Fishpond Water Improved By Ecological Measures

In freshwater aquaculture of pond, scientific water management is the foundation for healthy aquaculture. It is getting recognized to treat fishpondwater by ex-situ remediation of paddy field and lowland around the fishpond besides situ purification technology such as plant floating floor, microbial preparation and biological membrane etc, the above ex-situ purification measures are effective ecological engineering technology to solve environmental pollution that brought by high density aquacunlture and also they are convinent to achieve a healthy fish farming. Fishpond farming and aquatic cash crop cultivation are relatively popular in the southern plains, so that the area is equipped with the objective condition for a combination of fish farming and crop plantation, and it is essential for aquiculture wastewater purification and reuse to establish compound system that constitute aquaculture pond and plant purifying pond and paddy field which are linked by necessary farmland works. Nitrogen and phosphorous contented in the aquaculture wastewater are nutrient sources for crop production, an effective recombination of hydrophyte plantation and fishpond farming is advantageous to fishpond water improvement the nutrient cycling, and which is significant to prevent non-point agricultural pollution and to promote cleaning production.Closely combining the actuality of fishpond farming and crop plantation in the plain and lake are of Hubei, breaking through the traditional method that aquaculture and crop farming are done independently, multi-disciplinary knowledge and methods related to plant nutrition, soil science, irrigation and drainage engineering, agrometeorology, plant physiology, wetlands ecology and pond ecology ect, are comphrensively used for the study that is ex-situ purification of fishpond water through different ecological measures, and the experimental design based on previous experimental data obtained from the year of 2010 to 2012. The purpose of the study is to improve fishpond environment and to enhance utilization efficiency of the materials in the fishpond, thus to provide with scientific basis and then to form a compound pattern and technique for fish farming combining with lotus (rice) production which is characterized by healthy and sustainable.In our field trial base, the relevant experiments were carried out that fishpond water improved by lotus pond, paddy field, eco-ditchs and their combination. Based on comprehensive analysis of the experimental data, the main research results were obtained which are as follows:1) The retention of aquaculture water in the lotus pond can effectively reduce TP, TN, NH4+-N, NO3-N, NO2-N and CODm,,, the removal rate of these substances is increased with the extension of residence time. The removal rate for TN and NH4+-N was more than 30% and several other substances in more than 20% after staying 2 days in the lotus pond. The effect of the aquaculture water purified by the surface flow of lotus pond has a certain regularity:the removal rate for NH4+-N, NO3--N, NO2--N and CODMn in adult-plant stage is more than that in dormant stage and the effect in dormant stage is more than that in rooting stage, and for TP and TN the removal rate in dormant stage of lotus root is more than that in adult-plant stage and the effect in adult-plant stage is more than that in rooting stage.2) The removal rate for TP, TN, NO3--N and NH4+-N were 13.89%,11.43%,11.02 % and 5.73% after the system is running for 6 hours when the aquaculture water treated by the surface flow of lotus pond. Compared with the contrast fishpond, the water quality of the fishpond combining with lotus pond is good obviously, where water quality indicators such as TP, NO3-N, TURB (turbidity) and SD (water transparency) arrive to significant improvement, meanwhile TN, NH4+-N and CODmn get a marked improvement. On average, such a conclusion can be drawn that aquaculture in fishpond and plantation in lotus pond may be integrate, fishpond water may get an improvement by ex-situ treatment of lotus pond, and meanwhile the combination makes it possible that the nutrients contained in fishpond water are recycled.3) Microbial metabolic activity of the water at the inlet was higher than that at the outlet, which was founded in the system which lotus pond is used for aquaculture water purification. The possible reason is that:the water at the inlet of the lotus pond is from fishpond, which is rich in microorganisms (including bacteria) due to higher organic matter in fishpond water. In addition, microflora in the water at the inlet and outlet of the lotus pond has a maximium efficiency in carbohydrates use which range is 32.57%-46.81%, by which some materials transformed and their use efficiencies respectively are 17.37% ～ 23.66% for amino acid,12.51% ～ 16.44% for polymer and 10.08% ～ 15.42% for carboxylic acid.4) Fishpond water retented in the paddy field gets a better purification from jointing-booting stage to filling stage than that in tillering stage, an effect of fishpond water purification is more obvious with the increase of retention time that the water stay in the paddy field. During which the removal of TN is more than 60% after the aquaculture water stay in the paddy field for 6 days.5) The best effect for removal of NO3--N and TN is at rice filling stage and more than 35% of them are removed by surface flow over paddy field, the second effect is at the jointing-booting stage and the next is at the tillering stage. The highest removal for NH4+-N is at rice filling stage which average reaches to 30.87%, the second is at the earing-flowering stage and the next is at the jointing-booting stage. The maximum removal for DP and TP is at the jointing-booting stage when surface flow over the paddy field used for fishpond water purification, their removal rate is 27.70% and 23.94% respectively.6) The removal rate for nitrogen and phosphorus is different due to different irrigation sources and fertilizer dosage. Water from fishpond with higher nitrogen and phosphorus in constrast to lotus pond, so that several substances in it have a higher removal rate when it is irrigated into paddy field, the effect of water purification is more obvious especially at the jointing-booting stage and earing-flowering stage. In addition, when water from lotus pond is irrigated into paddy field the removal rate for several substances present a trendcy in different stages of rice that is:the value at the earing-flowering stage more than that at jointing-booting stage, and the value at jointing-booting stage more than that at the tillering stage.7) Constrast with normal fertilizering, the field that adop 80% of normal fertilizering dosage can remove more nitrogen and phosphorous at the jointing-booting stage and at the earing-flowering stage, the effect of water purification is obvious.8) The content of DP, DRP and TP in soil water taken at the 30 cm in the soli profile, decline with the increase of the distance that monitoring point away from the water inlet. The content of DRP in soil water is related to the irrigation water source and fertilizer dosage. Under the conventional fertilization, at 20 meters away from the water inlet, the content of DRP in soil water is significantly lower in paddy field that is irrigated by lotus pond water than that irrigated by fishpond water in tillering stage; when fishpond water is used for irrigating paddy field, the content of TP in soil water taken at the point away 20 meters from the inlet is significantly higher in the field that adopted normal fertilization dosage than that in that field adopted 80% of normal fertilization dosage at earing-flowering stage.9) The single use of eco-ditch or it combination with paddy field can inprove aquaculture water. When eco-ditch used for water purification alone, the effect increase with the increase of the flowpath and also related to the conditions of weed growing in the eco-ditche. Fishpond water treated only by eco-ditch has an obvious effect in August which is better than that in July, and the removal of nitrogen is more than that of phosphorousr. When eco-ditch combining with paddy field used for fishpond water purification, the best effect can be obtained in rice filling stage for nitrogen removal (78.26% of the N03-N and 68.16% of TN are removed), and in earing-flowering stage for phosphorous removal (more than 50% of TP is removed).The above results of the research provide a scientific basis and new technological way for ex-situ remedation of fishpond water, and that are advantageous to circulating utilization of water resources and to the zero-discharge of wastewater from aquaculture pond, which also give an effective method and new path for agricultural non-point source pollution control. For the above technological achievements to be applied to agricultural production, it is necessary to consider the microtopography in plain-lake area when engineering technology pattern for fishery combining with crop farming is studied and presented.