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Variation in dissolved organic matter (DOM) stoichiometry in UK freshwaters: Assessing the influence of land cover and soil C:N ratio on DOM composition

Variation in dissolved organic matter (DOM) stoichiometry in UK freshwaters: Assessing the influence of land cover and soil C:N ratio on DOM composition Thumbnail


Abstract

Dissolved organic matter (DOM) plays an important role in freshwater biogeochemistry. To investigate the influence of catchment character on the quality and quantity of DOM in freshwaters, 45 sampling sites draining subcatchments of contrasting soil type, hydrology, and land cover within one large upland-dominated and one large lowland-dominated catchment were sampled over a 1-yr period. Dominant land cover in each subcatchment included: arable and horticultural, blanket peatland, coniferous woodland, and improved, unimproved, acid, and calcareous grasslands. The composition of the C, N, and P pool was determined as a function of the inorganic nutrient species (NO3-, NO2-, NH4+, and PO43-) and dissolved organic nutrient (dissolved organic carbon [DOC], dissolved organic nitrogen [DON], and dissolved organic phosphorus [DOP]) concentrations. DOM quality was assessed by calculation of the molar DOC : DON and DOC : DOP ratios and specific ultraviolet absorbance (SUVA254). In catchments with little anthropogenic nutrient inputs, DON and DOP typically composed >?80% of the total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrations. By contrast, in heavily impacted agricultural catchments DON and DOP typically comprised 5–15% of TDN and 10–25% of TDP concentrations. Significant differences in DOC : DON and DOC : DOP ratios were observed between land cover class with significant correlations observed between both the DOC : DON and DOC : DOP molar ratios and SUVA254 (rs?=?0.88 and 0.84, respectively). Analysis also demonstrated a significant correlation between soil C : N ratio and instream DOC : DON/DOP (rs?=?0.79 and 0.71, respectively). We infer from this that soil properties, specifically the C : N ratio of the soil organic matter pool, has a significant influence on the composition of DOM in streams draining through these landscapes.

Acceptance Date Apr 3, 2019
Publication Date Nov 11, 2019
Publicly Available Date Mar 28, 2024
Journal Limnology and Oceanography
Print ISSN 0024-3590
Publisher Wiley
Pages 2328 - 2340
DOI https://doi.org/10.1002/lno.11186
Publisher URL http://doi.org/10.1002/lno.11186

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