Impacts of rewetting on peat, hydrology and water chemical composition over 15 years in two finished peat extraction areas in Sweden

Abstract

Restoration of wetlands is a high priority world-wide. Peat extraction areas can be restored by rewetting, however affecting the environment. It could be expected to turn the drained peat-cutover area from a source to a sink of most elements. This study examined effects of such rewetting on peat, hydrology and water chemistry over 15 years at two sites in Sweden; the nutrient-poor Porla peatland and the nutrient-rich Västkärr peatland. Rewetting caused minor changes to peat chemistry, but at the Västkärr site ammonium concentrations increased in superficial peat layers while nitrate decreased. In terms of hydrology, rewetting of the Porla site decreased annual runoff and both high and low discharges. Water pH at the Porla site stayed fairly stable, but at the Västkärr site pH, after an initial 4 years dip, gradually increased to higher values than before rewetting. Water colour and organic matter content were fairly stable, but slightly lower values were found after 15 years than in initial 4-5 years. The concentrations of base cations and of inorganic N were lower after rewetting, while total P was higher. However, these impacts could change from an initial phase as the wetlands in the long-term perspective develop into mires.

Effects of Drainage and Subsequent Restoration on Peatland Hydrological Processes at Catchment Scale

“…The low flow (base flow) quantified during no‐rainfall periods in Disturbed conditions (0.8 mm/day) was slightly lower (statistically not significant) than in Control‐D (0.9 mm/day) and almost similar to that in Restored conditions (0.8 mm/day). Not surprisingly, conflicting conclusions have been reported for low flows after drainage, for example, reduced low flows (Conway & Millar, ) and increased low flows (Ahti, ; Lundin, ; Lundin et al, ). Increased low flow after initial drainage of undisturbed peat is typically assumed to be due to dewatering of the peatland catchment facilitated by the drainage network (Holden et al, ).…”

“…Anthropogenic disturbance of peatlands (e.g., drainage) is known to affect catchment runoff generation processes, which change the shape and size of runoff hydrographs (Grayson et al, 2010;Holden et al, 2006). However, varying annual runoff changes after peatland drainage have been reported, with some studies showing increased annual runoff (Guertin et al, 1987;Lundin et al, 2016;Robinson, 1986) and others showing no significant change (Ayre, 1977;Holden et al, 2006) or reduced runoff (Lundin, 1988;Starr & Päivänen, 1981). With regard to rainfall-runoff event analysis, several studies seem to agree on increased peak flows and shortened lag times after peatland drainage at northern latitudes (Ahti, 1980;Ballard et al, 2012;Holden et al, 2006;Lundin, 1988;Robinson, 1986;Tuukkanen et al, 2016).…”

Methane and Nitrous Oxide Emission Fluxes Along Water Level Gradients in Littoral Zones of Constructed Surface Water Bodies in a Rewetted Extracted Peatland in Sweden

“…At the time just before rewetting, the bottom of the prospective constructed lakes consisted of 0.1-0.2 m highly decomposed fen peat (H 8 to H 10 [52]; bulk density of 0.2-0.3 g cm −3 , pH 5-6 and C/N ratio 21) on postglacial clay. Further site descriptions can be found in [16,17]. The northern part of the previous peat extraction area in Västkärr peatland (Figure 1b) was prepared for rewetting in 1998, with water storage starting in 1999.…”

“…Surface water conditions were characterised by pH 6,6 (median), electrical conductivity 89 µS cm −1 (median), DOC concentration of 39 mg −1 and total C concentration of 41 mg −1 (median values 2009). More environmental data over the entire period from before rewetting in 1997 until 2013 can be found in [17]. Mean values for soil and water temperature as well as water level categories on each measurement occasion are summarised in Table 2.…”

Water table evaluation post the construction of canal blocks on peatland in West Kalimantan, Indonesia

“…This is shown in the result of peatland restoration conducted in Porla and Vastkarr, Sweden. Both sites have previously degraded hydrological function of peat, but then returned to natural or semi-natural condition after restoration has been carried out in the form of peatland rewetting for 15 years [16]. The construction of canal block has also been proven to reduce carbon release and increase biodiversity [17].…”