Sensitivity of groundwater and surface water crustaceans to chemical pollutants and hypoxia: implications for pollution management

In order to test the hypothesis that groundwater organisms are more sensiti ve to stressors than surface water organisms, this study compares the respo nses of surface and groundwater isopods, cyclopoid copepods and ostracods t o inorganic chemicals (potassium chloride and potassium nitrate) and low ox ygen concentration (10 % oxygen saturation, hypoxia) in laboratory experime nts. Isopods displayed the highest sensitivity to the chemicals (LC50 value s for KCl: Proasellus slavus vindobonensis = 285 mg/l, and Asellus aquaticu s = 355 mg/l), ostracods turned out to be most tolerant (LC50 values for KC l: Fabaeformiscandona wegelini = 1932 mg/l, and Pseudocandona sp. = 2018 mg /l). Comparing the response of species within one taxonomic group (isopods, copepods, and ostracods), the exclusive groundwater species (stygobites) w ere more sensitive to the chemicals than closely related surface water spec ies (see above). The stygobite species displayed no differences between the metabolism measured under normoxic and hypoxic conditions. A copepod, Acan thocyclops vernalis, collected in a hypoxic groundwater habitat, showed sma ll metabolic differences (i.e., the metabolic rate measured in hypoxia amou nted to 61.8 +/- 5.5 % of the metabolism in normoxia), compared to a copepo d, Diacylops bicuspidatus, collected in a normoxic groundwater habitat (27. 3 +/- 6.9 %). Due to the low difference between the metabolic rates, the st ygobite organisms and A. vernalis were best adapted to low oxygen concentra tions among the tested species. The hypothesis was supported by this study. The high sensitivity of the gro und-water crustaceans to the chemical stressors suggests that existing grou ndwater quality criteria are insufficient to protect the groundwater biota and ecosystem, and further ecotoxicological studies with groundwater organi sms are required.