| 1. |
- Buffam, Ishi, et al.
(författare)
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Landscape-scale variability of acidity and dissolved organic carbon during spring flood in a boreal stream network
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112
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Tidskriftsartikel (refereegranskat)abstract
- Acidity is well known to influence stream biota, but the less well-studied spatial and temporal distributions of acidity are likely to play a larger ecological role than average values. We present data on spatial variability of chemical parameters contributing to acidity during winter baseflow and spring flood periods in Krycklan, a fourth-order boreal stream network in northern Sweden. Fifteen stream sites were monitored in subcatchments spanning 3 orders of magnitude in size and representing a wide range of percent wetland. At baseflow, pH ranged from 3.9 to 6.5 at the different sites. Baseflow dissolved organic carbon (DOC) concentration varied by an order of magnitude and was positively correlated with subcatchment percent wetland, resulting in high spatial variability in dissociated organic acids (OA(-)). During spring flood, DOC and OA(-) increased in forested sites and decreased in wetland sites, resulting in reduced spatial variability in their concentrations. In contrast, base cations and strong acid anions diluted throughout the stream network, resulting in decreased acid neutralizing capacity (ANC) at all sites. The spatial variability of base cations increased slightly with high flow. As a result of the changes in OA(-) and ANC, pH dropped at all but the most acidic site, giving a slightly narrowed pH range during spring flood (4.2-6.1). The transition from winter to spring flood stream chemistry could largely be explained by: (1) a shift from mineral to upper riparian organic soil flow paths in forested catchments and (2) dilution of peat water with snowmelt in wetland catchments.
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| 2. |
- Lyon, Steve, et al.
(författare)
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Variability of groundwater levels and total organic carbon in the riparian zone of a boreal catchment
- 2011
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 116:G01020
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Tidskriftsartikel (refereegranskat)abstract
- The riparian zone is a narrow corridor where hillslopes (and their associated hydrobiogeochemical processes) interface with the river system. As such, the riparian zone serves as the last piece of landscape with which water interacts as it transitions from being water flowing primarily through the landscape (i.e., shallow groundwater) to water flowing primarily on the landscape (i.e., stream water). This study investigates the spatiotemporal variability in riparian-zone soil water total organic carbon (TOC) and its relation to the shallow groundwater table using observations from the recently instrumented riparian observatory in the Krycklan catchment study area located in boreal northern Sweden. In general, there is a decrease in TOC concentration with depth down through the soil profile. The rate of this decrease was variable among the six monthly samplings used in this study. The spatial variability of soil water TOC in the riparian zone was connected to the spatial variability of the shallow groundwater levels. This demonstrated the importance of the temporal variation of flow pathways and the mixing of waters from different sources of TOC moving into and through the riparian zone. The coupled variation of the hydrologic and biogeochemical systems raised questions about the ability of simple lumped approaches to accurately predict how in-stream TOC concentrations will change with climate and/or land use. The integrated sampling approach in the riparian observatory covers both hydrologic and biogeochemical aspects of soil water TOC and provides a basis for development and testing of distributed, physically based transport models.
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| 3. |
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| 4. |
- Schelker, Jakob, et al.
(författare)
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Hydrological mobilization of mercury and dissolved organic carbon in a snow-dominated, forested watershed: Conceptualization and modeling
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227. ; 116
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Tidskriftsartikel (refereegranskat)abstract
- The mobilization of mercury and dissolved organic carbon (DOC) during snowmelt often accounts for a major fraction of the annual loads. We studied the role of hydrological connectivity of riparian wetlands and upland/wetland transition zones to surface waters on the mobilization of Hg and DOC in Fishing Brook, a headwater of the Adirondack Mountains, New York. Stream water total mercury (THg) concentrations varied strongly (mean = 2.25 +/- 0.5 ng L (1)), and the two snowmelt seasons contributed 40% (2007) and 48% (2008) of the annual load. Methyl mercury (MeHg) concentrations ranged up to 0.26 ng L (1), and showed an inverse log relationship with discharge. TOPMODEL-simulated saturated area corresponded well with wetland areas, and the application of a flow algorithm based elevation-above-creek approach suggests that most wetlands become well connected during high flow. The dynamics of simulated saturated area and soil storage deficit were able to explain a large part of the variation of THg concentrations (r(2) = 0.53 to 0.72). In contrast, the simulations were not able to explain DOC variations and DOC and THg concentrations were not correlated. These results indicate that all three constituents, THg, MeHg, and DOC, follow different patterns at the outlet: (1) the mobilization of THg is primarily controlled by the saturation state of the catchment, (2) the dilution of MeHg suggests flushing from a supply limited pool, and (3) DOC dynamics follow a pattern different from THg dynamics, which likely results from differing gain and/or loss processes for THg and/or DOC within the Fishing Brook catchment.
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| 5. |
- Wallin, Marcus, et al.
(författare)
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Temporal and spatial variability of dissolved inorganic carbon in a boreal stream network: Concentrations and downstream fluxes
- 2010
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Ingår i: Journal of Geophysical Research: Biogeosciences. - 2169-8953 .- 2169-8961. ; 115, s. G02014-
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide (CO(2)) and dissolved inorganic carbon (DIC) concentrations and export were analyzed throughout a 67 km(2) boreal stream network in northern Sweden. 700 DIC and CO(2) samples from 14 subcatchments were collected in 2006 and 2007. All sites were consistently supersaturated in CO(2) with respect to the atmosphere. Temporal variability of DIC and CO(2) concentration was best correlated with discharge, with concentrations generally diluting at high discharge. However, the variability in CO(2) concentration was also dependent on the specific pH range of the stream, as variability was greatest in acidic headwater streams and lowest in larger circumneutral streams. In the larger ones the increase in the CO(2) proportion of DIC at increased discharge counteracts the dilution of CO(2). The shift toward proportionally more CO(2) of the DIC at higher discharge is caused by decline in pH. Spatial patterns showed that DIC and CO(2) concentrations were best correlated with peatland coverage of the subcatchment. The highest concentrations were found in headwater streams draining peatlands. The downstream export of DIC from the catchment outlet constitutes 19% of the total downstream export of carbon (DIC + DOC), or 0.7 (+/-0.09) g C m(-2) yr(-1). This study demonstrates the importance of including fluvial fluxes of inorganic carbon in landscape carbon budgets via runoff, and also highlights the need to account for stream evasion of CO(2) to the atmosphere in such estimates since it can be larger than the downstream DIC export.
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| 6. |
- Ågren, Annelie, et al.
(författare)
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Importance of seasonality and small streams for the landscape regulation of dissolved organic carbon export
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112, s. Art. No. G03003-
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Tidskriftsartikel (refereegranskat)abstract
- The regulation of the spatial and seasonal variation in terrestrial dissolved organic carbon (DOC) exports was studied in a 68 km2 boreal stream system in northern Sweden. A total of 1213 DOC samples were collected in 15 subcatchments over a 3 year period (2003–2005). The mean annual DOC exports from the 15 subcatchments (0.03–21.72 km2) ranged from 14.8 to 99.1 kg ha−1 yr−1. Many catchment characteristics determined the spatial variation in DOC exports. The relative importance of the different catchment characteristics varied greatly between seasons because of differing hydrological conditions. During winter base flow the spatial variation was linked to patterns in wetland coverage. During snowmelt in spring the spatial variation was connected to characteristics describing size and location, i.e., median stream size, silty sediment distribution, stream order, altitude, and proportion of catchment above highest postglacial coastline (HC). During the snow-free season the spatial variation in DOC exports was regulated by the amount of wetlands and forests, particularly forests made up of Norway spruce (Picea abies). Median stream size also influenced the exports during this season. A striking result in this study was the effect of size implying that small headwaters may be the largest contributor to the terrestrial DOC export, per unit area.
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| 7. |
- Ågren, Anneli, et al.
(författare)
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Modeling stream dissolved organic carbon concentrations during spring flood in the boreal forest : A simple empirical approach for regional predictions
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115
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Tidskriftsartikel (refereegranskat)abstract
- Changes in dissolved organic carbon (DOC) concentration are clearly seen for streams in which chemistry is measured on a high-frequency/episode basis, but these high-frequency data are not available in long-term monitoring programs. Here we develop statistical models to predict DOC concentrations during spring flood from easily available geographic information system data and base flow chemistry. Two response variables were studied, the extreme DOC concentration and the concentration during peak flood. Ninety-seven streams in boreal Scandinavia in two different ecoregions with substantially different mean water chemistry and landscape characteristics (covering a large climatic gradient) were used to construct models where 56% of the extreme DOC concentration and 63% of the concentration during peak flood were explained by altitude. This highlights important regional drivers (gradients in altitude, runoff, precipitation, temperature) of material flux. Spring flood extreme DOC concentration could be predicted from only base flow chemistry (r(2) = 0.71) or from landscape data (r(2) = 0 .74) but combining them increased the proportion of explained variance to 87%. The "best" model included base flow DOC (positive), mean annual runoff (negative), and wetland coverage (positive). The root mean square error was 1.18 mg L-1 for both response variables. The different ecoregions were successfully combined into the same regression models, yielding a single approach that works across much of boreal Scandinavia.
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