In coastal area, salinization is a common and serious problem for crop cultivation and ecological restoration of degraded wetlands. Therefore, the soil salinity has attracted increasing attention from farmers, government and environmental scientists. The factors controlling the soil salinity distribution have become a hot point in saline soil studies. In this study, statistics and geostatistics were used to explore the distribution of soil salinity in the Yellow River Delta (YRD) based on 150 soil samples that were collected in June 2010. Besides the experimental work, a geographical information system technique was adopted in this study. The results showed that the soil salinity ranged from 0.11 to 10.50 dS m⁻¹ and the salinity in topsoil was higher than that in subsoil in the YRD, indicating that the salt in subsoil moved up and accumulated in topsoil as a function of evaporation. There was a significant difference among soil salinity spatial variances from different soil depths in the YRD. Generally, soil salinity of the topsoil was higher than that of the subsoil. Meanwhile, there were significant positive correlations in soil salinity between different soil depths. In addition, landforms, land uses, soil types and soil texture were important factors affecting soil salinity. The current distribution of soil salinity resulted from the comprehensive effects of anthropogenic activities and natural processes. The present study results suggest that the impacts of human activities were critical factors for salt redistribution in the coastal wetlands, which should be valuable for agricultural management and ecological restoration in the YRD.

Coastal ecosystems play significant ecological and economic roles but are threatened and facing decline. Microbes drive various biogeochemical processes in coastal ecosystems. Tidal flats are critical components of coastal ecosystems; however, the structure and function of microbial communities in tidal flats are poorly understood. Here we investigated the seasonal variations of bacterial communities along a tidal flat series (subtidal, intertidal and supratidal flats) and the factors affecting the variations. Bacterial community composition and diversity were analyzed over four seasons by 16S rRNA genes using the Ion Torrent PGM platform. Bacterial community composition differed significantly along the tidal flat series. Bacterial phylogenetic diversity increased while phylogenetic turnover decreased from subtidal to supratidal flats. Moreover, the bacterial community structure differed seasonally. Canonical correspondence analysis identified salinity as a major environmental factor structuring the microbial community in the sediment along the successional series. Meanwhile, temperature and nitrite concentration were major drivers of seasonal microbial changes. Despite major compositional shifts, nitrogen, methane and energy metabolisms predicted by PICRUSt were inhibited in the winter. Taken together, this study indicates that bacterial community structure changed along the successional tidal flat series and provides new insights on the characteristics of bacterial communities in coastal ecosystems.

Episodic flooding due to intense rainfall events is characteristic in many wetlands, which may modify wetland‐atmosphere exchange of CO₂. However, the degree to which episodic flooding affects net ecosystem CO₂ exchange (NEE) is poorly documented in supratidal wetlands of coastal zone, where rainfall‐driven episodic flooding often occurs. To address this issue, the ecosystem CO₂ 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 −1.4, −1.3, −1.0, and −1.3 g C m⁻² d⁻¹ for 2010, 2011, 2012, and 2013, respectively. On the annual scale, the supratidal wetland functioned as a strong sink for atmospheric CO₂, with the annual NEE of −223, −164, and −247 g C m⁻² yr⁻¹ 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 CO₂ uptake and the maximum rates of photosynthesis. In addition, flooding clearly suppressed the nighttime CO₂ 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.