Quantification of advective solute travel times and mass transport through hydrological catchments

Abstract

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.

The relationship between subsurface hydrology and dissolved carbon fluxes for a sub-arctic catchment

“…The advective travel times of dissolved carbon along subsurface transport pathways to the stream network reflect the purely physical rates of advection by the variable mean pore water velocity along and among these pathways (see the travel time-based modeling approaches of both conservative and reactive solute transport in Destouni and Graham, 1995;Eriksson and Destouni, 1997;Simic and Destouni, 1999;Malmström et al, 2004;Darracq et al, 2009;). We conceptualize the whole subsurface flow domain of active carbon release as a shallow and deeper flow domain.…”

“…The stream network was defined using a critical accumulated area threshold set at 5 km 2 . As the groundwater level and slope may be relatively unaffected by small-scale variations in surface elevation (Darracq et al, 2009), the hydraulic gradient was assumed to be equivalent to a hillslope average gradient derived from the DEM. Hillslopes were delineated using the stream network using the methodology described in Bogaart and Troch (2006).…”

“…942 S. W. Lyon et al: Relationship between subsurface hydrology and dissolved carbon fluxes The net effect of these opposing feedback mechanisms depends on the rates of respiration and weathering relative to the DOC and DIC mass transport rates along the different pathways of subsurface water flow. In order to predict the fates of solutes, the transport time of water and solutes along the diverse flow pathways through a catchment must be quantified (Destouni and Graham, 1995;Simic and Destouni, 1999;Kirchner et al, 2001;Malmström et al, 2004;Darracq et al, 2009;. Field-based identification of flow pathways and quantification of the travel time of water along such flow pathways, however, is difficult both in terms of collection of appropriate data and in terms of interpretation.…”

“…As hydrological mass transport remains poorly investigated at northern latitudes (Hannerz and Destouni, 2006;Bring and Destouni, 2009), an empirical identification of the main solute sources and transport pathways is difficult (Destouni et al, 2008a, b). One option is to estimate the distributions of solute travel times along different flow and transport pathways through catchments using physically-based modeling approaches (e.g., Darracq et al, 2009).…”

Saving the Baltic Sea, the Inland Waters of Its Drainage Basin, or Both? Spatial Perspectives on Reducing P-Loads in Eastern Sweden

“…A failure to fully meet these goals will occur for three main reasons: (i) Relatively radical measures are needed, such as extensive land use change (e.g., Wulff et al 2007), which are not feasible from a socio-economic perspective (Volk et al 2009). For example, in the most populated river basin district (RBD) of Sweden, the Northern Baltic Sea (NBS) RBD, the reduction demand of P from the RBD authority (RBDA) of 100 tons per year is larger than the estimated anthropogenic load contribution from agriculture within the RBD to the Baltic Sea (Larsson and Pettersson 2009). (ii) Retention processes and slow transport through the subsurface water systems (Darracq et al , 2010Destouni et al 2010;Persson et al 2011) can delay targeted effects of mitigation measures considerably. Furthermore, ecosystems need to respond to measures taken, which may considerably prolong the time it takes to reach WFD targets (Hering et al 2010).…”