Explorative analysis of depth-to-water index in identifying rewettable agricultural peat soils

Functional tools to implement peatland rewetting are essential to mitigate the negative environmental impacts of drained organic soils. Soil moisture indexes have been used to identify wet areas in forests but they have been applied to a lesser extent in agricultural areas. This research explores the potential of the depth-to-water index (DTW) to identify rewettable peat soils in agricultural areas and estimates the national rewetting potential of cultivated peat soils in Finland. We used water table level (WTL) measurements from five rewetted sites, combined with an analysis of the surrounding terrain, to assess the suitability of the index. The evaluation of DTW index maps in relation to observed WTL suggests that the DTW index has potential for predicting the suitability of specific field parcels for rewetting if the water flow can be modelled correctly. Using this approach, we identified 135,000 ha of Finnish cultivated peat soils that could be best suitable for rewetting. The method requires development particularly concerning input data. Lack of digital data on ditches in agricultural areas and their intersections with roads can lead to incorrect water flow modelling, resulting in over- or underestimation of mean DTW values for field parcels. Including the effects of existing agricultural drainage systems into the index calculation could improve accuracy, making it a more precise tool for authorities to target rewetting measures. Also, the position of the site within the watershed and the surrounding land use and drainage influence the rewetting success. Prioritising rewetting of large contiguous areas likely leads to better outcomes for biodiversity and climate mitigation, but rewetting single field parcels can also succeed if the surrounding terrain supports it.