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Springs ecosystems are globally abundant, geomorphologically diverse, and bioculturally productive, but are highly imperiled by anthropogenic activities. More than a century of scientific discussion about the wide array of ecohydrological factors influencing springs has been informative, but has yielded little agreement on their classification. This lack of agreement has contributed to the global neglect and degradation of springs ecosystems by the public, scientific, and management communities. Here we review the historical literature on springs classification variables, concluding that site-specific source geomorphology remains the most diagnostic approach. We present a conceptual springs ecosystem model that clarifies the central role of geomorphology in springs ecosystem development, function, and typology. We present an illustrated dichotomous key to terrestrial (non-marine) springs ecosystem types and subtypes, and describe those types. We identify representative reference sites, although data limitations presently preclude selection of continentally or globally representative reference springs of each type. We tested the classification key using data from 244 randomly selected springs of 13 types that were inventoried in western North America. The dichotomous key correctly identified springs type in 87.5% of the cases, with discrepancies primarily due to differentiation of primary vs. secondary typology, and insufficient inventory team training. Using that information, we identified sources of confusion and clarified the key. Among the types that required more detailed explanation were hypocrenes, springs in which groundwater is expressed through phreatophytic vegetation. Overall, springs biodiversity and ecosystem complexity are due, in part, to the co-occurrence of multiple intra-springs microhabitats. We describe microhabitats that are commonly associated with different springs types, reporting at least 13 microhabitats, each of which can support discrete biotic assemblages. Interdisciplinary agreement on basic classification is needed to enhance scientific understanding and stewardship of springs ecosystems, the loss and degradation of which constitute a global conservation crisis.

Introduction: While the biodiversity value of springs is recognised, it has not been systematically compiled. The aim of the current study is to highlight the extraordinary endemism associated with the isolated habitat of arid-land springs at three locations in two continents. Methods: The habitat endemism of the eukaryote species associated with the aquatic and terrestrial habitats at Ash Meadows in the USA, Byarri in Australia and Cuatro Ciénegas in Mexico was assembled based on their geographic distribution. Results: The currently-known aquatic and semi-aquatic endemic species number 27 at Ash Meadows, 31 at Byarri and 34 at Cuatro Ciénegas. Terrestrial endemic species are represented by two species at Ash Meadows, five at Byarri and 26 at Cuatro Ciénegas. The terrestrial endemics are associated with the scalded areas surrounding the springs impregnated with soda and gypsum. The persistence of the endemics is astonishing given that the wetlands represent tiny islands of habitat (216 small wetlands over 40 km 2 in the case of Byarri). Discussion: A key factor for the persistence and radiation of endemic species is the stability and permanence of the wetlands over evolutionary time-scales. Genetic evidence indicates the presence of both paleo-endemics, species that persisted in spring wetlands as relics of previous mesic climates; and neo-endemics that have dispersed from more mesic environments and subsequently radiated in the spring wetlands as distinct forms. The former evolved from their relatives greater than 106 ya and the latter less than 106 ya. The concentration of endemic species in and around arid-land springs is among the highest concentrations of endemic organisms specialised to a particular habitat and substantiates the paramount conservation significance of desert springs.

We describe a new springsnail species, Pyrgulopsis hualapaiensis, from the Lower Colorado River basin (northwestern Arizona) that has an ovate- to narrow-conic shell and narrow penis ornamented with a small gland on the distal edge of the lobe. This new species differs from closely similar congeners from the Lower Colorado River basin in several details of female reproductive anatomy and in its mtCOI haplotype (3.0%–5.0% mean sequence divergence). Bayesian, maximum parsimony, and distance-based phylogenetic analyses of COI data congruently resolved P. hualapaiensis as sister to a divergent lineage of Pyrgulopsis thompsoni in the middle Gila River watershed (southeastern Arizona), although this relationship was not well supported. Pyrgulopsis hualapaiensis is endemic to a spring complex in the Hualapai Indian Reservation that is a culturally sensitive site for the tribe. The small population of these snails appears to be robust despite recent habitat modifications (trenching of outflow and construction of a spring box) and disturbance from road traffic. Future conservation measures could include monitoring of the population and augmentation of the gravel habitat used by these snails.

Natural springs in water-limited landscapes are biodiversity hotspots and keystone ecosystems that have a disproportionate influence on surrounding landscapes despite their usually small size. Some springs served as evolutionary refugia during previous climate drying, supporting relict species in isolated habitats. Understanding whether springs will provide hydrologic refugia from future climate change is important to biodiversity conservation but is complicated by hydrologic variability among springs, data limitations, and multiple non-climate threats to groundwater-dependent ecosystems. We present a conceptual framework for categorizing springs as potentially stable, relative, or transient hydrologic refugia in a drying climate. Clues about the refugial capacity of springs can be assembled from various approaches, including citizen-science-powered ecohydrologic monitoring, remote sensing, landowner interviews, and environmental tracer analysis. Managers can integrate multiple lines of evidence to predict which springs may become future refugia for species of concern, strengthening the long-term effectiveness of their conservation and restoration, and informing climate adaptation for terrestrial and freshwater species.

In this overview (introductory article to a special issue including 14 papers), we consider all main types of natural and artificial inland freshwater habitas (fwh). For each type, we identify the main biodiversity patterns and ecological features, human impacts on the system and environmental issues, and discuss ways to use this information to improve stewardship. Examples of selected key biodiversity/ecological features (habitat type): narrow endemics, sensitive (groundwater and GDEs); crenobionts, LIHRes (springs); unidirectional flow, nutrient spiraling (streams); naturally turbid, floodplains, large-bodied species (large rivers); depth-variation in benthic communities (lakes); endemism and diversity (ancient lakes); threatened, sensitive species (oxbow lakes, SWE); diverse, reduced littoral (reservoirs); cold-adapted species (Boreal and Arctic fwh); endemism, depauperate (Antarctic fwh); flood pulse, intermittent wetlands, biggest river basins (tropical fwh); variable hydrologic regime—periods of drying, flash floods (arid-climate fwh). Selected impacts: eutrophication and other pollution, hydrologic modifications, overexploitation, habitat destruction, invasive species, salinization. Climate change is a threat multiplier, and it is important to quantify resistance, resilience, and recovery to assess the strategic role of the different types of freshwater ecosystems and their value for biodiversity conservation. Effective conservation solutions are dependent on an understanding of connectivity between different freshwater ecosystems (including related terrestrial, coastal and marine systems).

Although springs have been recognized as important, rare, and globally threatened ecosystems, there is as yet no consistent and comprehensive classification system or common lexicon for springs. In this paper, 12 spheres of discharge of springs are defined, sketched, displayed with photographs, and described relative to their hydrogeology of occurrence, and the microhabitats and ecosystems they support. A few of the spheres of discharge have been previously recognized and used by hydrogeologists for over 80 years, but others have only recently been defined geomorphologically. A comparison of these spheres of discharge to classification systems for wetlands, groundwater dependent ecosystems, karst hydrogeology, running waters, and other systems is provided. With a common lexicon for springs, hydrogeologists can provide more consistent guidance for springs ecosystem conservation, management, and restoration. As additional comprehensive inventories of the physical, biological, and cultural characteristics are conducted and analyzed, it will eventually be possible to associate spheres of discharge with discrete vegetation and aquatic invertebrate assemblages, and better understand the habitat requirements of rare or unique springs species. Given the elevated productivity and biodiversity of springs, and their highly threatened status, identification of geomorphic similarities among spring types is essential for conservation of these important ecosystems.

The Colorado River basin (CRB), the primary water source for southwestern North America, is divided into the 283,384 km2, water-exporting Upper CRB (UCRB) in the Colorado Plateau geologic province, and the 344,440 km2, water-receiving Lower CRB (LCRB) in the Basin and Range geologic province. Long-regarded as a snowmelt-fed river system, approximately half of the river’s baseflow is derived from groundwater, much of it through springs. CRB springs are important for biota, culture, and the economy, but are highly threatened by a wide array of anthropogenic factors. We used existing literature, available databases, and field data to synthesize information on the distribution, ecohydrology, biodiversity, status, and potential socio-economic impacts of 20,872 reported CRB springs in relation to permanent stream distribution, human population growth, and climate change. CRB springs are patchily distributed, with highest density in montane and cliff-dominated landscapes. Mapping data quality is highly variable and many springs remain undocumented. Most CRB springs-influenced habitats are small, with a highly variable mean area of 2200 m2, generating an estimated total springs habitat area of 45.4 km2 (0.007% of the total CRB land area). Median discharge also is generally low and variable (0.10 L/s, N = 1687, 95% CI = 0.04 L/s), but ranges up to 1800 L/s. Water pH and conductivity is negatively related to elevation, with a stronger negative relationship in the UCRB compared to the LCRB. Natural springs water temperature and geochemistry throughout the CRB varies greatly among springs, but relatively little within springs, and depends on aquifer hydrogeology, elevation, and residence time. As the only state nearly entirely included within the CRB, Arizona is about equally divided between the two geologic provinces. Arizona springs produce approximately 0.6 km3/year of water. Data on >330 CRB springs-dependent taxa (SDT) revealed at least 62 plant species; 216 aquatic and riparian Mollusca, Hemiptera, Coleoptera, and other invertebrate taxa; several herpetofanual species; and two-thirds of 35 CRB fish taxa. Springs vegetation structure, composition, and diversity vary strongly by springs type, and plant species density within springs is high in comparison with upland habitats. Plant species richness and density is negatively related to elevation below 2500 m. Human population in and adjacent to the CRB are growing rapidly, and ecological impairment of springs exceeds 70% in many landscapes, particularly in urbanized and rangeland areas. Anthropogenic stressors are primarily related to groundwater depletion and pollution, livestock management, flow abstraction, non-native species introduction, and recreation. Ensuring the ecological integrity and sustainability of CRB groundwater supplies and springs will require more thorough basic inventory, assessment, research, information management, and local ecosystem rehabilitation, as well as improved groundwater and springs conservation policy.

The Nevada and Utah Springsnail Conservation Strategy (the Strategy) is a comprehensive and proactive 10-year plan to protect 103 species of truncatelloidean springsnails and their habitats (primarily springs). Springsnails are tiny, aquatic, and often locally endemic truncatelloidea and cerithioidean snails threatened by both local and regional stressors. A bi-state agreement (the Agreement) was forged by state and federal agencies and The Nature Conservancy (TNC) in 2018 in a manner consistent with U.S. Fish and Wildlife Service (USFWS) conservation criteria. Successful achievement of Agreement objectives will protect springsnails and their habitats in the two states, precluding the need for a federal listing of those species. The objectives of the Agreement are to: (1) compile springsnail ecology and distribution data into a single database; (2) identify, assess, and reduce threats to the taxa and their habitats; (3) maintain, enhance, and restore spring habitats; (4) develop and maintain a springsnail conservation team (SCT); and (5) create an effective education and outreach program for landowners, agencies, and the general public. The SCT held in-person and multiple virtual meetings in 2019–2020 to initiate the Strategy, introduce and clarify member roles, and pursue the integration of available information. The SCT assembled information and literature on each taxon in the two states into the Springs Online database (springsdata.org), a password-protected, easily used online information management system for archiving and reporting on springs-dependent species taxonomy, distribution, associated species, and population and conservation status data. The information gathered was used to generate conservation reports for individual species that can be readily updated as new information emerges. Within each Agreement objective, we describe issues to ensure springsnail species representation, resiliency, and redundancy, which are USFWS metrics of population integrity. We describe springsnail diversity and distribution, the threats and challenges to effective springsnail conservation, and the process the SCT is using to address those issues. Development of the Strategy enables the SCT to monitor, prioritize, and readily report on springsnail conservation progress over the decadal life of the Agreement. As one of the largest springs and springs-dependent species conservation efforts in the world, the context and development of the Strategy provide key lessons for other such efforts.

Springs support some of the most diverse and unique ecosystems on Earth, but their stewardship has been hindered by the lack of knowledge of the distribution and density of springs across landscapes. Death Valley National Park (DEVA) and the State of Arizona in the USA are 2 landscapes for which significant knowledge exists about the distribution and density of springs. We used data on springs in DEVA to test the application of accumulation curves for estimating spring density. We used a spring-specific database in Arizona as an example of how to compile geospatial information for a large landscape. In both landscapes, springs are nonrandomly distributed because they emerge in topographically and geologically complex terrain and in clusters of multiple sources. Thus, estimates of their density depend on the spatial scale of inquiry and the extent to which sources are considered independent. For example, based on the current inventory, density in DEVA is estimated to be 0.033 to 0.074 springs/km² depending on whether springs are defined as individual orifices or as complexes (groups of related spring orifices). The best data for springs as individual orifices yield an estimated 0.035 springs/km² in Arizona. These densities are based on current data sets, and an unknown number of springs remain unmapped in both landscapes. To predict the total number of springs in DEVA, we used a modified density accumulation curve, involving the number of springs detected in surveys over the past century. The analysis indicated that undocumented springs may exist across the landscape. Knowledge of the distribution and density of the springs can help land and resource managers develop unbiased prioritizations of spring ecosystems for stewardship actions. Management actions could benefit further from an understanding of the emergence environment of a complex of springs, instead of each emergence point of a spring in a complex.

Ecosystem invasion by non-native plants depends on plant life history characteristics that influence the species’ invasiveness, as well as environmental factors that determine site invasibility. Small, insular ecosystems are thought be especially vulnerable to invasion but evidence for this pattern has been mixed. Freshwater springs form island-like ecosystems, allowing for a test of this proposal. Here, we investigated the effects of physical environmental factors, human disturbance, and plant life history traits on the occurrence of native and non-native plant species at 55 springs across different biomes in Alberta, Canada. A total of 526 plants were identified, 12.5% of which were non-native. Among these, species richness and abundance were greater at springs within biomes subject to increased land use intensity, especially livestock grazing, as compared to springs in parks and protected areas with limited land use. Subsequently, springs with higher human impact supported greater richness (r2 = 0.13) and abundance (r2 = 0.31) of non-native species, while native species abundance declined with increasing human impact (r2 = 0.14). Common native and non-native plant taxa exhibited life history traits that confer greater tolerance to human disturbance, such as that arising from livestock production that can disperse propagules, including clonal capacity and physical and chemical herbivory defenses. Our results indicated that springs ecosystems with greater human disturbance were more vulnerable to invasion by non-native plants, and this can reduce plant biodiversity and the ecological services provided by these distinctive, insular ecosystems.