Assessing the drivers of dissolved organic matter export from two contrasting lowland catchments, U.K

Chris Yates, Penny Johnes, Robert Spencer

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Abstract

Two lowland catchments in the U.K. were sampled throughout 2010–11 to investigate the dominant controls on dissolved organic matter quantity and composition. The catchments had marked differences in terms of nutrient status, land cover and contrasting lithologies resulting in differences in the dominant flow pathways (groundwater vs. surface water dominated). The Upper Wylye is a chalk stream with a baseflow index of 0.98, draining a catchment dominated by intensive agricultural production. Millersford Brook is a lowland peat catchment with a baseflow index of 0.43, draining a semi-natural catchment with heather moorland and coniferous forest. Samples were collected weekly between October 2010 and September 2011 from eleven sampling locations. Samples were analysed to determine dissolved organic carbon, nitrogen and phosphorus fractions with DOM composition evaluated via the DOC:DON ratio, DOC:DOP ratio, specific UV absorption at 254 nm, absorbance ratio (a250:a365) and the spectral slope parameter between 350 and 400 nm (S350–400). Significant differences were observed in all determinands between the catchments, over time, and spatially along nutrient enrichment and geoclimatic gradients. Seasonal variation in preferential flow pathways mobilising groundwater-derived DOM were identified as likely controls on the delivery of DOM in the permeable chalk dominated catchment. Steeper S350–400 values and elevated a250:a365 ratios in this catchment suggest material of a lower bulk aromatic C content and molecular weight delivered during the winter months when compared to the summer. DOC:DON ratios were markedly lower in the chalk catchment than the peatland catchment, reflecting the paucity of organic matter within the mineral soils of the chalk landscape, and higher fertiliser application rates. This manuscript highlights that DOM composition varies according to catchment landscape character and hydrological function.
Original languageEnglish
Pages (from-to)1330-1340
Number of pages11
JournalScience of The Total Environment
Volume569–570
Early online date12 Jul 2016
DOIs
Publication statusPublished - 1 Nov 2016

Keywords

  • Dissolved organic matter
  • Carbon
  • Nitrogen
  • Phosphorus
  • CDOM

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  • DOMAINE: Characterisation of the nature, origins and ecological significance of dissolved organic matter in freshwater ecosystems

    Johnes , P. J., Evershed, R. P., Jones, D., Maberly, S., Jickells, T., Yates, C. A., Lloyd, C. E. M., Glanville, H., Mackay, E., Harrison, R. V., Bayliss, C. E., Pemberton, J., Reay, M. K. M., Brailsford, F., Mcintyre, C. A., Owen, A. T., Hopes, M., Evans, C., Fenner, N., Golyshin, P., Ferrer, M., Marshall, M. & Cooper, D.

    1/04/1431/12/19

    Project: Research

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