Carbon sequestration in different wetland plant communities in the Big Cypress Swamp region of southwest Florida

Effects of Land Use Changes on the Plant Community Characteristics in the Wetlands of the Semi-Arid Regions

Human disturbance is the main driving factor of wetland vegetation degradation, and plant community changes can directly characterize the process of wetland degradation. The wetlands in semi-arid region of Songnen Plain perform the important ecological functions, especially the habitat of waterbirds. Recently, the succession of wetland plant community has been accelerated by land use changes. In this study, we investigated the variations of plant community in wetlands undergoing land use changes (natural, mowing, light grazing + mowing, moderate grazing and heavy grazing wetlands) in the western Songnen Plain. The results showed that the plant communities were significantly affected by land use changes. The typical wetland plant Calamagrostis angustifolia was the dominant species in natural wetlands, and its dominance was gradually decreased in mowing or grazing wetlands in where Carex spp. or Artemisia selengensis acting as the dominant species. The height, density, and biomass in natural wetlands were significantly higher than those in other wetlands, whereas the species diversity and richness in natural wetlands were significantly lower. The similarity index of plant community in wetlands undergoing land use changes to natural wetlands ranged from 17.7–45.1%, being the highest in mowed wetlands and the lowest in heavily grazed wetlands. The linear regression further indicated that the plant diversity index was negatively correlated with the aboveground biomass of grasses and positively correlated with the aboveground biomass of forbs. Therefore, the land use changes in wetlands drove the replacement of dominant species of wetland vegetation and changed plant community characteristics and the species diversity, and the maintenance of species diversity is linked with the variability in plant functional strategies. The results of community variations and their relationships with functional changes can be used for assessing the effects of degradation and ecological function in response of land use changes in wetlands.

Comparative assessment of carbon sequestration potential of different types of wetlands in lower Gangetic basin of West Bengal, India

Wetlands provide a great ecological service by accumulating and sequestering carbon in their soils and thus help in mitigating climate change caused due to global warming. However, the capacity and efficiency of different types of wetlands vary considerably depending upon the nature of the wetland, hydrology, biogeochemistry, climatic condition, and many other factors. In the present paper, we have studied the carbon accumulation and sequestration in three different wetlands, one sewage fed, and two floodplain oxbow lakes in the West Bengal state of India. The selected wetlands vary in terms of ecological regimes such as water volume, depth, link channel, agricultural runoffs, primary productivity, macrophyte coverage, and fishery. The carbon accumulation in the wetlands, which varied from 48.53 to 143.17 Mg/ha up to 30-cm depth of soil, was much higher than that in the corresponding upland sites. The difference was much higher in the floodplain wetlands. So the study revealed that wetlands are better carbon sinks than the corresponding reference sites and the carbon sequestration potential varies according to the type of wetlands. A positive correlation was also observed between macrophyte coverage and the amount of C stored in the wetlands.

Storage, patterns and influencing factors for soil organic carbon in coastal wetlands of China

Soil organic carbon (SOC) in coastal wetlands, also known as "blue C," is an essential component of the global C cycles. To gain a detailed insight into blue C storage and controlling factors, we studied 142 sites across ca. 5000 km of coastal wetlands, covering temperate, subtropical, and tropical climates in China. The wetlands represented six vegetation types (Phragmites australis, mixed of P. australis and Suaeda, single Suaeda, Spartina alterniflora, mangrove [Kandelia obovata and Avicennia marina], tidal flat) and three vegetation types invaded by S. alterniflora (P. australis, K. obovata, A. marina). Our results revealed large spatial heterogeneity in SOC density of the top 1-m ranging 40-200 Mg C ha^-1 , with higher values in mid-latitude regions (25-30° N) compared with those in both low- (20°N) and high-latitude (38-40°N) regions. Vegetation type influenced SOC density, with P. australis and S. alterniflora having the largest SOC density, followed by mangrove, mixed P. australis and Suaeda, single Suaeda and tidal flat. SOC density increased by 6.25 Mg ha^-1 following S. alterniflora invasion into P. australis community but decreased by 28.56 and 8.17 Mg ha^-1 following invasion into K. obovata and A. marina communities. Based on field measurements and published literature, we calculated a total inventory of 57 × 10⁶  Mg C in the top 1-m soil across China's coastal wetlands. Edaphic variables controlled SOC content, with soil chemical properties explaining the largest variance in SOC content. Climate did not control SOC content but had a strong interactive effect with edaphic variables. Plant biomass and quality traits were a minor contributor in regulating SOC content, highlighting the importance of quantity and quality of OC inputs and the balance between production and degradation within the coastal wetlands. These findings provide new insights into blue C stabilization mechanisms and sequestration capacity in coastal wetlands.

Hydrologic-induced concentrated soil nutrients and improved plant growth increased carbon storage in a floodplain wetland over wet-dry alternating zones

Hydrological gradient variations in wetlands have a vital impact on wetland carbon storage. However, the mechanisms by which hydrological gradient variations affect biomass and carbon storage by regulating the soil nutrient contents and plant diversity remain unclear. This study attempted to explore these influencing mechanisms by studying the relationships between hydrological gradient variations and carbon storage in wetlands. The results showed that the average nutrient content, plant biomass and soil carbon content values in the high-frequency wet-dry alternating zones (HFWA, zones where the frequency of water level occurs between -25 cm and 25 cm greater than 0.5) were 1.4 times, 2.3 times and 0.43 higher, respectively, than those in the low-frequency wet-dry alternating zones (LFWA, zones where the frequency of water level occurs between -25 cm and 25 cm less than 0.3). These results indicated that the HFWA zones had higher soil nutrients, higher plant dominance, higher biomass and higher soil carbon contents than the LFWA zones. The structural equation model revealed a significant positive correlation between wet-dry alternations and the soil nutrient-plant biomass-soil carbon relation in wetlands. Moreover, there was also a significant positive correlation between wet-dry alternations and the plant dominance-plant biomass-soil carbon relation in wetlands. This implied that the concentrated effect of HFWA on soil nutrients promotes plant growth, enhances plant dominance, promotes plant productivity, and enhances the capacities of plants to input carbon to the soil, thereby increasing the soil carbon content. This study closely linked wetland hydrological gradients, plant biodiversity and wetland carbon sequestration and profoundly revealed the mechanisms by which hydrological gradients in wetlands regulate the concentrations of nutrient elements, thereby affecting vegetation growth and carbon sequestration; these results could provide a new cognitive basis for understanding the coupling of carbon and water.

Recovering wetland biogeomorphic feedbacks to restore the world's biotic carbon hotspots

Biogeomorphic wetlands cover 1% of Earth's surface but store 20% of ecosystem organic carbon. This disproportional share is fueled by high carbon sequestration rates and effective storage in peatlands, mangroves, salt marshes, and seagrass meadows, which greatly exceed those of oceanic and forest ecosystems. Here, we review how feedbacks between geomorphology and landscape-building vegetation underlie these qualities and how feedback disruption can switch wetlands from carbon sinks into sources. Currently, human activities are driving rapid declines in the area of major carbon-storing wetlands (1% annually). Our findings highlight the urgency to stop through conservation ongoing losses and to reestablish landscape-forming feedbacks through restoration innovations that recover the role of biogeomorphic wetlands as the world's biotic carbon hotspots.

Carbon sequestration and methane emissions along a microtopographic gradient in a tropical Andean peatland

Tropical alpine peatlands are among the least studied wetlands types on earth. Their important ecosystem services at local and regional scope are currently threatened by climate and land use changes. Recent studies in these ecosystems suggest their importance to the provision of climate regulation services, prompting a better understanding of the underlying functions and their variability at ecosystem scales. The objective of this study is to determine the variability of methane (CH₄) fluxes and carbon (C) sequestration within a tropical alpine peatland in three locations along a microtopographic gradient and its associated plant diversity. These locations accounted for: 1) hummocks, found mostly near the edge of the peat with a water table below the soil surface, 2) lawns, in the transition zone, with a water-table near the soil surface, and 3) hollows, permanently flooded with a water table above the soil surface, composed of small patches of open water intermingled with unconsolidated hummocks that surface the water level. Results indicate that CH₄ flux is lowest in the lawns, while C sequestration is highest. Conversely, the hummock and hollow have higher CH₄ flux and lower C sequestration. In addition, plant diversity in the lawns is higher than in the hummock and hollow location. Dryer conditions brought by current climate change in the northern Andes are expected to lower the water tables in the peatland. This change is expected to drive a change in CH₄ flux and C sequestration at the lawns, currently dominating the peatland, towards values more similar to those measured in the hummocks. This decrease may also represent a change towards the lower plant diversity that characterized the hummock. Such changes will reduce the ratio of C sequestration:CH₄ flux signifying the reduction of resilience and increment of vulnerability of the climate-regulating service to further perturbations.

Carbon stocks, sequestration, and emissions of wetlands in south eastern Australia

Nontidal wetlands are estimated to contribute significantly to the soil carbon pool across the globe. However, our understanding of the occurrence and variability of carbon storage between wetland types and across regions represents a major impediment to the ability of nations to include wetlands in greenhouse gas inventories and carbon offset initiatives. We performed a large-scale survey of nontidal wetland soil carbon stocks and accretion rates from the state of Victoria in south-eastern Australia-a region spanning 237,000 km² and containing >35,000 temperate, alpine, and semi-arid wetlands. From an analysis of >1,600 samples across 103 wetlands, we found that alpine wetlands had the highest carbon stocks (290 ± 180 Mg C_org ha^-1 ), while permanent open freshwater wetlands and saline wetlands had the lowest carbon stocks (110 ± 120 and 60 ± 50 Mg C_org ha^-1 , respectively). Permanent open freshwater sites sequestered on average three times more carbon per year over the last century than shallow freshwater marshes (2.50 ± 0.44 and 0.79 ± 0.45 Mg C_org ha^-1  year^-1 , respectively). Using this data, we estimate that wetlands in Victoria have a soil carbon stock in the upper 1 m of 68 million tons of C_org , with an annual soil carbon sequestration rate of 3 million tons of CO₂ eq. year^-1 -equivalent to the annual emissions of about 3% of the state's population. Since European settlement (~1834), drainage and loss of 260,530 ha of wetlands may have released between 20 and 75 million tons CO₂ equivalents (based on 27%-90% of soil carbon converted to CO₂ ). Overall, we show that despite substantial spatial variability within wetland types, some wetland types differ in their carbon stocks and sequestration rates. The duration of water inundation, plant community composition, and allochthonous carbon inputs likely play an important role in influencing variation in carbon storage.