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
In the karst landscape of the Kras Plateau (south‐west Slovenia), we studied the impact of historical human‐induced land degradation on biodiversity by studying the characteristics and changes in ...vegetation of degraded and nondegraded karst depressions (dolines). Intensive human‐induced land degradation began as a consequence of the abandonment of traditional land use; thus, many dolines have disappeared by being completely filled with waste material and overgrowth. The study is based on a chronosequence approach and assesses whether vegetation (e.g., community succession stages) can be used as a (bio)indicator of land degradation to estimate approximately the duration of degradation on the basis of the stage of succession. The locations and duration of degradation of dolines were identified in advance by analysing a time series of historical aerial photographs, topographical maps, and digital elevation models. Ecological evaluation was based on sampling the floristic composition and the topsoil. In this study, three vegetation measures were established as indicative of degradation: (a) the appearance of ruderal species, (b) hemeroby, and (c) alien and invasive species. A succession model of degraded karst landscape was produced on the basis of identified chronosequences to assess the long‐term spatial impact of doline degradation on karst biodiversity. The model is showing the tendency towards the vegetation homogenization of karst landscape.
Under the influence of socio–economic changes in many regions in Europe, a trend of decreasing agricultural activity has been observed since the Second World War. The resulting reforestation ...profoundly changes water and sediment supply to river channels, deposition rates on the floodplains and erosion rates on the hillslopes. We studied these changes in the 91 km
2 Dragonja catchment in southwestern Slovenia.
With the spatially distributed erosion and sediment delivery model WATEM/SEDEM, the hillslope sediment delivery to the river channel was calculated on the basis of parameters (soil and precipitation parameters, a DEM and land use) measured in the field and laboratory in 2002 and land use maps based on aerial photographs from 1954, 1975, 1985 and 1994. For two independent calibrations WATEM/SEDEM modelled a sharp decline of 69% in total hillslope sediment delivery from 1954 to 2002.
As the sub-catchments Rokava and Upper-Dragonja did not reforest in the same way, the sediment yield response is different as well. Separate calculations show the same reduction (45%) in sediment yield from 1954 to 1975. After 1975 the sediment yield was stable in the Rokava sub-catchment. In the Upper-Dragonja the trend continued, to a total reduction of 76% of sediment outflow since 1954.
The sources of fine sediment were determined by analysing the hysteresis of the discharge waves, and the suspended sediment texture. The sediment that leaves the catchment originates from three sources: hillslopes, erosional bedrock banks and sedimentary riverbanks.
The analysis of the suspended sediment texture suggests that during a discharge wave the suspended sediment originates predominantly from the hillslopes. During low stage the sparse sediment in the water column largely originates from large bedrock banks. The sedimentary riverbanks are not an important source of suspended sediment.
•Streamflow recession information extracted from streamflow series.•Analysis of streamflow components based on two-component hydrograph separation.•Catchment hydrological response changes during ...increased-intensity rainfall events.•Hydrograph simulations performed by combining different hydrological concepts.•Streamflow recession provides insight into storage–discharge characteristics.
The simple dynamical system approach was implemented to analyze, explain and simulate streamflow fluxes in diverse seasonal hydrological conditions within the forested Padež stream catchment in SW Slovenia. The catchment is characterized by the flushing, torrential hydrological response conditioned by the flysch geological settings of a low hydraulic conductivity. Consequently, the streamflow formation is not controlled solely by the deeper subsurface catchment storage but is also strongly influenced by the rainfall–runoff that bypasses the deeper subsurface part of the total catchment storage. Therefore, fast component of the streamflow is identified using two-component hydrograph separation; the component recession behavior is described by a separate sensitivity function and used in a simple model to simulate the streamflow. According to the simulation results, the Padež stream catchment behaves primarily like a deeper subsurface storage-dependent system during most of the hydrological conditions. When rainfall intensities increase (rainfall intensities close to 10mm/h or higher), triggering of the secondary streamflow formation mechanism described by separate, bypassing flow sensitivity function becomes evident and causes fast hydrograph formation with steeply rising and falling limbs. To be able to implement the modeling concept for streamflow predictions, the rainfall losses, most likely associated with interception losses not covered under the potential evapotranspiration calculation, would have to be more thoroughly analyzed through rainfall interception measurements. Our study shows the possible way that two hydrological concepts, the streamflow recession analysis and the two-component hydrograph separation based on relatively easily measurable tracers, such as electrical conductivity, could be combined for analyzing streamflow fluxes.
In the Vipava Valley (SW Slovenia), various types of mass movements occur in a geologically and geomorphologically diverse setting. These comprise various types of landslides, creep, and Quaternary ...slope deposits of carbonate blocks and recent scree deposits. A general geological setting is represented as Mesozoic carbonate overthrust on Paleogene flysch (alternations of mostly sandstones and marlstones), resulting in steep slopes and mass movements. Our study is based on the automatic classification of various litho-geomorphological units including slope deposits, alluvial deposits, steep carbonate cliffs, flysch, two carbonate plateaus, and Quaternary deposits, based on supervised Maximum Likelihood Classification. Several polygons were used for training in the broader valley area, and later, the method was applied to automatically classify the complete area into the abovementioned six units. For input layers, we used data for elevation, slope, terrain ruggedness index (TRI), and curvature. Results show that generally, the method is suitable for classification of the litho-geomorphological units including slope deposits. However, comparison with a more detailed map, comprising mapped various mass movements indicated that the method correctly predicts high Trnovo plateau carbonates, steep carbonate slopes, translational carbonate blocks, and fossil rock avalanche deposits, and alluvial deposits, but is not able to clearly distinguish between flysch and more recent slope deposits of gravel and breccia due to their similar elevation, TRI, and slope values. The Slano blato mudflow and Stogovce landslide are not recognized. Therefore, this automatic classification can be carefully used to create a guidance map of general occurrences of litho-geomorphological units including slope deposits before going to the field, with the aim of delineation of slope deposits so they can be further studied in detail later in the field. However, such a map cannot be used as a direct substitute map for the geological and geomorphological map obtained in the field due to impossibility in distinguishing among the units with the same properties (elevation, slope, and TRI values).
The Selo landslide complex in the Vipava Valley (SW Slovenia) is a large fan-shaped sedimentary body that differs significantly from other slope deposits in the area in its exceptional size and ...considerable runout length. The landslide is predominantly composed of carbonate gravel deposited on a flysch paleo-relief. To determine the volume and geometry of the landslide and its potential source area, we integrated geological mapping, ground penetrating radar (GPR) and GIS techniques. The landslide deposits cover an area of about 10 km
2
with an average thickness of 10 m (maximum thickness reaching 56 m) and a maximum length of 5500 m. The volume of carbonate gravel was estimated from geological cross sections and GPR profiles. The base and top surfaces were interpolated by inverse distance and kriging methods, for which the Cut/Fill method was used in ESRI ArcGIS to determine the original landslide volume before the erosion. The estimated original volume is 190 × 10
6
m
3
. The recent volume after the erosion is 96 × 10
6
m
3
. The calculated volume of the Selo landslide, angle of reach θ = 10° and H/L ratio of 0.18 are in accordance with data for landslides of a comparable size. The most reasonable explanation for the development of the Selo landslide complex is a slope collapse involving the breakdown of the rock mass and the development of a high-mobility rock avalanche.
The analysis of high resolution airborne lidar topography represents an essential tool for the geomorphological investigation of surface features. Here we present a detailed lidar-based ...geomorphological analysis of the ravines cut into the slopes of the upper Vipava valley, NW Slovenia. The NE slopes are defined by an Oligocene thrust-front of Mesozoic carbonates overthrusted on Tertiary flysch and covered by numerous fan-shaped Quaternary gravity flows, deposited in palaeo-ravines cut into the flysch base rock. In contrast, the opposite SW slopes are composed solely of flysch. The large dextral-slip Vipava fault extending in the NW–SE direction is present in the central part of the valley. Our research revealed that although the ravines on both slopes of the Vipava valley are lithologically and tectonically controlled, significant statistical differences in their directions exist. Thus, ravines on opposite slopes are not solely related to the Vipava fault system deformation, but instead reflect a more complex tectonic setting. We believe that the ravines are controlled by second-order faults and fault zones that connect the Vipava fault with adjacent faults. On the SW slopes, these include connecting faults between the Vipava and the southwestern Raša fault, with the ravines on the NE slopes formed in fault zones connecting the Vipava and northeastern Predjama faults.
•Lidar is an essential tool for estimated ravines in different lithological basis.•The fractured zones functioned as a narrow channel and direct debris-flow path.•Ravines in the Upper Vipava valley controlled by second-order faults
Karst aquifer components that contribute to the discharge of a water supply well in the Classical Karst (Kras) region (Italy/Slovenia) were quantitatively estimated during storm events. Results show ...that water released from storage within the epikarst may comprise as much as two-thirds of conduit flow in a karst aquifer following rainfall. Principal components analysis (PCA) and end-member mixing analysis (EMMA) were performed using major ion chemistry and the stable isotopes of water (δ^sup 18^O, δ^sup 2^H) and of dissolved inorganic carbon (δ^sup 13^C^sub DIC^) to estimate mixing proportions among three sources: (1) allogenic river recharge, (2) autogenic recharge, and (3) an anthropogenic component stored within the epikarst. The sinking river most influences the chemical composition of the water-supply well under low-flow conditions; however, this proportion changes rapidly during recharge events. Autogenic recharge water, released from shallow storage in the epikarst, displaces the river water and is observed at the well within hours after the onset of precipitation. The autogenic recharge end member is the second largest component of the well chemistry, and its contribution increases with higher flow. An anthropogenic component derived from epikarstic storage also impacts the well under conditions of elevated hydraulic head, accounting for the majority of the chemical response at the well during the wettest conditions.PUBLICATION ABSTRACT
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