Carbon,Nitrogen And Phosphorus Budgets In Reclaimed Shrimp Ponds Of The Min River Estuary

With the decrease of global natural fishery resources and the increase of human demand for aquatic products,aquaculture in coastal areas has become one of the important ways for people to obtain aquatic products.Driven by the economic benefits,some problems have appeared,such as low utilization efficiency of nutrients,poor quality of cultured organisms,and the impact of environmental pollution load increased.By studying the budget of the biogenic elements（carbon,nitrogen,phosphorus）in the pond,we can clarify the source and destination of nutrient elements,and provide the basic data to improve the efficiency of nutrients utilization,formulate plans for reducing pollution,and promote sustainable development in the aquaculture process.The carbon and nitrogen gases emission are an important approach to take part in the carbon and nitrogen element budget in aquaculture ponds,and also an essential greenhouse gas in the world.However,few studies have involved carbon and nitrogen gas emission in element budgets.In view of this,by tracking the process of nutrient element budgets,this study determinated the element content of the budgets subject from May to October 2018 in shrimp ponds at the Min River estuary.It is expected to reveal the budget of carbon,nitrogen,phosphorus nutrients in shrimp ponds,and provide references for the water quality management and sustainable development of aquaculture.The specific results of this thesis are presented as follows:（1）Variations of environmental factors in shrimp ponds water during farming period at the Min River estuary.In shrimp ponds water,the environmental factors were determined in situ.Water samples were collected and the concentrations of chlorophyll a,carbon,nitrogen,and phosphorus in the samples were determined by laboratory analysis.The results showed that environmental factors in shrimp ponds water showed significant time differences at the Min River estuary.Water temperature,DO and salinity could meet the normal growth requirements of shrimp in the farming process,but the p H was at a high level in the middle and late period.Therefore,the p H might be an important factor,which affects the growth of shrimp.The nutrient elements of carbon,nitrogen and phosphorus in shrimp ponds water showed obvious time difference.The concentration of carbon and nitrogen was on the rise,while that of phosphorus was on the decline.It could be attributed to the strong affinity of sediment for phosphorus.（2）The budget of carbon during the farming period of shrimp ponds.Through the field sample collection,site investigation and laboratory analysis,the proportions of various budget approaches were obtained in shrimp ponds.The results showed that the total inputs of carbon in the shrimp ponds were 4,555.94–5,448.27kg/hm²,among which the main source of carbon were principally originated from primary production of phytoplankton and shrimp feed,the proportion of which were 58.50-61.63% and 31.80-35.28% respectively.Water inflow,rainfall and shrimp represented a small part of the input of carbon,accounted for 4.84-5.79%,0.41-0.49% and less than 0.01%of the total input respectively.In the experiment,the main part of output of carbon was phytoplankton respiration,which accounted for 47.25-53.42% of the total.The water outflow is the same as the harvest of cultured animals,accounted for 9.15-11.69% and 8.98-11.38% respectively.The sediment respiration,carbon gases emission through water-atmosphere interface represented a small part of the output of carbon,accounted for 0.04‰ and 2.30% respectively.The other unexplained losses were accounted for 2.89-8.37%.Carbon accumulated in sediment was accounted for 18.00-21.59%,which was a large proportion of the total input of carbon.The carbon use efficiency of harvested animals was 8.98-11.38%.Harvested each ton of shrimp generated 32.12-53.73 kg carbon to pond water.（3）The budget of nitrogen during the farming period of shrimp ponds.Through the field sample collection,site investigation and laboratory analysis,the proportions of various budget approaches were obtained in shrimp ponds.The results showed that the total inputs of nitrogen into the shrimp ponds were 262.01-331.65kg/hm².The shrimp feed contributed the largest proportion of total nitrogen,accounted for 90.92-92.82% of the total input.Water inflow,rainfall and cultured animals represented a small part of the input of nitrogen,accounted for 4.15-5.24%,3.02-3.83% and less than 0.01% of the total respectively.Shrimp harvested accounted for the largest proportion of nitrogen（42.54-49.12%）from the aquaculture ponds.The water outflow was followed,accounted for 7.82-13.27%.The N₂O emissions through water-atmosphere interface,represented a fraction of the output of nitrogen.The output was 4.51-9.40% by other means such as leakage,ammonia volatilization and denitrification.The accumulation of nitrogen in sediment was accounted for 28.22-44.00% of the total input.The nitrogen use efficiency of harvested animals was 42.54-49.12%.Harvested each ton of shrimp generated 1.67-3.88kg nitrogen to pond water.（4）The budget of phosphorus during the farming period of shrimp ponds.Through the field sample collection,site investigation and laboratory analysis,the proportions of various budget approaches were obtained in shrimp ponds.The results showed that the total inputs of carbon were 59.17-75.66kg/hm² in the shrimp ponds.The shrimp feed alone accounted for 95.37-96.38% of the total input of phosphorus.From water inflow,rainfall and stocked animals were low,with each contributing 3.06-3.91%,0.55-0.70% and less than 0.01%.Harvested organisms accounted for the greatest output of phosphorus（26.77-30.75%）from the aquaculture ponds.The proportion of phosphorus in outflow water ranged 4.93-5.65%.Because the sediment has a strong affinity for phosphorus,a relatively high proportion of phosphorus（54.84-68.40%）was accumulated in sediment.The phosphorus use efficiency of harvested animals was 26.77-30.76%.Harvested each ton of shrimp generated 0.15-0.27kg phosphorus to pond water.