Changes in the hydrological conditions of coastal wetlands may potentially affect the role of wetlands in the methane (CH4) cycle. In this study, the CH4 production potential and emissions from restored coastal reed wetlands at different water levels were examined in eastern China at a field scale in two phenological seasons. Results showed that the total CH4 flux from reeds at various water levels were positive, indicating that they were “sources” of CH4. During the peak growing season, CH4 flux from reeds was greater than that during the spring thaw. CH4 flux from reeds in inundated conditions was greater than that in non-inundated conditions. The CH4 production potential during the peak growing season was far greater than that during the spring thaw. However, the effect of water level on wetland CH4 production potential differed among seasons. The correlations among CH4 production potential, soil properties and CH4 flux change at different water level. These results demonstrate that water level was related to CH4 production and CH4 flux. The growing season also plays a role in CH4 fluxes. Controlling the hydrological environment in restored wetlands has important implications for the maintenance of their function as carbon sinks.

Phosphorus (P) in wetlands is mainly bound to sediment in various species, which is essential to predict water column P levels. The purpose of this work is to understand the influences of sediment properties and vegetation types on P speciation. Sediments under four vegetation types in the tidal flat and offshore sandbar in Hangzhou Bay of China were collected seasonally. The rank order of P species in sediment based on concentration was exchangeable P (Exch-P) < iron/aluminum-bound P (Fe/Al-P) < organic P (Org-P) < calcium-bound P (Ca-P). Sediment total phosphorus (TP) and Fe/Al-P concentrations were lower in offshore sandbar than those of tidal flat, reflecting effects of anthropogenic contamination in the latter. Sediment particle size distribution strongly affected P speciation, as indicated by a significant correlation between them. Total phosphorus and Org-P concentrations in vegetated sediments were higher than those of bare mudflat. Additionally, there was a significant negative correlation between Ca-P and Org-P, and Fe/Al-P, indicating the presence of vegetation which may result in P speciation by converting Ca-P to soluble and active P and higher Org-P. Overall, sediment particle size distribution is the most fundamental physical property that affects P speciation, and vegetation types are important factors that influence Org-P concentration.

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Water depth (WD) influences wetland methane (CH 4 ) emissions by affecting plant growth and the physical and chemical properties of soil. We studied the factors influencing CH 4 emission dynamics at different WD in reclaimed reed wetland in Hangzhou Bay, China. The annual average WD was set as WD0 (0 cm), WD1 (10 cm), WD2 (20 cm), and WD3 (35 cm). The transparent chamber-gas chromatography method was used to determine CH 4 fluxes during the growing season. Results showed that the average CH 4 flux was 7.03 mg m 22 h 21 , and that CH 4 fluxes under all 4 WDs presented as a CH 4 source. CH 4 emissions of the reed wetland showed obvious seasonal changes; summer was the peak period for CH 4 emissions. In a vigorous growth period of reeds, the CH 4 flux gradually increased as WD increased. However, in early and late growth periods of reed, CH 4 flux first increased (WD0 < WD1 < WD2) then decreased (WD2 > WD3) as WD increased. Correlation analysis showed that at the 4 WDs, CH 4 flux was significantly, positively correlated with air temperature, soil temperature, and aboveground biomass of reeds, and were highly significantly positively correlated with water temperature. In addition, at WD0, CH 4 flux also showed a significant, positive correlation with soil organic carbon content in the 0-5 and 5-10 cm soil layers, and was significantly negatively correlated with soil water content. Hence, WD significantly influenced wetland CH 4 emissions. Temperature and biomass were major influencing factors of CH 4 emission in reed wetland at different WDs.