Fixed Sampling Locations Research Articles

Oceanic Suess effect of δ13C in subpolar region: The North Pacific

We propose a simple approach for estimating the recent oceanic Suess effect of δ13C in the subpolar region of the North Pacific, an area which experiences a large seasonal variability of carbonate species, due to the biological activity and vertical water mixing. This approach is based simply on time‐series data of δ13C from July 1997 to July 2001 and an equation of the Fourier sine expansion. Applying our approach to the fixed sampling location in the western North Pacific, station ‘KNOT’, we estimated values of −0.012‰‐δ13C yr−1 for the Suess effect of δ13C with an amplitude of 1.3‰‐δ13C and 1.0 μmol‐C kg−1 yr−1 for the increase rate of dissolved inorganic carbon with an amplitude of 134 μmol‐C kg−1 in surface water. The Suess effect of δ13C in this region was a similar value to that estimated in the Southern Ocean producing the deep water, while it was half as much as values estimated in the subtropical regions which experience a small seasonal variability. The ratio of Suess effect to the increase rate of dissolved inorganic carbon was −0.012‰ (μmol kg−1)−1, which was different from the global mean values calculated by recent modeling study. Therefore, we conclude that the Suess effect of δ13C in the polar and subpolar regions is generally smaller than found in other regions, suggesting that it is necessary to reevaluate the uptake rate of anthropogenic carbon which has been based on the assumption that the ratio is uniform over the entire ocean.

Exposure to dust and particle-associated 1-nitropyrene of drivers of diesel-powered equipment in underground mining.

A field study was conducted in two mines in order to determine the most suitable strategy for ambient exposure assessment in the framework of a European study aimed at validation of biological monitoring approaches for diesel exhaust (BIOMODEM). Exposure to dust and particle-associated 1-nitropyrene (1-NP) was studied in 20 miners of black coal by the long wall method (Czech Republic) and in 20 workers in oil shale mining by the room and pillar method (Estonia). The study in the oil shale mine was extended to include 100 workers in a second phase (main study). In each mine half of the study population worked underground as drivers of diesel-powered trains (black coal) and excavators (oil shale). The other half consisted of workers occupied in various non-diesel production assignments. Exposure to diesel exhaust was studied by measurement of inhalable and respirable dust at fixed locations and by personal air sampling of respirable dust. The ratio of geometric mean inhalable to respirable dust concentration was approximately two to one. The underground/surface ratio of respirable dust concentrations measured at fixed locations and in the breathing zones of the workers was 2-fold or greater. Respirable dust was 2- to 3-fold higher in the breathing zone than at fixed sampling locations. The 1-NP content in these dust fractions was determined by gas chromatography-mass spectrometry/mass spectrometry and ranged from 0.003 to 42.2 ng/m(3) in the breathing zones of the workers. In mine dust no 1-NP was detected. In both mines 1-NP was observed to be primarily associated with respirable particles. The 1-NP concentrations were also higher underground than on the surface (2- to 3-fold in the coal mine and 10-fold or more in the oil shale mine). Concentrations of 1-NP in the breathing zones were also higher than at fixed sites (2.5-fold in the coal mine and 10-fold in the oil shale mine). For individual exposure assessment personal air sampling is preferred over air sampling at fixed sites. This study also suggests that particle-associated 1-NP much better reflects the ambient exposure to diesel exhaust particles than dust concentrations. Therefore, measurement of particle-associated 1-NP is preferred over measurement of dust concentrations by gravimetry, when linking ambient exposure to biomonitoring outcomes such as protein and DNA adducts and excretion of urinary metabolites of genotoxic substances.

Parasitism of Dinophysis norvegica by Amoebophrya sp. in the Baltic Sea

The temporal and vertical distribution of the infection of the dinoflagellate Dinophysis norvegica by the endoparasite Amoebophrya sp. was investigated at a fixed sampling location in the Baltic Sea during 2000 and 2001. Infected hosts were detected by epifluorescence microscopy after DAPI staining. The maximum depth-averaged parasite prevalence was 2.3 % in July 2000 and 1.8 % in August 2001. The percentage of infected hosts was usually higher close to the thermocline than at the surface. The highest parasite prevalence at a specific depth (4.8 %) was found at 20 m in August 2001. No correlation was observed between parasite prevalence and host abundance or dissolved nutrient (N and P) concentrations, neither for depth-averaged nor discrete depth measurements. However, temperature seemed to be an important factor influencing infection of D. norvegica by Amoebophrya sp., with infected host cells observed only above 12degreesC. Amoebophrya sp. was only sporadically observed inside other dinoflagellate species, indicating specificity towards D. norvegica. The seasonal pattern of infection suggests the existence of a dormancy stage of the parasite dinospores. The low prevalence observed during this study indicates that parasitism by Amoebophrya sp. is not a relevant loss factor for D. norvegica in the Baltic Sea. (Less)

The expected mass fraction

A new measure is introduced to characterize the reduction of concentration values found in a contaminant cloud. The “expected mass fraction” presents the mass of contaminant (or exposure time) at the various contaminant concentration values observed when a contaminant cloud passes over a fixed sampling location. This measure is shown to be easy to compile and to provide a reasonable ensemble average approximation with as few cloud releases as would be required for the more conventional dosage measurement. The new measure is shown to have a good prospect of theoretical predictability due to its definition in terms of the one-point probability density function of contaminant concentration and recent advances in predicting the moments of that probability density function. Experiments from the Warren Spring Laboratory are used to illustrate the application of the “expected mass fraction”.

Spatial Variation in Denitrification: Dependency of Activity Centers on the Soil Environment

AbstractThe spatial variation in field denitrification rates was studied in an acid soil where the sole denitrification end product was N2O. The rate of N2O accumulation was measured under a soil cover at 30 fixed sampling locations arranged in a grid. Water and NO3 were added prior to all measurements to provide soil water contents at or above field capacity and excess NO3 for denitrification. No significant differences in N2O production rates were observed in samples incubated with or without C2H2, indicting that nitrification is not a significant source of N2O in this soil. Denitrification was found to occur in “hot spots” in moist soil and throughout the soil volume if the soil was flooded. Denitrification rates followed a skewed frequency distribution when soil water content was at field capacity: most locations had low activity, and a few locations exhibited high activity. The frequency distribution of denitrification rates was less skewed in samples after flooding, following large additions of glucose, or when the vegetation underwent decay in the fall. The intensity of denitrification was much higher after flooding than following glucose addition. A few sample locations occasionally showed outstandingly high denitrification rates when at field capacity, as well as when flooded. The activity in these hot spots approximated the potential denitrification activity of that soil.

A Longitudinal Study of Screwworm Populations, Cochliomyia Hominivorax (Diptera: Calliphoridae), in Northern Veracruz, Mexico

Screwworm populations ( Cochliomyia hominivorax ) were followed continuously from May 1974 to September 1975 in a 5180-km2 area of northern Veracruz, Mexico. The census data were provided by screwworm ovipositions on the artificially inflicted wounds of sentinel sheep distributed among 9–13 fixed sampling locations. A weekly arithmetic mean of 3.68 egg masses per sampling site with variance 22.65 was estimated for the 73-wk study period. Maximum ovipositions were recorded in May–June and the minimum in November–February. High variance to mean ratios were typical of weekly data. The modal weekly number of ovipositions per station was zero followed in frequency by 1, 2, 3 … etc, egg masses. The spatially and temporally clustered pattern of ovipositions was shown to follow the negative binomial distribution. This aggregated distribution is consistent with an hypothesis that most ovipositions are generated by locally reared and mated screwworms. Census data from 2 pairs of contiguously located sampling stations were not significantly correlated, providing further support for the hypothesis of highly localized mating and subsequent oviposition. Schedules of adult survival and oviposition were estimated to a 1st approximation. The estimates allowed the establishment of a presumptive relationship between adult female density and the resulting density of screwworm ovipositions. In the cool months of November–March ca 3–6% of hypothetically stable screwworm populations oviposit daily. In the warm months of May–October ca 10–16% oviposit daily. Average cool-season screwworm oviposition densities were ca ¼ the mean warm-season magnitudes. When corrected for the effects of temperature on frequency of oviposition and expectation of life, it was found that the cool-season ovipositions were presumptively generated by approximately 2–4 times the adults than were equal warm-season ovipositions. The average density of screwworm adults in the cool season then becomes approximately equal to ½ the magnitude of warm-season adult populations.

The effect of drop size on emissions from the primary zone of a gas turbine type combustor

Some of the important variables influencing the processes of liquid fuel combustion and pollutant generation are: i) fuel drop size, ii) local equivalence ratio, iii) inlet air temperature, iv) combustor pressure, v) residence time, and vi) recirculation. In order to isolate the effects of these variables a research type combustor has been designed and is now operative. The combustor uses an air-fuel preparation system which allows independent and controlled variation of each of the above variables. A stable flame can be maintained within the combustor without the aid of an artificial flame holder. Pollutant level measurements have been made for the following range of conditions: o i) spray Sauter mean diameter 26–45 μm ii) primary zone equivalence ratio 0.9–1.1 Unheated inlet air was used for these tests with the combustor exhausting into the open atmosphere. The emission samples were extracted at a point 6-1/2 in. from the injector plate along the combustor axis. Results from the measurements made so far show the following trends at the fixed sampling location for decreasing drop size: i) a decrease in the unburned hydrocarbon levels, ii) an increase in CO level at the point of sapling, and iii) a decrease in the mean values of NO concentrations. Mathematical analysis of the emission data successfully predicted the presence of solid carbon for large drops and the lack of same with the smaller drops.