Climate and ditch management impact on decomposition in northern peatland: findings from the Tea Bag Index and dissolved organic carbon characteristics

Abstract

Carbon sequestration and long-term carbon storage are fundamental characteristics of northern peatland ecosystems. A key process influencing the carbon balance is the decomposition of litter and peat, which not only emits carbon to the atmosphere but also releases dissolved organic carbon (DOC) to recipient waters. However, these processes are susceptible to shifts, as climate change and management practices impact decomposition processes as well as the quality and quantity of the simultaneously released DOC. In this study, these disturbances were experimentally examined in a peatland mesocosm experiment, concurrently simulating three ditch management scenarios (ditch cleaning, left alone, rewetting) in two climate scenarios (present and RCP4.5). The Tea Bag Index (TBI) was utilised to evaluate the decomposition rate whilst the excitation emission matrix fluorescence spectroscopy with parallel factor analysis (EEM-PARAFAC) was used to determine the compositional changes in DOC components. It was hypothesised that in the ditch cleaning scenario and/or warming conditions, the decomposition rate (k), as well as the abundance of aromatic humic-like DOC components, would increase. In rewetting, the opposite, a decline in decomposition rate was anticipated with an increased occurrence of non-humic DOC such as protein-like components. The decomposition rate was found to be the highest in the ditch cleaning scenario for the RCP4.5 scenario, whilst for the present climate scenario the left alone management had the decomposition rate with the highest variance and values. The rewetted mesocosms had the lowest decomposition values in both climate simulations. Regarding DOC components, the expected increase in DOC aromaticity in ditch management scenarios was not consistent, as only one humic-like component showed increased values across both climate scenarios. In contrast, other humic-like components showed little change or, paradoxically, even higher values in rewetting management. Nonetheless, the protein-like components followed the predictions, having the highest values in rewetting scenarios. These results suggest that a specific ditch management method could significantly alter the carbon balance of the peatland and downstream ecosystems, regardless of the climate impacts.

Popular Abstract

Peatlands located in the northern regions are known to be immense natural carbon banks. This is due to the high water level in peatlands, which creates an oxygen-poor environment where organic matter breakdown is slow, thus increasing the accumulation of carbon. Unfortunately, the natural state of peatlands has often been disturbed by human activities like creating ditches and will be further affected by climate change in the future. When the water level is lowered due to these disturbances, oxygen can reach the peat, triggering decomposition. Decomposition is a process describing the breakdown of organic matter, which can affect and enhance the release of carbon dioxide (CO2) and dissolved organic carbon from peatland ecosystems. Therefore, the possible disturbances impacting decomposition can revert the role of peatlands from carbon sinks to carbon sources.
This project studied different water levels in peatlands, with a specific focus on ditches, as many peatlands are historically ditched and ditches affect the water level depth. The tested ditch managements included: cleaning existing drainage ditches to lower the water level, leaving ditches untouched to keep the water level at its unmanaged state, or blocking ditches to rewet the area with a higher water level. Each management approach was tested under both current and future climate conditions. Specially designed “mini peatlands”, called mesocosms, were used to simulate these scenarios in a laboratory experiment. To assess decomposition, the Tea Bag Index was used, a convenient method for measuring the decomposition rate. Additionally, fluorescence spectroscopy was introduced to analyse the type and quality of dissolved organic carbon released into water.
The results showed that cleaning the ditches led generally to a faster decomposition rate, especially under future warmer climate conditions. In contrast, rewetting the peatland by blocking the ditches slowed decomposition under both climate scenarios. This outcome is promising for maintaining high carbon capacity in peatlands when rewetted, although the ditch managements also change the kind of carbon that flows into nearby waters. Specifically, ditch cleaning slightly increased the release of more stable, humic-like carbon compounds, which can turn the water in downstream ecosystems browner as well as disturb the biodiversity. In rewetted sites, however, there was a greater release of labile, protein-like substances, which are more easily broken down and active in aquatic ecosystems, and affect the downstream ecosystems on a smaller scale.
In conclusion, how we manage water in peatlands has a significant impact, not only for the peatland ecosystem itself, but also on the scale of the global carbon cycle. If we want peatlands to continue to act as carbon sinks in a warming world, it is essential to maintain a high water table in these ecosystems.

• author: Vatsfeld, Johanna Liisa
• supervisor: Martin Berggren; Shokoufeh Salimi
• organization: Dept of Physical Geography and Ecosystem Science
• course: NGEM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Physical Geography and Ecosystem Science, Peatland, Decomposition Rate, Tea Bag Index, Dissolved Organic Carbon, Fluorescence Spectroscopy
• publication/series: Student thesis series INES
• report number: 723
• language: English
• additional info: Co-supervisor Shokoufeh Salimi, Department of Ecology and Genetics; Limnology at Uppsala University.
• id: 9205541
• date added to LUP: 2025-06-25 12:51:59
• date last changed: 2025-06-25 12:51:59