Abstract

Abstract. Drought conditions are expected to increase in frequency and severity as the climate changes, representing a threat to carbon sequestered in peat soils. Downstream water treatment works are also at risk of regulatory compliance failures and higher treatment costs due to the increase in riverine dissolved organic carbon (DOC) often observed after droughts. More frequent droughts may also shift dominant vegetation in peatlands from Sphagnum moss to more drought-tolerant species. This paper examines the impact of drought on the production and treatability of DOC from four vegetation litters (Calluna vulgaris, Juncus effusus, Molinia caerulea and Sphagnum spp.) and a peat soil. We found that mild droughts caused a 39.6 % increase in DOC production from peat and that peat DOC that had been exposed to oxygen was harder to remove by conventional water treatment processes (coagulation/flocculation). Drought had no effect on the amount of DOC production from vegetation litters; however large variation was observed between typical peatland species (Sphagnum and Calluna) and drought-tolerant grassland species (Juncus and Molinia), with the latter producing more DOC per unit weight. This would therefore suggest the increase in riverine DOC often observed post-drought is due entirely to soil microbial processes and DOC solubility rather than litter layer effects. Long-term shifts in species diversity may, therefore, be the most important impact of drought on litter layer DOC flux, whereas pulses related to drought may be observed in peat soils and are likely to become more common in the future. These results provide evidence in support of catchment management which increases the resilience of peat soils to drought, such as ditch blocking to raise water tables.

Highlights

  • Organic-rich peat soils are a major global carbon (C) sink (Limpens et al, 2008) which have formed due to the limited decay of recalcitrant plant litter found in peatland areas, coupled with anoxic conditions created by high water tables slowing decay (Billett et al, 2010; van Breemen, 1995)

  • The site is part of the Mires project (Arnott, 2010) and was chosen as this area has been highlighted as a marginal peatland which may be vulnerable to climate change (Clark et al, 2010)

  • No drought effects were observed for Dissolved organic carbon (DOC) removal or SUVA removal, the source had strong effects on these parameters

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Summary

Introduction

Organic-rich peat soils are a major global carbon (C) sink (Limpens et al, 2008) which have formed due to the limited decay of recalcitrant plant litter found in peatland areas, coupled with anoxic conditions created by high water tables slowing decay (Billett et al, 2010; van Breemen, 1995). Dissolved organic carbon (DOC) represents a significant flux of carbon from peatlands at around 24 % of net ecosystem exchange C uptake (Dinsmore et al, 2010) and can lead to difficulties for downstream drinking water treatment plants. Ritson et al.: The effect of drought on DOC release tion to form disinfection by-products (DBPs) (Rook, 1974) which may have human health implications due to their potential genotoxicity and carcinogenicity (Nieuwenhuijsen et al, 2009)

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