Spatial Patterns of Water Age: Using Young Water Fractions to Improve the Characterization of Transit Times in Contrasting Catchments

Lutz, Stefanie; Krieg, R.; Müller, Christin; Zink, Matthias; Knöller, Kay; Samaniego, Luis; Merz, Ralf

doi:10.1029/2017wr022216

Cited by 78 publications

(140 citation statements)

References 68 publications

(146 reference statements)

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“…4b), raising the question of whether a curve fit with R 2 adj = 0.6 is objectively better than a fit with R 2 adj = 0.3 when the underlying isotope data have completely different amplitudes. A decrease in the goodness of fit of the sine wave when amplitudes are low was also found by Lutz et al (2018).…”

Section: Fraction Of Young Watermentioning

confidence: 59%

“…The variability in Fyw(189) of this study could not be explained by meteorological or hydrometric variables. Lutz et al (2018) found a negative correlation between annual precipitation and Fyw. The study of 22 Swiss catchments by von Freyberg et al (2018) found significant positive correlations between Fyw and mean monthly discharge and precipitation volumes.…”

Section: Hypothesis 1 -Fyw Is Time-variantmentioning

confidence: 91%

“…These differences in Fyw results complicate catchment comparisons, as the result does not only depend on catchment characteristics but also on when isotope data were collected. As far as we can tell, the recent Fyw catchment comparison study of Lutz et al (2018) used the same sampling period for precipitation and streamflow for all 24 investigated catchments. In contrast, the studies of Jasechko et al (2016) andvon Freyberg et al (2018) had isotope sampling periods varying in start date and overall length for the 254 and 22 investigated catchments, respectively, potentially influencing the uncertainty for the inter-catchment comparison according to the results of our study.…”

Section: Hypothesis 1 -Fyw Is Time-variantmentioning

confidence: 99%

“…The results of this study suggest that care must be taken when comparing Fyw of catchments that were based on different calculation periods and that the influence of extreme events and snow must be considered. tion through a catchment (McGuire and McDonnell, 2006). One method that utilizes the water stable isotopes for investigating fast flow paths is the fraction of young water (Fyw).…”

mentioning

confidence: 99%

“…A higher sampling frequency led to higher Fyw, highlighting the sensitivity of Fyw to the temporal resolution of the available tracer data. Lutz et al (2018) investigated 24 catchments in Germany and used 10 000 Monte Carlo simulations with random errors in the isotope data of precipitation and streamflow to derive the 95 % confidence intervals of Fyw. Their confidence intervals indicated a robustness of Fyw against random errors in input data.…”

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confidence: 99%

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Time variability and uncertainty in the fraction of young water in a small headwater catchment

Stockinger

Bogena²,

Lücke³

et al. 2019

Hydrol. Earth Syst. Sci.

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The time precipitation needs to travel through a catchment to its outlet is an important descriptor of a catchment's susceptibility to pollutant contamination, nutrient loss, and hydrological functioning. The fast component of total water flow can be estimated by the fraction of young water (Fyw), which is the percentage of streamflow younger than 3 months. Fyw is calculated by comparing the amplitudes of sine waves fitted to seasonal precipitation and streamflow tracer signals. This is usually done for the complete tracer time series available, neglecting annual differences in the amplitudes of longer time series. Considering inter-annual amplitude differences, we employed a moving time window of 1 year in weekly time steps over a 4.5-year δ 18 O tracer time series to calculate 189 Fyw estimates and their uncertainty. They were then tested against the following null hypotheses: (1) at least 90 % of Fyw results do not deviate more than ±0.04 (4 %) from the mean of all Fyw results, indicating long-term invariance. Larger deviations would indicate changes in the relative contribution of different flow paths; (2) for any 4-week window, Fyw does not change more than ±0.04, indicating short-term invariance. Larger deviations would indicate a high sensitivity of Fyw to a 1-week to 4-week shift in the start of a 1-year sampling campaign;(3) the Fyw results of 1-year sampling campaigns started in a given calendar month do not change more than ±0.04, indicating seasonal invariance. In our study, all three null hypotheses were rejected. Thus, the Fyw results were timevariable, showed variability in the chosen sampling time, and had no pronounced seasonality. We furthermore found evidence that the 2015 European heat wave and including two winters into a 1-year sampling campaign increased the uncer-tainty of Fyw. Based on an increase in Fyw uncertainty when the mean adjusted R 2 was below 0.2, we recommend further investigations into the dependence of Fyw and its uncertainty to goodness-of-fit measures. Furthermore, while investigated individual meteorological factors did not sufficiently explain variations of Fyw, the runoff coefficient showed a moderate negative correlation of r = −0.50 with Fyw. The results of this study suggest that care must be taken when comparing Fyw of catchments that were based on different calculation periods and that the influence of extreme events and snow must be considered.

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Section: Fraction Of Young Watermentioning

confidence: 59%

Section: Hypothesis 1 -Fyw Is Time-variantmentioning

confidence: 91%

Section: Hypothesis 1 -Fyw Is Time-variantmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Time variability and uncertainty in the fraction of young water in a small headwater catchment

Stockinger

Bogena²,

Lücke³

et al. 2019

Hydrol. Earth Syst. Sci.

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Nitrate removal and young stream water fractions at the catchment scale

Benettin

Fovet

2020

Hydrological Processes

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Despite extensive research on nitrate export and removal, nutrient contamination remains a major threat to water bodies worldwide. At the local scale, nitrate removal is governed by biogeochemical conditions that vary in space and time, making integration to entire landscapes critical. Water transit times have often been used to describe solute transport, but the relation between water age and nitrate removal at the catchment scale is still poorly understood. We test the hypothesis that nitrate removal peaks when the fraction of young water in discharge is at its minimum, because nitrate removal occurs mostly under dry conditions where deeper, older groundwater dominates streamflow. We tested this hypothesis by exploring a detailed water quality record from the Kervidy-Naizin catchment (FR) and comparing the dynamics of nitrate to those of a conservative solute (chloride). We find that estimates of nitrate removal are consistent with previous estimates at the site and they show a good (inverse) correlation with the fraction of streamflow that is younger than 2.5 months. However, this young water fraction cannot be used to predict nitrate removal in the winter-spring period, when no removal is observed regardless of streamflow age. While this leads us to reject our hypothesis during the winter period, it also suggests that water age distributions and their correlation with nitrate removal can possibly reveal distinct sources of stream water at different hydrologic regimes and relevant biogeochemical reactions. K E Y W O R D Sagricultural catchment, chloride transport, denitrification, Naizin, nitrate removal, SAS function, water age, young water fraction

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Catchment storage and residence time in a periodically irrigated watershed

Grande

Visser

Moran

2020

Hydrological Processes

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Understanding anthropogenic impacts on water storage and water flow pathways in catchments is an ongoing challenge in hydrology. Here, we study the dynamics of subsurface storage and residence time of water in a catchment in Berkeley, California, that is within a regional park but contains diverse land use within its perimeter, including a periodically irrigated golf course. Our study combines several isotopic tracers with water budget data to examine sources of water in a stream draining the site. Irrigation water, applied to a small area of the watershed, is a minor component of the water budget. However, geochemical tracers reveal that irrigation water is a significant fraction of stream flow downstream of the golf course during baseflow and during precipitation events. Isotopic tracers indicate that the watershed has a preference to release young water for stream flow generation, resulting in contrasting tritium ages for stream water and groundwater of 1.3 ± 0.5 year and 8.2 ± 1.7 year, respectively. We determined that the older water is a very small component (0.7%) of the stream water in the tail of an assumed exponential distribution. We used the seasonal variation of stable water isotopes in precipitation and stream water over two water years to explain the damping of the isotopic signature of stream water, which yields information about the catchment's response to the input signal. The methods described here may be applicable to other urban or suburban headwater catchments in areas with a component of non‐natural recharge from, for example, leaky infrastructure, storm water routing or dry season irrigation.

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Spatial Patterns of Water Age: Using Young Water Fractions to Improve the Characterization of Transit Times in Contrasting Catchments

Cited by 78 publications

References 68 publications

Time variability and uncertainty in the fraction of young water in a small headwater catchment

Time variability and uncertainty in the fraction of young water in a small headwater catchment

Nitrate removal and young stream water fractions at the catchment scale

Catchment storage and residence time in a periodically irrigated watershed

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