An experimental study on the response of blanket bog vegetation and water tables to ditch blocking

We studied the effect of ditch blocking on vegetation composition and water-table depths in a blanket peatland. Measurements were made for a period of four years (water tables) and five years (vegetation) in the inter-ditch areas of three experimental treatments: (i) open ditches, (ii) ditches blocked with closely-spaced dams and (iii) ditches partially infilled with peat and blocked with dams. It is often assumed that ditch blocking will lead to an increase in the abundance of Sphagnum and, potentially, a reduction in the abundance of sedges, particularly the cotton grasses. However, our data show no treatment effects on the abundance of either group. We did find an effect of time, with the abundance of both sedges and Sphagnum spp. varying significantly between some years. For the sedges there was no systematic change over time, while for the Sphagnum spp. abundance tended to increase through the study period. This systematic change was not related to a measure of the vigour of the sedges, although vigour was lower towards the end of the study compared to the beginning. Our vegetation data are consistent with our water-table data. As with plant type abundance, we did not find any statistically significant differences in water-table depths between treatments, both for annual averages and summer averages. We comment on why ditch blocking does not seem to have affected water tables and vegetation composition at our study site

Infilled Ditches are Hotspots of Landscape Methane Flux Following Peatland Re-wetting

Peatlands are large terrestrial stores of carbon, and sustained CO2 sinks, but over the last century large areas have been drained for agriculture and forestry, potentially converting them into net carbon sources. More recently, some peatlands have been re-wetted by blocking drainage ditches, with the aims of enhancing biodiversity, mitigating flooding, and promoting carbon storage. One potential detrimental consequence of peatland re-wetting is an increase in methane (CH4) emissions, offsetting the benefits of increased CO2 sequestration. We examined differences in CH4 emissions between an area of ditch-drained blanket bog, and an adjacent area where drainage ditches were recently infilled. Results showed that Eriophorum vaginatum colonization led to a “hotspot” of CH4 emissions from the infilled ditches themselves, with smaller increases in CH4 from other re-wetted areas. Extrapolated to the area of blanket bog surrounding the study site, we estimated that CH4 emissions were around 60 kg CH4 ha−1 y−1 prior to drainage, reducing to 44 kg CH4 ha−1 y−1 after drainage. We calculated that fully re-wetting this area would initially increase emissions to a peak of around 120 kg CH4 ha−1 y−1, with around two-thirds of the increase (and 90% of the increase over pre-drainage conditions) attributable to CH4 emissions from E. vaginatum-colonized infilled ditches, despite these areas only occupying 7% of the landscape. We predicted that emissions should eventually decline toward pre-drainage values as the ecosystem recovers, but only if Sphagnum mosses displace E. vaginatum from the infilled ditches. These results have implications for peatland management for climate change mitigation, suggesting that restoration methods should aim, if possible, to avoid the colonization of infilled ditches by aerenchymatous species such as E. vaginatum, and to encourage Sphagnum establishment