Since 1988, there has been, on average, a 91% increase in dissolved organic carbon (DOC) concentrations of UK lakes and streams in the Acid Waters Monitoring Network (AWMN). Similar DOC increases have been observed in surface waters across much of Europe and North America. Much of the debate about the causes of rising DOC has, as in other studies relating to the carbon cycle, focused on factors related to climate change. Data from our peat-core experiments support an influence of climate on DOC, notably an increase in production with temperature under aerobic, and to a lesser extent anaerobic, conditions. However, we argue that climatic factors may not be the dominant drivers of DOC change. DOC solubility is suppressed by high soil water acidity and ionic strength, both of which have decreased as a result of declining sulphur deposition since the 1980s, augmented during the 1990s in the United Kingdom by a cyclical decline in sea-salt deposition. Our observational and experimental data demonstrate a clear, inverse and quantitatively important link between DOC and sulphate concentrations in soil solution. Statistical analysis of 11 AWMN lakes suggests that rising temperature, declining sulphur deposition and changing sea-salt loading can account for the majority of the observed DOC trend. This combination of evidence points to the changing chemical composition of atmospheric deposition, particularly the substantial reduction in anthropogenic sulphur emissions during the last 20 years, as a key cause of rising DOC. The implications of rising DOC export for the carbon cycle will be very different if linked primarily to decreasing acid deposition, rather than to changes in climate, suggesting that these systems may be recovering rather than destabilising. Nomenclature:AWMN 5 UK Acid Waters Monitoring Network;CET 5 Central England Temperature Record; DOC 5 dissolved organic carbon; SAA 5 sum of acid anions; xSO 4 5 nonmarine sulphate

Peatlands have been subject to artificial drainage for centuries. This drainage has been in response to agricultural demand, forestry, horticultural and energy properties of peat and alleviation of flood risk. However, the are several environmental problems associated with drainage of peatlands. This paper describes the nature of these problems and examines the evidence for changes in hydrological and hydrochemical processes associated with these changes. Traditional black-box water balance approaches demonstrate little about wetland dynamics and therefore the science of catchment response to peat drainage is poorly understood. It is crucial that a more process-based approach be adopted within peatland ecosystems. The environmental problems associated with peat drainage have led, in part, to a recent reversal in attitudes to peatlands and we have seen a move towards wetland restoration.However, a detailed understanding of hydrological, hydrochemical and ecological process-interactions will be fundamental if we are to adequately restore degraded peatlands, preserve those that are still intact and understand the impacts of such management actions at the catchment scale.Keywords: peat, moorland gripping, wetland restoration, water table, blanket peat, afforestation, drainage 2 I IntroductionPeat is decaying organic matter that has accumulated under saturated conditions. Formation of peat therefore occurs in areas of positive water balance. Peatlands are more likely to form in regions with high precipitation excess, such as upland areas of the temperate and boreal zones or in lowland areas where shallow gradients, impermeable substrates or topographic convergence maintain saturation.Classification of peatland types is generally related to two fundamental factors: source of nutrients and source of water. Bogs are ombrotrophic peatlands dependent on precipitation for water and nutrient supply, whereas minerotrophic peatlands or fens are reliant on groundwater for water and nutrient supply (Johnson and Dunham, 1963). Bogs are therefore highly acidic (pH < 4) and contain low amounts of calcium and magnesuim, whereas minertrophic peats are less acidic and tend to be base rich.In England and Wales peat is classified as a deposit of at least 30 cm depth (50 cm in Scotland) containing more than 50 % organic carbon (Johnson and Dunham, 1963).This definition is arbitrary as there is no clear break between a highly organic mineral soil (e.g. podzol) and an almost purely organic Sphagnum peat (Clymo, 1983).However, from this definition it is possible to say that 2.9 million ha or 13 % of Britain is covered in peat, most (2.6 million ha) of which is in Scotland (Milne and Brown, 1997). This represents less than 1 % of the 350 million ha of the northern peatlands that mainly occupy the boreal and subarctic zones (Gorham, 1991). In Britain the dominant peatland is blanket bog which occurs on the gentle slopes of upland plateaux, ridges and benches and is primarily supplied with water and nutrients in the form of precipitat...

A strong relationship between dissolved organic carbon (DOC) and sulphate (SO 4 2À ) dynamics under drought conditions has been revealed from analysis of a 10-year time series (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002). Soil solution from a blanket peat at 10 cm depth and stream water were collected at biweekly and weekly intervals, respectively, by the Environmental Change Network at Moor House-Upper Teesdale National Nature Reserve in the North Pennine uplands of Britain. DOC concentrations in soil solution and stream water were closely coupled, displaying a strong seasonal cycle with lowest concentrations in early spring and highest in late summer/early autumn. Soil solution DOC correlated strongly with seasonal variations in soil temperature at the same depth 4-weeks prior to sampling. Deviation from this relationship was seen, however, in years with significant water table drawdown (4À25 cm), such that DOC concentrations were up to 60% lower than expected. Periods of drought also resulted in the release of SO 4 2À , because of the oxidation of inorganic/organic sulphur stored in the peat, which was accompanied by a decrease in pH and increase in ionic strength. As both pH and ionic strength are known to control the solubility of DOC, inclusion of a function to account for DOC suppression because of drought-induced acidification accounted for more of the variability of DOC in soil solution (R 2 5 0.81) than temperature alone (R 2 5 0.58). This statistical model of peat soil solution DOC at 10 cm depth was extended to reproduce 74% of the variation in stream DOC over this period. Analysis of annual budgets showed that the soil was the main source of SO 4 2À during droughts, while atmospheric deposition was the main source in other years. Mass balance calculations also showed that most of the DOC originated from the peat. The DOC flux was also lower in the drought years of 1994 and 1995, reflecting low DOC concentrations in soil and stream water. The analysis presented in this paper suggests that lower concentrations of DOC in both soil and stream waters during drought years can be explained in terms of drought-induced acidification. As future climate change scenarios suggest an increase in the magnitude and frequency of drought events, these results imply potential for a related increase in DOC suppression by episodic acidification.

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