Microbial players in the biogeochemistry of methane in fiberbanks

Abstract

Fiberbanks have recently received attention as potential greenhouse gas (GHG) sources in Sweden. Fiberbanks are anthropogenically caused fibre-rich sediments in aquatic environments formed by unregulated discharge of fibrous wastewater from historical pulp and paper industries. A majority of fiberbanks show signs of gas ebullition, mainly consisting of methane and carbon dioxide, resulting from anaerobic digestion of organic material. Methane is biogenically produced by methanogens in anaerobic conditions. In natural systems, methanotrophs often oxidize the biogenically produced methane, limiting the methane emissions from these environments. Natural sediments have been investigated regarding the microbial methane cycle, but no studies have been done on the microbial community inhabiting the fiberbanks so far.

This study investigated the spatial and vertical distribution of methanogens, methanotrophs, and the total archaeal and bacterial communities of two Swedish fiberbanks (Askersund and Munksjön). The method of qPCR was employed for the absolute quantitation of key biomarkers: pmoA (methanotrophs), mcrA (methanogens), 16S rRNA (bacterial and archaeal). Results showed distinct depth distributions between fiberbanks of all biomarkers. In Askersund, highest abundances were measured at the sediment-water interface, decreasing with depth. At Munksjön, maximum abundances were observed in the mid-layers of the sampled sediment. There were no noticeable differences in total abundances between the two fiberbanks. The proportion of the pmoA biomarker compared to the bacterial 16S rRNA was very low, generally less than 0.05%, peaking at 0.5% for one location in Askersund. The mcrA relative abundances were more variable across sampled locations, ranging between 7% and 98%, but showing stable depth distribution. This study confirmed the presence of both methanogens and methanotrophs in fiberbank sediments. Further taxonomic studies could provide deeper insights into their role in GHG emissions.

Popular Abstract

Methane emissions from paper and pulp industrial waste sediments

In discussions about climate change, carbon dioxide is often the focus. However, methane is a far more potent greenhouse gas, with fossil fuels and agriculture being major sources of emissions. Recently, a type of human made sediment has been discovered as a potential source of methane. These are fiber-rich sediments, known as fiberbanks, that have formed due to discharge of untreated wastewater from the paper and pulp industries. This study investigates the microbial community in fiberbanks to assess their role in methane production and consumption.

Global warming affects both human societies and natural ecosystems. The main drivers of global warming are greenhouse gases (GHG), like carbon dioxide (CO2) and methane (CH4). While CO2 emissions often dominate discussions, CH4 is up to 34 times more potent in trapping heat. Global methane emissions are the combined result of human activities, like burning fossil fuels, and natural sources, like marine and lake sediments. Most natural methane is produced by microorganisms called methanogens, which live in oxygen-free environments such as lake sediments. Not all methane reaches the atmosphere, however. Methanotrophs, another type of microorganism, act as natural filters by consuming the methane before it reaches the atmosphere. The methane consumers are typically found in oxygen-containing environments, like the water above the sediments.

Scientists in Sweden have recently begun investigating a new potential source of GHG emissions: fibre-rich sediments formed by the waste from the paper and pulp (P&P) industry. Historically, these P&P factories discharged untreated wastewater into nearby waterbodies. This discharged material has over time settled and formed thick layers, known as fiberbanks. Now, studies have shown many fiberbanks to release both CH4 and CO2, suggesting that fiberbanks could be hotspots for GHG production. However, until now no studies on the microorganisms responsible for these emissions have been done.

This scientific study aimed to understand the microbial communities of methane consumers and producers in fiberbanks. Using a technique called quantitative polymerase chain reaction (qPCR), the number of these microorganisms were quantified and assessed in their proportion of the total microbial community. Two fiberbanks (Askersund and Munksjön) in the lake of Vättern were analysed.

The results showed that both methane consumers and producers were present in these fiberbank sediments. In Askersund, the numbers of both microorganisms were highest in the surface layers. The methane consumers were found in very low numbers, however, likely due to the low-oxygen conditions. In Munksjön, the highest abundances of both were found in the middle layers of the sampled sediment rather than at the surface. The proportion of methane consumers in the overall microbial community was consistently low, making up less than 0.5% of it. The relative abundance of methane producers was observed to vary more between the fiberbanks, generally ranging from approximately 10% to 60%. These results confirm that fiberbanks contain both methane producers and consumers. However, further studies are needed to compare these findings to fiberbanks in different water bodies and to better understand their role in global methane emissions.

Master’s Degree Project in Molecular Biology, 45 credits, 2025
Department of Biology, Lund University

Advisor: Catherine Paul
Division of Biotechnology and Applied Microbiology

• author: Mäkinen, Denise
• supervisor: Catherine Paul
• organization: Degree Projects in Molecular Biology
• course: MOBN02 20242
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9188414
• date added to LUP: 2025-05-14 15:29:21
• date last changed: 2025-05-14 15:29:21