The effects of multiple stressors in a subtropical river: a perspective from a microcosm experiment

Temperature and nutrient availability are critical for the growth and development of aquatic invertebrates. However, an increase in these factors, derived from human stressors, could impact their food resources, such as periphyton, and subsequently affect larval metabolism and growth. We investigated the combined effects of rising temperature and nutrient enrichment (N and P) on periphyton biomass and a subtropical mayfly nymph species, Thraulodes consortis, during a 15-day microcosm experiment in Northwest Argentina. Our findings revealed a positive synergistic effect on chlorophyll-a concentration with temperature increases of + 2.5 °C and + 5 °C when combined with nutrient enrichment (+ P or + N). Mayfly nymphs showed reduced survival rates in the + 5 °C scenario with low oxygen levels, and survival rates displayed an additive response in all multiple stressor scenarios. Furthermore, the head capsule width of the nymphs significantly increased at all three temperature scenarios over the 15-day experiment, particularly in the presence of increasing nutrient levels. This suggested a strong metabolic response to these multiple stressor scenarios. This study emphasizes the diverse impacts of temperature and nutrient enrichment (N and P) on primary productivity, which could potentially alter the water chemistry of a subtropical river and affect the metabolism of primary consumers.