Carson Desert Research Articles

Geochemistry of Tungsten and Arsenic in Aquifer Systems: A Comparative Study of Groundwaters from West Bengal, India, and Nevada, USA

Tungsten (W) concentrations were measured along with arsenic (As) in groundwaters from the Murshidabad district of West Bengal, India. Tungsten concentrations range from 0.8 to ~8 nmol kg-1 (0.15–1.5 μg kg-1) in the circumneutral pH (average pH ~ 7.3) Murshidabad groundwaters, and attain concentrations as high as 14 nmol kg-1 (2.5 μg kg-1) in local ponds (n = 2). Total dissolved As concentrations (AsT) range from 0.013 to 53.9 μmol kg-1 ( 8) from the Carson Desert in Western Nevada, USA, where W concentrations are reported to reach as high as 4,036 nmol kg-1 (742 μg kg-1). Although W is positively correlated with As in groundwaters from the Carson Desert, it is not correlated with AsT or As(III) in Murshidabad groundwaters, but does exhibit a weak relationship with As(V) in these groundwaters. Surface complexation modeling indicates that pH related adsorption/desorption can explain the geochemical behavior of W in Murshidabad groundwaters. However, the model does not predict the high As concentrations observed in Murshidabad groundwaters. The high As and low W concentrations measured in Murshidabad groundwaters indicate that either As and W originate from different sources or are mobilized by different biogeochemical processes within the Murshidabad aquifers. Mobilization of As in Murshidabad groundwaters is presumed to reflect reductive dissolution of Fe(III) oxides/oxyhydroxides and release of sorbed and/or coprecipitated As to the groundwaters. Multivariate statistical analysis of groundwater composition data indicate that W is associated with Mn and Cl-, which may point to a Mn oxide/oxyhydroxide, clay mineral, and/or apatite source for W in the Murshidabad sediments.

Major plant communities of the Carson Desert (Nevada), North America's coldest and driest desert

This paper describes the vegetation of the Carson Desert (Nevada, USA) based on a phytosociological analysis of its major plant associations, as determined by the Braun-Blanquet method. Diagnostic tables, climatic, edaphic, and biogeographical data were used to establish floristic affinities among identified plant communities and to interpret their distributions in zonal gradients. Their syntaxonomic positions in the classes Allenrolfeetea occidentalis and Artemisio tridentatae–Juniperetea osteospermae, and in the new class Sarcobatetea vermiculati were also established. Three associations (Atriplici confertifoliae–Sarcobatetum baileyi, Atriplici canescentis–Psorothamnetum polydenii, and Suaedo moquinii–Sarcobatetum vermiculati) are described here for the first time along with the order Sarcobatetalia vermiculati and the alliance Sarcobation vermiculati.

Factors controlling tungsten concentrations in ground water, Carson Desert, Nevada

An investigation of a childhood leukemia cluster by US Centers for Disease Control and Prevention revealed that residents of the Carson Desert, Nevada, are exposed to high levels of W and this prompted an investigation of W in aquifers used as drinking water sources. Tungsten concentrations in 100 ground water samples from all aquifers used as drinking water sources in the area ranged from 0.27 to 742 μg/l. Ground water in which W concentrations exceed 50 μg/l principally occurs SE of Fallon in a geothermal area. The principal sources of W in ground water are natural and include erosion of W-bearing mineral deposits in the Carson River watershed upstream of Fallon, and, possibly, upwelling geothermal waters. Ground water in the Fallon area is strongly reducing and reductive dissolution of Fe and Mn oxyhydroxides may be releasing W; however, direct evidence that the metal oxides contain W is not available. Although W and Cl concentrations in the Carson River, a lake, and water from many wells, appear to be controlled by evaporative concentration, evaporation alone cannot explain the elevated W concentrations found in water from some of the wells. Concentrations of W exceeding 50 μg/l are exclusively associated with Na – HCO 3 and Na–Cl water types and pH > 8.0; in these waters, geochemical modeling indicates that W exhibits <10% adsorption. Tungsten concentrations are strongly and positively correlated with As, B, F, and P, indicating either common sources or common processes controlling their concentrations. Geochemical modeling indicates W concentrations are consistent with pH-controlled adsorption of W. The geochemical model PHREEQC was used to calculate IAP values, which were compared with published Ksp values for primary W minerals. FeWO 4, MnWO 4, Na 2WO 4, and MgWO 4 were undersaturated and CaWO 4 and SrWO 4 were approaching saturation. These conclusions are tentative because of uncertainty in the thermodynamic data. The similar behavior of As and W observed in this study suggests ground water in areas where elevated As concentrations are present also may contain elevated W concentrations, particularly if there is a mineral or geothermal source of W and reducing conditions develop in the aquifer.

Prehistory of the Carson Desert and Stillwater Mountains: Environment, Mobility, and Subsistence in a Great Basin Wetland. Robert L. Kelly, with contributions by Virginia L. Butler, Linda Scott Cummings, Steven D. Grantham, Richard E. Hughes, Keith K. Katzer, Stephanie Livingston, David Rhode, Nancy D. Sharp, and Peter Wigand. 2001. University of Utah Press, Salt Lake City. University of Utah Anthropological

Prehistory of the Carson Desert and Stillwater Mountains: Environment, Mobility, and Subsistence in a Great Basin Wetland. Robert L. Kelly, with contributions by Virginia L. Butler, Linda Scott Cummings, Steven D. Grantham, Richard E. Hughes, Keith K. Katzer, Stephanie Livingston, David Rhode, Nancy D. Sharp, and Peter Wigand. 2001. University of Utah Press, Salt Lake City. University of Utah Anthropological Papers No. 123. vii + 325 pp., $45.00 (paper), ISBN 0-87480-672-0. - Volume 69 Issue 3

Sexual division of labor and central place foraging: a model for the Carson Desert of western Nevada

Archaeological models of hunter-gatherer subsistence often imply that the influence of men’s or women’s foraging effort on settlement patterns varied over time, but fail to consider how central place foraging may reflect conflicting subsistence interests between men and women. For example, earlier studies of Carson Desert prehistory suggest a semi-sedentary, gathering strategy replaced a mobile, hunting-oriented strategy in response to diminishing densities of large game. This implies that the influence of men’s and women’s work effort on residential location and mobility changed, but assumes both genders foraged for the common good rather than striving for different goals. A new central place foraging model based on a human behavioral ecology perspective of sexual division of labor considers how men and women might reconcile conflicting foraging interests given likely resource abundance, return rates, and transport costs. Men’s hunting returns must be high enough to reliably provision children for a hunting-oriented settlement pattern to occur. Otherwise, men should logistically hunt out of bases positioned to facilitate women’s foraging. Therefore, a hunting-oriented strategy seems unlikely in the Late Holocene Carson Desert.

Age and paleoclimatic significance of late Holocene lakes in the Carson Sink, NV, USA

New dating in the Carson Sink at the termini of the Humboldt and Carson rivers in the Great Basin of the western United States indicates that lakes reached elevations of 1204 and 1198 m between 915 and 652 and between 1519 and 1308 cal yr B.P., respectively. These dates confirm Morrison's original interpretation ( Lake Lahontan: Geology of the Southern Carson Desert, Professional Paper 40, U.S. Geol. Survey, 1964) that these shorelines are late Holocene features, rather than late Pleistocene as interpreted by later researchers. Paleohydrologic modeling suggests that discharge into the Carson Sink must have been increased by a factor of about four, and maintained for decades, to account for the 1204-m lake stand. The hydrologic effects of diversions of the Walker River to the Carson Sink were probably not sufficient, by themselves, to account for the late Holocene lake-level rises. The decadal-long period of increased runoff represented by the 1204-m lake is also reflected in other lake records and in tree ring records from the western United States.

Coprolites from Hidden Cave, revisited: evidence for site occupation history, diet and sex of occupants

Analysis of paleofeces from Hidden Cave, western Nevada provides new evidence for occupation history, diet and dietary change, and occupation of the cave by women. Dating of the coprolites shows two main periods of occupation, from 3800 to 3400 BP and 1900 to 1500 BP. Faunal and floral macrofossils, coupled with pollen analysis, show a dependence on wetland food resources, augmented with small seeds from dryland plants. Fecal steroid analysis indicates that the occupants of the cave were probably women. These results shed insights on prehistoric settlement patterns in the Carson Desert at times prior to major residential occupation of the Stillwater Marsh.

Prehistory of the Carson Desert and Stillwater Mountains: Environment, Mobility, and Subsistence in a Great Basin Wetland, by Robert L. Kelly, University of Utah Anthropological Papers Number 123, Salt Lake City, 2001

The Great Basin of Western North America is one of the. legendary deserts of the world. This rugged, wide open, and apparently harsh landscape has long served as a backdrop for human drama. Gold seekers and immigrants of the 19th century immortalized the rigors of travelling across the Great Basin on their way to greener grass in California and Oregon. But archaeological research has shown that human occupation of the Great Basin dates back for thousands of years, and ethnographic accounts of Native Americans who lived in this desert have played an important role in the development of concepts of hunter-gatherer subsistence and settlement patterns. It is the Indians of the Great Basin that Julian Steward (1938) studied for his well-known model of sodo-political organiza­tion and evolution (Steward 1955; also see Service 1975), Jesse Jennings (1957) later used Steward's model in his development of the Desert Culture concept, which was widely adapted to other North America deserts.

Factors controlling As and U in shallow ground water, southern Carson Desert, Nevada

Unusually high As and U concentrations (>100 μg/L) are widespread in shallow ground water beneath the southern Carson Desert. The high concentrations, which locally exceed 1000 μg/L, are of concern from a human health standpoint because the shallow ground water is used for domestic supply. Possible affects on wildlife are also of concern because the ground water flows into shallow lakes and marshes within wildlife refuges. Arsenic and U concentrations in ground water of the southern Carson Desert appear to be affected by evaporative concentration, redox reactions, and adsorption. The relation of these elements with Cl suggest that most of the high concentrations can be attributed to evaporative concentration of Carson River water, the primary source of recharge. Some ground water contains higher As and U concentrations that cannot be explained by evaporative concentration alone. Oxidation-reduction reactions, involving metal oxides and sedimentary-organic matter, appear to contribute As, U, inorganic C, Fe and Mn to the ground water. Arsenic in Fe-oxide was confirmed by chemical extraction and is consistent with laboratory adsorption studies. Uranium in both sedimentary-organic C and Fe-oxide coatings has been confirmed by fission tracks and petrographic examination. Arsenic concentrations in the ground water and chemical extracts of aquifer sediments are broadly consistent with adsorption as a control on some dissolved As concentrations. An apparent loss of As from some ground water as evaporative concentration proceeds is consistent with adsorption as a control on As. However, evidence for adsorption should be viewed with caution, because the adsorption model used values for the adsorbent that have not been shown to be valid for the aquifer sediments throughout the southern Carson Desert. Hydrologic and geochemical conditions in the Carson Desert are similar to other areas with high As and U concentrations in ground water, including the Salton Sea basin and southern San Joaquin Valley of California. Hydrologic and geochemical conditions that produced some sandstone-type U-ore deposits, including those in the non-marine, closed-basin sediments of the Morrison Formation near Grants, New Mexico, suggest that the Carson Desert may be a modern analog for those systems.

Carbonate deposition, Pyramid Lake subbasin, Nevada: 3. The use of 87Sr values in carbonate deposits (tufas) to determine the hydrologic state of paleolake systems

Abstract Sierran rivers that discharge to the Lahontan basin have much lower (∼4.5‰) δ87Sr values than the Humboldt River which drains northeastern Nevada. The δ87Sr values of tufas deposited during the last lake cycle were used to determine when Humboldt derived Sr entered the Pyramid Lake subbasin. Prior to ∼15,000 yr B.P., the Humboldt River flowed to the Smoke Creek-Black Rock Desert subbasin. During the recession of Lake Lahontan, the Humboldt River diverted to the Carson Desert subbasin. This study has demonstrated that 87Sr can be used to determine drainage histories of multi-basin lake systems if the δ87Sr values of rivers that discharge to the basins are sufficiently different.

Geomorphology of a Dry Valley: Adrian Pass, Lahontan Basin, Nevada

Adrian Pass is a dry valley that cuts across the present drainage divide separating the lower Carson and Walker River Basins. Previous studies of Adrian Pass have postulated that it is an abandoned channel of the Walker River. The evidence presented in this study suggests that Adrian Pass was formed by Quaternary lake overflow and was occupied by the Walker River for relatively brief periods. A landform chronology for Adrian Pass is developed using evidence that includes paleochannel deposits, comparison of the Post-Lake Lahontan history of Walker Lake with that of the Carson Desert, and Lake Lahontan shorelines in the Walker Basin. A historical analogue for Adrian Pass is Mud Lake Slough, which divides Pyramid Lake and Winnemucca Lake Basins. The Quaternary history of Adrian Pass, which has been affected by multiple events of both lake overflow discharge and river diversion, demonstrates how complex closed-basin hydrological changes can be through time.

Carbonate deposition, Pyramid Lake subbasin, Nevada: 1. Sequence of formation and elevational distribution of carbonate deposits (Tufas)

During the late Quarternary, the elevation of terrace cutting and carbonate deposition in the Pyramid Lake subbasin were controlled by constancy of lake level imposed by spill to adjoining subbasins. Sill elevations are 1177–1183 m (Mud Lake Slough Sill), 1207 m (Emerson Pass Sill), and 1265 m (Darwin Pass Sill). Carbonate deposition was favored by: (1) hydrologic closure, (2) proximity to a source of calcium, (3) elevated water temperature, and (4) a solid substrate. The thickness and aspect of tufa are a function oflake-level dynamics. Relatively thin sheets and pendant sheets were deposited during a rising or falling lake. The upper parts of thick reef-form tufas have a horizontal aspect and were deposited in a lake which was stabilized by spill to the Carson Desert subbasin. The lower parts of the reef-form tufas are thinner and their outer surface has a vertical aspect, indicating that the lower part formed in a receding lake. The thickest and most complete sequences of tufa are mounds that border the Pyramid Lake shore. The tops of the tallest mounds reach the elevation of the Darwin Pass Sill and many mounds have been eroded to the elevations of the Mud Lake Slough Sill of the Emerson Pass Sill. The sequence of tufa formation (from oldest to youngest) displayed in these mounds is: (1) a beachrock containing carbonate-cemented volcanic cobbles, (2) broken and eroded old spheroids that contain thinolitic tufa and an outer rind of dense laminated tufa, (3) large cylindrical (tubular) tufas capped by (4) coatings of old dense tufas, and (5) several generations of old branching tufa commonly associated with thin, platy tufas and coatings of thinolitic tufa, (6) young spheroids that contain poorly oriented young thinolitic tufa in the center and several generations of radially oriented young thinolitic tufas near the outer edge, (7) a transitional thinolite-to-branching tufa, (8) two or more layers of young branching tufa, (9) a 0.5-cm-thick layer of fine-grained dolomite, (10) a 2-cm-thick layer of young dense laminated tufa, (11) a 0.1-cm-thick layer of encrusting tufa that was covered by a beach deposit and (12) a 1.0-cm-thick layer of porous encrusting tufa that coated the beach deposit and the sides of tufa mounds. The elevational ranges of the principal varieties of tufa are not related to terrace or spill elevations. It seems likely that the distribution of tufa varieties is related to variation in the thermal structure or chemistry of Lake Lahontan. It is hypothesized that the thinolitic tufa (ikaite) formed in the near freezing hypolimnion and the braching tufa (calcite) formed in the seasonally warmer epiliminion of the lake.

Radionuclides in ground water of the Carson River Basin, western Nevada and eastern California, U.S.A.

Ground water is the main source of domestic and public supply in the Carson River Basin. Ground water originates as precipitation primarily in the Sierra Nevada in the western part of Carson and Eagle Valleys, and flows down gradient in the direction of the Carson River through Dayton and Churchill Valleys to a terminal sink in the Carson Desert. Because radionuclides dissolved in ground water can pose a threat to human health, the distribution and sources of several naturally occurring radionuclides that contribute to gross-alpha and gross-beta activities in the study area were investigated. Generally, alpha and beta activities and U concentration increase from the up-gradient to down-gradient hydrographic areas of the Carson River Basin, whereas 222Rn concentration decreases. Both 226Ra and 228Ra concentrations are similar throughout the study area. Alpha and beta activities and U concentration commonly exceed 100 pCi/l in the Carson Desert at the distal end of the flow system. Radon-222 commonly exceeds 2,000 pCi/l in the western part of Carson and Eagle Valleys adjacent to the Sierra Nevada. Radium-226 and 228Ra concentrations are <5pCi/l. Four ground water samples were analyzed for 210Po and one sample contained a high concentration of 21 pCi/l. Seven samples were analyzed for 210Pb; six contained <3pCi/l and one contained 12 pCi/l. Thorium-230 was detected at concentrations of 0.15 and 0.20 pCi/l in two of four samples. Alpha-emitting radionuclides in the ground water originated from the dissolution of U-rich granitic rocks in the Sierra Nevada by CO 2, oxygenated water. Dissolution of primary minerals, mainly titanite (sphene) in the granitic rocks, releases U to the water. Dissolved U is probably removed from the water by adsorption on Fe- and Mn-oxide coatings on fracture surfaces and fine-grained sediment, by adsorption on organic matter, and by coprecipitation with Fe and Mn oxides. These coated sediments are transported throughout the basin by fluvial processes. Thus, U is transported as dissolved and adsorbed species. A rise in the water table in the Carson Desert because of irrigation has resulted in the oxidation of U-rich organic matter and dissolution of U-bearing coatings on sediments, producing unusually high U concentration in the ground water. Alpha activity in the ground water is almost entirely from the decay of U dissolved in the water. Beta activity in ground water samples is primarily from the decay of 40K dissolved in the water and ingrowth of 238U progeny in the sample before analysis. Approximately one-half of the measured beta activity may not be present in ground water in the aquifer, but instead is produced in the sample after collection and before analysis. Potassium-40 is primarily from the dissolution of K-containing minerals, probably K-feldspar and biotite. Radon-222 is primarily from the decay of 226Ra in the aquifer materials. Radium in the ground water is thought to be mainly from alpha recoil associated with the decay of Th in the aquifer material. Some Ra may be from dissolution (or desorption) or Ra-rich coatings on sediments.

Prehistoric Human Geography in the Carson Desert, Part I: A Predictive Model of Land-Use in the Stillwater Wildlife Management Area. Christopher Raven and Robert G. Elston. Intermountain Research Reports, Silver City, 1989. ix + 183 pp., figures, tables, references, appendix, maps. No price given.

Prehistoric Human Geography in the Carson Desert, Part I: A Predictive Model of Land-Use in the Stillwater Wildlife Management Area. Christopher Raven and Robert G. Elston. Intermountain Research Reports, Silver City, 1989. ix + 183 pp., figures, tables, references, appendix, maps. No price given. - Volume 58 Issue 2

Temperature Profiles for Germination of Big Sagebrush Seeds from Native Stands

The germination of seeds of big sagebrush (Artemisia tridentata, Nutt.) from 5 locations on the margin of the Carson Desert, Nevada, was studied over 5 growing seasons. Temperature profiles for germination were developed for seeds collected from each location. The profile consisted of 55 constant or alternating temperatures from 0 through 40 degrees C. Seed quality was high with optimum germination, defined as germination not different from the maximum observed at the 0.01 level of probability, averaging 80% for all years and all locations. Differences in germination parameters existed among locations, but not within locations among years of production. Differences among years of production were most pronounced at extreme incubation temperatures. The most frequent temperature regime supporting optimum germination of big sagebrush seeds was 15/20 degrees C (15 degrees C for 16 hours and 20 degrees C for 8 hours in each 24-hour cycle).

Quaternary palaeolakes in the evolution of semidesert basins, with special emphasis on Lake Bonneville and the Great Basin, U.S.A

This paper reviews attributes of Quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts. Basin-floor and basin-closure morphometry have set limits on palaeolake sizes; lake morphometry and basin drainage patterns have influenced lacustrine processes; and water and sediment loads have influenced basin neotectonics. Information regarding inundated, runoff-producing, and extra-basin spatial domains is acquired directly from the palaeolake record, including the littoral morphostratigraphic record, and indirectly by reconstruction. Increasingly detailed hypotheses regarding Lake Bonneville, the largest late Pleistocene palaeolake in the Great Basin, are subjects for further testing and refinement. Oscillating transgression of Lake Bonneville began about 28 ka, the highest stage occurred about 15 ka, and termination occurred abruptly about 13 ka. A final resurgence of perennial lakes probably occurred in many subbasins of the Great Basin between 11 and 10 ka, when the highest stage of Great Salt Lake (successor to Lake Bonneville) developed the Gilbert shoreline — and when the Russell shoreline formed 500–600 km away, in the Carson Desert of the Lake Lahontan basin. The highest post-Gilbert stage of Great Salt Lake, which has been one of the few permanent lakes in the Great Basin during Holocene time, probably occurred between 3 and 2 ka. A set of eighteen general observations regarding geologic aspects of the palaeolake record in semidesert basins is helping to guide Quaternary studies in the Great Basin.

Reciprocal Common Garden Studies of the Germination of Seeds of Big Sagebrush (Artemisia tridentata)

Experiments were conducted to compare the influence of production site and seed source on the germination of big sagebrush seeds in relation to incubation temperatures. Seeds of big sagebrush were collected from five plant communities located on the margin of the Carson Desert in western Nevada. Seedlings were grown from the seeds and transplanted back to the sites of collection in reciprocal gardens. Seeds from 1-yr-old gardens were tested for germination at a constant 15 C for three consecutive years. The greater quantity of seeds produced by 2- and 3-yr-old gardens were tested at 55 constant or alternating temperature regimes. Seeds of big sagebrush produced in reciprocal gardens had lower germination than seeds collected from native stands at the same locations. The reduced germination disappeared as the reciprocally transplanted plants grew older and larger, but seeds from these plants did not reach the same levels of germination as those collected from native stands at the same location. Moisture stress and/or freezing temperature conditions during flowering may have directly influenced the quality of seeds produced or interacted with the inherent genotypes of big sagebrush to trigger seed production of variable quality in relation to germination characteristics.

Arsenic in Ground Water of the Western United States

ABSTRACTNatural occurrences of ground water with moderate (10 to 50 micrograms per liter) to high (greater than 50 micrograms per liter) concentrations of arsenic are common throughout much of the Western United States. High concentrations of arsenic are generally associated with one of four geochemical environments: (1) basin‐fill deposits of alluvial‐lacustrine origin, particularly in semiarid areas, (2) volcanic deposits, (3) geothermal systems, and (4) uranium and gold‐mining areas. These findings are based on an extensive literature review, compilation of unpublished reports and data, and the review of data bases containing more than 7,000 analyses of ground‐water samples for arsenic. In the first two environments, arsenic appears to be associated with sediments derived, in part, from volcanic rocks of intermediate to acidic composition. Dissolved arsenic concentrations in water from volcanic aquifers in the same regions, however, may be low (less than 10 micrograms per liter). Solid phases (minerals, amorphous solids, and sedimentary organic matter) that supply the dissolved arsenic have not been identified in most areas. Alluvial and lacustrine sedimentary deposits appear to be an important source of arsenic in volcanic areas (such as Lane County, Oregon) and in areas underlain by basin‐fill deposits (such as Carson Desert in Nevada and the Tulare Lake basin in California). Mobilization of arsenic in sedimentary aquifers may be, in part, a result of changes in the geochemical environment due to agricultural irrigation. In the deeper subsurface, elevated arsenic concentrations are associated with compaction caused by groundwater withdrawals.

Lake-level variation in the Lahontan basin for the past 50,000 years

Selected radiocarbon data on surficial materials from the Lahontan basin, Nevada and California, provide a chronology of lake-level variation for the past 50,000 yr. A moderate-sized lake connected three western Lahontan subbasins (the Smoke Creek-Black Rock Desert subbasin, the Pyramid Lake subbasin, and the Winnemucca Dry Lake subbasin) from about 45,000 to 16,500 yr B.P. Between 50,000 and 45,000 yr B.P., Walker Lake rose to its sill level in Adrian Valley and spilled to the Carson Desert subbasin. By 20,000 yr B.P., lake level in the western Lahontan subbasins had risen to about 1265 m above sea level, where it remained for 3500 yr. By 16,000 yr B.P., lake level in the western Lahontan subbasins had fallen to 1240 m. This recession appears synchronous with a desiccation of Walker Lake; however, whether the Walker Lake desiccation resulted from climate change or from diversion of the Walker River is not known. From about 15,000 to 13,500 yr B.P., lake level rapidly rose, so that Lake Lahontan was a single body of water by 14,000 yr B.P. The lake appears to have reached a maximum highstand altitude of 1330 m by 13,500 yr B.P., a condition that persisted until about 12,500 yr B.P., at which time lake level fell ≧100 m. No data exist that indicate the level of lakes in the various subbasins between 12,000 and 10,000 yr B.P. During the Holocene, the Lahontan basin was the site of shallow lakes, with many subbasins being the site of one or more periods of desiccation. The shape of the lake-level curve for the three western subbasins indicates that past changes in the hydrologic balance (and hence climate) of the Lahontan basin were large in magnitude and took place in a rapid step-like manner. The rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream, as it was forced north or south by the changing size and shape of the continental ice sheet.

Barbwire Russian Thistle Seed Germination

Barbwire Russian thistle (Salsola paulsenii) is the dominant species of severely degraded plant communities in the most arid portions of the Great Basin. The seed germination of this alien annual plant was compared with that of common Russian thistle (S. iberica). In general, the two species of Salsola have similar germination characteristics. However, there were important differences that apparently favor barbwire Russian thistle in arid environments. These advantages were (a) less restrictive afterripening requirements that allow some germination at a broader range of temperature sooner after maturity, (b) more rapid germination at low temperatures during the first 10 days of incubation, and (c) dehiscence of seeds without the necessity of the plants uprooting and tumbling. Barbwire Russian thistle (Salsola paulsenii) has only scant coverage in range management literature because only recently has it been widely recognized in the western United States as a separate species from Russian thistle (S. iberica). Russian thistle is one of the most widely occurring alien annuals in western North America. This weed was first introduced into the United States in 1873 or 1874 in flax (Linum sp.) seed brought from Russia and sown near Scotland, South Dakota (Stevens 1943; Robbins et al. 1952). Several Canadian proviinces and 16 western states of the United States were infested by 1895. Russian thistle now infests all of the western portion of North America. Barbwire Russian thistle is native to southeastern Russia and central Asia (Allen 1964). It was probably introduced to the far western United States sometime between 1891-1913 (Beatley 1973). Coville (1893) did not collect barbwire Russian thistle in his extensive botanical explorations on the Death Valley Expedition of 1891. Alice Eastwood, the noted California botanist, collected barbwire Russian thistle near Barstow, California in 1913 (Beatley 1973). Barbwire Russian thistle occurs in California, Nevada, and Utah (Munz 1968; Anonymilous 1969). We do not know exactly when barbwire Russian thistle invaded the Carson Desert of northwestern Nevada. During the 1960's Beatley (1971) established that there were distinct taxonomic entities of Russian thistle in the southern Great Basin. Publication of Beatley's work stimulated our interest and Authors are range scientists. U.S. Department of Agriculture Science and Education Admiiinistration. Agricultural Research. Renewable Resource Center, Univ. of Nevada. 920 Valley Rd.. Reno 89512. This study is a contribution from The U.S. Dep. Agr.. SEA. AR., and the Agr. Exp. Sta.. Univ. of Nevada. Reno. Journal Series No. 423. Manuscript received August 29. 1978. observation in the Carson Desert and we observed what appeared to be the last stages of replacement of Russian thistle by barbwire Russian thistle in the desert rangeland communities of the area. Such replacement has not occurred in many ruderal communities or in areas of irrigated, intensive agriculture. Previous studies (Young and Evans 1972; Evans and Young 1972) have enumerated many of the seed and seedbed ecology characteristics of Russian thistle. The purpose of this investigation was to conduct similar comparative studies of the seed and seedbed ecology of barbwire Russian thistle.