Hydrological intermittency drives diversity decline and functional homogenization in benthic diatom communities

Area of Science:

• Ecology
• Hydrology
• Environmental Science

Background:

• Mediterranean rivers face increasing hydrological alterations and habitat fragmentation due to climate change and land use.
• Benthic communities, particularly diatoms, are sensitive indicators of these environmental shifts.
• Flow intermittency is a key factor exacerbated by these changes, impacting riverine ecosystems.

Purpose of the Study:

• To investigate the impact of flow intermittency on benthic diatom communities in Mediterranean streams.
• To compare diatom diversity and functional traits in perennial versus intermittent river sections.
• To understand the role of climate and land use in driving flow intermittency and its ecological consequences.

Main Methods:

• Analysis of 11 years of data from perennial and intermittent stream reaches in NW Italy.
• Exclusion of sites with poor or bad water quality to isolate hydrological effects.
• Comparison of climatic variables, land use patterns, and diatom community metrics (taxonomic and functional).

Main Results:

• Intermittent sites exhibited higher temperatures, lower precipitation, and more extensive human land use compared to perennial sites.
• Flow intermittency led to a significant decline in diatom species diversity at both local and regional scales.
• Diatom communities in intermittent reaches were taxonomically and functionally less diverse, dominated by small, pioneer taxa, unlike the larger, stable-forming taxa in perennial reaches.

Conclusions:

• Hydrological alterations, particularly flow intermittency, pose a significant threat to Mediterranean stream biodiversity.
• Diatom communities show distinct taxonomic and functional differences between perennial and intermittent conditions.
• These findings are crucial for developing improved biological indices for assessing intermittent river health.