| Liaohe estuary wetland which was located in north of Liaodong bay was the largest one with a very high ecological value in the world. With increasing river crab breeding density and scale, there was a significant impact on the local ecological balance. In that context, based on the data collected from environmental and biological surveys in aquaculture demonstration area of Eriocheir sinensis in four reed lands (numbers as 1,2,3,4) which had different reed land areas, supply of seedling, quantity and composition of baits in Liaohe estuary wetland in 2014, the crab yields and nitrogen balance were studied and the eutrophication status for crab culture area were analyzed using principal component analysis to conduct comprehensive evaluation of reed fields environment and provide scientific basis for the reduction of pollution output of crab culture activities. The main results showed as follow:1、 There were certain differences between input and output in four reed fields. The weight of crab seed per unit area in No.4 was obviously lower than others and density of crab seed in No.2 was the highest. Ratios of benefit in No.3 and 4 were higher than other two reed fields. Harvest per unit area in No.1 was lower than others.2、 There was a similarity of input way for nitrogen among four reed fields. The main input source of nitrogen in reed fields was water injection, and the percentages of sampling sites were higher than 80% which were much more than them from baits and crab seeds. The output ways of nitrogen were different among different reed fields. The output of nitrogen for tail drainage in No.1 field was 36.62 kg which was main way of nitrogen output and its proportion was higher than 50%. These proportions of other fields were all lower than 40%. The proportion for other catches in No.4 was the highest. The proportions for tail drainage and accumulation and conversion were similar between No.2 and 3. There was a difference of input way for phosphorus among four reed fields. The main input source of phosphorus in reed fields was water injection which was higher than ways from baits and crab seeds. The proportion for water injection in No.4 was higher than 80% and the proportion in No.1 field was similar to that in No.2. There was an obvious difference among all reed fields. The amount for accumulation and conversion from No.1 was highest and more than 70%. The amount for accumulation and conversion and tail drainage from No.3 and 4 were similar that were lower than amounts from No.1 and 2.3、 There are obvious differences among various forms of nutrients which changed significantly in different reed fields. The result of PCA showed that the result of assessment for the degree of nitrogen eutrophication from best to worest is No.3, No.2, No.4 and No.1. The result of assessment for the degree of phosphorus eutrophication from best to worest is No.3, No.4, No.2 and No.1. The degree of water quality assessment from best to worest is No.3, No.4, No.2 and No.1. The degree of environmental quality assessment from best to worest is No.3, No.4, No.2 and No.1.Based on the above results, this paper got the following conclusions:Structure of bait, throw-in density of juvenile crabs, structure and area of reed fields are main factors to influence the production of crabs; Nitrogen and phosphorus output structure was influenced by structure of bait, throw-in density of crabs, structure and area of reed fields and so on; The obvious diference among aquatic ammonia nitrogen, nitrite, nitrate, phosphate, TN, TP and COD and TN, TP from sediment was caused by structure of reed fields and culture and these factors had a temporal variation. To compare in various aspects comprehensively, reed field 3 is the optimal mode. |
PDF Full Text Request