Measuring eddy covariance fluxes of ammonia using tunable diode laser absorption spectroscopy

Field measurements of NH₃ fluxes using an eddy covariance technique were made for a total of 60 days between July and September 2002 at an intensively managed grassland in Southern Scotland. The collected data demonstrate the suitability of a tuneable diode laser absorption spectroscopy (TDLAS) system coupled with a sonic anemometer for eddy covariance measurements. The novelty of these measurements is the application to ammonia, which has only become measurable using TDLAS techniques recently, because of its small ambient concentration. Data presented in this paper show typical features of the fluxes and concentration for the summer season. NH₃ concentration and flux values are in a similar range to previous studies using flux gradient methods at the same field site, although the particularly wet season reduced the concentration of NH₃ in the air. For an example day, measured NH₃ fluxes ranged between ?11 and 44 ng m^?2 s^?1 with an average value of 3.78 ng m^?2 s^?1 indicating a small net emission from the vegetation. Spectral analysis executed on the data shows the percentage of flux carried by the small eddies (from 0.2 to 2 m) suggesting that high detection frequency instruments are particularly suitable for estimating NH₃ fluxes between atmosphere and vegetation.     

Microbially Mediated In Situ Desorption Accelerates Remediation of Large Gasoline Product Plume

Remediation of a large separate‐phase hydrocarbon product and associated dissolved‐phase gasoline plume was accelerated by coupling multiphase extraction with in situ microbial stimulation. At the beginning of remediation activities, the separate‐phase hydrocarbon plume extended an estimated seven acres with product thickness measuring up to 2.1 feet thick. Within 18 months after beginning extraction, reduction of gasoline constituents in groundwater became asymptotic and measureable product disappeared from the upgradient source area. At that time, the remediation team initiated a program of limited in situ anaerobic bioremediation with the goal of stimulating production of natural surfactants from native microbes to release petroleum from the soil matrix. Groundwater concentrations of gasoline constituents increased gradually over the next three years, improving recovery without biofouling the pump‐and‐treat infrastructure. Using this approach, the groundwater component of the remedy was completed in less than five years, substantially less than the 10 years to 15 years predicted by modeling. This strategy demonstrated a more sustainable approach to remediation, reducing electrical usage by an estimated 800 megawatt hours, reducing infrastructure requirements, and preserving an estimated 150 million gallons of groundwater for this arid agricultural area. © 2014 Wiley Periodicals, Inc.     

In situ remediation of PCE at a site with clayey lithology and a significant smear zone

Groundwater at the former Serry's Dry Cleaning site in Corvallis, Oregon, was impacted by chlorinated volatile organic compounds (CVOCs). The primary CVOCs impacting the site include tetrachloroethene, trichloroethene, dichloroethene, and vinyl chloride, which were detected at concentrations up to 22,000, 1,700, 3,100, and 7 μg/L, respectively, prior to treatment. Large seasonal fluctuations in groundwater CVOC concentrations indicated that a significant fraction of the CVOC mass was present in the smear zone. Field‐scale pilot tests were performed for the Oregon Department of Environmental Quality's Dry Cleaner Program to evaluate the performance of EHC® in situ chemical reduction (ISCR) technology. The pilot study involved evaluating field performance and physical distribution into low‐permeability soil using basic Geoprobe® injection tooling. The testing results confirmed that bioremediation enhanced by ISCR supported long‐term treatment at the site. This article describes the implementation and results of the tests. Performance data are available from a three‐year period following the injections, allowing for a discussion about sustained performance and reagent longevity. © 2010 Wiley Periodicals, Inc.     

Quantifying dry NH3 deposition to an ombrotrophic bog from an automated NH3 field release system

Providing an accurate estimate of the dry component of N deposition to low N background, semi-natural habitats, such as bogs and upland moors dominated by Calluna vulgaris is difficult, but essential to relate nitrogen deposition to effects in these communities. To quantify the effects of NH₃ inputs to moorland vegetation growing on a bog at a field scale, a field release NH₃ fumigation system was established at Whim Moss (Scottish Borders) in 2002. Gaseous NH₃ from a line source was released along of a 60 m transect, when meteorological conditions (wind speed >2.5 m s^–1 and wind direction in the sector 180–215°) were met, thereby providing a profile of decreasing NH₃ concentration with distance from the source. In a complementary study, using a NH₃ flux chamber system, the relationships between NH₃ concentrations and cuticular resistances were quantified for a range of NH₃ concentrations and micrometeorological conditions for moorland vegetation. Cuticular resistances increased with NH₃ concentration from 11 s m^–1 at 3.0 g m^–3 to 30 s m^–1 at 30 g m^–3. The NH₃ concentration data and the concentration-dependent canopy resistance are used to calculate NH₃ deposition taking into account leaf surface wetness. The implications of using an NH₃ concentration-dependent cuticular resistance and the importance for refining critical loads are discussed.     

An Automated Wet Deposition System to Compare the Effects of Reduced and Oxidised N on Ombrotrophic Bog Species: Practical Considerations

Critical N loads for ombrotrophic bogs, which often contain rare and N-sensitive plants (especially those in lower plant groups: lichens, mosses and liverworts), are based on very few experimental data from measured, low background N deposition areas. Additionally the relative effects of reduced versus oxidised N are largely unknown. This paper describes an automated field exposure system (30 km S. of Edinburgh, Scotland) for treating ombrotrophic bog vegetation with fine droplets of oxidised N (NaNO₃) and reduced N (NH₄Cl). Whim Moss exists in an area of low ambient N deposition (ca. 8 kg N ha^–1 y^–1), the sources and quantification of which are described. The wet N treatment system is run continuously, and is controlled/activated by wind speed and rainfall to provide a unique simulation of real world treatment patterns (no rain=no treatment). Simulated precipitation is supplied at ionic concentrations below4mMin rainwater collected on site. Treatments provide a replicated dose response to 16, 32 and 64 kg N ha^–1 y^–1 adjusted for ambient deposition (8 kg N ha^–1 y^–1). The 16 and 64 kg N ha^–1 y^–1 are duplicated with a P+K supplement. Baseline soil chemistry and foliar nutrient status was established for all 44 plots for Calluna vulgaris, Sphagnum capillifolium, Hypnum jutlandicum and Cladonia portentosa.     

Spatially Disaggregated Inventories of Soil NO and N2O Emissions for Great Britain

Estimates of soil N₂O and NOemissions at regional and country scales arehighly uncertain, because the most widely usedmethodologies are based on few data, they do notinclude all sources and do not account forspatial and seasonal variability. To improveunderstanding of the spatial distribution of soilNO and N₂O emissions we have developedsimple multi-linear regression models based onpublished field studies from temperate climates.The models were applied to create spatialinventories at the 5 km² scale of soil NOand N₂O emissions for Great Britain. The N₂O regression model described soilN₂O emissions as a function of soil N input,soil water content, soil temperature and land useand provided an annual N₂O emission of 128 kt N₂O-N yr^-1. Emission rates largerthan 12 kg N₂O-N ha^-1 yr^-1 werecalculated for the high rainfall grassland areasin the west of Great Britain.Soil NO emissions were calculated using tworegression models, which described NO emissionsas a function of soil N input with and without afunction for the water filled pore space. Thetotal annual emissions from both methods, 66 and7 kt NO-N yr^-1, respectively, span the rangeof previous estimates for Great Britain.     

Turnover and vertical transport of zinc by the euphausiid Meganyctiphanes norvegica in the Ligurian Sea

Participatory turnover time is defined as the time required to cycle an element in a system through a given material in that system. The participatory turnover time of ionic zinc by the adult Meganyctiphanes norvegica population in the Ligurian Sea ranged between 498 and 1243 years, depending upon the available food supply, and considering the food chain as the only route for zinc accumulation by the population. A total-impact turnover time was calculated as the sum of the participatory turnover time for live individuals plus the time required for dead euphausiids to lose 90% of their zinc to the water. Carcasses lost zinc to the water slower than either feces or molts, and so established the maximum loss time for all particulate excretion products; nevertheless, total-impact turnover time for zinc did not differ significantly from the participatory turnover time. The net vertical transport of zinc by M. norvegica from the sea surface to any specified depth can be calculated as the sum of the dissolved zinc excreted below the depth plus the concentrations of zinc left in feces, molts, and carcasses after they have sunk to the specified depth. Carcasses sink the fastest and lose the smallest fraction of their zinc concentration during descent; fecal pellets sink the slowest and lose the greatest fraction of their zinc concentration, and molts are intermediate. Nevertheless, feces represents the major route for delivering zinc to the bottom of the Ligurian Sea (2500 m), because concentration of the element in the pellets is so much higher than in carcasses or molts. Excretion of dissolved zinc into the water at the vertical migration depth of the living population during daylight hours was also inconsequential. Feces zinc represented over 80% of the total zinc transported to the sea floor if only marginal food supplies were available to the euphausiids, and over 90% if food was in sufficient supply. M. norvegica can effect a net transport of about 98% of its body zinc concentration below 500 m daily, in conditions of sufficient food supply and assuming that no released products are eaten during descent. If the food supply in the Ligurian Sea is considered only marginal throughout the year, M. norvegica can still effect a daily net transport below 500 m of about 36% of its body concentration, and about 6% of its body concentration will reach 2500 m daily.     

The influence of long term trends in pollutant emissions on deposition of sulphur and nitrogen and exceedance of critical loads in the United Kingdom

In the United Kingdom, as with other European countries, land-based emissions of NO_x and SO₂ have fallen significantly over the last few decades. SO₂ emissions fell from a peak of 3185 Gg S in 1970 to 344 Gg S in 2005 and are forecast by business-as-usual emissions scenarios to fall to 172 Gg by 2020. NO_x emissions were at a maximum of 951 Gg N in 1970 and fell to 378 by 2005 with a further decrease to 243 Gg N forecast by 2020. These large changes in emissions have not been matched by emissions changes for NH₃ which decreased from 315 Gg N in 1990 to 259 in 2005 and are forecast to fall to 222 by 2020. The Fine Resolution Atmospheric Multi-pollutant Exchange model (FRAME) has been applied to model the spatial distribution of sulphur and nitrogen deposition over the United Kingdom during a 15-year time period (1990–2005) and compared with measured deposition of sulphate, nitrate and ammonium from the national monitoring network. Wet deposition of nitrogen and sulphur was found to decrease more slowly than the emissions reductions rate. This is attributed to a number of factors including increases in emissions from international shipping and changing rates of atmospheric oxidation. The modelled time series was extended to a 50-year period from 1970 to 2020. The modelled deposition of SO_x, NO_y and NH_x to the UK was found to fall by 87%, 52% and 25% during this period. The percentage area of sensitive habitats in the United Kingdom for which critical loads are exceeded is estimated to fall from 85% in 1970 to 37% in 2020 for acidic deposition and from 73% to 49% for nutrient nitrogen deposition. The significant reduction in land emissions of SO₂ and NO_x focuses further attention in controlling emissions from international shipping. Future policies to control emissions of ammonia from agriculture will be required to effect further significant reductions in nitrogen deposition.     

Americium adsorption on the surface of macrophytic algae

Data are presented on the rates at which americium (Am) deposits upon blade surfaces of three benthic algal species (Ulva rigida, Fucus vesiculosus and Gigartina stellata) following short-term exposures (1–6 h). Am is taken up in direct proportion to the ambient radionuclide concentration in sea water. Uptake by the green alga was 3 to 5 times greater than that for the brown and red species. Experimental evidence indicated that Am accumulation is a passive process and that adsorption takes place mainly on the thin outer organic coating of the seaweed. The Am transport coefficients (0·9–4·1 × 10?⁵ Bq cm?² s?¹ per Bq ml?¹ sea water) are quite similar to that previously found for the naturally occurring α-emitter ²¹⁰Po, but are an order of magnitude lower than a plutonium transport coefficient reported in the literature. Release of labelled extracellular products associated with the algal surface coating is considered to be responsible for the rapid loss of Am observed previously in macroalgae and may in fact serve as a mechanism for transferring Am to filter feeding zooplankton.     

Biokinetics of plutonium,americium and californium in the marine isopod Cirolana borealis,with observations on its feeding and molting behavior

In a series of laboratory experiments carried out during 1982, the biokinetics of ²³⁷Pu (IV), ²³⁷Pu (V), ²⁴¹Am (III), and ²⁵²Cf (III) were studied in the benthic marine isopod Cirolana borealis Lilljeb. Following a 3 wk exposure to labelled seawater, isopods reached non-equilibrium concentration factors of 52±15, 54±12, 176±14, and 185±53 for Pu (IV), Pu (V), Am and Cf, respectively. Uptake of these radionuclides occurred to a great extent by surface adsorption, with the major fraction of the accumulated radionuclides being associated with exoskeleton and lesser percentages located in gut, digestive gland, muscle and haemolymph. The pattern of radiotracer depuration was in all cases biphasic, with the long-lived retention compartment retaining the largest fraction of whole-body radioactivity. Biological half-lives for radionuclide turnover in the long-lived compartment were 60±3 d, 87±5 d, 261±12 d and 288±60 d for Pu (IV), Pu (V), Am and Cf, respectively. Examination of radionuclide distribution among tissues following longterm depuration showed that the radionuclides were eliminated from internal tissues more rapidly than from the exoskeleton. Uptake and depuration studies indicated that the biokinetics of americium and californium were similar to each other, but that they differed significantly from those of oxidized and reduced plutonium. In general, these experimental results support previous reports that americium and californium are more bioavailable than plutonium in the marine waters. The fraction americium and californium assimilated into tissue from food was very low and did not exceed 5%. Unassimilated labelled food was often retained in the gut for more than 2 mo and released only infrequently in a loosely bound condition. In the event of contamination, this particular feeding-digestion strategy in highly mobile, scavenging isopods could act as a potential biological mechanism for the widespread dispersion of radioactive wastes.