Search

Aims: Coastal salt marshes are productive ecosystems that are highly efficient carbon sinks, but there is uncertainty regarding the interactions among climate warming, plant species, and tidal restriction on C cycling. Methods: Open-top chambers (OTCs) were deployed at two coastal wetlands in Yancheng, China, where native Phragmites australis (Phragmites) and invasive Spartina alterniflora (Spartina) were dominant, respectively. Two study locations were set up in each area based on difference in tidal action. The OTCs achieved an increase of average daytime air temperature of ~ 1.11–1.55 °C. Net ecosystem CO2 exchange (NEE), ecosystem respiration (Reco), CH4 fluxes, aboveground biomass and other abiotic factors were monitored over three years. Results: Warming reduced the magnitude of the radiative balance of native Phragmites, which was determined to still be a consistent C sink. In contrast, warming or tidal flooding presumably transform the Spartina into a weak C source, because either warming-induced high salinity reduced the magnitude of NEE by 19% or flooding increased CH4 emissions by 789%. Remarkably, native Phragmites affected by tidal restrictions appeared to be a consistent C source with the radiative balance of 7.11–9.64 kg CO2-eq m–2 yr–1 because of a reduction in the magnitude of NEE and increase of CH4 fluxes. Conclusions: Tidal restrictions that disconnect the tidal hydrologic connection between the ocean and land may transform coastal wetlands from C sinks to C sources. This transformation may potentially be an even greater threat to coastal carbon sequestration than climate warming or invasive plant species in isolation. [ABSTRACT FROM AUTHOR]

China has a wetland area of 53.42 million hectares, the fourth largest in the world; it includes all types of wetlands defined by the Ramsar Convention and has a carbon sink capacity of more than 1.71 million metric tons per year. Inland wetlands in China are mainly distributed in 10 major catchments, among which the Yellow River, the Yangtze River, the rivers in the northwest, and the rivers in the northeast each have more than 8 million hectares of wetlands. There are 4220 species of plants and 4015 species of animals in China's wetland ecosystem. The wetland resources that have been developed and utilized include edible products, reeds for paper making, peat for fertilizer, fuel for power generation, and chemical, pharmaceutical, ceramic, and building materials. However, wetland areas in China have shrunk by about 54% since 1980. In recent years, China's central government has set great store by Chinese wetlands, and although 49.03% of wetland area is now officially protected, many issues have confounded the implementation of that protection. It is imperative that knowledge gained from scientific research be used to formulate a sound wetland protection and management plan that takes into consideration social, economic, and ecological issues in a way that facilitates the sustainable use of wetland resources and informs decision-makers of the paths that must be followed to achieve that goal. [ABSTRACT FROM AUTHOR]

The burial efficiency of biogenic silica (BSi) in deltaic sediments is associated both with the nutrient balance in estuarine ecosystems and with the carbon cycle and climate change. To explore these relationships, foraminifera data, physical and chemical parameters, and ages determined by accelerator mass spectrometry 14C and optically stimulated luminescence from a core drilled at the southwestern edge of the Lower Liaohe Plain in May 2012 were presented. The sedimentary environments since 33,000 cal yr BP were divided into four depositional units, namely, a fluvial deposit (U1), lacustrine deposit (U2), marine-related deposit (U3), and upper delta plain deposit (U4). Environmentally mediated differences in apparent mass accumulation rates (AMARs) of BSi and organic carbon (Corg) were significant. The BSi-AMAR in the later parts of U1 and U2 occurred mainly in the Pleistocene and averaged 11.34 ± 0.22 and 16.69 ± 0.91 g m−2 yr−1, which is lower than the analogues for U3 (23.59 ± 2.89-41.74 ± 6.37 g m−2 yr−1) and U4 (37.25 ± 9.96 g m−2 yr−1) that occurred during the Holocene. The BSi record responded more coherently and was more sensitive than Corg to Northern Hemisphere paleoclimatic variations on a long timescale and to abrupt/periodic winter monsoon winds or warming forcings on a short timescale. There was a negative correlation between the concentration of bioavailable Fe2O3 and the ratio of BSi/Corg, the implication being that Fe availability may have modulated silicic acid uptake on a very short timescale and in turn impacted the dynamics of carbon burial. [ABSTRACT FROM AUTHOR]

Enhanced sequestration of carbon in ocean sediments is a promising approach to mitigate the adverse effects of climate warming. To assess the capacity of coastal regions to uptake and bury carbon, a wetland restoration project was carried out in the degraded coastal wetlands of the Liaohe Delta between 2011 and 2013. A 13.33-ha degraded salt marsh was selected to create two enhanced carbon sink experimental areas, one dominated by Phragmites australis and the other dominated by Suaeda salsa. Improvements to the wetland matrix, hydrological processes, and vegetation colonization were designed and constructed. Results revealed that after the three-year restoration effort, the biomass of vegetation in the demonstration area was 1.2–4.0 times that of a natural wetland, and the rate of organic carbon sequestration in the sediments was about 60–80% of the rate in a natural salt marsh. We show that restoring vegetation can significantly increase the rate of sedimentation and thus enhance the carbon sequestration capacity of a wetland dominated by S. salsa or P. australis. Carbon sequestration capacity can be restored more rapidly in salt marsh wetlands than in mangrove wetlands, and we argue that restoration of salt marsh wetlands is an urgent task suitable for the application of large-scale ocean carbon sequestration technologies. • A case study on a novel technology for ocean negative ocean emissions was detailed. • Soil organic carbon sequestration rates of restored wetlands were about 60–80% of the rates in natural wetlands after three years. • Restoring vegetation can significantly increase the rate of sedimentation and thus enhance the carbon sequestration in the soils. [ABSTRACT FROM AUTHOR]

River deltas have contributed to the regulation of atmospheric CO 2 concentrations throughout Earth's history, but the capacity and controlling factors for deltas to serve as permanent carbon sinks over the long term are unclear. To address this issue, we carried out a high-resolution assessment of carbon burial in a well-dated sediment core (BXZK13) from the paleo-Yellow River delta on the west coast of the Bohai Bay. We found that the sedimentary environments in core BXZK13 since the Late Pleistocene (∼84 k cal yr B.P.) were divided into seven depositional units. The apparent mass accumulation rate (AMAR) of total organic carbon (TOC) and total inorganic carbon (TIC) varied significantly between depositional units. The average rates were highest in delta front deposits (TOC: 135 g m−2 yr−1, TIC: 333 g m−2 yr−1). Notably, the rates of carbon accumulation were dominated by TIC. The differences in the characteristics of TIC in the borehole compare to those of carbonates in Yellow River sediments and the positive correlation between TIC and Fe suggested that authigenic carbonate contributed significantly to long-term carbon burial in the delta. The apparent sedimentation rate (ASR) dominated the variations of the carbon AMAR, and the high clay and Fe content in the sediment enhanced TOC preservation and authigenic carbonate precipitation. Low concentrations of TIC were associated with several cold events, and there was a positive correlation between the chemical index of alteration and TIC. The implication was that climate may have affected the dynamics of inorganic carbon burial by regulating authigenic carbonate precipitation. These results enable a more thorough understanding of the factors that control long-term carbon sequestration, which is critical for both management purposes as well as assessment of the role of deltas in past and future climate change. • The apparent sedimentation rate dominated the variations of carbon sequestration. • Carbon concentration was closely related to Fe, clay content and climate change. • Long-term carbon sequestration rates were much smaller than that in short-term. • Authigenic carbonate plays an important role in long-term carbon burial in deltas. [ABSTRACT FROM AUTHOR]