Environmental flows for natural, hybrid, and novel riverine ecosystems in a changing world

Abstract

The term “environmental flows” describes the quantities, quality, and patterns of water flows required to sustain freshwater and estuarine ecosystems and the ecosystem services they provide. Environmental flows may be achieved in a number of different ways, most of which are based on either (1) limiting alterations from the natural flow baseline to maintain biodiversity and ecological integrity or (2) designing flow regimes to achieve specific ecological and ecosystem service outcomes. We argue that the former practice is more applicable to natural and semi‐natural rivers where the primary objective and opportunity is ecological conservation. The latter “designer” approach is better suited to modified and managed rivers where return to natural conditions is no longer feasible and the objective is to maximize natural capital as well as support economic growth, recreation, or cultural history. This permits elements of ecosystem design and adaptation to environmental change. In a future characterized by altered climates and intensive regulation, where hybrid and novel aquatic ecosystems predominate, the designer approach may be the only feasible option. This conclusion stems from a lack of natural ecosystems from which to draw analogs and the need to support broader socioeconomic benefits and valuable configurations of natural and social capital.

Research Priorities to Improve Future Environmental Water Outcomes

“…River ecosystems are influenced by a wide range of factors, including species interactions, temperature, and sediment dynamics, that may interact in numerous unspecified ways with flow alteration (Acreman et al, 2014). With much research still reliant on drawing patterns from uncontrolled changes in flow conditions during floods or droughts, a major challenge is to undertake controlled water management experiments at the catchment scale (Konrad et al, 2011;Olden et al, 2014).…”

“…Hybrid and novel ecosystems are likely to be created (Acreman et al, 2014;Moyle, 2014;Laizé et al, 2017). An understanding of ecological thresholds and resilience will become increasingly important as climate change further impacts river flow regimes and ecosystems (Rockström et al, 2014).…”

“…As climate change continues to impact upon water availability, major policy discussions will be required to consider how changes in resource availability are to be distributed amongst water users, and what changes may be required to river basin objectives (Acreman et al, 2014). Integration of environmental water consideration into existing consumptive water management activities requires new tools, skills and governance arrangements for water management institutions.…”

“…Continued population growth and changing life styles, coupled with climate change, will only increase competition for scarce water resources in many regions in the future, with commensurate increases in the threats to aquatic ecosystems (Meyer et al, 1999;Poff et al, 2002), and in some cases significantly modifying current river ecosystems and generating hybrid and novel systems (Acreman et al, 2014;Laizé et al, 2017). Environmental water management aims to respond to these threats by both protecting and where necessary restoring flow regimes to support aquatic ecosystem function and biodiversity (Meyer et al, 1999;Poff et al, 2002).…”

“…Environmental flow assessment methods are now cognizant of stakeholder participation and co-design, and recognize the dual role of environmental water in supporting ecological and social values, especially for those who rely on rivers and floodplains to support their livelihood (King and Brown, 2010;Finn and Jackson, 2011). Second, there has been significant progress in our understanding of the scientific concepts and ecological processes that underpin environmental flows Horne et al, 2010;Arthington, 2012;Acreman et al, 2014), and third, environmental water requirements have now been discussed and incorporated into high-level water policy and legislation in many countries across the globe (Hirji and Davis, 2009;Le Quesne et al, 2010;O'Donnell, 2014). This latter development is reflected in the growing number of government agencies and non-government entities funding environmental water projects (Garrick et al, 2011;Pahl-Wostl et al, 2013), and the large sums expended on river flow restoration projects.…”