Use of particulate surrogates for assessing microbial mobility in subsurface ecosystems

Mass fluxes from the ground surface can play a vital role in influencing groundwater ecosystems. Rates of delivery may influence intact ecosystem composition, while fluxes of substances associated with anthropogenic activity may critically alter the functioning of associated microbial assemblages. Field-based tracing experiments offer a valuable means of understanding mass transport rates and mechanisms, particularly in complex heterogeneous epikarst systems overlying vulnerable fissured aquifers. A short-term tracer experiment monitoring solute and particle tracer concentrations after they passed through a 10-m-thick sequence of limestone, capped by a thin soil, revealed rapid travel times and variable attenuation rates for the substances employed. Results demonstrated that particle tracers have shorter average travel times and can reach the subsurface in higher concentrations and over shorter times than non-reactive solutes. High recovery rates for the bacterial tracer Ralstonia eutropha H16 contrasted strongly with those of similarly sized fluorescent polystyrene microspheres, highlighting the importance of physico-chemical surface characteristics of particle tracers. Complementary laboratory batch experiments examined the role played by organic and inorganic soil/rock surfaces on particle tracer attenuation. Findings suggest that biofilms may significantly promote transport of particulate material below ground, i.e., the delivery of allochthonous microorganisms to karst groundwate

Forests for Participatory Democracy: Emergent Patterns in the Interaction of Actors and Space in a Community-Based Sustainable Forestry Project in San Francisco Libre, Nicaragua

The host of literature on community-based sustainable forestry initiatives cites a profound schism between theory and the actual devolution of power and conservation of natural environments. This thesis set out to analyze the workings of power in a decentralized sustainable forestry project in San Francisco Libre, Nicaragua, and to account for how the myriad relevant actors influence, and are influenced, by the interactions and opportunities that arose. Taking a co-constructivist, relational approach, the case study undertaken found sustainable forestry and participatory democracy to be co-constitutive. However, where modernity has been touted for freeing society from the constraints of the natural world through science and technology, the very democracy and sustainability these initiatives are striving for are constrained by the modern framework upon which many of our institutions are built. By abandoning such nature vs. society dichotomous frameworks, socio- political initiatives can better account for the place-based, relational agency human and non-human actors share, and therefore create more effective, participative democratic institutions

Multi-Axis Differential Optical Absorption Spectroscopy Measurements in Polluted Environments

In dieser Arbeit werden die Ergebisse von MAX-DOAS Messungen während zweier umfangreicher Meßkampagnen vorgestellt. Eine Meßkampagne fand im Sommer 2004 im Nordosten der USA statt (ICARTT), die andere im Frühling 2006 in Mexiko Stadt (MILAGRO). In beiden Meßkampagnen wurden mehrere MAX-DOAS Instrumente an verschiedenen Orten aufgestellt und Zeitserien von NO2, SO2, HONO, HCHO, CHOCHO und O4 sowie von Aerosolextinktion gewonnen. Die räumliche und zeitliche Variation dieser Messungen wurden untersucht, um die entsprechenden Emissionsquellen, die chemischen Transformationsprozesse und die Transportwege zu charakterisieren und zu quantifizieren. Insgesamt erfüllten sich die diesbezüglichen Vermutungen. In einigen Fällen konnten Wochengänge in den Zeitserien beobachtet werden, was eine klare zeitliche Verknüpfung zwischen den Rhythmen der Emissionen und den gemessenen Spurengasen bedeutet. In den meisten Fällen konnten die gemessenen Spurengase eindeutig bestimmten Emissionsquellen zugeordnet werden. Ein weiteres interessantes Ergebnis war die weitgehende Übereinstimmung der Zeitserien von Aerosolextinktion und der von Spurengasen. Als Entdeckung können die erstmaligen Messungen sowohl von Glyoxal als auch von salpetriger Säure mit der MAX-DOAS Methode angeführt werden. Beide Messungen ergaben teilweise unerwartete Erkenntnisse, was die sehr starken Absorptionen von salpetriger Säure in Mexiko Stadt und die von Glyoxal im Golf von Maine betreffen. Daher sollten die Forschungen in dieser Richtung weitergeführt werden. In dieser Arbeit wurden auch Inversionstechniken entwickelt, die einen quantitativen Vergleich von mit MAX-DOAS gemessenen Daten mit anderen Messungen von z. B. in-situ oder durch Satelliten ermöglichen. Aufgrund der Erfahrungen dieser beiden Meßkampagnen wird die Gründung eines globalen Netzwerks von automatisierten MAX-DOAS Instrumenten empfohlen

Enhanced tropospheric BrO concentrations over the Antarctic sea ice belt in mid winter observed from MAX-DOAS observations on board the research vessel Polarstern

International audienceWe present Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of tropospheric BrO carried out on board the German research vessel Polarstern during the Antarctic winter 2006. Polarstern entered the area of first year sea ice around Antarctica on 24 June 2006 and stayed within this area until 15 August 2006. For the period when the ship cruised inside the first year sea ice belt, enhanced BrO concentrations were almost continuously observed. One interesting exception appeared on 7 July 2006, when the sun elevation angle was 2 and/or HOBr is too slow to provide sufficient amounts of Br radicals. Before and after the period inside the first year sea ice belt, typically low BrO concentrations were observed. Our observations indicate that enhanced BrO concentrations around Antarctica exist about one month earlier than observed by satellite instruments. The small BrO concentrations over the open oceans indicate a short atmospheric lifetime of activated bromine without contact to areas of first year sea ice. From detailed radiative transfer simulations we find that MAX-DOAS observations are about one order of magnitude more sensitive to near-surface BrO than satellite observations. In contrast to satellite observations the MAX-DOAS sensitivity hardly decreases for large solar zenith angles and is almost independent from the ground albedo. Thus this technique is very well suited for observations in polar regions close to the solar terminator. Furthermore, combination of both techniques could yield additional information on the vertical distribution of BrO in the lower troposphere

Groundwater protection in fractured media: a vulnerability-based approach for delineating protection zones in Switzerland

A vulnerability-based approach for delineating groundwater protection zones around springs in fractured media has been developed to implement Swiss water-protection regulations. It takes into consideration the diversity of hydrogeological conditions observed in fractured aquifers and provides individual solutions for each type of setting. A decision process allows for selecting one of three methods, depending on the spring vulnerability and the heterogeneity of the aquifer. At the first stage, an evaluation of spring vulnerability is required, which is essentially based on spring hydrographs and groundwater quality monitoring. In case of a low vulnerability of the spring, a simplified method using a fixed radius approach ("distance method”) is applied. For vulnerable springs, additional investigations must be completed during a second stage to better characterize the aquifer properties, especially in terms of heterogeneity. This second stage includes a detailed hydrogeological survey and tracer testing. If the aquifer is assessed as slightly heterogeneous, the delineation of protection zones is performed using a calculated radius approach based on tracer test results ("isochrone method”). If the heterogeneity is high, a groundwater vulnerability mapping method is applied ("DISCO method”), based on evaluating discontinuities, protective cover and runoff parameters. Each method is illustrated by a case stud

The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH₃, NO₂ and C₂H₆

We describe the University of Colorado mobile Solar Occultation Flux instrument (CU mobile SOF). The instrument consists of a digital mobile solar tracker that is coupled to a Fourier transform spectrometer (FTS) of 0.5 cm−1 resolution and a UV–visible spectrometer (UV–vis) of 0.55 nm resolution. The instrument is used to simultaneously measure the absorption of ammonia (NH3), ethane (C2H6) and nitrogen dioxide (NO2) along the direct solar beam from a moving laboratory. These direct-sun observations provide high photon flux and enable measurements of vertical column densities (VCDs) with geometric air mass factors, high temporal resolution of 2 s and spatial resolution of 5–19 m. It is shown that the instrument line shape (ILS) of the FTS is independent of the azimuth and elevation angle pointing of the solar tracker. Further, collocated measurements next to a high-resolution FTS at the National Center for Atmospheric Research (HR-NCAR-FTS) show that the CU mobile SOF measurements of NH3 and C2H6 are precise and accurate; the VCD error at high signal to noise ratio is 2–7 %. During the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) from 21 July to 3 September 2014 in Colorado, the CU mobile SOF instrument measured median (minimum, maximum) VCDs of 4.3 (0.5, 45)  ×  1016 molecules cm−2 NH3, 0.30 (0.06, 2.23)  ×  1016 molecules cm−2 NO2 and 3.5 (1.5, 7.7)  ×  1016 molecules cm−2 C2H6. All gases were detected in larger 95 % of the spectra recorded in urban, semi-polluted rural and remote rural areas of the Colorado Front Range. We calculate structure functions based on VCDs, which describe the variability of a gas column over distance, and find the largest variability for NH3. The structure functions suggest that currently available satellites resolve about 10 % of the observed NH3 and NO2 VCD variability in the study area. We further quantify the trace gas emission fluxes of NH3 and C2H6 and production rates of NO2 from concentrated animal feeding operations (CAFO) using the mass balance method, i.e., the closed-loop vector integral of the VCD times wind speed along the drive track. Excellent reproducibility is found for NH3 fluxes and also, to a lesser extent, NO2 production rates on 2 consecutive days; for C2H6 the fluxes are affected by variable upwind conditions. Average emission factors were 12.0 and 11.4 gNH3 h−1 head−1 at 30 °C for feedlots with a combined capacity for  ∼  54 000 cattle and a dairy farm of  ∼  7400 cattle; the pooled rate of 11.8 ± 2.0 gNH3 h−1 head−1 is compatible with the upper range of literature values. At this emission rate the NH3 source from cattle in Weld County, CO (535 766 cattle), could be underestimated by a factor of 2–10. CAFO soils are found to be a significant source of NOx. The NOx source accounts for  ∼  1.2 % of the N flux in NH3 and has the potential to add  ∼  10 % to the overall NOx emissions in Weld County and double the NOx source in remote areas. This potential of CAFO to influence ambient NOx concentrations on the regional scale is relevant because O3 formation is NOx sensitive in the Colorado Front Range. Emissions of NH3 and NOx are relevant for the photochemical O3 and secondary aerosol formation

Global impacts of tropospheric halogens (Cl, Br, I) on oxidants and composition in GEOS-Chem [Discussion paper]

We present a simulation of the global present-day composition of the troposphere which includes the chemistry of halogens (Cl, Br, I). Building on previous work within the GEOS-Chem model we include emissions of inorganic iodine from the oceans, anthropogenic and biogenic sources of halogenated gases, gas phase chemistry, and a parameterised approach to heterogeneous halogen chemistry. Consistent with Schmidt et al. (2016) we do not include sea-salt debromination. Observations of halogen radicals (BrO, IO) are sparse but the model has some skill in reproducing these. Modelled IO shows both high and low biases when compared to different datasets, but BrO concentrations appear to be modelled low. Comparisons to the very sparse observations dataset of reactive Cl species suggest the model represents a lower limit of the impacts of these species, likely due to underestimates in emissions and therefore burdens. Inclusion of Cl, Br, and I results in a general improvement in simulation of ozone (O3) concentrations, except in polar regions where the model now underestimates O3 concentrations. Halogen chemistry reduces the global tropospheric O3 burden by 18.6 %, with the O3 lifetime reducing from 26 to 22 days. Global mean OH concentrations of 1.28  ×  106 molecules cm−3 are 8.2 % lower than in a simulation without halogens, leading to an increase in the CH4 lifetime (10.8 %) due to OH oxidation from 7.47 to 8.28 years. Oxidation of CH4 by Cl is small (∼  2 %) but Cl oxidation of other VOCs (ethane, acetone, and propane) can be significant (∼  15–27 %). Oxidation of VOCs by Br is smaller, representing 3.9 % of the loss of acetaldehyde and 0.9 % of the loss of formaldehyde

Iodine's impact on tropospheric oxidants : A global model study in GEOS-Chem

We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry, and simplified higher iodine oxide (I2OX, X=2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent iodine oxide (IO) observations, the simulation shows an average bias of ~+90% with available surface observations in the marine boundary layer (outside of polar regions), and of ~+73¯% within the free troposphere (350 hPa < p < 900 hPa)  over the eastern Pacific. Iodine emissions (3.8 Tg yr-1) are overwhelmingly dominated by the inorganic ocean source, with 76% of this emission from hypoiodous acid (HOI). HOI is also found to be the dominant iodine species in terms of global tropospheric IY burden (contributing up to 70%). The iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0%) compared to standard GEOS-Chem (v9-2). The iodine-driven OXloss rate1 (748 Tg OX yr-1) is due to photolysis of HOI (78%), photolysis of OIO (21%), and reaction between IO and BrO (1%). Increases in global mean OH concentrations (1.8%) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range of parameters and conclude that the simulation is sensitive to choices in parametrization of heterogeneous uptake, ocean surface iodide, and I2OX (X=2, 3, 4) photolysis. The new iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine- and iodine-driven tropospheric O3 burden decrease of 14.4% compared to a simulation without iodine and bromine chemistry in the model, and a small increase in OH (1.8%). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models. Here Ox is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN=peroxyacetyl nitrate, PPN=peroxypropionyl nitrate, MPN=methyl peroxy nitrate, and MPN=peroxymethacryloyl nitrate