Downstream trends of alluvial sediment composition and channel adjustment in the Llano River watershed, Central Texas, USA : the roles of a highly variable flow regime and a complex lithology

textThis study investigates the downstream controls of alluvial sediment composition and river channel adjustment in the Llano River watershed, Central Texas, USA. The Llano River watershed is characterized by a highly variable, flood-prone flow regime and a complex lithology of Cretaceous carbonate rock, Paleozoic sedimentary rock, and Precambrian igneous and metamorphic rock. Sedimentary variables for this study include particle size, sorting, carbonate content, and magnetic susceptibility. Channel adjustment includes the planform dimension and cross-sectional dimensions of bankfull- and macro-channels. Nineteen sites along the Llano River and selected tributaries were visited to measure cross-sectional channel geometry and sample bed, bank, and overbank sediment. Laboratory analyses of sediment and hydraulic analyses of cross sections were accompanied by analyses of partial-duration flood frequency, flow resistance, hydrography, digital elevation models, and statistical correlation. Findings include: (1) channel-bed material reduces in size with downstream distance, despite increasing valley confinement and bedrock exposure; (2) the downstream decrease in particle size is more evident for channel-bar deposits than for low-flow-channel (thalweg) deposits; (3) an abrupt gravel-to-sand transition occurs about 20 kilometers downstream of the Paleozoic-Precambrian contact; (4) an abrupt coarse- to fine-gravel transition occurs between 75 and 90 kilometers downstream the North Llano and South Llano Rivers; (5) channel-bank material increases downstream, contrasting with decreases in bed material; (6) carbonate content and magnetic susceptibility of alluvial sediment are inversely related, with carbonate content peaking near Junction; (7) four general categories to classify reaches of the North Llano, South Llano, and Llano Rivers are based on hydrology, planform morphology, lithology, and valley confinement; (8) mean depth increasingly compensates for bankfull discharge in a downstream direction; (9) mean depth compensates more than width for macrochannels; and (10) the return periods for bankfull and macro-channels are about 1 to 2 years and greater than 10 years, respectively. The results of this study will contribute to fluvial geomorphic theory of downstream trends in sediment composition and channel adjustment; as well as inform applied efforts related to aquatic biology, flood hazards, infrastructure design, and riparian and water-resource management in the region.Geography and the Environmen

Acute and Chronic Toxicity of Selenium to Estuarine Organisms

Acute toxicity tests were conducted with selenium and five estuarine organIsms, and chronic or early life stage tests were conducted with mysid shrimp (Mysidopsis bahia) and sheepshead minnows (Cyprlnodon varlegatus). The concentrations of selenium lethal to 50% of the test animals after 96 hours of exposure (96-hour LC50\u27s) ranged from 1.2 mg/l for brown shrimp (Penaeus aztecus) to 7.4 mg/l for sheepshead mlnnows. The maximum acceptable toxicant concentration (MATC) was \u3e 0.14 \u3c 0.32 mg/l for mysid shrimp and \u3e 0.47 \u3c 0.97 mg/l for sheepshead minnows. The application factor limits for mysid shrimp and sheepshead minnows were 0.09-0.21 and 0.06-0.13, respectively

Reducing uncertainty with flood frequency analysis: the contribution of palaeoflood and historical flood information

Using a combination of stream gauge, historical, and paleoflood records to extend extreme flood records has proven to be useful in improving flood frequency analysis (FFA). The approach has typically been applied in localities with long historical records and/or suitable river settings for paleoflood reconstruction from slack‐water deposits (SWDs). However, many regions around the world have neither extensive historical information nor bedrock gorges suitable for SWDs preservation and paleoflood reconstruction. This study from subtropical Australia demonstrates that confined, semialluvial channels such as macrochannels provide relatively stable boundaries over the 1000–2000 year time period and the preserved SWDs enabled paleoflood reconstruction and their incorporation into FFA. FFA for three sites in subtropical Australia with the integration of historical and paleoflood data using Bayesian Inference methods showed a significant reduction in uncertainty associated with the estimated discharge of a flood quantile. Uncertainty associated with estimated discharge for the 1% Annual Exceedance Probability (AEP) flood is reduced by more than 50%. In addition, sensitivity analysis of possible within‐channel boundary changes shows that FFA is not significantly affected by any associated changes in channel capacity. Therefore, a greater range of channel types may be used for reliable paleoflood reconstruction by evaluating the stability of inset alluvial units, thereby increasing the quantity of temporal data available for FFA. The reduction in uncertainty, particularly in the prediction of the ≤1% AEP design flood, will improve flood risk planning and management in regions with limited temporal flood data

Ecosystem development after mangrove wetland creation : plant–soil change across a 20-year chronosequence

This paper is not subject to U.S. copyright. The definitive version was published in Ecosystems 15 (2012): 848-866, doi:10.1007/s10021-012-9551-1.Mangrove wetland restoration and creation efforts are increasingly proposed as mechanisms to compensate for mangrove wetland losses. However, ecosystem development and functional equivalence in restored and created mangrove wetlands are poorly understood. We compared a 20-year chronosequence of created tidal wetland sites in Tampa Bay, Florida (USA) to natural reference mangrove wetlands. Across the chronosequence, our sites represent the succession from salt marsh to mangrove forest communities. Our results identify important soil and plant structural differences between the created and natural reference wetland sites; however, they also depict a positive developmental trajectory for the created wetland sites that reflects tightly coupled plant-soil development. Because upland soils and/or dredge spoils were used to create the new mangrove habitats, the soils at younger created sites and at lower depths (10–30 cm) had higher bulk densities, higher sand content, lower soil organic matter (SOM), lower total carbon (TC), and lower total nitrogen (TN) than did natural reference wetland soils. However, in the upper soil layer (0–10 cm), SOM, TC, and TN increased with created wetland site age simultaneously with mangrove forest growth. The rate of created wetland soil C accumulation was comparable to literature values for natural mangrove wetlands. Notably, the time to equivalence for the upper soil layer of created mangrove wetlands appears to be faster than for many other wetland ecosystem types. Collectively, our findings characterize the rate and trajectory of above- and below-ground changes associated with ecosystem development in created mangrove wetlands; this is valuable information for environmental managers planning to sustain existing mangrove wetlands or mitigate for mangrove wetland losses

Gender differences in the use of cardiovascular interventions in HIV-positive persons; the D:A:D Study

Peer reviewe

Development and Validation of a Risk Score for Chronic Kidney Disease in HIV Infection Using Prospective Cohort Data from the D:A:D Study

Ristola M. on työryhmien DAD Study Grp ; Royal Free Hosp Clin Cohort ; INSIGHT Study Grp ; SMART Study Grp ; ESPRIT Study Grp jäsen.Background Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice. Methods and Findings A total of 17,954 HIV-positive individuals from the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study with >= 3 estimated glomerular filtration rate (eGFR) values after 1 January 2004 were included. Baseline was defined as the first eGFR > 60 ml/min/1.73 m2 after 1 January 2004; individuals with exposure to tenofovir, atazanavir, atazanavir/ritonavir, lopinavir/ritonavir, other boosted protease inhibitors before baseline were excluded. CKD was defined as confirmed (>3 mo apart) eGFR In the D:A:D study, 641 individuals developed CKD during 103,185 person-years of follow-up (PYFU; incidence 6.2/1,000 PYFU, 95% CI 5.7-6.7; median follow-up 6.1 y, range 0.3-9.1 y). Older age, intravenous drug use, hepatitis C coinfection, lower baseline eGFR, female gender, lower CD4 count nadir, hypertension, diabetes, and cardiovascular disease (CVD) predicted CKD. The adjusted incidence rate ratios of these nine categorical variables were scaled and summed to create the risk score. The median risk score at baseline was -2 (interquartile range -4 to 2). There was a 1: 393 chance of developing CKD in the next 5 y in the low risk group (risk score = 5, 505 events), respectively. Number needed to harm (NNTH) at 5 y when starting unboosted atazanavir or lopinavir/ritonavir among those with a low risk score was 1,702 (95% CI 1,166-3,367); NNTH was 202 (95% CI 159-278) and 21 (95% CI 19-23), respectively, for those with a medium and high risk score. NNTH was 739 (95% CI 506-1462), 88 (95% CI 69-121), and 9 (95% CI 8-10) for those with a low, medium, and high risk score, respectively, starting tenofovir, atazanavir/ritonavir, or another boosted protease inhibitor. The Royal Free Hospital Clinic Cohort included 2,548 individuals, of whom 94 individuals developed CKD (3.7%) during 18,376 PYFU (median follow-up 7.4 y, range 0.3-12.7 y). Of 2,013 individuals included from the SMART/ESPRIT control arms, 32 individuals developed CKD (1.6%) during 8,452 PYFU (median follow-up 4.1 y, range 0.6-8.1 y). External validation showed that the risk score predicted well in these cohorts. Limitations of this study included limited data on race and no information on proteinuria. Conclusions Both traditional and HIV-related risk factors were predictive of CKD. These factors were used to develop a risk score for CKD in HIV infection, externally validated, that has direct clinical relevance for patients and clinicians to weigh the benefits of certain antiretrovirals against the risk of CKD and to identify those at greatest risk of CKD.Peer reviewe

Magnitude and Frequency Relations of Bankfull Flows and Bed-Material Entrainment in the Llano River Watershed, Central Texas, USA

Bankfull channel geometry and bed-material entrainment are examined in the Llano River watershed in central Texas, which is characterized by mixed alluvial-bedrock boundaries and a highly variable flow regime. Field data, including cross-section surveys and sediment samples from 17 sites, are coupled with one-dimensional hydraulic models and flood-frequency analyses to compute recurrence intervals of bankfull and entrainment conditions. Recurrence intervals of flows that entrain median-sized bed material (d 50) are consistently less than 1 year, whereas flows that define bankfull morphology range from one to four years (median of 1.75 years). Recurrence intervals of flows responsible for incipient entrainment of relatively coarse bed material (d 84) are typically less than 1.5 years, but complete mobilization of this size fraction occurs less frequently than bankfull flows. At multiple sites, morphologic surfaces defining bankfull stage are discontinuous and set within a macro-channel, which is formed by high-magnitude flows with recurrence intervals greater than five years. Finally, the frequency of bankfull flow in the lowermost, confined, sandbar-dominated channels is similar to the frequency of the mobilization of relatively coarse low-flow channel gravels; but discontinuous, sandy bank deposits indicate that sediment exchange with channel bars is the most important process for development of bankfull indicators

Channel Adjustments to Historical Disturbances Along the Lower Brazos and Sabine Rivers, South-Central USA

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. (C) 2013 Elsevier B.V. All rights reserved

Characteristics of Fluvial Bed Material In and Adjacent to Instream Aggregate Extraction Pits Along the Bouie River in Hattiesburg, Mississippi

A characterization of channel-bed and bottom sediments adjacent to and along a 3.6 mi (5.8 km) reach of inundated aggregate extraction pits along the Bouie River in Hattiesburg, Mississippi, was made to infer compositional differences upstream and downstream of the disturbed reach. Sedimentary data reveal the following: (i) organic carbon content of fine-grained pit bottom sediments systematically increases with depth and, thus, exhibits an inverse relationship with particle size; (ii) maximum organic carbon content of pit bottom sediments approaches 6.0%; (iii) particle size distributions of gravel and sand channel-bed deposits upstream and downstream of the extraction pit reach are quite similar, with median values mostly ranging from 10 to 20 mm for gravelly sites and 0.38 to 0.40 mm for sandy sites; (iv) pit bottom sediments display a general downstream-fining sequence from medium to coarse sands near channel inflows to fine-grained muds near pit outflows; and (v) variability in particle-size trends of pit bottom sediments is attributed to a subaqueous delta slope and relatively narrow zones that exhibit greater flow velocities during infrequent floods. The results indicate that well-documented channel changes downstream of the extraction pit reach are not necessarily contingent on changes to bed material composition, but are attributed to the overall decrease in sediment load. Furthermore, downstream sediment loads will not be fully restored to pre-disturbance conditions until the extraction pits are completely infilled with basal muds, overlying delta slope sands, and sand and gravel channel bars