Comparative analysis of two 16S rRNA gene-based PCR primer sets provides insight into the diversity distribution patterns of anammox bacteria in different environments.

Due to the high divergence among 16S rRNA genes of anammox bacteria, different diversity pattern of the community could be resulted from using different primer set. In this study, the efficiencies and specificities of two commonly used sets, Amx368F/Amx820R and Brod541F/Amx820R, were evaluated by exploring the diversity characteristics of anammox bacteria in sediments from marine, estuary, and freshwater wetland. Statistical analysis indicated that the base mispairing rate between bases on 16S rRNA gene sequences retrieved by Amx368F/Amx820R and their corresponding ones on primer Brod541F was quite high, suggesting the different efficiency and specificity of Amx368F/Amx820R and Brod541F/Amx820R. Further experimental results demonstrated that multiple genera of anammox bacteria, including Ca. Scalindua, Ca. Brocadia, and Ca. Kuenenia, were able to be detected by Amx368F/Amx820R, but only Ca. Scalindua could be retrieved by Brod541F/Amx820R. Moreover, the phylogenetic clusters of Ca. Scalindua by Amx368F/Amx820R were different completely from those by Brod541F/Amx820R, presenting a significant complementary effect. By joint application of these two primer sets, the diversity distribution patterns of anammox bacteria in different environments were analyzed. Almost all retrieved sequences from marine sediments belonged to Ca. Scalindua. Sequences from freshwater wetland were affiliated to Ca. Brocadia and two new clusters, while high diversity of anammox bacteria was found in estuary, including Ca. Scalindua, Ca. Brocadia, and Ca. Kuenenia, corresponding to the river-sea intersection environmental feature. In total, these two prime sets have different characteristic for anammox bacteria detecting from environmental samples, and their combined application could achieve better diversity display of anammox community.

[The fluorescence characteristics of dissolved organic matter (DOM) in the seagrass ecosystem from Hainan by fluorescence excitation-emission matrix spectroscopy].

The fluorescence characteristics of dissolved organic matter (DOM) were determined in the seagrass ecosystem collected in Xincun Bay of Hainan Island in late January, 2013, using fluorescence excitation-emission matrix spectroscopy (EEMs). EEMs spectra showed 2 types of fluorescence signals in DOM samples, three hurnic-like fluorescence peaks and two protein-like fluorescence peaks, respectively. The former included UVC peak A (Ex/Em: 230/430 nm), UVA peak C (Ex/Em: 350/440 nm), and UVA peak M (Ex/Em: 300/380-400 nm), while the latter included tryptophan-like peaks R (Ex/Em: 230/355 - 375 nm) and N (Ex/Em: 280-300/365-380 nm). Peak N was more like a combination of Peak M and Peak R. Moreover, free tyrosine-like molecules in DOM from the seagrass-beds ecosystem did not exist because the tyrosine-like fluorescence was not found. There were significant positive correlations of peak N with M and R (0. 97 and 0. 54 for R2, respectively), and peak A with C (0. 86 for R2), showing their same sources and biogeochemical behaviors. The change law of mean fluorescence intensities of those fluorescence signals was R (0. 304 RU) >A (0. 194 RU) >M (0. 147 RU) >N (0. 125 RU) >C (0. 051 RU). And, higher . L-1 concentrations of all the fluorescence occurred in the coastal waters inshore, with low values in two small regions located in the southwest and southeast of the bay where the seagrasses flourished. The distributions of those fluorescence signals in Xincun Bay suggested that the dynamics responsible for the humic-like fluorescence might be the same as that responsible for the protein-like fluorescence. The high fluorescence index (FI: 1. 81), high biological index (BIX: 1. 44) and low humification index (HIXa: 4. 2 and HIXb: 0. 81) showed that the DOM from the seagrass-dominant ecosystem has a strong autochthonous contribution and poor humification degree. The results clearly suggested that the DOM in this region has a rather unique fluorescence characteristic and is quite different from other aquatic environments.

Developing a salinity-based approach for the evaluation of DIN removal rate in estuarine ecosystems.

Estuaries play an important role in the removal of overloading nitrogen to relieve the eutrophic pressure of coastal seawater. However, the exact amount of nitrogen removed in estuarine ecosystems is difficult to be estimated because of the complex dynamic mixing process between riverine water and coastal seawater. In this study, a new method was developed to calculate the removal rate of dissolved inorganic nitrogen (DIN) in estuarine waters attributed to the mixing process and was based on the assumption that relative salinity can serve as an indicator of the degree of mixing. This assumption was supported by the experimental results that demonstrated a linear regression relationship between DIN decline and salinity increase Thus, the decreased amount of DIN in mixing waters attributed to the dilution effect could be determined with the salinity as an index. With this model, the DIN removal rate in both Chesapeake Bay and Pearl River Estuary were defined. As predicted, our analysis demonstrated that the DIN removal rate increased gradually from upstream to downstream in both studied estuaries with obvious seasonable variation pattern: high in warm seasons and low in cold seasons. The practical application of this method might be affected by multiple factors, including the geographic landform of estuaries, initial estuaries DIN concentration, the DIN concentration in seawater, DIN importing from tributaries, sewage discharge and hydrodynamic mixing. Therefore, the results supported the hypothesis that estuaries have a strong capability to remove the nitrogen inputted from human activities, especially in warm season and therefore should play an important role in regulating the balance of global nitrogen biogeochemical cycle.

Persistent organic pollutants in marine fish from Yongxing Island, South China Sea: levels, composition profiles and human dietary exposure assessment.

Little data is available on the bioaccumulation of persistent organic pollutants (POPs) in marine organisms from South China Sea (SCS). Five marine fish species were collected from Yongxing Island, SCS to investigate the presence of polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane and its metabolites (DDTs). PBDEs, PCBs, and DDTs concentrations ranged from 2.0-117, 6.3-199, and 9.7-5831 ng g(-1) lw, respectively. In general, contaminants measured in this study were at the lower end of the global range. Concentrations of PBDEs and PCBs were significantly correlated in fish samples, implying that PBDEs are as prevalent as PCBs in Yongxing Island. Among the five fish species studied, yellow striped goatfish had the highest concentrations of PBDEs, PCBs, and DDTs, probably attributed to its different living and feeding habits. The contaminant distribution pattern indicated that agrochemical source is more important than industrial source in Yongxing Island, SCS. The average estimated daily intakes of PBDEs, PCBs, and DDTs via fish consumption by local residents in the coastal areas of South China ranged from 1.42-5.91, 3.20-13.3, and 8.08-33.6 ng d(-1), which were lower than those in previous studies, suggesting that consumption of marine fish in Yongxing Island, SCS, might not subject local residents to significant health risk as far as POPs are concerned. This is the first study to report the occurrence of POPs in marine biota from SCS.

Heavy metal pollution in coastal areas of South China: a review.

Coastal areas of South China face great challenges due to heavy metal contamination caused by rapid urbanization and industrialization. In this paper, more than 90 articles on levels, distributions, and sources of heavy metals in sediments and organisms were collected to review the status of heavy metal pollution along coastal regions of South China. The results show that heavy metal levels were closely associated with local economic development. Hong Kong and the Pearl River Estuary were severely contaminated by heavy metals. However, concentrations of heavy metals in sediments from Hong Kong have continually decreased since the early 1990 s. High levels of heavy metals were found in biota from Lingdingyang in Guangdong province. Mollusks had higher concentrations of heavy metals than other species. Human health risk assessments suggested that levels of heavy metals in some seafood from coastal areas of South China exceeded the safety limit.