Impact of extreme drought on diatom traits and species composition in temperate lowland streams

Abstract

This study investigates how diatom assemblages respond to environmental conditions in Pampas ecoregion in Argentina during the most extreme drought in a century. It examines whether changes in diatom composition and traits are influenced by physical, chemical, hydrological factors, or their interactions. Additionally, it evaluates descriptors of diatom assemblages to distinguish between streams with continuous and interrupted flow during droughts. In 2022, three samplings were conducted in the Samborombón River basin, selecting three streams with interrupted flow and three with continuous flow. Diatom samples along with physical, chemical, and hydrological data were collected. Diatoms were identified, assigned to size classes, ecological guilds, salinity tolerance, and moisture requirements, and biotic indices (richness, diversity, evenness) were calculated. The partitioned analysis of variance revealed that species and trait composition were mainly influenced by the interaction of physical, chemical, and hydrological parameters. NMDS and ANOSIM analysis showed that species and traits distinguished between the two stream types. None of the biotic indices showed significant differences. Small-sized, aerophilic, and halophilic diatoms indicated interrupted flow streams, while larger, high-profile diatoms characterized continuous flow streams. This study provides information on how diatoms respond during drought phases, being relevant in the context of climate change and land-use transformations.