A guide to conservation land management and greenhouse gas emissionsRewetting drained peatlands not only prevents the release of large quantities of CO2, but also benefits wildife,and can reduce flood risk and the discoloration of drinking water. Wayne HUTCHINSON/Alamy Stock PhotoIt may come as a surprise that undamaged,near-natural bogs (i.e. undegraded blanket bogand lowland raised mires) exert only a smallcooling effect per unit area. Undamaged bogssequester carbon very slowly but, importantly,have been doing so over a long period of timeand have thereby accumulated large quantitiesof carbon in their peat. The big climate issueregarding these bogs is that, once artificiallydrained, they release large quantities of CO2 backinto the atmosphere through oxidation of thedried-out peat.Saline wetlandsThe components of the GHG flux of high-salinitylagoons and intertidal habitat differ again fromthose of freshwater wetlands. First, wetlandswith a salinity of more than about half thatof sea water release little or no methane (e.g.Poffenbarger et al. 2011). Moreover, intertidalhabitat accumulates carbon through twomechanisms. The first is by way of saltmarshplants, seagrass, algae and cyanobacteria takingup CO2 from the atmosphere via photosynthesis,with a proportion of the carbon from thisaccumulating in vegetation and estuarinesediment. The second is through the accumulationin estuarine sediment of particulate carbon thathas been transported to the estuary along rivers.Saltmarsh produces a greater cooling effect perunit area than mudflat, because its vegetationsequesters significant quantities of carbon. Thereis little information on the GHG flux of highsalinity lagoons, but they will probably have lessof a cooling effect than saltmarsh or mudflat,particularly because they do not accumulateorganic matter in sediment at such a high rate.The only type of conservation managementthat commonly takes place in intertidal areas isgrazing of saltmarsh by domestic livestock. Thisgrazing will again reduce the rate that carbonaccumulates in the vegetation and subsequentlyin estuarine sediment, while the livestock will alsorelease methane. Grazing, by reducing vegetationheight, also reduces the rate that sediment istrapped among the vegetation (e.g. Andresenet al. 1990), although this sediment and thecarbon within it should nevertheless accumulateelsewhere in the coastal system.Ways to benefit both the climateand wildlifeThe greatest possible benefits to both wildlife andthe climate per unit area can be provided throughrewetting drained blanket bogs and lowlandraised mires, and especially by (re)creatingvarious types of semi-natural habitat on formerlyintensively managed farmland. Far smallerbenefits for the climate might also be achievedby modifying ongoing conservation management22 Conservation Land Management Summer 2022 | Vol. 20 No. 2
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