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Forests cover one-third of all land on the planet. They support eighty 80% of the earth’s biodiversity and provide a livelihood for billions of individuals. Furthermore, they are carbon-sequestration powerhouses, absorbing up to 30% of our greenhouse gas emissions. As a result, forest wellness and conservation are critical weapons in the global fight against climate change.
The greenhouse gas (GHG) methane (CH4) level has increased significantly since industrialization. Anthropogenic sources account for over 60% of world emissions, with agriculture, waste treatment, biomass burning, and the fossil fuel industry accounting for the remainder. Furthermore, on average, drainage ditches and canals are projected to generate 1% of worldwide anthropogenic CH4 emissions, although their contribution to anthropogenic CH4 emissions might be significantly higher in heavily drained areas.
As a result, incorporating ditch and canal emissions into local and national GHG inventories will be critical in assessing the impact of drained land on CH4 budgets, particularly in densely drained countries such as Finland, where approximately 5.9 million ha of peatlands have been eliminated for forestry since the 1920s, an area equal to up to 40% of the global estimate of 15 million ha of forestry-drained peatlands.
Ditches in forestry-drained peatlands emit less methane into the atmosphere than previously thought, according to a study conducted through the Natural Resources Institute of Finland (Luke), the University of Tampere, and the University of Helsinki. According to the study, methane emissions are minimal in moss-covered forest ditches. As forestry subsidies expire, the percentage of such ditches in all forest ditches grows as ditch network upkeep decreases.
More than five million hectares of Finnish peatlands were drained for forestry, making up roughly 17% of Finland’s total land area. While draining has resulted in carbon dioxide and nitrous oxide emissions, it has also significantly reduced methane emissions from peat soil. Ditches, instead of soil, have become significant sources of methane emissions, which are accounted for in the nation’s greenhouse gas inventory as a component of the land use sector.
The current estimate of methane emissions from ditches in Finland’s forestry-drained peatlands in the greenhouse gas inventory is based on the Intergovernmental Panel on Climate Change (IPCC) Tier 1 emission factor. However, the studies to develop Tier 1 emission factors must adequately represent Finnish conditions, as only a few of the 11 study regions are in Finland. This is why the necessary information set needs to be significantly extended. Furthermore, the Tier 1 emission factor does not account for the fact that different types of ditches may emit varying amounts of methane. Based on prior research, it is assumed that methane emissions from ditches differ depending on the kind of ditch and, in particular, the type of flora in the ditch.
According to studies, moss-covered ditches emit extremely little methane, accounting for only one-eighth of moss-free water-covered ditches and Tier 1 emissions. As a result, the Tier 1 emission factor overestimates methane emissions from moss-covered forest ditches. These findings are most likely explained by microbial activity. Methanotrophs, or methane-consuming bacteria, live in and on mosses, consuming methane before it enters the atmosphere. It’s also likely that the organic substances exhaled by mosses inhibit the functioning of methanogenic microorganisms, which produce methane.
The above study also calculated the area of forestry-drained peatland ditches in Finland. Furthermore, the percentage of moss-covered and moss-free ditches was calculated. Two-thirds of all ditches are expected to be moss-covered, with only one-third being moss-free. The recent decline in ditch network maintenance likely explains the substantial proportion of moss-covered ditches.
The findings from the research on methane emissions from ditches of forestry-drained peatlands were roughly 8,600 metric tons per year, up to 63% lower than the current greenhouse gas inventory (approximately 23,200 metric tons) due to the low emissions and a high percentage of moss-covered forest ditches. When measured in carbon dioxide equivalents (CO2eq), the new emission value is around 0.4 million metric tons lower than the old one. The research group recommends the national emission factors determined from the findings be included in the greenhouse gas inventory since they more accurately reflect emissions from Finland’s forest ditches than Tier 1 emission factors.
Since the forest-drained peatlands’ forest floor is usually a tiny CH4 sink, emissions from the ditches decide whether these areas are net sources or sinks of CH4. Accurate methane budget estimations for forestry-drained peatlands would greatly benefit from creating emission variables that account for changes in CH4 emissions between ditches of varying age and vegetation cover. Furthermore, a more exact evaluation of the total area of various kinds of ditches is required for more precise estimations of the national GHG inventory.
Mosses establish the groundwork for plants to thrive in all environments; they may also significantly reduce climate change by absorbing massive amounts of carbon. While moss is essential for carbon dioxide absorption, these amounts of carbon capture are comparable to the greenhouse gas emissions from agricultural practices such as land removal and overgrazing. Moss alone was expected to take in and preserve 6.43 billion metric tons of CO2 from the atmosphere. Moss-free ditches in forestry-drained boreal peatlands may emit much more methane than moss-covered forest ditches. The IPCC’s default Tier 1 emission factor considerably overestimates CH4 emissions from moss-covered ditches in forestry-drained boreal peatlands in Finland.
Ditch-type-specific emission factors can improve ditch emissions estimates dramatically. The bulk of the ditches (67%) were classified as moss-covered forest ditches, which, combined with the new emission parameters, resulted in a 63% reduction in CH4 emissions. Furthermore, results show that the existing practice in Finland of minimizing ditch-network maintenance through ditch cleaning will likely reduce CH4 emissions from ditches because old moss-covered ditches emit very little CH4.
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