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The Leuciscidae (minnows, shiners and relatives) is a diverse family of freshwater fishes with many species endangered due to anthropogenic stressors. Notropis oxyrhynchus and Notropis buccula are two shiners found only in the upper Brazos River basin in Texas, USA and listed as endangered due to contracted habitat. The complete mitochondrial genome was sequenced for two vouchered specimens for each species; Notropis oxyrhynchus having a total mitogenome length of 16,711 bp and N. buccula having a total mitogenome length 16685–16686 bp, with both including 13 protein-coding genes, 22 transfer RNAs genes, and 2 ribosomal RNA genes. Phylogenetic analysis supports previous hypotheses regarding placement of these species. [ABSTRACT FROM AUTHOR]

The Leuciscidae (minnows, shiners and relatives) is a diverse family of freshwater fishes with many species endangered due to anthropogenic stressors. Notropis oxyrhynchus and Notropis buccula are two shiners found only in the upper Brazos River basin in Texas, USA and listed as endangered due to contracted habitat. The complete mitochondrial genome was sequenced for two vouchered specimens for each species; Notropis oxyrhynchus having a total mitogenome length of 16,711 bp and N. buccula having a total mitogenome length 16685–16686 bp, with both including 13 protein-coding genes, 22 transfer RNAs genes, and 2 ribosomal RNA genes. Phylogenetic analysis supports previous hypotheses regarding placement of these species.

Though bioaccumulation of pharmaceuticals by aquatic organisms continues to receive scientific attention, the internal disposition of these contaminants among different tissue compartments of fish species has been infrequently investigated, particularly among fish at different trophic positions. We tested a human to fish biological read‐across hypothesis for contaminant disposition by examining tissue‐specific accumulation in three understudied species, longnose gar (Lepisosteus osseus; piscivore), gizzard shad (Dorosoma cepedianum; planktivore/detritivore), and smallmouth buffalo (Ictiobus bubalus; benthivore), from a river influenced by municipal effluent discharge. In addition to surface water, fish plasma, and brain, gill, gonad, liver, and lateral muscle fillet tissues were analyzed via isotope dilution liquid chromatography tandem mass spectrometry. Caffeine and sucralose, two common effluent tracers, were quantitated at low micrograms per liter levels in surface water, while an anticonvulsant, carbamazepine, was observed at levels up to 37 ng/L. The selective serotonin reuptake inhibitors (SSRIs) fluoxetine and sertraline and primary metabolites were detected in at least one tissue of all three species at low micrograms per kilogram concentrations. Within each species, brain and liver of select fish contained the highest levels of SSRIs compared to plasma and other tissues, which is generally consistent with human tissue disposition patterns. However, we observed differential accumulation among specific tissue types and species. For example, mean levels of sertraline in brain and liver tissues were 13.4 µg/kg and 1.5 µg/kg in gizzard shad and 1.3 µg/kg and 7.3 µg/kg in longnose gar, respectively. In contrast, smallmouth buffalo did not consistently accumulate SSRIs to detectable levels. Tissue‐specific eco‐exposome efforts are necessary to understand mechanisms associated with such marked bioaccumulation and internal dispositional differences among freshwater fish species occupying different trophic positions. Environ Toxicol Chem 2024;43:1894–1902. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

This article focuses on developing models that estimate suspended sediment concentrations (SSCs) for the Lower Brazos River, Texas, U.S. Historical samples of SSCs from gauge stations and satellite imagery from Landsat Missions and Sentinel Mission 2 were utilized to develop models to estimate SSCs for the Lower Brazos River. The models used in this study to accomplish this goal include support vector machines (SVMs), artificial neural networks (ANNs), extreme learning machines (ELMs), and exponential relationships. In addition, flow measurements were used to develop rating curves to estimate SSCs for the Brazos River as a baseline comparison of the models that used satellite imagery to estimate SSCs. The models were evaluated using a Taylor Diagram analysis on the test data set developed for the Brazos River data. Fifteen of the models developed using satellite imagery as inputs performed with a coefficient of determination R2 above 0.69, with the three best performing models having an R2 of 0.83 to 0.85. One of the best performing models was then utilized to estimate the SSCs before, during, and after Hurricane Harvey to evaluate the impact of this storm on the sediment dynamics along the Lower Brazos River and the model's ability to estimate SSCs. [ABSTRACT FROM AUTHOR]

Freshwater invasions have occurred worldwide with significant ecological, evolutionary, and economic impacts on recipient ecosystems. Researchers now have access to a combination of approaches to better identify their potential ecological impacts on recipient communities. We used an integrative approach based on morphological traits, stomach contents, and stable isotope ratios (δ13C and δ15N) to examine multiple dimensions of the niche of native Texas cyprinodontids, Red River pupfish (Cyprinodon rubrofluviatilis) and plains killifish (Fundulus zebrinus), and their sympatric invasive congeners sheepshead minnow (C. variegates) and gulf killifish (F. grandis). We analyzed specimens from the Brazos River and Red River basins in Texas collected during multiple surveys. Because of their phylogenetic relatedness, we predicted high overlap in the feeding habits and habitat-use between native and invasive congeners. A principal component analysis performed on 24 morphological traits associated with habitat-use and feeding ecology suggested some overlap on trait space occupied by the two Cyprinodon species, but no overlap between the two Fundulus species. High overlap on dietary and isotopic niche space was observed between the native and invasive Cyprinodon congeners. There was a large degree of seasonal variation in all four species stomach contents and isotopic signatures, which could be partially explained by low sampling sizes across certain seasons. While species differed in their trait space, similarities in the feeding ecology between cyprinodontid congeners could lead to negative ecological interactions related to food resources depending on the time of year. Our findings highlight the needs for continued monitoring of invasive cyprinodontids to prevent their spread into upstream reaches of the Brazos River to ensure conservation of native congeners. [ABSTRACT FROM AUTHOR]

This article focuses on developing models that estimate suspended sediment concentrations (SSCs) for the Lower Brazos River, Texas, U.S. Historical samples of SSCs from gauge stations and satellite imagery from Landsat Missions and Sentinel Mission 2 were utilized to develop models to estimate SSCs for the Lower Brazos River. The models used in this study to accomplish this goal include support vector machines (SVMs), artificial neural networks (ANNs), extreme learning machines (ELMs), and exponential relationships. In addition, flow measurements were used to develop rating curves to estimate SSCs for the Brazos River as a baseline comparison of the models that used satellite imagery to estimate SSCs. The models were evaluated using a Taylor Diagram analysis on the test data set developed for the Brazos River data. Fifteen of the models developed using satellite imagery as inputs performed with a coefficient of determination R2 above 0.69, with the three best performing models having an R2 of 0.83 to 0.85. One of the best performing models was then utilized to estimate the SSCs before, during, and after Hurricane Harvey to evaluate the impact of this storm on the sediment dynamics along the Lower Brazos River and the model’s ability to estimate SSCs.

The Leuciscidae (minnows, shiners and relatives) is a diverse family of freshwater fishes with many species endangered due to anthropogenic stressors. Notropis oxyrhynchus and Notropis buccula are two shiners found only in the upper Brazos River basin in Texas, USA and listed as endangered due to contracted habitat. The complete mitochondrial genome was sequenced for two vouchered specimens for each species; Notropis oxyrhynchus having a total mitogenome length of 16,711 bp and N. buccula having a total mitogenome length 16685-16686 bp, with both including 13 protein-coding genes, 22 transfer RNAs genes, and 2 ribosomal RNA genes. Phylogenetic analysis supports previous hypotheses regarding placement of these species., Competing Interests: The authors have no conflict of interest to report., (© 2024 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Dajaus monticola (Bancroft, 1834) is an amphidromous species of mugilid known from South and Central America and the islands of the Caribbean but is rarely collected in Gulf coast states of the United States. Two new records of D. monticola collected from the Gulf of Mexico (Brazoria Co.) and the Brazos River (Washington Co.) are reported from Texas. The rare occurrence of D. monticola in Texas is discussed and diagnostic characters used to distinguish this species from other mugilids found in Texas are reevaluated.

The purpose of this paper was to choose an appropriate information dissimilarity measure for hierarchical clustering of daily streamflow discharge data, from twelve gauging stations on the Brazos River in Texas (USA), for the period 1989⁻2016. For that purpose, we selected and compared the average-linkage clustering hierarchical algorithm based on the compression-based dissimilarity measure (NCD), permutation distribution dissimilarity measure (PDDM), and Kolmogorov distance (KD). The algorithm was also compared with K-means clustering based on Kolmogorov complexity (KC), the highest value of Kolmogorov complexity spectrum (KCM), and the largest Lyapunov exponent (LLE). Using a dissimilarity matrix based on NCD, PDDM, and KD for daily streamflow, the agglomerative average-linkage hierarchical algorithm was applied. The key findings of this study are that: (i) The KD clustering algorithm is the most suitable among others; (ii) ANOVA analysis shows that there exist highly significant differences between mean values of four clusters, confirming that the choice of the number of clusters was suitably done; and (iii) from the clustering we found that the predictability of streamflow data of the Brazos River given by the Lyapunov time (LT), corrected for randomness by Kolmogorov time (KT) in days, lies in the interval from two to five days.

Using joint permutation entropy we address the issue of minimizing the cost of monitoring, while minimizing redundancy of the information content, of daily streamflow data recorded during the period 1989–2016 at twelve gauging stations on Brazos River, Texas, USA. While the conventional entropy measures take into account only the probability of occurrence of a given set of events, permutation entropy also takes into account local ordering of the sequential values, thus enriching the analysis. We find that the best cost efficiency is achieved by performing weekly measurements, in comparison with which daily measurements exhibit information redundancy, and monthly measurements imply information loss. We also find that the cumulative information redundancy of the twelve considered stations is over 10% for the observed period, and that the number of monitoring stations can be reduced by half bringing the cumulative redundancy level to less than 1%. [ABSTRACT FROM AUTHOR]

The tsunami generated by the Chicxulub impact eroded the uppermost Cretaceous surface of the Gulf Coast region (U.S.A.) forming a distinctive topography that was previously interpreted as a sequence boundary. At more distal sites, such as Stevns Klint (Denmark), there appears to be no sequence boundary at the Cretaceous/Paleogene boundary but there is one within the uppermost Maastrichtian, between the Sigerslev and Højerup members, and another in the lowermost Paleocene (top of Zone P1a). Both of these surfaces are identified by distinctive, phosphatized, and incipient hardgrounds. The changes in sea level involved in the generation of uppermost Cretaceous sequences are thought to have been minimal as, in the Gulpen and Maastricht formations of the Maastricht area (Netherlands), the presence of sea grasses and their associated foraminifera would indicate that the chalk sea floor remained within the range of water depth that would allow photosynthesis (< 20 m), even across the postulated sequence boundaries. The assemblages of foraminifera associated with sea grasses in the uppermost Maastrichtian are comparable in morphology with those associated with modern sea grass meadows and indicate a relationship that may have existed since, at least, the latest Cretaceous. [ABSTRACT FROM AUTHOR]

Globally, deltas are increasingly threatened by anthropogenic activities. As a result, deltas now evolve through the combined effects of natural and human-induced processes occurring throughout the fluvial–deltaic system. The Brazos River delta, located along the Texas coast in the northwestern Gulf of Mexico, and its watershed have been impacted by direct and indirect human activities since the late 19th century. This provides an opportunity to investigate how such alterations have shaped the evolution of a delta in the Anthropocene, a time when humans are drivers of geological change. Historic alteration to the delta and watershed include extensive agricultural activity, jetty construction at the mouth in the late 1890s, mouth diversion ~10 km to the southwest in 1929, and reservoir construction throughout the early and mid 20th Century. Three subaerial deltaic geometries provided the framework to connect subaerial deltaic responses, to the anthropogenic alterations, to the resulting stratigraphic characteristics observed in the subaqueous delta. This study utilized high-resolution geophysical data (swath bathymetry, side scan sonar, CHIRP subbottom profiling) on the subaqueous delta to investigate the subaqueous delta stratigraphy and infer the processes that shaped the deltaic record over time. The results showed distinct areas across the subaqueous delta that were dominated by erosion and deposition. Erosional areas corresponded to earlier growth phase depocenters being exposed at the surface, while the depositional areas corresponded to areas with the most recent growth phase depocenter overlying the earlier depocenters. These results highlight that the subaqueous depocenter has migrated westward over time, consistent with the observed changes to the subaerial delta. Additionally, the data showed that evidence for these past growth phases and depocenters may be preserved within the subaqueous delta, even after subaerial portions of the delta returned to pre-Anthropocene configurations. In general, this study showed that the subaqueous delta, similar to the subaerial delta, is impacted by human-driven alterations to the fluvial–deltaic system, and may preserve a more complete record of the evolution of deltas during the Anthropocene. [ABSTRACT FROM AUTHOR]

The Cretaceous/Paleogene (K/Pg) boundary extinction event is inextricably linked to the Chicxulub impact. Environmental changes like sea level changes and changes in food supply prior to or after the impact could however have contributed to the biotic turnover. In this study, benthic foraminifera from two cores from the Brazos River area in Texas are quantitatively analyzed in order to reconstruct environmental changes across the K/Pg boundary. Cluster analysis as well as non-metric multidimensional scaling reveals three distinct benthic foraminiferal assemblages: an upper Maastrichtian assemblage, a post-impact assemblage, and a lower Danian assemblage. The rather uniform upper Maastrichtian assemblage at Brazos River, composed of e.g. Clavulinoides midwayensis , Gavelinella dumblei , Cibicidoides harperi , Gyroidinoides aequilateralis and Bulimina kickapooensis , indicates a stable paleodepth of about 75–100 m up to the K/Pg boundary. Food supply indicators such as percentage Buliminaceae and foraminiferal numbers suggest a relatively low and stable food supply during this interval. Environmental disruption caused by the Chicxulub impact led to the settlement of a typical pioneer assemblage, characterized by endobenthic morphotypes such as Ammobaculites spp. and Pseudouvigerina naheolensis . During the early Danian, the typical Midway-type benthic foraminiferal shelf fauna (e.g. Alabamina midwayensis , Anomalinoides acutus , Gyroidinoides subangulatus , Praebulimina carseyae and Cibicidoides alleni ) developed, indicating a paleodepth of 75–100 m. No clear water depth changes can be derived from the benthic foraminiferal record during this interval, although the sedimentary record suggests a shallowing followed by a transgressive pulse in Zone P1a. Food supply indicators suggest a lower food supply in the early Danian than during the upper Maastrichtian. Because of the stability of the late Maastrichtian environment we conclude that environmental disruption caused by the impact was most likely the principal cause of the benthic foraminiferal turnover across the K/Pg boundary observed at Brazos River. [ABSTRACT FROM AUTHOR]

The Waco Mammoth Site (WMS) in central Texas contains the remains of the largest mammoth herd ( Mammuthus columbi ) in North America that died in a single catastrophic event. Most mammoths at the site died on a gravel bar of the ancient Bosque River adjacent to a collapsing tributary wall. However, the timing and cause of death of the 26 mammoths documented to date are controversial. The objectives of this research are to: describe and interpret the alluvial stratigraphy and infer the cause of death, employ optically stimulated luminescence (OSL) dating to determine the timing of death, and analyze stable C isotopes of pedogenic carbonate to infer local plant communities, dietary habits, and summer temperatures. Dating of quartz from seven sediment samples by OSL places the death event to a weighted mean of 66.8 ± 5.0 ka. The site is coeval with Marine Oxygen Isotope Stage 4, consistent with our reconstructed mean July temperatures ~ 4°C cooler than today based on a buried soil isotopic transfer function. Our buried soil isotopic interpretation of a dominance of C 3 plants is contrary to previous studies of mammoth tooth enamel at the site suggesting a dietary preference for warm season grasses (C 4 ). [ABSTRACT FROM AUTHOR]

River science and management often require a design or reference discharge. The common (and sometimes unavoidable) use of such discharges may, however, obscure the fact that the magnitude and frequency of critical flows can differ due to various hydrological, geomorphological, and ecological criteria. Threshold stages and discharges were identified for six lower Brazos River, Texas gaging stations corresponding to thalweg connectivity, bed inundation, high sub-banktop flows, channel–floodplain connectivity (CFC), and overbank flooding. Critical flows were also identified for estimated thresholds for sandy bedform and medium gravel mobility, critical specific stream power for potential channel modifications, and cohesive-bank channel erosion. These thresholds have variable relationships to mean, median, and maximum flows. For four of the six stations, daily recurrence probabilities for all but flood flows are at least 1%, and as high as 11%. All stations achieve channel–floodplain connectivity at stages less than banktop. Estimated threshold flows for sediment mobility and channel erosion occur relatively frequently, with daily probabilities of 2–77%. Critical flows for bank erosion occur least often, and for sandy bedform and gravel mobility most often. Thalweg connectivity is always maintained at all sites, while bed inundation flows have a daily probability of about 80% or more. Overall, results suggest that no single flow level is dominant in hydrological or geomorphic dynamics, and that the frequency of a given threshold varies considerably even along a single river. The results support the idea that multiple flow levels and ranges are necessary to create and maintain the hydrological, geomorphological, and ecological characteristics of rivers, and that no single flow level is a reliable determinant of fluvial state.Editor Z.W. Kundzewicz; Associate editor Q. Zhang [ABSTRACT FROM AUTHOR]

Genetic variation was evaluated for spotted bass ( Micropterus punctulatus) at the edge of the species native range in central Texas. We analyzed mitochondrial D-Loop sequences from 64 individuals representing nine sites within the Brazos and Trinity River watersheds. Our primary objectives were to 1) compare the genetic diversity of spotted bass in central Texas to genetic diversity estimates of conspecifics in other geographic regions and to other species from similar geographic regions, to 2) determine whether there was evidence for within or between drainage genetic structure, and to 3) test whether the D-Loop sequence was a reliable marker for discriminating among native and introduced Texas micropterids. Genetic diversity was low relative to sympatric micropterids, as well as for the marker in general, but our results are similar to patterns observed for this species in Oklahoma and fit with broader multi-species patterns observed for this geographic area. AMOVA, SAMOVA, and isolation by distance analyses provided evidence that genetic differentiation exists among population groups. The sequence data suggests the D-Loop would be useful for discriminating among M. floridanus, M. salmoides, and M. dolomieu, but not among M. punctulatus, M. coosae, M. henshalli, and M. treculii. [ABSTRACT FROM AUTHOR]

The Brazos River is second only to the Mississippi River in terms of sediment load discharged to the Gulf of Mexico (GOM). This study focused on the interaction between a salt wedge and suspended sediment in the lower Brazos River, and the implications for sediment export to the coastal ocean. Salinity and turbidity (optical backscatter sensor) data with depth, swath bathymetry, and CHIRP sub-bottom profiling data were collected from 2007 to 2012 over various river discharge stages. Sampling locations included the lower-most 15 km river reach and the coastal ocean proximal to the mouth. Results indicated that during low to moderate river discharges a salt wedge was present in the lower river, but absent during elevated fluvial discharge. Quantitative analysis showed the salt wedge within the river modulated sediment export to the GOM by trapping sediment along the lower most 9 km reach. Within this reach the trapped sediment formed a decimeter-thick mud layer observed in the CHIRP and bathymetric data. At elevated fluvial discharges the salt wedge was no longer observed in the river, and the lower river reach transitioned from depositional to erosional. Based on the observations and analysis from this study, a fluvial discharge threshold where the salt wedge is not present in the river and sediment export to the coastal ocean was maximized was estimated. This threshold has been met or exceeded only ~ 10% of time since the 1960s. These conditions imply that sediment transport to the coastal ocean is highly variable, and occurs during irregular, pulsed events. This study highlights how estuarine conditions at the river mouth can impact terrestrial material flux to the coastal ocean. [ABSTRACT FROM AUTHOR]

Abstract: Historical channel adjustments are documented and discussed in context with anthropogenic disturbances along two meandering, coastal plain rivers — the lower Brazos and Sabine Rivers in the south-central United States. Hard-copy streamflow-measurement notes of the U.S. Geological Survey were utilized to render historical cross sections (1925–2007) at nine gauging stations, which were complemented with repeat photographs and flood-frequency analysis to assess trajectories of channel change and interpret causative mechanisms. Downstream- and upstream-propagating disturbances caused episodes of channel-bed incision and aggradation at different locations for distinct time periods along both rivers. Incision associated with upstream dams is detected, but channels are compensated downstream with sediment inputs from lateral channel migration and tributaries. In one case, temporary aggradation along the Brazos River at Waco was likely caused by a combination of dam construction and regional soil erosion. Channel-bed incision on the lowermost Brazos River is unrelated to dams, but is associated with instream aggregate extraction, possibly in conjunction with downstream channelization. On the Sabine River, extensive aggradation during the 1930s might be associated with logging activities (1880s–1930s), but whether the cause is pervasive regional-scale hillslope erosion or local-scale mill-site activities is indeterminate. Following passage of this sediment, the river generally recovered to pre-disturbance conditions and has exhibited stability despite a mainstem reservoir. Translation of this sediment slug is attenuated by a transition to a flood-prone, distributary-dominated system downstream of the Holocene–Pleistocene terrace onlap position. Additional findings include cross-channel hingepoints separating thalweg incision from simultaneous point-bar or bank accretion at meander bends, which indicates channel adjustment occurs along non-cohesive beds in preference to cohesive or artificially reinforced banks. Also, flood reduction has resulted in bankfull stages that are higher than levels associated with the post-regulation 2-year return period. Finally, vegetation encroachment along banks since the 1970s coupled with reduced flooding along the lower Brazos River has promoted bank accretion deposits that, when fully developed, serve as morphologic indicators of the post-regulation 1- to 2-year return period stage. [Copyright &y& Elsevier]

Habitat associations of sharpnose shiner (Notropis oxyrhynchus) in the upper Brazos River, USA, were studied over a two-year period. We used generalized linear models with a logit link to assess the influence of individual physical and chemical habitat variables on the presence of sharpnose shiner at the microhabitat scale. Our models indicated that depth was the only habitat variable that significantly predicted sharpnose shiner presence during the first year of the study and that current velocity was the only variable that significantly predicted sharpnose shiner presence during the second year. Monthly plots of fitted regression estimates superimposed over frequency distributions for both significant variables revealed a distinct pattern of habitat use related to habitat availability. When only a narrow range of depths and current velocities was available, sharpnose shiner occurred more frequently in deeper and swifter microhabitats. In contrast, during periods with the greatest depths and current velocities, sharpnose shiner presence decreased with increasing depth and current velocity. Our results suggest that sharpnose shiner in the Brazos River exhibits habitat preferences but these preferences are conditional, based on the range of habitats available on a given date. [ABSTRACT FROM PUBLISHER]

We used logistic regression to model the persistence of two imperiled pelagic-spawn-ing cyprinids, sharpnose shiner Notropis oxyrhynchus and smalleye shiner N. buccula, endemic to the Brazos and Wichita Rivers, Texas, USA. There was a significant posi-tive relationship between persistence and river fragment length. Mean length of river fragments in which sharpnose shiner or smalleye shiner still occur was significantly greater (599 ± 27 km) than the mean length of fragments from which these species were absent (187 ± 20 km). Persistence of both species appears to depend on the pres-ence of river fragments long enough to allow spawned ova and swim-up fry time to de-velop and move out of the current into the backwater areas. [ABSTRACT FROM AUTHOR]

Instream-flow scientists embrace streamflow as the master variable driving aquatic and riparian ecosystems, and that natural flow variability is imperative for river conservation and restoration efforts. Sediment transport, which is critical for maintenance of physical habitats in rivers and floodplains, has received less direct attention from instream-flow practitioners. This article serves to highlight the roles of sediment-transport evaluations in modifying or verifying instream-flow prescriptions based on hydrology alone. Two examples of sediment-transport evaluations are discussed in relation to the Texas Senate Bill 3 Environmental Flows allocation process, a mandate to “develop environmental flow analyses and a recommended flow regime” that “maintain(s) the viability of the state's streams, rivers, and bay and estuary systems” using “reasonably available science”. The first example provides an evaluation of effective discharge of suspended-sediment load of the lower Brazos River. The magnitude and frequency of effective discharge occurs between typical high-flow pulses and overbank flows, indicating that hydrologic and physical processes are not optimally coupled in some flow-regime models. The second example utilizes the Hydrology-Based Environmental Flow Regime (HEFR) model to prescribe instream flows for the lower Sabine River, and compares modeled bed-material loads for observed and HEFR-prescribed flow regimes. Results indicate that annual water and sediment yields are greatly reduced for the modeled flow regime. It should be noted, however, that different input variables to the HEFR model would have resulted in different computations of water and sediment yields, reinforcing that instream-flow practitioners should exercise great caution when applying rule-of-thumb procedures to generate flow prescriptions. [ABSTRACT FROM AUTHOR]

Concentrations of several solutes - nitrate, arsenic, sulfate, boron, chloride, and bromide - along with total dissolved solids (TDS) in ten counties bordering the Brazos River in east-central Texas were compiled, mapped, and analyzed relative to regional land use and geology. Agriculture and oil/gas production are major activities and potential sources of groundwater contamination in the study area. Data were compiled from 104 water wells with a median depth of 446 ft (136 m) in the outcrop zones of six sedimentary aquifers: Carizzo-Wilcox, Queen City, Sparta, Yegua-Jackson, Gulf Coast, and Brazos Alluvium. Only two observations surpassed the 44.3 mg/L drinking water standard for nitrate, and four observations exceeded the 10 ug/L standard for arsenic. The median chloride concentration was 53 mg/L; however, the maximum level was almost three times the secondary drinking water standard of 250 mg/L. Chloride, bromide, sulfate, and boron concentrations resembled TDS patterns, with numerous samples exceeding secondary TDS drinking water standards in the Yegua-Jackson Aquifer. Most chloride/bromide ratios were between 100 and 300. Overall, results of this study suggest that natural processes exert a primary control on solute concentrations in the above aquifers, with a potential for modest anthropogenic impacts from agriculture and oil/gas production. [ABSTRACT FROM AUTHOR]

The Brazos River, the second largest basin in Texas, represents one of the most highly developed river systems in the state. Thirty-nine reservoirs with capacities greater than 5,000 acre-feet are currently in operation in the basin. Impacts on stream ecosystems are evidenced by changes in flow regimes and resulting changes in fish assemblages over the past 50 years. These changes have been widely attributed to human impacts, through the construction of dams, diversion of water supplies for agricultural and municipal uses, and land use change. However, streamflow regimes result from a complex mix of drivers that include climate, topography, land cover, land use practices, reservoir management practices, dam releases, and water consumption patterns, making determination of anthropogenic impacts problematic. This study quantifies changes in flow regime and probable historical drivers including precipitation, dam construction, population growth, and changing water demand in the Brazos River basin over the past 100 years. Results indicate that the climate of the basin has been relatively stable over the study period, while large-scale changes in human population densities and intense water resources development are correlated with impacts on flow regimes, decreasing the frequency and magnitude of high flow events and stabilizing low flows. These changes have resulted in an increase of habitat generalist fish species, a decrease of native obligate riverine fishes, and an overall homogenization of species assemblages. The results of this study indicate the importance of combining ecological data with an assessment of social drivers for a greater understanding of the dynamics of river basin systems. [ABSTRACT FROM AUTHOR]

Floodplain habitats have been inferred to provide a variety of functions for aquatic organisms, yet few studies have documented movement between channel and aquatic floodplain habitats. We exploited spatial variation in stable isotope ratios of gizzard shad ( Dorosoma cepedianum) to document movement between floodplain lakes and the main river channel of the Brazos River, Texas, during a period of frequent hydrologic connectivity. Additionally, we examined stomach contents of shad to determine if ontogenetic diet shifts or faunal exchange best explained variation in isotopic ratios. Regression analysis indicated significant relationships between gizzard shad size and isotopic ratios in oxbow lakes, whereas these relationships were not significant for the main channel. Plots of individual fish in each habitat suggested that adult shad migrated into oxbow lakes during floods whereas juveniles assimilated material produced in oxbows. Some adults in oxbows had signatures similar to juveniles, and these individuals were probably long-term oxbow residents. The proportion of adults with a “river” signature was greater in the oxbow with the shortest flood recurrence interval where opportunities for faunal exchange were more frequent. Analysis of stomach contents indicated almost total overlap between adult and juvenile diets indicating that movement between habitats having different isotopic ratios of basal resources rather than ontogenetic dietary shifts best explained patterns of isotopic variation in Brazos River gizzard shad. [ABSTRACT FROM AUTHOR]

Algal carbon has been increasingly recognized as the primary carbon source supporting large-river food webs; however, many of the studies that support this contention have focused on lotic main channels during low-flow periods. The flow variability and habitat- heterogeneity characteristic of these systems has the potential to significantly influence food web structure and must be integrated into models of large-river webs. We used stable-isotope analysis and IsoSource software to model terrestrial and algal sources of organic carbon supporting consumer taxa in the main channel and oxbow lakes of the Brazos River, Texas, USA, during a period of frequent hydrologic connectivity between these habitat types. Standardized sampling was conducted monthly to collect production sources and consumer species used in isotopic analysis. Predictability of hydrologic connections between habitat types was based on the previous 30 years of flow data. IsoSource mixing models identified terrestrial C3 macrophytes (riparian origin) as the primary carbon source supporting virtually all consumers in the main channel and most consumers in oxbow lakes. Small-bodied consumers (<100 mm) in oxbow lakes assimilated large fractions of algal carbon whereas this pattern was not apparent in the main channel. Estimates of detritivore trophic positions based on δ15N values indicated that terrestrial material was likely assimilated via invertebrates rather than directly from detritus. High flows in the river channel influenced algal standing stock, and differences in the importance of terrestrial and algal production sources among consumers in channel vs. oxbow habitats were associated with patterns of flooding. The importance of terrestrial material contradicts the findings of recent studies of large-river food webs that have emphasized the importance of algal carbon and indicates that there can be significant spatial, temporal, and taxonomic variation in carbon sources supporting consumers in large rivers. [ABSTRACT FROM AUTHOR]

Abstract: The “perfect landscape” concept is based on the notion that any specific geomorphic system represents the combined, interacting effects of a set of generally applicable global laws and a set of geographically and historically contingent local controls. Because the joint probability of any specific combination of local and global controls is low, and the local controls are inherently idiosyncratic, the probability of existence of any given landscape is vanishingly small. A perfect landscape approach to geomorphic complexity views landscapes as circumstantial, contingent outcomes of deterministic laws operating in a specific environmental and historical context. Thus, explaining evolution of complex landscapes requires the integration of global and local approaches. Because perfection in this sense is the most important and pervasive form of complexity, the study of geomorphic complexity is not restricted to nonlinear dynamics, self-organization, or any other aspects of complexity theory. Beyond what can be achieved via complexity theory, the details of historical and geographic contexts must be addressed. One way to approach this is via synoptic analyses, where the relevant global laws are applied in specific situational contexts. A study of non-acute tributary junctions in the lower Brazos River, Texas illustrates this strategy. The application of generalizations about tributary junction angles, and of relevant theories, does not explain the unexpectedly high occurrence or the specific instances of barbed or straight junctions in the study area. At least five different causes for the development of straight or obtuse junction angles are evident in the lower Brazos. The dominant mechanism, however, is associated with river bank erosion and lateral channel migration which encroaches on upstream-oriented reaches of meandering tributaries. Because the tributaries are generally strongly incised in response to Holocene incision of the Brazos, the junctions are not readily reoriented to the expected acute angle. The findings are interpreted in the context of nonlinear divergent evolution, geographical and historical contingency, synoptic frameworks for generalizing results, and applicability of the dominant processes concept in geomorphology. [Copyright &y& Elsevier]

Abstract: A shallow coring and geophysical logging program has recorded the sedimentary fill of the Brazos River valley in the Texas Gulf Coastal Plain. Thermoluminescence dates together with new and recalibrated published radiocarbon dates show the valley fill to include extensive, sandy, buried falling stage and lowstand Oxygen Isotope Stage (OIS) 3 and 2 deposits. These alluvial deposits are punctuated by numerous paleosoil horizons that record alternating periods of cutting, bypass and accumulation. Maximum valley incision and two periods of terrace formation preceded marine lowstand conditions, suggesting significant discordance between preserved fluvial and classical marine system tracts. The latest Pleistocene incision and fill history appears related to cycles of increased discharge and incision, followed by system equilibration and terrace formation. Analysis of the Brazos River incised valley and its contained paleochannels indicates that latest Pleistocene mean annual discharge was as much as four times greater than that of today. This magnitude of discharge in the Brazos would require a two-fold increase in precipitation across the drainage basin. Such an increase is comparable to the present day measured positive El Niño winter precipitation anomaly across the region. Paleochannel geometries and the stratigraphic and sedimentologic data from this investigation support the hypothesis that periods of high-amplitude, El Niño-like climatic perturbations characterized the late Quaternary climate of the south-central and southwestern U.S. This period of high discharge coincides, at least in part, with late OIS 3 progradation of the Brazos delta to the shelf margin, OIS 3 and 2 valley incision across the Texas shelf, and concomitant sand bypass to intraslope basins beyond the shelf edge. [Copyright &y& Elsevier]

Extreme episodic events have the capacity to transport large amounts of terrestrial material to the coastal ocean. While estuaries and deltas are typically thought to trap most of this material, some escapes these coastal features and is transported to distal depocenters along the continental shelf. Distal shelf depocenters can act as the ultimate sink for event deposits, yet event sedimentation and the impact of terrestrial carbon burial within these shelf deposits remains understudied. Therefore, this study investigated event sedimentation within the Texas Mud Blanket (TMB), a distal shelf depocenter of the Brazos River located in the northwestern Gulf of Mexico. Using a core that was collected from the TMB during a months-long elevated discharge event in late 2015 to early 2016 we applied a multi-proxy approach to delineate the event deposit. We utilized physical sediment properties (fabric, texture, and bulk density), radioisotopes (7Be and 210Pb), and organic geochemical properties (ẟ13C, C/N, and lignin-phenols) to identify a 10 cm event layer at the surface of the core. Within this 10 cm layer, we also distinguished two sub-layers associated with separate extreme discharge periods in the winter and spring, respectively. Using these event layer characteristics, we identified three other earlier potential event deposits in the core that we have attributed to events in 2010, 2007, and 2000–2001. From these results, this study has demonstrated that the TMB may be an archive for event deposits over multi-decadal time periods, in particular the transition from periods of prolonged drought to extreme wetness associated with the Brazos River. This event-dominated sedimentation regime can enhance long-term carbon burial, potentially increasing current estimates of carbon burial significantly in the TMB and other similar distal shelf depocenters. Ultimately this study highlights the potential for distal shelf depocenters as organic carbon burial "hotspots," and postulates that this role may expand in the future as climate change increases the intensity and frequency of extreme events. • Delineated and characterized a recent flood deposit in continental shelf sediments. • Identified older preserved flood deposits associated with drought to flood cycles. • Utilized sediment and organic geochemical characteristics to identify event layers. • Demonstrated that mid-shelf depocenters may be a location for organic carbon burial. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to choose an appropriate information dissimilarity measure for hierarchical clustering of daily streamflow discharge data, from twelve gauging stations on the Brazos River in Texas (USA), for the period 1989-2016. For that purpose, we selected and compared the average-linkage clustering hierarchical algorithm based on the compression-based dissimilarity measure (NCD), permutation distribution dissimilarity measure (PDDM), and Kolmogorov distance (KD). The algorithm was also compared with K-means clustering based on Kolmogorov complexity (KC), the highest value of Kolmogorov complexity spectrum (KCM), and the largest Lyapunov exponent (LLE). Using a dissimilarity matrix based on NCD, PDDM, and KD for daily streamflow, the agglomerative average-linkage hierarchical algorithm was applied. The key findings of this study are that: (i) The KD clustering algorithm is the most suitable among others; (ii) ANOVA analysis shows that there exist highly significant differences between mean values of four clusters, confirming that the choice of the number of clusters was suitably done; and (iii) from the clustering we found that the predictability of streamflow data of the Brazos River given by the Lyapunov time (LT), corrected for randomness by Kolmogorov time (KT) in days, lies in the interval from two to five days.