Four decades of changing dissolved organic matter quality and stoichiometry in a Swedish forest stream

Evans, Christopher D. ORCID: https://orcid.org/0000-0002-7052-354X; Jutterström, Sara; Stadmark, Johanna; Peacock, Mike; Futter, Martyn; Kothawala, Dolly; Monteith, Don ORCID: https://orcid.org/0000-0003-3219-1772; Moldan, Filip. 2024 Four decades of changing dissolved organic matter quality and stoichiometry in a Swedish forest stream. Biogeochemistry. 10.1007/s10533-024-01166-8

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Abstract/Summary

Dissolved organic matter (DOM) concentrations have risen by a factor of two or more across much of Europe and North America during recent decades. These increases have affected the carbon cycle, light regime, drinking water treatability, and the energy and nutrient budgets of lakes and streams. However, while trends in DOM quantity are well characterised, information on how/whether qualitative properties of DOM have changed are scarce. Here, we describe over 40 years of monitoring data from a forested headwater stream in the Gårdsjön experimental catchment, southwest Sweden, which provides a unique record of biogeochemical change, including optical and stoichiometric DOM quality metrics, spanning the entire period of recovery from acidification. For the period 1980–2020 we find a 71% reduction in decadal mean sulphate concentrations, and a similar reduction in inorganic aluminium concentrations, alongside a 64% increase in dissolved organic carbon (DOC) concentrations. Over the same period, colour (absorbance at 420 nm) increased almost twice as much as DOC, whereas dissolved organic nitrogen (DON) increased by only one third as much. These results demonstrate a shift in stream water composition, with DOM becoming dominated by highly coloured, complex, nitrogen-poor compounds. This material is likely more resistant to biological degradation, but more susceptible to photochemical degradation. Changes in DOM stoichiometry could lead to intensified nitrogen and/or phosphorus limitation in surface waters, while increased colour/DOC ratios could intensify light-limitation of primary production beyond that expected from DOC increases alone. We observed increases in organic matter associated metals (iron 117%, organically complexed aluminium 85%) that exceeded the increase in DOC, consistent with their increased mobilisation by more aromatic organic matter. All observed changes are consistent with recovery from acidification being the primary driver of change, implying that past acidification, and ongoing recovery, have profoundly affected terrestrial and aquatic biogeochemistry, ecology and the carbon cycle.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1007/s10533-024-01166-8
UKCEH and CEH Sections/Science Areas:	Soils and Land Use (Science Area 2017-)
ISSN:	1573-515X
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	dissolved organic matter, aquatic carbon, forest catchments, stoichiometry, longterm, biogeochemical trends
NORA Subject Terms:	Hydrology Agriculture and Soil Science Data and Information
Related URLs:	Dataset
Date made live:	06 Aug 2024 14:43 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537811

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