| Pond aquaculture is the main way of aquaculture in China, which is also the main source of aquatic product. According to the China Fisheries Yearbook of 2010, the area of aquaculture pond reached to 4,164,000 hm2 in 2009; and the production reached to 18,529,100 tons, which occupied above 51.2% of the total aquaculture production. The pond aquaculture in China has a long history, and China is one of earliest countries of the world to develop ecological aquaculture. The ecological aquaculture model of "fisheries based on mulberry culture", "fisheries based on sugarcane culture", and so on, and the "intensive aquaculture based on 8 kinds of aspects" culture technique, which was created by Chinese people, make a great contribution to the world aquaculture.As the Chinese ponds were mainly constructed during 1970s to 1980s, the problems of environmental degradation of aquaculture, old and ruined facilities, heavy collapse and sedimentation, heavy contamination and waste of water source and so on, are common. Meanwhile, as the pond aquaculture always used the traditional mode of production, the problems of simple mode in aquaculture, low ecological and economic efficiency, limit the sustainable development of pond aquaculture heavily.Aquaculture pond ecological system is a relatively independent and integrated system, in which the culture organisms are affected by the biotic and abiotic environment. The factors affecting pond aquaculture include pond’s orientations, depths, length-width ratios, and so on. The physical factors affecting it mainly include solar radiation, weather and climate, temperature and layering, hydrology and water current. The chemical factors affecting it mainly include the water composition, soil property, salinity, pH value, alkalinity and CO2, hardness, acidity, decomposition of organic matter, oxidation-reduction potential, nitrogen, phosphorus, sulphur, and so on. The biotic factors mainly contain the community and population of the pond ecosystem.This research was mainly carried on to the mass pond aquaculture of freshwater fish in Jiangsu and Zhejiang regions, from the 4 aspects of pond aquaculture pollution, pond ecology, engineering techniques of pond ecology and regulation and control of ecological engineering aquaculture system, to provide certain theoretical guidance and technical reference for establishing pond ecological engineering techniques. The main contents and results are as follows.The research results found that, the water quality of most rivers and lakes in Jiangsu and Zhejiang regions at present was in level IV or even worse, which was not fit for aquaculture, and water treatment is in need for aquaculture. The water requirement of traditional aquaculture is about 4-6.5 m3/kg fish. The direct discharge of TSS, CODMn, TN and TP of the pond was about 2,280kg/hm2·a,199 kg/hm2·a,101 kg/hm2·a and 5.0 kg/hm2·a, respectively. During August and September, the mean concentration of the total nitrogen, ammonium nitrogen, nitrate nitrogen and total suspended solids was above 2.44 mg/L,0.56 mg/L,7.38 mg/L,0.01 mg/L and 165 mg/L, respectively. The level of total nitrogen, total phosphorus and organic matter of the pond sediment was 6.9,1.5 and 3.9 times higher than that of natural soil, and the rank order of the sedimentation was nitrogen> organic matter> phosphorus. Water discharge and dredging were the main pollution discharge of pond aquaculture.According to the analysis methods on budget of the nitrogen and phosphorus at home and abroad, the results showed, the input of nitrogen of mass freshwater pond aquaculture in Jiangsu and Zhejiang regions was about 90.24 g/kg fish, in which the feed, fertilizer and external water source accounted to about 80%,11% and 9%, respectively. The nitrogen discharge of pond water and sediment was 13.76 g/kg fish and 57.04 g/kg, respectively, which accounted for 15.2% and 63.2% of the nitrogen input, respectively.And the input of phosphorus was 21 g/kg fish, while the input from feed, fertilizer, water source and precipitation was 82%,9.5%,8% and 0.2%, respectively. The aquatic product accounted for 45.2% of the total phosphorus input. The phosphorus discharge of pond water was 1.1 g/kg fish, which occupied 5.3% of the phosphorus input and 9.7% of the phosphorus discharge. The phosphorus sedimentation was 10.38 g/kg fish, which occupied 49.4% of the phosphorus input and 90.3% of the phosphorus discharge.The analysis found, there were 48 species of phytoplankton,24 species of zooplankton and 15 species of benthos in the pond. The mean density of the phytoplankton, zooplankton and benthos was 3.10×107 cell/L,15.8 ind./L and 1,079 ind./L, respectively. The mean biomass was 475 g/m2. The dominant algae were blue-green algae, green algae and diatom. The dominant zooplankton was Brachionus calyciflorus, Diaphanosoma brachyurum and Cyclops vicinus. And the dominant benthos was B. purificata, B. purificat and A. longicornis.The range of Shannon Wiener index (H’) of the pond phytoplankton and zooplankton during July and September was 1.60-2.10 and 0-1.83, respectively. The chlorophyll a content was 104.8±12.3μg/L. The range of TSI was 65-86, and the Margalef diversity index was 1.0-10.4. The range of Goodnight revised index (G.B.I) of benthos was 0.30-0.88, and the index of biology pollution (BPI) was 1.1, which showed the eutrophication of aquaculture ponds.Study on the variations of the pond algae and the relationship with nitrogen and phosphorus concentration. The results showed, there were obvious seasonal, diurnal and layering changes of the pond algae, and the mean density during winter and spring was the highest, while that of the autumn was the lowest. The dominant algae of the pond were green algae, blue-green algae, Cryptomonas and diatom, with obvious seasonal variations. The proportion of different algae occupied depended on different time.There were direct relationship between the algae density and the concentrations of ammonium nitrogen and soluble reactive phosphorus. The highest level of ammonium nitrogen occurred at about 05:00 a.m., and the lowest happened at about 17:00 p.m., while the highest level of soluble reactive phosphorus appeared at about 01:00 a.m., and the lowest level occurred at about 13:00 p.m., which was negative related to the algal density.. These showed the situation of assimilation of algae for nitrogen and phosphorus. The key physiochemical indexes affecting the phytoplankton depended on the seasons. Water temperature, nutrients, pH values were the main factors affecting the density and species of the phytoplankton. The changes of chlorophyll a depended on the seasons, and had good relationship with TP, however, its relationship with TN and COD was not significant. It showed that Chi.a was affected by the non-point source of P, and the main limitive factor was P.Study on the growth characteristics of Chlorella in the aquaculture system and its effects on the culture. The results found, under the situation of light density of 4500 Lx and water temperature of 25℃, Chlorella’s growth was in Logistic, and the K value was 2543×104, while r value was 0.5913. The maximum sustainable yield (MSY) was 375.91×104cell/(mL·d), and the Chlorella’s productivity of each 106cell/L was 9.4 J/(L·d). The nitrogen and phosphorus concentration affected the density of Chlorella, but it didn’t affect the algal growth cycle significantly (P<0.05). Chlorella can effectively absorb the nitrogen and phosphorus, and there were some differences between the absorbance for the three state of nitrogen. Under the water temperature of 25℃, the restriction density for juvenile Tilapia was 4.47 g/L, and Chlorella can alleviate the restriction. Compared with the aquaculture of no Chlorella, the aquaculture with Chlorella can improve the juvenile Tilapia’s, relative weight growth rate by above 37%, and reduce the food coefficient rate by 4.1%-45.8%. Culturing Chlorella in the aquaculture water can improve the water quality and culture effect.Study on the constructing techniques and purification affectfound thatbiological slope is a kind of wetland system between surface flow wetland and undercurrent wetland. The purification rate of biological slope on total nitrogen, total phosphorus, COD of the pond water was 0.27g/h·m2,0.015 g/h·m2 and 0.94 g/h·m2, respectively. And the removal rate of the ammonium nitrogen, nitrite nitrogen and chlorophyll a was 46%,65% and 8.8%, respectively. Building biological water treatment facilities using pond slope is not only good for purifying pond water, but also good for lengthening the pond life. And it is also good for saving land for building artificial wetland.Under the water current speed of 0.0061 m/s, the removal rate of the biological bag for ammonium nitrogen and nitrite nitrogen in the pond discharged water was 19% and 45.5%, respectively. And the removal rate for the pond water was 0.61 g/h·m3 and 0.133 g/h·m3, respectively.When the residence time was 0.75 h, the removal rate of the ceramsite biochemical filter bed for chlorophyll a, total phosphorus, total nitrogen reached 62%, 3.7%,53.8%, respectively. And the removal efficiency for chlorophyll a, total phosphorus, total nitrogen was 2.7 g/h·m3,0.07 g/h·m3,1.65 g/h·m3, respectively.The removal rate of ammonium nitrogen, total nitrogen, total phosphorus, soluble reactive phosphorus, BOD5 and CODMn of the biological pond for the discharged pond water was 19.8%,14.3%,29.6%,29.1%,21.3% and 43.1%, respectively. The area rate range of the ecological pond and traditional pondwas about 1:3-7.Study on the common biological floating bed found that the range of TN in the pond water was 1.65-5.42 mg/L,1.62-3.13 mg/L,1.63-2.62 mg/L, respectively, when the floating bed accounting for 5%,10%,20% of the aquaculture area. And the range of TP was 0.18-0.28 mg/L,0.17-0.26 mg/L,0.18-0.21 mg/L, respectively. Comprehensive analyses consider that the coverage rate of the common biological floating bed should not exceed 20% of the pond area.Complex biological floating bed can purify biochemically and biologically, whose purification rate was well above that of the common floating bed. Under the load capacity of 1kg/m3 of traditional mass freshwater aquaculture, the rate of complex biological floating bed accounted was about 8.5% of the pond area. The purification effect was related to the aquaculture density, culturing species, filter specific surface area and aeration amount.Usually, the purification effect of the ecological ditch is related to the vegetal growth and temperature. The construction of the ecological ditch should accord to the habit of the vegetal with combination of their habitat to proceed spatial and temporal distribution, which could improve the water quality and landscape construction in a long term. Study on the choosing vegetal for the wetland and purification effect of the aquatic vegetal. Wetland plants not only remove nutrients and pollutant, but also provide appropriate micro-environment for the substrate microorganisms. The general principle of choosing wetland plants was introduced, and the purification effect of aquatic plants, such as Hydrocharis dubia, Nymphaea tetragona, Elodea nuttallii, Hydrilla verticillata, Ceratophyllum demersum, Oenanthe Javanica, Phragmites australis, Iris tectorum, Acorus calamus, and so on. The purification effects of different combination of aquatic plants were analyzed, and the results showed the nutrients absorbance effect depended on different plants and their different growth cycle. According to their biomass, purification effect and whether easy for planting, Aponogeton lakhonensis, Zizania aquatic, Scirpus tabernaemontani, Typha angustifolia, Canna lily, Iris tectorum and Thalia dealbata, which were fit for Zhejiang and Jiangsu regions were chosen.The aquatic plant, such as lotus and Zizania aquatic, has good purification effect and economical efficiency for water. The results found that, compared with the traditional culture way, ecological culture of lotus can reduce the concentration of total nitrogen, total phosphorus and COD as high as 24 times,10.3 times and 3 times, respectively. And the reduction of total nitrogen, total phosphorus and COD of ecological Zizania aquatic culture water was as high as 2.3 times,3.3 times and 5.6 times, respectively. Each 100 kg lotus and Zizania aquatic can absorb 2.4 kg nitrogen and 40% of the phosphorus.Study on the system of ecological engineering water recirculation ponds aquaculture Found, the total nitrogen, total phosphorus and CODMn of the system of ecological engineering water recirculation ponds aquaculture was lower than 2.18±1.09 mg/L, 0.46±0.12 mg/L,9.0 mg/L, respectively, which was 52%,29% and 73% of the control pond and significantly lower than the control pond (P<0.05). The results found that, the removal rates of total nitrogen, total phosphorus and CODMn from the aquaculture emissions were 52%-59%,39%-69% and 17%-35%, respectively, in the constructed underflow wetlands; and the average removal rates of total nitrogen and total phosphorus were 18.5% and 17%, respectively, in the ecological ditch; and the average removal rates of total nitrogen, total phosphorus and CODMn were 24.7%, 27.1% and 26.75%, respectively, in the eco-pond. Compared to the traditional pond aquaculture, the ecological engineering water recirculation ponds aquaculture system can save as much as 63.6% water and reduce 81.9% COD emissions, which show significant effects on water saving and reducing pollution emission.The dominant algae of the system were green algae, including Chlorella, Chroococcus and Cyclotella, in the recirculation system. And the dominant algae of the control pond were Microcystis, Merismopedia and Ulothrix. The removal rate for algae of underflow wetland and ecological ditch was 75.9% and 55.2%, respectively. And the removal rate for chlorophyll of surface flow wetland and underflow was 58.3% and 91.6%, respectively. The area ratio of the ecological ditch, ecological pond, underflow wetland and aquaculture pond in the recirculation system should be on the basis of the culture species and density, and the area ratio of the ecological engineering facility usually shouldn’t exceed 20%.Study on the regular pattern of the physiochemical indexes of the pond and the effects of water layer exchange found that the DO, water temperature, ORP, pH in daytime was usually higher than that of the night, and the highest level was usually at about 13:00 when the light was the strongest, and the lowest level was at 3:00-5:00 a.m. However, the changes of ammonium nitrogen and reactive phosphorus were the opposite. The changes of DO, pH and water temperature reduced with the increase of the water depth.Water layer exchange can mix the water and increase the DO of the sediment and ameliorate oxygen debt, and activate the ecological effect of the sediment, and boost the remnant feed’s sedimentation, excrement decomposition and transformation, which can effectively reduce the harmful matters, such as nitrite nitrogen, ammonium nitrogen, hydrogen sulfide, Escherichia coli, suppress the rot of the water.The combined study showed that the discharge pollution was severe and the external water source was not fit for aquaculture. Sedimentation pollution and discharge pollution were the main form of pond pollution. And the pollution biology characteristics of the aquaculture pond showed the eutrophic state of the pond. The seasonal, diurnal and layering changes of the algae in the pond had great relationship with the nutrients’ content, illumination, and temperature. Chlorella was the dominant alga. The algal population composition had effect on the aquaculture. The relative study is helpful for providing theory of building ecological regulation.Ecological slope, stereoscopic elastic filler purification bed, ceramsite biochemical filter bed, ecological pond, biological floating bed, ecological ditch, and so on, are the main ecological engineering regulation facilities with special purification efficiency each other. Aquatic plant is one of the important parts of the ecological engineering system, and reasonable plants match is good for establishing stable and effective system. The model of ecological engineering pond recirculation aquaculture system is "ecological, safe and efficient", which is the effective way to change the traditional aquaculture way and improve the aquaculture benefit. Water layer and DO regulation is important regulation, which can save energy and feed, and improve the aquaculture effect and protect the safety of aquaculture. |
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