Oxidative stress and metabolic adaptation in Synurella ambulans: Assessing pollution impact in the hyporheic zone

Oxidative stress is a prevalent mechanism of physiological stress caused by exposure to pollutants or environmental hypoxia in aquatic organisms. The hyporheic zone (HZ), a transitional area between surface and groundwater with distinct ecological conditions, is highly susceptible to pollution and hypoxia, but the physiological responses of its aquatic inhabitants to these stressors remain poorly understood. The aim of this study was to investigate the effect of wastewater treatment plant (WWTP) effluent as a point source of contamination on the battery of biomarkers of antioxidant defence (catalase, CAT; glutathione reductase, GR), xenobiotic biotransformation (glutathione-S-transferase, GST), and aerobic/anaerobic energy metabolism (pyruvate kinase, PK; phosphoenolpyruvate carboxykinase, PEPCK; lactate dehydrogenase, LDH) in a stygophilous freshwater amphipod Synurella ambulans from the Sava River HZ. The samplings were conducted in relation to the Sava River's hydrologic regime after low river discharge (in September 2020) and after high river discharge (in April 2021) at one site (Medsave) upstream of the WWTP outflow and at two sites downstream (Podsused and Jarun). S. ambulans populations at sites downstream of the WWTP showed higher CAT, GR, GST and LDH activity than population at the upstream site. PK/PEPCK ratio was significantly lower in the S. ambulans populations at Podsused and Jarun sites compared to Medsave population after low river discharge, indicating lower aerobic capacity and greater reliance on anaerobic metabolic pathways. This study improves the understanding of the physiological responses of crustaceans exposed to chemical pollution and environmental stressors, thus contributing to the ecological assessment of groundwater connected ecosystems.