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The availability of O₂ regulates carbon preservation through mechanisms other than the often‐cited high free energy yield of aerobic respiration, a thermodynamic constraint on decomposition rates. By contrast, kinetic constraints are imposed by the activity of extracellular enzymes required to break chemical bonds. As discussed earlier (see Phenolic inhibition in Section 3.3.2), the enzymic latch hypothesis states that the absence of O₂ triggers a series of events leading to the accumulation of phenolic compounds, which inhibit the hydrolase enzymes that cleave organic bonds (Fig. 3.3; Freeman, Ostle, et al., 2001). The hypothesis has been invoked to explain slow decomposition rates in peatlands and to speculate that the concentration of inhibitory phenolics 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).

The response of extracellular enzymes such as phenol oxidase to management can be complex and generate a wide range of carbon responses ranging from increased carbon preservation to increased carbon mineralization. In an elaboration of the enzymic latch hypothesis, the increase in enzyme activity and decomposition rate triggered by O₂ exposure leads to higher nutrient availability and soil pH, which in turn increases decomposition in a positive feedback loop that persists for months to years after the soil has been rewetted (Bonnett et al., 2017; Fenner & Freeman, 2011). Another nuance of the enzymic latch hypothesis is that drainage or drought may inhibit phenol oxidase activity due to low soil water content. Under such conditions, rewetting will increase the activity of the enzyme and stimulate decomposition rates (H. Wang et al., 2015). Management activities based on assumptions about water level controlling decomposition rate should also consider the response of inhibitory phenolic compounds.

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.