No abstract

Pond freshwater aquaculture, an important production mode, provides aquatic product for people, especially in south of China. Meanwhile, with the development of aquaculture technology of higher density and intensification, the environmental problem and pollution in freshwater pond have become even more acute. In this case, the water purification technology plays an important role in maintenance of the healthy aquaculture and there are a variety of water purification technologies in production practice. This paper is divided into four parts: a) the analysis of the causes of water quality deterioration in freshwater pond, b) the summary of water purification technologies in present, c) the brief analysis of the advantages and disadvantages of the in-situ remediation and ex-situ remediation, d) the prospection of pond water purification technologies in the future.

The middle and lower reaches of the Yangtze River is an important base for producing grain, cotton and oil plants, one of the most rapidly developing areas economically in China. Along with the rapid development of the economy, its environmental quality related to water, soil and atmosphere decline rifely and obviously compared with that in twenty years ago. In the meantime, flood menace still exists, drought and waterlogging coexists, and water environment and water ecology have been deteriorating. This paper emphasized more important issues related to the regional water environment and water ecology, and put forward corresponding countermeasures based on domestic and foreign experiences, so as to drive social-economy sustainable development of the region.

Chinese domestic satellite HJ-1 was launched in 2008, now it has become a significant resource for environment monitoring because its Multispectral data are characterized by 2-day temporal resolution, 30 m spatial resolution and 700 km breadth. A study case was made that HJ-1 multispectral data were used for retrieving aggregative trophic level index (TLI()) of water body of lakes in Wuhan, China. The aim of this study is to evaluate the probability of HJ-1 Multispectral data on estimating the eutrophic level of inland water. At first, the TLI() of sampling spots of some lakes in Wuhan were calculated using the monitoring water quality data. In the mean time, the NDVI of corresponding spots were calculated from the HJ-1 multispectral data which had been taken radiometric calibration and geometric correction beforehand. After that, a remote sensing inversion model for TLI() had been built through linear regression using the NDVI as independent variables. Finally, the TLI() of all water bodies of Wuhan lakes were inversed with this model and a map for its spatial distribution was drawn up. Results demonstrated that there were good linear correlation relationships between the TLI() and NDVI of HJ-1 Multispectral data, and the distribution of inversed TLI() of the lakes accorded with the reality quite well. According to the above, an inference can be made that the methods to evaluate lakes eutrofication based on the HJ-1 satellite multispectral data may provide a cheap and rapid way for real-time monitoring and evaluation of lakes eutrophication.

Water quality is important to fishpond culture, and it is required to improvement in the process of aquiculture especially as it impact on normal growth for aquatic animals. Usually the purification of fishpond water adopt two methods that are in-situ and ex-situ purification, water from fishpond purified by paddy field then to return the pond belongs to ex-situ purification of fishpond water. The field experiment results showed that water form fishpond flowing through the paddy field surface more than 20%~24% of total phosphorus and 25%~33% of total nitrogen are removed which is beneficial to both fertilizer-saving for rice production and water environment improvement for pond culture, so it is liable to popularize in the middle and lower reaches of the Yangtze Rive, China. In order to extend the ex-situ purification of fishpond water by paddy field, it is needed to determine suitable size of paddy field. Based on field experiment and the results analysis, the paper gave a method to determine the length and width of the land block. The size of paddy field in long dimension is determined by flow path necessary for water quality indicators to achieve their allowable emission, the width of paddy field is calculated according to the relevant parameters including daily hydraulic load which is a total quantity of water from fishpond into paddy field, inflow rate per unit width in paddy field, a duration that fishpond water flow into paddy field for purification. Calculation and analysis showed that, for ordinary decentralized fishpond managed by peasant household, paddy field block with long side of 100 m long can satisfy the removals of TN and NH3-N contained in fishpond water through surface flow in paddy field, but can not meet the removal of TP which can be solved by flow path extension using series connection of the two adjacent plots set in standardization field block, or by setting up ecological ditch in paddy field so as to strengthen water purification.