Least Disturbed Condition for European Mediterranean rivers.

Area of Science:

• Environmental Science
• Ecology
• Hydrology

Background:

• Mediterranean streams face diverse pressures including pollution and habitat alteration.
• Defining a 'Least Disturbed Condition' is crucial for ecological assessment and water management.
• Previous assessments lacked standardized thresholds for Mediterranean stream types.

Purpose of the Study:

• To characterize and define thresholds for the Least Disturbed Condition in Mediterranean streams.
• To assess impacts of organic pollution, nutrients, hydrological and morphological alterations, and land use.
• To establish reference conditions for aquatic ecosystem health in the Mediterranean region.

Main Methods:

• A three-step approach was employed using a database of 929 reference sites from seven countries.
• Invertebrates, diatoms, and macrophytes were sampled to assess biological communities.
• Statistical analyses identified stressors and defined thresholds for water quality and habitat variables.

Main Results:

• Small streams (<100 km²) were impacted by channelization, bank alteration, and hydropeaking.
• Medium-sized siliceous rivers showed widespread alterations (25-43%) in morphology and riparian vegetation.
• Temporary streams exhibited lower dissolved oxygen (DO) thresholds but were less affected by hydromorphological changes.

Conclusions:

• Thresholds for organic pollution, nutrients, and land use were established for different Mediterranean stream types.
• Distinct biological community groups (invertebrates, diatoms, macrophytes) were identified, each with indicator taxa.
• The study provides a framework for assessing the ecological status of Mediterranean streams and managing water resources.