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Research article - Peer-reviewed, 2020

Changing Source-Transport Dynamics Drive Differential Browning Trends in a Boreal Stream Network

Fork, Megan L.; Sponseller, Ryan A.; Laudon, Hjalmar

Abstract

Dissolved organic carbon (DOC) concentrations are increasing in freshwaters worldwide, with important implications for aquatic ecology, biogeochemistry, and ecosystem services. While multiple environmental changes may be responsible for these trends, predicting the occurrence and magnitude of "browning" and relating such trends to changes in DOC sources versus hydrologic transport remain key challenges. We analyzed long-term trends in DOC concentration from the two dominant landscape sources (riparian soils and mire peats) and receiving streams in a boreal catchment to evaluate how browning patterns relate to land cover and hydrology. Increases in stream DOC were widespread but not universal. Browning was most pronounced in small, forested streams, where trends corresponded to twofold to threefold increases in DOC production in riparian soils and increases in annual DOC export from a forested headwater. By contrast, DOC did not change in mire peats or streams draining catchments with high lake or mire cover, nor did we observe trends in DOC export from a mire-dominated headwater. The distinct long-term trends in DOC sources also altered concentration-discharge relationships, with a forested headwater shifting from transport-limited toward chemostasis, and a mire outlet stream shifting from chemostasis to source-limitated. Modified DOC supply to headwaters, together with altered seasonal hydrology and differences in the dominant water source along the stream network gave rise to predictable browning trends and consistent concentration-discharge relationships. Overall, our results show that the sources of DOC to boreal aquatic ecosystems are responding to environmental change in fundamentally different ways, with important consequences for browning along boreal stream networks.

Keywords

brownification; wetland; riparian; concentration-discharge; flux; DOC

Published in

Water Resources Research
2020, volume: 56, number: 2, article number: e2019WR026336
Publisher: AMER GEOPHYSICAL UNION

Authors' information

Fork, Megan L.
Cary Inst Ecosyst Studies
Fork, Megan L.
Umea Univ
Sponseller, Ryan A.
Umea Univ
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management

UKÄ Subject classification

Ecology
Environmental Sciences

Publication Identifiers

DOI: https://doi.org/10.1029/2019WR026336

URI (permanent link to this page)

https://res.slu.se/id/publ/107076