Lake Texoma Research Articles

Post-Burn, Post-Flood Effects In A Degraded Grassland, Lake Texoma, Bryan County, Oklahoma

Plant communities change over time, sometimes leading to an increase or decrease in biological diversity. Often, absence of active management of a site leads to its degradation including loss of native species and invasion by non-native weeds. Lake Texoma, Texas and Oklahoma, represents an area where extensive landscape change has happened over the course of almost a century. The Denison Dam was completed in 1938, forming the lake, which over time has altered conditions in the forested and formerly-grazed locations surrounding it. The location studied in this paper is a 186-ha tract of land situated between Johnson Creek and the Roosevelt Bridge in Bryan County, Oklahoma. In summer 2000, a species list was compiled for a grassland located at the lake site as part of a larger study. This grassland comprised ~10% of the total site area. Following two major floods and an extended drought, the site was resampled in 2018. Results indicated it had suffered a serious decline in species richness and an increase in abundance of invasive or encroaching species. Species richness was reduced by approximately 50% between 2000 and 2018. Fewer transects were sampled in 2018 because of woody encroachment on the original site. In spring 2021, following an extensive prescribed burn, the site was resampled to see if burning led to any reduction in undesirable species. The most frequent species in 2000 included Panicum philadelphicum, Lespedeza virginica, Rudbeckia hirta and Ambrosia psilostachya and in 2018 they were Lespedeza cuneata, Ambrosia psilostachya, and Dichanthelium oligosanthes. It is possible that the invasive Lespedeza cuneata (sericea lespedeza) spread after a 2007 flood because of some combination of reduced competition and transport of seed in floodwater. In 2021, the most frequent species were the same as in 2018, showing little effect of the burn. However, the Shannon diversity and evenness in both early and late summer sampling periods after the burn were higher than those for the 2018 data, suggesting that the burn may have had some effect. To attempt to restore the site to more “native” conditions would probably require some combination of regular burning, flash grazing, and possibly herbicide use. Once sericea lespedeza establishes, it is very difficult to eradicate from a location.

Factors associated with Paddlefish (Polyodon spathula) restoration success in Oklahoma

AbstractThe Paddlefish (Polyodon spathula) has been extirpated from portions of its native range due to anthropogenic habitat degradation and fragmentation, most notably the impoundment of rivers. To mitigate some of these losses in Oklahoma, Paddlefish have been stocked into reservoirs throughout the state, with variable success in establishing self‐sustaining populations. Two factors thought to contribute to success of Paddlefish stocking are spawning substrate and prey availability, which were quantified in six reservoirs and nine reservoir tributaries. Side‐scan sonar and supervised classification of aerial imagery were used to classify 4517‐ha of river substrate upstream of the river‐reservoir interface in reservoir tributaries. Zooplankton community structure, water clarity, and nutrient availability were also assessed in the same reservoirs and tributaries. One tributary had suitable spawning substrate (>40%), and the rest had minimal (<1.5%), which suggested that availability of suitable spawning substrate was not directly correlated with Paddlefish stocking success. Reservoirs with self‐sustaining Paddlefish populations had higher abundance of large zooplankton (copepods and cladocerans) than reservoirs without a reproducing population. Notably, tributaries associated with Lake Texoma, the one known example of failed restoration, were much more turbid than other rivers. We conclude that abiotic factors such as water clarity may contribute more to variable recruitment than spawning substrate or zooplankton abundance by mediating foraging success of Paddlefish post‐larvae.

Bowfishing shoot and release: High short‐term mortality of nongame fishes and its management implications

AbstractObjectiveAlthough bowfishing is legal in all 50 states in the USA, the practice of releasing shot fish is only legal in 8 states. An argument favoring this practice has been that survival of fish after shoot‐and‐release fishing is high. Bowfishing mortality trials were conducted in 2021–2022 in Lake Texoma, Oklahoma, to quantify shoot‐and‐release mortality and characterize the mortality via the location of the wound associated with the release of fish shot by bowfishing.MethodsA total of 240 nongame fish were shot by experienced bowfishers with conventional bowfishing equipment and held in convalescent pools, with control fish captured by electrofishing to document short‐term mortality up to 5 days.ResultOverall mortality of bowfished fish was 87% versus 0% for control fish. Fish shot in critical areas (head, internal organs, or spine; 78% of total) suffered 96% mortality, whereas fish shot in noncritical areas (dorsal musculature, tail, or fins) experienced 52% mortality. In addition, 13.7% of fish shot were not successfully retrieved. Shot fish were generally older (mean = 19.4 years, range = 3–54) and contained more females (62%) than control fish (mean = 12.5 years, range = 2–39; 37% female), providing evidence that bowfishing can remove individuals of great recruitment value. The shoot‐and‐release mortality rates in this study, for fish shot in both critical and noncritical areas, exceeded mortality from a wide range of angler catch and release in other studies.ConclusionThe high mortality rate associated with shoot and release observed in this study and as practiced by recreational bowfisheries renders shoot and release inconsistent with scientifically regulated and sustainable bowfisheries for native nongame species. These results provide evidence that the bow and arrow, when aimed at animals, is a weapon that is intended to kill. Bowfishing should realistically be managed as a 100% consumptive (i.e., kill) pursuit in which shoot and release is prohibited and nonretrieval of shot fish is accounted for.

LIFE HISTORY CHARACTERISTICS OF ALLIGATOR GAR (ATRACTOSTEUS SPATULA) IN THE UPPER RED RIVER (OKLAHOMA–TEXAS)

Alligator gar (Atractosteus spatula) populations are declining in the southern United States and Mexico, prompting increasing efforts by state and federal agencies to manage populations. We sampled the alligator gar population in the Red River drainage of Oklahoma–Texas from March 2006 to April 2008 to evaluate population characteristics, identify efficient sampling techniques, and evaluate aging techniques. Catch rates for adult fish were highest using multifilament trammel nets (n = 80) during cold water periods (<12°C) and for young-of-year fish using mini-fyke nets (n = 60) during warm water periods (>18°C). Movements and home range were examined using ultrasonic telemetry. Home-range areas of six individuals were from 4.93 to 17.13 km2 during a 4–9-month period. Spawning in Lake Texoma was documented in spring 2007. Sixty-four alligator gar were aged using double-blind methods of scale cross sections. A subsample of 14 individuals was also aged using whole otoliths to cross-reference scale ages. Age determinations ranged from 0 to 28 years at date of capture and suggest that the youngest gar were spawned in 2006 and 2007. Age determination of alligator gar using scale sections proved to be imprecise and biased toward overestimation of age in adults when compared with whole otolith ages. The alligator gar population in Lake Texoma and the Red River upstream of the reservoir appeared to be stable, represented by varied age and length classes, and is experiencing regular recruitment.

Morphological and Molecular Characterisation of Myxidium kudoi Meglitsch, 1937 from the Blue Catfish Ictalurus furcatus, Valenciennes in Oklahoma, USA

Myxidium kudoi Meglitsch, 1937 has been described from the type host, blue catfish Ictalurus furcatus, with no additional host records or molecular data available for this species. To provide molecular data and a novel host locality for this species and carry out phylogenetic analyses to infer the evolutionary relationship of the species to other members of the family Myxidiidae for which DNA sequence data is available. These data were collected using myxospores from the gallbladder of a blue catfish, Ictalurus furcatus collected from Lake Texoma, Oklahoma, USA. Myxospores were morphologically consistent with the only other account of this species and not any other Myxidium species described from siluriform fishes. Myxospores were oblong with rounded ends and were 10.8-12.6 (11.6 ± 0.5) µm in length and 4.7-6.6 (5.7 ± 0.5) µm in width. Polar capsules were subspherical and 2.7-3.9 (3.4 ± 0.3) µm in length and 2.4-3.5 (3.1 ± 0.3) µm in diameter, with each capsule containing a polar filament with 3-4 coils. Molecular data consisted of a 2918-bp sequence of the partial 18S, complete ITS1, 5.8S, ITS2, and partial 28S ribosomal rRNA regions as well as a 2455-bp sequence of partial 28S ribosomal RNA. The partial 18S and 28S data was used in a concatenated Bayesian phylogenetic analysis to further infer the evolutionary relationships of the Myxidiidae. Additionally, the partial 18S data was used in a separate phylogenetic analysis. The present work reports novel morphological and molecular data for Myxidium kudoi as well as a novel locality of occurrence for this species. In concatenated phylogenetic analysis using 18S and 28S data and other molecular data from Myxozoa, M. kudoi grouped with other freshwater Myxidiidae. In the single-locus, 18S analysis, M. kudoi grouped with Myxidium rhodei from Rutilus rutilus and Myxidium amazonense from Corydoras melini, the only other Myxidium species of catfish for which molecular data are available.

Hybridization and Population Genetics of Alligator Gar in Lake Texoma

AbstractThe Alligator Gar Atractosteus spatula (AG) is a long‐lived fish of growing management and conservation interest. Situated on the border of Texas and Oklahoma, Lake Texoma supports one of the last robust AG populations in Oklahoma; however, a genetic evaluation of this population is lacking. We genotyped AG individuals with 17 microsatellite loci, 7 of which also cross‐amplified in three sympatric Lepisosteus species: the Longnose Gar L. osseus (LN), Shortnose Gar L. platostomus (SN), and Spotted Gar L. oculatus (SP). Bayesian assignment analyses conducted in STRUCTURE and NewHybrids confirmed that a field‐identified hybrid was an F1 AG × LN and identified five other individuals that were suspected backcrosses (three LN × SN; two SN × SP). Alligator Gar had the lowest observed heterozygosity (0.179) and the lowest allelic richness (1.682) among the nonhybrid individuals of the four gar species examined. We also examined the potential for population structure and differences in pairwise relatedness (r) between two areas where AG are commonly encountered within Lake Texoma: the Red River and Washita River arms. No population structure was detected using noninformative or location priors in STRUCTURE, and estimates of r produced by the TrioML estimator in COANCESTRY were not significantly different between arms (overall mean r = 0.199). Point estimates of effective population size ranging from 16.3 to 29.2 suggested that the AG population may be vulnerable to the effects of inbreeding depression and random genetic drift. Results provide a genetic status assessment of AG in Lake Texoma and a baseline for future management and conservation decisions within Lake Texoma and surrounding regions.

Use of fragmented reservoir habitats by larval fish assemblages across years with contrasting hydrological conditions

Sedimentation in aging reservoirs generally reduces fish habitat quality and quantity, often isolating coves and pools from the main body of the reservoir. In some cases, however, habitat fragments created by sediment deposition in the river-reservoir interface zone support high fish diversity, and they could potentially replicate features of nursery habitats in natural river floodplains if they are regularly connected to the greater river-reservoir. We examined the structure of larval fish assemblages in fragmented coves and pools within the transitional zone of an aging reservoir (Lake Texoma) over 2 years with contrasting hydrological conditions (dry year with low connectivity versus wet year with high connectivity to the main body of the reservoir). We found that larval assemblage structure varied spatially across the two river arms of the reservoir and temporally across the dry and wet year. In both years, assemblages were dominated by Dorosoma species and Menidia beryllina, taxa considered habitat generalists. The abundance of other taxa, particularly Lepomis, Pomoxis, and Morone species, increased with greater habitat connectivity in the wet year. Many taxa considered dependent upon riverine or floodplain habitats were collected during the wet year at sites where they had not been collected in the dry, low-connectivity year. Our results suggest that these fragmented habitats can provide nursery habitats for a variety of fish taxa, but that the structure of larval assemblages using them varies widely based on hydrological connectivity.

Ecological Patterns Among Bacteria and Microbial Eukaryotes Derived from Network Analyses in a Low-Salinity Lake.

Microbial communities are comprised of complex assemblages of highly interactive taxa. We employed network analyses to identify and describe microbial interactions and co-occurrence patterns between microbial eukaryotes and bacteria at two locations within a low salinity (0.5-3.5ppt) lake over an annual cycle. We previously documented that the microbial diversity and community composition within Lake Texoma, southwest USA, were significantly affected by both seasonal forces and a site-specific bloom of the harmful alga, Prymnesium parvum. We used network analyses to answer ecological questions involving both the bacterial and microbial eukaryotic datasets and to infer ecological relationships within the microbial communities. Patterns of connectivity at both locations reflected the seasonality of the lake including a large rain disturbance in May, while a comparison of the communities between locations revealed a localized response to the algal bloom. A network built from shared nodes (microbial operational taxonomic units and environmental variables) and correlations identified conserved associations at both locations within the lake. Using network analyses, we were able to detect disturbance events, characterize the ecological extent of a harmful algal bloom, and infer ecological relationships not apparent from diversity statistics alone.

Environmental conditions increase growth rates and mortality of zebra mussels (Dreissena polymorpha) along the southern invasion front in North America

Environmental conditions found along an invasion front can mediate spread dynamics of an invasive species. Conditions that affect survival and individual growth rates of founder propagules and the first young-of-year generation can have a profound effect on establishment dynamics. Responses of younger, more sensitive individuals to these novel conditions, in part, determine establishment success. The southern invasion front of zebra mussels in North America expanded into Texas in 2009. To determine mechanisms that could affect establishment of zebra mussel populations at low latitudes in North America, an in situ study was conducted in Lake Texoma, on the Texas-Oklahoma border. Survival and growth were measured of young-of-year juveniles at multiple sites within the reservoir. Age-specific mortality was significantly positively correlated with temperature at all sites and no mortality occurred when temperatures were <26 °C. Shell-length growth rates were the highest ever reported for lentic environments. A decrease in shell-length growth rates was associated with an increase in soft tissue mass, possibly resulting from flexible energy allocation from shell development to gametogenesis after maturation. Overall, survivorship and growth were related to water temperatures and chlorophyll-a concentrations. Warm waters found at lower latitudes along the invasion front could facilitate establishment of populations by increasing growth rates and decreasing time to maturity. However, due to extreme climate events (e.g. drought and flooding) and a strong temperature-mortality relationship, mortality likely will also be high beyond the southern invasion front, resulting in highly dynamic boom and bust cycles.

Geochemistry of a large impoundment – Part II: Fe and Mn cycling and metal transport

Depletion of oxygen in lakes and reservoirs due to summer stratification has significant effects on many aspects of water chemistry, including lake productivity, elemental cycling and water quality. We have studied the redox conditions of Lake Texoma, a large impoundment lake on the border of Texas and Oklahoma, USA, formed from the confluence of the Red and Washita rivers, in order to understand the impact of summer anoxia on metal distribution. In summer, dissolved oxygen decreases with depth (from c. 7.0 to 0.1 mg/L), whereas dissolved (&lt;0.45 µm) Fe (and Fe 2+ ), Mn and HS − concentrations show complementary increases in the hypolimnion. Summer anoxia is, to a large degree, responsible for vertical variations in Fe and Mn concentrations, and Fe speciation is controlled by Fe-oxyhydroxide reduction and subsequent pyrite precipitation in sulphide-rich bottom waters. Summer anoxia is also responsible for vertical variations in the concentration of other metals including Ba, Pb and Ni in the deepest portion (main lake) of the lake. Lake Texoma and its two river arms show relatively minor variation in δ 34 S CDT (from +11.5 to +13.4‰), mirroring variation in Permian/Cretaceous marine gypsum and anhydrite deposits (δ 34 S CDT +10 to +15‰) in the headwater regions of the catchment. Increasing δ 34 S CDT with depth (&gt;16 m) in the main lake is consistent with fractionation associated with sulphate reduction in anoxic bottom waters. δ 13 C PDB values of dissolved inorganic carbon (DIC) become more negative (from –2.5 to –8.2 ‰) with depth in summer, due to bacterial oxidation of organic matter linked to sulphate reduction. Summer anoxia may induce temporal degradation of water quality in the central three zones of the lake with elevated Fe and Mn concentrations owing to breakdown of oxyhydroxides and release of adsorbed heavy metals, such as Pb and Ni. However, complete turnover of the water column in the autumn lowers dissolved Fe, Mn and heavy metal concentrations by oxidation and formation of oxyhydroxides . The characterization of anoxia in Lake Texoma provides the background for further water quality research and management for the rapidly increasing population of North Texas and improves our understanding of redox cycling and metal mobility in reservoirs.

Geochemistry of a large impoundment, Part I: solute sources, mixing dynamics, and seasonal anoxia

Lake Texoma is a large impoundment on the border of Texas and Oklahoma, formed from the confluence of two river systems with different salinities, the Red River (total dissolved salt, TDS, of 2700–11 900 mg/l, average of 4862 mg/l) and the Washita River (TDS of 420–915 mg/l, average of 701.4 mg/l). Systematic analyses for major and trace elements were conducted of water samples collected spatially and with depth in the lake in different seasons. Overall, Lake Texoma waters are characterized by Na-Ca-Cl-SO 4 -type waters with spatial distribution shifting from Na-Cl type to Ca-SO 4 type from the Red River arm to the main lake and to the Washita River arm. In addition, vertical and seasonal variations in major and trace elements concentrations indicate major elements in the lake are mainly controlled by different bedrock weathering from the two river systems. Trace elements that exhibit different distribution patterns to the major species are associated with variable sources such as river inflow, summer stratification effects, biological effects and anthropogenic activities. In Lake Texoma, differential inflow volumes and summer stratification are principal factors controlling the variation and geochemistry of lake waters and mixing dynamics. Supplementary material: Summary of major and trace element chemistry in the five zones of Lake Texoma for summer, fall and spring seasons (2003–2004) is available at http://www.geolsoc.org.uk/SUP18771

Rapid recovery of a fish assemblage following an ecosystem disruptive algal bloom

Disturbance of freshwater ecosystems through cultural eutrophication has resulted in an increased global occurrence of harmful algal blooms (HABs). Ecosystem disrupting algal blooms (EDABs) are a subset of HABs that produce extensive disturbances across entire ecosystems. Prymnesium parvum is an EDAB species that has invaded freshwater systems worldwide, causing massive fish kills and other negative effects. Fish kills frequently occur during HABs and EDABs, but few studies exist of the long-term implications of these fish kills and the resilience and recovery of fish assemblages following kills. We sampled fish near- and offshore over an annual cycle encompassing a P. parvum EDAB in 2 coves (i.e., a bloom site and a reference site) of a southern Great Plains reservoir, Lake Texoma, Oklahoma–Texas (USA). Our objective was to document the extirpation and recovery of a fish assemblage in response to the disturbance of an EDAB event. Prymnesium parvum bloomed in 1 cove from mid-December 2008 until May 2009 and eliminated all fish during this period. Fish toxicity bioassays indicated no substantial differences in susceptibility among fish species to P. parvum toxins. Fish recolonized the bloom site rapidly in May 2009 after the bloom diminished. Fish assemblages were resilient to the P. parvum EDAB, and recovered to previous abundance, richness, and composition within 6 mo. Our results suggest that the reservoir-wide fish meta-assemblage enabled a rapid recovery of local fish assemblages after a spatially heterogeneous EDAB.

Spatio-temporal spawning and larval dynamics of a zebra mussel (Dreissena polymorpha) population in a North Texas Reservoir: implications for invasions in the southern United States

long-term monitoring program were analyzed to determine if spatio-temporal zebra mussel spawning and larval dynamics were related to physicochemical water properties in Lake Texoma. Reproductive output of the local population was significantly related to water temperature and lake elevation. Estimated mean date of first spawn in Lake Texoma was approximately 1.5 months earlier and peak veliger densities were observed two months earlier than in Lake Erie. Annual maximum veliger density declined significantly during the study period (p < 0.0001). A population crash occurred as a result of thermal stress and variability of lake elevation. In summer 2011, water temperatures peaked at 34.3°C and lake elevation declined to the lowest level recorded during the previous 18 years, which resulted in desiccation of substantial numbers of settled mussels in littoral zones. Veliger spatial distributions were associated with physicochemical stratification characteristics. Veligers were observed in the deepest oxygenated water after lake stratification, which occurred in late spring. Results of this study indicate environmental conditions can influence variability of population sizes and spatial distributions of zebra mussels along the current southern frontier of their geographic range. Although the future population size trajectory and geographic range are uncertain, increased temperatures and intermittent, extreme droughts likely will affect spatio-temporal dynamics of established populations if zebra mussels spread farther into the southern and southwestern United States.

Endozoochory of seeds and invertebrates by migratory waterbirds in Oklahoma, USA

Endozoochory of seeds and invertebrates by migratory waterbirds in Oklahoma, USA Given their abundance and migratory behavior, waterbirds have major potential for dispersing plants and invertebrates within North America, yet their role as vectors remains poorly understood. We investigated the numbers and types of invertebrates and seeds within freshly collected faecal samples (n = 22) of migratory dabbling ducks and shorebirds in November 2008 in two parts of Lake Texoma in southern Oklahoma. Killdeer Charadrius vociferus were transporting a higher number and diversity of both plants and invertebrates than the green-winged teal Anas carolinensis. Ten plant taxa and six invertebrate taxa were identified to at least genus level, although viability was not confirmed for most of these taxa. Bryozoan statoblasts (from four species not previously recorded from Oklahoma) were especially abundant in killdeer faeces, while the ostracod Candona simpsoni was detected as a live adult in torpor in the teal faeces. Cyperaceae and Juncaceae were the most abundant plant families represented and Cyperus strigosus seeds germinated after extraction from killdeer faeces. This snapshot study underlines the importance of waterbirds as vectors of passive dispersal of many organisms and the need for more research in this discipline.

Seasonality and disturbance: annual pattern and response of the bacterial and microbial eukaryotic assemblages in a freshwater ecosystem

High-throughput pyrosequencing of SSU rDNA genes was used to obtain monthly snapshots of eukaryotic and bacterial diversity and community structure at two locations in Lake Texoma, a low salinity lake in the south central United States, over 1 year. The lake experienced two disturbance events (i) a localized bloom of Prymnesium parvum restricted to one of the locations that lasted from January to April, and (ii) a large (17 cm), global rain event in the beginning of May, overlaid onto seasonal environmental change. Eukaryotic species richness as well as both eukaryotic and bacterial community similarity exhibited seasonal patterns, including distinct responses to the rain event. The P. parvum bloom created a natural experiment in which to directly explore the effects of an Ecosystem Disruptive Algal Bloom (EDAB) on the microbial community separated from seasonal changes. Microbial species richness was unaffected by the bloom, however, the eukaryotic community structure (evenness) and the patterns of both eukaryotic and bacterial community similarity at bloom and non-bloom sites were statistically distinct during the 4 months of the bloom. These results indicate that physical and biological disturbances as well as seasonal environmental forces contribute to the structure of both the eukaryotic and bacterial communities.

First-Year Growth of Longnose Gar (Lepisosteus osseus) from Zygote to Autumn Juvenile

We determined total growth of an individual longnose gar, Lepisosteus osseus, from Lake Texoma, Oklahoma–Texas, from 18 May 2010 when the egg was spawned and fertilized in the reservoir, until 31 October (166 days later), when we recovered it as a juvenile from a small pond where it had been housed throughout the growing season. Total length was 261 mm, equivalent to a mean growth of 1.57 mm/day. This is the first determination of growth for this species during its first year of life, beginning with a known date of formation of the zygote in the wild.Determinamos el crecimiento total de un individuo de gaspar picudo (Lepisosteus osseus) del lago Texoma, Oklahoma-Texas, desde el 18 de mayo del 2010, cuando el huevo fue puesto y fertilizado en el embalse, hasta el 31 de octubre (166 días después), cuando lo recuperamos como juvenil en un estanque pequeño donde se lo mantuvo durante el periodo de crecimiento. La longitud total fue de 261 mm, equivalente a una tasa media de crecimiento de 1.57 mm por día. Ésta es la primera determinación del crecimiento de ésta especie en el primer año de vida, que comenzó con una fecha conocida de la formación del zigoto en el campo.

Genetic structure of a native cyprinid in a reservoir‐altered stream network

Summary1. Reservoirs modify riverine ecosystems worldwide, and often with deleterious impacts on native biota. The immediate effects of reservoirs on native fish species below dams and in impounded reaches have received considerable attention, but it is unclear how reservoirs may affect fish species at larger spatial and temporal scales. Documented declines of stream fish populations in direct tributaries of reservoirs suggest reservoir pools may reduce gene flow among historically connected populations.2. Because of increased predator densities in reservoirs and the extent of habitat alteration in impounded reaches, I predicted reservoir habitats would reduce gene flow among small‐bodied fish populations separated by reservoir habitat. I used microsatellite markers to assess the spatial genetic structure of populations of the red shiner (Cyprinella lutrensis), in a reservoir‐fragmented stream network (Lake Texoma, U.S.A.). I also tested the prediction that populations in two direct tributaries that have experienced population declines would have low genetic diversity. Individuals were collected from six sites upstream of the reservoir, three sites in the reservoir and three sites in direct tributaries of the reservoir during 2008 and 2009.3. Results indicate that most populations were isolated by distance with little divergence among populations. In one direct tributary population, however, there was substantial genetic divergence, and genetic diversity was significantly lower than in other populations. Gene flow also seemed to be lower in reservoir habitats than in intact stream habitats, suggesting reservoir habitats may be reducing gene flow among the reservoir‐separated populations. These results indicate that reservoirs may reduce gene flow among reservoir‐fragmented stream fish populations, altering the evolutionary trajectories of fragmented populations.

Interplay between river discharge and topography of the basin floor in a hyperpycnal lacustrine delta

AbstractBasin‐floor topography influences the flow path of hyperpycnal plumes and delta morphology during progradation of the Red River delta in Lake Texoma, USA. The Red River discharge is typically a hyperpycnal plume due to elevated total dissolved solids. Because the river plume is a bottom‐hugging hyperpycnal flow, lake bathymetry and topography strongly influence deposition and subsequent delta morphology. In addition to elevated total dissolved solid concentrations compared with Lake Texoma water, the density contrast of the Red River outflow is increased by high suspended‐sediment concentrations during high‐discharge events. Steep lateral slopes in the Lake Texoma basin deflect hyperpycnal river plumes and, subsequently, change the delta progradation direction before the delta reaches the opposite bank of the lake. Analysis of multi‐temporal aerial and satellite images indicates that the hyperpycnal delta follows the steepest lake‐bottom gradients, corresponding to the pre‐impoundment river thalweg (i.e. bypassing shallow parts of the lake). An analytical model for the hyperpycnal‐plume trajectory indicates plume deflection during low‐discharge or high‐discharge events, towards the deepest part of the basin. The magnitude of plume deflection is a function of river discharge and basin‐margin gradients. Plume deflection can vary between 10° and 80° from the channel axis towards the old river thalweg. The high deflection appears in the case of maximum basin side gradients of 12·8° and in conditions of low river discharge. During low‐discharge periods, the Red River delta builds a lobate shape with multiple terminal distributary channels whereas, during high‐discharge periods the Red River delta builds an elongate shape with a single large distributary channel. The elongate morphology of the delta is formed through the development of a single distributary channel and abandonment of the other distributaries. Therefore, the lobate shaped delta is expected to be preserved in the rock record.

Strontium isotope constraints on solute sources and mixing dynamics in a large impoundment, South-Central USA

Strontium concentration and isotope composition ( 87Sr/ 86Sr) are important proxies for tracing solute and suspended load origins in surface water systems, but have not been widely applied to lakes. We determined these proxies, in addition to major ion compositions, in waters collected from Lake Texoma, a large crescent-shaped (concave-west) impoundment on the border of Texas and Oklahoma that marks the downstream culmination of the Upper Red River Basin (URRB), and its major influent rivers. These rivers enter the lake at its southerly and northerly arms and have distinctly different salinities and discharges, respectively: the more saline Red River (mean total dissolved solids, TDS = 2930 mg/L; 1290 mg/L weighted for discharge, Gainesville gauging station) and the fresher Washita River (TDS = 634 mg/L; 376 mg/L weighted for discharge, Dickson gauging station). These two influent river systems combine to mix in the deepest (main) part of the lake. The URRB involves a heterogeneous mix of bedrock geologies, notably high solubility Permian marine evaporites (gypsum, halite) and carbonates, and riverine solute load and composition can vary accordingly with regional precipitation. Most river and lake waters show an strong positive correlation between 87Sr/ 86Sr and 1/Sr. Red River system waters have variable 87Sr/ 86Sr values, ranging from 0.7076 to 0.7097 (n = 34), whereas the Washita River system appears to be less isotopically variable, with 87Sr/ 86Sr values ranging from 0.7082 to 0.7087 (n = 16). Lake Texoma 87Sr/ 86Sr varies spatially between 0.7087 and 0.7092, reflecting mixing of the two input rivers. Variations in Sr isotope composition, Ca/Na and Sr/Ca of river and lake waters are consistent with the majority of the solute load being derived from dissolution of Permian marine chemical sediments, dominantly halite with lesser gypsum. Waters with Sr isotope composition more radiogenic than Permian seawater reflect the contribution of Permian and Pennsylvanian siliciclastic sediments in the case of the Red River watershed, and Precambrian granite in the Washita River watershed. In the main lake water column, Sr concentrations and filtered 87Sr/ 86Sr increase substantially with depth during summer stratification (from 0.7087 to 0.7091), likely reflecting desorption of Sr from suspended solid surfaces and breakdown of oxyhydroxides below the metalimnion. The differences in 87Sr/ 86Sr between filtered and unfiltered aliquots suggest that Sr associated with the suspended load (calcite) is either less radiogenic than the dissolved load or more radiogenic than surface waters but only released to the dissolved pool under deeper reducing conditions below the metalimnion. Either possibility has important implications for Sr cycling in binary mixing models and paleolake reconstruction from Sr isotopes.

Can a highly invasive species re-invade its native community? The paradox of the red shiner

Red shiners (Cyprinella lutrensis) are among the most widespread, ecologically general, and environmentally tolerant fish species in North America, and are highly invasive where they have been introduced outside their native range. However, long-term data on fish assemblages showed that red shiners gradually (1980s to 2006) disappeared from creeks that are direct tributaries of Lake Texoma (Oklahoma, USA) where they are native and historically had been numerically dominant. Following a major flood in 2007, red shiners were detected anew in some of these creeks, but repeatedly disappeared and re-appeared through November 2009. Given their invasive abilities where they are not native, their failure to become re-established prompted us to examine factors that affect their apparent inability to re-invade their native habitat. We established assemblages of five common fish taxa native to Brier Creek in 12 large, outdoor mesocosm stream units. Subsequently, we introduced red shiners at two densities of 10 or 30 per unit, six replicates each, to examine potential effects of propagule pressure on establishment success. Approximately six months later, we ended the experiment and recovered all fish. Red shiners failed to become established in the experimental units, regardless of initial stocking density. They also exhibited much lower survival than other species in the native community, which not only survived well but exhibited some recruitment. Red shiner survival was significantly negatively related to the number of sunfish (Lepomis spp.) that grew to adult size in experimental units, suggesting that predation can inhibit early stages of invasion by red shiners.