Restored wetlands - point sources of methane emissions and mercury methylation?

Background

Around Sweden, extensive restoration of wetlands is being carried out, both by authorities and private actors. Restoring wetlands in the landscape contributes to several of the Swedish Environmental Quality Goals adopted by the Swedish Parliament, primarily “Thriving Wetlands”; “A rich flora and fauna”; “Good quality groundwater”; “No eutrophication and balanced seas” and “Living coast and archipelago”. The interest and commitment to restoring wetlands is often great and significant financial resources have been allocated both nationally and within the EU. However, restoring wetlands does not only lead to positive environmental effects. Raising the water level and recreating oxygen-free environments can generate a number of less desirable processes. One such is the formation and release of methane, the second most important greenhouse gas after carbon dioxide. Another threat is increased methylation of mercury. Most of all drainage projects were carried out 50-100 years ago, or more, which means that the soil that has been drained has undergone extensive chemical and physical changes and is therefore significantly different from soil in wetlands that have never been drained.

Purpose

Therefore, there are currently large knowledge gaps about the processes that are affected by a restoration effort. The main goal of this project is to compare the conditions for methane production, methane oxidation, and methylation and reduction of mercury in restored wetlands with natural wetlands that have never been drained. This knowledge is fundamental for the design of effective restoration strategies that avoid potential negative effects linked to the restoration of wetlands in the landscape.

Implementation

The project will utilize existing restoration projects and will be implemented in collaboration with, above all, several county administrative boards, which also guarantees the transfer of knowledge from the project to central actors. Sampling will take place on drained wetlands, restored wetlands and natural wetlands. We will focus on the upper 50 cm of the peat profile where it is known that most of the organisms that methylate mercury, and form and consume methane are found. The overall steps linked to the implementation of the project include:

Characterization of the physical and chemical properties of the peat profiles and how drainage and restoration affect these in comparison to pristine systems.
Characterization and quantification of the microbial populations whose activity leads to mercury methylation and methane release.
Investigate the contribution of methane formation and methane oxidation in the peat profiles by analyzing patterns in the stable isotopes of methane (13C and deuterium).

Determine the ratio between methylmercury and total mercury, which can be used as a proxy for the rate and extent of mercury methylation.
By linking the biogeochemical markers with the physical and chemical properties of the peat profile, as well as the character of the different catchments, we aim to identify easily measurable characteristics linked to negative environmental impacts of restoration. These characteristics can then be used to evaluate which wetlands are most suitable for restoration or should be avoided to minimize the risk of negative biogeochemical consequences.