Vertical Hydrologic Exchange Flows Control Methane Emissions from Riverbed Sediments.

CH4 emissions from inland waters are highly uncertain in the current global CH4 budget, especially for streams, rivers, and other lotic systems. Previous studies have attributed the strong spatiotemporal heterogeneity of riverine CH4 to environmental factors such as sediment type, water level, temperature, or particulate organic carbon abundance through correlation analysis. However, a mechanistic understanding of the basis for such heterogeneity is lacking. Here, we combine sediment CH4 data from the Hanford reach of the Columbia River with a biogeochemical-transport model to show that vertical hydrologic exchange flows (VHEFs), driven by the difference between river stage and groundwater level, determine CH4 flux at the sediment-water interface. CH4 fluxes show a nonlinear relationship with the magnitude of VHEFs, where high VHEFs introduce O2 into riverbed sediments, which inhibit CH4 production and induce CH4 oxidation, and low VHEFs cause transient reduction in CH4 flux (relative to production) due to reduced advective CH4 transport. In addition, VHEFs lead to the hysteresis of temperature rise and CH4 emissions because high river discharge caused by snowmelt in spring leads to strong downwelling flow that offsets increasing CH4 production with temperature rise. Our findings reveal how the interplay between in-stream hydrologic flux besides fluvial-wetland connectivity and microbial metabolic pathways that compete with methanogenic pathways can produce complex patterns in CH4 production and emission in riverbed alluvial sediments.

Ebullition dominates methane fluxes from the water surface across different ecohydrological patches in a temperate freshwater marsh at the end of the growing season.

Measurements of the spatial heterogeneity of methane fluxes in wetlands are critical to better understand and predict methane emissions at the ecosystem scale. However, the within-wetland spatial heterogeneity of fluxes is rarely assessed. Here, we use a spatially balanced rapid chamber-based survey of methane at different ecohydrological patches within a temperate freshwater marsh. We measured fluxes exclusively from the water surface without including vegetation. We further used the data from chamber measurements to partition diffusive and ebullitive fluxes. Three ecohydrological patches were distinguishable in the marsh, defined by the type and presence/absence of vegetation. These patches were emergent vegetation, floating-leaved, and open water. Net methane fluxes from the water surface (diffusion plus ebullition) in emergent vegetation patches were larger than in the floating-leaved vegetation and open water patches (p < 0.05). Diffusive fluxes, representing a sizable smaller fraction of net fluxes, were larger in vegetated than in unvegetated patches (p < 0.05), while ebullitive fluxes mirrored the magnitude and differences observed in the net fluxes. Moreover, pooled net and ebullitive fluxes across patches (but not diffusive fluxes) were negatively correlated with water levels, the primary variable affecting patch distribution. Altogether, our results indicate that the differences among ecohydrological patches are driven by ebullition, ultimately highlighting challenges faced by scientists and practitioners in the field and modelers seeking to improve the predictability and resolution of wetland biogeochemical models.

Methane and nitrous oxide porewater concentrations and surface fluxes of a regulated river.

Greenhouse gas (GHG) emissions from rivers are a critical missing component of current global GHG models. Their exclusion is mainly due to a lack of in-situ measurements and a poor understanding of the spatiotemporal dynamics of GHG production and emissions, which prevents optimal model parametrization. We combined simultaneous observations of porewater concentrations along different beach positions and depths, and surface fluxes of methane and nitrous oxide at a plot scale in a large regulated river during three water stages: rising, falling, and low. Our goal was to gain insights into the interactions between hydrological exchanges and GHG emissions and elucidate possible hypotheses that could guide future research on the mechanisms of GHG production, consumption, and transport in the hyporheic zone (HZ). Results indicate that the site functioned as a net source of methane. Surface fluxes of methane during river water stages at three beach positions (shallow, intermediate and deep) correlated with porewater concentrations of methane. However, fluxes were significantly higher in the intermediate position during the low water stage, suggesting that low residence time increased methane emissions. Vertical profiles of methane peaked at different depths, indicating an influence of the magnitude and direction of the hyporheic mixing during the different river water stages on methane production and consumption. The site acted as either a sink or a source of nitrous oxide depending on the elevation of the water column. Nitrous oxide porewater concentrations peaked at the upper layers of the sediment throughout the different water stages. River hydrological stages significantly influenced porewater concentrations and fluxes of GHG, probably by influencing heterotrophic respiration (production and consumption processes) and transport to and from the HZ. Our results highlight the importance of including dynamic hydrological exchanges when studying and modeling GHG production and consumption in the HZ of large rivers.

Impacto del índice de masa corporal en la presión arterial medida con esfigmomanómetro de mercurio en niños y adolescentes con diabetes mellitus tipo 1 / The impact of body mass index on blood pressure measured with mercury sphygmomanometer in children and adolescents with type 1 diabetes mellitus

Resumen Introducción Los pacientes con diabetes mellitus tipo 1 (DM1) y sobrepeso tienen más riesgo de desarrollar cambios en la presión arterial (PA), y esto incrementa su morbilidad y mortalidad cardiovascular. En este estudio se determinó la relación entre la PA y el índice de masa corporal (IMC) y el promedio de las tres últimas mediciones de hemoglobina glucosilada (HbA1c) de pacientes con DM1. Métodos Estudio transversal analítico en niños y adolescentes con DM1 con más de un año de evolución. Las variables dependientes fueron la PA sistólica y diastólica medidas con esfigmomanómetro y las variables independientes, IMC y promedio de las últimas tres mediciones de la HbA1c. Se utilizó regresión lineal múltiple con intervalo de confianza del 95%. Resultados Se estudiaron 75 pacientes con DM1. La mediana del tiempo de evolución de la DM1 fue de 3.5 años (mínimo 1 año-máximo 14.8 años), el IMC 19.5 ± 3.1 kg/cm2 y la HbA1c 8.3 ± 2.4%. De los 75 pacientes, 66 presentaron PA < percentil 90 y 9 PA ≥ percentil 90 (12%). Se construyeron dos modelos de regresión lineal múltiple, con PA sistólica y diastólica como variables dependientes. Las posibles variables predictoras fueron sugeridas por el contexto teórico y el análisis estadístico. El IMC expresado en puntuación zeta (zIMC) fue predictor para PA sistólica/diastólica. Los modelos sugirieron que a cada incremento de unidad del zIMC corresponde un aumento de 5.1 y 3.6 mmHg de PA sistólica y diastólica, respectivamente. Conclusiones Se observó una correlación positiva de la PA sistólica y la diastólica con el zIMC.

Abstract Background Patients with type 1 diabetes mellitus (T1DM) and overweight have more risk to develop changes in blood pressure that increase cardiovascular morbidity and mortality. In this study, the relationship between blood pressure (BP) with the body mass index (BMI) and the average of the last three measurements of glycated hemoglobin (HbA1c) in patients with T1DM was determined. Methods A cross-sectional analytical study was conducted in children and adolescents with T1DM with over a year since diagnosis. The dependent variables were systolic and diastolic BP, measured with a mercury sphygmomanometer. The independent variables were BMI and average of the last three measurements of HbA1. A linear regression with a 95% confidence interval was used. Results Seventy-five patients with T1DM were studied. The median of disease duration was 3.5 years (min 1-max 14.8 years), BMI 19.5 ± 3.1 kg/cm2 and HbA1c 8.3 ± 2.4%. Sixty-six patients showed BP < percentile 90 and 9 BP ≥ percentile 90 (12%). Two models of linear regression were constructed, with systolic and diastolic BP as dependent variables. The possible predictor variables were suggested by theoretical context and statistical analysis. The predictive variable of high BP was zBMI (body mass index expressed in z-score) for systolic and diastolic BP. Also, the models suggested that for an increase of one unit of zBMI, corresponded a rise of 5.1 and 3.6 mmHg in systolic and diastolic BP, respectively. Conclusions A positive correlation between systolic and diastolic BP with zBMI was observed.

The impact of body mass index on blood pressure measured with mercury sphygmomanometer in children and adolescents with type 1 diabetes mellitus.

Background: Patients with type 1 diabetes mellitus (T1DM) and overweight have more risk to develop changes in blood pressure that increase cardiovascular morbidity and mortality. In this study, the relationship between blood pressure (BP) with the body mass index (BMI) and the average of the last three measurements of glycated hemoglobin (HbA1c) in patients with T1DM was determined. Methods: A cross-sectional analytical study was conducted in children and adolescents with T1DM with over a year since diagnosis. The dependent variables were systolic and diastolic BP, measured with a mercury sphygmomanometer. The independent variables were BMI and average of the last three measurements of HbA1. A linear regression with a 95% confidence interval was used. Results: Seventy-five patients with T1DM were studied. The median of disease duration was 3.5 years (min 1-max 14.8 years), BMI 19.5 ± 3.1 kg/cm2 and HbA1c 8.3 ± 2.4%. Sixty-six patients showed BP < percentile 90 and 9 BP ≥ percentile 90 (12%). Two models of linear regression were constructed, with systolic and diastolic BP as dependent variables. The possible predictor variables were suggested by theoretical context and statistical analysis. The predictive variable of high BP was zBMI (body mass index expressed in z-score) for systolic and diastolic BP. Also, the models suggested that for an increase of one unit of zBMI, corresponded a rise of 5.1 and 3.6 mmHg in systolic and diastolic BP, respectively. Conclusions: A positive correlation between systolic and diastolic BP with zBMI was observed.

Introducción: Los pacientes con diabetes mellitus tipo 1 (DM1) y sobrepeso tienen más riesgo de desarrollar cambios en la presión arterial (PA), y esto incrementa su morbilidad y mortalidad cardiovascular. En este estudio se determinó la relación entre la PA y el índice de masa corporal (IMC) y el promedio de las tres últimas mediciones de hemoglobina glucosilada (HbA1c) de pacientes con DM1. Métodos: Estudio transversal analítico en niños y adolescentes con DM1 con más de un año de evolución. Las variables dependientes fueron la PA sistólica y diastólica medidas con esfigmomanómetro y las variables independientes, IMC y promedio de las últimas tres mediciones de la HbA1c. Se utilizó regresión lineal múltiple con intervalo de confianza del 95%. Resultados: Se estudiaron 75 pacientes con DM1. La mediana del tiempo de evolución de la DM1 fue de 3.5 años (mínimo 1 año-máximo 14.8 años), el IMC 19.5 ± 3.1 kg/cm2 y la HbA1c 8.3 ± 2.4%. De los 75 pacientes, 66 presentaron PA < percentil 90 y 9 PA ≥ percentil 90 (12%). Se construyeron dos modelos de regresión lineal múltiple, con PA sistólica y diastólica como variables dependientes. Las posibles variables predictoras fueron sugeridas por el contexto teórico y el análisis estadístico. El IMC expresado en puntuación zeta (zIMC) fue predictor para PA sistólica/diastólica. Los modelos sugirieron que a cada incremento de unidad del zIMC corresponde un aumento de 5.1 y 3.6 mmHg de PA sistólica y diastólica, respectivamente. Conclusiones: Se observó una correlación positiva de la PA sistólica y la diastólica con el zIMC.

Carbon sequestration and methane emissions along a microtopographic gradient in a tropical Andean peatland.

Tropical alpine peatlands are among the least studied wetlands types on earth. Their important ecosystem services at local and regional scope are currently threatened by climate and land use changes. Recent studies in these ecosystems suggest their importance to the provision of climate regulation services, prompting a better understanding of the underlying functions and their variability at ecosystem scales. The objective of this study is to determine the variability of methane (CH4) fluxes and carbon (C) sequestration within a tropical alpine peatland in three locations along a microtopographic gradient and its associated plant diversity. These locations accounted for: 1) hummocks, found mostly near the edge of the peat with a water table below the soil surface, 2) lawns, in the transition zone, with a water-table near the soil surface, and 3) hollows, permanently flooded with a water table above the soil surface, composed of small patches of open water intermingled with unconsolidated hummocks that surface the water level. Results indicate that CH4 flux is lowest in the lawns, while C sequestration is highest. Conversely, the hummock and hollow have higher CH4 flux and lower C sequestration. In addition, plant diversity in the lawns is higher than in the hummock and hollow location. Dryer conditions brought by current climate change in the northern Andes are expected to lower the water tables in the peatland. This change is expected to drive a change in CH4 flux and C sequestration at the lawns, currently dominating the peatland, towards values more similar to those measured in the hummocks. This decrease may also represent a change towards the lower plant diversity that characterized the hummock. Such changes will reduce the ratio of C sequestration:CH4 flux signifying the reduction of resilience and increment of vulnerability of the climate-regulating service to further perturbations.

Author Correction: Nitrogen-rich organic soils under warm well-drained conditions are global nitrous oxide emission hotspots.

The original version of this Article contained an error in the first sentence of the Acknowledgements section, which incorrectly referred to the Estonian Research Council grant identifier as "PUTJD618". The correct version replaces the grant identifier with "PUTJD619". This has been corrected in both the PDF and HTML versions of the Article.

Nitrogen-rich organic soils under warm well-drained conditions are global nitrous oxide emission hotspots.

Nitrous oxide (N2O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N2O, predicting soil response to changes in climate or land use is central to understanding and managing N2O. Here we find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3-), water content and temperature using a global field survey of N2O emissions and potential driving factors across a wide range of organic soils. N2O emissions increase with NO3- and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N2O emission from all organic soils. Above 5 mg NO3--N kg-1, either draining wet soils or irrigating well-drained soils increases N2O emission by orders of magnitude. As soil temperature together with NO3- explains 69% of N2O emission, tropical wetlands should be a priority for N2O management.