Drivers of increased organic carbon concentrations in stream water following forest disturbance: Separating effects of changes in flow pathways and soil warming

Abstract

[1] Forest disturbance such as clear-cutting has been identified as an important factor for increasing dissolved organic carbon (DOC) concentrations in boreal streams. We used a long-term data set of soil temperature, soil moisture, shallow groundwater (GW) levels, and stream DOC concentrations from three boreal first-order streams to investigate mechanisms causing these increases. Clear-cutting was found to alter soil conditions with warmer and wetter soils during summer. The application of a riparian flow concentration integration model (RIM) explained a major part of variation in stream [DOC] arising from changing flow pathways in riparian soils during the pretreatment period (r 2 = 0.4-0.7), but less well after the harvest. Model residuals were sensitive to changes in soil temperature. The linear regression models for the temperature dependence of [DOC] in soils were not different in the disturbed and undisturbed catchments, whereas a nonlinear response to soil moisture was found. Overall these results suggest that the increased DOC mobilization after forest disturbance is caused by (i) increased GW levels leading to increased water fluxes in shallow flow path in riparian soils and (ii) increased soil temperature increasing the DOC availability in soils during summer. These relationships indicate that the mechanisms of DOC mobilization after forest disturbance are not different to those of undisturbed catchments, but that catchment soils respond to the higher hydro-climatic variation observed after clear-cutting. This highlights the sensitivity of boreal streams to changes in the energy and water balance, which may be altered as a result of both land management and climate change.Citation: Schelker, J., T. Grabs, K. Bishop, and H. Laudon (2013), Drivers of increased organic carbon concentrations in stream water following forest disturbance: Separating effects of changes in flow pathways and soil warming, J. Geophys.

Colonization Habitat Controls Biomass, Composition, and Metabolic Activity of Attached Microbial Communities in the Columbia River Hyporheic Corridor

“…Two potential mechanisms for DOC release during the desorption experiments include (i) actual desorption from surface binding sites on sediment/sand particles and (ii) release associated with POC decomposition. There is ample evidence for sorption of DOC to soil and sediment particle surfaces (3,(42)(43)(44)(45)(46) and for the release of sorbed DOC during hydrologic disturbance (47)(48)(49). Numerous studies have documented the release of DOC during POC decomposition in soils and sediments (e.g., see references 50-56).…”

Representation of dissolved organic carbon in the JULES land surface model (vn4.4_JULES-DOCM)

“…the proportion transported to the coast or respired and emitted to the atmosphere, is the key to understanding the link to the other compartments of the Earth system (Cole et al, 2007;Battin et al, 2009). Nevertheless, it is a difficult task to link riverine and terrestrial fluxes by empirical methods because (1) riverine fluxes are integrating fluxes from different land use systems Boyer and Groffman, 1996) with different leaching rates and DOC quality, (2) in-stream transformation makes it difficult to trace back terrestrial DOC sources, and (3) it is difficult to separate natural and anthropogenic perturbation fluxes (Schelker et al, 2013;Regnier et al, 2013).…”

Impact of forest harvesting on water quality and fluorescence characteristics of dissolved organic matter in eastern Canadian Boreal Shield lakes in summer

“…These lakes receive allochthonous inputs of dissolved and particulate matter from natural sources and anthropic activities (Schindler et al, 1992). Forestry activities in the Canadian Boreal region have increased in the last decades, raising concerns about their potential impact on natural biogeochemical processes in soils and the export pathways that deliver dissolved nutrients and organic matter to aquatic ecosystems.…”

“…Studies on the effects of logging activities on aquatic ecosystems in the boreal region have mostly been oriented to lotic systems (e.g., Smith et al, 2003;Laudon et al, 2009; Published by Copernicus Publications on behalf of the European Geosciences Union. Löfgren et al, 2009).…”