Benthic metabolism and nutrient dynamics of a hyperturbid and hypernutrified estuary

The biogeochemical role of the sediments in the Guadalquivir River estuary, a vital region in the SW Iberian Peninsula, has been considerably neglected. The benthic microalgae (microphytobenthos, MPB) inhabiting the sediment surface could contribute to the autochthonous primary production and influence nutrient recycling in this hyper-turbid and hypernutrified estuary. Sediment–water column fluxes of O2 and dissolved inorganic nitrogen species (DIN = NH4+ + NO3− + NO2−) were assessed in laboratory incubations of sediment cores from Bonanza (mouth) and Lebrija (middle) during a 1-year study. Vertical profiles down to the 10-cm depth of photosynthetic pigments, organic C, total nitrogen, DIN, Fe2+, SO42−, and dissolved inorganic carbon (DIC) were also measured. Chlorophyll a in the sediment surface was higher at the estuarine mouth, exhibiting a seasonal pattern at both sites with highest values in winter and lowest in summer. Net community production (NCP) was higher in Bonanza compared with Lebrija and showed positive values most of the year, indicating that MPB contributed to the overall autochthonous primary production of the estuary. Seasonal changes in chlorophyll a and NCP were not parallel, suggesting different ecological controls. The sediment was generally a net sink of NO3− and NH4+ in both sites, with several fold higher rates for NO3− uptake. MPB N demand could account for the entire sediment DIN uptake in Bonanza and 21% in Lebrija. The remaining high NO3− uptake rates indicate that they sustain elevated sediment denitrification rates. In contrast, rates of anaerobic oxidation of organic matter by Fe reduction and SO42− reduction, estimated from Fe2+ and SO42− vertical concentration profiles, were several orders of magnitude lower than the estimated water column-dependent denitrification rates. Overall, this study shows the importance of MPB in the Guadalquivir Estuary and the potential dominant role of denitrification in the anaerobic mineralization of organic matter

Experimental determination of pyrite and molybdenite oxidation kinetics at nanomolar oxygen concentrations

Constraining the rate at which sulfide minerals undergo oxidative weathering at low atmospheric O2 is crucial for understanding the evolution of the Archean and Proterozoic biosphere when O2 was a trace atmospheric gas. However, recent studies attempting to constrain sulfide oxidation rates, atmospheric O2 sinks, and trace metal delivery to seawater under Archean conditions are limited by the need to extrapolate from experimental pyrite oxidation kinetics determined at much higher O2 levels. Extrapolation of those data sets to Archean levels of O2 (&lt;10−5 present atmospheric level or PAL prior to 2.4 Ga) leads to more than an order of magnitude uncertainty in sulfide mineral oxidation rates, hampering efforts to quantify oxidative weathering under early Earth conditions. To quantify sulfide oxidation kinetics at low pO2, we conducted aqueous pyrite and molybdenite oxidation experiments at ∼2–1200 nM dissolved O2 and pH values 1.83, 5.08, and 8.58. Our experimental approach used LUMOS O2 sensors to extend the pO2 range explored by oxidation experiments down to 10−5 PAL pO2, the limit of the sensors, which is up to three orders of magnitude lower than the pO2 range explored in previous work. From these experiments, we use 28 independent rate measurements to derive a new rate law for the oxidation of pyrite as a function of pO2: rpyrite=10-8.83(±0.27)O2 0.50±0.04H+ -0.25±0.02, Where rpyrite is the rate of oxidation in mol/m2 sec, and the activities of dissolved [O2] and [H+] are in (mol/L). Our results most closely match the previous rate law presented by Williamson and Rimstidt (1994), but indicate a stronger pH dependence than previous studies. We also present the first kinetic rate law for molybdenite oxidation at low O2, based on 13 independent rate measurements: rmolybdenite=10-8.3(±2.3)O2 0.5±0.3, Where rmolybdenite is the rate of oxidation in mol/m2 sec, and the activity of dissolved [O2] is in (mol/L). We find molybdenite oxidation to be nearly as rapid as pyrite oxidation even at low concentrations of dissolved O2 (equivalent to &lt;10−5 PAL pO2), in contrast to previous work which argued for a threshold effect for molybdenite oxidation. Both pyrite and molybdenite oxidation kinetics exhibit a constant half-order dependence on dissolved O2 down to nanomolar levels of O2. We show that this behavior is best explained by a reaction mechanism in which O2 undergoes dissociative adsorption to the sulfide mineral surface. This mechanism helps to resolve major uncertainties regarding the reaction mechanism of O2 with pyrite and molybdenite mineral surfaces and provides a strong theoretical basis for the robust extrapolation of present results to higher and lower O2 concentrations.</p

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Sobre mecanismos de participación ciudadana para fortalecer alertas tempranas de inundaciones urbanas en el contexto de cambio climático

Este trabajo describe las tareas realizadas por el proyecto interdisciplinario Anticipando la Crecida, que tuvo el objetivo general de contribuir en la gestión de riesgos ante desastres asociados a inundaciones por sudestadas y lluvias intensas a través del diálogo con los diferentes actores de diferentes barrios del Área Metropolitana de Buenos Aires. La estrategia fue explorar las causas sociales y físico-naturales, en articulación con la adaptación a dichos eventos, y destacar el conocimiento y las tecnologías relativas a su predicción. Los objetivos específicos fueron identificar las necesidades de pronóstico meteorológicos y generar diálogos con los tomadores de decisiones y los habitantes del barrio para la adecuación de la gestión de riesgos ante desastres como las inundaciones por sudestadas y/o lluvias intensas en el área metropolitana de Buenos Aires. El proyecto propone producir conocimiento de manera participativa mediante talleres intersectoriales a escala barrio como estrategia de adaptación al cambio climático.Trabajo publicado en Acta Bioquímica Clínica Latinoamericana; no. 52, supl. 2, parte II, diciembre de 2018.Universidad Nacional de La Plat

A Global Ocean Oxygen Database and Atlas for Assessing and Predicting Deoxygenation and Ocean Health in the Open and Coastal Ocean

In this paper, we outline the need for a coordinated international effort toward the building of an open-access Global Ocean Oxygen Database and ATlas (GO2DAT) complying with the FAIR principles (Findable, Accessible, Interoperable, and Reusable). GO2DAT will combine data from the coastal and open ocean, as measured by the chemical Winkler titration method or by sensors (e.g., optodes, electrodes) from Eulerian and Lagrangian platforms (e.g., ships, moorings, profiling floats, gliders, ships of opportunities, marine mammals, cabled observatories). GO2DAT will further adopt a community-agreed, fully documented metadata format and a consistent quality control (QC) procedure and quality flagging (QF) system. GO2DAT will serve to support the development of advanced data analysis and biogeochemical models for improving our mapping, understanding and forecasting capabilities for ocean O2 changes and deoxygenation trends. It will offer the opportunity to develop quality-controlled data synthesis products with unprecedented spatial (vertical and horizontal) and temporal (sub-seasonal to multi-decadal) resolution. These products will support model assessment, improvement and evaluation as well as the development of climate and ocean health indicators. They will further support the decision-making processes associated with the emerging blue economy, the conservation of marine resources and their associated ecosystem services and the development of management tools required by a diverse community of users (e.g., environmental agencies, aquaculture, and fishing sectors). A better knowledge base of the spatial and temporal variations of marine O2 will improve our understanding of the ocean O2 budget, and allow better quantification of the Earth’s carbon and heat budgets. With the ever-increasing need to protect and sustainably manage ocean services, GO2DAT will allow scientists to fully harness the increasing volumes of O2 data already delivered by the expanding global ocean observing system and enable smooth incorporation of much higher quantities of data from autonomous platforms in the open ocean and coastal areas into comprehensive data products in the years to come. This paper aims at engaging the community (e.g., scientists, data managers, policy makers, service users) toward the development of GO2DAT within the framework of the UN Global Ocean Oxygen Decade (GOOD) program recently endorsed by IOC-UNESCO. A roadmap toward GO2DAT is proposed highlighting the efforts needed (e.g., in terms of human resources)

Determination of respiration rates in water with sub-micromolar oxygen concentrations

It is crucial for our study and understanding of element transformations in low-oxygen waters that we are able to reproduce the in situ conditions during laboratory incubations to an extent that does not result in unacceptable artefacts. In this study we have explored how experimental conditions affect measured rates of O2 consumption in low-O2 waters from the anoxic basin of Golfo Dulce (Costa Rica) and oceanic waters off Chile-Peru. High-sensitivity optode dots placed within all-glass incubation containers allowed for high resolution O2 concentration measurements in the nanomolar and low µmolar range and thus also for the determination of rates of oxygen consumption by microbial communities. Consumption rates increased dramatically (from 3 and up to 60 times) by prolonged incubations, and started to increase after 4-5 hours in surface waters and after 10-15 h in water from below the upper mixed layer. Estimated maximum growth rates during the incubations suggest the growth of opportunistic microorganism with doubling times as low as 2.8 and 4.6 h for the coastal waters of Golfo Dulce (Costa Rica) and oceanic waters off Chile and Peru, respectively. Deoxygenation by inert gas bubbling led to increases in subsequently determined rates, possibly by liberation of organics from lysis of sensitive organisms, particle or aggregate alterations or other processes mediated by the strong turbulence. Stirring of the water during the incubation led to an about 50% increase in samples previously deoxygenated by bubbling, but had no effect in untreated samples. Our data indicate that data for microbial activity obtained by short incubations of minimally manipulated water are most reliable, but deoxygenation is a prerequisite for many laboratory experiments, such as determination of denitrification rates, as O2 contamination by sampling is practically impossible to avoid

CO₂ and O₂ dynamics in leaves of aquatic plants with C₃ or CAM photosynthesis - application of a novel CO₂ microsensor

Background and Aims Leaf tissue CO2 partial pressure (pCO2) shows contrasting dynamics over a diurnal cycle in C3 and Crassulacean Acid Metabolism (CAM) plants. However, simultaneous and continuous monitoring of pCO2 and pO2 in C3 and CAM plants under the same conditions was lacking. Our aim was to use a new CO2 microsensor and an existing O2 microsensor for non-destructive measurements of leaf pCO2 and pO2 dynamics to compare a C3 and a CAM plant in an aquatic environment. Methods A new amperometric CO2 microsensor and an O2 microsensor elucidated with high temporal resolution the dynamics in leaf pCO2 and pO2 during light-dark cycles for C3 Lobelia dortmanna and CAM Littorella uniflora aquatic plants. Underwater photosynthesis, dark respiration, tissue malate concentrations and sediment CO2 and O2 were also measured. Key Results During the dark period, for the C3 plant, pCO2 increased to approx. 3.5 kPa, whereas for the CAM plant CO2 was mostly below 0.05 kPa owing to CO2 sequestration into malate. Upon darkness, the CAM plant had an initial peak in pCO2 (approx. 0.16 kPa) which then declined to a quasi-steady state for several hours and then pCO2 increased towards the end of the dark period. The C3 plant became severely hypoxic late in the dark period, whereas the CAM plant with greater cuticle permeability did not. Upon illumination, leaf pCO2 declined and pO2 increased, although aspects of these dynamics also differed between the two plants. Conclusions The continuous measurements of pCO2 and pO2 highlighted the contrasting tissue gas compositions in submerged C3 and CAM plants. The CAM leaf pCO2 dynamics indicate an initial lag in CO2 sequestration to malate, which after several hours of malate synthesis then slows. Like the use of O2 microsensors to resolve questions related to plant aeration, deployment of the new CO2 microsensor will benefit plant ecophysiology research

Incubation bottle.

<p>Glass bottle for incubations with a volume of 1160 mL (red ink was injected to increase the contrast). A) Opening (internal diameter 8.1 mm) for insertion of the STOX sensor; B) long open glass tube (internal diameter 2.5 mm) for pressure compensation (blue ink was injected inside the tube to increase the contrast); C) glass coated magnet (2.5 cm) for constant stirring.</p

A New Highly Sensitive Method to Assess Respiration Rates and Kinetics of Natural Planktonic Communities by Use of the Switchable Trace Oxygen Sensor and Reduced Oxygen Concentrations

<div><p>Oxygen respiration rates in pelagic environments are often difficult to quantify as the resolutions of our methods for O₂ concentration determination are marginal for observing significant decreases during bottle incubations of less than 24 hours. Here we present the assessment of a new highly sensitive method, that combine Switchable Trace Oxygen (STOX) sensors and all-glass bottle incubations, where the O₂ concentration was artificially lowered. The detection limit of respiration rate by this method is inversely proportional to the O₂ concentration, down to <2 nmol L⁻¹ h⁻¹ for water with an initial O₂ concentration of 500 nmol L⁻¹. The method was tested in Danish coastal waters and in oceanic hypoxic waters. It proved to give precise measurements also with low oxygen consumption rates (∼7 nmol L⁻¹ h⁻¹), and to significantly decrease the time required for incubations (≤14 hours) compared to traditional methods. This method provides continuous real time measurements, allowing for a number of diverse possibilities, such as modeling the rate of oxygen decrease to obtain kinetic parameters. Our data revealed apparent half-saturation concentrations (K_m values) one order of magnitude lower than previously reported for marine bacteria, varying between 66 and 234 nmol L⁻¹ O₂. K_m values vary between different microbial planktonic communities, but our data show that it is possible to measure reliable respiration rates at concentrations ∼0.5–1 µmol L⁻¹ O₂ that are comparable to the ones measured at full air saturation.</p></div