Tidal Flushing Time of Marine Fish Culture Zones in Hong Kong

Accurate determination of flushing time is crucial for maintaining sustainable production in fish culture zones （FCZs）, as it represents the physical self-purification capability via tidal exchange with clean water in the outer sea. However, owing to the temporal and spatial complexity of the coastal flushing process, existing methods for determining flushing time may not be generally applicable. In this paper, a systematic method for determining the flushing time in FCZs is presented, in which bathymetry, runoff, tidal range and stratification are properly accounted for. We determine the flushing time via numerical tracer experiments, using robust 3D hydrodynamic and mass transport models. For FCZs located in sheltered and land-locked tidal inlets, the system boundary can be naturally defined at the connection with the open sea. For FCZs located in open＇waters, hydrodynamic tracking is first used to assess the extent of tidal excursion and thus delimit the initial boundary between clean water and polluted water. This general method is applied to all designated marine FCZs in Hong Kong for both the dry and wet seasons, including 20 sheltered FCZs （in semi-enclosed waters of Tolo Harbour, Mirs Bay, and Port Shelter） and 6 FCZs in open waters. Our results show that flushing time is the longest in inner Port Shelter （about 40 days in dry season）, and the shortest for the FCZs in open waters （less than one week in dry season）. In addition, the flushing time in dry season is commonly longer than that in wet season： 20%~40% for most well-sheltered FCZs; 2.6-4 times for the others. Our results indicate a positive correlation between the flushing time and distance to open boundary, supporting the view that the flushing time of a FCZ is closely related to its location. This study provides a solid basis for mariculture management such as the determination of carrying capacity of FCZs.

The Effects of Pen Fish Culture on the Ecological Environments of Taihu Lake

Effects of pen fish culture in Taihu lake were studied and summarized. During 1984 to 2001, pen fish culture of Taihu lake developed from extensive models to intensive and high-returned ones, the cultured species were shifted from fishes to crabs. Pen fish culture has caused eutrophication and detrimental effect to the ecological environment and fishery. The measures of sustainable development for pen fish culture and ecological environment protection were suggested.

The Program of Fish Culture in rice fields has been developed in Zhejiang Province

1996 is the first year for realizing the object of fish culture in 66,600 ha of rice field in Zhejiang Province. The provincial government has appropriated $ 24,000 per ha for starting capital. Starting from this year, counties with the tradition of fish culture in rice fields as Youngjia and Qingtian have put stress on popularizing the new technique of fish culture in ditches and puddles to raise the yield for per unit area. In areas of Central Zhejiang and North Zhejiang with hilly land and plain area with double—season rice, people have changed traditional fish varieties into special and excellent fish varieties.

Improving water use efficiency by integrating fish culture and irrigation in coconut based farming system:A case study in Kasaragod District of Kerala(India)

The crop production in the district of Kasaragod in Kerala State(India)is characterized by low input-low yield concept and rain-fed agriculture.A field study was conducted in Western Ghat region of the district to develop a suitable rainwater harvesting system adoptable to hilly terrains and to test its efficacy for improving the use efficiency of the harvested water by its multiple uses.The cost-benefit analysis of the water harvesting system was also carried out to find out its affordability to farmers.The water harvesting system has been developed by integrating three components:(i)improving the productivity of coconut and component crops in the cropping units(ii)developing multiple water use systems,and(iii)the conjunctive use of the harvested water along with other surface and groundwater resources.Based on the estimated annual costs and returns,the Benefit-Cost ratio was found to be 1.69 and all other financial viability criteria(IRR and NPV)were also found favourable for investment on a lined water harvesting tank integrated with a micro-irrigation system and fish farming.The study suggested that the rainwater harvesting could be implemented as a viable alternative to conventional water supply or on-farm irrigation projects considering the fact that any land anywhere can be used to harvest rainwater.Further,the water use efficiency can be improved through effective harvesting and subsequent multiple uses of stored water.

Analysis and Evaluation of Nutrient Composition in the Wild, Pond- and Lake-Cultured Topmouth Culter (Culter alburnus)

Research was conducted on topmouth culter (Culter alburnus) grown in ponds and lakes as well as wild types in order to determine their chemical composition and nutritional value. There are three types of fish that differ in their proximate composition, amino acids, fatty acids, and minerals. Wild fish had a significantly lower crude lipid contents than cultured fish (P P ∑PUFAs) showed an obviously opposite trend. As compared with cultured fish, wild fish had significantly higher levels of n-3 PUFAs, arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahxaenoic acid (DHA) (P P > 0.05), except for Na, Fe and Se. In conclusion, diet composition and external aqueous environment may determine the differences between wild and cultured topmouth culter.

Globally Important Agricultural Heritage Systems(GIAHS)of China:the challenge of complexity in research

The challenge of researching Globally Important Agricultural Heritage Systems(GIAHS)as complex systems forms the subject matter of this study.Complex adaptive systems are those that combine natural ecological processes with human interactions to produce a mutually supportive agro-ecological system.In China,these highly varied systems have the added dimension of long historical time,in that they have evolved over many centuries and thus add a historical dimension to the natural and human dimensions of complexity.In preparing research on GIAHS,it is clear that seeing GIAHS sites as whole systems is an essential starting and ending point.Examining the adaptive capacity of a GIAHS with its multiple scales and complex interdependencies is a major challenge for researchers accustomed to specialized disciplinary thinking.A GIAHS represents a mature agro-ecological system with human agency as a central component that has been honed over many centuries,and has already adapted to many perturbations and changes.The beauty of the GIAHS is in the integration of custom,knowledge,and practice,and it should be studied for its"wholeness"as well as for its resilience and capacity for"self organization."The agro-ecological approach opens the possibility of researching a system as a whole and of taking its complexity seriously.This study reviews the essential features of the GIAHS as a complex adaptive system where uncertainty is normal and surprise is welcome and,in a case study of Qingtian rice–fish culture system,focuses on new perturbations,namely loss of young people and the introduction of tourism.