Lake eutrophication is an ecological issue,and a concentrated reflection of the environmental problems in the catchment where the lake lies.An ecological problem should be solved through ecological ways.The key to regulating water environment lies mainly in rural area,while controlling rural environment pollution depends mainly on ecological means.Only when a catchment is deemed as a holistic ecological system,within which relationships between various factors are regulated to realize balanced ecosystem,can the water environment problem of lakes be solved at the root.

Proceeding from the concept of integrity and systematicity of the basin,relationships of the water environment quality of the Taihu Lake Basin with the social economy,resources exploitation and other human activities in that region were investigated and analyzed and so was the need for early warning of water environmental risks of the basin.On such a basis,overall objectives and structural design of the water environmental risk early warning system was put forth,and such an early warning system was built up integrating three sub-systems,early warning program customization,early warning model library and three-dimensional display of prediction results,thus laying down a solid foundation for water environment risk assessment and setting up of an early warning platform for the Taihu Lake Basin.

In the headwater area of the Taihu Lake Basin,lakes are dotted extensively and linked to each other with rivers.A case study was conducted of the Gehu Lake-Taige Canal and Caoqiao River-Taihu Lake to explore characteristics,ecological status,and water environment pollution of the water system and major problems existing with the system.On such a basis,a pollution control program was put forth for waterbodies linking river and lake.Due to the dense water network and shallow lake in the Taihu Lake Basin,hydrological conditions and water pollutants in the environment under the river-lake linked are extensively explored in this study.The program includes the following strategies: intensify control of pollutants at the source,mitigate pollution load,and combine pollution control with ecological remediation,so as to raise the self-purification capacity of lakes and self-remediation capacity of the ecosystem;intercept pollutants and purify in-flowing rivers so as to ensure provision of clean water sources for in-coming rivers;manage various pollutant sources in watersheds of in-coming rivers and intercept and control pollutants alongside the river banks from coming into the in-coming rivers,so as to build up clean rivers and improve the natural purification capacity of in-coming rivers and hence to further reduce pollutants moving with the water of in-coming rivers;set up ecological interception projects at the joints of river and lake and other key waters to intensify purification of water off pollutions so as to further reduce pollutant flow into lakes;and implement system regulation and optimal configuration so as to construct a safety shelter system to control pollution and protect water environment of the Taihu Lake at its headwater areas.Migration,transformation and movement behavior of pollutants under above-mentioned conditions are the major scientific problems.Cooperative method and optimization plan of ecological regulation for waterbody treatment in the river-lake linked basin should be developed based on regional water shed characteristics and ecological environment issue.Meanwhile,the non-point pollutant from town and villages along the rivers are also the main control strategy.Rural domestic wastewater disposal should be conducted by using the solid waste as carrier under the conditions of the natural decomposition on pollutants.Pollutants degradation process was examined to the rate and mechanism for the ecosystem in the shallow lake under various hydraulic condition and main biological factors configuration.The self purification capacity of the scientific issues on the shallow lake must be addressed.

Multi-media-soil-layering(MSL) is a new type of decentralized domestic wastewater treatment system,especially fit for rural areas.In the experiment four MSL systems were constructed in box(50 cm×10 cm×60 cm) comprising typically soil mixture layers alternated with permeable layers.The soil mixture layer contained sandy soil,sawdust and charcoal/straw,iron scraps/bentonite mixed at a ratio of 7∶2∶1 by dry weight,and the permeable layer was composed of zeolite and gravel.The MSL systems ran continuously for two months at a hydraulic loading rate(HLR) of 500 L·m^-2·d^-1.Results show that the four MSL systems did not differ much in average COD_Cr removal rate,varying in the range of 79.58%-80.22%;and their TP removal rate was in the range of 47.83%-82.60%,and addition of zeolite and bentonite in the permeable layers increased TP removal rate by a large margin;their TN removal rate varied in the range of 29.74%-57.89%.Permeable layers of zeolite were better than those of gravel.The mixture of charcoal and sawdust was more suitable as organic carbon source than straw in the MSL systems.

The technology of anaerobic fermentation for biogas production using domestic decayable solid waste from rural disperse households as base substance and flowing domestic wastewater from the households as nutrient distributor is developed to realize co-disposition of the two types of waste in the rural area.Tests of the technology show that the use of the wastewater increased biogas generation from the solid waste.The treatment of filling of wastewater once every 5 days is higher in cumulative biogas production than the treatment of filling of wastewater once every 3 days.With the water filling rate set at 100 mL,the methane concentration in the digester was 2.4 times(P>0.05,n=6) higher in the treatment of filling of wastewater once every 3 days than in the control(filling of distilled water) and the cumulative methane production was 4.9 times higher in the former than in the latter in 45 days.Methane accumulation in the digester was in direct proportion to wastewater filling rate.With the wastewater filling rate increasing from 50 to 150 mL,methane accumulation increased by 2.1-4.5 times.The outflow from the digester was>10 g·L^-1 in CODCr ca 600 mg·L^-1 in TN and ca 100 mg·L^-1 in TP.So it can be used as liquid fertilizer for direct application in the farm fields. 

The technique of complex three-dimensional ecological floating-bed is an effective water pollution control technology.The complex floating-bed is composed of a framework with grids made of bamboo,plants and mollusks,such as snails and mussels,on the grids,an elastic material placed on or under the framework.Colocasia esculenta,Sagittaria sagittifolia,Eleocharis dulcis,Oenantha javanica,Ipomoea aquatica and Ganna generalis were used as subjects in the research on their effect in removing nitrogen and phosphorus from slightly polluted water body in summer and fall.Results show that the N and P removing effects of the six floating-beds different in plant on the bed followed the order of Ipomoea aquatica>Ganna generalis,Eleocharis dulcis,Colocasia esculenta>Sagittaria sagittifolia,Oenantha javanica in summer and Colocasia esculentat>Sagittaria sagittifolia,Ganna generalis,Ipomoea aquatica>Eleocharis dulcis,Oenantha javanica in fall.Obviously Colocasia esculenta showed good N-removing effect in both summer and fall,with maximum removal rate reaching 71% and 62%,respectively,of total N,while Ipomoea aquatica is good in P removing with maximum removal rate reaching 30% and 81%,respectively,of total P.Comparison between the new floating-bed with the traditional flat floating bed in N and P removing effect demonstrates that the former enjoys a bright prospect in application to ecological remediation of slightly polluted water bodies.

According to the designing idea of integration system,a river-lake waterbody purification system powered by green energy(solar and wind energy) was developed.The system is composed of three sub-systems,i.e.solar and wind power generator system,aerobic biological contact oxidation system and phyto-biological system.The tests of water quality after the system operated continuously for over 7 months demonstrate that the system performed quite well,in oxygenating the waterbody and improving its water quality.The content of dissolved oxygen in aerated zone was maintained in the range of 6.5-11.2 mg·L^-1.The water after treatment in the purification system was uplifted by one grade in quality.

Based on the features of the major water source areas in the lower reaches of the Changjiang River and characteristics of water pollution accidents,a water flow and quality prediction model,one-dimensional for the whole and two-dimensional for subsection,was established,using the Jiangsu section of the Changjiang River as a case for study,and further on,a risk early warning model was built up for water source areas in that region,thus realizing dynamic simulation of processes and early warning of water pollution risks of fixed and moving sources.By combining the water quality prediction model,risk early warning model,GIS,remote controlling and automation technology,a water source sudden water pollution incident early warning system was developed.The system may accurately and visually display scopes and trends of the impacts of water pollution accidents and provide scientific basis for decision-making in risk early warning and addressing water pollution accidents in water source areas.

Based on the hydrodynamic features of river networks in plains,a hydrodynamic model for the river network in Changzhou was set up with the aid of MIKE11 modeling system,and its parameters were calibrated and validated with the hydrological data monitored in 1997,1999 and 2009.It was found that with the river bed roughness varying in the range of 0.020-0.035,the calculated results agree well with the measured data,properly reflecting the major hydrodynamic feature of the river networks.

Under the current technological conditions,a relatively simple method was used to estimate non-point source pollution(NPS) load in the Taihu Lake Basin.Through field survey and investigation,pollutant producing coefficients of various types of pollution sources,i.e.,farming,rural and urban domestic wastes,livestock and poultry breeding,and aquiculture were obtained.The coefficients were used in combination with remote sensing and GIS data to calculate pollution loads of various types of pollution sources,separately.Results show that domestic activity and livestock and poultry breeding are the main sources of NPS in the region,contributing 34%,58% and 61% to the total pollution load of the region in TN,TP and COD,respectively,while farmland has a relatively small share in NPS.Therefore,it is essential to set livestock and poultry breeding and domestic activity as priority for control of NPS in the Taihu Lake Basin.

The National Water-Quality Assessment Program(NAWQA) implemented by the U.S.Geological Survey(USGS) has been introduced.The program has a section dedicated to study of pesticide pollution in surface water of the country,which includes a nation-wide survey and study of pesticide pollution in surface water(rivers and lakes) of the country in 1992-2001.Based on the study of the data collected during the survey,the section summed up a list of pesticides detected in the surface waters,their concentrations and geographic distribution,and seasonal variation of the concentrations as well,which are believed to be closely related to the use of pesticides and also to a series of factors,such as climate,physico-chemical properties of the pesticides and local hydraulic systems.A screening-level perspective on potential significance of pesticides to aquatic life and fish-eating wildlife was obtained by comparing concentrations measured in streams with water-quality benchmarks in the guidelines established by USEPA.The levels of pesticides detected in surface waters and seasonal variation patterns of pesticide concentrations in European countries have also been briefed.Shortcomings in the formulation of the existent water quality standard system of China were analyzed as well.Based on the above-mentioned studies,it is recommended that China should perform selective monitoring of the pesticides commonly used in China and find out characteristics of the temporal-spatial distributions of these pesticides in surface waters,and based on the laws of seasonal variations of their concentrations,push forward the work of formulation of benchmark criteria for evaluation of surface water quality and define risk assessment methods for pesticide residues in the surface waters of the country,and hence exercise overall control and management of pesticide pollution of surface waters in the country.

A case study was performed of the "pig-biogas-fruit-fish" eco-agriculture model in Xinglin Farm,which is located in Longtang Township,Dingnan County,Jiangxi Province,for systematic study on key techniques and agricultural non-point pollution control effect of the model.The farm planted trees on top of the hills for soil and water conservation,and navel orange trees in terrace fields with grasses growing like a cover on the hillside,kept protective vegetation belts at the foot of the hills,set up pigsties and biogas digestors in the valley and built up multi-leveled fish ponds in the downward,thus forming an integrated "pig-biogas-fruit-fish" eco-agricultural system that features closed material cycle,cascade use of energy and ecological protection.The extension of this model may effectively help the control of agricultural non-point pollution,prevent water quality degradation of the headwaters of Dongjiang River and yield remarkable ecological,economic and social benefits as well.

Through household interviews,input of fertilizers and pesticides in citrus orchards and its potential environmental impact in the headwater area of the Dongjiang River(HDR) was investigated and analyzed.Results show that the input is lower in cultivation of Wengan citrus than in that of navel orange.Inputs of fertilizers differ sharply between cultivation patterns,i.e."pig-biogas-fruit","fruit-tree only" and "organic".Moreover,the farmers generally apply fertilizers and spray pesticides only by experience.Over 50% of the farmers apply fertilizers excessively and most of them spray pesticides 12-13 times a year on average,which brings about a great pollution risk to the environment,especially water environment.Analysis shows that to intensify training and technical guidance of farmers in applying fertilizers and pesticides scientifically,to readjust the species composition of the orchards,and to promote organic cultivation through adoption of ecological compensation mechanisms are effective measures to reduce the environmental pollution caused by citrus orchards in HDR bring about to the environment.

Establishment of an applicable indicator system for assessment of comprehensive benefit of water pollution control projects is a sign of scientific,standardized and quantitative testing of levels and effectiveness of water pollution control projects.Principles and methods for the establishment of such a system are systematically put forth.Based on purposes of the water pollution control projects,an indicator system for assessment of comprehensive benefit of water pollution control projects has been established.This indicator system is concise,practical,user-friendly and able to objectively,accurately,and comprehensively reflect quality of water pollution control projects.On such a basis,standards and their weights of various grades of the assessment indicator system for the Gehu Lake region have been worked out according to the rural characteristics,water environment,economic and technological conditions of this area.

Industry restructuring is a critical condition and an effective means as well for controlling amount and types of pollution.Take the Jiangsu and Zhejiang section of the Taihu Lake Basin as an example,industrial structure of its GDP,internal structure of its secondary industry and COD it discharged to rivers in 2007 were analyzed with COD discharge per 10 000 Yuan GDP as quantitative index.Results show that its GDP in 2007 was 1 753 billion,of which the three industries formed a ratio of 2.6∶56.6∶40.8 and its average COD discharge per 10 000 Yuan GDP was 1.76 kg.The primary industry was the highest in average COD discharge,reaching 13.86 kg per 10 000 Yuan,followed by the secondary industry and the tertiary industry,being 2.41 and 0.08 kg per 10 000 Yuan,respectively.But in terms of total amount of discharge,the secondary industry ranked first,responsible for most of the organic pollutants in the waterbody.Scenario analysis reveals that to increase the proportions of the tertiary industry and machine manufacturing industry of the secondary industry,both being low in COD discharge per unit value of GDP,and reduce the proportions of textile,printing and dyeing,paper-making,beverage,and food industries may effectively reduce COD discharge per unit GDP.