Tributary-to-mainstem discontinuities (TMDs) are understudied, but are likely common in river networks, arising from abrupt transitions in stream order and dominant ecological factors. We present a conceptual model of aquatic macroinvertebrate (AMI) TMD directionality and relative magnitude by contrasting the impacts of hydrography, geochemistry, and sediment transport on tributary-related channel-floor precipitate cementation and the mainstream embeddedness (burial) of channel-floor substrata in fine sediment. We test that model using AMI assemblage density/m2, species richness/sample, and diversity data from 24 tributaries confluent with the regulated Colorado River in Grand Canyon through pairwise and multivariate analyses of long-term discharge records and substrate and water-quality data in three habitats: tributaries, their confluences, and adjacent mainstream habitats. Mean AMI density decreased 2.7-fold from low to high cementation, 6.1-fold from low-to-high embeddedness, and 136.0-fold across combined gradients. We also analyzed pre-dam aquatic insect literature, finding that TMDs were naturally common in Glen Canyon upstream but were more strongly tributary-positive (discontinuity magnitude, Dmag = 0.62 in pre-dam Glen Canyon) compared to tributaries in the post-dam Grand Canyon (Dmag = 0.31). We conclude that, depending on Dmag directionality, tributary confluences can function as hotspots or barriers to AMI assemblage development. Our results demonstrate that TMDs are and were common in the contemporary regulated and natural unregulated Colorado River corridor, and we expand the concept of biotic discontinuity to improve understanding of fluvial ecosystem ecology and constraints on river and dam management.

Oases are key to humanity’s settlement in drylands in the past, today, and in the future. They form complex geo-bio-cultural systems of pivotal importance. Present climatic, economic, and social changes may lead to the demise of tangible and intangible values in and of oases, potentially affecting 500 million people. We aim at raising awareness of the accelerating threat to oases and argue for immediate action to protect this unique system.

Cultures in Mediterranean climate zones (MCZs) around the world have long been reliant on groundwater and springs as freshwater sources. While their ecology and cultural sustainability are recognized as critically important, inter-relationships between springs and culture in MCZs have received less attention. Here we augmented a global literature review with case studies in MCZ cultural landscapes to examine the diversity and intensity of cultural and socio-economic relationships on spring ecohydrogeology. MCZs are often oriented on western and southern coasts in tectonically active landscapes which control aquifer structure, the prevalence of westerly winds, and aridity, and generally expose associated habitats and cultures to harsh afternoon sunlight. Cultural appreciation and appropriation of springs ranges widely, from their use as subsistence water supplies to their roles in profound traditions such as Greco-Roman nymphalea as well as Asian and Abrahamic spiritual cleansing and baptism. The abandonment of traditional ways of life, such as rural livestock production, for urban ones has shifted impacts on aquifers from local to regional groundwater exploitation. The commoditization of water resources for regional agricultural, industrial (e.g., mining, water bottling, geothermal resorts), and urban uses is placing ever-increasing unsustainable demands on aquifers and spring ecosystems. When the regional economic value of springs approaches or exceeds local cultural values, these irreplaceable aquatic ecosystems are often degraded, over-looked, and lost. Sustainable stewardship of springs and the aquifers that support them is a poorly recognized but central conservation challenge for modern Mediterranean societies as they face impending impacts of global climate change. Solutions to this crisis require education, societal dialogue, and improved policy and implementation.

An 'oasis' signifies a refugium of safety, recovery, relaxation, fertility, and productivity in an inhospitable desert, a sweet spot in a barren landscape where life-giving water spills forth from the Earth. Remarkable mythological congruencies exist across dryland cultures worldwide where oases or 'arid-land springs' occur. In many places they also provide specialised habitats for an extraordinary array of endemic organisms. To inform their management, and maintain their integrity, it is essential to understand the hydrogeology of aquifers and springs. Gravity-fed vs artesian aquifers; actively recharged vs fossil aquifers, and sources of geothermal activity are important concepts presented here. There consequences for oases of sustainable and unsustainable groundwater extraction, and other examples of effective conservation management. Oases are archetypes for human consciousness, habitats that deserve protection and conservation, and a lingua franca for multicultural values and scientific exchange. We represent an international Fellowship of the Spring seeking to encompass and facilitate the stewardship of oases and aquifers through improved knowledge, outreach, and governance.

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.

Over the past century, the white-nosed coati (WNC; Nasua narica ) has expanded its northernmost range from the United States-Mexico border into northern Arizona. WNC are medium-sized, opportunistic omnivores that often occur in large groups (“bands”) and forage on insects, fruits, and small vertebrates. We compiled data from iNaturalist, published literature, Arizona Game and Fish records, museum collections, personal communications, and our own camera trap photography to chronicle this range expansion. Historical records documented WNC populations in mountainous areas along the US-Mexican border but rarely north of Tucson, AZ. The popularity of using wildlife cameras in both research and recreation, paired with the advancement of citizen science projects like iNaturalist have generated a vast amount of new data on species distributions. With this new body of information we report the range of WNC now occurs over 400 km farther north, extending north of Flagstaff, Arizona. Recent records include occurrence in ponderosa pine forest that sustain sometimes heavy winter snow – an environment vastly different from the species’ normal range. The northward expansion of this meso-carnivore invites many questions about drivers of range expansion, including climate change, mesopredator release, or simple opportunism. More research into the behavior and ecology of WNC in the northern extent of their range is needed to guide understanding and potential future management of this species, its impacts, and prediction of other such range expansions.

The watershed-continuum model (WCM) describes fluvial-riparian ecosystems (FREs) as dynamic reach-based ecohydrogeological riverine landscapes linking aquatic, riparian, and upland domains within watersheds. FRE domains include aquatic (channels, hyporheic zones, springs, other groundwater zones and in-channel lakes), riparian, and adjacent upland zones, all of which can interact spatio-temporally. Occupying only a minute proportion of the terrestrial surface, FREs contain and process only a tiny fraction of the Earth’s freshwater, but often are highly productive, flood-disturbed, and ecologically interactive, supporting diverse, densely-packed biotic assemblages and socio-cultural resource uses and functions. FRE biodiversity is influenced by hydrogeomorphology, ecotonal transitions, and shifting habitat mosaics across stage elevation. Thus, the WCM integrates physical, biological, and socio-cultural characteristics, elements, and processes of FREs. Here, we summarize and illustrate the WCM, integrating diverse physical and ecological conceptual models to describe natural (unmanipulated) FRE dynamics. We integrate key processes affecting FRE forms and functions, and illustrate reach-based organization across temporal and spatial scales. Such a holistic approach into natural FRE structure and functions provides a baseline against which to measure and calibrate ecosystem alteration, management, and rehabilitation potential. Integration of groundwater, fluvial, and lacustrine ecological interactions within entire basins supports long-term, seasonally-based sustainable river management, which has never been more urgently needed.

Springs are ecosystems influenced by the exposure of groundwater at the Earth's surface. Springs are abundant and have played important, highly interactive ecological, cultural, and socio-economic roles in arid, mesic, and subaqueous environments throughout human evolution and history. However, springs also are widely regarded as being highly threatened by human impacts. Cantonati et al. (2020a) recommended increased global awareness of springs, including basic mapping, inventory and assessment of the distribution and ecological integrity of springs. We conducted a preliminary global analysis on the ecological integrity of springs by reviewing information on the distribution, ecohydrogeology, associated species, kinds and intensity of human uses, and level of ecological impairment of spring ecosystems. We reviewed information on an estimated 250,000 spring ecosystems among 78 countries across much of the world. Available literature on spring ecological integrity is sparse, widely scattered, and spatially erratic, with major gaps in knowledge. We report large differences in the quality and extent of information among countries and continents, with only moderate data availability even among developed countries, and limited information across most of the developing world. Among countries with available data, ecological impairment of springs is everywhere rampant, sometimes exceeding 90% in developed regions. Impairment among Holarctic nations is generally negatively related to distance from human development, elevation, and latitude, but such patterns are less evident in Africa, Australia, and South America. Declining trends in ecosystem condition, compounding threat factors, and spring-dependent population declines, extirpation, and extinctions of plants, invertebrates, fish, and herpetofauna are widely reported. Overall, available information indicates a global crisis in spring ecosystem integrity, with levels of ecosystem impairment ranging from Vulnerable to fully Collapsed. The threats to aquifers and the ecological integrity of springs vary spatially. Many springs are impaired by local impacts due to flow diversion, geomorphic alteration, land use practices, recreation impacts, and the introduction of non-native species. These threats can be reduced through education, rehabilitation of geomorphology and habitat quality, and species reintroductions if the supporting aquifer remains relatively intact. However, springs also are widely threatened by regional to global factors, including groundwater extraction and pollution, as well as climate change. Such coarse-scale, pre-emergence impacts negatively affect the sustainability of spring ecosystems and the aquifers that support them. Improving understanding and stewardship of springs will require much additional systematic inventory and assessment, improved information management, and reconsideration of basic conservation concepts (e.g., habitat connectivity), as well as cultural and socio-economic valuation. Substantial societal recognition, discussion, and policy reform are needed within and among nations to better protect and sustainably rehabilitate springs, their supporting aquifers, and the spring-dependent human and biotic populations that depend upon them.

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.

Abstract Considerable attention has been paid to perennial aridland rivers due to their disproportionate importance both ecologically and socially within aridlands. The Verde River Basin (VRB) is a large aridland watershed in central-northern Arizona. The river is subject to variable surface flow inputs, but its baseflow is sourced from springs. We investigated trends in increasing summer temperature and reduced June baseflow beginning in 1990 and continuing through the present. We discuss the potential impacts on the 965 reported springs in the watershed. Springs of the VRB support a wide array of flora and fauna. Early summer dry-season flows are almost entirely derived from springs making the aquatic species of the VRB almost entirely springs-dependent. VRB baseflow was increasing prior to 1990, with a change in trend that coincides with a change in air temperature. Declining snowpack and infiltration, coupled with warming temperatures since 1990 have reduced baseflow basin-wide through reduced groundwater supply, with likely impacts to springs ecosystems, especially springs fed by “younger” groundwater that is most vulnerable to reduction in aquifer recharge. The empirical results of this study indicate a trend of warming temperature correlated to diminishing groundwater dependent resources; supporting recent hydrological and climate projections for the American Southwest.

Springs ecosystems are globally abundant, geomorphologically diverse, and bio-culturally 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.

Comparative analysis of factors influencing benthic macro invertebrate (BMI) assemblages in unregulated tributaries can inform management about tributary to mainstream discontinuities (TMDs) with adjacent regulated mainstream rivers. Tapeats Creek is a cool-water tributary of the highly regulated Colorado River ecosystem in Grand Canyon downstream from Glen Canyon Dam, having similar geochemistry, water temperature, and annual relative flow variability compared to the mainstream. The creek supports a diverse BMI assemblage, including Ephemeroptera, Plecoptera, and Trichoptera (EPT) that are absent in the mainstream. We used field measurements and experiments in six microhabitats around the creek mouth to test the impacts of water quality (temperature, geochemistry), flow variability, and substrate embeddedness impacts on BMI distribution, particularly during stepped hydropower-related mainstream stage shifts. The Tapeats Creek TMD was not attributable to temperature, geochemistry, or contemporary low-level hydropower flow fluctuations, but rather to natural embeddedness in mainstream substrata. Tap eats Creek is floored with gravel and cobble, with much interstitial space, whereas the mainstream benthos was composed of cobble/boulders embedded in fine sand, with marginal to suboptimal EPT habitat. The TMD was likely more pronounced in pre-dam time and from 1964-1990 due to larger seasonal and daily flow fluctuations and more prolonged confluence inundation, respectively. The Colorado River in Grand Canyon is adaptively managed to balance hydropower production, fine sediment mass balance for recreational camping and shoreline habitat, as well as native and recreational fisheries. However, strategies to promote both fine sediment storage and an optimal mainstream food base for fish are not be mutually compatible. Thus, not all desired river ecosystem conditions may be simultaneously achieved. Keywords: Benthic macro invertebrate ecology, discontinuity, Colorado River, embeddedness, EPT, Glen Canyon Dam, Grand Canyon, tributary

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.

Forest thinning has been used as a management tool to reverse the adverse impacts of decades of fire suppression in the western USA. Research into the impacts of thinning on surface water, soil, and vegetation re-growth have occurred concurrently with the growing popularity of forest thinning; however, its potential impact on groundwater recharge and related springs ecosystems has largely been ignored until recently. This systematic review provides an overview of some of the tools used to measure the influence of forest management on groundwater recharge, including numerical and process based modeling, empirical paired-watershed approaches, and statistical stochastic techniques. A brief discussion of the benefits and drawbacks of each method also is provided. The paper provides a literature review of existing studies of groundwater recharge and forest management from 1971 to 2018. The review of 35 studies indicates a range of results and highlights differences between studies of clear-cut forests versus thinned forests. Forests that were thinned had a greater amount of groundwater recharge than clear-cut forests, indicating that recharge responds positively and more strongly to reduced sublimation and evaporation in partially thinned forests than to clear-cut removal of mature trees. A similar test with forest encroachment studies revealed no differences between forest encroachment and either thinning regime. The number of forest management-groundwater recharge studies has dramatically increased over the last two decades, indicating increased interest in finding tools to increase groundwater yields for societal use in rapidly populating aridland forests. To our knowledge there have been no studies of forest thinning impacts on springs ecosystems, a field of study rich with possibilities for ecologists, hydrologists, rangeland and forestry scientists, and interdisciplinary ecohydrology practitioners.