Spatial Variability in and Hotspots of Methane Concentration in a Large Temperate River

Rivers are significant sources of greenhouse gases (GHGs; e.g., CH4 and CO2); however, our understanding of the large-scale longitudinal patterns of GHG emissions from rivers remains incomplete, representing a major challenge in upscaling. Local hotspots and moderate heterogeneities may be overlooked by conventional sampling schemes. In August 2020 and for the first time, we performed continuous (once per minute) CH4 measurements of surface water during a 584-km-long river cruise along the German Elbe to explore heterogeneities in CH4 concentration at different spatial scales and identify CH4 hotspots along the river. The median concentration of dissolved CH4 in the Elbe was 112 nmol L−1, ranging from 40 to 1,456 nmol L−1 The highest CH4 concentrations were recorded at known potential hotspots, such as weirs and harbors. These hotspots were also notable in terms of atmospheric CH4 concentrations, indicating that measurements in the atmosphere above the water are useful for hotspot detection. The median atmospheric CH4 concentration was 2,033 ppb, ranging from 1,821 to 2,796 ppb. We observed only moderate changes and fluctuations in values along the river. Tributaries did not obviously affect CH4 concentrations in the main river. The median CH4 emission was 251 μmol m−2 d−1, resulting in a total of 28,640 mol d−1 from the entire German Elbe. Similar numbers were obtained using a conventional sampling approach, indicating that continuous measurements are not essential for a large-scale budget. However, we observed considerable lateral heterogeneity, with significantly higher concentrations near the shore only in reaches with groins. Sedimentation and organic matter mineralization in groin fields evidently increase CH4 concentrations in the river, leading to considerable lateral heterogeneity. Thus, river morphology and structures determine the variability of dissolved CH4 in large rivers, resulting in smooth concentrations at the beginning of the Elbe versus a strong variability in its lower parts. In conclusion, groin construction is an additional anthropogenic modification following dam building that can significantly increase GHG emissions from rivers

Importance of structural history in the summit area of Stromboli during the 2002–2003 eruptive crisis inferred from temperature, soil CO2, self-potential, and electrical resistivity tomography

International audienceThe 2002-2003 eruptive crisis of Stromboli volcano in the Aeolian Islands raised the question of how to assess the stability of the flanks of this volcanic edifice during such a crisis. To provide a response to this question, we analyzed a detailed fluid flow mapping plus the reiteration of a profile located in the vicinity of the active vents using the self-potential method, temperature data, soil-gas (CO2) measurements, and electric resistivity tomography. Coupling the interpretation of these methods that are sensitive to the flow of gas and water in the ground indicates the position of areas of mechanical weakness. In addition, they can be used to monitor the change in the discharge of fluids associated with these features before and during the 2002-2003 eruptive crisis. Our results emphasize the importance of old structural boundaries, such as the Large Fossa crater, in the development of the new set of fractures observed during the 2002-2003 eruptive crisis. Between October 2002 and January 2003, the use of CO2 soil-gas technique evidenced an increase in the discharge of CO2 outside the Large Fossa crater boundaries, along the failure boundary of the southern Sciara del Fuoco area. Self-potential and temperature measurements made before the 2002-2003 eruptive crisis reveal significant changes along the main structural boundaries of the Fossa area. The development of these anomalies is interpreted as an increase of the permeability of the structure from May 2000 to May 2002. Between January 2003 and March 2003 the reiteration of self-potential, temperature, and CO2 measurements shows an increase of fluid discharge along weakness planes located inside the Large Fossa crater boundary. They evidence no change outside this structural boundary. The importance of the Large Fossa crater boundary in controlling the deformation and fluid flow from January to March 2003 has been attested by the development of the fractures inside the Large Fossa crater boundary, and also with a network of electrooptical distance measurement stations located inside and outside this ancient crater. This multidisciplinary approach to fluid flow assessment before and during an eruptive crisis is complementary to geodetic measurements of the deformation of the edifice. It demonstrates for the first time the powerful potential of combining electrical resistivity tomography, self-potential, temperature, and soil CO2 measurements in assessing the position of the planes of mechanical weakness in a volcanic edifice

Characteristics of dissolved and atmospheric methane concentrations along a freshwater-seawater transect from the River Elbe into the North Sea

Surface waters are known to be significant sources of greenhouse gases (CH4 and CO2), but our understanding of large scale patterns is still incomplete. The greenhouse gases in rivers originate both from in-stream processes and interactions with the catchment. For coastal seas, rivers are suspected to be one of the main source of greenhouse gases, while the role of the interjacent tidal flats is still ambiguous. Especially the reaction of the entire system on terrestrial hydrological extremes such as low flow situations are still under consideration. The functional understanding of such events and their impacts on the water chemistry along its transition pathway in the terrestrial and limnic compartment as well as in the coastal marine environment is crucially needed for the evaluation of its relevance in the Earth system. As part of a MOSES campaign (Modular Observation Solutions for Earth Systems) spanning disciplines as well as earth system compartments we investigated the aquatic as well as the atmospheric compartemt in and above the Elbe River from inland waters through the tidal section of the river and the estuary to the North Sea with the goal to explore spatial heterogeneity of CO2 and CH4 concentrations in the water and in ambient air above the water during a low water period in summer 2020. Overall, dissolved CH4 concentrations ranged over three orders of magnitude. Along the freshwater part of the transect, dissolved CH4 increased and weirs and harbors appeared to be hot spots of elevated CH4 concentrations both for the dissolved and atmospheric phase. We observed a longitudinal gradient of CO2 in the river which was closely linked to primary production. In the estuary and the marine part, dissolved CH4 concentrations of the transect were determined by the variability of temperature and salinity. Correlations with other water parameters revealed the complex regulation of dissolved CH4 concentrations along the freshwater-seawater continuum. For atmospheric CH4 above the North Sea, wind direction and wind speed proved to be crucial. Besides the typical diurnal fluctuations of atmospheric CO2 and CH4, an observed link between dissolved and atmospheric concentrations has to be further clarified

Influence of wind speed and wind direction above the sea surface on the diffusive methane flux and the atmospheric methane concentration at the North Sea

The estimations of the diffusive methane flux from the water phase into the atmosphere in coastal waters is relevant for a better estimate of the atmospheric greenhouse-gas budget. Unfortunately, so far, the numerical determination of the fluxes has a high level of uncertainty in coastal waters. To improve the estimation of coastal methane fluxes, not only a high temporal and spatial sampling resolution of the dissolved methane in the water are required. Besides, also the atmospheric methane concentration and the wind speed and wind direction above the surface is important. In most cases, these atmospheric data are obtained from near-by atmospheric and meteorologic monitoring stations. In this study, we measured wind speed, direction and atmospheric methane local directly on board of three research vessel cruising in the southern North Sea within the MOSES project and compared the effects of local versus remote measurements of these data on the flux data. In addition, using the wind direction and speed, we try to assess the origin of the atmospheric methane measured in the study area. Using these “improved” data sets, we discuss if local measurements of auxiliary data provide better insights in the determining factors of the methane flux, and thus also improve the regional aquatic methane budget

Obesity or diet? Levels and determinants of phthalate body burden – A case study on Portuguese children

In this study we analyzed one of the most comprehensive sets of 21 urinary phthalate metabolites representing exposure to 11 parent phthalates (DEP, DMP, DiBP, DnBP, BBzP, DEHP, DiNP, DiDP, DCHP, DnPeP, DnOP) in first morning urine samples of 112 Portuguese children (4-18 years) sampled in 2014/15. The study population consisted of two groups: group 1 with normal weight/underweight children (N = 43) following their regular diet and group 2 with obese/overweight children (N = 69) following a healthy diet (with nutritional counselling). Most of the metabolites were above the limits quantification (81-100%) except for MCHP, MnPEP and MnOP. Metabolite levels were generally comparable to other recent child and general populations sampled worldwide, confirming the steady decline in exposures to most phthalates. Compared to Portuguese children sampled in 2011/2012, median urinary metabolite levels decreased by approximately 50% for DEHP, DnBP, DiBP and BBzP. Risk assessments for individual phthalates and the sum of the anti-androgenic phthalates did not indicate to attributable health risks, also at the upper percentiles of exposure. In the healthy diet group the median concentration of the DEHP metabolites was significant lower, while all phthalate metabolites except MEP tended to be lower compared to the regular diet group. Multiple log-linear regression analyses revealed significantly lower daily intakes (DIs) for all phthalates in the healthy diet group compared to the regular diet group (geometric mean ratios (gMR) between 0.510-0.618; p ≤ 0.05), except for DEP (gMR: 0.811; p = 0.273). The same analyses with the continuous variable body mass index instead of the diet groups also showed effects on the DIs (gMRs between 0.926-0.951; p ≤ 0.05), however much smaller than the effects of the diet. The results indicate that obese children following a healthy diet composed of fresh and less packaged/processed food can considerably reduce their intake for most phthalates and can have lower phthalate intakes than regular weight/regular diet children.Luísa Correia-Sá is grateful to Fundação para a Ciência e a Tecnologia (FCT) by the grant (SFRH/BD/87019/2012), financed by POCH, subsidized by Fundo Social Europeu and Ministério da Ciência, Tecnologia e Ensino Superior. The authors are thankful to the project Qualidade e Segurança Alimentar – uma abordagem (nano)tecnológica, reference NORTE-01-0145-FEDER-000011.info:eu-repo/semantics/publishedVersio

Nutrient and carbon dynamics along the river-estuary-ocean continuum on Central European scale

Nutrient and carbon dynamics within the river-estuary-coastal water systems are key processes to understand the matter fluxes from the terrestrial environment to the ocean. In a large-scale study we analysed those dynamics with the focus of the prevailing low water conditions by following a sampling approach based on the travel time of water. We started with a nearly Lagrangian sampling along the River Elbe (German part; 580 km within 8 days travel time). After a subsequent investigation of the estuary, the plume of the river was followed by raster sampling the German Bight (North Sea) using three ships simultaneously. In the river, intensive growth of phytoplankton was determined connected with high oxygen saturation and pH values as well as under-saturation of CO2, whereas concentrations of dissolved nutrients declined. In the estuary, the Elbe shifted from an autotrophic to a heterotrophic system: Phytoplankton died off upstream of the salinity gradient causing minima in oxygen saturation and pH, supersaturation of CO2, and a release of nutrients. In the coastal region, phytoplankton and nutrient concentrations were low, oxygen close to saturation, and pH in a typical marine range. We detected a positive relationship between pH values and oxygen saturation and a negative one between pCO2 and oxygen saturation. Corresponding to the significant particulate nutrient flux via phytoplankton, flux rates of dissolved nutrients from the river into the estuary were low and determined by depleted concentrations. In contrast, fluxes from the estuary to the coastal waters were higher and the pattern was determined by tidal currents. Overall, the presented observation approach is appropriate to better understand land-ocean fluxes, particularly if it is performed under different hydrological conditions including extremes and seems to be suitable to investigate the impact of such events in freshwater on coastal systems in future. The study was conducted within the frame of the Helmholtz MOSES initiative (Modular Observation Solutions for Earth Systems) targeting processes and impacts of hydrological extremes

“Are Machines Better Than Humans in Image Tagging?” - A User Study Adds to the Puzzle

“Do machines perform better than humans in visual recognition tasks?” Not so long ago, this question would have been considered even somewhat provoking and the answer would have been clear: “No”. In this paper, we present a comparison of human and machine performance with respect to annotation for multimedia retrieval tasks. Going beyond recent crowdsourcing studies in this respect, we also report results of two extensive user studies. In total, 23 participants were asked to annotate more than 1000 images of a benchmark dataset, which is the most comprehensive study in the field so far. Krippendorff’s α is used to measure inter-coder agreement among several coders and the results are compared with the best machine results. The study is preceded by a summary of studies which compared human and machine performance in different visual and auditory recognition tasks. We discuss the results and derive a methodology in order to compare machine performance in multimedia annotation tasks at human level. This allows us to formally answer the question whether a recognition problem can be considered as solved. Finally, we are going to answer the initial question