Christoph Külls

Tracers in hydrology

Preface. Acknowledgements. 1 Introduction. 2 The Integrated Concept of Tracers in Hydrology. 2.1 System approach. 2.2 Definition of tracers. 2.3 Modelling in the context of integrated tracerhydrology. 2.4 Fields of application. 3 Environmental Tracers. 3.1 Introduction. 3.2 Stable isotopes of water. 3.3 Stable isotopes in soil. 3.4 Stable isotopes in surface and groundwater. 3.5 The use of environmental isotopes for hydrological system analysis. 3.6 Nitrogen isotopes and origin assignment. 3.7 Age dating. 4 Artificial Tracers. 4.1 Fluorescent tracers. 4.2 Salt tracers. 4.3 Drifting particles as tracers. 4.4 Radioactive tracers. 4.5 Other tracers. 5 Mathematical Modelling of Experimental Data. 5.1 Artificial tracer (ideal) under saturated flow conditions. 5.2 Tracer experiments under unsaturated flow conditions. 5.3 Tracer experiments in streams and rivers. 5.4 Environmental tracer data. 5.5 The goodness-of-fit of a model. 6 Technical Instructions. 6.1 Planning and execution of a tracer study. 6.2 Estimation of tracer injection mass. 6.3 Gauging discharge. 6.4 Chloride method for groundwater recharge estimation. 6.5 Hydrograph separation using the end member mixing analysis (EMMA). 7 Case Studies. 7.1 Groundwater. 7.2 Case studies in the unsaturated zone and in soils. 7.3 Surface water. 7.4 Glaciers. 7.5 Catchment scale. Colour Plate Section. References. Index.

Dynamics of Flood Water Infiltration and Ground Water Recharge in Hyperarid Desert

A study on flood water infiltration and ground water recharge of a shallow alluvial aquifer was conducted in the hyperarid section of the Kuiseb River, Namibia. The study site was selected to represent a typical desert ephemeral river. An instrumental setup allowed, for the first time, continuous monitoring of infiltration during a flood event through the channel bed and the entire vadose zone. The monitoring system included flexible time domain reflectometry probes that were designed to measure the temporal variation in vadose zone water content and instruments to concurrently measure the levels of flood and ground water. A sequence of five individual floods was monitored during the rainy season in early summer 2006. These newly generated data served to elucidate the dynamics of flood water infiltration. Each flood initiated an infiltration event which was expressed in wetting of the vadose zone followed by a measurable rise in the water table. The data enabled a direct calculation of the infiltration fluxes by various independent methods. The floods varied in their stages, peaks, and initial water contents. However, all floods produced very similar flux rates, suggesting that the recharge rates are less affected by the flood stages but rather controlled by flow duration and available aquifer storage under it. Large floods flood the stream channel terraces and promote the larger transmission losses. These, however, make only a negligible contribution to the recharge of the ground water. It is the flood duration within the active streambed, which may increase with flood magnitude that is important to the recharge process.

Investigations on Water Management and Water Quality in Picos/PI and Tauá/CE

The WAVES program (Water Availability, Vulnerability of Ecosystems and Society in Northeastern Brazil) aims at creating a knowledge base and strategies for sustainable development for the drought-prone northeast of Brazil. The perspective of climate change in a semiarid area with marginal water supplies requires strategic measures in order to avoid or at least mitigate severe water scarcity problems. Water scarcity results from the imbalance in a tripartite system between (1) the availability of natural resources with specific hydrochemical characteristics, (2) the state of development of water supply structures, and (3) water demand for specific uses. Seen trom such a perspective, it is obvious that water quality is an important and integral aspect of water availability. Hence, the analysis of water availability needs to integrate quantitative and qualitative studies.

A toolkit for groundwater mean residence time interpretation with gaseous tracers

An analytical Excel-based toolkit called Gas-Tracer-Interpretation (GTI) was developed for determining mean residence time (MRT) of groundwater samples and for validating conceptual model assumptions. This novel data interpretation toolkit improves data handling during analysis and resolves some problems in the interpretation of data from environmental tracers. The toolkit can assist error detection, uncertainty and ambiguity during data analysis, particularly ambiguity due to the decline in atmospheric data of CFC input functions (air-mixing ratios of tracers). The innovative interpretation methodologies are: (1) corrections of environmental tracer data are conducted in concentrations in water instead of air (atmosphere), allowing comparison of different tracer input functions under similar conditions and thereby replacing the use of unique global atmospheric data; (2) a multi-model, multi-tracer approach is adopted to improve the number of different combinations of environmental tracers and lumped-parameter models (piston flow (PM), exponential (EM), exponential-piston flow (EPM), advection-dispersion (DM) and gamma (GM)); and (3) generation of sufficient information for determination of erroneous, unclear and ambiguous outcomes. Results are linked to graphical analysis to improve data view. GTI supports the environmental tracers CFC-11, CFC-12, CFC-113, SF6, 3H, and also SF5CF3, which is included as it represents a promising environmental tracer in hydrological research. The toolkit compares modeled input functions of tracers and data from samples. The apparent recharge age and MRT are estimated by combining explicit graphical and numerical data presentation. Due to the multi-model approach, it is possible to contrast selected models and estimate the best fit for a given sample, which is particularly useful for validating conceptual model assumptions. The toolkit has been developed in Microsoft ?Excel, and hence is user-friendly such that advanced programming skills or detailed understanding of the calculations and mathematical procedures are unnecessary. Display Omitted Software for multi-tracer and multi-model residence time analysis of groundwater.Optimization approach for joint residence time analysis of matrix of tracers.New algorithm for the standardization of dissolution of gaseous components.Analysis of uncertainty, ambiguity, error, degradation and contamination.

Application of a laser-based spectrometer for continuous insitu measurements of stable isotopes of soil CO 2 in calcareous and acidic soils

The short-term dynamics of carbon and water fluxes across the soil–plant–atmosphere continuum are still not fully understood. One important constraint is the lack of methodologies that enable simultaneous measurements of soil CO2 concentration and respective isotopic composition at a high temporal resolution for longer periods of time. δ13C of soil CO2 can be used to derive information on the origin and physiological history of carbon, and δ18O in soil CO2 aids in inferring the interaction between CO2 and soil water. We established a real-time method for measuring soil CO2 concentration, δ13C and δ18O values across a soil profile at higher temporal resolutions (0.05–0.1 Hz) using an off-axis integrated cavity output spectroscopy (OA-ICOS). We also developed a calibration method correcting for the sensitivity of the device against concentration-dependent shifts in δ13C and δ18O values under highly varying CO2 concentration. The deviations of measured data were modelled, and a mathematical correction model was developed and applied for correcting the shift. By coupling an OA-ICOS with hydrophobic but gas-permeable membranes placed at different depths in acidic and calcareous soils, we investigated the contribution of abiotic and biotic components to total soil CO2 release. We found that in the calcareous Gleysol, CO2 originating from carbonate dissolution contributed to the total soil CO2 concentration at detectable degrees, potentially due to CO2 evasion from groundwater. The C-CO2 of topsoil at the calcareous soil site was found reflect δ13C values of atmospheric CO2, and the δ13C of topsoil CO2 at the acidic soil site was representative of the biological respiratory processes. δ18O values of CO2 in both sites reflected the δ18O of soil water across most of the depth profile, except for the 80 cm depth at the calcareous site where a relative enrichment in 18O was observed.