Playa Basins Research Articles

Salt ramps: Wind‐induced depositional features on Tunisian playas

AbstractSemicircular and crescent‐shaped accumulations of salt crystals developed on salt crusts were measured on three Tunisian playas in September 1990. These features have been termed salt ramps. Their morphology and chemistry suggest that they are formed in the late stages of shallow ephemeral lake desiccation in playa basins. They form by salt precipitation from shallow brine lakes that are blown across salt‐encrusted playa surfaces by the wind. Moreover, they appear to be short‐lived features and their degradation is related to the flooding of playas with less saline water, and possibly rainfall and deflation.

Subterranean termites: regulators of soil organic matter in the Chihuahuan Desert

Soil organic matter and the abundance of subterranean termites were measured at 89 locations spaced at 30-m intervals from the bottom to the top of a small desert watershed. There was no correlation between soil organic matter content and topographic position on the watershed. Analysis by autocorrelogram demonstrated that the soil organic matter content was randomly distributed on the watershed. There was a highly significant negative correlation between termite abundance and soil organic matter, r=−0.97. Soils characterized by horizon in soil pits within each vegetation type (soil type) showed some relationships to erosion-deposition areas on the watershed, with surface organic matter contents varying between 3.4% in the playa basin where termites were absent to 0.4% in a sparse shrubland on erosional soils. In the northern Chihuahuan Desert, subterranean termites appear to be responsible for most of the variation in soil organic matter.

Groundwater Quality Near Two Cattle Feedlots in Texas High Plains: A Case Study

A groundwater sampling study was conducted at two cattle feedlots with capacities of 45,000 (Feedlot A) and 42,500 head (Feedlot B), respectively, in Castro and Parmer Counties in the Southern High Plains of Texas. At both feedlots, groundwater was sampled from the Ogallala Aquifer at four water wells supplying cattle drinking water and from 10 or 11 irrigation wells within a distance of 1.07 to 1.41 km (0.67 to 0.88 mile) from the feed pens or playa basins (natural depressions) used for collection of feedlot runoff. Water table depth was 82.3 to 97.5 m (270 to 320 ft). Nitrate-nitrogen (NO3 N) concentrations averaged less than 1.2 mg/L at Feedlot A (maximum value of 2.23 mg/L) and 5.21 mg/L at Feedlot B (maximum value of 9.54 mg/L). These are below the USEPA primary drinking water standard of 10.0 mg/L NO3-N. Other nutrient and salinity values were low. The well water in all feedlot wells and in farm irrigation wells appears to be suitable for irrigation, livestock watering, and human consumption. Minimal differences were found between parameter concentrations in feedlot wells and adjacent farm irrigation wells. Groundwater quality near these two feedlots met primary and secondary EPA drinking water standards for those parameters tested.

Subsidence beneath a playa basin on the Southern High Plains, U.S.A.: Evidence from shallow seismic data

Shallow seismic data from Sevenmile Basin, a large ephemeral lake (playa) basin in the Texas Panhandle, reveal that subsidence has been an important agent in basin formation. Several hypotheses exist for the origin of thousands of playa basins on the Southern High Plains of Texas and New Mexico, including eolian deflation, evaporite or carbonate dissolution and subsidence, piping, and animal activity. Sevenmile Basin is 5.5 x 3.6 km across and 14 m deep and contains 20 m of lacustrine and eolian sediments that interfinger with the Quaternary Blackwater Draw Formation. Below these sediments is the upper Tertiary Ogallala Formation, which overlies Permian or Triassic bedrock. Seismic reflection and refraction data were collected from the unlithified and variably saturated clastic sequence beneath Sevenmile Basin to investigate the geological history and hydrogeological framework of playa basins, which recharge the regionally important Ogallala aquifer. Three-layer velocity models provide good solutions for reversed refraction data. Near-surface p-wave velocities (layer 1) range from 349 to 505 m/s, layer 2 velocities range from 806 to 851 m/s, and layer 3 velocities range from 2,037 to 2,161 m/s. Shallow test holes and drillers' logs suggest that layer 1 is composed of playa and upper Blackwater Draw Formation deposits, layer 2 consists of lower Blackwater Draw Formation and upper Ogallala Formation deposits, and layer 3 represents a competent and partly saturated zone near the top of the Ogallala aquifer. Reflection sections show a middle Ogallala reflector, a reflector at the top of Permian or Triassic bedrock, and internal bedrock reflectors that indicate a structural low beneath Sevenmile Basin. Increasing relief with age, from 14 m at the surface to 70 m on the middle Ogallala reflector to 110 m at the base of the Ogallala, is interpreted as evidence of subsidence of underlying Permian evaporite-bearing strata before or during Ogallala deposition. Ogallala and Blackwater Draw Formation thicknesses greater than bedrock Ogallala deposition and may continue to the present. Virtually all playa basins on the Southern High Plains are underlain by Permian evaporite-bearing strata; some basins have been affected by dissolution-induced subsidence. Shallow seismic methods are an ideal approach to determine the relative importance of subsidence in basin formation.

Environmental and Demographic Correlates of Spatial and Seasonal Genetic Structure in the Eastern Cottontail (Sylvilagus floridanus)

Elucidation of the complex interactions of forces that affect genetic structure within and among populations is important in the assessment of short-term viability and evolution of natural populations. We examined spatial and temporal changes in genetic, demographic, and ecologic characteristics of the eastern cottontail (Sylvilagusfloridanus; n = 543) within two isolated populations inhabiting playa lake basins in the Texas Panhandle. Spatial autocorrelation and contiguous clustering analyses documented nonrandom dispersion of genotypes within both populations, during each of four consecutive seasons. Considerable seasonal variation in genotypic autocorrelative patterns and size, position, and genotypic composition of significant contiguous clusters also was observed. Genotypic structuring within playa basins was particularly evident during spring, summer, and autumn; greater randomization of genetic distributions occurred in the winter, prereproductive season. Presence of spatial associations of genotypes and changes in their position and composition over seasons were influenced by episodic exchange of individuals from genetically different populations, subsequent random mating and restoration of Hardy-Weinberg genotypic proportions in resulting offspring, and patchy distribution of habitat types within playa basins. Mantel matrix regressions, which were used to test relationships among demographic, habitat, and genotypic variables show that the relative importance of each factor changes seasonally. Differences in habitat use among individuals were significantly correlated with genotypic cluster affiliation during the prereproductive period, whereas age structure became increasingly important in explaining spatial arrangement of genotypes during later periods. Although populations from different playa basins differ in gene frequency, seasonal changes in genetic structure within each population were correlated.

Perched Aquifers-Their Potential Impact On Contaminant Transport in the Southern High Plains, Texas

Understanding the hydrogeology and hydrochemistry of perched aquifers at potential and known contaminated waste sites has become increasingly important because of the impact these aquifers may have on contaminant transport independent of regional aquifer processes. Investigations of a perched aquifer above the Ogallala aquifer are being conducted in the region of the U.S. Department of Energy's Pantex Plant, a proposed Superfund site, located approximately 20 mi northeast of Amarillo, Texas. Since the early 1950s, a small playa basin located on the Pantex Plant has been used as a waste-water discharge pond with daily discharge rates ranging from 400,000 to 1 million gal. The focus of this investigation is an unconfined, perched aquifer that overlies a thick silty clay sequence within the upper, mostly unsaturated part of the Ogallala Formation (Neogene). In the area of the Pantex Plant, measured depths to the perched aquifer range from 200 to 300 ft below land surface, whereas depth to the regional Ogallala aquifer ranges from 375 to 500 ft. The potentiometric surface of the perched aquifer typically represents groundwater mounds proximal to the playas and thins into trough in the interplaya areas. Hydrologic gradients of the primary mound under investigation are relatively high, rangingmore » from 28 to 45 ft/mi. Calculated transmissivities have a geometric mean of 54 ft[sup 2]/day, with saturated thicknesses ranging from 4 to 1000 ft. Modeling of the perched aquifer was designed to determine how much, if any, discharge to the small playa basin has enhanced recharge to the perched aquifers and increased the vertical and lateral extent of the perched aquifer. Preliminary results indicate that measurements of vertical conductance through the perching silty-clay sequence and recharge rates through playas are critical for calibrating the model. Accurate delineation of rates and flow directions in the perched aquifer is critical to any successful remediation effort.« less

Sedimentologic and geochemical constraints on the evolution of Bristol Dry Lake Basin, California, U.S.A

Two continuous cores over 400 m in length drilled in Bristol Dry Lake, a large playa in the Mojave Desert, California, U.S.A., provide sedimentologic and isotopic information which can be integrated with surface trenches and groundwater analyses. The combination of these data provide three-dimensional data on the facies distribution and geochemical evolution of the basin for the last 4 Ma. At the surface, the basin exhibits a generalized bulls-eye facies distribution. Low-gradient alluvial fans ring the playa. Extensive calcrete and pedogenic calcite associated with halophyte plants cement the mid-to-distal fan gravels and sands. Basinward of the distal fans, in the playa margin facies, an extensive gypsum zone is over 300 m wide. Within the gypsum zone, celestite forms large decimetre-size nodules which may coalesce into metre-size patches. Basinward of the playa margin facies, halite hopper crystals (up to 0.5 m in diameter) form in water-saturated muds of the saline mud-flat facies. Finally, in the basin-centre a 0.2-m thick chevron halite crust (salt pan) forms from evaporation of ponded ephermeral water. The lateral facies distribution seen at the surface is found throughout the entire length of the cores. The core drilled in the basin-centre exhibits beds of alternating salt pan and saline mud-flat facies, whereas the core drilled in the playa margin exhibits alternating beds of playa margin sediments and saline mud-flat for most of the length of the core. Towards the base of the playa-margin core, distal alluvial fan sediments are also present. Stable oxygen isotopes of basin-centre calcite concretions from the surface and core indicate that the isotopic composition of the water precipitating the concretions has not changed substantially throughout the evolution of the basin. The sulfur isotopic composition of the surface gypsum, anhydrite and celestite show little variation. However, δ 34S values of anhydrite from core are isotopically lighter relative to surface gypsum and anhydrite. This isotopic depletion indicates that bacterial sulfate-reduction is involved in the dehydration of gypsum to anhydrite, and is not caused by evolving isotopic composition of sulfate in the brine. At the surface, gypsum δ 34S values show no statistically significant trends with lateral distribution. Chemical analyses from shallow groundwater wells and basin-centre brines from up to 150 m depth indicate that: (1) the brine is dominated by Na, Cl, and Ca. (2) Na, Ca, Mg, K, and Cl contents increase toward the basin-centre, SO 4 increases from the alluvial fan facies to the playa margin and then sharply decreases in the basin-centre, and Si, and HCO 3 decrease slightly toward the basin-centre. This pattern is consistent with the observed evaporite mineral distribution in the basin. (3) molar Na:Cl and Ca:Cl ratios demonstrate that the simple dissolution of previously deposited halite deposits, as has been suggested for other playa basins, cannot account for the proportions of these ions present in the brine. (4) Chemical budget calculations suggest that Cl can be accounted for by atmospheric input, although hydrothermal sources cannot be discounted. The repititious nature of the alternating shallow brine-pond halite and siliciclastics, the consistency of the carbonate isotopic data from the surface and core, and the agreement of water chemistry data with observed evaporite sequences, indicate a relatively stable brine composition for most of the history of Bristol Dry Lake. All sedimentary structures and primary halite fabrics in the core indicate shallow-water, brine-pond halite alternated with halite-saturated siliciclastic muds in the basin-centre. A delicate balance between subsidence, and mechanical and chemical deposition of minerals was necessary to maintain the largely ephemeral environment of deposition during the deposition of over 500 m of basin fill.

Seasonal Demography and Movements of Cottontail Rabbits on Isolated Playa Basins

We examined spatial and temporal changes in population density, age structure, and individual movement distances of eastern cottontail rabbits (Sylvilagus floridanus) on 2 playa lake basins in the Texas Panhandle. We obtained 1,857 captures of 931 individual rabbits during 7,450 trap nights from February through November 1981. Population densities during prereproductive periods were 8.2 and 11.6 cottontails per ha on playa basins A and B, respectively. Subsequent changes in density were related to reproductive recruitment and to dispersal. Densities peaked at 28.4 and 26.9 cottontails per ha on playa basins A and B, respectively, during summer trapping periods. Adult :juvenile ratios declined coincident with the production of 7 litters. Distribution of captures within each playa basin and dispersal patterns were related to seasonal maturation and harvest of surrounding crops. A greater (P 2 times revealed that seasonal movement distances reflected the availability of habitats (i.e., crops) surrounding playa basins. J. WILDL. MANAGE. 54(3):403-409 Fragmentation and isolation of wildlife habitats by agricultural practices in the United States have dramatically reduced the abundance and diversity of native wildlife (Burger 1978). In fragmented habitat, native wildlife populations have been subdivided spatially and restricted to small areas of permanent cover such as fence rows and shelter belts (Swihart and Yahner 1982). These populations may be regulated as much by the availability, spatial arrangement, and interconnected nature of habitat as they are by fecundity and mortality rates (Fahrig and Merriam 1985). In regions of intensive agricultural activity, wildlife inhabiting small relic areas of native habitat may represent source populations (Pulliam 1988) where reproduction exceeds available cover, food resources, and breeding sites. Similarly, surrounding agricultural areas may constitute population sinks. Crops provide marginal habitat for a portion of the year, but are eliminated after harvest. Agricultural habitats might be expected to alter seasonal movements and dispersion of individuals, increase the potential productivity of source populations, and facilitate dispersal among isolated areas of permanent cover. The eastern cottontail rabbit inhabits earlymidsuccessional habitats over much of the continental United States, including all but the southwestern portion of Texas (Davis 1974). Previous studies of cottontail reproductive phenology (Chapman and Morgan 1973) and population dynamics (Bothma and Teer 1977) were done in southern and southeastern Texas and over much of the species' native range (see Chapman et al. 1982). However, relatively little work has been done on cottontails in finite and dispersed playa basin habitats that dominate most of the southern Great Plains. We present data on seasonal changes in cottontail demographic characteristics and movements for discrete populations inhabiting playa basins in the Texas Panhandle. Our objectives were to document seasonal variations in population densities, age structure, and breeding chronology. Further, analyses of cottontail movements and dispersion were examined relative to changing population age structure and the influences of adjacent agricultural activities. This work was funded by the Caesar Kleberg Foundation for Wildlife Conservation, The Noxious Brush and Weed Control Program at Texas Tech University, and through contract DEAC09-765R00819 between the U.S. Department of Energy and the University of Georgia's Institute of Ecology. This paper is Manuscript Number T-9-291, College of Agricultural Sciences, Texas Tech University. i'Present address: Department of Zoology, University of Georgia, Athens, GA 30602. 2 Present address: School of Forest Resources, University of Georgia, Athens, GA 30602.

Paleochemistry and paleohydrology of Ceylon Lake, a salt-dominated playa basin in the northern Great Plains, Canada

Paleochemistry and paleohydrology of Ceylon Lake, a salt-dominated playa basin in the northern Great Plains, Canada

Playa Lakes: Prairie Wetlands of the Southern High Plains

Slayas are shallow, circular basins dotting the surface of plains and desert landscapes. Whereas playa basins occur elsewhere in the world (e.g., in the Sahara and Mohave deserts), they are nowhere as numerous or dense as on the Southern High Plains (SHP) or Llano Estacado, an 82,000-square-kilometer tableland south of the Canadian River in Texas and New Mexico (Figure 1). Playas average 6.3 ha in size; 19,340 of the basins occur in Texas and 2,460 in New Mexico, with another 3,590 playas found in plains states north of the Canadian River (Guthery and Bryant 1982). Most playas on the SHP may have formed during the Pleistocene from the deflating erosion of prairie winds, although theories vary (Osterkamp and Wood 1987). Popular notions

Evaporites and strata-bound tungsten mineralization

Research Article| February 01, 1989 Evaporites and strata-bound tungsten mineralization G. Todd Ririe G. Todd Ririe 1Unocal Science and Technology Division, P.O. Box 76, Brea, California 92621 Search for other works by this author on: GSW Google Scholar Geology (1989) 17 (2): 139–143. https://doi.org/10.1130/0091-7613(1989)017<0139:EASBTM>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation G. Todd Ririe; Evaporites and strata-bound tungsten mineralization. Geology 1989;; 17 (2): 139–143. doi: https://doi.org/10.1130/0091-7613(1989)017<0139:EASBTM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Discoidal gypsum crystal cavities occur in quartzites that host varying amounts of stratabound scheelite mineralization near Halls Creek in Western Australia. The host quartzites have been regionally metamorphosed to greenschist facies and are contained within a Middle Proterozoic sequence that includes pelites, mafic and felsic volcanics, and voicaniclastic rocks. Textural, fluid inclusion, and oxygen isotope data indicate that scheelite was present in the host quartzites prior to regional metamorphism. The presence of crystal cavities after gypsum in the quartzites implies an evaporitic origin for this sequence.The continental-sabkha playa basins of the Mojave Desert, California, are suggested to be possible modern analogs—e.g., Searles Lake, where the tungsten content is up to 70 PPM WO3 in brines and 118 ppm in muds, and exceeds the amount of tungsten in all known deposits in the United States. Metamorphism of a continental evaporitic sequence containing tungsten could produce an assemblage of rocks very similar to those reported from several stratabound tungsten deposits. Some of these, such as at Halls Creek, may be related to original accumulations of tungsten in nonmarine evaporitic environments. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Abundance and Diversity of Surface-active Collembola along a Watershed in the Northern Chihuahuan Desert

Jackknife diversity estimates (N2 = inverse Simpson diversity index) for surface-active Collembola were examined along a watershed in the Chihuahuan desert of southern New Mexico. Chord distance measures indicated low similarity in collembolan species composition among the six sites. However, assemblages at the top (black grama grassland) and bottom (mesquite fringe of playa) of the gradient were similar to each other, possibly reflecting available soil nitrogen. There was no significant correlation between Collembola and either weekly or long-term precipitation patterns. Populations of truly epigeic Collembola appeared unaffected by rainfall but were significantly, though weakly, correlated with long-term temperatures. INTRODUCTION Temporal and spatial distributions of soil microarthropods in desert ecosystems have been studied by several workers (Wood, 1971; Wallwork, 1972; Santos et al., 1978; Franco et al., 1979; Greenslade, 1981; Santos and Whitford, 1983; Steinberger and Whitford, 1984; Kamill et al., 1985). Considerably less work has been done examining the distribution and activity patterns of epigeic microarthropods in arid environments. Greenslade and Greenslade (1973) reported that some epigeic Collembola (e.g, Entomob7ya spp.) in semiarid Australia were active on sand dunes throughout the hottest part of the year. Comparing the taxonomic similarities of, and adaptations by, collembolan faunas in arid areas of Australia and Africa, Greenslade (1981) found several genera which were resistant to desiccation and concluded that populations of many species are underestimated in arid or semiarid areas. Pefaur (1981) showed that the abundance of epigeic microarthropods varied along an altitudinal gradient (300-1000 m) in a Peruvian desert, though there was little correlation between elevation and abundance of each species. Pefaur (1981) hypothesized that the abundance of epigeic species populations should increase in response to the increase of surface litter, which would provide greater shade and humidity. Except for Hypogastruridae (= Poduridae), he collected most Collembola from moist areas. In the Chihuahuan Desert of southern New Mexico, differences in soil type and drainage patterns produce distinct plant communities. Some of these produce more organic litter than others. Our objectives in this study were to examine the composition of epigeic collembolan communities associated with different plant communities along a watershed and to determine the seasonal activity of epigeic Collembola in this system. MATERIALS AND METHODS The study was conducted at the Jornada Long Term Ecological Research Site (LTER) located 40 km NNE of Las Cruces, New Mexico. The LTER area encompasses a watershed extending from the base of Mt. Summerford down a drainage slope (bajada) to a temporary lake basin (playa) 2850 m distant. Soils vary from coarse gravels on the bajada to sandy loam on the playa edge and clay silt on the playa basin. Pitfall traps were placed in six plant communities distributed along the watershed. From the bottom to the top of the drainage slope, these were: 1) playa, dominated by

Seed reserves in the tailwater pits of playa lakes in relation to waterfowl management

Seed reserves were monitored in the tailwater pits of 10 playa lakes on the Southern High Plains of Texas. These deep, steep-sided pits are excavated by famers to store water for irrigation and livestock. Unfortunately, pits partially drain the productive littoral zones of playa basins and thus, often have a negative effect on, wetland wildlife. We constructed experimental pits with step-like terraces on one side to create artificial liuoral zones in playa pits. Post-excavation seed numbers were near zero, but rainwater and irrigation tailwater later washed large numbers of seeds into the pits from the playa basins. The resulting seed bank was large and diverse enough to produce dense stands of wetland vegetation in all parts of the pits. Terraces produced more (P 0.05) in deep areas during winter, but seeds were depleted (P<0.05) on the terraces. All pits will produce wetland vegetation each year under almost any water regime because of the variety of seeds present.

Genetic differentiation among cottontails from isolated playa basins.

Protein variation in 182 Sylvilagus floridanus from 19 playa basins in Castro Co., Texas was examined using starch-gel electrophoresis. Heterozygote deficiencies were noted for all populations. This heterozygote deficiency may be due to differential selection against heterozygous individuals over the winter months. Results of F-statistics indicated a significant degree of population differentiation at six loci. Nei's genetic distance between populations ranged from 0.20 to 0.388 and a significant association between genetic distance and linear geographic distance among playas was found. These results suggest that genetic exchange and long-distance dispersal may be hindered by expanses of unsuitable habitat.

Playa-lake basins on the Southern High Plains of Texas and New Mexico: Part II. A hydrologic model and mass-balance arguments for their development

Research Article| August 01, 1987 Playa-lake basins on the Southern High Plains of Texas and New Mexico: Part II. A hydrologic model and mass-balance arguments for their development WARREN W. WOOD; WARREN W. WOOD 1U.S. Geological Survey, 431 National Center, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar W. R. OSTERKAMP W. R. OSTERKAMP 1U.S. Geological Survey, 431 National Center, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar Author and Article Information WARREN W. WOOD 1U.S. Geological Survey, 431 National Center, Reston, Virginia 22092 W. R. OSTERKAMP 1U.S. Geological Survey, 431 National Center, Reston, Virginia 22092 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 99 (2): 224–230. https://doi.org/10.1130/0016-7606(1987)99<224:PBOTSH>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WARREN W. WOOD, W. R. OSTERKAMP; Playa-lake basins on the Southern High Plains of Texas and New Mexico: Part II. A hydrologic model and mass-balance arguments for their development. GSA Bulletin 1987;; 99 (2): 224–230. doi: https://doi.org/10.1130/0016-7606(1987)99<224:PBOTSH>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Hydrologic, geologic, geomorphic, and mass-balance data suggest that most of the ∼30,000 playa lake basins on the Southern High Plains have developed by a combination of dissolution of caliche and piping of surface material into the unsaturated zone rather than by eolian processes as has generally been stated. A conceptual model suggests that particulate organic material, much of which is sorbed on smectite clays, is carried downward from the surface into the unsaturated zone by recharging water. The organic material is oxidized to CO2, which dissolves in the water, forms carbonic acid, and dissolves lithologic carbonates. Because organic material is transported and oxidized deep in the unsaturated zone, CO2 concentrations are much higher at depth than in the soil zone, and recharging water remains thermodynamically subsaturated with respect to carbonates and thus able to dissolve them throughout the unsaturated zone. Dissolution promotes lithologic instability, leading to piping and eluviation of material within the unsaturated zone. Playa basins expand laterally as recharge is concentrated at the edge of the playa floor because of lowered permeability in the center that results from accumulation of clays and other fine sediment.Mass-balance calculations of gas, liquid, and solid fluxes beneath a playa basin suggest that sufficient mass is transported to account for the volume of the depression. Particulate flux is estimated by relating it to the CO2 flux out of the unsaturated zone. Solute flux is estimated from the difference between input values from the playa lake water and that observed in ground water. Gas flux is measured directly from gas samples at specific depths below the: surface. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Remote sensing of sediment transfer processes in playa basins

Summary Landsat Thematic Mapper and Multispectral Scanner data have been used to detect changes in the spectral reflectance and absorption of three playas in south-central Tunisia. Change detection images have been used to analyse changes between wet and dry seasons and between different years. Changes in geomorphological phenomena are interpreted from changes in soil and foliar moisture levels, differences in reflectance between different salts and sediments, and the spatial expression of geomorphological features. The intra-annual changes that can be detected from multidate imagery include surface moisture, texture and chemical composition, vegetation cover and the extent of aeolian activity. Detected inter-annual changes are divisible into those restricted to playa margins—sedimentation from sheetwash and alluvial fans, erosion from surface runoff, and cliff retreat—and those found at central playa locations which are related to the redistribution of water, salt and sediment.

Sedimentology of playa lakes of the northern Great Plains

The semi-arid plains of western Canada and northern United States contain a large number of saline and hypersaline lakes, with many of the shallow lakes exhibiting playa characteristics. For over 60 years a number of these playas have provided a source of valuable industrial minerals. The present study deals with the modern sediments and sedimentary processes operating in selected playa basins located throughout the northern Great Plains region.The playas generally occupy small, closed basins commonly having an elongate, riverine shape. Most of the brines are dominated by sodium, magnesium, and sulfate ions; however, examples of lakes rich in chloride and bicarbonate ions are also present. Significant variation in the brine chemistry can exist on a seasonal as well as a diurnal basis. The modern sediments of the playas consist of: (1) very soluble salts of mainly sodium and magnesium sulfates and carbonates; (2) sparingly soluble precipitates, including calcite, protodolomite, gypsum, and mixed layer clays; (3) detrital minerals consisting dominantly of quartz, carbonates, feldspars, and clays; and (4) organic matter.Much of the physical and mineralogical character of the playas is due to processes that are largely of a chemical nature and are associated with either evaporative concentration of the brines or groundwater discharge. The most significant processes include: cyclic flooding and desiccation of the playa surface, formation of salt crusts, efflorescent crusts, spring deposits, and intrasedimentary salts, formation of solution pits and chimneys, wind displacement of brines, and periodic detrital sedimentation by sheet flow and wind. These processes combine to create a very dynamic modern depositional environment. The establishment and prolonged maintenance of delicate physical and chemical equilibria have allowed the deposition of over 40 m of salt in some basins.

Ring-Necked Pheasant Movements, Home Ranges, and Habitat Use in West Texas

Ring-necked pheasant (Phasianus colchicus) movements, home ranges, and habitat use were studied in the High Plains of Texas. Day-to-day movements were highest in fall and winter, intermediate in spring, and lowest in summer. Monthly home ranges were largest in summer and fall and smallest in spring and winter. Pheasants were restricted to playas in winter, moved into cool-season crops during spring, and preferred row crops, small grains, and playas during summer and fall. Habitat management for pheasants in west Texas, given prevailing land-use practices and economic constraints, should include (1) the planting of a summer crop (corn or sorghum) and a spring crop (wheat) adjacent to an ungrazed playa or (2) the planting of corn, wheat, sorghum, and any other crop, adjacent to an ungrazed playa. A management unit for pheasants in west Texas should include all land (400 ha) within a 1.13-km radius of a playa lake where the birds overwinter. J. WILDL. MANAGE. 47(4):1097-1104 Pheasants became established in the Texas Panhandle about 1940 (Jones and Felts 1950). Despite their importance as a game species and their southern location, they have received little research attention. Guthery et al. (1980) analyzed pheasant habitat in the Texas Panhandle and reported deficiencies in nesting and winter cover, and travel lanes. The nesting ecology of pheasants in the panhandle of Texas has been documented (Taylor 1980), but area-specific data on other aspects of their life history are lacking. The High Plains area of Texas is similar to other pheasant ranges in that small grains are a major crop. Otherwise, this region is unique because cotton is also a major crop, because forage crops, including alfalfa, occupy a small percentage of the area, and because winters are mild compared to northern pheasant ranges. Travel lanes are limited because there are few permanent fences or topographic draws and roadside vegetation is rigorously controlled by state and county agencies and farmers. With the exception of playa basins, which occupy about 1% of the southern Great Plains, and abandoned farmsteads, idle areas are limited. Although the High Plains of Texas would appear to be marginal habitat, pheasants doubled their range in this region from 1950 through 1977 (Guthery et al. 1980). The objectives of this study were to investigate mobility, home ranges, and habitat use and preference of pheasants in the Texas High Plains. We thank N. Herbert and R. Linex for laboratory assistance, and landowner cooperators, C. Bruegel, G. Sides, D. Smith, and D. Warren for trespass rights. The U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, Great Plains Wildlife Research Laboratory, Lubbock, Texas, funded the study. F. A. Stormer, D. R. Krieg, and R. J. Warren reviewed the manuscript.

Spatial and Temporal Genetic Variability of the Eastern Cottontail on West Texas Playa Basins

Spatial and temporal changes in allelic frequency, genotypic proportions, and total and single locus heterozygosity of the eastern cottontail ( Sylvilagus floridanus ) were studied on two playa lake basins in the Texas Panhandle. Playa basins in this region are separated by extensive areas of agricultural and pasture lands, and therefore constitute the only significant cottontail habitat. Blood plasma samples were obtained from 543 individuals captured on both playa basins, during seven live-trapping periods from February through November, 1981. Adult and seven juvenile age classes were identified. Prereproductive adult cottontail populations had observed genotypic proportions that deviated significantly from expected Hardy-Weinberg equilibrium, seemingly the result of heterozygote deficiencies related to differential overwinter selection and/or nonrandom genotypic dispersal. These findings are inconsistent with previous studies in which increases in heterozygosity were shown to correlate with superior fitness. Significant ( P > 0.05) changes in allelic frequencies, genotypic proportions, and heterozygosity were related to population demographic characteristics. Apparent random matings by individuals of parental genotypes and subsequent juvenile recruitment dampened or eliminated the disequilibrium in Hardy-Weinberg proportions. Changes in population number due to reproductive recruitment and dispersal were accompanied by changes in gene frequency and heterozygosity. Spatial differences in genetic attributes were maintained between the two playa basins throughout the study because of the large distances between breeding groups. However, parallel trends were observed in population genetic and demographic characteristics on both playa basins.

Sedimentology and evaporite genesis in a Holocene continental‐sabkha playa basin—Bristol Dry Lake, California

ABSTRACTBristol Dry Lake, a 155 km2 continental‐sabkha playa basin in the Mojave Desert of south eastern California, is filled with at least 300 m of interbedded terrigenous clastics, gypsum, anhydrite, and halite. Evaporite facies conform approximately to a bull's eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite. Transects through Bristol Dry Lake, from the alluvial fan to the centre of the playa, reveal: (1) crudely‐bedded, alluvial fan clastics interfingering with (2) playa‐margin sand flat and wadi sand and silt, followed by (3) gypsum, anhydrite, chaotic mud halite, and clay of the saline mud flat, and (4) salt‐pan halite beds.Terrigenous clastics were deposited in Bristol Dry Lake by sheetflow and by suspension settling from ponded floodwater. Some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin. Thin nodular‐like beds of anhydrite and several types of gypsum occur across most of the playa. Giant hopper‐shaped halite cubes are suspended in saline mud flat facies, suggesting that they grew displacively in brine soaked sediment just below the surface. Thick beds (4 m) of halite, in the playa centre, may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods, intense evaporation and brine‐level lowering, and capillary discharge of brines.The stratigraphy in the playa centre is cyclic. An ideal cycle consists of: (1) chaotic mud halite at the base overlain by (2) green to red clay with abundant, giant hoppers, and at the top (3) red clay, gypsum, and anhydrite with flaser‐ to wavy‐bedded sand and silt. This type of cycle probably records a gradual progradation of mud‐flat facies over salt pans.Bristol Dry Lake sediments are nearly identical to some of the Permian evaporites of the Permian Basin region, U.S.A. and they can serve as modern analogues for ancient‐sabkha facies analysis.