| 1. |
- McDonnell, J.J., et al.
(författare)
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How old is streamwater? : Open questions in catchment transit time conceptualization, modelling and analysis
- 2010
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Ingår i: Hydrological Processes. - : John Wiley & Sons. - 0885-6087 .- 1099-1085. ; 24:12, s. 1745-1754
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Tidskriftsartikel (refereegranskat)abstract
- The time water spends travelling subsurface through a catchment to the stream network (i.e. the catchment water transit time) fundamentally describes the storage, flow pathway heterogeneity and sources of water in a catchment. The distribution of transit times reflects how catchments retain and release water and solutes that in turn set biogeochemical conditions and affect contamination release or persistence. Thus, quan- tifying the transit time distribution provides an important constraint on biogeochemical processes and catchment sensitivity to anthropogenic inputs, contamination and land-use change. Although the assumptions and limitations of past and present transit time modelling approaches have been recently reviewed (McGuire and McDonnell, 2006), there remain many fundamental research challenges for understanding how transit time can be used to quantify catchment flow processes and aid in the development and testing of rainfall–runoff models. In this Commen- tary study, we summarize what we think are the open research questions in transit time research. These thoughts come from a 3-day workshop in January 2009 at the International Atomic Energy Agency in Vienna. We attempt to lay out a roadmap for this work for the hydrological commu- nity over the next 10 years. We do this by first defining what we mean (qualitatively and quantitatively) by transit time and then organize our vision around needs in transit time theory, needs in field studies of tran- sit time and needs in rainfall – runoff modelling. Our goal in presenting this material is to encourage widespread use of transit time information in process studies to provide new insights to catchment function and to inform the structural development and testing of hydrologic models.
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| 2. |
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| 3. |
- Brooks, P, et al.
(författare)
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A predictive framework for coupling Hydrology, Biogeochemistry, and Ecology
- 2008
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Ingår i: Vol. 10, EGU2008-A-09502, 2008.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The coupling of hydrological, biogeochemical, and ecological processes at catchment to landscape scale results in observable patterns in ecosystem structure, the amount and chemistry of stream discharge, and landsurface-atmosphere exchanges of energy and biogeochemicals. All of these patterns result from the close coupling of water, energy, carbon, and nutrient cycling, yet rarely are both the vertical (landsurfaceatmosphere) and lateral (hydrological residence time and streamflow) exchanges associated with a particular ecosystem structure studied in concert. Our research attempts to bridge this gap by focusing on how ecosystem structure, specifically vegetation, mediates four-dimensional (X,Y,Z, and time) fluxes of water, carbon, and nutrients in semi-arid environments of the southwestern United States. Our generalized approach involves an iterative combination of measurement, modeling, and experimentation where process-level inferences drawn from one research activity are used to develop testable hypothesis for related efforts. Preliminary results have linked spatial variability in hydrologic residence time to seasonal variability in nutrient limitation; spatial and interannual variability in water source with carbon uptake and isotopic signature; vegetation controls on both snow water input and soil moisture; and the importance of alluvial aquifers in stream and river biogeochemistry.
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| 4. |
- Broxton, P, et al.
(författare)
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On the role of aspect to quantify water transit times in small mountainous catchments
- 2009
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 45, s. W08427-W08427
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Tidskriftsartikel (refereegranskat)abstract
- In the current empirical study, we provide evidence about how the hydrologic responses of small mountain catchments are related to aspect (slope direction; exposure) at Redondo Peak, located in the Valles Caldera, New Mexico, USA. Specifically, we test the hypothesis that the transit time of water is related to the catchment aspect. Aspect is an easily measurable and transferable topographic characteristic that is related to the amount of direct solar radiation a particular catchment receives, and therefore, different catchments with different aspects have different rates of snow ablation, evapotranspiration, and water cycling in general. Transit times, which describe the time between when water enters the catchment as precipitation and when it leaves as stream flow, captures many hydrologic features such as flowpath variability and the combined effects of water storage and water fluxes. We have designed an experiment that involves field data collection, isotopic analysis of stream and precipitation samples, and the estimation of transit times using lumped-parameter convolution for 15 sites in small (1-15 km2) catchments that drain different aspects of Redondo Peak. Our data suggests that isotopic variability and estimated transit times are both related to aspect. Other potential relationships between topographical features (such as flowpath length, slope gradient, and elevation) and isotopic measurements of streamwater suggest that landscape and hydrological features are interconnected at Redondo Peak, but these links are not conclusive, suggesting that these topographic indicators do not fully explain the variability of water cycling in these small mountain catchments.
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| 5. |
- Lyon, Steve, et al.
(författare)
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Combining radar and rain gauges to capture the space-time variability of monsoon rainfall during an extreme flood event
- 2008
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Ingår i: EGU General Assembly.
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Konferensbidrag (refereegranskat)abstract
- Monsoon rainfall events are typified by high spatial and temporal variability in both rainfall amount and intensity. Monsoon rainfall events occurring in Tucson, AZ, USA over seven consecutive days in July, 2006 lead to the highest ever recorded stream flows in Sabino Canyon Creek and resulted in flash flooding that caused large-scale property damage. Concurrent to these monsoon events, a network of 40 tipping bucket rain gauges were in place throughout the Sabino Canyon Creek watershed. In addition to this rain gauge network, radar data (NEXRAD) was collected during this monsoon period and used to derive rainfall accumulation maps with at 15-minute temporal resolution and 1 km2 spatial resolution. An event based, kinematic-wave overland flow runoff model (KINEROS) was used to model stream flow in Sabino Canyon Creek for the largest of the flooding events using rainfall data from both rain gauge observations and radar estimation. While the modeling results based solely on rain gauge observations agreed well with observed flow, the results were highly reliant on the extent of the spatial coverage of the rain gauge network. To overcome the reliance, geostatistics (kriging with external drift) were used to combine the rain gauge data with the radar data. By combining these two datasets, we could compensate for restricted spatial coverage in the rain gauge network. This allowed for high quality modeling of the flood event even with a great reduction in the spatial extent of the observational rain gauge network. Techniques to combine data from rain gauge networks and radar estimates are quite valuable as the development of real-time rain gauge network with good spatial extent and high spatial density is difficult and costly.
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| 6. |
- Harpold, A, et al.
(författare)
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Effects of preferential hydrological pathways in a galciated watershed in the Northeastern USA
- 2010
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 9:2, s. 397-414
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Tidskriftsartikel (refereegranskat)abstract
- Despite observational evidence of lateral preferential flow paths in northeastern U.S. watersheds, their effects on the sources of runoff remain unclear. An intense field survey was undertaken during the 2007 growing season to determine the sources of stream runoff from a 2.51 km2 watershed in the Catskill Mountains, New York State. Lateral preferential flow paths are caused by groundwater springs and soil piping in this region. A two-component hydrograph separation using δ18O showed that event water (rain water) was a significant source of runoff during nine rainfall events (from July to October). With these rainfall events, 14 to 37% of the volume and 18 to 49% of the peak streamflow was attributable to event water. Further, end-member mixing analysis (EMMA), using δ18O, Si, and dissolved organic carbon (DOC), showed that saturated areas accounted for 2 to 24% of the total volume and 4 to 59% of peak streamflow but that groundwater was the dominant source of runoff volume during all events. Field surveys of saturated areas also suggested that near-stream areas were insufficient to generate the observed stream chemistry during rainfall events larger than 8 mm. A connection with the hillside saturated areas was therefore required to explain the results of the hydrograph separations, which were corroborated by the timing of the transient (perched) groundwater and overland flow. The hydrometric measurements confirmed that hillside lateral preferential flow paths rapidly transported water to near-stream saturation areas during runoff events under relatively dry antecedent conditions. A qualitative comparison with conventional techniques for distributing variable saturation areas (VSA) using surface topography and soil transmissivity (i.e., topographic index and soil topographic index), which do not consider the effects of lateral preferential flow paths, demonstrated that typical parameterizations (on the order of <10−1 m) would not have the spatial resolution to represent the measured lateral preferential flow paths (on the order of <10−3 m). Overall, the results suggest that the lateral redistribution of water from hillside areas reduces the influence of surface topography and channel topology on the sources of stream runoff, a finding that is consistent with recent ones from other landscapes where glacial soils have coevolved with the terrestrial hydrology.
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| 7. |
- Lyon, Steve, 1978-, et al.
(författare)
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A tale of two isotopes: differences in hydrograph separation fora runoff event when using δD versus δ18O
- 2009
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Ingår i: Hydrological Processes. - : Wiley InterScience. - 0885-6087 .- 1099-1085. ; 23:14, s. 2095-2101
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Tidskriftsartikel (refereegranskat)abstract
- It is often assumed that stable water isotopes (dD and d18O) provide redundant information for a given sample of water. In this note we illustrate that the choice of isotope used may influence the resultant hydrograph separation. This is especially true in light of the spatial and temporal variability in the isotopic composition of rainfall water at the catchment scale. We present several possible hydrograph separations based on both dD and d18O observed in rainfall for a single runoff event occurring in the southwest USA. This study demonstrates the potential of using both stable water isotopes by showing that dD and d18O may provide unique information for catchment hydrologists. We also report on the utility of new technology capable of simultaneous measurements of both dD and d18O using off-axis integrated cavity output spectroscopy (OA-ICOS) methods. This may be of interest to catchment hydrologists seeking to incorporate this type of equipment into their laboratory.
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| 8. |
- Lyon, Steve, et al.
(författare)
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Development and application of a catchment similarity index for subsurface flow
- 2010
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 46:3
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we develop a similarity parameter to describe shallow subsurface hydrological response of small catchments on the basis of the hillslope-Péclet number. This new similarity parameter, named the catchment-Péclet (caPe) number, provides a theoretical framework to compare the relative hydrologic response derived from shallow subsurface flow of small catchments on the basis of geomorphic properties. Using 400,000 synthetically derived catchments to model catchment-scale characteristic response functions (CRFs), we see good agreement between the synthetic and theoretical relationships relating the caPe number to the first two dimensionless moments of the CRF of small catchments. Working with real-world data, however, requires the estimation of hydrologic parameters and delineation of hillslopes to apply the caPe number. Allowing for uncertainty in the estimation of hydrologic parameters and in the definition of the extent of the channel network, the caPe number is able to recreate the observed moments of an approximate catchment-scale CRF for four small catchments ranging in size from 0.025 to 880 ha in two distinct climatic and geologic settings. By using physics to underpin the link between landscape and hydrological response, the caPe number creates a functional relationship between hydraulic theory and a catchment's pedogeomorphological structure. While this study is limited to small headwater catchments, it lays the groundwork for a catchment-scale similarity parameter that could be expanded to larger scales where channel network structure and storage become more important.
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| 9. |
- Lyon, S.W., et al.
(författare)
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Estimation of permafrost thawing rates in a sub-arctic catchment using recession flow analysis
- 2009
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 13, s. 595-604
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Tidskriftsartikel (refereegranskat)abstract
- Permafrost thawing is likely to change the flow pathways taken by water as it moves through arctic and sub-arctic landscapes. The location and distribution of these pathways directly influence the carbon and other biogeochemical cycling in northern latitude catchments. While permafrost thawing due to climate change has been observed in the arctic and sub-arctic, direct observations of permafrost depth are difficult to perform at scales larger than a local scale. Using recession flow analysis, it may be possible to detect and estimate the rate of permafrost thawing based on a long-term streamflow record. We demonstrate the application of this approach to the sub-arctic Abiskojokken catchment in northern Sweden. Based on recession flow analysis, we estimate that permafrost in this catchment may be thawing at an average rate of about 0.9 cm/yr during the past 90 years. This estimated thawing rate is consistent with direct observations of permafrost thawing rates, ranging from 0.7 to 1.3 cm/yr over the past 30 years in the region.
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| 10. |
- Wang, Chaozi, et al.
(författare)
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Particle tracer transport in a sloping soil lysimeter under periodic, steady state conditions
- 2019
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 569, s. 61-76
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Tidskriftsartikel (refereegranskat)abstract
- Colloid transport through complex and dynamic (i.e. non-steady-state) hydrologic systems is rarely studied, owing to the difficulty of constraining initial and boundary conditions and quantifying colloid-porous media and colloid-colloid interactions in transient flow systems. Here we present a particle tracer experiment conducted on a sloped lysimeter receiving periodic rainfall events for 10 days. Four unique, DNA-labelled particle tracers were injected both in sequence and in parallel, together with a conservative tracer (deuterium), over the course of the first day and allowed to move through the system. Discharge-particle tracer concentration curves and the spatial distribution of particle tracer mass retained in the soil at the end of the experiment were found to be highly dependent on the timing of the tracer injection and the precipitation input and subsequent dynamic response of the water table. Overall, neglecting the total DLT recovery rate, the DLT particle tracer breakthrough trend (DNA-labelled particle tracer 4) was similar to deuterium and decreased over time with the exception of a few peaks later in the experiment. The individual particle tracer breakthrough curves suggest a complex system with different fast transport mechanisms (e.g. capillary barrier and size exclusion effect) and slow retention-release mechanisms (e.g. straining, physical-chemical adsorption), which resulted in particle tracers transferring faster than deuterium in the first 10 h of the experiment but being exceeded by deuterium soon after deuterium started to break through. The experiment not only highlights the interaction of repeated colloidal pollution events in hydrologic systems with different pre-event saturation conditions, but also the benefits of using multiple synchronous or sequential tracer applications to dissect explicit formulations of water flow and colloid transport processes in complex and dynamic hydrological systems. Such explicit process formulations could help improve understanding hydrologically-controlled transport through catchments and the quantitative prediction of these processes with water quality models.
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| 11. |
- Wang, Chaozi, et al.
(författare)
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Simulation of experimental synthetic DNA tracer transport through the vadose zone
- 2022
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 223
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Tidskriftsartikel (refereegranskat)abstract
- Although multiple experimental studies have proven the use of free synthetic DNA as tracers in hydrological systems, their quantitative fate and transport, especially through the vadose zone, is still not well understood. Here we simulate the water flow and breakthrough of deuterium (D) and one free synthetic DNA tracer from a 10-day experiment conducted in a transient variably saturated 1m3 10° sloped lysimeter using the HYDRUS-2D software package. Recovery and breakthrough flux of D (97.78%) and the DNA tracer (1.05%) were captured well with the advection-dispersion equation (R2 = 0.949, NSE = 0.937) and the Schijven and Šimůnek two-site kinetic sorption model recommended for virus transport modeling (R2 = 0.824, NSE = 0.823), respectively. The degradation of the DNA tracer was very slow (estimated to be 10% in 10 days), because the “loamy sand” porous media in our lysimeter was freshly crushed basaltic tephra (i.e., crushed rocks) and the microbes and DNase that could potentially degrade DNA in regular soils were rare in our “loamy sand”. The timing of the concentration peaks and the HYDRUS-2D simulated temporal and spatial distribution of DNA in the lysimeter both revealed the role of the solid-water-air contact lines in mobilizing and carrying DNA tracer under the experimental variably saturated transient flow condition. The free DNA was nearly non-selectively transported through the porous media, and showed a slightly early breakthrough, possibly due to a slight effect of anion exclusion or size exclusion. Our results indicate that free DNA have the potential to trace vadose zone water flow and solute/contaminant transport, and to serve as surrogates to trace viral pathogen pollution in soil-water systems. To our knowledge, this study is the first to simulate transport mechanisms of free synthetic DNA tracers through real soil textured porous media under variably saturated transient flow condition.
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