Combined effect of stream drying and nutrient enrichment on macroinvertebrate community: experimental study from artificial stream mesocosms

Ongoing climate change and rising water demands are resulting in the increasingly frequent occurrence of stream drying, particularly in smaller streams in humid temperate climates. These streams are often situated in outlying regions with insufficient wastewater treatment management leading to inconsistent inputs of nutrients into receiving water systems. Both stream drying and nutrient enrichment negatively affect local aquatic macroinvertebrate communities, but their combined effect is still unclear. This study aimed to investigate the combined effect of stream drying and nutrient enrichment on taxonomic and functional composition of aquatic macroinvertebrate communities. Towards this aim, an artificial stream system was used consisting of 36 mesocosms with aquatic macroinvertebrates. The mesocosms were exposed to four independent treatments based on different flow (perennial-drying) and nutrient (pristine-nutrient enriched) status. After 28 days of experiment, samples from different treatments were compared to evaluate combined effect of stream drying and nutrient enrichment. Despite expectations, no effect of drying on taxonomic and functional alpha diversity was observed, but beta diversity has significantly increased. Nutrient enrichment though caused to decrease in the alpha diversity indices, which resulted in high pre- and post-experiment samples dissimilarity within all treatments. Moreover, the combined effect of both stressors was antagonistic as stream drying moderated harsher impact of nutrient enrichment. Results emphasize an unexplored role of intermittent streams in nutrient cycling in temperate climates and highlight the need for further investigation of recently novel intermittent streams since they provide different environmental conditions for macroinvertebrates than perennial streams.