Various multivariate statistical techniques (MST) can provide valuable insights into water quality variability. Despite numerous studies in which these methods have been used, their potential has not ...been fully exploited. This paper presents an improved approach to better understand the hydrodynamics of karst systems. The integrated application of hierarchical cluster and principal component analysis in combination with factor analysis allowed the construction of an advanced multivariate chemograph. The analytical procedure was applied in a binary karst aquifer known for its complex hydrodynamics and mixing of water with similar hydrochemical composition. In addition, the study area provides access to an integral groundwater flow system (ponor‐cave‐spring) and offers extensive prior hydrogeological knowledge. The approach allowed reduction and discrimination of the main parameters affecting water quality characteristics. Their identification enabled recognition of three predominant recharge components: (a) stored water impact with Cl and electrical conductivity, (b) sinking stream impact with turbidity and bacteria composition and (c) karst aquifer impact with Ca/Mg ratio as principal parameters. The results supported innovative characterization of the dominant processes and isolation of temporal hydrodynamic phases of individual monitoring points within the aquifer system. On this basis, a spatio‐temporal conceptual model was developed and the hydrodynamic behavior of the main springs was revealed. The applied methodology demonstrated to be useful in ascertaining functioning of a complex karst system under flood event conditions.
Plain Language Summary
Karst aquifer systems contain important water resources. The quality of karst springs can deteriorate significantly after rain events, but it is difficult to distinguish how water flows and mixes in the subsurface, especially in large and complex systems. Statistical methods are powerful tools for studying these issues, but most common approaches are inadequate in some cases to reveal the origin of the water and its fate. In this paper, we present an approach in which we combined different statistical methods to explain the dynamics of water flow based on the physicochemical and microbiological properties of water. The application of these methods led to the discrimination of parameters most useful for a reliable interpretation of statistical results, such as turbidity, bacteria, Cl, EC, and Ca/Mg, and to the construction of an advanced diagram that we called a multivariate chemograph. This diagram allowed us to see where the water was coming from at any given time to our monitoring points, which allowed us to construct a detailed explanation of water flow dynamics in space and time. Our contribution is important to better predict the fate of contaminants in karst underground and to develop an early warning system for better water supply management.
Key Points
A new approach to study and explain hydrodynamics of karst aquifers was developed
It offers an innovative solution to distinguish influential monitoring parameters
Multivariate chemographs allowed spatio‐temporal detection of recharge phases
Tracer tests are rarely applied in mountainous karst aquifers due to difficult or limited basic data acquisition, problems of access and expected strong tailing effects in tracer breakthrough. They ...are, however, a straightforward method for learning about the characteristics of underground water flow. The main aim of this study was to better understand the processes of flow and storage in the karst aquifer and its unsaturated (vadose) zone, which is several hundreds of metres thick. A tracer test was conducted with injection from the surface into a shaft in the central part of the aquifer. The results were compared to a previous tracer test with similar injection characteristics (the same tracer, injection into shaft vs karren) but with a significantly different vadose zone thickness. For this purpose, direct information obtained through tracer breakthrough curves analysis was modified in accordance with the distance factor, normalised as a function of tracer mass injected, and expressed as a residence time distribution. A conceptual model of flow and transport duality through the karst system was elaborated: part of the tracer flows rapidly through the primary drainage channels, while the other part is predominantly characterised by prolonged retention in less permeable zones. The results obtained support the idea that the thickness of the vadose zone has a very strong influence on residence times and dispersion. The subsequent outflow of the tracer and its detection greatly depend on the meteorological conditions. Our study suggests that the greater the thickness of the vadose zone, the better its protective function. In addition, the study was also relevant from the regional perspective, in that it enabled us to identify more closely the location of the Adriatic-Black Sea watershed.
Significance of hydrological variability in karst is presented, which also discusses factors inducing such variability and consequences it may cause. Groundwater flow in karst aquifers is often ...characterized by strong variability of flow dynamics in response to different hydrologic conditions within a short time period. Consequently, water table fluctuations are often in the order of tens of meters, differences in flow velocities between low- and high-flow conditions can reach ten or even more times. In dependence to respective hydrologic conditions groundwater flow also results in variations of flow directions, and thus in contribution of different parts of the aquifer to a particular spring. The described hydrological variability has many implications for contaminant transport, groundwater availability and vulnerability. Groundwater level rising reduces thickness of the unsaturated zone and decreases protectiveness of the overlying layers. Higher water flow velocities reduce underground retention. Due to more turbulent flow, transport and remobilization of solute and insoluble matter is more effective. During high-flow conditions there is usually more surface flow and hence more concentrated infiltration underground. Particularly in karst systems that show very high hydrologic variability, this should be considered to correctly characterize, understand or predict the aquifers’ hydrological behaviour and to prepare proper protection strategies. Keywords: karst aquifer, temporal hydrological variability, groundwater flow, transport processes, karst spring, water source protection. DOI: 10.3986/ac.v42i2.644
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