Anthropogenic impact on the karst aquifer quality: preliminary results from Damiș – Ponoraș karst area, Romania

Karst aquifers are crucial water resources but are highly vulnerable due to their geological fragility and anthropogenic pressures. This study assesses water quality in the Damiș-Ponoraș Karst Area (DPKA), where the expansion of the drinking water network has occurred without proper sewerage systems. The investigation focused on the Dămișenilor Karst System (DKS) and included, for comparison, the Ponoraș Karst System and three other springs from the Brătcuței Valley that also collect discharge from the DPKA resurgences. In total, twelve water sources were sampled seasonally from 2023 to 2025, with analysis of physicochemical parameters, microbial content, and aquatic invertebrate assemblages. The geological structure of the DPKA shapes distinct physical and chemical properties among springs, ponors, and resurgences, as well as within its drainage systems. While all waters exhibit typical karst characteristics, including high alkalinity, conductivity, dissolved solids, and hardness, DKS sites show specific variations: springs had lower pH, calcium hardness and conductivity, ponors showed higher turbidity and lower redox potential, suggesting pollutant susceptibility, while the increased magnesium hardness at resurgence indicates flow through dolomitic strata. Measured concentrations of nitrates, nitrites, ammonia, and phosphates were low and complied with drinking water quality standards, but widespread microbial contamination with total mesophilic bacteria, Klebsiella oxytoca, Pseudomonas aeruginosa, and Escherichia coli was present. In the DKS resurgence, anthropogenic pressures, mainly bacterial contamination from domestic wastewater, are linked to reduced invertebrate richness and abundance, indicating declining ecological quality. A concurrent, gradual decrease in microbial and invertebrate abundance along the karst hydrological continuum, from springs to ponors and resurgence points, suggests the influence of poorly understood subsurface processes. These results highlight that ongoing human impacts may threaten aquifer water quality and ecological stability, underscoring the need for integrated monitoring using abiotic and biotic indicators to support timely management actions.