McAvoy, 1988).
Anthropogenic disturbances including drainage, deforestation, and fire can substantially change DOC dynamics and the chemical composition of the exported DOC (S. Moore et al., 2013; Rixen et al., 2016; Strack et al., 2008; Urbanová et al., 2011). The drainage of wetlands increases DOC export (Drösler et al., 2014; Kreutzweiser et al., 2008; S. Moore et al., 2013; Rixen et al., 2016). The rewetting of wetlands can return DOC export rates to pre‐drainage levels, although there may be a short‐term DOC pulse during the initial stages of rewetting (Blain et al., 2014). Further, disturbances such as drainage and deforestation cause an increasing fraction of the DOC to be derived from preserved soil carbon rather than recent plant production (Gandois et al., 2013; S. Moore et al., 2013). Over time, the depletion of soil carbon due to disturbance can reduce the export of DOC (Sippo et al., 2019). Fires in peatlands can cause a short‐term increase in DOC concentrations and export (Clay et al., 2009; Olivares et al., 2019; Zhao et al., 2012) but a decrease over the longer‐term (1–10 years post‐fire; Shibata et al., 2003; Worrall et al., 2007). The effects of fire on DOC export may be less important than the effects of climate change in northern peat‐dominated catchments (Burd et al., 2018). Lastly, wetlands export substantially more DOC per unit area to aquatic systems than do other land use types (Raymond & Hopkinson, 2003) so where wetlands have been lost, there likely has been a substantial reduction in the amount of DOC export (Kristensen et al., 2008; Raymond et al., 2004).
3.6. CONCLUSIONS
The redox environment, organic matter characteristics, and physicochemical factors are well understood to be the fundamental attributes that determine the capacity of wetlands to capture, preserve, and release carbon. Just one of these – the redox environment – has been the focus of most management‐informed research and management activities. Yet even this relatively rich body of knowledge has proven insufficient to accurately predict counterintuitive responses that have been observed in response to drainage or impoundment. Developing a more robust predictive capacity for carbon‐focused management activities in wetlands requires a nuanced application of the biogeochemical processes discussed in this chapter. Examples include the responses of extracellular enzymes to water table manipulation and the influence of plant traits related to O2 transport on rates of organic matter decomposition, CH4 production, and CH4 oxidation. Advances in wetland carbon biogeochemistry can be incorporated into management plans to enhance carbon preservation, prevent the destabilization of accumulated soil carbon, and reduce greenhouse gas emissions, thus maintaining the role of wetlands as regulators of global climate. Given the present limits on our ability to optimize wetland creation and restoration for specific carbon and greenhouse gas emission goals, it is wise to prioritize conservation of existing wetland carbon stocks over restoration and management (Moomaw et al., 2018; Neubauer & Verhoeven, 2019). In addition to the biogeochemical considerations we have discussed in this chapter, the cost effectiveness of various restoration and management actions (e.g., Taillardat et al., 2020) has real‐world implications for how wetlands are managed. Managing wetlands for climate regulation should be one facet of a comprehensive plan that also considers valuable co‐benefits of wetlands including water quality improvement, wildlife support, water storage, and cultural services.
ACKNOWLEDGMENTS
During the preparation of this chapter, SCN was supported by Virginia Commonwealth University and JPM was supported by the Smithsonian Institution.
REFERENCES
1 Ainsworth, E. A., & Long, S. P. (2005). What have we learned from 15 years of free‐air CO2 enrichment (FACE)? A meta‐analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. New Phytologist, 165(2), 351–372. https://doi.org/10.1111/j.1469‐8137.2004.01224.x
2 Anderson, B., Barlett, K., Frolking, S., Hayhoe, K., Jenkins, J., & Salas, W. (2010). Methane and nitrous oxide emissions from natural sources (No. EPA 430‐R‐10‐001). US Environmental Protection Agency, Office of Atmospheric Programs, Washington, DC, USA. Retrieved from https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100717T.TXT
3 Angle, J. C., Morin, T. H., Solden, L. M., Narrowe, A. B., Smith, G. J., Borton, M. A., et al. (2017). Methanogenesis in oxygenated soils is a substantial fraction of wetland methane emissions. Nature Communications, 8(1), 1–9. https:10.1038/s41467‐017‐01753‐4
4 Armentano, T. V, & Menges, E. S. (1986). Patterns of change in the carbon balance of organic soil‐wetlands of the temperate zone. The Journal of Ecology, 74(3), 755. https:10.2307/2260396
5 Aufdenkampe, A. K., Hedges, J. I., Richey, J. E., Krusche, A. V., & Llerena, C. A. (2001). Sorptive fractionation of dissolved organic nitrogen and amino acids onto fine sediments within the Amazon Basin. Limnology and Oceanography, 46(8), 1921–1935. https://doi.org/10.4319/lo.2001.46.8.1921
6 Bailey, V. L., Smith, A. P., Tfaily, M., Fansler, S. J., & Bond‐Lamberty, B. (2017). Differences in soluble organic carbon chemistry in pore waters sampled from different pore size domains. Soil Biology and Biochemistry, 107, 133–143. https://doi.org/10.1016/j.soilbio.2016.11.025
7 Baldock, J. A., Masiello, C. A., Gélinas, Y., & Hedges, J. I. (2004). Cycling and composition of organic matter in terrestrial and marine ecosystems. Marine Chemistry, 92(1–4 Spec. Iss.), 39–64. https://doi.org/10.1016/j.marchem.2004.06.016
8 Bansal, S., Johnson, O. F., Meier, J., & Zhu, X. (2020). Vegetation affects timing and location of wetland methane emissions. Journal of Geophysical Research: Biogeosciences, 125(9), e2020JG005777. https://doi.org/10.1029/2020jg005777
9 Bartlett, K. B., Harriss, R. C., & Sebacher, D. I. (1985). Methane flux from coastal salt marshes. Journal of Geophysical Research: Atmospheres, 90(D3), 5710–5720. https://doi.org/10.1029/JD090iD03p05710
10 Basiliko, N., Stewart, H., Roulet, N. T., & Moore, T. R. (2012). Do root exudates enhance peat decomposition? Geomicrobiology Journal, 29(4), 374–378. https://doi.org/10.1080/01490451.2011.568272
11 Beal, E. J., House, C. H., & Orphan, V. J. (2009). Manganese‐ and iron‐dependent marine methane oxidation. Science, 325(5937), 184–187. https://doi.org/10.1126/science.1169984
12 Bedford, B. L., Walbridge, M. R., & Aldous, A. (1999). Patterns in nutrient availability and plant diversity of temperate North American wetlands. Ecology, 80(7), 2151–2169. https://doi.org/10.1890/0012‐9658(1999)080[2151:PINAAP]2.0.CO;2
13 Beltman, B., Van Den Broek, T., Barendregt, A., Bootsma, M.., & Grootjans, A. P. (2001). Rehabilitation of acidified and eutrophied fens in The Netherlands: Effects of hydrologic manipulation and liming. Ecological Engineering, 17(1), 21–31. https://doi.org/10.1016/S0925‐8574(00)00128‐2
14 Belyea, L. R. (1996). Separating the effects of litter quality and microenvironment on decomposition rates in a patterned peatland. Oikos, 77(3), 529. https://doi.org/10.2307/3545942
15 Benner,
