of water quality in 3 Eriocheir sinensis eco-culture ponds and water source area from May to October 2014. The results showed that: the main excessive water quality indicators are TP and TN, excessive rate were 232.7% and 78.5%; CODMn and TP are the main excessive water quality factors, excessive rate were 80.8% and 129.5%, excessive amplitude were lower than water source area。The plants in Eriocheir sinensis pond can fully absorbed nitrogen and phosphorus. Therefore, despite a large amount of nitrogen and phosphorus was putted into the Eriocheir sinensis eco-culture ponds every day, it changed slightly. Overall, the water in Eriocheir sinensis pond was better than water source area, the water would not pollute the surrounding environment.We monitored water quality factor of top, middle and bottom layers in 3 consecutive sunny in August 2014 in 3 Eriocheir sinensis eco-culture ponds in Maogang town, Songjiang District, Shanghai. The results showed that all the water quality factors existed diurnal variation and stratification, but water temperature, potential of hydrogen（p H）, chemical oxygen required by permanganate method（CODMn） and phosphate(PO₄^3--P) changed little in three layers（P>0.05）. Ammonium-nitrogen（NH₄+^-N） and nitrate nitrogen（NO₃^--N） had a obviously difference in three layers（P<0.05）. Ammonium-nitrogen（NH₄+^-N） and nitrite nitrogen（NO₂^--N） reached the highest at 5:00,but water temperature, DO, p H and nitrate nitrogen（NO₃^--N） reached the lowest at 5:00. The diurnal variation of ammonium-nitrogen（NH₄+^-N） and dissolved Oxygen（DO） showed negative correlation.To study the influence of Hydrilla verticillata,Elodea nuttallii and Antirrhinum majus decomposition on water quality in Eriocheir sinensis eco-culture pond in july to September 2015 in in Maogang town, Songjiang District, Shanghai. The results indicated that decomposition rates of three kinds of plants have the same characteristics, it was rapid in the early but slow in the late. The decompose rate of Hydrilla verticillata and Elodea nuttallii were approximated and faster than Ceratophyllum demersum.At the end of experiment, the mass loss rate of Hydrilla verticillata, Elodea nuttalliiare and Ceratophyllum demersum were（72.3±2.1）%,（71.7±1.5）% and（58.3±0.6）%.Each water quality indicators changed great in the early stage of decomposing, TN concentration changed the biggest in all the indicators. The first three days, TN concentration of Hydrilla verticillata, Elodea nuttalliiare and Ceratophyllum demersum increased about 123,124 and 66 times. Along with the experiment, part of nitrogen and phosphorus in the water deposited into the sediment. So, the large biomass residues of submerged plants should be controlled avoid secondary pollution caused by excessive decomposition of submerged plants.