How much groundwater can we pump and protect environmental flows through time? Presumptive standards for conjunctive management of aquifers and rivers

Abstract

Groundwater is a critically important source of water for river, wetland, lake, and terrestrial ecosystems, yet most frameworks for assessing environmental flows have ignored or not explicitly included the potential impacts of groundwater pumping on environmental flows.After assessing the processes and existing policies for protecting streamflow depletion from groundwater pumping, we argue that a new groundwater presumptive standard is critical as a placeholder to protect environmental flows in rivers lacking detailed assessments. We thus extend the previous presumptive standard to groundwater pumping, a different and important driver of changes to streamflow. We suggest that "high levels of ecological protection will be provided if groundwater pumping decreases monthly natural baseflow by less than 10% through time." The presumptive standard is intended to be a critical placeholder only where detailed scientific assessments of environmental flow needs cannot be undertaken in the near term. We also suggest a new metric, the environmental flow response time, that allows water managers to quantify the timescales of the impacts of groundwater pumping on the loss or gain of environmental flows.

Habitat‐specific invertebrate responses to hydrological variability, anthropogenic flow alterations, and hydraulic conditions

“…effluent water returns) hydrological changes. There is a paucity of information on how groundwater abstraction influences riverine ecosystems globally (Gleeson & Richter, ; Poff & Zimmerman, ). Given that groundwater abstraction practices are increasingly and severely depleting subsurface water resources (Gleeson, Wada, Bierkens, & van Beek, ) and substantially reducing river discharges globally (De Graaf et al., ), studies such as this are vital for guiding e‐flow science and sustainable groundwater management operations.…”

“…Flow regime variability is widely recognised as a primary factor shaping riverine ecosystems (Ledger & Milner, ; Monk et al., ; Poff, ; Thompson, King, Kingsford, Mac Nally, & Poff, ). However, land use changes (Chadwick et al., ; López‐Moreno et al., ) and water resource management practices have profoundly altered river flow regimes (De Graaf, Van Beek, Wada, & Bierkens, ; Gleeson & Richter, ; Lehner et al., ), significantly threatening the integrity of lotic ecosystems globally (Bunn & Arthington, ; Poff et al., ; Vörösmarty et al., ). For example, groundwater abstraction substantially reduces river discharges worldwide (De Graaf et al., ) and profoundly alters lotic ecosystems (Bradley, Streetly, Farren, Cadman, & Banham, ; Bradley et al., ; Kennen, Riskin, & Charles, ).…”

The Brisbane Declaration and Global Action Agenda on Environmental Flows (2018)

“…These include aquifer and cave systems; "ecosystems fully or partly dependent on the surface expression of groundwater including wetlands, lakes, seeps, springs, river baseflow, coastal areas, estuaries, and marine ecosystems"; and "ecosystems dependent on subsurface presence of groundwater (via the capillary fringe), including terrestrial vegetation that depends on groundwater fully or on an irregular basis to meet water requirements." Environmental flow management must address the lotic, lentic and groundwater phases of all freshwater-dependent aquatic ecosystems, including their riparian and basin surroundings, to sustain their ecological integrity, ecosystem services and societal values (Bunn, 2016;Datry et al, 2017;Gleeson and Richter, 2017;Horne et al, 2017c;Kennen et al, 2018). To achieve a more integrated approach that considers the water requirements of inter-connected surface and GDEs will be one of the next grand challenges of environmental flows science and management.…”

Recent advances in environmental flows science and water management—Innovation in the Anthropocene

“…More attention, improved assessment methods, modelling and ecological response monitoring are needed to integrate groundwater‐dependent ecosystems into environmental flows assessment and management (e.g. Arthington, ; Eamus & Froend, ; Gleeson & Richter, ; Richardson et al., ). Quantify/predict the interaction between hydrology, sedimentary processes, geomorphology, hydraulics, temperature and ecological variables: Improved understanding of these interactions will help parse out the degree to which flow variability and management are the main drivers of ecological change, and how each affects physical elements (e.g. sediment, temperature) that in turn shape habitat, biological communities and ecosystem processes (e.g.…”

“…This section outlines themes where advances in management tools and approaches could be accomplished: Include additional waterbody types in water allocation strategies: Relatively, little work has been carried out on the water requirements of lentic waterbodies, wetlands, groundwater‐dependent ecosystems and coastal systems, even though these may be particularly impacted by hydrologic alteration (e.g. Arthington, ; Gleeson & Richter, ). Expanding the scope of environmental watering beyond flowing waters has generated debate around terminology.…”