Hypersaline mining effluents affect the structure and function of stream biofilm

Area of Science:

• Environmental Science
• Ecotoxicology
• Freshwater Ecology

Background:

• Salinization of freshwater ecosystems is a growing global concern.
• Mining effluents contribute significantly to increased salinity levels.
• Freshwater biofilms are crucial for ecosystem functioning.

Purpose of the Study:

• To assess the impact of a realistic salinity gradient on freshwater biofilm structure and function.
• To determine salt threshold concentrations affecting algal cells.
• To understand biofilm adaptation to salinity stress.

Main Methods:

• Biofilm from a pristine stream was exposed to five increasing salinities (3-100 g L⁻¹) in artificial streams for 21 days.
• Functional responses (photosynthetic efficiency, nutrient uptake, respiration) and structural responses (community composition, biomass) were evaluated.
• Pollution-Induced Community Tolerance (PICT) was measured.

Main Results:

• Biofilm functionality decreased significantly in the short-term, while structure was impacted in the long-term.
• Community composition shifted towards more tolerant species.
• Salt concentrations between 15-30 g L⁻¹ substantially damaged algal cells, and PICT increased along the gradient.

Conclusions:

• Freshwater biofilms exhibit reduced functionality and altered structure under realistic salinity gradients.
• Community tolerance increases with salinity, indicating adaptation.
• The study provides critical data on salt thresholds impacting freshwater ecosystems.