Tracking microbial responses to rewetting and nutrient mobilisation during agricultural peatland restoration

Degradation of the UK’s peatlands has turned these landscapes from long-term carbon sinks to net sources, with lowland peatlands contributing a majority of these emissions. Rewetting is the primary means of restoring these peatlands, with the aim of limiting microbial aerobic decomposition of organic matter by raising the water table and reestablishing anoxic conditions. However, rewetting of former agricultural peat may also disrupt the cycling of redox-sensitive compounds, mobilise organic and mineral-bound nutrients, and modify the source of water supplying the peatland. How microbial communities respond to these hydrological and geochemical alterations remains unclear, even though they represent the primary control on peatland carbon balance and ecosystem function.  

We have established a multi-year study at a former dairy farm on lowland peat soils in the Somerset Levels. We are conducting paired comparisons of drained and rewetted peat profiles within the same context that have resulted from blocking drainage ditches with sheet pile dams. Ditch blocking has been conducted at the site to facilitate rewetting but is also expected to alter the availability of nutrients within the peatland. We are investigating the primary geochemical controls on the microbiome, combining seasonal geochemical characterisation (water-extractable NO₃^-, NO₂^-, NH₄⁺, PO₄^3-, Fe²⁺, Fe³⁺), 16S rRNA gene sequencing; and bulk peat organic matter characterisation. Our findings highlight some of the challenges in restoring agricultural peatlands with both legacy and catchment-derived nutrient inputs. We find that macronutrient availability (in particular, water-extractable NH₄⁺ and PO₄^3-) remains elevated under the rewetting scenario, suggesting a potential legacy influence of prior land use on nutrient cycling. Moreover, across much of the peat profile, the major microbial constituents are shared between the drained and rewetted sites despite intervention. We identify taxa which may serve as markers of the redox interface, such as microaerophilic iron-oxidising bacteria, and explore the utility of such microbial indicators as a potential approach for predicting peatland function. The project demonstrates how microbial community sequencing can shed light on in-situ elemental cycling to inform ongoing management practices.