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Soil microbial organisms are central to carbon (C) and nitrogen (N) transformations in soils, yet not much is known about the stable isotope composition of these essential regulators of element cycles. We investigated the relationship between C and N availability and stable C and N isotope composition of soil microbial biomass across a three million year old semiarid substrate age gradient in northern Arizona. The δ15N of soil microbial biomass was on average 7.2‰ higher than that of soil total N for all substrate ages and 1.6‰ higher than that of extractable N, but not significantly different for the youngest and oldest sites. Microbial 15N enrichment relative to soil extractable and total N was low at the...
Knowledge about the condition of vegetation cover and composition is critical for assessing the structure and function of ecosystems. To effectively quantify the impacts of a rapidly changing environment, methods to track long-term trends of vegetation must be precise, repeatable, and time- and cost-efficient. Measuring vegetation cover and composition in arid and semiarid regions is especially challenging because vegetation is typically sparse, discontinuous, and individual plants are widely spaced. To meet the goal of long-term vegetation monitoring in the Sonoran Desert and other arid and semiarid regions, we determined how estimates of plant species, total vegetation, and soil cover obtained using a widely-implemented...
Plant detritus is an important source of labile C that drives soil microbial growth and regulates the balance of N mineralization and immobilization. In semiarid ecosystems, timing of plant detrital inputs may be especially important in regulating microbial C and N cycling because of the relatively short window of time when moisture is available. Low soil moisture in early-summer may inhibit microbial colonization of recently released detritus, resulting in C-limitations to microbial growth, and this may explain the NO3? accumulation commonly observed in semiarid, arid, and Mediterranean ecosystems. We examined linkages between soil C availability and gross N cycling rates during summer in three common semiarid...
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Geomorphic features mapped from historical aerial photographs (1935, 1950s, 1970s, and 1996), satellite imagery (November 2006), and digital aerial imagery (Standard Imagery LiDAR Composite; Spectrum Mapping, LLC, 2005) are provided in shapefiles for each year of data. Features mapped are tops of the arroyo walls, edges of the arroyo bottom (covering the active floodplain and channel), tops of channel banks, the channel centerline, canopy cover, and 2006 flood sand deposits. In addition, shapefiles containing a reference arroyo centerline, points at 0.5-km intervals along the arroyo centerline, and polygons identifying the 0.5-km arroyo segments are provided. Individual metadata files describe the contents of each...
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High-precision (Real-time kinematic) Global Positioning System (GPS) surveys were conducted along the lower Rio Puerco in April 2002, January 2007, April 2010, and April 2014 to support a long-term study of geomorphic processes and the geomorphic history of the arroyo. The study reach extends from the confluence with the Rio San Jose 67 km downvalley to the old Highway 85 bridge near the USGS streamgage near Bernardo, NM. Individual shapefiles were created for data from each survey. Associated metadata files include the names of surveyors and equipment used. The survey extents varied, but all have overlapping points, including repeat surveys of arroyo cross sections. Results from analyses of these data were published...
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A long-term study of the geomorphic history of the lower Rio Puerco arroyo in north-central New Mexico included the collection of high-precision (Real-time kinematic) GPS survey data (2002, 2007, 2010, and 2014), registration and rectification of historical aerial photographs (1935, 1950s, 1970s, and 1996), an aerial LiDAR survey (2005) with collection of digital imagery, and acquisition of post-flood (2006) satellite imagery. The Rio Puerco is a single-thread, meandering stream inset within an arroyo located in semiarid north-central New Mexico. The study reach extent is from the confluence with the Rio San Jose 67 km downvalley to the Rio Puerco streamgage near Bernardo, NM. Arroyo and channel geomorphic features...
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Defining site potential for an area establishes its possible long-term vegetation growth productivity in a relatively undisturbed state, providing a realistic reference point for ecosystem performance. Modeling and mapping site potential helps to measure and identify naturally occurring variations on the landscape as opposed to variations caused by land management activities or disturbances (Rigge et al. 2020). We integrated remotely sensed data (250-m enhanced Moderate Resolution Imaging Spectroradiometer (eMODIS) Normalized Difference Vegetation Index (NDVI) (https://earthexplorer.usgs.gov/)) with land cover, biogeophysical (i.e., soils, topography) and climate data into regression-tree software (Cubist®). We...
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A study of arroyo evolution in northern New Mexico (Friedman and others, 2015) assessed geomorphic change in the Chaco Wash arroyo from the 1930s to 2000. As part of this study, in October 2000 a trench was excavated across the arroyo bottom and a high-precision (Real-time kinematic) GPS survey was conducted. GPS survey data were used to georeference a 1930s topographic map and to identify key geomorphic features, including the tops of the arroyo walls and the channel thalweg. Linear features were mapped in a GIS for use in extracting channel thalweg profiles, an arroyo cross section, and arroyo widths (1930s and 2000) as a function of distance down-valley. These features have been converted to shapefiles included...
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Biological soil crusts (BSCs), a consortium of cyanobacteria, lichens, and mosses, are essential in most dryland ecosystems. As these organisms are relatively immobile and occur on the soil surface, they are exposed to high levels of ultraviolet (UV) radiation and atmospheric nitrogen (N) deposition, rising temperatures, and alterations in precipitation patterns. In this study, we applied treatments to three types of BSCs (early, medium, and late successional) over three time periods (spring, summer, and spring–fall). In the first year, we augmented UV and altered precipitation patterns, and in the second year, we augmented UV and N. In the first year, with average air temperatures, we saw little response to our...
Hazard-zone delineation for extreme events is essential for floodplain management near mountain fronts in arid and semiarid regions. On 31 July 2006, unprecedented debris flows occurred in the Santa Catalina Mountains of southeastern Arizona following extreme multiday precipitation (recurrence interval > 1000 years for 4-day precipitation). Most mobilized sediment contributing to debris flows was derived from shallow-seated failures of colluvium on steep slopes. A total of 435 slope failures in the southern Santa Catalina Mountains released 1.34 million Mg of sediment into the channels of 10 drainage basins. Five drainages produced debris flows that moved to the apices of alluvial fans on the southern edge of the...
Water availability defines and is the most frequent control on processes in arid and semiarid ecosystems. Despite widespread recognition of the importance of water in dry areas, knowledge about key processes in the water balance is surprisingly limited. How water is partitioned between evaporation and transpiration is an area about which ecosystem ecologists have almost no information. We used a daily time step soil water model and 39 years of data to describe the ecohydrology of a shortgrass steppe and investigate how manipulation of soil and vegetation variables influenced the partitioning of water loss between evaporation and transpiration. Our results emphasize the overwhelming importance of two environmental...
    map background search result map search result map Global change and biological soil crusts: effects of ultraviolet augmentation under altered precipitation regimes and nitrogen additions Lower Rio Puerco geospatial data, 1935 - 2014 Lower Rio Puerco GPS survey data collected in 2002, 2007, 2010, and 2014 Lower Rio Puerco mapped geomorphic features (shapefiles), 1935, 1950s, 1970s, 1996, 2005, and 2006 Chaco Canyon 1930s and 2000 geospatial data Using Targeted Training Data to Develop Site Potential for the Upper Colorado River Basin from 2000 - 2018 Chaco Canyon 1930s and 2000 geospatial data Lower Rio Puerco geospatial data, 1935 - 2014 Lower Rio Puerco GPS survey data collected in 2002, 2007, 2010, and 2014 Lower Rio Puerco mapped geomorphic features (shapefiles), 1935, 1950s, 1970s, 1996, 2005, and 2006 Global change and biological soil crusts: effects of ultraviolet augmentation under altered precipitation regimes and nitrogen additions Using Targeted Training Data to Develop Site Potential for the Upper Colorado River Basin from 2000 - 2018