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Episodic flooding due to intense rainfall events is characteristic in many wetlands, which may modify wetland-atmosphere exchange of CO 2 . However, the degree to which episodic flooding affects net ecosystem CO 2 exchange (NEE) is poorly documented in supratidal wetlands of coastal zone, where rainfall-driven episodic flooding often occurs. To address this issue, the ecosystem CO 2 fluxes were continuously measured using the eddy covariance technique for 4 years (2010-2013) in a supratidal wetland in the Yellow River Delta. Our results showed that over the growing season, the daily average uptake in the supratidal wetland was À1.4, À1.3, À1.0, and À1.3 g C m À2 d À1 for 2010, 2011, 2012, and 2013, respectively. On the annual scale, the supratidal wetland functioned as a strong sink for atmospheric CO 2 , with the annual NEE of À223, À164, and À247 g C m À2 yr À1 for 2011, 2012, and 2013, respectively. The mean diurnal pattern of NEE exhibited a smaller range of variation before episodic flooding than after it. Episodic flooding reduced the average daytime net CO 2 uptake and the maximum rates of photosynthesis. In addition, flooding clearly suppressed the nighttime CO 2 release from the wetland but increased its temperature sensitivity. Therefore, effects of episodic flooding on the direction and magnitude of NEE should be considered when predicting the ecosystem responses to future climate change in supratidal wetlands.

Mercury is a hazardous pollutant in the Bohai marine environments due to its high toxicity to the marine organisms and subsequent ecological risk. Manila clam Ruditapes philippinarum is one of important sentinel organisms in 'Mussel Watch Program' launched in China and therefore used as a bioindicator in marine and coastal ecotoxicology. There are dominantly distributed three pedigrees of clam (White, Liangdao Red and Zebra) in Yantai population endowed with different tolerances to environmental stressors. In this study, gill tissues were collected from both untreated and mercury exposed White, Liangdao Red and Zebra clams, and the extracts were analyzed by NMR-based metabolomics to compare the original metabolomes and the toxicological effects induced by mercury exposure in three pedigrees. The major abundant metabolites in White clam sample were branchedchain amino acids, lactate, alanine, arginine, acetoacetate, glutamate, succinate, citrate, malonate and taurine, while the metabolite profile of Liangdao Red clam sample comprises relative high levels of alanine, arginine, glutamate, succinate and glycogen. For Zebra clam sample, the metabolite profile exhibited relatively high amount of aspartate, acetylcholine and homarine. After 48 h exposure of 20 lg l -1 Hg 2? , the metabolic profiles from all the three pedigrees of clams commonly showed significant increases in alanine, arginine, glutamate, aspartate, a-ketoglutarate, glycine and ATP/ADP, and decreases in citrate, taurine and homarine. The unique metabolic differences between the metabolomes of gill tissues from Hg 2? -exposed White, Liangdao Red and Zebra clams were found, including elevated acetylcholine and branched-chain amino acids in White clams, and the declined succinate in both White and Liangdao Red samples as well as the declined betaine in Zebra and White clams. Overall, our findings showed the differential toxicological responses to mercury exposure and that White clams could be a preferable bioindicator for the metal pollution monitoring based on the metabolic changes from gill compared with other two (Liangdao Red and Zebra) pedigrees of clams.

Using the Eddy Covariance (EC) technique, we analyzed temporal variation in net ecosystem CO 2 exchange (NEE) and determined the effects of environmental factors on the balance between ecosystem photosynthesis and respiration in a reed (Phragmites australis) wetland in the Yellow River Delta, China. Our results indicated that diurnal and seasonal patterns of NEE and its components (ecosystem respiration (R eco ), gross primary production (GPP)) varied markedly among months for the growing season (May to October). The cumulative CO 2 emission was 1,657 g CO 2 m . The ratio of R eco to GPP in reed wetland was 0.68, which was close to other temperate wetlands. Soil temperature and soil moisture exerted the primary controls on R eco during the growing season. Daytime NEE values during the growing season were strongly correlated with photosynthetically active radiation. Aboveground biomass showed significant linear relationships with 24-h average NEE, daytime GPP, and R eco , respectively. Thus, we conclude that the coastal wetland acted as a carbon sink during the growing season despite the variations in environmental conditions, and long-term flux measurements over these ecosystems are undoubtedly necessary.

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