Groundwater & rewilding: the hidden foundation of ecological recovery

Groundwater-dependent ecosystems (GDEs) are ecosystems that rely on access to groundwater to maintain their ecological structure and function. Understanding them is essential to successful rewilding: surface restoration projects fail when the underlying groundwater system is compromised. They fall into three broad categories (Eamus et al., 2006; Springer Nature, 2016):

• Aquifer and cave ecosystems: where stygofauna (specialised subterranean invertebrates) live permanently in groundwater within rock pores, fractures, and cave systems. These are among the most isolated and evolutionarily distinct communities on Earth.
• Surface expression ecosystems: rivers, streams, springs, wetlands, and fens that depend on groundwater discharge for their baseflow, especially during dry periods. Remove the groundwater and the river stops flowing; the wetland dries out.
• Terrestrial vegetation ecosystems: phreatophytic plants (deep-rooted species like cottonwood, willow, and some oaks) that draw water directly from the water table via their root systems, particularly in arid and semi-arid landscapes.

These three categories are not independent. Groundwater discharge sustains river flow, supports riparian and wetland communities, feeds springs and seeps, and maintains the moisture conditions that terrestrial vegetation depends on (Boulton & Hancock, 2006; McCarthy, 2006). Degrade the groundwater system and surface ecosystems unravel from below.

Source: Gleeson et al. (2015), cited in groundwaterecology.wordpress.com; Boulton et al., Invertebrate Systematics.

Stygofauna, named from the Greek Styx, the river forming the boundary between Earth and the underworld, are invertebrates that live exclusively in groundwater or aquifers. They include copepods, ostracods, amphipods, isopods, syncarids, oligochaetes, nematodes, and molluscs, ranging from 0.05 to 5 mm in size (Gibert et al., 1994).

These organisms are not ecological curiosities. They perform critical ecosystem services within aquifers:

• Water purification: stygofauna graze biofilms, preventing overgrowth and sediment clogging that would reduce water infiltration and quality.
• Carbon and nutrient cycling: stygofauna and associated microbes influence carbon cycling and nutrient processing within aquifer systems (Hose & Stumpp, 2019; Saccò et al., 2022).
• Pathogen removal: microbial communities associated with stygofauna contribute to natural pathogen removal, supporting water quality for surface users.
• Groundwater quality indicators: the ratio of stygobite (groundwater-specialist) to non-specialist species is used as a reliable indicator of aquifer health and contamination status.

Stygofauna communities are characterised by high local endemism, with many species found in one aquifer and nowhere else on Earth. Many have slow reproductive rates making them highly vulnerable to groundwater depletion and contamination. Once lost from an aquifer, they are unlikely to recolonise.

Sources: Boulton et al., Invertebrate Systematics; Saccò et al., Freshwater Biology (2022). onlinelibrary.wiley.com →

Surface rewilding projects, such as wetland restoration, river recovery, and riparian woodland planting, are far more likely to succeed when the underlying groundwater system is intact or being restored alongside them.

Springs and seeps

Springs are points where groundwater discharges to the surface, creating some of the most biodiverse and stable habitats in any landscape. Spring-fed streams maintain constant temperatures year-round, providing critical habitat for cold-water fish, amphibians, and invertebrates during drought. Spring habitats are disproportionately important to biodiversity relative to their area.

Fens, one of the most threatened wetland types in Britain and Europe, depend entirely on the throughflow of springs and groundwater. Drain the aquifer and the fen disappears; restore the groundwater and the fen can recover.

Source: Rewilding Britain. Restoring Wetlands. rewildingbritain.org.uk →

River baseflow and drought resilience

In arid, semi-arid, and Mediterranean climates, groundwater discharge provides the dry-weather baseflow that keeps rivers running between rainfall events. Without it, perennial rivers become ephemeral, and the aquatic communities they support collapse.

Wet meadow and floodplain restoration projects that restore groundwater connectivity consistently show increased downstream baseflow. A restoration project on Cottonwood Creek in California's Plumas National Forest increased baseflow below the restored reach and reduced maximum stream temperatures by more than 3°C, critical for cold-water fish populations.

Source: Frontiers in Environmental Science (2025). Wet meadow regeneration through restoration of biophysical feedbacks. doi.org/10.3389/fenvs.2025.1592036 →

Wetlands and peatlands

Wetland rewilding is fundamentally a groundwater restoration exercise. The health and species richness of any wetland is determined by its water source, whether spring water, groundwater, rainwater, or surface runoff, and restoring natural hydrological processes is the prerequisite for ecological recovery.

Aquifers regulate flooding by absorbing and storing runoff, releasing it slowly to surface systems. Peatlands, which depend on sustained high water tables, act as both groundwater regulators and carbon stores, functions that are destroyed when drainage lowers the water table and can only be recovered by restoring groundwater levels.

Sources: Rewilding Britain. Restoring Wetlands; IGRAC Groundwater-Dependent Ecosystems (2026). un-igrac.org →

Groundwater systems face several well-documented threats that directly undermine rewilding efforts:

• Over-extraction: pumping groundwater faster than aquifers recharge lowers water tables, dries springs, reduces river baseflow, and destroys stygofaunal habitat. This is the primary threat to groundwater-dependent ecosystems globally.
• Agricultural contamination: nitrogen, pesticides, and pathogens from agriculture infiltrate aquifers, altering water chemistry and disrupting stygofaunal communities that have no tolerance for contamination.
• Drainage and urbanisation: field drainage ditches, stream channelisation, and urban impermeable surfaces reduce groundwater recharge and disconnect surface water from aquifer systems.
• Climate change: altered rainfall patterns reduce recharge, while rising temperatures increase evaporation and water demand. Coastal aquifers face saline intrusion as sea levels rise (IGRAC, 2026).
• Mining and dewatering: mine drainage disrupts groundwater stratification and can contaminate aquifers, destroying cave and subterranean ecosystems that cannot recover once species are lost (Springer Nature, 2016).
• Data centers and digital infrastructure: the rapid expansion of large-scale data centers poses a direct threat to groundwater systems, particularly in water-stressed regions. Data centers require enormous volumes of water for cooling; a single hyperscale facility can consume millions of gallons per day, drawing heavily on local aquifers already under extraction pressure. Construction of data center campuses replaces permeable land with impermeable surfaces including buildings, parking, and roads, dramatically reducing groundwater recharge. In karst landscapes, even localised impermeable cover over recharge zones can have outsized impacts on aquifer levels.

A sinkhole near San Marcos, Texas. Features like this are direct recharge points into the aquifer below, and exactly what impermeable development paves over.

Sources: Springer Nature: Groundwater Dependent Ecosystems: Classification, Identification Techniques and Threats (2016). link.springer.com → IGRAC Groundwater-Dependent Ecosystems (2026). un-igrac.org →

Groundwater restoration is an integral part of landscape rewilding, not a separate discipline. Key approaches include:

• Reducing pumping: the most direct intervention. Reducing groundwater pumping allows water tables to recover, springs to reflow, and surface-groundwater connectivity to re-establish.
• Blocking drainage ditches: raising water tables in drained peatlands and wet meadows by blocking field drains is one of the most effective and lowest-cost rewilding interventions available. It restores groundwater recharge, increases carbon storage, and initiates wetland recovery.
• Beaver reintroduction: beaver dams raise local water tables, recharge shallow aquifers, and restore groundwater connectivity with floodplains. This is one of the most ecologically efficient groundwater restoration tools available, delivered by a single species.
• Floodplain reconnection: removing embankments and allowing rivers to reconnect with their floodplains restores hyporheic exchange (water movement between river and groundwater), recharging aquifers and improving water quality.
• Reducing agricultural contamination: buffer strips, cover crops, and reduced fertiliser use lower nitrate and pesticide infiltration, protecting aquifer water quality and the stygofaunal communities that depend on it.
• Protected area designation for aquifers: several countries are beginning to designate groundwater bodies and cave systems as protected areas in their own right, recognising their biodiversity value independently of their water supply function.

Karst landscapes, formed from soluble rocks such as limestone and dolomite, are among the most groundwater-dependent ecosystems on Earth. Rainwater dissolves rock over millennia to create cave systems, sinkholes, underground rivers, and springs that function as both biodiversity habitats and water supply infrastructure for millions of people.

Cave ecosystems are entirely dependent on groundwater quality and flow. They support communities of stygofauna, cave fish, salamanders, and microbial mats found nowhere else, often with extremely limited ranges, sometimes restricted to a single aquifer or cave system. The loss of groundwater quality or quantity in a karst system can cause irreversible biodiversity loss within it.

Ezell's Cave, San Marcos. One of only a handful of known sites for the critically endangered, fully aquatic Texas blind salamander, found nowhere else on Earth.