From science to action: environmental flows for estuary restoration

Global climate change creates the urgency for sustainable resource use such as the wise management of freshwater resources. One of the primary drivers of modification or deterioration of estuarine ecosystems, especially in arid and semi-arid countries is freshwater flow reduction. The determination and implementation of environmental flows (E-Flows) has been informed by studies on the freshwater inflow requirements of estuaries and responses of estuaries to upstream dam releases. The quality, quantity and timing of freshwater inputs is identified to improve the health of estuaries to ensure the delivery of multiple ecosystem services to society. To facilitate improved implementation of E-Flow restoration, a Socio-Ecological management framework has been used to link ecological health to societal benefits and ensure source-to-sea connectivity. While restoration needs in estuaries are certainly not limited to E-Flows, adequate freshwater inputs are critical to the long-term effectiveness of most other restoration efforts, such as habitat restoration. Freshwater inflow maintains critical abiotic processes such as hydrological connectivity, in situ circulation and sediment transport. The prioritisation of estuaries for E-Flow restoration, underpins blue carbon ecosystem restoration, as for example salt marsh productivity relies on hydrological connectivity with the sea to ensure tidal exchange and the rewetting of dry or saline habitats. Despite progress in E-Flow determination and prioritisation, implementation of environmental flows is still lacking. Some global case studies are described where science has informed actions such as freshwater releases from dams to improve estuary health and downstream societal benefits. Freshwater releases have been used to keep the estuary mouth open to the sea, ensured mixing and provided recruitment pulses to the marine environment for invertebrates and fish.  Challenges associated with the implementation of E-Flow restoration include political will and a willingness to address past overallocation and illegal catchment activities; addressing this will be critical to ensure future resilience and estuary health. Climate change also results in implementation challenges, as this has created a shifting climatic and rainfall baseline with ripple effects in freshwater use and delivery to estuaries. These changes affect the state of estuaries after restoration, and will require revised management practices, especially a “learning-by-doing” approach.