Research Feature: Ecozones
Composition of Stream Dissolved Organic Matter across Canadian Forested Ecozones Varies in Three Dimensions Linked to Landscape and Climate

Key messages

  • We analyzed dissolved organic matter composition in samples from 52 streams across six forested regions in Canada using multiple analytical techniques.

  • Dissolved organic matter composition varied in three dimensions: aromaticity, oxygenation and biopolymer content, linked to climate, wetlands and lakes.

  • Our subcontinental-scale assessment provides insights for monitoring program design, dissolved organic matter data interpretation, and land management.
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Summary

Dissolved organic matter (DOM) is a principal variable influencing aquatic ecosystem processes and the treatability of drinking water. The concentration and composition of DOM in streams depend on both the delivery of DOM from terrestrial sources and on aquatic DOM production and degradation. However, there is limited understanding of the variability of stream DOM composition at continental scales and the influence of landscape characteristics and disturbances on DOM across different regions. We assessed DOM composition in 52 streams at seven research sites across six forested ecozones in Canada using 25 indices derived from five analytical approaches; absorbance and fluorescence spectroscopy, liquid chromatography – organic carbon detection, Fourier-transform ion cyclotron resonance mass spectrometry, and asymmetric flow field-flow fractionation. Combined analyses showed clear clustering and redundancy across analytical techniques, and indicated that compositional variations were primarily related to three axes of DOM
composition: a) DOM aromaticity, which was greater in low-relief, wetland-dominated catchments, b) DOM oxygenation, which was greater in colder and drier ecozones, and c) DOM biopolymer content, which was greater in lake-influenced catchments. Variability in DOM composition among research sites was greater than variability of streams within a site and variability over time within a stream. Disturbance (forest harvesting and wildfire) had no common influence on DOM composition across sites, emphasizing the need for regional studies. Overall, this study is a unique assessment of the variability of stream DOM composition and its drivers at a subcontinental scale. Our findings are useful for future studies, aiding in choice of methodological approaches, and helping put regional findings into a broader context. Our findings will be key to understanding the differences in drinking water treatability among different regions and the effects of disturbances and climate change on DOM composition in surface waters.


Publications

Orlova J, Amiri F, Bourgeois AK, Buttle JM, Cherlet E, Cuss CW, Devito KJ, Emelko MB, Floyd WC, Foster DE, Hutchins RHS, Jamieson R, Johnson MS, McSorley HJ, Silins U, Tank SE, Thompson LM, Webster KL, Williams CHS, Olefeldt D, 2024. Composition of Stream Dissolved Organic Matter Across Canadian Forested Ecozones Varies in Three Dimensions Linked to Landscape and Climate. Water Resources Research, 60(5):e2023WR035196.
Photo: Working onsite with partner X.

Contributors

UofA: Orlova J, Bourgeois A, Cherlet E, Cuss C, Devito K, Silins U, Tank S, Thompson L, Williams C, Olefeldt D

UWaterloo: Amiri F, Emelko MB, Hutchins R

TrentU: Buttle J

VIU: Floyd W 
DalhousieU: Foster D, Jamieson R

UBC: Johnson M, McSorley H

NRCAN: Webster K