Multiple stressor effects act primarily on microbial leaf decomposers in stream mesocosms

Area of Science:

• Ecology
• Environmental Science
• Freshwater Biology

Background:

• Global stream ecosystems face multiple anthropogenic stressors, including eutrophication, habitat degradation, and water scarcity.
• While effects of multiple stressors on stream biodiversity are known, their impact on ecosystem processes remains understudied.

Purpose of the Study:

• To investigate how combinations of reduced flow, increased nutrients, and fine sediment affect fungal and macroinvertebrate decomposers.
• To assess the influence of these stressors on leaf decomposition rates in stream ecosystems.

Main Methods:

• Conducted mesocosm (stream channel) and microcosm (feeding trial) experiments.
• Manipulated flow, nutrient concentrations, and fine sediment levels.
• Measured fungal biomass, species composition, and leaf decomposition rates; assessed macroinvertebrate feeding behavior.

Main Results:

• Increased fine sediment significantly reduced fungal biomass, aquatic hyphomycete species, and microbial leaf decomposition.
• Macroinvertebrate decomposition rates correlated with fungal biomass and community composition.
• Reduced flow and increased nutrients did not significantly impact decomposer communities or decomposition rates.

Conclusions:

• Fine sediment alters energy and material flux in the detrital food chain by regulating fungal decomposition (bottom-up control).
• Reduced leaf consumption by Gammarus pulex on sediment-affected leaf material highlights food web impacts.
• Mitigating fine sediment in streams is crucial for maintaining detrital food chain functioning.