scholarly journals Reevaluation of transit time distributions, mean transit times and their relation to catchment topography

2014 ◽  
Vol 18 (12) ◽  
pp. 4751-4771 ◽  
Author(s):  
S. Seeger ◽  
M. Weiler
Keyword(s):  
Transfer Function ◽  
Transit Time ◽  
Gamma Distribution ◽  
Water Isotopes ◽  
Transfer Model ◽  
Stable Water Isotopes ◽  
Point Energy ◽  
Transit Times ◽  
Wide Range ◽  
The Mean

Abstract. The transit time of water is a fundamental property of catchments, revealing information about the flow pathways, source of water and storage in a single integrated measure. While several studies have investigated the relationship between catchment topography and transit times, few studies expanded the analysis to a wide range of catchment properties and assessed the influence of the selected transfer function (TF) model. We used stable water isotopes from mostly baseflow samples with lumped convolution models of time-invariant TFs to estimate the transit time distributions of 24 meso-scale catchments covering different geomorphic and geologic regions in Switzerland. The sparse network of 13 precipitation isotope sampling sites required the development of a new spatial interpolation method for the monthly isotopic composition of precipitation. A point-energy-balance based snow model was adapted to account for the seasonal water isotope storage in snow dominated catchments. Transit time distributions were estimated with three established TFs (exponential, gamma distribution and two parallel linear reservoirs). While the exponential TF proved to be less suitable to simulate the isotopic signal in most of the catchments, the gamma distribution and the two parallel linear reservoirs transfer function reached similarly good model fits to the fortnightly observed isotopic compositions in discharge, although in many catchments the transit time distributions implied by equally well fitted models differed markedly from each other and in extreme cases, the resulting mean transit time (MTT) differed by orders of magnitude. A more thorough comparison showed that equally suited models corresponded to agreeing values of cumulated transit time distributions only between 3 and 6 months. The short-term (< 30 days) component of the transit time distributions did not play a role because of the limited temporal resolution of the available input data. The long-term component (> 3 years) could hardly be assessed by means of stable water isotopes, resulting in ambiguous MTT and hence questioning the relevance of an MTT determined with stable isotopes. Finally we investigated the relation between MTT estimates based on the three different TF types as well as other transit time properties and a range of topographical catchment characteristics. Depending on the selected transfer model, we found a weak correlation between transit time properties and the ratio between flow path length over the flow gradient, drainage density and the mean discharge. The catchment storage derived from MTTs and mean discharge did not show a clear relation to any catchment properties, indicating that in many studies the mean annual discharge may bias the MTT estimates.

scholarly journals Bayesian estimates of the mean recharge elevations of water sources in the Central America region using stable water isotopes

2020 ◽  
Vol 32 ◽  
pp. 100739
Author(s):  
L. Nicole Arellano ◽  
Stephen P. Good ◽  
Ricardo Sánchez-Murillo ◽  
W. Todd Jarvis ◽  
David C. Noone ◽  
...  
Keyword(s):  
Central America ◽  
Water Sources ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Bayesian Estimates ◽  
The Mean

scholarly journals New water fractions and transit time distributions at Plynlimon, Wales, estimated from stable water isotopes in precipitation and streamflow

2019 ◽  
Author(s):  
Julia L. A. Knapp ◽  
Colin Neal ◽  
Alessandro Schlumpf ◽  
Margaret Neal ◽  
James W. Kirchner
Keyword(s):  
Time Series ◽  
Stable Isotope ◽  
Transit Time ◽  
Transport Processes ◽  
Water Isotopes ◽  
Data Sets ◽  
Hydrograph Separation ◽  
Stable Water Isotopes ◽  
Isotope Data ◽  
Water Fractions

Abstract. Long-term, high-frequency time series of passive tracers in precipitation and streamflow are essential for quantifying catchment transport and storage processes, but few such data sets are publicly available. Here we describe, present, and make available to the public two extensive data sets of stable water isotopes in streamflow and precipitation at the Plynlimon experimental catchments in mid-Wales. Stable isotope data are available at 7-hourly intervals for 17 months, and at weekly intervals for 4.25 years. Precipitation isotope values were highly variable in both data sets, and the high temporal resolution of the 7-hourly streamwater samples revealed rich isotopic dynamics that were not captured by the weekly sampling. We used ensemble hydrograph separation to calculate new water fractions and transit time distributions from both data sets. Transit time distributions estimated by ensemble hydrograph separation were broadly consistent with those estimated by spectral fitting methods, suggesting that they can reliably quantify the contributions of recent precipitation to streamflow. We found that on average, roughly 3 % of streamwater was made up of precipitation that fell within the previous 7 hours, and 13–15 % of streamwater was made up of precipitation that fell within the previous week. The contributions of recent precipitation to streamflow were highest during large events, as illustrated by comparing new water fractions for different discharges and precipitation rates. This dependence of new water fractions on water fluxes was also reflected in their seasonal variations, with lower new water fractions and more damped catchment transit time distributions in spring and summer compared to fall and winter. We also compared new water fractions obtained from stable water isotopes against those obtained from concentrations of chloride, a solute frequently used as a passive tracer of catchment transport processes. After filtering the chloride data for dry deposition effects, we found broadly similar new water fractions using chloride and stable water isotopes, indicating that these different tracers may yield similar inferences about catchment storage and transport, if potentially confounding factors are eliminated. These stable isotope time series comprise some of the longest and most detailed publicly available catchment isotope data sets. They complement extensive solute data sets that are already publicly available for Plynlimon, enabling a wide range of future analyses of catchment behavior.

How geomorphology shapes groundwater transit times at the hillslope scale?

2021 ◽  
Author(s):  
Jean-Raynald De Dreuzy ◽  
Alexandre Gauvain ◽  
Sarah Leray ◽  
Jean Marçais ◽  
Clément Roques ◽  
...  
Keyword(s):  
Transit Time ◽  
Coefficient Of Variation ◽  
Average Distance ◽  
Environmental Tracers ◽  
Analytical Approximations ◽  
Overland Flows ◽  
Transit Times ◽  
The Mean ◽  
Constant Slope ◽  
Saturation Excess

&lt;p&gt;We investigate how geomorphological structures shape Transit Time Distributions (TTDs) in shallow aquifers. We show that the TTD is determined by integrated features of the groundwater structure and of the repartition of seepage in convergent/divergent hillslopes of constant slope. More specifically, the coefficient of variation of the TTD (standard deviation divided by the mean) scales linearly with the mean distance of the groundwater volume to the river. The extent and structure of seepage modify the groundwater contribution to the transit time distribution and increase its variability.&lt;/p&gt;&lt;p&gt;Extensive 3D simulations were performed to determine the TTDs synthetic convergent, straight and divergent hillslope models of constant slope. The recharge was applied uniformly on top of the aquifer and transferred to the receiving stream through steady-state groundwater flows, return flows and saturation excess overland flows. Without seepage, TTDs evolve from uniform- to power law-like- distributions depending on the average distance of the groundwater volume to the river. Remarkably, the coefficient of variation of the TTDs scales linearly with the groundwater volume to the river at any hillslope convergent/divergent rate in agreement with a theoretical prediction based on three analytical approximations. With seepage, the TTD progressively displays three separate modes corresponding (1) to the rapid saturation excess overland flows, (2) to the intermediary circulations ending up in seepage area and (3) to the slower circulations going from a recharge upstream the seepage zone to a discharge in the river. The coefficient of variation additionally depends on the extent of the seepage area.&lt;/p&gt;&lt;p&gt;Applied to a natural hillslope in the crystalline basement of Normandy (France), the same synthetic analysis demonstrates that the coefficient of variation is not only determined by the extent of the seepage zone but also by its structure in relation to the geomorphological local and global organizations. These results suggest the possibility to assess the variability of transit times by combining geomorphological analysis, surface soil saturation observations and environmental tracers.&lt;/p&gt;

scholarly journals An introduction to stable water isotopes in climate models: benefits of forward proxy modelling for paleoclimatology

2010 ◽  
Vol 6 (1) ◽  
pp. 115-129 ◽  
Author(s):  
C. Sturm ◽  
Q. Zhang ◽  
D. Noone
Keyword(s):  
Atmospheric Circulation ◽  
Climate Models ◽  
Regional Climate ◽  
Isotopic Fractionation ◽  
Water Isotopes ◽  
Mean Annual Temperature ◽  
Stable Water Isotopes ◽  
Wide Range ◽  
Precipitation Seasonality ◽  
Isotopic Signal

Abstract. Stable water isotopes have been measured in a wide range of climate archives, with the purpose of reconstructing regional climate variations. Yet the common assumption that the isotopic signal is a direct indicator of temperature proves to be misleading under certain circumstances, since its relationship with temperature also depends on e.g. atmospheric circulation and precipitation seasonality. Here we introduce the principles, benefits and caveats of using climate models with embedded water isotopes as a support for the interpretation of isotopic climate archives. A short overview of the limitations of empirical calibrations of isotopic proxy records is presented. In some cases, the underlying hypotheses are not fulfilled and the calibration contradicts the physical interpretation of isotopic fractionation. The simulation of climate and its associated isotopic signal, despite difficulties related to downscaling and intrinsic atmospheric variability, can provide a "transfer function" between the isotopic signal and the considered climate variable. The relationship between modelled temperature and isotopic signal is analysed under present-day, pre-industrial and mid-Holocene conditions. The linear regression relationship is statistically more significant for precipitation-weighted annual temperature than mean annual temperature, yet the regression slope varies greatly between the time-slice experiments. Temperature reconstructions that do not account for the slope variations will in this case underestimate the low-frequency variability and overestimate high-frequency variability from the isotopic proxy record. The spatial variability of the simulated δ18O-temperature slope further indicates that the isotopic signal is primarily controlled by synoptic atmospheric circulation rather than local temperature.

scholarly journals Temperature and vapour-trajectory controls on the stable-isotope signal in Canadian Rocky Mountain snowpacks

2009 ◽  
Vol 55 (191) ◽  
pp. 485-498 ◽  
Author(s):  
K.E. Sinclair ◽  
S.J. Marshall
Keyword(s):  
Rocky Mountain ◽  
Water Isotopes ◽  
Canadian Rocky Mountains ◽  
Deuterium Excess ◽  
Stable Water Isotopes ◽  
Air Mass ◽  
Trajectory Classification ◽  
The Mean ◽  
Effects Of Temperature ◽  
Using Data

AbstractThe effects of temperature and seasonal air-mass trajectories on stable water isotopes in alpine snowpacks are investigated using meteorological and snow-pit data at two alpine field sites in the Canadian Rocky Mountains: Haig Glacier, Alberta, and Opabin Glacier, British Columbia. Snow pits were sampled through three accumulation seasons (October–June, 2004/05, 2005/06 and 2006/07) for δ18O, δD, temperature and density. The isotopic characteristics of precipitation over these time periods, including the local meteoric waterline and average δ18O, δD and deuterium excess, were defined using this dataset. Individual snowfall events over the three seasons were identified in the accumulation records from both sites and then fit to snow-pit stratigraphies to determine their mean isotopic characteristics. A trajectory classification was produced for all events, and the key meteorological characteristics of each trajectory class were investigated using data from alpine field sites and a suite of meteorological records from the region. An analysis of the relative influences of temperature and air-mass trajectory on snow isotope ratios reveals some separation in mean δ18O between storm classes. However, the separation appears to be driven primarily by the mean temperature of each class rather then being a direct effect of vapour pathway.

scholarly journals Dating of streamwater using tritium in a post-bomb world: continuous variation of mean transit time with streamflow

2010 ◽  
Vol 7 (4) ◽  
pp. 4731-4760 ◽  
Author(s):  
U. Morgenstern ◽  
M. K. Stewart ◽  
R. Stenger
Keyword(s):  
New Zealand ◽  
Transit Time ◽  
Time Series Data ◽  
Stream Water ◽  
Mean Transit Time ◽  
Low Flow ◽  
Series Data ◽  
Transit Times ◽  
Bomb Test ◽  
The Mean

Abstract. Tritium measurements of streamwater draining the Toenepi catchment, a small dairy farming area in Waikato, New Zealand, have shown that the mean transit time of the water varies with the flow of the stream. Mean transit times through the catchment are 2–5 years during high baseflow conditions (in winter), becoming older as streamflow decreases (in summer), and then quite dramatically older during drought conditions, with ages of more than 100 years. Older water seems to be gained in the lower reaches of the stream, compared to younger water in the headwater catchment. The groundwater store supplying baseflow was estimated from the mean transit time and average baseflow to be 15.4×106 m3 of water, about 1 m water equivalent over the catchment and 2.3 times total annual streamflow. Nitrate from recent intensified land use is relatively high at normal streamflow, but is low at times of low flow with old water. This reflects both lower nitrate loading in the catchment several decades ago, and active denitrification processes in older groundwater. Silica, leached from the aquifer material and accumulating in the water in proportion to contact time, is high at times of low streamflow. There was a good correlation between silica and streamwater age, which potentially allows silica concentrations to be used as a proxy for age when calibrated by tritium measurements. This study shows that tritium dating of stream water is possible with single tritium measurements now that bomb-test tritium has effectively disappeared from hydrological systems in New Zealand, without the need for time-series data.

scholarly journals Lumped convolution integral models revisited: on the meaningfulness of inter catchment comparisons

2014 ◽  
Vol 11 (6) ◽  
pp. 6753-6803 ◽  
Author(s):  
S. Seeger ◽  
M. Weiler
Keyword(s):  
Transfer Function ◽  
Transit Time ◽  
Transfer Functions ◽  
Interpolation Method ◽  
Mean Annual Precipitation ◽  
Minor Importance ◽  
Good Prediction ◽  
Transit Times ◽  
Physically Based ◽  
Snow Model

Abstract. The transit time distribution of a catchment is linked to the water storage potential and affects the susceptibility of a catchment to pollution. However, this characteristic of a catchment is still problematic to determine within a catchment and to predict among catchments based on physiographic or geological properties. In this study, lumped response and transit time convolution models coupled with a distributed physically based snow model were applied to simulate the stable water isotope compositions in stream discharge measured fortnightly in 24 meso-scale catchments in Switzerland. Three different types of transfer function (exponential, gamma distribution and two parallel linear reservoirs) in two different implementation variants (strictly mathematical and normalised) were optimised and compared. The derived mean transit times varied widely for one and the same catchment depending on the chosen transfer function, even when the model simulations led to very similar predictions of the tracer signal. Upon closer inspection of the transit time distributions, it appeared that two transfer functions mainly have to agree on an intermediate time scale around three months to reach similarly good prediction results in respect to fortnightly discharge samples, while their short-term and long-term behaviour seem to be of minor importance for the evaluation of the models. A couple of topographic indices showed significant correlations with the derived mean transit times. However, the collinearity of those indices, which were also correlated to mean annual precipitation sums, and the differing results among the different transfer functions, did not allow for the clear identification of one predictive topographical index. As a by-product of this study, a spatial interpolation method for monthly isotope concentrations in precipitation with modest input data requirement was developed and tested.

scholarly journals Dating of streamwater using tritium in a post nuclear bomb pulse world: continuous variation of mean transit time with streamflow

2010 ◽  
Vol 14 (11) ◽  
pp. 2289-2301 ◽  
Author(s):  
U. Morgenstern ◽  
M. K. Stewart ◽  
R. Stenger
Keyword(s):  
New Zealand ◽  
Transit Time ◽  
Time Series Data ◽  
Stream Water ◽  
Mean Transit Time ◽  
Dairy Farming ◽  
Low Flow ◽  
Series Data ◽  
Transit Times ◽  
The Mean

Abstract. Tritium measurements of streamwater draining the Toenepi catchment, a small dairy farming area in Waikato, New Zealand, have shown that the mean transit time of the water varies with the flow rate of the stream. Mean transit times through the catchment are 2–5 years during high baseflow conditions in winter, increasing to 30–40 years as baseflow decreases in summer, and then dramatically older water during drought conditions with mean transit time of more than 100 years. Older water is gained in the lower reaches of the stream, compared to younger water in the headwater catchment. The groundwater store supplying baseflow was estimated from the mean transit time and average baseflow to be 15.4 × 106 m3 of water, about 1 m water equivalent over the catchment and 2.3 times total annual streamflow. Nitrate is relatively high at higher flow rates in winter, but is low at times of low flow with old water. This reflects both lower nitrate loading in the catchment several decades ago as compared to current intensive dairy farming, and denitrification processes occurring in the older groundwater. Silica, leached from the aquifer material and accumulating in the water in proportion to contact time, is high at times of low streamflow with old water. There was a good correlation between silica concentration and streamwater age, which potentially allows silica concentrations to be used as a proxy for age when calibrated by tritium measurements. This study shows that tritium dating of stream water is possible with single tritium measurements now that bomb-test tritium has effectively disappeared from hydrological systems in New Zealand, without the need for time-series data.

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