Geology topics

Research about Chihuahuan Desert

Source-linked reports with geographic coverage including Chihuahuan Desert.

10 recordsLinked to original sources

USGS2021

Discovery of a large subsoil nitrate reservoir in an arroyo floodplain and associated aquifer contamination

In an area of elevated nitrate (NO 3 ) groundwater concentrations in the northern Chihuahuan Desert in central New Mexico (United States), a large reservoir of nitrate was found in the subsoil of an arroyo floodplain. Nitrate inventories in the floodplain subsoils ranged from 10,000 to 38,000 kg NO 3 -N/ha—over twice as high as any previously measured arid region. The floodplain subsoil NO 3 reservoir was over 100 times higher than the adjacent desert (59–95 kg NO 3 -N/ha). Chloride mass balance calculations of subsoils indicate arroyo floodplain subsoils have undergone negative recharge since 2600–8600 yr ago, while the surrounding desert has had negative recharge since 13,000–17,000 yr ago. Compared to the adjacent desert, plant communities are larger and more abundant in the floodplain, though subsoil NO 3 is apparently not utilized. We demonstrate that NO 3 accumulates in the subsoil of the floodplain through evaporation of monsoon season precipitation funneled into the arroyo. Through a one-dimensional vadose zone model, we show that the NO 3 inventories in the arroyo floodplain could be acquired 8 to 75 times faster than through atmospheric deposition through the lateral movement

New Mexico↗

USGS2019

Geospatial scaling of runoff and erosion modeling in the Chihuahuan Desert

Large-scale assessments of rangeland runoff and erosion require methods to extend plot-scale parameterizations to large areas. In this study, Rangeland Hydrology and Erosion Model (RHEM) parameters were developed from plot-scale foliar and ground-cover transect data for an arid, grass-shrub rangeland in southern New Mexico, and a method was assessed to upscale transect-plot parameters to a large landscape. The transect-plot data compared favorably to corresponding cell data generated from publicly available geospatial data for total foliar cover but less favorably for litter cover and poorly for rock cover. The RHEM effective hydraulic conductivity (K e ) parameter was comparable between transect-plot and geospatial-cell methods, but the splash and sheet erosion factor (K ss ) had poor agreement between the two methods. Simulated runoff and erosion reflected differences in transect-plot and geospatial-cell-based RHEM parameterizations, with low error and very good agreement for runoff but high error and poor agreement for soil loss. These results demonstrate that K e parameters developed using geospatial data calibrated to plot data can be extrapolated to large spatial areas and provide reasonable simulation of runoff using RHEM. However, these same geospatial methods do not provide reasonable estimation of K ss or simulation of soil loss. Poor representation of litter and rock cover variables, which are highly spatially heterogeneous at the plot scale, was inadequate to accurately represent K ss or soil loss using RHEM. High resolution ground cover data, such as from unmanned aerial systems, may improve parameterization of K ss , and, ultimately, arid rangeland soil erosion simulation.

New Mexico↗

USGS2018

The spatial scale of biotic change in Chihuahuan Desert fish assemblages

1. We examined riverine desert fish assemblages in the Chihuahuan Desert, USA at multiple spatial scales of similarity to assess long-term changes to assemblage distinctiveness, identify individual species responsible for changes, and determine the importance of geographic context and species resolution in interpreting patterns of change. 2. We used a well-documented historical data set on fish distribution and abundance, and recent collections of fishes that provided a paired analytical design across 36 localities spanning nearly three decades of time. Patterns of faunal homogenization and differentiation were assessed at basin-wide, sub-basin and river-reach scales with species occurrence and relative abundance data. Individual species responses were examined to identify the drivers of assemblage change across time. 3. Patterns of similarity varied across spatial scales and produced seemingly incongruous trends in assemblage similarity across time. Patterns of assemblage distinctiveness depended on the spatial extent of the analyses, the geographical structuring of the fish assemblages, and whether occurrence or relative abundance data were used. These dependencies led to interesting and conflicting patterns of homogenization and differentiation. The Rio Grande sub-basin showed strong homogenization with convergence between upstream and downstream reaches that corresponded to declining water quality and quantity from the Rio Conchos in Mexico. In contrast, the Pecos River sub-basin showed strong differentiation between upstream and downstream reaches that corresponded to the successful colonization and spread of the non-native gulf killifish (Fundulus grandis) in the highly degraded upper reach. Spatial variability in fish assemblages and their degree of change from historical conditions were largely dependent on anthropogenic modifications to the flow regime and variability in the success of invasive gulf killifish in the basin. 4. The use of species occurrence or abundance data, and the spatial scale of analysis are crucial choices in studies of faunal homogenization and differentiation, and we have demonstrated how these choices lead to variable results for our study system. Our multi-scale approach and examination of individual species responses identified the ultimate drivers of these differences and illustrated the importance of scale-dependent effects and geographical context on patterns of assemblage distinctiveness, especially with regard to species invasion, species loss and abundance shifts.

Texas↗

USGS2018

Post-fire redistribution of soil carbon and nitrogen at a grassland-shrubland ecotone

The rapid conversion of grasslands into shrublands has been observed in many arid and semiarid regions worldwide. Studies have shown that fire can provide certain forms of reversibility for shrub-grass transition due to resource homogenization and shrub mortality, especially in the early stages of shrub encroachment. Field-level post-fire soil resource redistribution has rarely been tested. Here we used prescribed fire in a shrubland-grassland transition zone in the northern Chihuahuan Desert to test the hypothesis that fire facilitates the remobilization of nutrient-enriched soil from shrub microsites to grass and bare microsites and thereby reduces the spatial heterogeneity of soil resources. Results show that the shrub microsites had the lowest water content compared to grass and bare microsites after fire, even when rain events occurred. Significant differences of total soil carbon (TC) and total soil nitrogen (TN) among the three microsites disappeared one year after the fire. The spatial autocorrelation distance increased from 1~2 m, approximately the mean size of an individual shrub canopy, to over 5 m one year after the fire for TC and TN. Patches of high soil C and N decomposed one year after the prescribed fire. Overall, fire stimulates the transfer of soil C and N from shrub microsites to nutrient-depleted grass and bare microsites. Such a redistribution of soil C and N, coupled with the reduced soil water content under the shrub canopies, suggests that fire might influence the competition between shrubs and grasses, leading to a higher grass, compared to shrub, coverage in this ecotone.

Arizona, Chihuahua, New Mexico, Texas↗

USGS2014

Scale-dependent feedbacks between patch size and plant reproduction in desert grassland

Theoretical models suggest that scale-dependent feedbacks between plant reproductive success and plant patch size govern transitions from highly to sparsely vegetated states in drylands, yet there is scant empirical evidence for these mechanisms. Scale-dependent feedback models suggest that an optimal patch size exists for growth and reproduction of plants and that a threshold patch organization exists below which positive feedbacks between vegetation and resources can break down, leading to critical transitions. We examined the relationship between patch size and plant reproduction using an experiment in a Chihuahuan Desert grassland. We tested the hypothesis that reproductive effort and success of a dominant grass ( Bouteloua eriopoda ) would vary predictably with patch size. We found that focal plants in medium-sized patches featured higher rates of grass reproductive success than when plants occupied either large patch interiors or small patches. These patterns support the existence of scale-dependent feedbacks in Chihuahuan Desert grasslands and indicate an optimal patch size for reproductive effort and success in B. eriopoda . We discuss the implications of these results for detecting ecological thresholds in desert grasslands.

New Mexico↗

USGS2012

Quantifying soil surface change in degraded drylands: shrub encroachment and effects of fire and vegetation removal in a desert grassland

Woody plant encroachment, a worldwide phenomenon, is a major driver of land degradation in desert grasslands. Woody plant encroachment by shrub functional types ultimately leads to the formation of a patchy landscape with fertile shrub patches interspaced with nutrient-depleted bare soil patches. This is considered to be an irreversible process of land and soil degradation. Recent studies have indicated that in the early stages of shrub encroachment, when there is sufficient herbaceous connectivity, fires (prescribed or natural) might provide some reversibility to the shrub encroachment process by negatively affecting shrub demography and homogenizing soil resources across patches within weeks to months after burning. A comprehensive understanding of longer term changes in microtopography and spatial patterning of soil properties following fire in shrub-encroached grasslands is desirable. Here, we investigate the changes in microtopography with LiDAR (light detection and ranging), vegetation recovery, and spatial pattering of soil properties in replicated burned, clipped, and control areas in a shrub-grass transition zone in the northern Chihuahuan Desert four years after prescribed fire or clipping. Results indicate a greater homogeneity in soil, microtopography, and vegetation patterning on burned relative to clipped and control treatments. Findings provide further evidence that disturbance by prescribed fire may allow for reversal of the shrub encroachment process, if the event occurs in the early stages of the vegetation shift. Improved understanding of longer-term effects of fire and associated changes in soil patterning can inform the use and role of fire in the context of changing disturbance regimes and climate.

Chihuahuan Desert↗

USGS2011

Understanding interaction effects of climate change and fire management on bird distributions through combined process and habitat models

Avian conservation efforts must account for changes in vegetation composition and structure associated with climate change. We modeled vegetation change and the probability of occurrence of birds to project changes in winter bird distributions associated with climate change and fire management in the northern Chihuahuan Desert (southwestern U.S.A.). We simulated vegetation change in a process-based model (Landscape and Fire Simulator) in which anticipated climate change was associated with doubling of current atmospheric carbon dioxide over the next 50 years. We estimated the relative probability of bird occurrence on the basis of statistical models derived from field observations of birds and data on vegetation type, topography, and roads. We selected 3 focal species, Scaled Quail ( Callipepla squamata ), Loggerhead Shrike ( Lanius ludovicianus ), and Rock Wren ( Salpinctes obsoletus ), that had a range of probabilities of occurrence for our study area. Our simulations projected increases in relative probability of bird occurrence in shrubland and decreases in grassland and Yucca spp. and ocotillo ( Fouquieria splendens ) vegetation. Generally, the relative probability of occurrence of all 3 species was highest in shrubland because leaf-area index values were lower in shrubland. This high probability of occurrence likely is related to the species' use of open vegetation for foraging. Fire suppression had little effect on projected vegetation composition because as climate changed there was less fuel and burned area. Our results show that if future water limits on plant type are considered, models that incorporate spatial data may suggest how and where different species of birds may respond to vegetation changes.

Chihuahuan Desert↗

USGS2006

Inferences about winter temperatures and summer rains from the late Quaternary record of C 4 perennial grasses and C 3 desert shrubs in the northern Chihuahuan Desert

Late Quaternary histories of two North American desert biomes—C 4 grasslands and C 3 shrublands—are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C 4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial-interglacial cycle. By contrast, key C 3 desert shrubs appeared somewhat abruptly after 5000cal.yrBP. Bioclimatic envelopes for select C 4 and C 3 species are mapped to interpret the glacial-interglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C 4 grasses, whereas winters were probably too cold (or too wet) for C 3 desert shrubs. Contrary to climate model results, core processes associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial-interglacial cycle. Mid-latitude effects, however, truncated midsummer (July-August) moisture transport north of 35° N. The sudden expansion of desert shrublands after 5000cal.yrBP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño-Southern Oscillation variability.

Arizona, New Mexico, Texas↗

USGS2002

Long-term dynamics of winter and summer annual communities in the Chihuahuan Desert

Winter and summer annuals in the Chihuahuan Desert have been intensively studied in recent years but little is known about the similarities and differences in the dynamics between these two communities. Using 15 yr of census data from permanent quadrats, this paper compared the characteristics and temporal dynamics of these two distinct, spatially co-existent but temporally segregated communities. Although the total number of summer annual species recorded during our 15 yr of observation was higher than winter annuals, the mean number of species observed each year was higher in the winter community. The winter community exhibited lower temporal variation in total plant abundance and populations of individual species, lower species turnover rate and higher evenness than the summer community. The rank abundances of species in winter were significantly positively correlated for a period of up to 7 yr while in summer significant positive correlations in rank abundance disappeared after 2 to 3 yr. The higher seasonal species diversity (i.e. number of species observed in each season) in winter rather than the overall special pool (over 15 yr) may be responsible for the greater community stability of winter annuals. The difference in long-term community dynamics between the two communities of annual plants are likely due to the differences in total species pool, life history traits (e.g. seed size), and seasonal climatic regimes.

Portal↗

USGS2001

Bird-landscape relations in the Chihuahuan Desert: Coping with uncertainties about predictive models

During the springs of 1995–1997, we studied birds and landscapes in the Chihuahuan Desert along part of the Texas–Mexico border. Our objectives were to assess bird–landscape relations and their interannual consistency and to identify ways to cope with associated uncertainties that undermine confidence in using such relations in conservation decision processes. Bird distributions were often significantly associated with landscape features, and many bird–landscape models were valid and useful for predictive purposes. Differences in early spring rainfall appeared to influence bird abundance, but there was no evidence that annual differences in bird abundance affected model consistency. Model consistency for richness (42%) was higher than mean model consistency for 26 focal species (mean 30%, range 0–67%), suggesting that relations involving individual species are, on average, more subject to factors that cause variation than are richness–landscape relations. Consistency of bird–landscape relations may be influenced by such factors as plant succession, exotic species invasion, bird species' tolerances for environmental variation, habitat occupancy patterns, and variation in food density or weather. The low model consistency that we observed for most species indicates the high variation in bird–landscape relations that managers and other decision makers may encounter. The uncertainty of interannual variation in bird–landscape relations can be reduced by using projections of bird distributions from different annual models to determine the likely range of temporal and spatial variation in a species' distribution. Stochastic simulation models can be used to incorporate the uncertainty of random environmental variation into predictions of bird distributions based on bird–landscape relations and to provide probabilistic projections with which managers can weigh the costs and benefits of various decisions. Uncertainty about the true structure of bird–landscape relations (structural uncertainty) can be reduced by ensuring that models meet important statistical assumptions, designing studies with sufficient statistical power, validating the predictive ability of models, and improving model accuracy through continued field sampling and model fitting. Uncertainty associated with sampling variation (partial observability) can be reduced by ensuring that sample sizes are large enough to provide precise estimates of both bird and landscape parameters. By decreasing the uncertainty due to partial observability, managers will improve their ability to reduce structural uncertainty.

Chihuahua, Coahuila, Nuevo León, Tamaulipas, Texas↗