Variations In Nutrients And COD And Water Quality Evaluation In Chinese River Crab Aquaculture Areas In Reed Wetland Of Liaohe Estuary

In order to find out the variations in the content of water and sediment quality index and water quality evaluation in the river crab culture areas in reed land of Liaohe Estuary Wetland and provide basic data for the health aquaculture of river crab, based on the data collected in the river crab aquaculture areas in reed land of Liaohe Estuary Wetland in April. June, July, August, September,2014, the variations in the content of water and Sediment quality indexes (ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, phosphorous,total nitrogen, total phosphorous, COD) were analyzed and the water quality was evaluated using comprehensive water quality index (Iwq) and potential eutrophication.The results showed that in the water of the river crab culture areas in reed land of Liaohe Estuary Wetland ammonia nitrogen changed from 0.04 mg/L to 1.25mg/L generally and it was the highest in late July and the lowest in September. Besides,it was higher in zone 1 and zone 2 than it was in the other two zones; nitrite nitrogen varied from 0.0017mg/L to 0.0147 mg/L and it was low all the time. The changes of nitrite nitrogen in the four river crab culture areas were different.The concentration of nitrite nitrogen was the lowest in August in all the culture areas,but the highest concentration appeared in different months; nitrate nitrogen changed from 0.0015 mg/L to 0.0636 mg/L; phosphorous changed from 0.0024 mg/L to 0.0660 mg/L; total nitrogen varied from 0.65 mg/L to 6.88 mg/L and was the highest in June or July and the lowest in April; total phosphorous ranged between 0.05mg/L and 0.31 mg/L and it was the highest in middle July and the lowest in late July, CODwas from 1.54 mg/L to 4.68 mg/L and the highest in middle July and the lowest in June.While the variation was different in sediment.It showed that total nitrogen in sediment varied from 1.282 mg/g to 7.048 mg/g; total phosphorous ranged between 0.726mg/g and 0.947mg/g and it was high in April, late July and September.When it comes to water quality in the river crab aquaculture areas, the results of Iwq showed that it was the worst in late July while it was the best in April. Total nitrogen was the main pollution factor.The results of potential eutrophication showed that the water quality was the worst in June while it was better in April and September. The results of the two evaluation methods was the same on the whole.The water quality was the worst in June and July, while it was better in April and September.The water quality was different among different culture conditions, and it was suggested that some management measurements including reducing the quantity of feeding, reasonable culture density, proper feeding interval and regular cleaning of the sediment should be taken in order to reduce the aquaculture pollution and improve the water quality.