Microorganisms Produce Various Greenhouse Gases in Wetland Drainage

Peatlands are a distinct form of wetland that significantly influence intricate climates. These ecosystems develop in elevated areas, such as Iceland and Russia, characterized by high rainfall. Although they occupy only 3% of the Earth’s land surface, they hold 10-30% of the planet’s soil carbon.

The substantial carbon storage capability of peatlands is due to water-saturated soil. In typical soil, water occupies only part of the pore space, while the remainder is filled with oxygen and other gases. However, in peatland soils, water occupies all pore spaces, minimizing gas volume. The lack of oxygen causes soil microorganisms, such as bacteria and archaea, to decompose dead flora and fauna at a slower pace. This results in the accumulation of carbon-enriched organic matter, known as peat.

Research indicates that while peatlands are effective carbon sinks, they can also emit greenhouse gases that contribute to global warming, including methane, carbon dioxide, and nitrous oxide. These gases, collectively referred to as greenhouse gases, trap heat in the Earth’s atmosphere, raising global temperatures.

In recent decades, farmers and developers worldwide have drained peatlands to make room for livestock and agricultural practices. Previous studies have indicated that draining peatlands can lead to increased GHG emissions by enhancing soil oxygen levels, thus accelerating microbial activity and plant decomposition. As peatland soils are typically low in oxygen, microorganisms resort to alternative energy sources when decomposing organic matter. For instance, some microorganisms metabolize carbon dioxide for energy, producing methane, while others utilize nitrogen compounds and generate nitrous oxide, known as methane-producing and nitrogen-fixing organisms, respectively.

Estimates suggest that microbial decomposition is the primary source of GHG emissions in northern peatland soils, generating up to 2 gigatonnes of carbon dioxide and 0.046 gigatonnes of methane annually. However, these figures are derived from a limited number of studies, prompting scientists to call for further measurements of carbon dioxide, methane, and nitrous oxide emissions from both saturated and drained peatlands.

In an effort to fill this knowledge gap, researchers from Iceland and Italy compared GHG emissions and microbial communities across various peatlands in southwestern Iceland. They analyzed four water-saturated peatlands, four drained peatlands, and four peatlands previously converted to pastures. The researchers posited that drained peatlands would alter microbial communities, resulting in increased emissions of carbon dioxide and nitrous oxide.

The research team identified four sampling locations within each of the twelve peatlands. They collected soil samples to assess temperature, moisture, carbon, and nitrogen content. Additionally, they installed a plastic chamber—similar in size to a gallon bucket—into the soil to capture gas emissions. These samples were then analyzed using a device that heats the gas to separate its components, known as a gas chromatograph. Through this analysis, researchers measured the levels of carbon dioxide, nitrous oxide, and methane in each sample, while also examining specific genes in microbial DNA to identify the microorganisms present and their functions via amplicon gene sequencing.

The researchers concluded that water-saturated peatlands emit three times more methane than their drained counterparts, with a greater abundance of methane byproducts identified in the saturated peatlands. Because methanogenesis is sensitive to oxygen and is inhibited even by low levels of it, they suggested that higher water levels allow for the replacement of oxygen, thus facilitating methane production.

Moreover, they estimated that drained peatlands emit 2.5-4.5 times more carbon dioxide and 2-4 times more nitrous oxide compared to water-saturated peatlands. The presence of nitrites in more poulticed bodies of the nitrous oxide-producing wastewater from peat confirmed their hypothesis. It was observed that both nitrous oxide and carbon dioxide have a greater heat-trapping potential in the atmosphere compared to methane, indicating that drained peatlands likely exacerbate global warming more than water-saturated ones.

In conclusion, the study found that emissions from peatlands increase nitrous oxide and carbon dioxide levels, adversely affecting the climate. They noted that microbial communities adapt to shifts in energy sources, with nitrous oxide-producing microorganisms becoming more prevalent in drained peatlands. The researchers recommend implementing sustainable land-use practices, such as reducing nitrogen fertilizer use, to mitigate these climate issues.

Post view: 40