Underground mining magnifies drought impacts in an adjacent protected raised bog

Abstract

Stable and high water levels are crucial for wetland ecosystems, impacting their state, vegetation and conservation. To make informed conservation decisions, it is essential to consider the full range of ecosystem‐level threats associated with artificially lowered water levels. This becomes particularly challenging when dealing with diffuse and indirect impacts, such as ombrotrophic bogs near underground mining activities that extract groundwater. In this study, we monitored water tables using automatic pressure loggers over an 11‐year period in a protected hemiboreal bog and in drained peatland surrounding it in northeastern Estonia. The bog is located within the groundwater cone of depression caused by an adjacent oil‐shale mine, approximately 60–70 m deep. By comparing monitoring points along the bog‐drained forest gradient and analysing time series data, we were able to distinguish the influences of climate and mining activities on water levels in the bog. Our findings indicate that mining activities have clear effects on deeper bedrock aquifers and the bog itself, exacerbating the impacts of recent drought events. The dynamics of the hydraulic heads at different monitoring points reveal local infiltration ‘windows’ within the bog, likely resulting from underlying fracture zones in the bedrock. Considering the escalating intensity of climate change, mires' vulnerability to these combined impacts is expected to increase. Therefore, adopting a precautionary and forward‐thinking conservation strategy is crucial when addressing ongoing or future drainage and mining activities near protected wetlands.

Determining peat's vertical hydraulic diffusivity and hydraulic conductivity from naturally occurring hydraulic pressure fluctuations measured at various depths

“…This information is essential for understanding the hydrological functioning of peatlands, particularly regarding their hydrogeological connection to underlying geological formations and the interplay of water movement between them, as the bottommost low hydraulic conductivity layers limit the water flow through the peat column. Such knowledge is crucial, for instance, in assessing underlying aquifer drainage to peatlands (e.g., Balliston & Price, 2023; Kohv et al, 2023; Whittington & Price, 2013) or assessing the impacts of anthropogenic or natural stresses where the hydraulic conductivity of the bottommost peat layer plays a pivotal role. Moreover, this method proves to be usable for measuring hydraulic properties of the deeper and more decomposed peat layers, which could be difficult with other more widely used methods.…”

“…The duration of the period should be determined based on prevailing weather conditions, capturing significant pressure fluctuations while avoiding long-term trends, e.g. drought, or anthropogenic effects (see Kohv et al, 2023) on hydraulic pressures which could complicate subsequent data analysis (seasonal trend seen in Selisoo 5.3 m). For example, in sub-boreal regions, the optimal timing would be during winter with snow cover or following snowmelt and subsequent high-water levels (but before the summer dry period), minimizing the long-period evapotranspiration trends on water levels.…”

“…To apply this methodology, a case study was carried out in two peatlands, more precisely in raised bogs Kaasiksoo and Selisoo, situated in northeastern Estonia (Figure 2). The structure and hydraulic properties of peat in these sites have been extensively studied before (Hiiemaa et al, 2014; Kohv et al, 2023; Paat et al, 2022). These sites represent a typical “eastern‐type” bog (Masing, 1984), that is, a bog with a convex surface and well‐developed concentric pattern.…”

“…Stable water levels near the surface are crucial for the development and preservation of peatlands (Ingram, 1983). The condition and stability of water levels have been found to be intricately linked to the hydrogeological units underlying peat deposits, influenced by a variety of anthropogenic and climatic factors (e.g., Kohv et al, 2023; Kværner & Snilsberg, 2011; Regan et al, 2019; Whittington & Price, 2013). To enhance our understanding and predict how changes in groundwater levels impact the hydrological functioning and ecology of peatlands, comprehensive knowledge about the hydraulic properties of peat becomes imperative.…”