Ouachita Mountains Research Articles

Statistical characterization of a confined submarine fan system: The Pennsylvanian Lower Atoka Formation, Ouachita Mountains, USA

AbstractCurrent knowledge of submarine fan deposits has historically relied heavily on qualitative field and subsurface observations and interpretations, but recent studies using statistical analyses have enhanced the understanding of submarine fan sub‐environments, including the degree of confinement, stratigraphic patterns and potential control factors. The purpose of this study is to improve the quantitative understanding of synorogenic submarine fan deposition at foreland basin settings with a statistical approach. A suite of statistical methods is integrated and developed (Hurst Statistics/rescaled range analysis, bed thickness frequency distribution analysis, Markov Chains and time‐series analysis), and applied to the well‐understood Pennsylvanian lower Atoka submarine fan system in the Ouachita Mountains, United States, for this purpose. The results of the Hurst Statistics and bed thickness analyses corroborate qualitative interpretations that: (i) the lower Atoka is lobe‐dominated; and (ii) the south‐eastern (wedge top) portion of the system is more strongly confined than the northern (foredeep) portion. The Markov Chains and time‐series analyses reveal the prevalence (56% of the measured sections) of stratigraphic orderliness and cyclicity; these results are used to discuss potential control signals, which are otherwise difficult to distinguish, on the turbidite sandstone recurrence cycles. The results of this study demonstrate that these integrated statistical methods can be utilized to quantify depositional interpretations and extract hidden information using outcrops with limited exposures.

Tectonic–sedimentary interplay of a confined deepwater system in a foreland basin setting: the Pennsylvanian lower Atoka Formation, Ouachita Mountains, U.S.A.

ABSTRACT Submarine fans deposited in structurally complex settings record important information on basin evolution and tectonic–sedimentary relationships but are often poorly preserved in outcrops due to syndepositional and post depositional deformation. This study aims to understand the influence of tectonics on the deposition of the synorogenic Pennsylvanian lower Atoka submarine fan system deposited in a structurally complex foreland basin during the Ouachita orogeny. This study is a synthesis of new outcrop stratigraphic data as well as published stratigraphic and structural data. The lower Atoka crops out in the Ouachita Mountains and the southern Arkoma Basin and is divided into three structural–depositional zones: the foredeep, the wedge top, and the continental foreland. The mean paleoflow is axial, and each zone exhibits unique patterns in facies distribution. The foredeep consists of two fan systems, a large westward-prograding fan that exhibits significant longitudinal and lateral facies changes, and a small eastward-prograding fan on the western part. The wedge top consists of a westward-prograding fan that exhibits subtle longitudinal facies change. The continental foreland consists of small slope fan systems along the northern and western margins. By comparing to basin morphology and structural styles, we interpret the facies distribution patterns in the three zones as the result of different combinations of lateral structural confinement, axial and lateral sediment supply, and paleogeography. This study provides an improved and comprehensive understanding of the lower Atoka deepwater system and has implications for deciphering the tectonic–sedimentary relationships in laterally confined submarine fan systems.

Interannual climate variation influences nest initiation date and nest productivity of the Red-cockaded Woodpecker at the northwestern edge of its range

AbstractClimate change, including directional shifts in weather averages and extremes and increased interannual weather variation, is influencing demography and distributions for many bird species. The Ouachita Mountains ecoregion in southeast Oklahoma and west-central Arkansas contains 2 populations of the Red-cockaded Woodpecker (Dryobates borealis, RCW), a federally endangered, cooperatively breeding species. Since this region is at the RCW’s northwestern range periphery, ecological thresholds likely are limiting for the species. Therefore, populations in this region may be more sensitive to climate change-associated weather variation and unpredictability. We used 26 years of nesting data (1991–2016) from the 2 RCW populations to determine if interannual weather variation has affected nesting phenology and productivity. For each population, we used daily temperature and precipitation data for 3 periods (30 and 60 days before nesting; 40 days overlapping the nesting period) to determine how weather influences median nesting date and average clutch size and numbers of fledglings. In a separate analysis, we used shorter time windows with individual nests as replicates to determine how discrete weather events (e.g., minimum and maximum temperatures and intense precipitation events) affect nest success and partial brood loss. For both Oklahoma and Arkansas populations, warmer early spring temperatures generally advanced nesting and increased clutch size and fledgling number. However, the effects of average precipitation varied depending on the amount and duration of precipitation in different time periods. At the nest level, most variables reflecting discrete temperature and precipitation events were unrelated to nest success and brood loss, suggesting that factors other than weather (e.g., habitat quality and predation) more strongly influenced the nesting output of individual RCW broods. Our results indicate RCWs are responding to interannual weather variation in complex and variable ways. However, warming trends may generally be having positive effects on the species at the northwestern edge of its range.

Effects of timber harvest on survival and movement of stream salamanders in a managed forest landscape

AbstractWith escalating anthropogenic alteration of landscapes worldwide, managed forests are increasingly important as providers of ecosystem services and wildlife habitat. Therefore, it is crucial to maintain a balance between producing forest products and biodiversity conservation. Several studies have reported negative effects of forest management on terrestrial plethodontid salamanders, but fewer have focused on stream‐dwelling species or evaluated mechanisms for shifts in their abundance (e.g., mortality vs. movement). We used a before–after–control–impact design to examine the effects of clear‐cut harvesting on a semi‐aquatic stream‐breeding salamander endemic to the Ouachita Mountains, Desmognathus brimleyorum. We conducted a three‐year capture–mark–recapture (CMR) study at three streams within a managed pine (Pinus spp.) landscape in west‐central Arkansas, USA. Loblolly pine (Pinus taeda) stands surrounding two of the streams were clear‐cut (leaving a 14–21 m wide forested buffer on each side of the stream) midway through the study; the third stream served as a control site and remained unharvested. We estimated apparent survival using open CMR models and compared salamander movement over time and between harvested and control streams. Overall, our models revealed seasonal and temporal variation in salamander survival and abundance, but little evidence for strong immediate effects of timber harvesting on post‐metamorphic salamanders within two years postharvest. However, there was increased salamander movement at sites where forest harvest occurred. Our results suggest that streamside buffers of at least 14–28 m on either side of a stream are effective for minimizing immediate effects of forestry activities on juvenile and adult stream‐dwelling salamanders, when timber harvest occurs in the winter months. These results will inform management decisions aimed at conserving biodiversity and ecosystem integrity in managed forest landscapes while also filling a critical gap in the knowledge of stream salamander demographic parameters.

Conservation genetics of the threatened plant species Physaria filiformis (Missouri bladderpod) reveals strong genetic structure and a possible cryptic species.

Understanding genetic diversity and structure in a rare species is critical for prioritizing both in situ and ex situ conservation efforts. One such rare species is Physaria filiformis (Brassicaceae), a threatened, winter annual plant species. The species has a naturally fragmented distribution, occupying three different soil types spread across four disjunct geographical locations in Missouri and Arkansas. The goals of this study were to understand: (1) whether factors associated with fragmentation and small population size (i.e., inbreeding, genetic drift or genetic bottlenecks) have reduced levels of genetic diversity, (2) how genetic variation is structured and which factors have influenced genetic structure, and (3) how much extant genetic variation of P. filiformis is currently publicly protected and the implications for the development of conservation strategies to protect its genetic diversity. Using 16 microsatellite markers, we genotyped individuals from 20 populations of P. filiformis from across its geographical range and one population of Physaria gracilis for comparison and analyzed genetic diversity and structure. Populations of P. filiformis showed comparable levels of genetic diversity to its congener, except a single population in northwest Arkansas showed evidence of a genetic bottleneck and two populations in the Ouachita Mountains of Arkansas showed lower genetic variation, consistent with genetic drift. Populations showed isolation by distance, indicating that migration is geographically limited, and analyses of genetic structure grouped individuals into seven geographically structured genetic clusters, with geographic location/spatial separation showing a strong influence on genetic structure. At least one population is protected for all genetic clusters except one in north-central Arkansas, which should therefore be prioritized for protection. Populations in the Ouachita Mountains were genetically divergent from the rest of P. filiformis; future morphological analyses are needed to identify whether it merits recognition as a new, extremely rare species.

Managed Wildfire, Drought, and Overstory Survival: A Case Study in the Ouachita Mountains of Arkansas

Fire managers are increasingly using natural ignitions to restore and maintain fire-adapted ecosystems. Managing natural ignitions after decades of suppression, however, holds inherent ecological, economic, and personal risks. During the severe drought of 2011, fire management staff on the Ouachita National Forest used a range of strategies to manage the lightning-ignited High Peak Wildfire because full suppression was infeasible and there were potential resource benefits (e.g., restoration of desired forest structure and composition). Because of concerns that the combined effect of drought and fire could adversely affect overstory tree health and timber value, we established plots in burned and unburned areas in dry and dry-mesic pine-oak forests and loblolly pine (Pinus taeda) plantations immediately after the fire, and remeasured them 2 and 5 y post-burn. Between inferred pre-burn condition and 2 y post-burn, overstory trees across community types were resistant to fire (94% survival) while midstory trees were less resistant (35% survival). Survival between 2 and 5 y post-burn was near 100% for both overstory and midstory. Both the density and diversity of the midstory were reduced by 2 y post-burn, which had the desired effect of moving forest structure and composition toward an open woodland condition. This study provides evidence that wildfire, even in a drought, can be used in restoration efforts and that overstory trees in dry and dry-mesic pine-oak forests and pine plantations of the Ouachita Mountains can survive with little effect on resource values, provided that weather and fuel conditions are conducive to low- and moderate-severity burning.

A conservation-oriented SNP panel for Smallmouth Bass (Micropterus dolomieu), with emphasis on Interior Highlands lineages

The Smallmouth Bass (Micropterus dolomieu; SMB) is a widely distributed black bass species, but the southwestern edge of the species range within the Interior Highlands contains some of the most divergent ecotypes. The Neosho subspecies (M. d. velox) inhabits tributaries of the Arkansas River within the Ozark Mountains and a second lineage is reported from drainages of the Ouachita Mountains. We sought to develop a single nucleotide polymorphism (SNP) panel to (1) diagnose hybridization with sympatric Spotted Bass (Micropterus punctulatus; SPB) and non-native Northern SMB (M. d. dolomieu) stocked in the region, and (2) delineate population structure within the ranges of the Neosho and Ouachita SMB lineages. We obtained 76 individual SMB samples from across their range but concentrated within the Interior Highlands (n = 50). We also included 3 SPB to allow for hybrid detection and 3 Shoal Bass (Micropterus cataractae) as an outgroup. Phylogenetic trees constructed with the generated SNP data corroborated the existence of at least three major lineages of SMB (Northern, Neosho, and Ouachita), each containing varying degrees of differentiation among major drainages. Simulation analyses revealed that chosen SNPs had high power (> 0.9) to assign SMB × SPB hybrid categories and similarly high power (> 0.8) for Northern SMB × Interior Highlands SMB hybrids. Clustering methods delineated major inter-basin population structure within the native ranges of Neosho and Ouachita SMB with chosen SNPs. Anticipated uses of the resulting 192-loci SNP panel include conservation planning, fisheries management assessments, and ecological investigations of the Neosho and Ouachita SMB lineages.

Effects of transportation infrastructure on fishes in the Ozark and Ouachita Mountains

Rivers worldwide are fragmented by transportation infrastructure that blocks the movements of aquatic organisms. To assess the effects of road culverts on stream fishes in the Ozark and Ouachita Mountains regions of Oklahoma, we surveyed 39 free-flowing sites, 29 sites upstream and 29 sites downstream of culverts. We observed differences in species richness and abundance between free-flowing sites, sites upstream of a culvert, and downstream sites. We also found that the degree to which a culvert affected richness and abundance depended on culvert type and length. Furthermore, the culverts in the poorest condition had the greatest effects on abundance and richness. Replacement of these poor condition culverts is likely a high priority for both conservation groups and infrastructure agencies. Our findings enable conservation practitioners to identify structures that may be high priorities for aquatic organism passage projects, including those that may benefit from cost-sharing or collaboration with infrastructure agencies.

Concentration and divergence of sediment in an erosional landscape

In an eroding landscape, the erosional source area (Ae) may be larger or smaller than the depositional or storage area (Ad). This corresponds to areal concentration (Ae/Ad > 1) or divergence (Ae/Ad < 1) of sediment. We investigated this in an area of the Ouachita Mountains for three different time periods: before the early 1800s (pre-European settlement), early 1800s to 1990s, and post 1990s. Pre-1800, the forest was mainly undisturbed and soil loss was dominated by slow erosion and mass wasting from ridge tops. In the latter period establishment of all-terrain vehicle (ATV) trails created a small area of rapid, concentrated, persistent erosion. In the middle period, logging operations resulted in short-lived erosion hotspots scattered throughout the landscape. For the pre-1800s period, we estimated Ae/Ad based on the spatial distribution of alluvial, colluvial, and upland potential source area soils. Ae/Ad = 0.81, and <1 even when alluvial soils are not included. For the most recent era, field studies documented the eroding surface area of trails, as well as the area of near-trail sediment deposits and of deposition in smaller stream channels. Ae/Ad = 6.60, indicating concentration. In the intermediate era, conditions were more similar to the pre-European condition, as harvested areas and temporary unpaved roads recover quickly to pre-disturbance conditions and use of permanent roads was far lower before the ATV trails. The strongly dissected, steep topography, humid subtropical climate, limited potential for agriculture, and the nature of the ATV trail erosion all play roles in creating the sediment divergence in earlier eras and sediment concentration more recently. This suggests a need for more case studies to develop more general principles or guidelines to predict sediment concentration and divergence.

Survival and persistence of tricolored bats hibernating in Arkansas mines

AbstractWhite-nose syndrome (WNS) has caused large declines in bat populations across eastern North America, making information on demographics of affected species critical to determining their risk for extinction. We used Cormack–Jolly–Seber models to estimate apparent survival rates of hibernating tricolored bats (Perimyotis subflavus) for 5 years in four small abandoned mines in the Ouachita Mountains of Arkansas, located within the WNS endemic area of the United States. Populations in individual mines varied greatly in survival rates, with one mine displaying annual survival rates as high as 0.706 and another as low as 0.101. Differences in survival among bats in different mines could not definitively be attributed to WNS, but may have varied based on a combination of WNS, disturbance, mine climate, and other unknown factors. Further, some hibernacula may have served as temporary winter shelter for young transient males. Sites housing small colonies of hibernating bats may result in high survival rates despite WNS, and protecting these smaller sites may be important for overall species perseverance.

&lt;p&gt;&lt;strong&gt;Geographic variation in a restricted-range endemic dragonfly &lt;em&gt;Gomphurus&lt;/em&gt; &lt;em&gt;ozarkensis&lt;/em&gt; (Odonata: Gomphidae), with description of a new subspecies&lt;/strong&gt;&lt;/p&gt;

The geographic distribution of Gomphurus ozarkensis (Westfall, 1975), a species described to science only four decades ago, is confined to a four-state area in the central United States: southeastern Kansas, eastern Oklahoma, western and northern Arkansas, and southern Missouri. Its small range has led some to classify it a species of conservation concern. We examined geographic variation in the species, which despite its small range exists in three distinct subpopulations: one in the Ouachita Mountains of western Arkansas and southeastern Oklahoma; one on the Ozark Plateau of northeastern Oklahoma, southeastern-most Kansas, southern Missouri, and northern Arkansas; and one in the Osage/Flint hills of southeastern Kansas and northeastern Oklahoma. Clinal variation is evident in the extent of yellow on the terminal abdominal segments and the extent to which certain thoracic stripes are fused. A population in a separate watershed basin in the southern Osage Hills of Oklahoma is taxonomically distinct, with some phenotypic characters tending toward G. externus (Hagen, 1858). We describe this population as a new subspecies of G. ozarkensis.

Differential responses of amphibian and reptile assemblages to size of riparian buffers within managed forests.

Streamside management zones (i.e., riparian buffers; SMZs) are commonly implemented within managed forests to protect water quality but may also provide habitat for riparian-associated wildlife. Yet, little research has rigorously addressed the value of SMZs for wildlife, particularly for cryptic species such as amphibians and reptiles. Previous studies of herpetofauna within SMZs have focused on one or a few stream-associated species, and questions remain regarding variation among species or guilds and what role SMZs serve toward conservation of herpetofaunal diversity in managed forests. However, recent statistical advances have improved our ability to analyze large multi-species presence-absence data sets, accounting for low detection rates typical for some herpetofaunal species. Our study represents an extensive landscape-scale examination of herpetofaunal communities within SMZs using a multi-species occupancy approach. We conducted four replicate surveys at 102 headwater streams, spanning a gradient of SMZ widths and adjacent forest stand ages, within the Ouachita Mountains, Arkansas, USA. We used a hierarchical Bayesian community occupancy model to estimate species richness and species-specific occupancy responses to SMZ and overstory characteristics, accounting for variation in occupancy and detection attributable to site and sampling covariates. We documented high richness (37 species) within SMZs. Across the herpetofaunal community, occupancy and species richness were consistently positively associated with SMZ width, with maximum predicted richness of 30 species occurring at sites with buffers extending 51m on either side of the stream. However, we documented considerable variation among groups and species within groups, underscoring the potential for different responses to forest management among taxa. Reptile predicted richness increased more rapidly up to SMZs of ~35m, whereas maximum salamander predicted richness was not seen until an SMZ width of 55m. Estimated salamander richness was highest within SMZs embedded in mature managed pine stands and was higher in SMZs comprised of a deciduous or mixed overstory vs. a pine overstory. Compared to salamanders, more anuran species showed high mean estimated occupancy (>75%) at narrower SMZs (<30m). Collectively, our results indicate that SMZs surrounding small first-order streams in intensively managed forests not only protect water quality, but also can support diverse amphibian and reptile communities.

Sediment Availability and Erosion Rates on Off‐Highway Vehicle Trails in the Ouachita Mountains, USA

AbstractFactors influencing sediment availability are assessed and erosion rates are quantified for an off‐highway vehicle (OHV) trail system in the Ouachita Mountains of Arkansas. As of May 2012, the Wolf Pen Gap trail system included 77.0 km of "trails" which consist of county roads; open and closed Forest Service roads; and open and closed OHV trails. For a given trail length, the sediment volume available to be eroded is determined by bare trail width and sediment depth. Four condition types are defined that group trail sections based on statistically different trail widths or depths. Trail construction method appears to influence sediment availability differences more than erosion potential (as indexed by trail slope gradient and length). The range for annual trail erosion rates is estimated as 75 and 210 tonne/ha/yr. The high and low rates are obtained using two independent methods. The 210 tonne/ha/yr rate is computed from mean sediment capture at 30 sediment traps installed for 0.5–1.0 year. The 75 tonne/ha/yr rate is computed assuming all available trail sediment measured in a one‐time sampling is eroded over the next year. We argue in support of this assumption and suggest both rate values may be conservative. Trail erosion rates and sediment trap observations indicate frequent trap cleanout will be needed to continue sediment capture from All Terrain Vehicle trails.

Post-Pleistocene differentiation in a Central Interior Highlands endemic salamander.

AimFor many endemic species with limited dispersal capacities, the relationship between landscape changes and species distributions is still unclear. We characterized the population structure of the endemic ringed salamander (Ambystoma annulatum) across its distribution in the Central Interior Highlands (CIH) of North America, an area of high species endemism, to infer the ecological and evolutionary history of the species.MethodsWe sampled 498 individuals across the species distribution and characterized the population genetic structure using nuclear microsatellite and mitochondrial DNA (mtDNA) markers.Results Ambystoma annulatum exist in two strongly supported nuclear genetic clusters across the CIH that correspond to a northern cluster that includes the Missouri Ozark populations and a southern cluster that includes the Arkansas and Oklahoma Ozarks and the Ouachita Mountains. Our demographic models estimated that these populations diverged approximately 2,700 years ago. Pairwise estimates of genetic differentiation at microsatellite and mtDNA markers indicated limited contemporary gene flow and suggest that genetic differentiation was primarily influenced by changes in the post‐Pleistocene landscape of the CIH.Main ConclusionsBoth the geologic history and post‐European settlement history of the CIH have influenced the population genetic structure of A. annulatum. The low mtDNA diversity suggests a retraction into and expansion out of refugial areas in the south‐central Ozarks, during temperature fluctuations of the Pleistocene and Holocene epochs. Similarly, the estimated divergence time for the two nuclear clusters corresponds to changes in the post‐Pleistocene landscape. More recently, decreased A. annulatum gene flow may be a result of increased habitat fragmentation and alteration post‐European settlement.

Temporal changes in fruit production between recurrent prescribed burns in pine woodlands of the Ouachita Mountains

The use of prescribed fire is integral to the restoration of open woodlands and savannas, including shortleaf pine (Pinus echinata) woodlands in the Ouachita Mountains of Oklahoma and Arkansas. Fire offers many potential benefits to numerous wildlife; however, short-term implications for understory fruit production are not fully understood, especially in stands subjected to frequent, recurrent burns. We examined the effects of dormant-season prescribed burns on woody fruit production (kg ha−1) and fruit producing vegetative cover in the understory of restored pine woodlands. We inventoried 32 stands during four temporal periods after dormant season prescribed fires: 1, 2, 3, and 5 growing seasons post-burn. We counted fruit (<2m above the ground) throughout the summer and visually estimated vegetative cover of fruit producing plants. Fruit production was greatest in the 3rd year (18.2 kg ha−1), followed by 5th (10.9 kg ha−1) and 2nd (9.8 kg ha−1) years after burns. Overall, 87% of total production consisted of three genera: American beautyberry (Callicarpa americana [38%]), Vitis spp. (summer grapes [Vitis aestivalis; 11%] and muscadine grape [V. rotundifolia; 10%]), and Rubus spp. (blackberry [20%] and dewberry [R. flagellaris; 8%]). Production was recorded in 13 of the 14 fruit producing species present during the 5th year post-burn, indicating that production diversity increased over time. Percent cover and species richness (26 taxa) of fruit producing taxa were greatest in the 3rd year post-burn. Taxa such as poison ivy (Toxicodendron radicans) and sumac (Rhus spp.) comprised a sizable percent of coverage (>7% each), but this did not translate into substantial fruit production. American beautyberry and summer grape had both substantial coverage and production. Results suggest that burning on a 3-year rotation maximizes and prolongs fruit production; however, occasional burning on a 5-year rotation will promote a higher diversity of woody mast-producing understory species.

A geochemical evaluation of the genetic relationship between Ouachita Mountains Paleozoic rocks and the Mississippi Valley-type mineralization in the southern Ozark Region, USA

The Pb and/or Zn deposits of the Tri-State and the Northern Arkansas Mississippi Valley-type (MVT) districts in the southern Ozark Region, located north of the Arkoma Basin and the Ouachita fold-thrust belt in North America, are genetically connected to the Pennsylvanian-Permian Ouachita orogeny. This orogenic event triggered a south-north topographic gradient flow of basinal brines, leaching metal-rich sediments en route. To establish whether the organic-rich shales of the Ouachita Mountains and the Ozark Region provided metals during the mineralization event, the Pb isotope compositions of the ores (sphalerite) have been compared to those of the sedimentary rocks (whole-rocks and leachates) of the Ouachita Mountains (Cambrian Collier Shale, Early Ordovician Mazarn Shale, Middle Ordovician Womble Shale, Late Ordovician Polk Creek Shale, Mississippian Stanley Shale, and Pennsylvanian Jackfork Sandstone) and the Ozark Plateau (Devonian/Mississippian Chattanooga Shale and Mississippian Fayetteville Shale). The Pb isotope compositions of ores in both districts show a broad and a linear range of isotopic values. This trend suggests mixing of Pb from two distinct end-member components. One end-member must be highly radiogenic, with Pb isotope ratios equal to or higher than the highest noticed value for ores. The other end-member must be less radiogenic, with Pb isotope ratios equal to or lower than the lowest value recorded for ores. The Pb isotope compositions of the analyzed whole rocks and leachates indicate that the best candidates for contributing the less radiogenic Pb to the ores are the sandstone members of the upper and middle Jackfork Sandstone and the lowermost section of the Chattanooga Shale.The depositional environment of the potential source rocks and their ability to sequester metals has been appraised using redox sensitive trace elements (Cd, Co, Cr, Cu, Mo, Ni, Pb, Th, U, V, Zn). Paleoredox proxies (e.g., enrichment factors of redox sensitive trace elements and V/V + Ni ratios) indicate deposition of the analyzed rocks mainly under anoxic and euxinic conditions, which are favorable for metal enrichment. However, oxic-suboxic conditions are also indicated by other geochemical proxies, suggesting a possible first order control of primary production that has resulted in an increased flux of organic matter. A disagreement in the redox conditions yielded by the paleoredox proxies has been noticed in several cases. This inconsistent behavior may be associated with several factors, including redox potential, pH, sulfur abundance, chemical availability, TOC values, and sediment provenance. The authigenic flux is the only fraction needed to unravel past redox conditions; however, the analyzed bulk sediments consist of authigenic, biogenic, and siliciclastic components, which may also have led to the observed disagreement in the redox conditions. Additional factors such as the basin geometry, the rates of sediment accumulation, the post depositional alteration processes associated with diagenesis and low-grade metamorphism during the Ouachita orogeny might have overprinted the depositional signatures.

Palaeomagnetic dating of hydrothermal alteration in the Woodford Shale, Oklahoma, USA

AbstractAn oriented Woodford Shale core from the eastern Ardmore Basin was sampled to test if the shale was an open or closed system to hydrothermal fluids, and to determine the timing of alteration. Mineralized fractures are ubiquitous in the core, and the shale exhibits a complex paragenesis with multiple hydrothermal minerals, including biotite, magnesite, norsethite, gorceixite and potassium feldspar present in and around the fractures. These minerals suggest that the Woodford Shale was an open system during part of its diagenetic history. Vitrinite reflectance (Ro) measurements indicate values of ∼1.81 % (∼230 °C). Palaeomagnetic analysis reveals a characteristic remanent magnetization (ChRM) with south-southeasterly declinations and shallow inclinations that resides in magnetite. This ChRM is interpreted to be either a chemical remanent magnetization (CRM) or a thermochemical remanent magnetization (TCRM) that was acquired at 245 ± 10 Ma during Late Permian time based on the pole position (51.0° N, 115.6° E). Because the palaeomagnetic specimens show evidence of extensive hydrothermal alteration, the CRM/TCRM is interpreted to date the migration of hydrothermal fluids through the shale. The agreement in timing with other studies that report hydrothermal alteration in southern Oklahoma and the Ouachita Mountains in Late Permian time, suggest that there were post-collisional fluid-flow events which accessed reservoirs of warm fluids.

Predicting hydrologic disturbance of streams using species occurrence data

Aquatic organisms have adapted over evolutionary time-scales to hydrologic variability represented by the natural flow regime of rivers and streams in their unimpaired state. Rapid landscape change coupled with growing human demand for water have altered natural flow regimes of many rivers and streams on a global scale. Climate non-stationarity is expected to further intensify hydrologic variability, placing increased pressure on aquatic communities. Using a machine learning approach and georeferenced species occurrence data, we modeled and mapped spatial patterns of hydrologic disturbance for streams in Arkansas, Missouri, and eastern Oklahoma. Random forest (RF) models trained on fish community data, hydrologic, and landscape metrics for gaged streams in the National Hydrography (NHDPlusV2) database were used to predict a hydrologic disturbance index (HDI) for ungaged streams. The HDI is part of the USGS Geospatial Attributes of Gages for Evaluating Streamflow (GAGESII) database and is a composite index of watershed-scale disturbance from anthropogenic stressors. Fish presence/absence data had similar overall model prediction accuracy (77%; 95% CI: 0.74, 0.80) as flow variables (76%; CI: 0.73, 0.80). Including topographic variables increased the RF prediction accuracy of both the fish (90%; CI: 0.88, 0.92) and flow models (86%; CI: 0.84, 0.89). Spatial patterns of hydrologic disturbance suggest distinct ecohydrological regions exist where conservation actions may be focused. Streams with low HDI were predominately located in the Ozark Highlands, Boston Mountains, and Ouachita Mountains. Correlation analysis of HDI by flow regime showed groundwater stable streams had the lowest disturbance frequency, with over 50% of stream reaches with low HDI located in forested land cover. HDI was highest for big rivers, intermittent runoff streams and streams in areas of agricultural land use. Our results show long-term georeferenced biological data can provide a valuable resource for predictive modeling of hydrologic disturbance for ungaged rivers and streams.

Influence of riparian buffers and habitat characteristics on salamander assemblages in headwater streams within managed forests

Streamside management zones (SMZs), buffers of forest retained along streams when adjacent areas are harvested, are a primary tool for maintaining ecological functions in managed forests. However, few studies have examined the influence of SMZs on salamanders, and none have examined variation in salamander occupancy, species richness, and abundance across a gradient of SMZ widths at a large spatial scale. Further, because previous studies had limited ability to detect responses of uncommon species, little is known about interspecific variation in salamander responses or whether SMZs serve as refuges for terrestrial species during harvesting. To evaluate the role of SMZs in maintaining salamander species, we conducted four replicate surveys at 102 headwater stream sites, spanning a gradient of SMZ widths and adjacent forest stand ages, within the Ouachita Mountains, Arkansas, USA. We used a hierarchical Bayesian community occupancy model to estimate salamander species richness and species-specific occupancy responses to SMZ and overstory characteristics, while accounting for variation in occupancy and detection attributable to site and sampling covariates. Additionally, we used Bayesian binomial mixture models to examine the influence of SMZ width and surrounding stand age on abundance of two stream-associated salamanders [Ouachita dusky salamander (Desmognathus brimleyorum) and many-ribbed salamander (Eurycea multiplicata)] and three terrestrial salamanders [red-backed salamander (Plethodon serratus), slimy salamander (P. glutinosus complex), and Caddo Mountain salamander (P. caddoensis)]. Occupancy, species richness, and abundance increased with increasing SMZ width, but the strength of responses varied among species. Occupancy of uncommon species was highest at sites with wide SMZs, likely because of the need for specific habitat elements (e.g., wetlands, rocky talus). Richness was lowest in SMZs dominated by pine overstory, and lowest in mid-aged stands, consistent with a lagged decrease in richness within SMZs following harvest. Finally, we documented patterns of abundance consistent with the evacuation hypothesis, indicating that salamanders may leave recently harvested areas seeking more suitable habitat and microclimate within SMZs. Collectively, results indicate that SMZs in intensively managed forests can support robust salamander communities, provided managers continue to retain wide SMZs at some key sites across the landscape (i.e., ≥55 m on each side of the stream), a value larger than current Forestry BMP guidelines.

Habitat Associations of Three Crayfish Endemic to the Ouachita Mountain Ecoregion

Many crayfish are of conservation concern because of their use of unique habitats and often narrow ranges. In this study, we determined fine-scale habitat use by 3 crayfishes that are endemic to the Ouachita Mountains, in Oklahoma and Arkansas. We sampled Faxonius menae (Mena Crayfish), F. leptogonopodus (Little River Creek Crayfish), and Fallicambarus tenuis (Ouachita Mountain Crayfish) from wet and dry erosional channel units of 29 reaches within the Little River catchment. We compared channel-unit and microhabitat selection for each species. Crayfish of all species and life stages selected erosional channel units more often than depositional units, even though these sites were often dry. Accordingly, crayfish at all life stages typically selected the shallowest available microhabitats. Adult crayfish of all species and juvenile Little River Creek Crayfish selected patches of coarse substrate, and all crayfish tended to use the lowest amount of bedrock available. In general, we showed that these endemic crayfish used erosional channel units of streams, even when the channel units were dry. Conservation efforts that protect erosional channel units and mitigate actions that cause channel downcutting to bedrock would benefit these crayfish, particularly during harsh, summer drying periods.