| 1. |
- Ali, Genevieve, et al.
(författare)
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Comparison of threshold hydrologic response across northern catchments
- 2015
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 29:16, s. 3575-3591
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Tidskriftsartikel (refereegranskat)abstract
- Nine mid-latitude to high-latitude headwater catchments - part of the Northern Watershed Ecosystem Response to Climate Change (North-Watch) programme - were used to analyze threshold response to rainfall and snowmelt-driven events and link the different responses to the catchment characteristics of the nine sites. The North-Watch data include daily time-series of various lengths of multiple variables such as air temperature, precipitation and discharge. Rainfall and meltwater inputs were differentiated using a degree-day snowmelt approach. Distinct hydrological events were identified, and precipitation-runoff response curves were visually assessed. Results showed that eight of nine catchments showed runoff initiation thresholds and effective precipitation input thresholds. For rainfall-triggered events, catchment hydroclimatic and physical characteristics (e.g. mean annual air temperature, median flow path distance to the stream, median sub-catchment area) were strong predictors of threshold strength. For snowmelt-driven events, however, thresholds and the factors controlling precipitation-runoff response were difficult to identify. The variability in catchments responses to snowmelt was not fully explained by runoff initiation thresholds and input magnitude thresholds. The quantification of input intensity thresholds (e.g. snow melting and permafrost thawing rates) is likely required for an adequate characterization of nonlinear spring runoff generation in such northern environments.
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| 2. |
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| 3. |
- Buffam, Ishi, et al.
(författare)
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Spatial heterogeneity of the spring flood acid pulse in a boreal stream network.
- 2008
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 407:1, s. 708-22
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Tidskriftsartikel (refereegranskat)abstract
- Spatial and temporal patterns in streamwater acidity are ecologically important, but difficult to measure in parallel. Here we present the spatial distribution of streamwater chemistry relevant to acidity from 60 stream sites distributed throughout a 67 km(2) boreal catchment, sampled during a period of winter baseflow (high pH) and during a spring flood episode (low pH). Sites were grouped based on pH level and pH change from winter baseflow to spring flood. The site attributes of each pH group were then assessed in terms of both stream chemistry and subcatchment landscape characteristics. Winter baseflow pH was high throughout most of the stream network (median pH 6.4), but during the spring flood episode stream sites experienced declines in pH ranging from 0-1.6 pH units, resulting in pH ranging from 4.3-6.3. Spring flood pH was highest in larger, lower altitude catchments underlain by fine sorted sediments, and lowest in small, higher altitude catchments with a mixture of peat wetlands and forested till. Wetland-dominated headwater catchments had low but stable pH, while the spring flood pH drop was largest in a group of catchments of intermediate size which contained well-developed coniferous forest and a moderate proportion of peat wetlands. There was a trend with distance downstream of higher pH, acid neutralizing capacity (ANC) and base cation concentrations together with lower dissolved organic carbon (DOC, strongly negatively correlated with pH). This apparent scale-dependence of stream chemistry could be explained by a number of environmental factors which vary predictably with altitude, catchment area and distance downstream-most notably, a shift in surficial sediment type from unsorted till and peat wetlands to fine sorted sediments at lower altitudes in this catchment. As a result of the combination of spatial heterogeneity in landscape characteristics and scale-related processes, boreal catchments like this one can be expected to experience high spatial variability both in terms of chemistry at any given point in time, and in the change experienced during high discharge episodes. Although chemistry patterns showed associations with landscape characteristics, considerable additional variability remained, suggesting that the modeling of dynamic stream chemistry from map parameters will continue to present a challenge. (C) 2008 Elsevier B.V. All rights reserved.
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| 4. |
- Carey, Sean K., et al.
(författare)
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Inter-comparison of hydro-climatic regimes across northern catchments : synchronicity, resistance and resilience
- 2010
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 24:24, s. 3591-3602
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Tidskriftsartikel (refereegranskat)abstract
- The higher mid-latitudes of the Northern Hemisphere are particularly sensitive to climate change as small differences in temperature determine frozen ground status, precipitation phase, and the magnitude and timing of snow accumulation and melt. An international inter-catchment comparison program, North-Watch, seeks to improve our understanding of the sensitivity of northern catchments to climate change by examining their hydrological and biogeochemical responses. The catchments are located in Sweden (Krycklan), Scotland (Mharcaidh, Girnock and Strontian), the United States (Sleepers River, Hubbard Brook and HJ Andrews) and Canada (Catamaran, Dorset and Wolf Creek). This briefing presents the initial stage of the North-Watch program, which focuses on how these catchments collect, store and release water and identify 'types' of hydro-climatic catchment response. At most sites, a 10-year data of daily precipitation, discharge and temperature were compiled and evaporation and storage were calculated. Inter-annual and seasonal patterns of hydrological processes were assessed via normalized fluxes and standard flow metrics. At the annual-scale, relations between temperature, precipitation and discharge were compared, highlighting the role of seasonality, wetness and snow/frozen ground. The seasonal pattern and synchronicity of fluxes at the monthly scale provided insight into system memory and the role of storage. We identified types of catchments that rapidly translate precipitation into runoff and others that more readily store water for delayed release. Synchronicity and variance of rainfall-runoff patterns were characterized by the coefficient of variation (cv) of monthly fluxes and correlation coefficients. Principal component analysis (PCA) revealed clustering among like catchments in terms of functioning, largely controlled by two components that (i) reflect temperature and precipitation gradients and the correlation of monthly precipitation and discharge and (ii) the seasonality of precipitation and storage. By advancing the ecological concepts of resistance and resilience for catchment functioning, results provided a conceptual framework for understanding susceptibility to hydrological change across northern catchments.
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| 5. |
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| 6. |
- Grabs, Thomas, 1980-, et al.
(författare)
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Modeling spatial patterns of saturated areas: A comparison of the topographic wetness index and a dynamic distributed model
- 2009
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 373:1-2, s. 15-23
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Tidskriftsartikel (refereegranskat)abstract
- Topography is often one of the major controls on the spatial pattern of saturated areas, which in turn is akey to understanding much of the variability in soils, hydrological processes, and stream water quality.The topographic wetness index (TWI) has become a widely used tool to describe wetness conditions atthe catchment scale. With this index, however, it is assumed that groundwater gradients always equalsurface gradients. To overcome this limitation, we suggest deriving wetness indices based on simulationsof distributed catchment models. We compared these new indices with the TWI and evaluated the differ-ent indices by their capacity to predict spatial patterns of saturated areas. Results showed that the model-derived wetness indices predicted the spatial distribution of wetlands significantly better than the TWI.These results encourage the use of a dynamic distributed hydrological model to derive wetness indexmaps for hydrological landscape analysis in catchments with topographically driven groundwater tables.
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| 7. |
- Grabs, Thomas, et al.
(författare)
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Modelling spatial patterns of saturated areas: a comparison of the topographic wetness index and a distributed model
- 2007
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Ingår i: Geophysical Research Abstracts. - : European Geoscience Union. ; , s. vol 9-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The spatial distribution of saturated areas within a catchment is a key factor to understanding and predicting hydrological response and stream water quality at the catchment scale. The topographic wetness index (TWI, ln(a/tan(beta))) is a widely used measure for assessing the spatial distribution of wetness conditions and only requires distributed elevation data as input. The predicted pattern is constant in time because the index is a static representation of the landscape. In this study we examined the predictions of saturated areas using this static topographic wetness index and compared the spatial predictions with temporally aggregated simulations of a distributed hydrological model. The model was calibrated against discharge measured at the outlet and at two internal points of a small forested catchment in northern Sweden. After calibration the model was applied to a larger 68 km2 catchment which included the subcatchment used for calibration. The dynamic groundwater level simulations of this model were temporally aggregated into dynamic indices. These indices were compared to the static topographic wetness index (TWI). We used the ability to spatially predict the occurrence of wetlands as a validation of the static and dynamic indices. First results indicate that the dynamic approach is superior to the static TWI.
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| 8. |
- Grabs, Thomas, et al.
(författare)
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Riparian zone hydrology and soil water total organic carbon (TOC) : implications for spatial variability and upscaling of lateral riparian TOC exports
- 2012
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 9:10, s. 3901-3916
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater flowing from hillslopes through riparian (near-stream) soils often undergoes chemical transformations that can substantially influence stream water chemistry. We used landscape analysis to predict total organic carbon (TOC) concentration profiles and groundwater levels measured in the riparian zone (RZ) of a 67 km2 catchment in Sweden. TOC exported laterally from 13 riparian soil profiles was then estimated based on the riparian flow-concentration integration model (RIM). Much of the observed spatial variability of riparian TOC concentrations in this system could be predicted from groundwater levels and the topographic wetness index (TWI). Organic riparian peat soils in forested areas emerged as hotspots exporting large amounts of TOC. These TOC fluxes were subject to considerable temporal variations caused by a combination of variable flow conditions and changing soil water TOC concentrations. Mineral riparian gley soils, on the other hand, were related to rather small TOC export rates and were characterized by relatively time-invariant TOC concentration profiles. Organic and mineral soils in RZs constitute a heterogeneous landscape mosaic that potentially controls much of the spatial variability of stream water TOC. We developed an empirical regression model based on the TWI to move beyond the plot scale and to predict spatially variable riparian TOC concentration profiles for RZs underlain by glacial till.
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| 9. |
- Grabs, Thomas, 1980-, et al.
(författare)
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Riparian zone processes and soil water total organic carbon (TOC) : Implications for spatial variability, upscaling and carbon exports
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Considerable amounts of groundwater inflows pass through riparian soils before discharging into stream networks. The interaction of groundwater inflows from adjacent hillslopes with riparian soils often changes the biogeochemical signature of the water. This mechanism often makes (near stream) riparian zones (RZs) key areas in the landscape that substantially influence stream water chemistry. Here we combine landscape analysis with total organic carbon (TOC) concentrations and groundwater levels measured at the riparian observatory in the boreal Krycklan catchment to investigate how terrain has shaped riparian processes and TOC characteristics. A considerable spatial variability of riparian TOC concentrations is presented in this system which can be related to variable groundwater levels and values of the topographic wetness index (TWI). Organic-rich riparian peat soils in forested areas emerged as hotspots exporting large amounts of TOC. These exports are subject to considerable temporal variations caused by variable flow conditions and changing TOC concentrations. Organic-poor riparian soils, on the other hand, exported only small and relatively time-invariant amounts of TOC. Organic-rich and organic-poor soils in RZs combine to a landscape mosaic that regulates much of spatial variability of stream water TOC. We finally present an empirical regression-model based on the TWI to predict spatially variable riparian TOC concentration profiles for areas in the Krycklan catchment that are underlain by glacial till.
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| 10. |
- Grabs, Thomas, 1980-
(författare)
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Water quality modeling based on landscape analysis: importance of riparian hydrology
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several studies in high-latitude catchments have demonstrated the importance of near-stream riparian zones as hydrogeochemical hotspots with a substantial influence on stream chemistry. An adequate representation of the spatial variability of riparian-zone processes and characteristics is the key for modeling spatio-temporal variations of stream-water quality. This thesis contributes to current knowledge by refining landscape-analysis techniques to describe riparian zones and by introducing a conceptual framework to quantify solute exports from riparian zones. The utility of the suggested concepts is evaluated based on an extensive set of hydrometric and chemical data comprising measurements of streamflow, groundwater levels, soil-water chemistry and stream chemistry. Standard routines to analyze digital elevation models that are offered by current geographical information systems have been of very limited use for deriving hydrologically meaningful terrain indices for riparian zones. A model-based approach for hydrological landscape analysis is outlined, which, by explicitly simulating groundwater levels, allows better predictions of saturated areas compared to standard routines. Moreover, a novel algorithm is presented for distinguishing between left and right stream sides, which is a fundamental prerequisite for characterizing riparian zones through landscape analysis. The new algorithm was used to derive terrain indices from a high-resolution LiDAR digital elevation model. By combining these terrain indices with detailed hydrogeochemical measurements from a riparian observatory, it was possible to upscale the measured attributes and to subsequently characterize the variation of total organic-carbon exports from riparian zones in a boreal catchment in Northern Sweden. Riparian zones were recognized as highly heterogeneous landscape elements. Organic-rich riparian zones were found to be hotspots influencing temporal trends in stream-water organic carbon while spatial variations of organic carbon in streams were attributed to the arrangement of organic-poor and organic-rich riparian zones along the streams. These insights were integrated into a parsimonious modeling approach. An analytical solution of the model equations is presented, which provides a physical basis for commonly used power-law streamflow-load relations.
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