Differences in potassium and chlorine incorporation in members of an alpine stream food web in the West Carpathians

Introduction High mountain streams are experiencing pronounced shifts in precipitation regimes and water chemistry; however, it remains unclear how organisms inhabiting these systems influence the transfer of chemical elements through food webs. Methods We measured concentrations of potassium and chlorine in algae, grazing mayflies, predatory stoneflies, and Alpine Bullhead ( Cottus poecilopus ) across seasons in an alpine stream. Results Algae exhibited marked seasonal variation, with higher potassium accumulation during the main summer growth period despite relatively stable water concentrations. Grazing mayflies maintained stable potassium levels but showed increased chlorine during colder months when chlorine concentrations in water were elevated. Predatory stoneflies showed only minor seasonal variation, with a slight increase in potassium in winter. The Alpine Bullhead did not exhibit significant seasonal changes in potassium or chlorine accumulation in its skull. Following major flood events, potassium and chlorine concentrations tended to co-vary across trophic levels, whereas under baseflow conditions they often varied independently. Discussion These patterns suggest that different trophic groups regulate element accumulation according to their physiology, life history, and ecological roles. The decoupling of organismal and water chemistry indicates that environmental concentrations alone do not fully explain element distribution within alpine stream food webs. Our findings provide new insights into element dynamics and highlight the importance of biological mediation in high-mountain ecosystems under changing environmental conditions.