Effects of peatland management on aquatic carbon concentrations and fluxes

Abstract

Abstract. Direct land-to-atmosphere carbon exchange has been the primary focus in previous studies of peatland disturbance and subsequent restoration. However, loss of carbon via the fluvial pathway is a significant term in peatland carbon budgets and requires consideration to assess the overall impact of restoration measures. This study aimed to determine the effect of peatland land management regime on aquatic carbon concentrations and fluxes in an area within the UK's largest tract of blanket bog, the Flow Country of northern Scotland. Three sub-catchments were selected to represent peatland land management types: non-drained, drained, and restoration (achieved through drain blocking and tree removal). Water samples were collected on a fortnightly basis from September 2008 to August 2010 at six sampling sites, one located upstream and one downstream within each sub-catchment. Concentrations of dissolved organic carbon (DOC) were significantly lower for the upstream non-drained sub-catchment compared to the drained sub-catchments, and there was considerable variation in the speciation of aquatic carbon (DOC, particulate organic carbon (POC), CO2, and CH4) across the monitoring sites, with dissolved gas concentrations inversely correlated with catchment area and thereby contributing considerably more to total aquatic carbon in the smaller headwater catchments. Significantly higher POC concentrations were observed in the restored sub-catchment most affected by tree removal. Aquatic carbon fluxes were highest from the drained catchments and lowest from the non-drained catchments at 23.5 and 7.9 g C m−2 yr−1, respectively, with variability between the upstream and downstream sites within each catchment being very low. It is clear from both the aquatic carbon concentration and flux data that drainage has had a profound impact on the hydrological and biogeochemical functioning of the peatland. In the restoration catchment, carbon export varied considerably, from 21.1 g C m−2 yr−1 at the upper site to 10.0 g C m−2 yr−1 at the lower site, largely due to differences in runoff generation. As a result of this hydrological variability, it is difficult to make definitive conclusions about the impact of restoration on carbon fluxes, and further monitoring is needed to corroborate the longer-term effects.

Dissolved organic carbon export in a small, disturbed peat catchment: Insights from long‐term, high‐resolution, sensor‐based monitoring

“…More recent work at multiple (20) sites on Eaglesham Moorland recorded [DOC] ranging from 6.1 to 137.0 mg L −1 (Heal et al 2020). DOC concentrations at Drumtree were higher than drained, nondrained, and restored peatlands in far‐north Scotland, which ranged from 3.8 mg L −1 (nondrained) to 42.2 mg L −1 (drained) (Pickard et al 2022). The nondrained sites, likely to reflect the peat status most closely at Drumtree, had lower TOC export (7.9–9.2 g C m −2 yr −1 ).…”

Reviews and syntheses: Understanding the impacts of peatland catchment management on dissolved organic matter concentration and treatability

“…The 11 studies reviewed showed a mean 8 % increase in DOM concentrations following ditch blocking, although this figure is skewed by the large increases reported by Worrall et al (2007b) and Haapalehto et al (2014) (100 % increase immediately following ditch blocking and 50 %-75 % increases after 10 and 5 years, respectively); the median change is zero. Importantly, no significant change in DOM concentration was reported in over half of these studies (O'Brien et al, 2008;Gibson et al, 2009;Armstrong et al, 2010;Wilson et al, 2011;Evans et al, 2018;Pickard et al, 2022). Likewise, a recent study found no reduction in DOM concentrations at a restored site compared to a ditched site 6 years after ditch blocking, while both the drained and restored site DOM concentrations remained elevated compared with the non-drained control (Pickard et al, 2022).…”

“…Importantly, no significant change in DOM concentration was reported in over half of these studies (O'Brien et al, 2008;Gibson et al, 2009;Armstrong et al, 2010;Wilson et al, 2011;Evans et al, 2018;Pickard et al, 2022). Likewise, a recent study found no reduction in DOM concentrations at a restored site compared to a ditched site 6 years after ditch blocking, while both the drained and restored site DOM concentrations remained elevated compared with the non-drained control (Pickard et al, 2022). Differences between studies with respect to the apparent effect size may in part be related to the experimental design, including whether the work included a simultaneous control, and the time period over which post-restoration monitoring was carried out.…”

“…The time frame for complete recovery to preintervention levels is inconsistent to date, with some areas still showing elevated DOM at the restoration sites relative to the control sites after 17 years (Gaffney et al, 2018). At other sites, DOM concentrations had returned to those seen in intact blanket bog within the same time frame (Howson et al, 2021) or were showing inconsistent effects across subcatchments (Pickard et al, 2022). Other studies have reported Table 3.…”

An examination of the influence of drained peatlands on regional stream water chemistry

“…The potential effects on water-related ecosystem services are intrinsically linked (Flynn et al, 2021 ; Pschenyckyj et al, 2021 ), with the relationship between peatlands and water quality being internationally recognised (Rothwell et al, 2010 ; Nieminen et al, 2021 ; Williamson et al, 2021 ; Pickard et al, 2022 ). According to the latest Water Quality in Ireland report, just over half of surface water bodies in the country meet satisfactory water quality levels, with quality continuing to decline (O’Boyle et al, 2019 ).…”