Wetland Carbon and Environmental Management. Группа авторов

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Wetland Carbon and Environmental Management - Группа авторов


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could be manipulated to suppress decomposition rates in peatlands (Freeman et al., 2012). Raising the water table depth achieves this by limiting O2 availability, but it may be possible to achieve similar results by altering pH, adding reductants, or manipulating plant traits through genetic engineering or plant species composition (Freeman et al., 2012).

      Microbial access to organic matter can be physically inhibited by mineral‐carbon interactions that operate in intact wetlands via sorption onto surfaces and coprecipitation of DOC (Hedges & Keil, 1995; Lalonde et al., 2012). Mineral soils tend to be rich in Fe‐ and Al‐oxides that preserve organic matter by forming bonds and physical structures that interfere with microbial degradation (LaCroix et al., 2018), so increasing the availability of minerals could enhance carbon preservation. Dredged sediments from navigation channels are sometimes used to create new wetland islands or are added to tidal marshes to increase elevation (Cornwell et al., 2020; Streever, 2000). The ability of dredge spoils to enhance the preservation of wetland carbon through physical inhibition of decomposition depends on whether their mineral surfaces are already saturated with organic carbon, which is likely to be site specific. Some deltaic sediments tend to have less than a monolayer‐equivalent coating of organic carbon due to enhanced mineralization resulting from O2 exposure during periodic reworking events (Blair et al., 2004), but we do not know the extent to which this applies to river and harbor sediments. Organic‐mineral interactions are promoted in the wetland plant rhizosphere by root O2 loss driving deposition of poorly crystalline iron oxides (Weiss et al., 2005), some of which are stable under anaerobic conditions (Henneberry et al., 2012; Shields et al., 2016). Drainage triggers ferrous iron oxidation and increases mineral protection of organic matter, provided there is sufficient iron in the soil to support this carbon‐stabilizing process (LaCroix et al., 2018). The possibility that iron amendments could be used to stabilize carbon in drained soils has not been investigated to our knowledge. Biochar amendments may enhance wetland carbon preservation by altering microbial assemblages and stabilizing existing organic‐mineral complexes (Zheng et al., 2018); the same mechanism helps explains the high‐organic terra preta soils in the Amazon basin (B. Glaser & Birk, 2012).

      Soil pH also exerts strong control on decomposition rates and is negatively correlated with soil carbon preservation. Regulation of extracellular enzyme activity is one mechanism by which pH interferes with decomposition and has been cited as a reason why soil carbon pools sometimes increase in response to drainage or decrease in response to rewetting (Fenner & Freeman, 2011). In northern peatlands, pH exerts indirect control on soil carbon stocks by favoring Sphagnum species that decompose slowly (low pH) or vascular species that decompose relatively quickly (high pH). Thus, pH manipulation to favor one functional plant group over another is one option for altering carbon preservation (e.g., Beltman et al., 2001).

      Temperature regulates the rates of all biological, physical, and chemical processes that control organic matter decomposition, and is another physicochemical factor that may cause unexpected soil carbon responses to drainage. For example, short‐term lab and field drainage in wet tussock tundra tends to increase soil organic matter decomposition rates, as expected, but feedbacks operating at larger spatiotemporal scales involving plant community shifts and their effects on snow cover, albedo, and thermal balance have the potential to slow permafrost degradation and preserve soil carbon (Göckede et al., 2019). Feedbacks involving wetland responses to a warming planet include shifting plant distributions, changing estuarine salinity distributions, and altered wetland hydrology, all of which can directly or indirectly impact the preservation of wetland carbon. Incorporating large‐scale feedbacks into wetland management activities is a contemporary challenge.

      3.5.4. Managing Greenhouse Gas Emissions

      Coastal wetlands have the potential to sequester carbon at relatively high rates while emitting CH4 at low rates (Poffenbarger et al., 2011), making them attractive for ecosystem management and carbon financing projects (Needelman et al. 2018, Moomaw et al. 2018). Hydrologic restoration and management of degraded sites tends to increase soil carbon sequestration, achieving rates similar to natural sites after two decades in many cases (Craft et al., 2003; O’Connor et al., 2020). However, the increase in carbon sequestration can be accompanied by an increase in CH4 emissions resulting in net radiative forcing (O’Connor et al., 2020). Uncertainty in spatiotemporal variation in CH4 emissions and the factors that regulate this variation are a significant barrier to wetland management for greenhouse gas reduction (Holmquist et al., 2018).


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