Geology topics

Research about Arkansas

Source-linked reports with geographic coverage including Arkansas.

At least 55 records · Page 3Linked to original sources

USGS2021

Effects of climate and land-use change on thermal springs recharge—A system-based coupled surface-water and groundwater-flow model for Hot Springs National Park, Arkansas

A three-dimensional hydrogeologic framework of the Hot Springs anticlinorium beneath Hot Springs National Park, Arkansas, was constructed to represent the complex hydrogeology of the park and surrounding areas to depths exceeding 9,000 feet below ground surface. The framework, composed of 6 rock formations and 1 vertical fault emplaced beneath the thermal springs, was discretized into 19 layers, 429 rows, and 576 columns and incorporated into a 3-dimensional steady-state groundwater-flow model constructed in MODFLOW-2005. Historical daily mean thermal spring flows were simulated for one stress period of approximately 34 years (1980–2014), chosen to represent the period of record for historical climate data used in the quantification of the boundary conditions. The groundwater-flow model was manually calibrated to historical daily mean thermal spring flows of 88,000 cubic feet per day observed over a 12-year period of record (1990–1995 and 1998–2005) at the thermal springs collection system. Calibration was achieved by calculating starting heads and general head boundary conditions from the Bernoulli equation and then adjusting the horizontal and vertical hydraulic conductivities of the rock formations and vertical fault and the hydraulic conductance of head-dependent flux boundaries. The groundwater-flow model was coupled to a surface-water model developed in the Precipitation-Runoff Modeling System (PRMS) by using PRMS-simulated gravity drainage as a specified flux recharge boundary condition in the groundwater-flow model. Together, the coupled models were used to (1) locate the areas of groundwater recharge to the thermal springs in the discretized hydrogeologic framework by using forward and reverse particle-tracking capabilities of MODPATH, (2) simulate the effects of variable recharge rates on the spring flows at the thermal springs, and (3) assess possible effects of climate and land-use change on the long-term variability of spring flows at the thermal springs. Forward and backward particle-tracking maps indicated that the most prevalent areas of recharge in the discretized hydrogeologic framework used in this study were within about 0.6–0.9 mile of the thermal springs. Forward particle tracking indicated a recharge area southwest of the thermal springs that corresponded to a location where the predominant lithologies are the Arkansas Novaculite, Hot Springs Sandstone, and Bigfork Chert. Backward particle tracking indicated a second localized area of recharge to the northeast of the thermal springs that corresponded to a location where the dominant lithology is the Bigfork Chert. The groundwater-flow model indicated that the most probable recharge formations are the Arkansas Novaculite, Bigfork Chert, and Hot Springs Sandstone. The simulated effects of climate and land-use changes on the variability of the spring-flow rates at the thermal springs generally resulted in reductions of thermal spring flow attributed to urban development and more extreme climates characterized by elevated mean surface air temperatures. The groundwater-flow model predicted a linear relation between the thermal spring discharge and the cumulative recharge volume applied to the hydrogeologic framework, and the positive slope of the predicted relation between recharge and simulated thermal spring flow indicates that more extreme precipitation events that supply more recharge may in fact increase the thermal spring-flow rates.

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USGS2021

Seasonal periphyton response to low-level nutrient exposure in a least disturbed mountain stream, the Buffalo River, Arkansas

Like most streams located in the Ozark Plateaus, the Buffalo River in Arkansas generally has excellent water quality. Water-quality conditions in Big Creek, however, a major tributary of the middle Buffalo River, have been less favorable than that of other Buffalo River tributaries. Concerns regarding the influence of water quality in Big Creek on the Buffalo River magnified in 2013 when a large confined animal feeding operation (CAFO) began operating in the watershed. In response to these concerns, the U.S. Geological Survey compared monthly nutrient concentrations and seasonal periphyton assemblage metrics of a site on Big Creek downstream of the CAFO, two Buffalo River control sites upstream of the confluence with Big Creek, and three Buffalo River test sites downstream of the confluence with Big Creek. In addition to identifying potential nutrient patterns and periphyton responses along a low-level nutrient exposure gradient, the study determined how nutrient contributions from Big Creek (and the CAFO) are affecting ecological conditions and consequent ecosystem services in the Buffalo River. Nutrient and periphyton data exhibited more temporal than spatial variability. Nutrient concentrations were generally highest of all sites at the Big Creek site. Concentrations at the five sites on the Buffalo River were typically low (near laboratory reporting limits), and concentrations at the three test sites rarely exceeded those of the two control sites. An index developed with three ecologically relevant periphyton metrics (oligotrophic taxa and Homoeothrix percent relative abundance and mesotrophic diatoms percent taxa richness) suggested that nutrient uptake at sites downstream of the Big Creek-Buffalo River confluence resulted in subtle shifts in downstream periphyton assemblages. The periphyton index of biological integrity at control sites was slightly and generally more favorable compared to test sites. Even so, when periphyton data were considered in conjunction with both hydrology and water-quality data, the negative consequences of antecedent high flows and associated scouring exceeded the potential positive effects that low-level nutrients had on algal productivity. These findings emphasize the importance of comparing biological and chemical data across extended temporal scales, particularly when working with low-level nutrient gradients.

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USGS2021

Population density and stream-habitat relations of the Yellowcheek Darter (Nothonotus moorei) among the headwaters of the Little Red River in Arkansas

Nothonotus moorei (Yellowcheek Darter [YCD]) is an endangered species endemic to the headwaters of the Little Red River in north-central Arkansas. Population decline, habitat loss and fragmentation, and threats from land use and seasonal drought necessitate monitoring of population density and distribution to determine ecological and habitat associations. We evaluated YCD density and associated stream-habitat variables from 9 sites in the South Fork, Archey Fork, Middle Fork, and Beech Fork of the Little Red River from March to April 2018. Yellowcheek Darters were present at all 9 sites and 19 of 23 riffles sampled. Densities were generally comparable or higher than reported in previous studies, and we collected YCD at some sites at which they were considered previously extirpated, suggesting a rather stable population and evidence of recolonization of some sites since they were last surveyed. Yellowcheek Darter density was significantly negatively related to substrate embeddedness, and the consistent relation to embeddedness in this study and other studies suggest that this species is vulnerable to sedimentation.

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USGS2021

Stable isotope and geochemical characterization of nutrient sources and surface water near a confined animal feeding operation in the Big Creek watershed of northwest Arkansas

A concentrated animal feeding operation (CAFO) established in Newton County, Arkansas, near Big Creek, a tributary of the Buffalo National River, raised concern about potential degradation of water quality in the karst watershed. In this study, isotopic tools were combined with standard geochemical approaches to characterize nutrient sources and dynamics in the Big Creek watershed. An isotopic and geochemical reference database of potential nutrient sources in the Big Creek watershed was constructed based on samples collected from representative potential sources. Nutrient sources and stream samples were analyzed for delta (δ) 15 N-NO 3 , δ 18 O NO 3 , and a suite of selected dissolved ions. Data provide evidence of modification of potential local nutrient source signatures by nitrification, atmospheric deposition, evaporation, and denitrification. Samples taken from the CAFO waste pond, a septic system, field and parking lot runoff, fertilizer, and hog manure exhibited different δ 15 N-NO 3 and δ 18 O-NO 3 values as compared to stream samples. Stream δ 15 N-NO 3 and δ 18 O-NO 3 values cannot be explained by direct input of any one of these potential sources without modification of the isotopic composition by mixing or fractionation. Big Creek nitrate isotope values (-3.4 per mil [‰] to 6.7‰ δ 15 N-NO 3 and -7.6 to 9.1‰ δ 18 O-NO 3 ) were similar to values expected from nitrification of nitrogen stored in soils sampled in the watershed (2.8 to 7.6‰ δ 15 N-NO 3 and 3.4 to 4.8‰ δ 18 O-NO 3 ).

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USGS2020

Water levels and selected water-quality conditions in the Mississippi River Valley alluvial aquifer in eastern Arkansas, 2014

In 2014, the U.S. Geological Survey, in cooperation with the Arkansas Geological Survey and the Arkansas Natural Resources Commission, determined water-level altitudes in 468 wells in eastern Arkansas and collected water-quality samples from 144 wells. Water-level altitudes were calculated based on the measured depth to water in each well and used to construct a potentiometric-surface map of the Mississippi River Valley alluvial aquifer, and the water-quality samples were analyzed for chloride and bromide concentrations. Upon completion of the potentiometric-surface map, 10 depressions in the potentiometric surface were identified in the Mississippi Alluvial Plain: two large depressions, five small depressions, and three areas of decreased water levels. Analyses of water-quality samples identified several areas of elevated chloride/bromide ratios. A water-level altitude difference map was constructed using 345 groundwater levels measured in 2010 and 2014. Differences in water-level altitude ranged from –10.2 feet in Craighead County to 18.00 feet in Prairie County. Analysis of the overall water-level altitude differences indicated a decline in approximately 84 percent of the wells measured in both 2010 and 2014, including in areas where previous studies indicated water-level altitude increases between 2008 and 2012. Analysis of long-term hydrographs of wells in the study area indicated that mean annual water levels declined in all but two counties. The decline in water levels observed in the hydrographs suggests continued growth of the cones of depression caused by groundwater use in the Mississippi River Valley alluvial aquifer.

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USGS2019

Bathymetric map and surface area and capacity table for Beaver Lake near Rogers, Arkansas, 2018

Beaver Lake was constructed in 1966 on the White River in the northwest corner of Arkansas for flood control, hydroelectric power, public water supply, and recreation. The surface area of Beaver Lake is about 27,900 acres and approximately 449 miles of shoreline are at the conservation pool level (1,120 feet above the North American Vertical Datum of 1988). Sedimentation in reservoirs can result in reduced water storage capacity and a reduction in usable aquatic habitat. Therefore, accurate and up-to-date estimates of reservoir water capacity are important for managing pool levels, power generation, recreation, and downstream aquatic habitat. Many of the lakes operated by the U.S. Army Corps of Engineers are periodically surveyed to monitor bathymetric changes that affect water capacity. In October 2018, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, completed one such survey of Beaver Lake using a multibeam echosounder. The echosounder data were combined with light detection and ranging (lidar) data to prepare a bathymetric map and a surface area and capacity table.

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USGS2019

Flood-frequency comparison from 1995 to 2016 and trends in peak streamflow in Arkansas, water years 1930–2016

In 2016, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers and the Federal Emergency Management Agency, began a study in Arkansas to investigate possible increasing trends in annual peak streamflow data and the possible resulting increase in the annual exceedance probability flood (AEPF) predictions. Temporal trends of peak streamflow were investigated at 15 selected streamgages on unregulated streams in Arkansas having 30 or more years of peak streamflow data through the 2016 water year. For the period of record at each streamgage, the Mann-Kendall trend test indicated that 14 of the 15 streamgages had no statistically significant peak streamflow trends and 1 streamgage had a statistically significant decreasing peak streamflow trend. Visual examination of the locally estimated scatterplot smoothing technique trend lines of the peak streamflow data indicated a possible increasing peak streamflow trend at 8 of the 15 streamgages since the 1990s. A sequential series analysis of the 1-percent AEPF at each of the 15 selected streamgages was completed by selecting an initial subset of the oldest peak streamflow data from each site to estimate the initial 1-percent AEPF. This initial peak streamflow data subset was subsequently appended with 10-year increments of additional peak streamflow data until the full period of peak streamflow data was analyzed. The maximum increase in the 1-percent AEPF was 113 percent, and the maximum decrease was 31.9 percent. Percentage differences between the AEPFs derived from regional regression equations presented in the 1995 and 2016 Arkansas flood-frequency reports were compared. The average percentage differences for the 74 selected locations indicate that the 4-, 2-, 1-, and 0.2-percent AEPFs computed using the 2016 regional regression equations were higher by 3.52, 5.10, 8.59, and 13.31 percent, respectively (25-, 50-, 100-, and 500-year recurrence interval floods), than the same percentage AEPFs computed using the 1995 regional regression equations. The average percentage differences between the 1995 and 2016 AEPFs for the 10-percent AEPF (10-year recurrence interval flood) resulted in 2016 AEPF predictions being 0.41 percent higher. For the 50- and 20-percent AEPFs (2- and 5-year recurrence interval floods), the 2016 AEPFs were less than the 1995 AEPFs by 2.53 and 0.31 percent, respectively.

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USGS2019

Potentiometric surface of groundwater-level altitudes near the planned Highway 270 bypass, east of Hot Springs, Arkansas, July–August 2017

The Ouachita Mountains aquifer system potentiometric-surface map is one component of the Hot Springs Bypass Groundwater Monitoring Project. The potentiometric-surface map provides a baseline assessment of shallow groundwater levels and flow directions before the construction of the Arkansas Department of Transportation planned extension of the Highway 270 bypass, east of Hot Springs, Arkansas. The map provides data regarding status of groundwater levels and potential effects on the recharge area in the Hot Springs National Park and to groundwater that supplies water to domestic users near the Highway 270 bypass. Groundwater levels from 66 wells were measured in July–August 2017. Fifty nine of the 66 groundwater-level altitudes measured, along with select surface-water features and springs, were used to construct the Ouachita Mountains aquifer system potentiometric-surface map. The potentiometric surface, a two-dimensional representation, shows groundwater-level altitudes ranging from a maximum of 766 ft above the North American Vertical Datum of 1988 (NAVD 88) to a minimum of 443 ft NAVD 88. The spring altitudes on the potentiometric-surface map range from 534 ft to 927 ft above NAVD 88. The study area, located in the Ouachita Mountains physiographic section of the Ouachita physiographic province, comprises narrow valleys and high ridges of Stanley Shale, Hot Springs Sandstone, Arkansas Novaculite, Missouri Mountain-Polk Creek Shale, and Bigfork Chert. The highest groundwater-level altitudes observed were in the Hot Springs Sandstone, Arkansas Novaculite, and Missouri Mountain-Polk Creek Shale. The springs discharge in outcrop areas of the Stanley Shale, Bigfork Chert, and Arkansas novaculite. The planned Highway 270 bypass will cut across ridges and valleys comprising these formations and, very importantly, across areas with elevations above 660 ft above NAVD 88 that define the hot springs recharge zone. This potentiometric-surface map defines the status of the shallow groundwater potentiometric surface near the Highway 270 bypass prior to initiation of construction activities. A post-construction potentiometric map is planned. It must be noted that shallow groundwater levels are also subject to climatic effects including changes in amount and timing of precipitation and changes in temperature.

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USGS2019

Quaternary displacement on the Joiner Ridge Fault, eastern Arkansas

The New Madrid seismic zone of the central United States is an intraplate seismic zone with blind structures that are not seismically active but may pose seismic hazards. The Joiner Ridge fault is the 35 km long east-bounding fault of the Joiner Ridge blind horst located in eastern Arkansas approximately 50 km northwest of Memphis, Tennessee. Shallow S-wave (SH-mode) seismic reflection profiles, continuous cores, and radiometric dating of Quaternary alluvium across the Joiner Ridge fault reveal down-to-the-east reverse faulting and folding within of the top of the Eocene strata and overlying Quaternary Mississippi River alluvium. The base of the Quaternary alluvium has an age of 20.3 ka and is vertically displaced 12 m, resulting in an average slip rate of 0.6 + 0.1 mm/yr over the past 20.3 ka. The overlying late Wisconsinan and Holocene alluvial facies are also displaced by the Joiner Ridge fault. These facies increase in thickness across the Joiner Ridge fault and were used to calculate late Wisconsinan and Holocene slip rates. The JRF slipped 7 m between 20.3 ka and 17.5 ka (2.8 ka), reflecting a slip rate of 2.5 + 0.3 mm/yr. From 12.3 ka to 11.5 ka (0.8 ka) the JRF slipped 3 m at an average slip rate of 3.8 + 0.9 mm/yr. There were 2 m of slip on the JRF between 11.5 ka and 8.9 ka (2.6 ka), reflecting a slip rate of 0.8 + 0.3 mm/yr. No apparent slip has occurred on the JRF within the last 8.90 ka. This research illustrates that slip rates on the JRF have varied through the late Wisconsinan and early Holocene, but the Joiner Ridge fault has been inactive since the middle Holocene.

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USGS2019

Interpretation of dye tracing data collected November 13–December 2, 2017, at the Savoy Experimental Watershed as part of the Advanced Groundwater Field Techniques in Karst Terrains course, Savoy, Arkansas

The first course on the use of advanced groundwater field techniques for karst aquifers was conducted November 13–17, 2017, at the University of Arkansas Savoy Experimental Watershed (SEW), which is located on pastures for beef livestock research conducted by the Department of Animal Sciences at the University of Arkansas at Savoy, Arkansas. The SEW is an interdisciplinary, collaborative, long-term research site for the study of animal-waste management in a mantled karst setting. The course focused on advanced field activities appropriate for karst aquifer studies: dye tracing, groundwater/surface-water interactions, geophysical methods, and geochemistry. This report summarizes the data collected and interpreted from the dye tracing part of the November 2017 course, other USGS field courses, and past dye tracing investigations conducted by University of Arkansas students.

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USGS2019

Regional hydraulic geometry characteristics of stream channels in the Ouachita Mountains of Arkansas

Many stream channel infrastructure, habitat, and restoration projects are being undertaken on small streams throughout Arkansas by various Federal, State, and local agencies and by private organizations and businesses with limited data on local geomorphology and streamflow relations. Equations are needed that relate drainage area above stable stream reaches and the associated basin characteristics to bankfull streamflow and the associated channel dimensions. These equations, along with streambed material particle information, provide information that can improve stream channel projects. The U.S. Geological Survey and the Arkansas Natural Resources Commission in cooperation with the U.S. Army Corps of Engineers, Little Rock District, undertook a study to develop these equations for streams in the Ouachita Mountains of Arkansas. Seventeen streamgages operated by the U.S. Geological Survey, located on streams in the Ouachita Mountains, were selected for analysis. Regional hydraulic geometry curves that express the mathematical relation between the bankfull channel dimensions (cross-sectional area, top width, mean depth, and streamflow) and the contributing drainage areas were developed. Streambed material measurements were collected to develop descriptive statistics of the streambed particle-size distributions and percentages of substrate type at each study site. Stream reaches at each study site were classified to the Rosgen level II stream type based on the average of stream channel metrics collected from site cross sections and profiles. Of the 17 selected Ouachita Mountain stream reaches, 6 were classified as B stream types, and 11 were classified as C stream types. The B stream types have infrequently spaced pools; very stable plan forms, profiles, and banks; and narrow, gently sloping valleys, where bank vegetation is a moderate component of stability. The C stream types are meandering, point bar, riffle-pool channels associated with broad valleys having well-defined flood plains and terraces composed of alluvial soils, where bank vegetation is typically a high component of stability.

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USGS2019

DNA Sequencing confirms Tundra Bean Goose (Anser serrirostris serrirostris) occurrence in the Mississippi Alluvial Valley in Arkansas, USA

—First sighting records of rare occurrences may become increasingly important for recognizing changes in distribution, changes in migratory strategies, or increases in hybridization. We focumented the first record of a Tundra Bean Goose in the Mississippi Alluvial Valley, the outlet and historic floodplain for much of North America and one of the most important waterfowl wintering areas on the continent. We also document the first genetically confirmed record in the contiguous USA. Bean Goose (Anser fabalis and A. serrirostris) occurrences in North America are rare, especially outside of Alaska. On 24 January 2018, a Tundra Bean Goose (A. s. serrirostris) was harvested by a hunter in a winter-flooded rice field in Desha County, Arkansas, USA, near Dumas. The goose was mixed with a flock of 50 Greater White-Fronted Geese (A. albifrons). Because this individual was legally, albeit accidentally shot, we had the rare and exciting opportunity to obtain morphometric measurements and biological samples. As a result, we were able to verify the species and subspecies through genetic and morphological analysis. We determined the goose was an adult female Tundra Bean Goose, and mitochondrial DNA control region sequence data indicated this specimen was the subspecies A. s. serrirostris.

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USGS2019

Population characteristics of Ozark Bass (Ambloplites constellatus) in the upper White River basin of northern Arkansas

Ozark Bass ( Ambloplites constellatus ) is an understudied, endemic fish species in the Upper White River Basin of northern Arkansas. This study was part of an effort by fisheries managers to gather baseline data about the Ozark Bass to aid in understanding population dynamics and contribute to the limited data available for use in determining the efficacy of harvest regulations. Select population characteristics of Ozark Bass in two northern Arkansas streams were determined, population characteristics of Ozark Bass were compared to Shadow Bass ( Ambloplites ariommus ) and Rock Bass ( Ambloplites rupestris ) data collected from previous studies in southern Missouri, and relative condition, length-at-age, and annual survival of Ozark Bass were compared between sample streams. Sampling occurred in Crooked Creek and the Buffalo River during summer 2013 via boat electroshocking. Length and weight data were recorded for all Ozark Bass collected, and fish ages were determined through selective otolith retrieval and age-length keys. Ozark Bass in Crooked Creek had greater relative condition than Ozark Bass in Buffalo River ( P < 0.001). Neither Ozark bass lengths nor log-transformed weights differed ( P > 0.05) between sexes for fish collected from only the Buffalo River. Ozark Bass mean annual survival was similar between Crooked Creek (55% ± 5% as 95% confidence interval (CI)) and the Buffalo River (50% ± 7% CI) for fish age 2 to 9. Calculated Ozark Bass lengths-at-age for fish from both streams were comparable to the Von Bertalanffy growth estimates, except the Buffalo River age 7 categor y where there was only one observation. The relationship between Ozark Bass age and length differed between sampled streams, and variability in growth rates and length-at-age were observed among Ambloplites species. Results of this study contribute to the understanding of the population dynamics of the Ozark Bass that will lead to improved fisheries management.

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USGS2018

Coupling high-frequency stream metabolism and nutrient monitoring to explore biogeochemical controls on downstream nitrate delivery

Instream biogeochemical process measurements are often short-term and localized. Here we use in situ sensors to quantify the net effects of biogeochemical processes on seasonal patterns in baseflow nitrate retention at the river-reach scale. Dual-station high-frequency in situ nitrate measurements, were coupled with high-frequency measurements of stream metabolism and dissolved inorganic carbon, in a tributary of the Buffalo National River, Arkansas. Nitrate assimilation was calculated from net primary production, and combined with mass-balance measurements, to estimate net nitrification and denitrification. The combined net effects of these instream processes (assimilation, denitrification, and nitrification) removed >30–90% of the baseflow nitrate load along a 6.5 km reach. Assimilation of nitrate by photoautotrophs during spring and early summer was buffered by net nitrification. Net nitrification peaked during the spring. After midsummer, there was a pronounced switch from assimilatory nitrate uptake to denitrification. There was clear synchronicity between the switch from nitrate assimilation to denitrification, a reduction in river baseflows, and a shift in stream metabolism from autotrophy to heterotrophy. The results show how instream nitrate retention and downstream delivery is driven by seasonal shifts in metabolic pathways; and how continuous in situ stream sensor networks offer new opportunities for quantifying the role of stream biota in the dynamics, fate, and transport of nitrogen in fluvial systems.

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USGS2018

Geologic map of the Osage SW 7.5ʹ quadrangle, Newton, Madison, and Carroll Counties, Arkansas

This map summarizes the geology of the U.S. Geological Survey Osage SW 7.5-minute quadrangle in the Ozark Plateaus region of northern Arkansas. Physiographically, the Osage SW quadrangle is located within a transitional area between the Boston Mountains to the south, and the Springfield Plateau to the north. Geologically, the area is on the southern flank of the Ozark dome; an uplift with the oldest rocks exposed at its center in the St. Francois Mountains in Missouri. Exposed within the quadrangle is an approximately 1,460-foot-thick sequence of Ordovician, Mississippian, and Pennsylvanian carbonate and clastic sedimentary rocks that have been mildly deformed by a series of faults and folds. The southeasternmost corner of the map area falls within the Buffalo National River—a park which encompasses the Buffalo River and adjacent land that is administered by the National Park Service.

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USGS2018

Forecasting effects of angler harvest and climate change on smallmouth bass abundance at the southern edge of their range

Climate change will affect stream systems in numerous ways over the coming century. Globally, streams are expected to experience changes in temperature and flow regime. Previous work has indicated that these changes will likely affect fish distributions, but little work has been conducted examining population level effects of climate change on warmwater fish at the warmest portion of their range. We model several potential climate change-related stressors and the resulting effects on smallmouth bass Micropterus dolomieu populations in the Buffalo National River, Arkansas, USA, located near the southern extent of smallmouth bass range. Smallmouth bass are a popular recreational fish in the region and angler harvest likely contributes substantially to annual mortality. We created a simulation model parameterized with data collected from the Buffalo National River to evaluate the relative importance of climate stressors and angler harvest on smallmouth bass populations. Our simulations suggest that increases in springtime temperature and reductions in river discharge during the spawning period could increase recruitment, resulting in increases in adult abundance (8% higher). However, when increased flooding and drought probabilities are considered, our model indicates the Buffalo National River could experience large reductions in adult smallmouth bass abundance (≥50% decline) and increased probability of extinction compared to present levels. Simulations showed that harvest reduction could be a viable strategy to reduce the negative effects of climate change, but that even with complete closure of harvest, smallmouth bass population levels would still be well below present abundance (46% lower than present). Efforts to reduce flooding and drought effects related to climate change in the Buffalo National River could help offset the predicted reduction in the smallmouth bass population.

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USGS2018

Straczekite, a new calcium barium potassium vanadate mineral from Wilson Springs, Arkansas

Straczekite occurs as a rare secondary mineral in fibrous seams, along with other V minerals (A.M. 64-713), in ore from the vanadium mine in Wilson Springs (formerly Potash Sulfur Springs), Garland County, Arkansas. It forms soft, thin laths of dark greenish black crystals up to 0.5 mm in length. Indexed XRD data are tabulated; strongest lines 3.486(100), 10.449(50), 1.8306(50), 1.9437(15) A; a 11.679, b 3.6608, c 10.636 A, beta 100.53o; space group C2/m, C2 or Cm. Chemical analysis gave V2O5 66.4, V2O4 15.3, Fe2O3 0.9, Na2O 0.4, K2O 1.8, CaO 2.5, BaO 5.5, H2O 7.2, = 100.0, leading to the formula (Ca0.39Ba0.31K0.33Na0.11)- 196(V4+1.59V5+6.31Fe3+0.10)O20.02(H2O)2.9; Dcalc. 3.21 g/cm3. A possible layer structure is discussed. The name is for J. A. Straczek, Chief Geologist at Union Carbide Corp.-R.A.H.

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USGS2018

Delindeite titanosilicates and lourenswalsite, two new from the Magnet Cove region, Arkansas

Delindeite and lourenswalsite are two new barium titanosilicate minerals found as microscopic crystals in miarolitic cavities in nepheline syenite in the Diamond Jo quarry, Hot Spring County, Arkansas. Delindeite is found as aggregates of flake-like crystallites in compact spherules, light pinkish grey in colour, with a resinous, pearly lustre. The flakes are biaxial positive with average n ∼ 1.813; the measured density is 3.3 g/cm 3 . Electron diffraction revealed a monoclinic unit cell in space group C 2 l m or subgroup, with a = 21.617(13), b = 6.816(5), c = 5.383(3) Å, β = 94.03(5)° (refined from X-ray powder data). The strongest X-ray lines are ( hkl , d obs , I rel ): (200, 10.80, 100); (311, 3.54, 24); (6̄01, 3.083, 28); (601, 2.888, 31); (2̄21, 2.806, 20); (910, 2.262,18). The crystals are submicroscopically twinned on (100) and also produce additional continuous diffraction streaks parallel to a *, which double the b and c axes. The formula derived from electron and ion probe analyses (H 2 O by difference), as constrained by density and molar volume data, is approximately (Na,K) 2.7 (Ba,Ca) 4 (Ti,Fe,Al) 6 Si 8 O 26 (OH) 14 , with Na > K, Ba ≫ Ca, Ti ≫ Fe,Al; Z = 1. Lourenswalsite occurs as very thin hexagonal plates in rosettes, silver grey to light brownish grey in colour. The crystals are biaxial negative with very low 2 V angle. Indices of refraction are n α = 1.815, n β ≈ n γ = 1.840; the measured density is 3.17 g/cm = 1.840; the measured density is 3.17 g/cm 3 . X-ray and electron diffraction show a sharp pseudohexagonal lattice with a = 5.244 Å, but extremely diffuse diffraction streaks normal to the hk 0 plane. In these streaks a period of 20.5 Å can be discerned. A hexagonal unit cell with a = 5.244(2) Å, c = 20.49(3) Å can be refined from the powder diffraction data but does not account for some lines, probably because of extreme layer disorder as shown by precession single-crystal patterns. The strong X-ray powder lines are (002, 10.22, 20); (-, 3.93, 20); (111, 2.608, 100); (300, 1.5145, 80); (220, 1.3111, 25). The formula given by microprobe analyses, constrained by density and molar volume data, is approximately (K,Ba) 2 (Ti,Mg,Ca,Fe) 4 (Si,Al,Fe) 6 O 14 (OH) 12 with K > Ba, Ti ≫ (Mg,Ca,Fe), Si > Al > Fe; Z = 1. These minerals are formed under oxidizing weathering conditions, and iron is assumed to be in the Fe 3+ state.

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