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Quantifying pollutant spreading and the risk of water pollution in hydrological catchments: A solute travel time-based scenario approach
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The research presented in the thesis develops an approach for the estimation and mapping of pollutant spreading in catchments and the associated uncertainty and risk of pollution. The first step in the approach is the quantification and mapping of statistical and geographical distributions of advective solute travel times from pollutant input locations to downstream recipients. In the second step the travel time distributions are used to quantify and map the spreading of specific pollutants and the related risk of water pollution. In both steps, random variability of transport properties and processes is accounted for within a probabilistic framework, while different scenarios are used to account for statistically unquantifiable uncertainty about system characteristics, processes and future developments. This scenario approach enables a transparent analysis of uncertainty effects that is relatively easy to interpret. It also helps identify conservative assumptions and pollutant situations for which further investigations are most needed in order to reduce the uncertainty. The results for different investigated scenarios can further be used to assess the total risk to exceed given water quality standards downstream of pollutant sources.

Specific thesis results show that underestimation of pollutant transport variability, and in particular of those transport pathways with much shorter than average travel times, may lead to substantial underestimation of pollutant spreading in catchment areas. By contrast, variations in pollutant attenuation rate generally lead to lower estimated spreading than do constant attenuation conditions. A scenario of constant attenuation rate and high travel time variability, with a large fraction of relatively short travel times, therefore appears to be a reasonable conservative scenario to use when information is lacking for more precise determination of actual transport and attenuation conditions.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2011. , 35 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 28
Keyword [en]
water pollution, catchment, pollution risk, scenario analysis, uncertainty
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-63465ISBN: 978-91-7447-207-3 (print)OAI: oai:DiVA.org:su-63465DiVA: diva2:450172
Public defence
2011-11-21, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2011-10-30 Created: 2011-10-19 Last updated: 2011-11-15Bibliographically approved
List of papers
1. Waterborne spreading of pollutants through hydrological catchments: a general approach to its quantification
Open this publication in new window or tab >>Waterborne spreading of pollutants through hydrological catchments: a general approach to its quantification
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In order to protect water resources from contamination, it is necessary to assess the waterborne spreading of contaminants, both from all existing sources of pollution and from potential new sources (as a consequence of, for example, management changes and accidents or incidents that lead to discharge of pollutants). In this paper we adopt an approach that has previously been mostly used to quantify solute transport in soil and groundwater systems. Here, we develop the approach and apply it at the catchment scale for the estimation of waterborne contaminant spreading and the related risk for contamination of sensitive water environments within and downstream from a catchment area.

The proposed approach consists of two calculation steps: (1) calculation and mapping of travel times and travel time distributions for flowing water, and waterborne non-reactive substances that directly follow the movement of the water, from identified or potential sources of pollution to sensitive downstream waters, and (2) the previously estimated travel time distributions are used for calculation and mapping of the transport of specific reactive pollutants with the water, and of the related risks for contamination of sensitive water environments.

In the two calculation steps, random variability of transport properties and processes is represented statistically, while a scenario analysis is used to account for uncertainty about present or future conditions that cannot be quantified in statistical terms (e.g. uncertainties related to the characterisation of the sources of pollution, the water flow, and the transport of substances with the water). Through this approach one can relatively easily assess how large the uncertainties are, and identify those intervals of transport conditions and substance-specific mass attenuation properties for which the uncertainties are of great practical significance for water management in a catchment area, as well as the remaining intervals for which they are not of such significance. In cases where the uncertainties are found to be of minor importance from a management point of view, the scenario analysis provides a relatively robust basis on which to make decisions concerning, for example, urban planning, emergency preparedness and the appropriate measures to reduce the spreading of contaminants. Also, by clearly identifying the cases for which the uncertainties are of great practical significance, one obtains a rational basis on which to assess the value of further investigations in order to reduce the uncertainties.

National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-63420 (URN)
Available from: 2011-10-20 Created: 2011-10-18 Last updated: 2011-10-20Bibliographically approved
2. Quantification of advective solute travel times and mass transport through hydrological catchments
Open this publication in new window or tab >>Quantification of advective solute travel times and mass transport through hydrological catchments
Show others...
2010 (English)In: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 10, no 1-2, 103-120 p.Article in journal (Refereed) Published
Abstract [en]

This study has investigated and outlined the possible quantification and mapping of the distributions of advective solute travel times through hydrological catchments. These distributions are essential for understanding how local water flow and solute transport and attenuation processes affect the catchment-scale transport of solute, for instance with regard to biogeochemical cycling, contamination persistence and water quality. The spatial and statistical distributions of advective travel times have been quantified based on reported hydrological flow and mass-transport modeling results for two coastal Swedish catchments. The results show that the combined travel time distributions for the groundwater-stream network continuum in these catchments depend largely on the groundwater system and model representation, in particular regarding the spatial variability of groundwater hydraulic parameters (conductivity, porosity and gradient), and the possible contributions of slower/deeper groundwater flow components. Model assumptions about the spatial variability of groundwater hydraulic properties can thus greatly affect model results of catchment-scale solute spreading. The importance of advective travel time variability for the total mass delivery of naturally attenuated solute (tracer, nutrient, pollutant) from a catchment to its downstream water recipient depends on the product of catchment-average physical travel time and attenuation rate.

Keyword
Hydrology, Travel time, Solute transport, Natural attenuation, Catchment, Groundwater surface water interactions
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-31257 (URN)10.1007/s10652-009-9147-2 (DOI)000274197800007 ()
Available from: 2009-11-09 Created: 2009-11-09 Last updated: 2017-12-12Bibliographically approved
3. Propagation of water pollution uncertainty and risk from the subsurface to the surface water system of a catchment:
Open this publication in new window or tab >>Propagation of water pollution uncertainty and risk from the subsurface to the surface water system of a catchment:
2009 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 377, no 3-4, 434-444 p.Article in journal (Refereed) Published
Abstract [en]

This paper investigates the propagation of quantifiable probability and quantification uncertainty of water pollution from local pollutant sources at and below the land surface, through the groundwater system, to downstream surface water recipients. Methodologically, the study shows how the risk and uncertainty of surface water pollution within a catchment may be assessed by a combined methodology of a Lagrangian stochastic advective-reactive modelling approach, which accounts for the quantifiable pollutant transport randomness, and a scenario analysis approach, which accounts for different quantification uncertainties. The results show that, in general, unambiguous risk assessment requires at least a reliable order-of-magnitude quantification of the prevailing relation between the average rate of physical pollutant transport from source to recipient and the average rate of pollutant attenuation. If this average relation can be reliably estimated to fall within two identified, relatively wide open value ranges, the assessment of pollution risk to surface waters from localised sources at or below the soil surface may be unambiguous even under otherwise large quantification uncertainty. For a relatively narrow, closed value range of this average rate relation, however, risk assessment must either rely on conservative assumptions, or else be based on a more detailed and resource demanding quantification of pollutant transport.

Keyword
water pollution, risk assessment, contaminant transport, stochastic modelling
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-31156 (URN)10.1016/j.jhydrol.2009.09.001 (DOI)
Available from: 2009-12-07 Created: 2009-11-06 Last updated: 2017-12-12Bibliographically approved
4. Diffuse hydrological mass transport through catchments: scenario analysis of coupled physical and biogeochemical uncertainty effects
Open this publication in new window or tab >>Diffuse hydrological mass transport through catchments: scenario analysis of coupled physical and biogeochemical uncertainty effects
2011 (English)In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 15, no 10, 3195-3206 p.Article in journal (Refereed) Published
Abstract [en]

This paper quantifies and maps the effects of coupled physical and biogeochemical variability on diffuse hydrological mass transport through and from catchments. It further develops a scenario analysis approach and investigates its applicability for handling uncertainties about both physical and biogeochemical variability and their different possible cross-correlation. The approach enables identification of conservative assumptions, uncertainty ranges, as well as pollutant/nutrient release locations and situations for which further investigations are most needed in order to reduce the most important uncertainty effects. The present scenario results provide different statistical and geographic distributions of advective travel times for diffuse hydrological mass transport. The geographic mapping can be used to identify potential hotspot areas with large mass loading to downstream surface and coastal waters, as well as their opposite, potential lowest-impact areas within the catchment. Results for alternative travel time distributions show that neglect or underestimation of the physical advection variability, and in particular of those transport pathways with much shorter than average advective solute travel times, can lead to substantial underestimation of pollutant and nutrient loads to downstream surface and coastal waters. This is particularly true for relatively high catchment-characteristic product of average attenuation rate and average advective travel time, for which mass delivery would be near zero under assumed transport homogeneity but can be orders of magnitude higher for variable transport conditions. A scenario of high advection variability, with a significant fraction of relatively short travel times, combined with a relevant average biogeochemical mass attenuation rate, emerges consistently from the present results as a generally reasonable, conservative assumption for estimating maximum diffuse mass loading, when the prevailing physical and biogeochemical variability and cross-correlation are uncertain.

Keyword
mass transport, catchment, uncertainty
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-63419 (URN)10.5194/hess-15-3195-2011 (DOI)000296745600014 ()
Available from: 2011-10-18 Created: 2011-10-18 Last updated: 2017-12-08Bibliographically approved

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