Electromagnetic Induction as a means to assess the hydrological impact of rewetting agricultural fen peat sites

Globally, there is an increasing focus on the rehabilitation of organic soils currently under agricultural management, particularly modified peatlands which are significant net emitters of greenhouse gases. These carbon-rich landscapes have been extensively modified through drainage and agricultural intervention, transforming natural ecosystems into agricultural production systems.

Traditional land use practices have involved drainage to lower water tables, enabling agricultural productivity but simultaneously triggering significant carbon emissions. A potential approach for rehabilitation of these soils is "rewetting" - a strategic intervention aimed at restoring hydrological conditions closer to the soil's natural state. Rewetting offers a potential nature-based solution to reduce greenhouse gas emissions while simultaneously preserving these ecologically rich landscapes.

The primary objective of rewetting is to manage the water table to be, on average, within 30 cm of the surface throughout the year. This is conventionally achieved by infilling or damming open drainage channels that historically surrounded agricultural fields. However, a critical knowledge gap exists regarding the precise spatial extent and effectiveness of such rewetting efforts.

In Ireland, the ReWET project aims to contribute critical knowledge to emerging global strategies for peatland restoration and climate change mitigation on agriculturally altered peat soils sites. This is achieved by partial rewetting of several agricultural sites under various management practices, primarily cattle grazing, and subsequent monitoring of the impact of rewetting on several key indicators, such as water table depth.

Geophysical techniques offer promising methodological approaches to address the understanding of spatial extend of rewetting efforts. Electrical geophysical methods, which measure soil electrical conductivity, are particularly sensitive to water content and can provide detailed insights into subsurface moisture dynamics. Specifically, Electro-Magnetic Induction (EMI) surveys provide non-invasive, high-resolution mapping of subsurface electrical properties, which can correlate with soil moisture conditions.

In this study, EMI using a CMD Mini-Explorer 6L instrument was deployed several times on one ReWET site in Ireland, classified as a fen peat, to assess the hydrological modifications induced by rewetting interventions. Combining EMI measurements with advanced machine learning clustering, in-situ water table depth and soil moisture data, this study was able to identify the hydrological influence and extent of the rewetting, allowing for a quantitative assessment as to the efficacy of the rewetting operation.

Methodologically, this study demonstrates the utility of geophysical techniques in monitoring and evaluating field-scale hydrological interventions. The approach developed could be readily translated to other peatland restoration projects, providing a robust, non-destructive monitoring framework.

By quantifying the spatial and temporal dynamics of rewetting efforts, this research supports more precise, evidence-based approaches to peatland management. The insights generated are crucial for environmental managers, climate policy makers, and agricultural stakeholders seeking to balance productive land use with ecological conservation and carbon sequestration objectives.