A GIS-Based Assessment of Potential Pollution Risk and Environmental Vulnerability in Natura 2000 Underground Karst Sites of Croatia’s Mediterranean Region

Abstract

Within the Natura 2000 network, Europe’s primary framework for conserving species and habitats of community importance, subterranean ecosystems remain among the least explored yet most vulnerable components. In Croatia’s Mediterranean karst region, these underground environments are increasingly exposed to anthropogenic pressures linked to urbanization, infrastructure development, and waste management, while the high permeability of karst formations facilitates rapid transfer of surface-derived pressures into subsurface environments.
This study employs Geographic Information Systems (GIS) to analyse spatial relationships between anthropogenic pressures and visible pollution occurrence in Natura 2000 underground karst sites across Croatia’s Mediterranean biogeographical region. Spatial analyses, including proximity, buffer, hotspot, and multi-criteria vulnerability modelling, were applied to high-resolution datasets representing road networks, waste disposal facilities, land cover, and population density.
Results indicate that pollution incidence is higher in caves located closer to certain anthropogenic features. A Mann–Whitney U test showed that polluted caves were significantly closer to local roads (U = 17.0, p = 0.007) and legal waste disposal sites (U = 1664.0, p = 0.037) compared with clean caves, while no statistically significant differences were found for distances to county roads (p = 0.172) or illegal waste dumps (p = 0.828). In addition, a Chi-square test of independence revealed a significant association between visible pollution occurrence and land cover type (χ² = 11.10, df = 4, p = 0.025), with caves located in settlements and cropland landscapes showing higher pollution rates than those in forested or grassland environments. The GIS-based vulnerability model identifies high-risk zones where multiple anthropogenic factors converge, offering a spatially explicit framework to support targeted conservation and management actions.

Popular Abstract

Keeping Croatia’s Hidden Caves Clean
Croatia’s karst landscape is famous for its mountains, sinkholes, rivers and caves. Beneath the surface lies another world that supports unique ecosystems and species, many of which are protected through the European Natura 2000 network. However, these underground environments are not isolated from human activities above ground. Roads, settlements, agriculture and waste disposal can create pathways for pollution to reach caves and groundwater. Because karst rocks are highly permeable, pollution entering the landscape can move through cracks and underground channels relatively quickly.
This project investigated where protected underground karst sites in Croatia’s Mediterranean region are most exposed to human-related pollution. The study examined 133 Natura 2000 cave sites, of which 24 were recorded as polluted and 109 as clean. Geographic Information Systems (GIS) were used to map the caves together with roads, waste disposal sites, land cover and population density. The locations were then compared to identify patterns and areas where several potential pressures occur together.
Where are the greatest risks?
The results show that human accessibility is an important factor. Polluted caves were generally located closer to local roads and legal waste disposal sites than clean caves. In contrast, the distance to county roads and illegal dumping sites did not show a statistically significant relationship with recorded cave pollution. The study also found that pollution was more common around settlements and agricultural areas, while caves surrounded by forests and grasslands were more often clean.
Illegal waste dumping was widespread across the region. The analysis identified 29 statistically significant dumping hotspots, with the strongest concentration occurring in Istria. These hotspots highlight areas where waste management and environmental monitoring may deserve particular attention.
Population density also showed a clear relationship with pollution. Only about 12% of caves in low-density areas were polluted, compared with approximately 20% in medium-density areas and 34% in high-density areas. These patterns suggest that areas with greater human activity and accessibility can place additional pressure on vulnerable underground environments.
The study combined these different factors to create a vulnerability map showing which cave sites are potentially most exposed to pollution. The results were encouraging: four of the five sites classified as highly vulnerable were already recorded as polluted. This indicates that spatial information can help identify places that may require closer monitoring and protection.
The findings demonstrate how GIS can support the conservation of Croatia’s hidden karst environments. By bringing together information about people, infrastructure, land use, waste and the natural environment, GIS can help environmental managers identify vulnerable sites and better target future monitoring and conservation efforts.

• author: Posavac, Tomislav
• supervisor: Harry Lankreijer
• organization: Department of Earth and Environmental Sciences (MGeo)
• course: GISM01 20262
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: GIS, Karst Ecosystems, Pollution, Natura 2000, Vulnerability Modelling, Biodiversity Conservation
• publication/series: Master Thesis in Geographical Information Science
• report number: 219
• language: English
• id: 9250645
• date added to LUP: 2026-09-10 11:11:54
• date last changed: 2026-09-10 11:11:54