A novel probe for point injections in groundwater monitoring wells [Eine neuartige Sonde für Punktinjektionen in Grundwassermessstellen]

Groundwater monitoring wells or boreholes often show complex flow behaviors that are essential to understand for the characterization of aquifer systems. In karst or fractured aquifers, where complex conduit and/or fracture networks with differing hydraulic heads can be intersected by a well or borehole, vertical flow is highly probable. Single-borehole dilution tests (SBDT) with uniform injections are, in general, a good method to gain knowledge about a specific well or borehole, but tend to deliver ambiguous results regarding vertical flow, while SBDTs with point injections are an effective method to identify vertical flow. This technical note introduces a newly developed probe for point injections in groundwater without disturbing the natural flow field. In order to evaluate this probe, several tests were conducted in the laboratory and in groundwater monitoring wells that show vertical flow. During repeated tests in the laboratory, the new point injection probe showed a good reproducibility regarding the shape and extent of the tracer cloud after an injection. The opening mechanism was found to be well-functioning and reliable. Field tests lead to significant results for all tested wells and showed that the probe can easily be operated by a single person. Due to the flexibility regarding tracer, aquifer and injection depth, combined with the easy handling, it is a useful device, suitable for the investigation of boreholes and groundwater monitoring wells, and a good alternative to existing methods

Comparative application and optimization of different single-borehole dilution test techniques

Single-borehole dilution tests (SBDTs) are a method for characterizing groundwater monitoring wells and boreholes, and are based on the injection of a tracer into the saturated zone and the observation of concentration over depth and time. SBDTs are applicable in all aquifer types, but especially interesting in heterogeneous karst or fractured aquifers. Uniform injections aim at a homogeneous tracer concentration throughout the entire saturated length and provide information about inflow and outflow horizons. Also, in the absence of vertical flow, horizontal filtration velocities can be calculated. The most common method for uniform injections uses a hosepipe to inject the tracer. This report introduces a simplified method that uses a permeable injection bag (PIB) to achieve a close-to-uniform tracer distribution within the saturated zone. To evaluate the new method and to identify advantages and disadvantages, several tests have been carried out, in the laboratory and in multiple groundwater monitoring wells in the field. Reproducibility of the PIB method was assessed through repeated tests, on the basis of the temporal development of salt amount and calculated apparent filtration velocities. Apparent filtration velocities were calculated using linear regression as well as by inverting the one-dimensional (1D) advection-dispersion equation using CXTFIT. The results show that uniforminjection SBDTs with the PIB method produce valuable and reproducible outcomes and contribute to the understanding of groundwater monitoring wells and the respective aquifer. Also, compared to the hosepipe method, the new injection method requires less equipment and less effort, and is especially useful for deep boreholes

Deep desiccation of soils observed by long-term high-resolution measurements on a large inclined lysimeter

Availability of long-term and high-resolution measurements of soil moisture is crucial when it comes to understanding all sorts of changes to past soil moisture variations and the prediction of future dynamics. This is particularly true in a world struggling against climate change and its impacts on ecology and the economy. Feedback mechanisms between soil moisture dynamics and meteorological influences are key factors when it comes to understanding the occurrence of drought events. We used long-term high-resolution measurements of soil moisture on a large inclined lysimeter at a test site near Karlsruhe, Germany. The measurements indicate (i) a seasonal evaporation depth of over 2 m. Statistical analysis and linear regressions indicate (ii) a significant decrease in soil moisture levels over the past 2 decades. This decrease is most pronounced at the start and the end of the vegetation period. Furthermore, Bayesian change-point detection revealed (iii) that this decrease is not uniformly distributed over the complete observation period. The largest changes occur at tipping points during years of extreme drought, with significant changes to the subsequent soil moisture levels. This change affects not only the overall trend in soil moisture, but also the seasonal dynamics. A comparison to modeled data showed (iv) that the occurrence of deep desiccation is not merely dependent on the properties of the soil but is spatially heterogeneous. The study highlights the importance of soil moisture measurements for the understanding of moisture fluxes in the vadose zone

Physicochemical and major ion data for springs in the Black Forest National Park, Germany

The dataset in this article consists of the general physicochemical parameters (temperature, pH, specific electrical conductivity, dissolved oxygen, redox potential, alkalinity) and concentrations of major ions (Ca2+, Mg2+, K+, Na+, Cl-, SO42-, NO3-) of water samples collected at 19 springs and the surface stream in the water catchment area of the upper Schönmünz river in the Black Forest National Park, Germany. Data on concentrations of dissolved organic carbon (DOC), total organic carbon (TOC), spectral absorbance at different wavelengths and fluorescence as well as microbiological indicators (E. coli, total coliforms, enterococci) are also reported. Sampling was conducted during five field campaigns between spring 2016 and spring 2017. Knowledge of the current physicochemical parameters and concentrations of dissolved organic and inorganic constituents provides a baseline to assess future changes and serves as a supplement to ongoing studies of the spring ecosystems. Understanding the specific processes influencing the water chemistry will aid in their effective protection. For more details and further discussion on this dataset, the reader is referred to the associated research article “Processes controlling spatial and temporal dynamics of spring water chemistry in the Black Forest National Park

Use of major ion chemistry and trace and rare earth elements to characterize hydraulic relations, mixing processes and water–rock interaction in the Dong Van karst aquifer system, Northern Vietnam

The effectiveness of using a groundwater geochemistry approach in karst hydrogeologic research is highlighted. In particular, this approach is useful for preliminary investigations, such as for the study described here on the Dong Van karst aquifer system in Northern Vietnam. Analyses of different groundwater chemistry parameters complement each other, to clarify hydrochemical processes that are occurring in the karst system. The results of this study show that major ion composition can be used to clarify water chemistry signatures, as well as to identify the mixing processes and water–rock interactions in aquifers. Meanwhile, trace element concentrations and rare earth element patterns can be used as potential natural tracers when some processes are not revealed through conventional hydrochemical methods. These natural tracers can also be used to identify contaminant sources and/or contaminant transport pathways in karst aquifers. Viewed holistically, the groundwater geochemistry approach provides scientific information to establish a basic hydrogeological conceptual model and to estimate the water balance, which has implications for water resources protection and management in karstic systems

Spatial and temporal dynamics of suspended particles and E. coli in a complex surface-water and karst groundwater system as a basis for an adapted water protection scheme, northern Vietnam [复杂地表水和喀斯特地下水系统中悬浮颗粒和大肠杆菌的时空动态演变–越南北部调整水资源保护方案的基础] [Dynamique spatiale et temporelle des particules en suspension et d’E. Coli dans un système complexe d’eaux de surface et d’eaux souterraines karstiques comme base d’un programme adapté à la protection de l’eau, nord du Vietnam] [Dinâmica espacial e temporal de partículas suspensas e E. coli em um sistema complexo de águas superficial e subterrânea cársticas como base para um esquema adaptado de proteçã o de água, norte do Vietnã] [Dinámica espacial y temporal de partículas en suspensión y E. coli en un complejo sistema de aguas superficiales y subterráneas kársticas como base para un plan adaptativo de protección del agua, norte de Vietnam]

Karst aquifers in subtropical regions are characterized by high variability of water availability and quality due to changes associated with rainy and dry seasons. An additional challenge for water management is the combination of surface-water and karst groundwater systems since high spatiotemporal dynamics cause high variability of water quality. In these cases, adapted protection strategies are required. In this study, a protection approach for the catchment of a river-water diversion point in a rural area in northern Vietnam is developed. The variability of water quality was evaluated by rainy and dry season synoptic surveys of suspended particles and microbial contamination at 49 sites and time series at three sets of paired sites under constant hydraulic conditions. The anthropogenic land-use activities in the catchment were mapped to identify potential contamination sources and to highlight the challenging combination of surface-water and karst groundwater management. The analyzed data indicate differences in water quality between the dry and rainy seasons and a higher influence on water quality from land use than from hydrologic conditions. Furthermore, the results suggest a high risk of contamination resulting from residential areas, agriculture, and livestock farming, and reveal the necessity of implementation of appropriate measures such as restricted farming and the hook-up of buildings to municipal sewage disposal. Finally, the data show that water quality can be improved by adjusting water withdrawals by the time of day. The applied methods can be transferred to other surface-water and karst groundwater systems in similar subtropical environments

Hydrochemical evaluation of water resources and human impacts on an urban karst system, Jordan

Urban karst aquifers are threatened by anthropogenic activities, especially in semiarid developing countries. Recent water-sampling campaigns assessed the extent of groundwater-quality impairment in the Wadi Shueib in Jordan by a comprehensive hydrogeological and hydrochemical characterization of groundwater, wastewater, and imported water with its endmembers Lake Tiberias, Yarmouk River and Mukheiba wellfield. The results of a ternary mixing model with the mass ratios of Cl$^{-}$/Br$^{-}$ and Ca$^{2+}$/Mg$^{2+}$ indicate that Lake Tiberias and Yarmouk River provide most of the imported water at the time of sampling in 2017 and Mukheiba wellfield provided minor amounts. The similarity in seasonal variations of Br$^{-}$ concentrations in the springs and the imported water revealed that imported water has generally a greater impact on groundwater than wastewater. However, the Br$^{-}$ concentrations also showed that the spatial wastewater impact is more visible towards urbanized areas due to increased infiltration of pollutants. The analysis of historical data series demonstrated the long-term urban impact on groundwater by an electrical conductivity increase over several decades, particularly since the mid-1990s, which is related to a doubling of Jordan’s population since that time and the associated urban growth. In this context, increased chloride and sulfate concentrations are noticeable due to the increased impact of more highly mineralized imported water and wastewater and decreasing recharge of low-mineralized rainwater. This study showed the hydrochemical differences in the Wadi Shueib groundwater system and serves as an example for the spatial and long-term response of karst aquifers to anthropogenic, seasonally variable input of imported water and wastewater

From cave to spring: Understanding transport of suspended sediment particles in a fully phreatic karst conduit using particle analysis and geochemical methods

Karst aquifers are vulnerable to contamination, especially in the context of heavy rainfall events. Contamination is often associated with turbidity that can originate from the soil zone, infiltrating surface waters or resuspension of previously deposited sediments within the aquifer. While turbidity events can be well monitored at karst springs, related information about the sediment origin and the spatiotemporal input function usually remain unknown. Thus, the mobility and attenuation of the particulate matter and associated pollutants can hardly be determined quantitatively. A tracer test with suspended cave sediments and solute tracers for comparison has hence been performed in a karst aquifer at the Blue Spring (Blautopf) in Southern Germany. The tracers were injected in the cave system, at the beginning of a fully phreatic karst conduit, and monitored at the spring after a travel distance of 1250 m. The particle-size distribution was monitored using a particle counter and sediment samples were filtered with 0.45-μm cellulose acetate filters. Particles on the filter were analysed for major and trace elements as well as rare earth elements (REE) by ICP-MS after acid digestion. Results show that (1) sediment particles were transported faster than solutes, which was interpreted as a transport in the main flow path of the conduit, whereas conservative tracers tend to diffuse into smaller fissures as well. (2) All measured particles sizes were transported at similar flow velocities. (3) A transport associated to sediment particles could be shown for all measured elements. This study presents a methodological improvement of comparative sediment tracer tests as well as deeper insights into particle and element transport processes in karst aquifers, originating from previously deposited cave sediment. Results provide deeper knowledge into transport processes of sediment-associated contaminants, such as heavy metals which may strongly be affected by the particle size. This knowledge contributes to a better management of karst water resources in the context of turbidity events