D. O'Leary, P. Tuohy, O. Fenton, M.G. Healy, H. Pierce, A. Shnel,  E. Daly: Assessing the impact of rewetting agricultural fen peat soil via open drain damming: an agrogeophysical approach, SOIL Special Issue: Agrogeophysics: illuminating soil's hidden dimensions (Pre-Print) https://doi.org/10.5194/egusphere-2025-1966, 2025.

Abstract: Open drainage ditch (i.e. open drain) damming aims to raise the water table in agricultural grassland peat soils thereby reducing greenhouse gas (GHG) emissions. A current knowledge gap is how to examine the spatial and temporal effectiveness of such an action i.e., assessing the behaviour of the water table in the adjoining field. To address this gap, at a drained agricultural grassland site with shallow fen peat soils (ranging from 0 to 2 m depth), water level in an open drain was raised by installing a dam. Associated changes to the water table depth (WTD) were monitored using two nests of dip wells installed at two locations (Rewetted and Normal areas) in the adjoining field. Soil profile volumetric water content (VWC) data were obtained in these two areas in addition to the temperature, salinity, pH, and electrical conductivity signature of the water in the open drain. These data were integrated with geophysical (electromagnetic induction (EMI)) survey data conducted during summer and winter. Results from the dip wells (located > 20 m from dam) indicated that no measurable change in WTD occurred due to the dam installation, aligning with previous studies suggesting limited spatial influence in agricultural fen peat soils. VWC profiles, while consistent with peat physical properties, showed no deviation attributable to drain damming. The EMI results identified a distinct zone with electrical conductivity values similar to those of open drain water, suggesting localised water infiltration within ~20 m of the dammed drain during summer. This spatial impact was less evident during winter, likely due to increased precipitation and regional groundwater influence. This study demonstrates that EMI surveys, shown here in combination with other high-resolution data capture, can detect rewetting effects when combined with neural network clustering and Multi-Cluster Average Standard Deviation analysis, highlighting its value for rapid site assessment. Moreover, the results underscore the importance of survey timing, as summer measurements provided clearer evidence of drain damming impact than winter measurements.

D. O'Leary, C. Brown, J. Hodgson, J. Connolly, L. Gilet, P. Tuohy, O. Fenton, E. Daly: Airborne radiometric data for digital soil mapping of peat at broad and local scales, Geoderma, Volume 453, https://doi.org/10.1016/j.geoderma.2024.117129.

Abstract: Peat soils are high in soil organic matter (SOM) and are recognised stores of carbon. Knowledge of the spatial distribution of peat soils is becoming the focus of many studies and is related closely to peatland mapping. Accurate maps of peat soils have many applications of international importance e.g., gaseous emission inventory reporting or soil organic carbon stock accounting. Traditional mapping methods include in-situ soil auger sampling or peat probing (for depth) while modern methods also incorporate satellite data (optical and radar). However, both methods have limitations. Traditional sampling often omits boundaries and transition zones between peat and mineral soils, while satellite data only measure the surface and may not be able to penetrate landcover, potentially omitting areas of peat under, for example, grassland or forestry. Radiometrics is a measurement of naturally occurring gamma radiation. Peat soils attenuate this radiation through high soil moisture content. For the present study in Ireland, the supervised classification of gridded airborne radiometric data, acquired over multiple years, is performed using neural network pattern recognition to identify areas of peat and non-peat soils. Classification confidence values are used to identify the transition zone between these soil types, providing a simplified visualisation of this transition. Validation is performed using Loss on Ignition (LOI %) point data and several different (blanket bog, raised bog, transition zone) sites in Ireland, showing classified data can detect the presence of peat soils from broad to local scales. Airborne geophysical methods, in particular airborne radiometrics, can bridge the gap between the accuracy of point measurement and the spatial coverage of satellite data to identify peat soils by providing uniform data and objective analysis. The resulting map is a step towards understanding the true spatial distribution of peat soils in Ireland, including transition zones.

P. Tuohy, L. O' Sullivan, C.J. Bracken, O. Fenton: Drainage status of grassland peat soils in Ireland: Extent, efficacy and implications for GHG emissions and rewetting efforts, Journal of Environmental Management, Volume 344, https://doi.org/10.1016/j.jenvman.2023.118391.

Abstract: Peatlands have been artificially drained and degraded over 100s of years and have released huge amounts of carbon dioxide (CO2) as a result. In organic grassland soils, raising the water table to prevent such emissions is being proposed to meet national greenhouse gas emission targets for the land use sector. At present, all of these soils (335,000 ha) are assumed to be drained (as no information has been available on their drainage status) within national emission inventory reporting and are therefore responsible for significant emissions (8–9 million tonnes CO2-equivalent annually). The objective of the present study was to collate studies relating to the drainage status of peat soils in Ireland to present alternative scenarios with regard to actual drainage status of organic soils and their estimated emissions. From a drainage design perspective, evidence suggests that relatively small proportions of the grassland peat area was drained effectively using optimal in-field drain spacings required to control the water table at 0.4–0.5 m. Open drains excavated on such soils have limited capacity to laterally control the water table depth beyond short distances. Furthermore, the lack of long-term routine maintenance post installation ensures the redundancy of many drainage systems over time. New drainage installations are therefore likely replacing existing infrastructure and not necessarily increasing the drained area at any given time. This evidence supports literature from the 1980s which state that relatively low proportions of the grassland peat area has been subjected to effective drainage. Scenario testing results showed that likely emissions from the most probable scenario (with total area drained equating to 90,000–120,000 ha) are 3.6–4.7 million tonnes CO2-equivalent, approximately 40–53% of current national emission inventory estimates. The incorporation of such a refinement into the national inventory could offer a significant reduction in estimated GHG emissions from the grassland land use sector in national emission inventory reporting.