Declines in the dissolved organic carbon (DOC) concentration and flux from the UK

Fred Worrall*, Nicholas J.K. Howden, Tim P. Burt, Rebecca Bartlett

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

13 Citations (Scopus)
295 Downloads (Pure)

Abstract

Increased concentrations of dissolved organic carbon (DOC) have been reported for many catchments across the northern hemisphere. Hypotheses to explain the increase have varied (eg. increasing air temperature or recovery from acidification) but one test of alternative hypotheses is the trend over the recent decade, with the competing hypotheses predicting: continuing increase; the rate of increase declining with time; and even decrease in concentration. In this study, records of DOC concentration in non-tidal rivers across the UK were examined for the period 2003–2012. The study found that:

i) Of the 62 decade-long concentration trends that could be examined, 3 showed a significant increase, 17 experienced no significant change and 42 showed a significant decrease; in 28 of the 42 significant decreases, a significant step change was apparent with step changes being a decrease in concentration in every case.

ii) Of the 118 sites where annual flux and concentration records were available from 1974, 28 showed a significant step change down in flux and 52 showed a step down in concentration. The modal year of the step changes was 2000 with no step changes observed before 1982.

iii) At the UK national scale, DOC flux peaked in 2005 at 1354 ktonnes C/yr (5.55 tonnes C/km2/yr) but has declined since.

The study suggests that there is a disconnection between DOC records from large catchments at their tidal limits and complementary records from headwater catchments, which means that mechanisms believed to be driving increases in DOC concentrations in headwaters will not necessarily be those controlling trends in DOC concentration further downstream. We propose that the changes identified here have been driven by changes in in-stream processing and changes brought about by the Urban Waste Water Treatment Directive. Therefore, signals identified in headwater catchments may bear little relation to those observed in large rivers much further downstream and vice versa.

Original languageEnglish
Pages (from-to)775-789
Number of pages15
JournalJournal of Hydrology
Volume556
Early online date2 Dec 2017
DOIs
Publication statusPublished - 1 Jan 2018

Keywords

  • DOM
  • Peat
  • Uplands
  • Urban wastewater

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