Carbon Loss Pathways in Degraded Peatlands: New Insights From Radiocarbon Measurements of Peatland Waters

Abstract

Harden et al., 1992), so that the long-term accumulation of organic matter represents an important component of the terrestrial carbon cycle. However, peatlands are under widespread pressure with stressors, such as plantation forestry and agriculture (

Peatland pools are tightly coupled to the contemporary carbon cycle

“…That DOC is the youngest C form in these peatland inland water bodies follows previous 14 C studies on peatland streams, and rivers globally, where DOC is generally found to be modern (Billett et al, 2007(Billett et al, , 2012Dean et al, 2019;Evans et al, 2007Evans et al, , 2022Marwick et al, 2015;Tipping et al, 2010), except where there is clear disturbance within their catchments (Butman et al, 2015;Hulatt et al, 2014;Moore et al, 2013). DOC-F 14 C was positively correlated with DOC concentration in the Cross Lochs pools, indicating that increasing DOC concentrations may be driven by contemporary C inputs (Table S3).…”

“…This model conceptually follows empirical observations of both C accumulation and loss in peatland soils (Ratcliffe et al., 2018) and that discharge contributions to pools in blanket peatlands are mainly generated from near‐surface flow paths (Holden et al., 2018). We estimate the age contribution to each 14 C mixture (sample) based on reconstructed atmospheric 14 CO 2 which was assumed to be fixed into plant material and formed the organic matter in peat soils each year over the past 10,000 years by solving Equation (1) for λ (the rate parameter, termed “ k ” in e.g., Evans et al., 2022):$$$$ {\mathrm{F}}^{14}{\mathrm{C}}_{\mathrm{aq}}(t)=\int_0^{\operatorname{inf}}\lambda {e}^{-\lambda T}\ {\mathrm{F}}^{14}{\mathrm{C}}_{\mathrm{air}}\left(t-T\right)\ {2}^{\frac{T}{5730}} dT, $$$$where F 14 C aq is sample 14 C content in F 14 C, F 14 C air is atmospheric 14 C‐CO 2 content at time ( t ), and T is the age of the sample in years before sampling date (yBSD). Atmospheric 14 CO 2 was derived from Reimer et al.…”

“…The aquatic samples we collected contain mixtures of C of different ages that contribute to a single "'bulk" F 14 C value for each sample (Dean et al, 2019). We used an age distribution model to estimate the different age contributions to a given mixture for each 14 C sample (Dean, van der Velde, et al, 2018;Evans et al, 2014Evans et al, , 2022Raymond et al, 2007;Tanentzap et al, 2021). This approach assumes that C sources in a given mixture are dominated by C fixed into peat soils in the year prior to sampling, with contributions of exponentially less C from each preceding year up to a maximum peat age of 10,000 years.…”

“…This model conceptually follows empirical observations of both C accumulation and loss in peatland soils (Ratcliffe et al, 2018) and that discharge contributions to pools in blanket peatlands are mainly generated from near-surface flow paths (Holden et al, 2018). We estimate the age contribution to each 14 C mixture (sample) based on reconstructed atmospheric 14 CO 2 which was assumed to be fixed into plant material and formed the organic matter in peat soils each year over the past 10,000 years by solving Equation (1) for λ (the rate parameter, termed "k" in e.g., Evans et al, 2022):…”

“…Often, 14 C markers associated with disturbance can be hidden within the larger signal of contemporary C turnover (Dean et al, 2019). In these cases, age distribution modelling can provide estimates of the likely contributions of different soil C layers to the mixture of C sources found in a single inland water 14 C sample (Dean, van der Velde, et al, 2018;Evans et al, 2014Evans et al, , 2022Raymond et al, 2007;Tanentzap et al, 2021).…”