The black olm (Proteus anguinus parkelj Sket & Arntzen) is an endemic subspecies confirmed to live in an area of less than 3 km2 in the western Bela Krajina. The karst landscape is characterised by the rapid and direct flow of water through the underground, which at the same time allows the rapid transport of anthropogenic pollutants that threaten groundwater quality and the preservation of underground biodiversity. Nitrates, mainly from agricultural sources such as fertilisers and wastewater, can be transported via surface and groundwater to the habitat of olm. The upper limit of nitrate concentration for the acceptable chemical status of the habitat of the olm is 9.2 mg NO3-/l, while measured values in individual karst springs exceed 20 mg NO3-/l and pose a serious risk to the existence of the olm. Using the SWAT model, which assesses the impacts of different land management and land use scenarios on nitrate leaching to groundwater and surface water, we found that adjusting agricultural rotations, reducing fertilisation and introducing greening significantly reduces nitrate concentrations in water. The most effective scenarios involve combinations of different measures, which could reduce nitrate leaching below the soil profile by more than 30% compared to current practice. The results of the model validation confirm the suitability of the SWAT model for assessing the impacts of agricultural activities on karst soils, while highlighting the need for further adaptation of agricultural practices to protect the vulnerable habitat of the black olm.
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