scholarly journals Insights on the water mean transit time in a high-elevation tropical ecosystem

2016 ◽  
Author(s):  
G. M. Mosquera ◽  
C. Segura ◽  
K. B. Vaché ◽  
D. Windhorst ◽  
L. Breuer ◽  
...  
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
High Elevation ◽  
Lumped Parameter Model ◽  
Data Set ◽  
Shallow Subsurface ◽  
Discharge Rates ◽  
Lumped Parameter ◽  
High Storage Capacity ◽  
Stream Waters

Abstract. This study focuses on the investigation of the yet unknown mean transit time (MTT) of stream waters and its spatial variability in tropical alpine ecosystems (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in south Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs. We used a unique data set of δ18O and δ2H isotopic composition of rainfall and streamflow water samples collected for three years (May 2011-May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to determine controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15-0.73 yr, 53-264 days). Regression analysis revealed negative correlation between the catchment’s average slope and MTT (R2 = 0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables whereas MEC increases with MTT (R2 = 0.89 p < 0.001). Overall, we conclude that: 1) MTT of streams confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; 2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and 3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.

scholarly journals Insights into the water mean transit time in a high-elevation tropical ecosystem

2016 ◽  
Vol 20 (7) ◽  
pp. 2987-3004 ◽  
Author(s):  
Giovanny M. Mosquera ◽  
Catalina Segura ◽  
Kellie B. Vaché ◽  
David Windhorst ◽  
Lutz Breuer ◽  
...  
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
High Elevation ◽  
Lumped Parameter Model ◽  
Data Set ◽  
Shallow Subsurface ◽  
Discharge Rates ◽  
Lumped Parameter ◽  
High Storage Capacity ◽  
Specific Discharge

Abstract. This study focuses on the investigation of the mean transit time (MTT) of water and its spatial variability in a tropical high-elevation ecosystem (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in southern Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs under steady-state conditions (i.e., baseflow MTT). We used a unique data set of the δ18O isotopic composition of rainfall and streamflow water samples collected for 3 years (May 2011 to May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to explore controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15–0.73 years, 53–264 days). Regression analysis revealed a negative correlation between the catchment's average slope and MTT (R2 =  0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables, whereas MEC increases with MTT (R2 =  0.89, p < 0.001). Overall, we conclude that (1) baseflow MTT confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; (2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and (3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.

scholarly journals An Evaluation of Catchment Transit Time Model Parameters: A Comparative Study between Two Stable Isotopes of Water

Geosciences ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 318
Author(s):  
Samuel Bansah ◽  
Samuel Ato Andam-Akorful ◽  
Jonathan Quaye-Ballard ◽  
Matthew Coffie Wilson ◽  
Solomon Senyo Gidigasu ◽  
...  
Keyword(s):  
Time Series ◽  
Transit Time ◽  
Mean Transit Time ◽  
Model Parameters ◽  
Flow Process ◽  
Time Model ◽  
Shallow Subsurface ◽  
Behavioral Parameter ◽  
Stable Isotopes Of Water ◽  
Generalized Likelihood Uncertainty Estimation

Using δ18O and δ2H in mean transit time (MTT) modeling can ensure the verifiability of results across catchments. The main objectives of this study were to (i) evaluate the δ18O- and δ2H-based behavioral transit time distributions and (ii) assess if δ18O and δ2H-based MTTs can lead to similar conclusions about catchment hydrologic functioning. A volume weighted δ18O (or δ2H) time series of sampled precipitation was used as an input variable in a 50,000 Monte Carlo (MC) time-based convolution modeling process. An observed streamflow δ18O (or δ2H) time series was used to calibrate the model to obtain the simulated time series of δ18O (or δ2H) of the streamflow within a nested system of eight Prairie catchments in Canada. The model efficiency was assessed via a generalized likelihood uncertainty estimation by setting a minimum Nash–Sutcliffe Efficiency threshold of 0.3 for behavioral parameter sets. Results show that the percentage of behavioral parameter sets across both tracers were lower than 50 at the majority of the studied outlets; a phenomenon hypothesized to have resulted from the number of MC runs. Tracer-based verifiability of results could be achieved within five of the eight studied outlets during the model process. The flow process in those five outlets were mainly of a shallow subsurface flow as opposed to the other three outlets, which experienced other additional flow dynamics. The potential impacts of this study on the integrated use of δ18O and δ2H in catchment water storage and release dynamics must be further investigated in multiple catchments within various hydro-physiographic settings across the world.

scholarly journals Nonparametric lower bounds to mean transit times

2017 ◽  
Author(s):  
Earl Bardsley
Keyword(s):  
Lower Bound ◽  
Transit Time ◽  
Time Distribution ◽  
Mean Transit Time ◽  
Mean Value ◽  
System A ◽  
Lumped Parameter ◽  
Transit Times ◽  
Lumped Parameter Models ◽  
Transit Time Distribution

Abstract. Mean transit time μT, also called mean residence time, has been used widely in hydrological studies as an indicator of catchment water storage characteristics. Typically μT is estimated by the nature of catchment transformation of a natural input tracer time series. For example, increased damping and delaying of 18O seasonal isotopic variation may be taken to indicate longer mean transit times. Part of a μT estimation process involves specification of a lumped parameter flow model which provides the basis for a parametric transit time distribution. However, μT estimation has been called into question because catchment flow systems have a degree of complexity which may not justify use of simple parametric distributions. Moving toward a related index, the question is raised here as to the extent to which an arbitrary transit time distribution might enable a model mean transit time to be minimized before the fit to catchment output tracer data becomes unacceptably poor. This minimized mean value μ* represents a lower bound to μT, whatever the true transit time distribution might be. The lower bound is not necessarily an approximation to μT but might serve as an index for catchment comparisons or detect when μT is large. For a linear catchment system a simple nonparametric linear programming (LP) approach can be utilised to obtain μ*, which is conditional on a user-specified acceptable level of data fit. The LP method presented is applicable to both steady state and time-varying catchment systems and has the advantage of not requiring specification of lumped parameter models or use of explicit transit time distributions.

scholarly journals ‘Teflon Basin’ or Not? A High-Elevation Catchment Transit Time Modeling Approach

Hydrology ◽  
2019 ◽  
Vol 6 (4) ◽  
pp. 92 ◽  
Author(s):  
Jan Schmieder ◽  
Stefan Seeger ◽  
Markus Weiler ◽  
Ulrich Strasser
Keyword(s):  
Transit Time ◽  
Amplitude Ratio ◽  
Mean Transit Time ◽  
High Elevation ◽  
Subsurface Water ◽  
Balance Model ◽  
Water Volume ◽  
Time Model ◽  
Water Fraction ◽  
Ice Melt

We determined the streamflow transit time and the subsurface water storage volume in the glacierized high-elevation catchment of the Rofenache (Oetztal Alps, Austria) with the lumped parameter transit time model TRANSEP. Therefore we enhanced the surface energy-balance model ESCIMO to simulate the ice melt, snowmelt and rain input to the catchment and associated δ18O values for 100 m elevation bands. We then optimized TRANSEP with streamflow volume and δ18O for a four-year period with input data from the modified version of ESCIMO at a daily resolution. The median of the 100 best TRANSEP runs revealed a catchment mean transit time of 9.5 years and a mobile storage of 13,846 mm. The interquartile ranges of the best 100 runs were large for both, the mean transit time (8.2–10.5 years) and the mobile storage (11,975–15,382 mm). The young water fraction estimated with the sinusoidal amplitude ratio of input and output δ18O values and delayed input of snow and ice melt was 47%. Our results indicate that streamflow is dominated by the release of water younger than 56 days. However, tracers also revealed a large water volume in the subsurface with a long transit time resulting to a strongly delayed exchange with streamflow and hence also to a certain portion of relatively old water: The median of the best 100 TRANSEP runs for streamflow fraction older than five years is 28%.

Cerebral vascular mean transit time determined by PET and DSC-MRI

2005 ◽  
Vol 25 (1_suppl) ◽  
pp. S676-S676
Author(s):  
Masanobu Ibaraki ◽  
Hiroshi Ito ◽  
Eku Shimosegawa ◽  
Hideto Toyoshima ◽  
Keiichi Ishigame ◽  
...  
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
Dsc Mri ◽  
Cerebral Vascular
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