Ravbar et al. (2026) Integrated multi-scale ecohydrogeological monitoring of spatio-temporal dynamics in karst critical zones

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-01-30
• Authors: N. Ravbar, Silvia Cleva, Abies Alba, Uroš Novak, Mitja Ferlan, Lado Kutnar, Aleksander Marinšek, Daniel Žlindra, Blaž Kogovšek, Erika Kozamernik, Cyril Mayaud, David Stefanic, Sara Skok, Janez Mulec, Stanka Šebela, Urša Vilhar
• DOI: 10.1016/j.jhydrol.2026.135027

Research Groups

• Karst Research Institute ZRC SAZU, Postojna, Slovenia
• UNESCO Chair on Karst Education, University of Nova Gorica, Vipava, Slovenia
• Slovenian Forestry Institute, Ljubljana, Slovenia
• Slovenian Environment Agency, Ljubljana, Slovenia

Short Summary

This paper proposes and assesses an integrated multi-scale ecohydrogeological monitoring approach for karst critical zones, demonstrating its effectiveness in capturing spatio-temporal variability and improving data representativeness in a forested karst aquifer in Slovenia. The study highlights the benefits of this interdisciplinary strategy for understanding complex ecohydrological processes in heterogeneous karst environments.

Objective

• To critically review the current state of ecohydrological research in karst environments and identify key research gaps.
• To propose a unified, integrated multi-scale ecohydrogeological monitoring strategy tailored to karst critical zones, focusing on spatial and temporal variability.
• To assess the strengths and limitations of the proposed monitoring framework using an established monitoring network in a forested karst aquifer in Slovenia as a case study.

Study Configuration

• Spatial Scale: Multi-scale, covering the vertical profile from the forest canopy to the saturated groundwater zone. This includes plot-level (0.5 to 1 hectare for forest, 1 to 10 square meters for ground vegetation/soil), local (1:5,000 to 1:10,000 for structural mapping), and regional (1:50,000 for geological mapping) scales. The case study is located in the Postojna-Planina Karst area, southwestern Slovenia, with 21 monitoring sites (10 surface, 11 underground) spanning altitudes between 530 meters and 640 meters.
• Temporal Scale: Continuous monitoring (e.g., hourly for surface meteorological data, 30-minute intervals for underground hydrological parameters since October 2020), event-based monitoring (e.g., for precipitation events and solute transport), one-off field campaigns (e.g., geomorphological and structural-geological mapping, vegetation and soil inventories), and weekly or bi-weekly measurements (e.g., Leaf Area Index from April to November in 2021, 2022, and 2023).

Methodology and Data

• Models used: No specific models were applied to generate the main results presented in this paper, which focuses on the monitoring framework itself. However, the data collected is intended for future model development and calibration (e.g., V2Karst, BROOK90, Watbal, and distributed hydrology-soil-vegetation models mentioned in the literature review).
• Data sources:
  • Surface Monitoring:
    • Meteorological: Precipitation (canopy gap), throughfall (enhanced tipping bucket rain gauge system with 875.5 square centimeters sampling area), air temperature, relative humidity (Sensirion SHT21), wind speed, wind direction, global solar radiation (Davis sensors).
    • Soil: Soil temperature, volumetric soil moisture content (METER Group ECH2O EC-5, DS18B20 at 30 centimeters and 60 centimeters depths), soil samples (organic horizons, mineral soil at 10-centimeter increments), bulk density, field capacity, permanent wilting point, available water content, soil texture, chemical properties.
    • Vegetation: Leaf Area Index (LAI2200 Plant Canopy Analyzer), vegetation inventory (woody and herbaceous species composition, abundance, percentage of tree, shrub, and herb layers).
    • Geological/Geomorphological: Geomorphological field mapping (based on airborne LiDAR Digital Elevation Model), detailed structural-geological field mapping (1:5,000 scale).
    • Water Chemistry: Precipitation, throughfall, and soil solution samples analyzed for pH, electrical conductivity, alkalinity, main anions (NO3–, NO2–, Cl-, PO43-, SO42-), main cations (NH4+, Na+, K+, Mn2+, Ca2+, Mg2+), total nitrogen, and Dissolved Organic Carbon (DOC). Soil solution collected using newly developed gravity lysimeters.
  • Underground Monitoring:
    • Hydrological: Flow rate, water level, temperature, and electrical conductivity of cave drips (Stalagmate drip counter, Onset Hobo U20 divers, Hobo U24), sinking streams, underground streams, and springs (HOBO U20, U24). Discharge measurements using SonTek's FlowTracker2 and RiverSurveyor M9, and vessel/stopwatch for drips.
    • Water Chemistry: Water samples from cave drips and streams analyzed for natural tracers (e.g., calcium, magnesium, nitrate).

Main Results

• The structural-lithological mapping identified predominant NW-SE trending Dinaric faults and associated karstified features (karrenfields, dolines) as key pathways for water flow between the surface and underground.
• Significant spatial variability was observed in vegetation cover (tree canopy 15% to 70%+), soil depths (shallower on doline slopes, deeper in interdoline areas), and available water content (10.7 vol% to 122 vol%), highlighting the heterogeneity of karst environments.
• The enhanced precipitation monitoring system increased the sampling area by 4.8 times (from 182.4 cm² to 875.5 cm²), improving the representativeness of precipitation and throughfall measurements in heterogeneous forest vegetation.
• During a significant autumn 2022 rainfall event, precipitation amounts were higher in regeneration canopy gaps than large canopy gaps, and soil moisture dynamics varied distinctly between these gap types due to rooting patterns and evaporation.
• Underground hydrological responses showed varied delays: cave drip D3 reacted within 2 hours, cave stream D4 within 4 hours, and the Rak sinking river and Unica Spring within 4-6 hours, demonstrating complex flow dynamics.
• Solute transport analysis revealed significant increases in calcium and magnesium concentrations from precipitation to soil solution and further into cave waters, reflecting carbonate rock dissolution. Nitrate concentrations varied significantly between surface sites and cave drips, indicating the strong influence of local conditions and heterogeneous karst structure on solute transport.

Contributions

• Proposes and assesses an innovative, integrated multi-scale ecohydrogeological monitoring approach for karst critical zones, addressing key research gaps in large-scale, holistic, and interdisciplinary studies of karst hydrology.
• Introduces a novel multispheric monitoring strategy that integrates atmospheric, biospheric, hydrospheric, and geospheric components, providing a holistic understanding of ecohydrological processes in karst environments.
• Develops and implements customized monitoring solutions specifically adapted to the complex and heterogeneous nature of karst landscapes, including:
  • An enhanced precipitation monitoring system that significantly increases the sampling area (by 4.8 times) for improved representativeness.
  • Tailored stainless-steel gravity lysimeters for precise soil solution extraction in shallow calcareous soils.
  • Microscale adaptations for soil moisture/temperature sensors and non-invasive underground monitoring equipment.
• Provides a robust framework for understanding intricate interactions and ecosystem dynamics across multiple spatial and temporal scales, essential for accurate data collection and change detection in karst systems.
• Lays the foundation for future research by generating comprehensive datasets suitable for developing and calibrating mathematical, numerical, and conceptual models, thereby advancing water resource management and conservation strategies in karst regions.

Funding

• eLTER Preparatory Phase Project (eLTER PPP)
• eLTER Advanced Community Project (eLTER PLUS)
• »Development of research infrastructure for the international competitiveness of the Slovenian RRI space – RI-SI-LifeWatch« (financed by the Republic of Slovenia, Ministry of Education, Science and Sport, and the European Union from the European Regional Development Fund)
• Slovenian Research Agency projects:
  • Infiltration processes in forested karst aquifers under changing environment (No. J2-1743)
  • Ecohydrological study of spatio-temporal dynamics in karst critical zones under different climate conditions (No. NK-0002)
  • Evaluate the impact of climate change on the groundwater reserves and ecology of a karst aquifer flooding intermittently: the Upper Pivka Valley (No. J1-60004)
• Research Programmes:
  • “Karst Research” (No. P6-0119)
  • “Forest biology, ecology and technology” (No. P4–0107)

Citation

@article{Ravbar2026Integrated,
  author = {Ravbar, N. and Cleva, Silvia and Alba, Abies and Novak, Uroš and Ferlan, Mitja and Kutnar, Lado and Marinšek, Aleksander and Žlindra, Daniel and Kogovšek, Blaž and Kozamernik, Erika and Mayaud, Cyril and Stefanic, David and Skok, Sara and Mulec, Janez and Šebela, Stanka and Vilhar, Urša},
  title = {Integrated multi-scale ecohydrogeological monitoring of spatio-temporal dynamics in karst critical zones},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135027},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135027}
}