Hypoxic events in freshwater ecosystems: A literature review to inform regional management and policy

Dissolved oxygen (DO) is a master variable that fundamentally controls the ecological quality of freshwaters and their associated capacity to support aquatic life, potable water uses, and cultural values.

The perennial or periodic occurrence of low DO concentrations (hypoxia) or complete depletion of DO (anoxia) is a natural feature of some aquatic ecosystems such as wetlands. However, anthropogenically mediated increases to the magnitude, frequency, duration, and spatial extent of hypoxia in aquatic ecosystems such as lakes and rivers can have major adverse ecological effects, including fish kills.

Developing effective tools and strategies to manage hypoxia in the region’s freshwaters has been identified as a priority by Waikato Regional Council.

This literature review considers causes, effects, forecasting approaches, and mitigation of hypoxia in lakes, streams, and rivers worldwide to inform regional policy and management by synthesising lessons from elsewhere in the context of the Waikato.