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Water quality modeling based on landscape analysis: importance of riparian hydrology
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2010. , 39 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 24
Keyword [en]
Water quality model, terrain analysis, geographical information system GIS, riparian zone, total organic carbon TOC, boreal catchments
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-42729ISBN: 978-91-7447-135-9 (print)OAI: oai:DiVA.org:su-42729DiVA: diva2:351398
Public defence
2010-10-18, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
Swedish Research Council (VR, grant no. 2005-4289)
Note
At the time of doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: In press; Paper 4: Manuscript.Available from: 2010-09-24 Created: 2010-09-13 Last updated: 2010-09-27Bibliographically approved
List of papers
1. Modelling spatial patterns of saturated areas: a comparison of the topographic wetness index and a distributed model
Open this publication in new window or tab >>Modelling spatial patterns of saturated areas: a comparison of the topographic wetness index and a distributed model
2007 (English)In: Geophysical Research Abstracts, European Geoscience Union , 2007, vol 9- p.Conference paper, Published paper (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
European Geoscience Union, 2007
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-21097 (URN)
Note
SRef-ID: 1607-7962/gra/EGU2007-A-00894Available from: 2007-12-05 Created: 2007-12-05 Last updated: 2010-09-15Bibliographically approved
2. Calculating terrain indices along streams - a new method for separating stream sides
Open this publication in new window or tab >>Calculating terrain indices along streams - a new method for separating stream sides
2010 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46Article in journal (Refereed) Published
Abstract [en]

There is increasing interest in assessing riparian zones and their hydrological and biogeochemical buffering capacity with indices derived from hydrologic landscape analysis of digital elevation data. Upslope contributing area is a common surrogate for lateral water flows and can be used to assess the variability of local water inflows to riparian zones and streams. However, current GIS algorithms do not provide a method for easily separating riparian zone and adjacent upland lateral contributions on each side of the stream. Here we propose a new algorithm to compute side-separated contributions along stream networks. We describe the new algorithm and illustrate the importance of distinguishing between lateral inflows on each side of streams with hillslope – riparian zone – stream hydrologic connectivity results from high frequency water table data collected in the 22km 2  Tenderfoot Creek catchment, Montana.

Place, publisher, year, edition, pages
American Geophysical Union, 2010
Keyword
riparian, hillslope, topography, stream network, terrain analysis, GIS
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-42727 (URN)10.1029/2010WR009296 (DOI)
Projects
Swedish Research Council (VR, grant no. 2005-4289)
Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2017-12-12Bibliographically approved
3. Linking soil- and stream-water chemistry based on a Riparian Flow-Concentration Integration Model
Open this publication in new window or tab >>Linking soil- and stream-water chemistry based on a Riparian Flow-Concentration Integration Model
Show others...
2009 (English)In: Hydrology and earth system sciences, ISSN 1607-7938, Vol. 13, no 12, 2287-2297 p.Article in journal (Refereed) Published
Abstract [en]

The riparian zone, the last few metres of soil through which water flows before entering a gaining stream, has been identified as a first order control on key aspects of stream water chemistry dynamics. We propose that the distribution of lateral flow of water across the vertical profile of soil water chemistry in the riparian zone provides a conceptual explanation of how this control functions in catchments where matrix flow predominates. This paper presents a mathematical implementation of this concept as well as the model assumptions. We also present an analytical solution, which provides a physical basis for the commonly used power-law flow-load equation. This approach quantifies the concept of riparian control on stream-water chemistry providing a basis for testing the concept of riparian control. By backward calculation of soil-water-chemistry profiles, and comparing those with observed profiles we demonstrate that the simple juxtaposition of the vertical profiles of water flux and soil water chemistry provides a plausible explanation for observed variations in stream water chemistry of several major stream components such as Total Organic Carbon (TOC), magnesium, calcium and chloride. The "static" implementation of the model structure presented here provides a basis for further development to account for seasonal influences and hydrological hysteresis in the representation of hyporheic, riparian, and hillslope processes.

Place, publisher, year, edition, pages
Copernicus Publications, 2009
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-32026 (URN)000273059900002 ()1027-5606 (ISBN)
Available from: 2009-12-07 Created: 2009-12-02 Last updated: 2010-09-15Bibliographically approved
4. Riparian zone processes and soil water total organic carbon (TOC): Implications for spatial variability, upscaling and carbon exports
Open this publication in new window or tab >>Riparian zone processes and soil water total organic carbon (TOC): Implications for spatial variability, upscaling and carbon exports
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keyword
total organic carbon, TOC, riparian zone, boreal headwater, topographic wetness index, upscaling
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-42728 (URN)
Projects
Swedish Research Council (VR, grant no. 2005-4289)
Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2010-09-17Bibliographically approved

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