Continuous precipitation loss induced more pronounced compositional and diversity changes in the lotic phytobenthos than one-off drought events

Abstract

Changing precipitation dynamics is one of the most important mechanisms that, by affecting the water regime, modifies the physical and chemical environment of aquatic assemblages. Thus, hydrological extremes can be considered as key drivers that shape algal assemblages and lead to diversity changes even in large rivers. Here, we investigated the long-term changes in the benthic diatom composition of the Rába River (River Raab), the watershed of which experienced continuous loss of precipitation in the last five years. We aim to answer the main question: Do one-off drought events and trend-like (continuous) precipitation decrease result in similar changes within diatom assemblages of this perennial river? Because, it has been already demonstrated that resilience and resistance of assemblages may vary depending on whether the drought occurs regularly or only occasionally. Our results demonstrated that one-off dry events hardly affected either assemblages’ composition or biodiversity. In contrast, continuously decreasing precipitation (drying period) had a pronounced effect on taxa and trait distribution and resulted in a significant decrease in taxonomic diversity and in functional richness. It is important to stress that the observed deteriorating diversity anticipates that a lasting drought period is likely to upset the ecological balance of the ecosystem and lead to remarkable natural damage. Since the climate scenarios project extremes in water regime in the near future, including longer periods of low precipitation, any knowledge that predicts changes in microflora can help to develop action plans by authorities to save lotic ecosystems.

Keywords

• Climate change
• Compositional alterations
• Ecological status
• One-off dry events
• Trend-like changes