[Analysis of the changes of microbial community structure on bio-carrier of recirculating aquaculture systems (RAS)].

In order to study the variation of microbial community structure and the mechanism of denitrification on bio-carrier in recirculating aquaculture systems (RAS) during the periods of bio-film formation and operation the systems, traditional microbiological methods were applied to count the quantity of heterotrophic bacteria, ammonia oxidize bacteria and nitrite oxidize bacteria. The amplified products of variable V3 region of bacterial 16S rDNA were separated by using denaturing gradient gel electrophoresis (DGGE). And bacterial community DNA fingerprint was obtained. The sequences retrieved from the DGGE bands were used for homology analysis and construction of phylogenetic tree. It presented a trend that the quantity of the three types of bacteria increased gradually to a top and then fallen slowly to a stable level. The composition of microbial community of bio-carrier was very abundant in all periods, and the Shannon index was 1.53, 1.44, 1.57, 1.08, 1.27 and 1.30, respectively. During different periods, there was a certain shift in the microbial community structure, while the C(s) value (similar index) in two adjacent periods was high, indicating the variation and succession of the microbial community was slow and regular. Several bacteria had an effect on removal of pollutants for farming water and the effluent water quality could meet the requirements of high-density culture. Among them, Proteobacteria and Flavobacteria were main communities. The Nitrosomonas and some other facultative anaerobic bacteria (Flavobacteriaceae bacterium) were identified, which indicated that there may be coexisted pathways of nitrification and denitrification in bio-filter.

[Distribution of organic carbon and carbon fixed strength of phytoplankton in Enteromorpha prolifera outbreak area of the Western South Yellow Sea, 2008].

Based on the analysis of dissolved organic carbon (DOC), particulate organic carbon (POC) and particulate nitrogen (PN) of the samples collected from stations in Enteromorpha prolifera outbreak area of the Western South Yellow Sea during the period August 9-13 of 2008, combining with the data of environmental hydrology, the horizontal distribution, source and influential factors of organic carbon and carbon fixed strength of phytoplankton were discussed. The results showed that the concentrations of DOC and POC ranged from 1.55 mg/L to 3.22 mg/L, 0.11 mg/L to 0.68 mg/L, with average values of 2.44 mg/L and 0.27 mg/L. The horizontal distributions of DOC and POC were similar in study area. The concentrations of DOC and POC in coastal area were higher than that in the outer sea and the concentrations of DOC and POC at surface water layer were higher than those at the bottom water layer. There were a positive correlation between POC and TSS, indicating that the concentrations and source of TSS were main factors for the POC. According to the univariate linear regression model between POC and PN, the concentrations of particulate inorganic nitrogen (PIN) were evaluated. Removing the content of PIN in the samples, the average POC/PON values in most coastal waters were less than 8, combining with the values of POC/chlorophyll a, suggesting that the marine primary production were the important source of POC in most coastal waters, and the presence of degraded organic matter which derived from degraded Enteromorph prolifera was in the latter period of green tide outbreak. The results of evaluated carbon fixed strength based on primary productivity showed that carbon fixed strength of phytoplankton in Enteromorpha prolifera outbreak area of the Western South Yellow Sea ranged from 167 mg/(m2 x d) to 2017 mg/(m2 x d), with the average of 730 mg/(m2 x d). The daily carbon fixed quantities of the study area were up to 2.95 x 10(4) t. Then the daily carbon fixed quantities of the Yellow Sea were 28.03 x 10(4) t.