No abstract

The Yellow River Delta Wetland is one of the youngest wetlands, and also the most complete, extensive wetlands in China. The wetland in this delta is ecologically important due to their hydrologic attributes and their roles as ecotones between terrestrial and aquatic ecosystems. In the study, the spatial and temporal variation characteristics of CH4 and CO2 emission flux under five kinds of land use types in the wetland were investigated. The results indicated that the greenhouse gas emission flux, especially the CO2 and CH4, showed distinctly spatial and temporal variation under different land use types in the wetland. In the spring, the emission flux of CO2 was higher than that of CO2 in the autumn, and appeared negative in HW3 and HW4 in the autumn. CH4 emission flux of HW4 and HW5 was negative in the spring and autumn, which indicated that the CH4 emission process was net absorption. Among the five kinds of land use types, the CO2 emission flux of HW4 discharged the largest emission flux reaching 29.3 mg•m −2 •h −1 , but the CH4 emission flux of HW2 discharged the largest emission flux reaching 0.15 mg•m −2 •h −1 . From the estuary to the inland, the emission flux of CO2 was decreased at first and then appeared increasing trend, but the emission flux of CH4 was contrary to CO2.

Marine dumping of dredged sediment results in the release of considerable amounts of nitrogen and phosphorus into the seawater. In this study, we evaluated the release pattern of nitrogen and phosphorus during sediment dumping through experimental simulation under different mixing ratios and temperatures. The concentration of NO3-N, PO4-P, and total phosphorus (TP) in seawater quickly increased in less than 1 h after mixing of sediment and seawater and remained stable thereafter. The concentration of NH4-N increased and peaked at 0.25 h, but quickly decreased thereafter. The concentration of NO3-N, NH4-N, PO4-P, and TP in seawater showed a positive correlation with the mixing ratio. The contribution of NO2-N from sediment to water was negligible and there was no obvious difference in the release amount among different mixing ratios. The release amount of each measured nutrient at 25°C was marginally higher than that at 15°C, suggesting that marine dredging and dumping should be performed in winter rather than in summer. The release amount of NO3-N, NO2-N, NH4-N, PO4-P, and TP in a 5000-m3 vessel reached 26.5, 17.6, 0.28, 1.68, and 1.68 kg, respectively. This study provides a detailed evaluation of nitrogen and phosphorus release pattern in marine sediment dumping process, which will be helpful for the conservation and selection of marine dumping areas.

No abstract