Saturated hydraulic conductivity of boreal peat and its relationships with peat properties and sampling depth

Abstract

The boreal region is a significant peat‐forming area. With peat, there lie other natural resources, including mineral ores and fossil fuels needed by our economy. However, mining for mineral resources or any other activity that leads to large‐scale groundwater extraction in the near vicinity or underneath the mires can alter the water levels in the overlaying ecosystems and thus have a damaging effect on them, raising concerns about the mires' preservation. Peat itself may isolate surface vegetation from drainage caused by nearby mining when its hydraulic conductivity is sufficiently low. More is known about the hydraulic properties of the uppermost layers of the peat column, but there is very little data about deeper, generally more decomposed peat layers that may potentially act as drainage barriers. Carrying out in situ hydraulic conductivity tests in less conductive peat can be laborious and time‐consuming, and not always practical. This research aims to study and verify statistical relationships between easy‐to‐measure peat properties and hydraulic conductivity over the entire peat column, covering the knowledge deficit that is important in the context of indirect drainage effects related to mining or any other large‐scale groundwater extraction. For that, we sampled peat and conducted in situ saturated hydraulic conductivity tests in several mires in northeast Estonia to gather information about the hydraulic properties of boreal peat. Collected data were fitted with linear mixed‐effects models to link hydraulic conductivity with the degree of decomposition, dry bulk density, depth of measurement, and peatland growth phase. The results indicate that these parameters are strongly correlated with saturated hydraulic conductivity and can serve as predictors of this parameter. Constructed statistical models exhibit relatively high explanatory power and show potential usage for characterizing the hydraulic conductivity of peat. The findings of this study may be helpful in the efforts of mire conservation.

Underground mining magnifies drought impacts in an adjacent protected raised bog

“…Mires in the Tomsk region (Dyukarev & Pologova, 2011; Kopysov et al, 2020) with thicker peat deposits have been reported to be more resistant to the vertical drainage. The hydraulic conductivity can vary by several orders of magnitude, even for the same peat type (Morris et al, 2022; Paat et al, 2022). Direct measurements and indirect estimates show that the lowest conductivity values in raised bogs of northeastern Estonia occur near the bottom of the peat column in highly decomposed ( von Post score H7‐H10) peats formed at the fen and transitional mire growth stages.…”

“…Direct measurements and indirect estimates show that the lowest conductivity values in raised bogs of northeastern Estonia occur near the bottom of the peat column in highly decomposed ( von Post score H7‐H10) peats formed at the fen and transitional mire growth stages. The hydraulic conductivity of those layers may be as low as 10 −10 to 10 −8 m/s (Paat et al, 2022). However, the thickness of the layer, in unison with its conductivity, determines whether it can effectively limit vertical infiltration rates to a level that would be lower from the leftover precipitation after evapotranspiration or fully isolate aquifers above and below.…”

“…Many studies have documented peat hydraulic properties (e.g. Chason & Siegel, 1986; Morris et al, 2015; Paat et al, 2022).…”

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

“…(K oed ). The oedometer ring permeameter test results can be found in the separately provided dataset (Paat et al, 2024). It seems that in Kaasiksoo, the determined K v values for bottommost fen peat are an order of magnitude higher than measured in the laboratory…”

“…The dried and weighed peat samples were then ground using a pestle and mortar for humification determination. Humification was chosen instead of the more commonly used von Post score to describe the degree of decomposition, as it is a more objective measuring technique and has shown a good correlation with peat's saturated hydraulic conductivity values(Paat et al, 2022).The separately collected 0.5 m interval peat samples were utilized to determine compressibility and vertical hydraulic conductivity through permeameter tests. Compressibility of the collected peat samples was assessed using standard oedometer tests (ISO 17892-5, 2017) with a Matest S260 front-loaded oedometer.…”