Although occupying only approximately 0.3% of the total surface area of Arizona (U.S. Census Bureau 2010), aquatic systems play an outsized role in supporting the biodiversity of our state’s flora and fauna. Many of Arizona’s SGCN are only found in aquatic systems while many more species utilize the associated riparian areas during at least a portion of their life cycle (Ffolliot et al. 2004; Zaines 2007).
Aquatic systems are bodies of water that support water-dependent communities of plants and animals. These systems occur as rivers and streams, ponds and lakes, wetlands and springs. Aquatic systems are home to fishes, many invertebrates, some mammals (e.g., beaver and muskrat), amphibians and reptiles, waterbirds, algas and aquatic plants. These systems also act as important habitat for early life stages of amphibians and many insects. Arizona’s aquatic systems support 34 native fish species and numerous non-native fishes including sport fish. Depending on life stage and species, these fishes play multiple roles in the aquatic food web (Bunn et al. 2007). Meanwhile, sport fish support recreational opportunities while contributing to local economies throughout the state. Aquatic invertebrates are important parts of the food web, and are eaten by predatory invertebrates, fishes, amphibians, birds, and even a few mammals. Those species that metamorphose into winged adults are important food sources for a variety of birds, bats, and other wildlife. A wide variety of Arizona’s wildlife utilize aquatic systems for water sources, and many plants would not exist without this surface or subsurface water source. The AWCS identifies four main categories of aquatic systems in Arizona:
Lentic and Lotic Systems
Lentic systems are areas that possess stationary surface water, such as a lake or pond. Lotic systems have flowing surface water, such as a river or stream (Zaimes et al. 2007). In Arizona, lotic systems can be perennial (surface water present year-round), intermittent (surface water present seasonally), or ephemeral (surface water present only following precipitation events). Both lentic and lotic systems possess unique hydrologic regimes as well as hosting communities of plants and animals. See the lentic and lotic systems habitat profiles for more details.
Wetlands are areas where frequent and prolonged presence of water at or near the surface, creates an ecosystem with unique hydrology and soil composition as well as an obligate community of plants and wildlife species. We separated wetlands from lentic systems to focus attention on them. In Arizona, wetlands include ciénegas (marshes) as well as ephemeral and intermittent pools, sites that hold water seasonally (e.g., after snow melt) or only following rain events. Wetlands, whether perennial or intermittent, provide water for all wildlife and important habitat for migrating waterfowl as well as some species of amphibians, reptiles, and invertebrates (Minckely et al. 2013). These increasingly rare wetland habitats also support riparian vegetation which is often more diverse and lush than surrounding vegetation. See the wetlands habitat profile for more details.
Springs are points at which a groundwater aquifer intersects the surface (Stevens et al. 2016). A spring might flow continuously or respond to precipitation events, and can range from simple seeps to flows of thousands of gallons each day. Spring ecosystems typically have shallow flowing water with flora and fauna quite distinct from the surrounding terrestrial environment. They often play an important role in arid environments, providing a critical source of water not only for plants and animals, but for humans as well. Arizona has more than 10,200 mapped springs, but many have been degraded and reduced due to groundwater pumping, diversion, livestock and wildlife grazing, development, and invasive species (SSI 2020). Extended drought and climate change threaten the remaining functional spring ecosystems. See the springs habitat profile for more details.
Riparian Areas and Aquatic Systems
Riparian areas are terrestrial habitats that are closely associated with aquatic systems and play a critical role in supporting a large portion of Arizona’s wildlife. Riparian areas are defined as vegetation, habitats, or ecosystems that are associated with bodies of water (streams or lakes) or are dependent on the existence of perennial, intermittent, or ephemeral surface or subsurface water drainage (Arizona Riparian Council 1994). Riparian areas serve as transition zones between aquatic ecosystems and the surrounding upland terrestrial environment.
Riparian areas exist within all major terrestrial habitat types in Arizona, however vegetation composition and structure varies based on region, elevation, climatic conditions, flow patterns, and water levels and quality. Common tree species in riparian areas include: Fremont cottonwood, Goodding’s willow, Arizona sycamore, velvet ash, Arizona walnut, red willow, Arizona alder, boxelder, and mesquite. Rushes, sedges, and cattails are a few of the common herbaceous plants found in the riparian zone. Non-native species like salt cedar and Russian olive tree have invaded many of the lower-elevation riparian areas in Arizona, oftentimes at the expense of native species.
Riparian areas provide essential habitats for wildlife and are also some of the most degraded, altered, and threatened habitats in Arizona (Stomberg and Tellman 2009). Because of the high moisture content of riparian areas, vegetation and wildlife abundance and diversity is exceedingly high within and directly adjacent to these habitats (Levick et al. 2008). Up to 80% percent of Arizona wildlife species are dependent on riparian areas for breeding, migration, shelter, and seasonal forage during some part of their life cycle (Chaney et al. 1990). Wildlife also rely on riparian areas for a dependable water source. Many species unique to the Southwest rely solely on riparian areas for breeding, including the endangered southwestern willow flycatcher, the threatened western yellow-billed cuckoo, and Mexican gartersnake. Other SGCN of note include gray hawk, common black hawk, and white-nosed coati. Game species such as Gambel’s quail, mule deer, and javelina also rely on riparian areas.
Whether endangered or common, game species or not, many of Arizona’s wildlife rely on riparian areas to facilitate movement from habitat to habitat (Zaines 2007). From dry washes to flowing rivers, these riparian areas act as wildlife corridors — the landscape linkages which provide habitats and allow for species to safely move from habitat to habitat throughout the year as conditions change. Riparian areas act as important linkages in the landscape to facilitate daily, seasonal, and annual movements of individuals and populations of species. Keeping these connections intact ensures the long-term viability of all wildlife species, as well as plants, by promoting genetic exchange between individuals and populations.
Water resources throughout the state are currently over-allocated such that conflicts are increasing between societal needs and maintenance of functioning ecosystems (ADWR 2018; Tiller et al. 2012). Active land and water management planning is critical to accommodating the anticipated human population growth while maintaining biological diversity. Thankfully, these richly diverse and extremely valuable areas are a primary focus of much of the conservation and restoration efforts by agencies, organizations, and private landowners throughout the state. These partners all help monitor, conserve, restore, and protect riparian areas and aquatic systems in Arizona. Here are just a few examples:
TNC, ADEQ, BLM, and Pima County annually monitor the wet-dry extent (wet-dry mapping) of stream courses. This information can be used to track the effects of natural processes and human impacts of surface water in streams.
The Arizona Land and Water Trust launched its Desert Rivers and Riparian Heritage Initiative to develop and implement water stewardship tools that will sustain the rural livelihoods and riparian habitats that enrich Arizona’s natural and cultural landscapes.
Pima County protects riparian habitat for future generations by ensuring the long-term stability of natural floodplains, allowing for the survival of native plants and animals, while also helping to maintain the area’s quality of life for County residents.
Nonprofit organizations, such as Arizona Riparian Council and Verde Watershed Restoration Coalition, and others, provide for the exchange of information on the status, protection, and management of riparian systems in Arizona. Membership is open to any person or organization interested in the conservation, restoration, or scientific study of riparian systems.
The Spring Stewardship Institute (SSI) was established in 2013 through the Museum of Northern Arizona to improve our collective understanding of spring ecology and to increase stewardship of these valuable and vulnerable resources. In addition to a central hub and collaboration platform for sharing information on springs and spring ecosystems, SSI developed a searchable database to make this information easily accessible for researchers and land managers.
These partnerships and collaborations are guided by dedicated staff and organizations that have been instrumental in conserving and protecting these valuable resources. However, aquatic and riparian systems have been and continue to be highly impacted and altered by diversion, impoundment, dewatering, erosion, sedimentation, non-native and invasive species, and prolonged drought. These, and many other challenges facing Arizona’s wildlife and habitats, are summarized in Chapter 3: Conservation Challenges of the AWCS. Specific threats facing riparian areas and aquatic systems — along with conservation actions — can be found in the individual habitat profiles for lentic, lotic, wetland, and spring systems found in Chapter 8: Threats and Conservation Actions.