Coupled reservoir-river systems: Lessons from an integrated aquatic ecosystem assessment

Area of Science:

• Environmental Science
• Ecosystem Management
• Water Resource Engineering

Background:

• Sustainable reservoir-river management necessitates balancing human water demands with ecological health.
• Existing models optimize for human uses but often neglect ecosystem dynamics.
• Assessing ecosystem responses to reservoir operations and climate is crucial for integrated management.

Purpose of the Study:

• To develop and demonstrate an ecosystem assessment approach for coupled reservoir-river systems.
• To evaluate the impact of reservoir operations and climatic forcing on aquatic ecosystems.
• To explore reservoir operational flexibility for improving ecosystem function.

Main Methods:

• A ten-year study employing a series of numerical, statistical, and empirical models.
• Linking environmental processes to ecosystem responses within a headwater reservoir-river system.
• Analyzing seasonal biogeochemical changes to inform environmental flow releases.

Main Results:

• Reservoir management can enhance ecological function under specific climatic conditions.
• High post-irrigation releases in dry years increased downstream primary (99%) and macroinvertebrate (45%) production.
• These releases reduced reservoir fish biomass by 16%, highlighting ecosystem trade-offs.
• Low winter flows supported conditions for downstream river ice cover, benefiting ecosystem function.

Conclusions:

• Understanding seasonal reservoir biogeochemistry is critical for effective environmental flow management.
• Reservoir operational flexibility can improve aquatic ecosystem health, despite management trade-offs.
• The ecosystem assessment approach supports transparent decision-making and environmental policy development.