Soil enzyme activities and moss biomonitoring as complementary bioindicators of environmental status and toxic and potentially toxic element contamination in a karst cave and its catchment: Brestovská Cave, Slovakia

Brestovská Cave (Western Tatras, Slovakia), a show cave opened to the public in 2016, is characterised here for the first time by combining toxic and potentially toxic element (TPTE) contents, soil enzyme activities and moss biomonitoring. Twelve TPTEs were determined in soils at eight sites along a hydrological transect from the swallow hole to the resurgence, plus an external forest control, and in three moss taxa above each site. Indices were computed against the world-soil average, the Slovak national median and the local forest control. Two independent gradients were resolved. The first is natural: most lithophile elements lie at or below the world-soil average, and enzyme activities decline by close to an order of magnitude towards the aphotic interior, tracking organic substrate availability rather than the element burden and so reflecting oligotrophy rather than contamination. In the second, the choice of reference proved decisive. Cadmium exceeded the Slovak statutory limit at every site (CF = 4.53 against both references), yet varied by less than a factor of two across the transect, was most enriched at the external forest control on an aluminium-normalised basis, and lay below the national moss median in moss, indicating a carbonate parent-material origin rather than external input. Selenium behaved oppositely: strongly enriched against the national median (CF = 14.5; EF = 32, reaching 88 at the swallow hole) and highly variable, it carries, with mercury at the resurgence, the clearest localised external signal. The degree of contamination was 14.9 and 26.9 against the two references, and the ecological risk index of 212 remained moderate under all threshold scales. Dicranum sp. was the strongest accumulator, and no moss-soil relationship was detected for any element or taxon. Screening-level health risk was acceptable for visitors and guides (HI at most 0.59; As-CR at most 8.3 × 10 −6 ).