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Are dissolved organic carbon concentrations in riparian groundwater linked to hydrological pathways in the boreal forest?

Ploum, Stefan and Laudon, Hjalmar and Tapia, Andres Peralta and Kuglerova, Lenka (2020). Are dissolved organic carbon concentrations in riparian groundwater linked to hydrological pathways in the boreal forest? Hydrology and Earth System Sciences. 24 , 1709-1720
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Abstract

The riparian zone (RZ), or near-stream area, plays a fundamental role in the biogeochemistry of headwaters. Here, wet, carbon-rich soils can change groundwater chemistry before it enters the stream. In the boreal forest, the RZ plays an especially important role in the export of dissolved organic carbon (DOC) to streams. However, the RZ is not uniform, and spatial variability of riparian groundwater hydrology and chemistry can be large. Terrestrial topographic depressions create hydrological pathways towards focal points in the RZ, which we refer to as "discrete riparian inflow points" (DRIPs). Combining the chemical function of the RZ and the convergence of hydrological pathways, we hypothesize that DRIPs play a disproportionally large role in conveying DOC to small streams. Earlier work has demonstrated that runoff from DRIPs can make up the majority of riparian flow contributions to streams, but it is currently unknown how their groundwater chemistry differs from the rest of the RZ. Therefore, we ask the following question: are DOC concentrations in riparian groundwater linked to hydrological pathways in the boreal forest? To answer this question, we sampled riparian groundwater during six campaigns across three boreal headwater streams in Sweden. The groundwater wells were distributed into 10 DRIP and non-DRIP pairs (60 wells), following transects from the upland (20m lateral distance from the stream bank) to the near-stream area (< 5m lateral distance from the stream bank). The variability in DOC, pH, and electrical conductivity (EC) was analyzed using linear mixed-effects models (LMMs). We explained the variability using three factors: distance from the stream, seasonality, and DRIP/non-DRIP. Our results showed that DRIPs provided DOC-rich water (34 mg L-1) with relatively low EC (36 mu S cm(-1)). The "non-DRIP" riparian water had 40% lower DOC concentrations (20 mg L-1) and a 45% higher EC (52 mu S cm(-1)) on average. Moreover, groundwater chemistry from DRIPs was spatially and temporally relatively homogeneous. In contrast, non-DRIP water transformed distinctly in the last 25m towards the stream, and the chemical variability was also larger between seasons. We concluded that hydrological pathways and spatial variability in riparian groundwater DOC concentrations are linked, and that DRIPs can be seen as important control points in the boreal landscape. Characterizing DRIPs in headwater catchments can be useful for upscaling carbon inputs in boreal stream ecosystems and for delineating hydrologically adapted buffers for forest management practices.

Authors/Creators:Ploum, Stefan and Laudon, Hjalmar and Tapia, Andres Peralta and Kuglerova, Lenka
Title:Are dissolved organic carbon concentrations in riparian groundwater linked to hydrological pathways in the boreal forest?
Year of publishing :2020
Volume:24
Page range:1709-1720
Number of Pages:12
Publisher:Copernicus Publications on behalf of the European Geosciences Union
ISSN:1027-5606
Language:English
Publication Type:Journal article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 105 Earth and Related Environmental Sciences > Oceanography, Hydrology, Water Resources
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Forest Science
Keywords:biogeochemistry, riparian zone (RZ), near-stream area, boreal forest, dissolved organic carbon (DOC)
URN:NBN:urn:nbn:se:slu:epsilon-p-105370
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-105370
Additional ID:
Type of IDID
DOI10.5194/hess-24-1709-2020
Web of Science (WoS)000526032400001
ID Code:16949
Faculty:S - Faculty of Forest Sciences
Department:(S) > Dept. of Forest Ecology and Management
Deposited By: SLUpub Connector
Deposited On:02 Jun 2020 07:28
Metadata Last Modified:02 Jun 2020 07:28

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