Abstract
Peatland ecosystem services include drinking water provision, flood mitigation, habitat provision and carbon sequestration. Dissolved organic carbon (DOC) removal is a key treatment process for the supply of potable water downstream from peat-dominated catchments. A transition from peat-forming Sphagnum moss to vascular plants has been observed in peatlands degraded by (a) land management, (b) atmospheric deposition and (c) climate change. Here within we show that the presence of vascular plants with higher annual above-ground biomass production leads to a seasonal addition of labile plant material into the peatland ecosystem as litter recalcitrance is lower. The net effect will be a smaller litter carbon pool due to higher rates of decomposition, and a greater seasonal pattern of DOC flux. Conventional water treatment involving coagulation-flocculation-sedimentation may be impeded by vascular plant-derived DOC. It has been shown that vascular plant-derived DOC is more difficult to remove via these methods than DOC derived from Sphagnum, whilst also being less susceptible to microbial mineralisation before reaching the treatment works. These results provide evidence that practices aimed at re-establishing Sphagnum moss on degraded peatlands could reduce costs and improve efficacy at water treatment works, offering an alternative to ‘end-of-pipe’ solutions through management of ecosystem service provision.
Highlights
The system and most likely originates from decaying litter and the upper soil horizons[13,14]
We consider how effective water treatment processes are for different Dissolved organic carbon (DOC) sources, the persistence of this organic carbon as well as how the different vegetation litters decompose, both in laboratory and field experiments, and the implication this will have for C retention in peatlands and downstream water treatment works
Samples of DOC extracted from Sphagnum, Calluna, Juncus, Molinia and a peat soil, sourced from Exmoor National Park (51°07′23.3′′N 3°45′11.8′′W) were subject to coagulation/flocculation ‘jar testing’ with ferric sulfate, a practice used in the water industry to simulate DOC removal at water treatment works
Summary
Ease of DOC removal during the treatment process for different peatland sources. First, we evaluated how easy it was to treat DOC from different vegetation types using conventional methods. The vascular plants, in contrast, showed high DOC production on a mg per g basis in the laboratory decomposition yet showed very rapid mass loss in the field, suggesting the overall litter carbon pool in a vascular plant dominated system will comprise just a few years’ worth of litter This could have important implications for DOC flux from catchments where grassland species are encroaching on Sphagnum peatlands[33] as higher peaks in flux may be observed from vascular plant biomass as it rapidly decays, as the size of the carbon pool is likely to decrease, DOC flux may reduce overall. As we showed in the previous experiments, this adds a large amount of labile material to the litter layer, resulting in greater DOC production This suggests that a shift from Sphagnum to Calluna, Molinia or Juncus dominated areas could lead to a stronger seasonal signal in DOC fluxes from the litter layer. These results show that changes in vegetation can have a large effect on the seasonality and treatability of DOC in peatland catchments and managing vegetation type could be a method of improving raw water quality rather than ‘end-of-pipe’ solutions at the treatment works
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