Interactive effects of ozone and elevated carbon dioxide on the growth and physiology of black cherry, green ash, and yellow-poplar seedlings

Potted seedlings of black cherry (Prunus serotina Ehrh.) (BC), green ash (Fraxinus pennsylvanica Marsh.) (GA), and yellow-poplar (Liriodendron tulipifera L.) (YP) were exposed to one of the four treatments: (1) charcoal-filtered air (CF) at ambient CO(2) (control); (2) twice ambient O(3) (2 x O(3)); (3) twice ambient CO(2) (650 microl l(-1)) plus CF air (2 x CO(2)); or (4) twice ambient CO(2) (650 microl l(-1)) plus twice ambient O(3) (2 x CO(2) + 2 x O(3)). The treatments were duplicated in eight continuously stirred tank reactors for 10 weeks. Gas exchange was measured during the last 3 weeks of treatment and all seedlings were destructively harvested after 10 weeks. Significant interactive effects of O(3) and CO(2) on the gas exchange of all three species were limited. The effects of elevated CO(2) and O(3), singly and combined, on light-saturated net photosynthesis (A(max)) and stomatal conductance (g(s)) were inconsistent across species. In all three species, elevated O(3) had no effect on g(s). Elevated CO(2) significantly increased A(max) in GA and YP foliage, and decreased g(s) in YP foliage. Maximum carbon exchange rates and quantum efficiencies derived from light-response curves increased, while compensation irradiance and dark respiration decreased in all three species when exposed to 2 x CO(2). Elevated O(3) affected few of these parameters but any change that was observed was opposite to that from exposure to 2 x CO(2)-air. Interactive effects of CO(2) and O(3) on light-response parameters were limited. Carboxylation efficiencies, derived from CO(2)-response curves (A/C(i) curves) decreased only in YP foliage exposed to 2 x CO(2)-air. In general, growth was significantly stimulated by 2 x CO(2) in all three species; though there were few significant growth responses following exposure to 2 x O(3) or the combination of 2 x CO(2) plus 2 x O(3). Results indicate that responses to interacting stressors such as O(3) and CO(2) are species specific.     

The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater

Data from long-term groundwater sampling, limited coring, and associated studies are synthesised to assess the variability and intrinsic remediation/natural attenuation of a dissolved hydrocarbon plume in sulphate-rich anaerobic groundwater. Fine vertical scale (0.25- and 0.5-m depth intervals) and horizontal plume-scale (>400 m) characteristics of the plume were mapped over a 5-year period from 1991 to 1996. The plume of dissolved BTEX (benzene, toluene, ethylbenzene, xylene) and other organic compounds originated from leakage of gasoline from a subsurface fuel storage tank. The plume was up to 420 m long, less than 50 m wide and 3 m thick. In the first few years of monitoring, BTEX concentrations near the point of leakage were in approximate equilibrium with non-aqueous phase liquid (NAPL) gasoline. NAPL composition of core material and long-term trends in ratios of BTEX concentrations in groundwater indicated significant depletion (water washing, volatilisation and possibly biodegradation) of benzene from residual NAPL after 1992. Large fluctuations in BTEX concentrations in individual boreholes were shown to be largely attributable to seasonal groundwater flow variations. A combination of temporal and spatial groundwater quality data was required to adequately assess the stationarity of plumes, so as to allow inference of intrinsic remediation. Contoured concentration data for the period 1991 to 1996 indicated that plumes of toluene and o-xylene were, at best, only partially steady state (pseudo-steady state) due to seasonal groundwater flow changes. From this analysis, it was inferred that significant remediation by natural biodegradation was occurring for BTEX component plumes such as toluene and o-xylene, but provided no conclusive evidence of benzene biodegradation. Issues associated with field quantification of intrinsic remediation from groundwater sampling are highlighted. Preferential intrinsic biodegradation of selected organic compounds within the BTEX plume was shown to be occurring, in parallel with sulphate reduction and bicarbonate production. Ratios of average hydrocarbon concentrations to benzene for the period 1991 to 1992 were used to estimate degradation rates (half-lives) at various distances along the plume. The estimates varied with distance, the narrowest range being, for toluene, 110 to 260 days. These estimates were comparable to rates determined previously from an in situ tracer test and from plume-scale modelling.     

Measurements of peroxyacyl nitrates (PANS) in Mexico City: implications for megacity air quality impacts on regional scales

Peroxyacyl nitrates (PANs) were measured using gas chromatography with electron capture detection (GC/ECD) in north central Mexico City during February–March of 1997. Peroxyacetyl nitrate (PAN) was observed to exceed 30 ppb during five days of the study, with peroxypropionyl nitrate (PPN) and peroxybutryl nitrate (PBN) reaching 6 and 1 ppb maximum, respectively. Levels of total PANs typically exceeded 10 ppb during the period of measurement and showed a very strong diurnal variation with PANs maximum during the early afternoon and falling to less than 0.1 ppb during the evening hours. These levels of PANs are the highest reported values in North America (and the world) for an urban center, since levels of approximately 30 ppb were reported during the late 1970s in the Los Angeles area (South Coast Air Basin, Tuazon et al., 1978). Hydrocarbon measurements indicate that the levels of olefins, specifically butenes are significant in Mexico City. A time series taken of source indicator hydrocarbons taken before and during a Mexican National Holiday with reduced automobile traffic clearly show that mobile sources of butenes are as important as liquefied petroleum gas. Observations of 10–40 ppb C methyl-t-butyl ether (MTBE) are consistent with MTBE/gasoline fuel usage as a source of isobutene and formaldehyde. Both these reactive species can lead to increased oxidant and PAN formation. The strong diurnal profiles of PANs are consistent with regional clearing of the Mexico City air basin on a daily basis. Estimates are given using a simple box model calculation for a number of key primary and secondary pollutant emissions from this megacity on an annual basis. These calculations indicate that megacities can be important sources of both primary and secondary pollutants, and that PANs produced in megacity environments are likely to contribute strongly to regional scale ozone and aerosol productions during long range transport.     

Ozone patterns for three metropolitan statistical areas in North Carolina, USA

As part of an effort by the state of North Carolina to develop a State Implementation Plan (SIP) for 1-h peak ozone control, a network of ozone stations was established to monitor surface ozone concentrations across the state. Between 19 and 23 ozone stations made continuous surface measurements between 1993 and 1995 surrounding three major metropolitan statistical areas (MSAs): Raleigh/Durham (RDU), Charlotte/Mecklenburg (CLT), and Greensboro/High Point/Winston-Salem (GSO). Statistical averages of the meteorological and ozone data were performed at each Metropolitan Statistical Area (MSA) to study trends and/or relationships on high ozone days (days in which one of the MSA sites measured an hourly ozone concentration90.0 ppbv). County emission maps of precursor gases, wind roses, total area averages of ozone, total downwind averages of ozone deviations, upwind averages of ozone, and a modified delta ozone analysis were all obtained and analyzed. The results of this study show a reduction in the delta ozone relative to an earlier study at RDU, but no average significant change at CLT (no comparison can be made for GSO). The statistical data analyses in this study are used to quantify the importance of local contributions and regional transport, to ozone air pollution in the MSAs.     

Organochlorine pesticide residues in human milk in Punjab, India

Human milk samples collected from areas having intensive cotton cultivation and sparse cotton cultivation in Punjab (India) were analysed for organochlorine insecticides. Both DDT and HCH were detected in almost all the samples analysed. The average levels of Sigma-DDT and Sigma-HCH residues in samples from cotton-growing areas were significantly higher than in those from areas where cotton is sparsely grown. Residues of Sigma-DDT mainly comprised p,p'-DDT and p,p'-DDE, while those of Sigma-HCH residues were mainly in the form of its beta-isomer. Median values of 0.52 microg g(-1) of Sigma-DDT and 0.19 microg g(-1) of Sigma-HCH in samples of human milk from cotton-growing areas of Punjab (India) were higher than those reported from most other countries in the World.     

Sensitivity of the terrestrial biosphere to climatic changes: impact on the carbon cycle

The biosphere is a major pool in the global carbon cycle; its response to climatic change is therefore of great importance. We developed a 5 degrees x 5 degrees longitude-latitude resolution model of the biosphere in which the global distributions of the major biospheric variables, i.e. the vegetation types and the main carbon pools and fluxes, are determined from climatic variables. We defined nine major broad vegetation types: perennial ice, desert and semi-desert, tundra, coniferous forest, temperate deciduous forest, grassland and shrubland, savannah, seasonal tropical forest and evergreen tropical forest. Their geographical repartition is parameterized using correlations between observed vegetation type, precipitation and biotemperature distributions. The model computes as a function of climate and vegetation type, the variables related to the continental biospheric carbon cycle, i.e. the carbon pools such as the phytomass, the litter and the soil organic carbon; and carbon fluxes such as net primary production, litter production and heterotrophic respiration. The modeled present-day biosphere is in good agreement with observation. The model is used to investigate the response of the terrestrial biosphere to climatic changes as predicted by different General Circulation Models (GCM). In particular, the impact on the biosphere of climatic conditions corresponding to the last glacial climate (LGM), 18 000 years ago, is investigated. Comparison with results from present-day climate simulations shows the high sensitivity of the geographical distribution of vegetation types and carbon content as well as biospheric trace gases emissions to climatic changes. The general trend for LGM compared to the present is an increase in low density vegetation types (tundra, desert, grassland) to the detriment of forested areas, in tropical as well as in other regions. Consequently, the biospheric activity (carbon fluxes and trace gases emissions) was reduced.     

Short-term effects of metals on the filtration rate of the zebra mussel Dreissena polymorpha

In order to study the short-term ecotoxicity of metals to the freshwater mussel Dreissena polymorpha, the effects of Cu, Zn and Cd on the filtration rate of this mussel were determined in laboratory experiments. Filtration rate was chosen as the endpoint, because it is a sensitive sublethal parameter compared to mortality and it is an important parameter given the ecological role D. polymorpha fulfills. The filtration rate was calculated from the decrease in algal concentration, fed to mussels in aquaria, containing different metal concentrations. The EC50 for Cu (41 microg litre(-1)) was lower than for Cd (388 microg litre(-1)) and Zn (1350 microg litre(-1)). The NOEC(accumulation) for the essential metal Zn was higher than for the essential metal Cu. Cadmium, a non-essential metal, was accumulated at all elevated water concentrations, so the NOEC(accumulation) was the concentration in the control water (<0.2 microg litre(-1)). All (no) effect concentrations found in this study were above the quality criteria set for metal concentrations in Dutch surface water, suggesting that the zebra mussel is sufficiently protected by these quality criteria.     

Polycyclic aromatic compounds in Northwest Atlantic COD (Gadus morhua)

Twenty-seven polycyclic aromatic compounds (PAC) including polycyclic aromatic hydrocarbons (PAH) and polycyclic aromatic sulphur heterocycles were analysed in muscle, liver and ovaries of cod (Gadus morhua) from the Northwest Atlantic. These PAC include the 16 PAH priority pollutants (EPA recommendation), alkylated naphthalenes, phenanthrene-anthracenes as well as dibenzothiophenes (DBT). Aromatics were undetectable in muscle. One of the analysed PAC was detected in one ovary and six in another ovary sample. Liver samples contained between 1 and 9 PAC. Of the parental PAH, only acenapthene (18 ng/g, dry weight), fluorene (28 ng/g) and chrysene (22 ng/g) were detected once each in two liver samples, while fluorene (72 ng/g) was detected once in one of the ovaries. C-2 DBT was the major component in ovaries and liver (8-86 ng/g), while C-3 and C-4 alkylated phenanthrene-anthracene (12-78 ng/g) were the next major components detected in the liver samples. This is the first detailed study of PAH and PAC in finfish from the Northwest Atlantic.     

Petroleum hydrocarbons in the nearshore marine sediments of the United Arab Emirates

The concentrations of total petroleum hydrocarbons (TPH) were determined in nearshore sediment samples collected from 28 sampling sites along the United Arab Emirates shorelines on the Arabian Gulf, the Gulf of Oman and seven major creeks (khors) extending from them. Concentrations were highly variable and ranged between <0.4 and 212 microg g(-1) dry weight, and the highest values obtained were in the top sediment (1 cm) layer near a fuel filling station and port areas. Locally high levels of TPH were found in Dubai, Sharjah and Ajman semi-enclosed creeks where boat activities and land-based wastewater discharges are most common. Data support the premise that port activities, fuel filling stations and land-based wastewater discharges are major sources of pollution in the study area. Correlations with sediment grain size, total organic carbon (TOC) and distance from pollution sources are discussed.     

Simulation of pesticide runoff at Rosemaund Farm (UK) using the SoilFug model

A validation exercise of the SoilFug model using field runoff data from Rosemaund Farm (UK) is described. A comparison has been made of modelled and measured concentrations of several pesticides in surface water and soil during and after specific rain events following application. The field experiments were designed to obtain data on rainfall, outflows of water, pesticide application rates and concentrations in soil and water. The results were satisfactory for the undissociated pesticides (atrazine, carbofuran, dimethoate, isoproturon, lindane, simazine and trifluralin), whose concentrations in water were mostly predicted within an order of magnitude of measured data. The results for the dissociated pesticides (dichlorprop, MCPA, mecoprop) were less satisfactory, giving generally much higher predicted concentrations in water. The use of the SoilFug model is suggested for the calculation of predicted environmental concentrations (PECs) in water, since it generally produces acceptable results from a relatively small set of input data, most of which is generally available.