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USGS2016

Climate change and the eco-hydrology of fire: Will area burned increase in a warming western USA?

Wildfire area is predicted to increase with global warming. Empirical statistical models and process-based simulations agree almost universally. The key relationship for this unanimity, observed at multiple spatial and temporal scales, is between drought and fire. Predictive models often focus on ecosystems in which this relationship appears to be particularly strong, such as mesic and arid forests and shrublands with substantial biomass such as chaparral. We examine the drought–fire relationship, specifically the correlations between water-balance deficit and annual area burned, across the full gradient of deficit in the western USA, from temperate rainforest to desert. In the middle of this gradient, conditional on vegetation (fuels), correlations are strong, but outside this range the equivalence hotter and drier equals more fire either breaks down or is contingent on other factors such as previous-year climate. This suggests that the regional drought–fire dynamic will not be stationary in future climate, nor will other more complex contingencies associated with the variation in fire extent. Predictions of future wildfire area therefore need to consider not only vegetation changes, as some dynamic vegetation models now do, but also potential changes in the drought–fire dynamic that will ensue in a warming climate.

Western United States↗

USGS2024

Germination information for common Arizona restoration species

Seed-based ecological restoration is an approach used to revegetate damaged and disturbed habitats by spreading seed with the expectation that germination will occur and plants will become established and flourish. Although restoration can enhance the health and productivity of landscapes by reinvigorating ecosystem services both directly and indirectly, successful restoration is difficult to achieve – particularly in arid systems (Copeland et al. 2018). Germination is a well known bottleneck to plant growth that prohibits successful restoration (James at al. 2011).

Cooperative Extension Publication↗

USGS2012

The role of fire on soil mounds and surface roughness in the Mojave Desert

A fundamental question in arid land management centers on understanding the long-term effects of fire on desert ecosystems. To assess the effects of fire on surface topography, soil roughness, and vegetation, we used terrestrial (ground-based) LiDAR to quantify the differences between burned and unburned surfaces by creating a series of high-resolution vegetation structure and bare-earth surface models for six sample plots in the Grand Canyon-Parashant National Monument, Arizona. We find that 11 years following prescribed burns, mound volumes, plant heights, and soil-surface roughness were significantly lower on burned relative to unburned plots. Results also suggest a linkage between vegetation and soil mounds, either through accretion or erosion mechanisms such as wind and/or water erosion. The biogeomorphic implications of fire-induced changes are significant. Reduced plant cover and altered soil surfaces from fire likely influence seed residence times, inhibit seed germination and plant establishment, and affect other ecohydrological processes.

Arizona↗

USGS2018

A semi-arid river in distress: Contributing factors and recovery solutions for three imperiled freshwater mussels (Family Unionidae) endemic to the Rio Grande basin in North America

Freshwater resources in arid and semi-arid regions are in extreme demand, which creates conflicts between needs of humans and aquatic ecosystems. The Rio Grande basin in the southwestern United States and northern Mexico exemplifies this issue, as much of its aquatic biodiversity is in peril as a result of human activities. Unionid mussels have been disproportionately impacted, though the specific factors responsible for their decline remain largely unknown. This is problematic because the Rio Grande basin harbors one federally endangered unionid mussel ( Popenaias popeii , Texas Hornshell) plus two other mussel species ( Potamilus metnecktayi , Salina Mucket; and Truncilla cognata , Mexican Fawnsfoot), which are also being considered for listing under the U.S. Endangered Species Act. To date, surveys for these species have not corrected for variability in detection so current range estimates may be inaccurate. Using single occupancy-modeling to estimate detection and occupancy at 115 sites along ~800 river kilometers of the Rio Grande in Texas, we found that detection probabilities were relatively high, indicating that our survey design was efficient. In contrast, the estimated occupancy was low, indicating that our focal species were likely rare within the Rio Grande drainage. In general, the predicted occupancy of our focal species was low throughout their respective ranges, indicating possible range declines. A comparison of currently occupied ranges to presumptive ranges underscores this point. The best-approximating models indicated that occupancy was influenced by habitat, water quantity and quality, and proximity to large-scale human activities, such as dams and major urban centers. We also discuss a series of conservation options that may not only improve the long-term prognosis of our focal species but also other aquatic taxa.

Rio Grande basin↗

USGS2024

A multiscale perspective for improving conservation of Conchos pupfish

Desert spring systems of the American southwest hold high local fish endemism and are ranked among the most threatened ecosystems in the world. The prioritization of conservation resources to protect species living within these arid landscapes requires knowledge of species abundance and distribution. The plight of Conchos pupfish ( Cyprinodon eximius ) is representative of freshwater fishes the world over, including population extirpations caused by human poisoning of streams and reservoir construction, to the extent that the species was once considered extinct in the USA. We developed a distance-sampling framework to monitor Conchos pupfish abundance and coupled this approach with species distribution modeling to guide conservation actions. Our multiscale approach included surveying abundances within 5-m transects at three reaches of the Devils River, where the last known USA populations persist. We combined this fine-scale analysis with species distribution modeling for stream segments across the range of the species in Mexico and USA. Modeling revealed Conchos pupfish abundance among transects was negatively correlated with current velocity and detection was negatively correlated with water depth. Estimated abundance at a reach where the species was previously reintroduced was greater than other reaches combined in November 2019, lowest in March 2021 when reach water levels were very low, then equivalent with other reaches by October 2021 after water returned to the reach. Modeled Conchos pupfish distribution illustrated a high probability of occurrence on the periphery of the species' overall range within Texas, USA and broadly across Chihuahua, Mexico, where proposed protected areas might benefit the species. Our study provides conservation guidance by establishing (1) baseline and trajectory values for abundance, (2) transect locations where abundances might be managed within existing protected areas, (3) reaches where high abundances could be used for future repatriation, and (4) stream segments where future surveys might be conducted to assess conservation opportunities.

Animal Conservation↗

USGS2010

Carbon exchange in biological soil crust communities under differential temperatures and soil water contents: Implications for global change

Biological soil crusts (biocrusts) are an integral part of the soil system in arid regions worldwide, stabilizing soil surfaces, aiding vascular plant establishment, and are significant sources of ecosystem nitrogen and carbon. Hydration and temperature primarily control ecosystem CO 2 flux in these systems. Using constructed mesocosms for incubations under controlled laboratory conditions, we examined the effect of temperature (5–35 °C) and water content (WC, 20–100%) on CO 2 exchange in light (cyanobacterially dominated) and dark (cyanobacteria/lichen and moss dominated) biocrusts of the cool Colorado Plateau Desert in Utah and the hot Chihuahuan Desert in New Mexico. In light crusts from both Utah and New Mexico, net photosynthesis was highest at temperatures >30 °C. Net photosynthesis in light crusts from Utah was relatively insensitive to changes in soil moisture. In contrast, light crusts from New Mexico tended to exhibit higher rates of net photosynthesis at higher soil moisture. Dark crusts originating from both sites exhibited the greatest net photosynthesis at intermediate soil water content (40–60%). Declines in net photosynthesis were observed in dark crusts with crusts from Utah showing declines at temperatures >25 °C and those originating from New Mexico showing declines at temperatures >35 °C. Maximum net photosynthesis in all crust types from all locations were strongly influenced by offsets in the optimal temperature and water content for gross photosynthesis compared with dark respiration. Gross photosynthesis tended to be maximized at some intermediate value of temperature and water content and dark respiration tended to increase linearly. The results of this study suggest biocrusts are capable of CO 2 exchange under a wide range of conditions. However, significant changes in the magnitude of this exchange should be expected for the temperature and precipitation changes suggested by current climate models.

New Mexico, Utah↗

USGS2016

U.S. Geological Survey science for the Wyoming Landscape Conservation Initiative—2015 annual report

This is the eighth annual report highlighting U.S. Geological Survey (USGS) science and decision-support activities conducted for the Wyoming Landscape Conservation Initiative (WLCI). The activities address specific management needs identified by WLCI partner agencies. In 2015, USGS scientists continued 24 WLCI projects in 5 categories: (1) acquiring and analyzing resource-condition data to form a foundation for understanding and monitoring landscape conditions and projecting changes; (2) using new technologies to improve the scope and accuracy of landscape-scale monitoring and assessments, and applying them to monitor indicators of ecosystem conditions and the effectiveness of on-the-ground habitat projects; (3) conducting research to elucidate the mechanisms that drive wildlife and habitat responses to changing land uses; (4) managing and making accessible the large number of databases, maps, and other products being developed; and (5) coordinating efforts among WLCI partners, helping them to use USGS-developed decision-support tools, and integrating WLCI outcomes with future habitat enhancement and research projects. Of the 24 projects, 21 were ongoing, including those that entered new phases or more in-depth lines of inquiry, 2 were new, and 1 was completed. A highlight of 2015 was the WLCI science conference sponsored by the USGS, Bureau of Land Management, and National Park Service in coordination with the Wyoming chapter of The Wildlife Society. Of 260 participants, 41 were USGS professionals representing 13 USGS science centers, field offices, and Cooperative Wildlife Research Units. Major themes of USGS presentations included using new technologies for developing more efficient research protocols for modeling and monitoring natural resources, researching effects of energy development and other land uses on wildlife species and habitats of concern, and modeling species distributions, population trends, habitat use, and effects of land-use changes. There was also a special session on the effectiveness of Wyoming’s Sage-Grouse Executive Order. Combined, USGS presentations provided WLCI partners with a wealth of information and conservation tools. The project completed in 2015 yielded an index of important agricultural lands in the WLCI region. The index improves upon existing measures of agricultural productivity and provides planners and managers with additional values to consider when making decisions about land use and conservation actions. The two new projects include an analysis of satellite imagery to quantify sagebrush productivity and mortality, and an evaluation of how groundwater and small streams interact in the upper Green River Basin. Initiated in response to concern among WLCI partners that large areas of sagebrush appear to have died recently, the sagebrush study objectives are to assess effects of these mortality events on overall sagebrush ecosystem productivity, evaluate the feasibility of using satellite imagery to detect patterns in sagebrush mortality over time, and identify factors driving these mortality events. The groundwater-streamflow interaction study is being conducted by hydrologists and fish ecologists to better understand how groundwater-streamflow interactions are affected by energy-resource development and how native fish communities are affected by these factors. Expected outcomes of both new projects will provide WLCI partners with additional information and decision-support tools. Highlights of ongoing science foundation activities included simulations of nine alternative build-out scenarios for oil and gas development and an associated online fact sheet that explains how the simulations were conducted, with an applied example for the Atlantic Rim. Also completed in 2015 was an update of the USGS online inventory of mineral resources data, and publication of a USGS uranium resource survey for the WLCI region. Combined, the outcomes of this work provide decisionmakers and managers with important baseline information for existing and (or) future planning and monitoring efforts. Terrestrial monitoring activities in 2015 emphasized the use of satellite data in combination with other technologies and field data to monitor, assess, and (or) forecast distribution patterns and (or) trends in sagebrush ecosystems, seasonal and migration stopover habitats used by mule deer and elk, and semi-arid aspen woodlands. Several professional papers detailing new monitoring models and results have been published. Combined, this and related work will help managers understand distribution patterns and trends among priority habitats, identify areas in need of restoration or conservation, and monitor the effectiveness of habitat-management actions. Aquatic monitoring activities entailed not only the new groundwater-streamflow interaction study already mentioned, but also continued monitoring with streamgages paired with nearby wells in the Green River Basin to assess groundwater effects on streamflow and surface water temperatures. A map that portrays groundwater levels and general direction of flow in the Green River Basin was published as well . Overall, outcomes of USGS hydrological research and monitoring will inform WLCI partners about water resources in the WLCI region and help to explain fish-community responses to energy-resource development. In 2015, USGS terrestrial wildlife ecologists continued to make crucial strides towards better understanding wildlife species responses to energy-resource development and other land-use changes. This body of research includes six taxa that require or heavily depend on sagebrush habitats: sage-grouse, pygmy rabbits, 3 songbird species, and mule deer. Native fish communities are also being evaluated. Approaches include modeling and mapping wildlife species distributions, abundances, and trends; using satellite and other technologies to track wildlife seasonal movements; conducting successive phases of research that build on the knowledge gained through prior phases to reveal the specific factors or thresholds that drive population- or individual-level responses to changes; and conducting population viability analyses. Additionally, wildlife habitat association models for pygmy rabbit and sage-grouse were combined with the oil and gas build-out scenarios to project species responses to alternative energy development scenarios. Outcomes of the wildlife response research are helping decisionmakers and managers identify specific factors that contribute to species population trends, the potential for spatial overlap between important wildlife habitats and proposed energy-resource development, locations of priority habitats for restoration and conservation, and more. Data and WLCI Web site management highlights of 2015 included not only ongoing software upgrades, but also an update of the datasets displayed in two of the online products developed for the WLCI effort: (1) a map of 15,532 oil and natural gas well pad scars and other features associated with oil and gas extraction, and (2) a map of oil and gas, oil shale, uranium, and solar energy production, both for southwestern Wyoming. In addition, a map viewer was developed for a previously published map of coal and wind production in relation to sage-grouse distribution and core management areas in southwestern Wyoming. Combined, these maps place valuable decision-support tools in the hands of WLCI partners. The USGS coordination efforts on behalf of the WLCI in 2015 included significant work on planning and executing the WLCI science conference. They also included ongoing efforts to support Local Project Development Teams and the WLCI Coordination Team (CT) with developing conservation priorities and strategies, identifying priority areas for future conservation actions, supporting the evaluation and ranking of conservation projects, and evaluating the ways in which proposed habitat projects relate to WLCI priorities. In 2015, the USGS also assisted the WLCI CT with updating the WLCI Conservation Action Plan.

Wyoming↗

USGS1997

Potential effects of climate change on aquatic ecosystems of the Great Plains of North America

The Great Plains landscape is less topographically complex than most other regions within North America, but diverse aquatic ecosystems, such as playas, pothole lakes, ox-bow lakes, springs, groundwater aquifers, intermittent and ephemeral streams, as well as large rivers and wetlands, are highly dynamic and responsive to extreme climatic fluctuations. We review the evidence for climatic change that demonstrates the historical importance of extremes in north-south differences in summer temperatures and east-west differences in aridity across four large subregions. These physical driving forces alter density stratification, deoxygenation, decomposition and salinity. Biotic community composition and associated ecosystem processes of productivity and nutrient cycling respond rapidly to these climatically driven dynamics. Ecosystem processes also respond to cultural effects such as dams and diversions of water for irrigation, waste dilution and urban demands for drinking water and industrial uses. Distinguishing climatic from cultural effects in future models of aquatic ecosystem functioning will require more refinement in both climatic and economic forecasting. There is a need, for example, to predict how long-term climatic forecasts (based on both ENSO and global warming simulations) relate to the permanence and productivity of shallow water ecosystems. Aquatic ecologists, hydrologists, climatologists and geographers have much to discuss regarding the synthesis of available data and the design of future interdisciplinary research.

Hydrological Processes↗

USGS2023

Plant water-use strategies predict restoration success across degraded drylands

Plant strategies for coping with water limitation are likely to mediate restoration outcomes in degraded dryland ecosystems. Trade-offs in traits related to water acquisition and use can intensify in more arid environments, making their effects on dryland restoration success even more salient. However, isolating the effects of drought responses from those of other environmental factors, as well as identifying the specific drought resistance traits that influence restoration success, can be difficult. In the present study, we couple a controlled dry-down experiment with a cross-site restoration field trial of out-planted seedlings (RestoreNet) using a suite of dryland herbaceous plant species from the same seed sources. We quantified interspecific variation in physiological responses to drought, specifically reductions in stomatal conductance ( g s ) and stem water potential (SWP), by comparing well-watered control plants to those experiencing decreasing soil moisture. Drought responses of SWP and g s varied independently among species, but both were related to survival in the cross-site restoration field trial when effect sizes were aggregated across all sites. Responses were consistent with acquisitive water-use strategies resulting in greater success, where species with greater declines in SWP or weaker declines in g s under drought had greater survival. The correlation between SWP drought response and survival also intensified in sites with lower accumulated precipitation following restoration. Differences among functional groups revealed two different paths to restoration success: forbs that maintain high g s and narrow safety margins to maximize exploitation of moisture pulses before going into drought dormancy, or C 4 grasses that maintain efficient water uptake in drying soils while risking cavitation. C 3 grass species varied between these two strategies. Synthesis and applications . Taken together, the results of this study and others conducted at RestoreNet sites indicate that while a diversity of physiological responses to drought may exist in dryland plant communities, successfully restoring herbaceous species through out-planting in degraded conditions is likely to be achieved with species that maximize water uptake via one of two strategies, with tolerance of low SWP being particularly important in the most arid settings.

Journal of Applied Ecology↗

USGS2022

Seed germination responses to salinity for three rare wetland plants of spring-fed arid systems

Spring-fed wetlands within arid systems host unique species of plants, many of which are threatened due to the vulnerability of these ecosystems. Increased salinity and drier hydrologic regimes due to anthropogenic activities threaten these systems. Furthermore, limited knowledge regarding key life history traits of species jeopardize the restoration and management of their rare plants. Here, we evaluated key aspects of the seed ecophysiology of three rare plants of the Southwestern United States: Helianthus paradoxus (Pecos sunflower), Cirsium wrightii (Wright's marsh thistle), and Agalinis calycina (Leoncita false-foxglove). We examined seed dormancy break under controlled conditions and evaluated the effects of field-derived salinity gradients on seed dormancy break and germination. Seeds of C. wrightii were nondormant at dispersal, germination was high (>70%) under all treatments and was not affected by the tested salinities. Germination in H. paradoxus was high (>70%) following cold stratification, but increasing salinities reduced germination. A. calycina seeds required cold stratification, but germination was low (<50%) under all tested treatments and increasing salinities during incubation had the greatest negative effects in this species. Our findings contribute to the restoration of rare wetland plants within spring-fed arid marshes susceptible to groundwater declines and human-induced salinization.

New Mexico↗

USGS1989

Riparian ecosystem creation and restoration: a literature summary

Riparian ecosystems generally compose a minor proportion of surrounding areas, but typically are more structurally diverse and more productive in plant and animal biomass than adjacent upland areas. Riparian areas supply food, cover, and water (especially important in the arid West) for a large diversity of animals, and serve as migration routes and forest connectors between habitats for a variety of wildlife, particularly ungulates and birds. Because riparian ecosystems often are relatively small areas and occur in conjunction with waterways, they are vulnerable to severe alteration. Riparian ecosystems throughout the U.S. have been heavily impacted by man's activities. Riparian ecosystem creation and restoration have been used as mitigation for project impacts from highway, bridge, and pipeline construction; water development; flood control channel modifications; industrial and residential development; agriculture; irrigation; livestock grazing; mining; and accidental habitat loss. Creation of a riparian ecosystem in| a more mesic upland area (e.g., ‘grassland or cropland) adjacent to a river requires appropriate water supply and grading the topography to suitable elevations to support plantings of riparian vegetation. Restoration involves returning the ecosystem to pre disturbance conditions and typically implies revegetation. Removing exotic vegetation or restoring water supplies to pre disturbance level also may be involved. Enhancement of riparian ecosystems commonly refers to improving existing conditions to increase habitat value, usually by increasing plant or community diversity to increase value for wildlife. Managing a riparian ecosystem typically involves enhancement techniques. However, creation and restoration projects often involve use of techniques considered more management-oriented (e.g., fencing to prevent cattle grazing until planted vegetation of a created or restored wetland is established). Protection of an existing riparian ecosystem from impact should be of utmost importance during planning and construction phases of development projects. If loss or damage is unavoidable, wetland creation or restoration can be used as mitigation. Compared to other wetland types (e.g., coastal wetlands), projects and techniques involving creation or restoration of riparian ecosystems are not well documented. For example, only 8% of the records in the WCR Data Base contained information on riparian ecosystems, whereas 31% of the records contained information on coastal emergent or forested ecosystems. To provide a source of currently available literature, riparian information from 92 records (primarily published papers or reports) in the U.S. Fish and Wildlife Service's (FWS) Wetland Creation-Restoration (WCR) Data Base (Schneller-McDonald et al. 1988) was used to develop a literature summary of creation and restoration of riparian ecosystems. The summary provides an overview of the status of riparian ecosystems in the U.S., a discussion of several riparian functions, and a review of some techniques used for planning, implementing, monitoring, and measuring project success of creation-restoration efforts. Case studies of various creation or restoration projects are used to demonstrate these techniques and to report some results of their use. Several well-documented case studies are discussed in detail to illustrate more extensive efforts to plan, implement, or monitor riparian ecosystem creation-restoration projects. For the purpose of this report, riparian ecosystems are defined as landscapes adjacent to drainageways of floodplains that exhibit vegetation, soil, and hydrologic mosaics along topographic and moisture gradients that are distinct from the predominant landscape surface types. Major plant communities are described under palustrine system in Cowardin et al. (1979). Literature from the WCR Data Base was used to provide a summary of riparian ecosystem creation-restoration literature. Thus, information concerning natural systems is not included unless discussed in these articles. This focus allows the reader to compare relative information available on riparian ecosystem creation-restoration efforts. However, this focus also results in limited information in some sections of the report (e.g., Status of Riparian Ecosystems in the U.S.). Individuals involved in riparian ecosystem creation-restoration efforts are encouraged to thoroughly examine available literature on natural and altered systems. Brinson et al. (1981) provide a comprehensive review and synthesis of the ecology and status of riparian ecosystems. Over 500 articles are cited in their 124-page report. Chapters include the following topics: status of riparian ecosystems in the U.S., ecological functions and properties of riparian ecosystems (e.g., geomorphology, primary productivity, nutrient cycling, hydrology), importance of riparian ecosystems to fish and wildlife, and considerations in valuation (ecologic and economic) of riparian ecosystems. Brinson et al. (1981) also discuss management of riparian ecosystems. Riparian ecosystem management literature was not included in the WCR Data Base, unless the article also discussed creation or restoration.

Report↗

USGS2006

Carbon and nitrogen fixation differ between successional stages of biological soil crusts in the Colorado Plateau and Chihuahuan Desert

Biological soil crusts (cyanobacteria, mosses and lichens collectively) perform essential ecosystem services, including carbon (C) and nitrogen (N) fixation. Climate and land-use change are converting later successional soil crusts to early successional soil crusts with lower C and N fixation rates. To quantify the effect of such conversions on C and N dynamics in desert ecosystems we seasonally measured diurnal fixation rates in different biological soil crusts. We classified plots on the Colorado Plateau (Canyonlands) and Chihuahuan Desert (Jornada) as early (Microcoleus) or later successional (Nostoc/Scytonema or Placidium/Collema) and measured photosynthesis (Pn), nitrogenase activity (NA), and chlorophyll fluorescence (Fv/Fm) on metabolically active (moist) soil crusts. Later successional crusts typically had greater Pn, averaging 1.2-1.3-fold higher daily C fixation in Canyonlands and 2.4-2.8-fold higher in the Jornada. Later successional crusts also had greater NA, averaging 1.3-7.5-fold higher daily N fixation in Canyonlands and 1.3-25.0-fold higher in the Jornada. Mean daily Fv/Fm was also greater in later successional Canyonlands crusts during winter, and Jornada crusts during all seasons except summer. Together these findings indicate conversion of soil crusts back to early successional stages results in large reductions of C and N inputs into these ecosystems.

Journal of Arid Environments↗

USGS2006

Precipitation history and ecosystem response to multidecadal precipitation variability in the Mojave Desert region, 1893-2001

Precipitation varied substantially in the Mojave Desert through the 20th century in a manner broadly similar to the other warm North American deserts. Episodes of drought and prolonged dry conditions (1893-1904, ca. 1942-1975, and 1999-present) alternated with relatively wet periods (1905-ca. 1941 and ca. 1976-1998), probably because of global-scale climate fluctuations. These are the El Nin??o-Southern Oscillation that affects interannual climate and the Pacific Decadal Oscillation that evidently causes decadal-scale variability such as prolonged dry and wet episodes. Studies done in the late 20th century demonstrate that precipitation fluctuations affected populations of perennial vegetation, annuals, and small herbivores. Landscape rephotography reveals that several species, particularly creosote bush, increased in size and density during the ca. 1976-1998 wet period. A brief, intense drought from 1989 to 1991 and the ongoing drought caused widespread mortality of certain species; for example, chenopods and perennial grasses suffered up to 100% mortality. Drought pruning, the shedding of above-ground biomass to reduce carbon allocation, increased substantially during drought. Overall, drought had the greatest influence on the Mojave Desert ecosystem. ?? 2006.

Journal of Arid Environments↗

USGS2011

Differences in macroinvertebrate community structure in streams and rivers with different hydrologic regimes in the semi-arid Colorado Plateau

Aquatic macroinvertebrates are sensitive to changes in their chemical and physical environment, and as such, serve as excellent indicators of overall ecosystem health. Moreover, temporal and spatial differences in macroinvertebrate community structure can be used to investigate broad issues in aquatic science, such as the hypothesis that changes in climate are likely to have disproportionately large effects on small, intermittent stream ecosystems. We quantified macroinvertebrate community structure and abiotic conditions at ten stream sites with different dominant hydrologic regimes in the Colorado Plateau, ranging from small, intermittent desert streams to large perennial mountain rivers. Considerable differences were observed in community structure between sites with differing hydrologic regimes. Quantitative results of non-metric multidimensional scaling (NMDS) ordination and Spearman rank correlations between physical habitat and macroinvertebrate resemblance matrices indicate that discharge, geomorphic channel unit type (% pools vs. % riffles), percent of substrate composed of sand, and velocity were the subset of measured habitat variables that best explained the differences in macroinvertebrate community structure among sites. Of the 134 taxa identified, nine taxa explained 95 % of the variability in community structure between sites. These results add to a growing base of knowledge regarding the functioning of lotic ecosystems in the Colorado Plateau, and provide timely information on anticipated changes in the structure and function of aquatic ecosystems in response to predicted future environmental conditions.

Colorado Plateau↗

USGS2021

Reconstructing paleohydrology in the northwest Great Basin since the last deglaciation using Paisley Caves fish remains (Oregon, U.S.A.)

The arid northwest Great Basin underwent substantial hydroclimate changes in the past 15,000 years, greatly affecting its desert ecosystems and prehistoric people. There are conflicting interpretations of the timing of hydrologic changes in this region, requiring more records to resolve the dominant climatic drivers. The Paisley Caves archaeological site, located near former pluvial Lake Chewaucan, contains well-dated, stratified sediments best known for evidence of early human occupation in North America. We present a novel paleohydrologic record for the Chewaucan basin based on the frequency of fish remains (Salmonidae and Cypriniformes, likely tui chub) and their carbon, oxygen, and strontium isotope compositions, from the Paisley Caves. Cypriniformes abundance peaks first at the start of the Bølling/Allerød warm interval (∼14.7 ka) and again during the early Younger Dryas (∼12.8 ka). Isotope compositions indicate tui chub were derived from an expansive Lake Chewaucan throughout the Bølling/Allerød, but mainly from spring- or stream-influenced sources by the late Younger Dryas to the present. Fish abundance dropped sharply through the Younger Dryas and early Holocene, when isotope compositions indicate a mix of habitats. Isotope compositions indicate the driest conditions during the middle Holocene, followed by slightly wetter conditions up to the present. This record agrees with recent pluvial lake reconstructions, supporting the hypothesis that a northward shift in the winter storm track supported deep lakes throughout the Bølling/Allerød in the northwest Great Basin. Lake level decline during the Younger Dryas suggests drying climate, differing from more southerly records. During the Holocene, however, shifts in Chewaucan basin hydrology are consistent with the rest of the western U.S. This highlights the need for region-specific records to inform predictions of the hydrologic impact of climate change on arid regions.

Oregon↗

USGS2017

Response of deep groundwater to land use change in desert basins of the Trans-Pecos region, Texas, USA: Effects on infiltration, recharge, and nitrogen fluxes

Quantifying the effects of anthropogenic processes on groundwater in arid regions can be complicated by thick unsaturated zones with long transit times. Human activities can alter water and nutrient fluxes, but their impact on groundwater is not always clear. This study of basins in the Trans-Pecos region of Texas links anthropogenic land use and vegetation change with alterations to unsaturated zone fluxes and regional increases in basin groundwater NO 3 − concentrations. Median increases in groundwater NO 3 − (by 0.7–0.9 mg-N/l over periods ranging from 10 to 50+ years) occurred despite low precipitation (220–360 mm/year), high potential evapotranspiration (~1570 mm/year), and thick unsaturated zones (10–150+ m). Recent model simulations indicate net infiltration and groundwater recharge can occur beneath Trans-Pecos basin floors, and may have increased due to irrigation and vegetation change. These processes were investigated further with chemical and isotopic data from groundwater and unsaturated zone cores. Some unsaturated zone solute profiles indicate flushing of natural salt accumulations has occurred. Results are consistent with human-influenced flushing of naturally accumulated unsaturated zone nitrogen as an important source of NO 3 − to the groundwater. Regional mass balance calculations indicate the mass of natural unsaturated zone NO 3 − (122–910 kg-N/ha) was sufficient to cause the observed groundwater NO 3 − increases, especially if augmented locally with the addition of fertilizer N. Groundwater NO 3 − trends can be explained by small volumes of high NO 3 − modern recharge mixed with larger volumes of older groundwater in wells. This study illustrates the importance of combining long-term monitoring and targeted process studies to improve understanding of human impacts on recharge and nutrient cycling in arid regions, which are vulnerable to the effects of climate change and increasing human reliance on dryland ecosystems.

Texas↗

USGS2000

Seasonal estimates of riparian evapotranspiration using remote and in situ measurements

In many semi-arid basins during extended periods when surface snowmelt or storm runoff is absent, groundwater constitutes the primary water source for human habitation, agriculture and riparian ecosystems. Utilizing regional groundwater models in the management of these water resources requires accurate estimates of basin boundary conditions. A critical groundwater boundary condition that is closely coupled to atmospheric processes and is typically known with little certainty is seasonal riparian evapotranspiration ET). This quantity can often be a significant factor in the basin water balance in semi-arid regions yet is very difficult to estimate over a large area. Better understanding and quantification of seasonal, large-area riparian ET is a primary objective of the Semi-Arid Land-Surface-Atmosphere (SALSA) Program. To address this objective, a series of interdisciplinary experimental Campaigns were conducted in 1997 in the San Pedro Basin in southeastern Arizona. The riparian system in this basin is primarily made up of three vegetation communities: mesquite (Prosopis velutina), sacaton grasses (Sporobolus wrightii), and a cottonwood (Populus fremontii)/willow (Salix goodingii) forest gallery. Micrometeorological measurement techniques were used to estimate ET from the mesquite and grasses. These techniques could not be utilized to estimate fluxes from the cottonwood/willow (C/W) forest gallery due to the height (20-30 m) and non-uniform linear nature of the forest gallery. Short-term (2-4 days) sap flux measurements were made to estimate canopy transpiration over several periods of the riparian growing season. Simultaneous remote sensing measurements were used to spatially extrapolate tree and stand measurements. Scaled C/W stand level sap flux estimates were utilized to calibrate a Penman-Monteith model to enable temporal extrapolation between Synoptic measurement periods. With this model and set of measurements, seasonal riparian vegetation water use estimates for the riparian corridor were obtained. To validate these models, a 90-day pre-monsoon water balance over a 10 km section of the river was carried out. All components of the water balance, including riparian ET, were independently estimated. The closure of the water balance was roughly 5% of total inflows. The ET models were then used to provide riparian ET estimates over the entire corridor for the growing season. These estimates were approximately 14% less than those obtained from the most recent groundwater model of the basin for a comparable river reach.

Conference Paper↗

USGS2022

Seed menus: An integrated decision-support framework for native plant restoration in the Mojave Desert

The combination of ecosystem stressors, rapid climate change, and increasing landscape-scale development has necessitated active restoration across large tracts of disturbed habitats in the arid southwestern United States. In this context, programmatic directives such as the National Seed Strategy for Rehabilitation and Restoration have increasingly emphasized improved restoration practices that promote resilient, diverse plant communities and enhance native seed reserves. While decision-support tools have been implemented to support genetic diversity by guiding seed transfer decisions based on patterns in local adaptation, less emphasis has been placed on identifying priority seed mixes composed of native species assemblages. Well-designed seed mixes can provide foundational ecosystem services including resilience to disturbance, resistance to invasive species, plant canopy structure to facilitate natural seedling recruitment, and habitat to support wildlife and pollinator communities. Drawing from a newly developed dataset of species distribution models for priority native plant taxa in the Mojave Desert, we created a novel decision support tool by pairing spatial predictions of species habitat with a database of key species traits including life history, flowering characteristics, pollinator relationships, and propagation methods. This publicly available web application, Mojave Seed Menus, helps restoration practitioners generate customized seed mixes for native plant restoration in the Mojave Desert while emphasizing key species traits. Our application forms an essential part of an integrated Mojave Desert restoration program designed to help practitioners identify species to include in local seed mixes and nursery stock development while accounting for local adaptation by identifying appropriate seed sources within key restoration species.

Arizona, California, Nevada, Utah↗