title: Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry.
abstract: Several hypotheses have been proposed to explain recent, widespread increases in concentrations of dissolved organic carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.
authors.affiliation: Environmental Change Research Centre, UCL, London, WC1E 6BT, UK. dmonteit@geog.ucl.ac.uk
authors.forename: Donald T
authors.initials: DT
authors.lastname: Monteith
authors.forename: John L
authors.initials: JL
authors.lastname: Stoddard
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Evans
authors.forename: Heleen A
authors.initials: HA
authors.lastname: de Wit
authors.forename: Martin
authors.initials: M
authors.lastname: Forsius
authors.forename: Tore
authors.initials: T
authors.lastname: Høgåsen
authors.forename: Anders
authors.initials: A
authors.lastname: Wilander
authors.forename: Brit Lisa
authors.initials: BL
authors.lastname: Skjelkvåle
authors.forename: Dean S
authors.initials: DS
authors.lastname: Jeffries
authors.forename: Jussi
authors.initials: J
authors.lastname: Vuorenmaa
authors.forename: Bill
authors.initials: B
authors.lastname: Keller
authors.forename: Jiri
authors.initials: J
authors.lastname: Kopácek
authors.forename: Josef
authors.initials: J
authors.lastname: Vesely
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002244:Carbon / Q000032:analysis* / Q000737:chemistry*; D017753:Ecosystem; D005060:Europe; D005618:Fresh Water / Q000737:chemistry*; D049673:History, 20th Century; D049674:History, 21st Century; D046448:Ice Cover / Q000737:chemistry; D009656:North America; D045483:Rivers / Q000737:chemistry; D012623:Seawater / Q000737:chemistry; D012995:Solubility; D013997:Time Factors
chemical_list: D002244:Carbon