Fate and transport of N-nitrosamines under conditions simulating full-scale groundwater recharge operations.

The key objective of this study was to investigate the attenuation mechanisms of seven N-nitrosamine compounds at environmental concentrations and under conditions relevant to groundwater recharge operations. The study used a combination of controlled laboratory-scale soil-column experiments and groundwater monitoring at a full-scale river-bank filtration facility. Findings of the controlled column experiments suggest that N-nitrosodimethylamine and six other N-nitrosamines (N-nitrosodiethylamine, N-nitrosomethylethylamine, N-nitroso-n-propylamine, N-nitrosodi-n-butylamine, N-nitrosopiperidine, and N-nitrosopyrrolidine) are biodegradable under oxic and anoxic oxidation-reduction conditions. Half lives determined in this study for the targeted compounds varied between 1.3 and 7 days, which will ensure a removal to below detection limits (< 2 ng/L) within short travel times in groundwater recharge systems. Findings of this study suggest that complete removal of N-nitrosamines requires the presence of an adapted biocommunity, which will be established over several weeks to months.     

Regional variation in the chemical composition of winter snow pack and terricolous lichens in relation to sources of acid emissions in the Usa river basin,northeast European Russia

The chemical composition of snow and terricolous lichens was determined along transects through the Subarctic towns of Vorkuta (130 km west-east), Inta (240 km south-north) and Usinsk (140 km, southwest-northeast) in the Usa river basin, northeast European Russia. Evidence of pollution gradients was found on two spatial scales. First, on the Inta transect, northward decreases in concentrations of N in the lichen Cladonia stellaris (from 0.57 mmol N g(-1) at 90 km south to 0.43 mmol N g(-1) at 130 km north of Inta) and winter deposition of non-sea salt sulphate (from 29.3 to 12.8 mol ha(-1) at 90 km south and 110 km north of Inta, respectively) were attributed to long range transport of N and S from lower latitudes. Second, increased ionic content (SO42-, Ca2+, K+) and pH of snow, and modified N concentration and the concentration ratios K+:Mg2+ and K+: (Mg2++Ca2+) in lichens (Cladonia arbuscula and Flavocetraria cucullata) within ca. 25-40 km of Vorkuta and Inta were largely attributed to local deposition of alkaline coal ash. Total sulphate concentrations in snow varied from ca. 5 micromol l(-1) at remote sites to ca. 19 micromol l(-1) near Vorkuta. Nitrate concentration in snow (typically ca. 9 micromol l(-1)) did not vary with proximity to perceived pollution sources.     

Coping with uncertainty: a call for a new science-policy forum

The scientific and policy worlds have different goals, which can lead to different standards for what constitutes "proof" of a change or phenomena, and different approaches for characterizing and conveying uncertainty and risk. These differences can compromise effective communication among scientists, policymakers, and the public, and constrain the types of socially compelling questions scientists are willing to address. In this paper, we review a set of approaches for dealing with uncertainty, and illustrate some of the errors that arise when science and policy fail to coordinate correctly. We offer a set of recommendations, including restructuring of science curricula and establishment of science-policy forums populated by leaders in both arenas, and specifically constituted to address problems of uncertainty.     

Concentrations of dioxin-like PCB congeners in unweathered Aroclors by HRGC/HRMS using EPA Method 1668A

We have determined the congener compositions of nine commercial Aroclor products of polychlorinated biphenyls (PCBs) to the sub-part-per-million level using high-resolution gas chromatography combined with high-resolution mass spectrometry according to US Environmental Protection Agency (EPA) Method 1668A. These Aroclor composition data should allow improved characterization and risk assessment of PCB contamination at hazardous waste sites, particularly for dioxin-like PCB congeners. By combining the data on the concentrations of each dioxin-like congener with its World Health Organization toxicity equivalency factor, we have established dioxin toxic equivalent concentrations for each pure Aroclor product.     

A lysimeter experiment to investigate temporal changes in the availability of pesticide residues for leaching

Leaching of three pesticides (isoproturon, chlorotoluron and triasulfuron) and a tracer (bromide) were determined in four contrasting soils ranging in texture from sandy loam to clay. The compounds were applied to undisturbed columns of soil and four columns for each soil were randomly selected and leached with 24-mm equivalent of water at prescribed time intervals (3, 9, 24, 37 and 57 d after application). A rapid decline in leached loads of isoproturon and chlorotoluron as time from application to irrigation increased was observed in all soils. In contrast, triasulfuron and bromide loads only decreased rapidly in the clay soil. Bromide losses decreased with decreasing clay contents of the soil and therefore with a decrease in structural development. Magnitudes of pesticide losses varied from soil to soil, depending on structural development and the organic carbon content. Pesticide degradation experiments on disturbed and undisturbed soil samples showed that the rapid decline of leached loads with time was faster than could be explained by degradation alone. Five physico-chemical processes are put forward to explain the different patterns of pesticide leached loads observed in the soils: (1) relative extent of preferential flow, (2) sorption capacity of the compounds to the different soils, (3) extent of degradation of the compounds in the soil, (4) variation in sorption kinetics between compounds associated with pesticide diffusion into soil aggregates, and (5) protection of the compounds by a combination of intra-aggregate diffusion and the presence of preferential flow pathways.     

Global change and the boreal forest: thresholds, shifting states or gradual change?

Changes in boreal climate of the magnitude projected for the 21st century have always caused vegetation changes large enough to be societally important. However, the rates and patterns of vegetation change are difficult to predict. We review evidence suggesting that these vegetation changes may be gradual at the northern forest limit or where seed dispersal limits species distribution. However, forest composition may be quite resilient to climate change in the central portions of a species range until some threshold is surpassed. At this point, changes can be rapid and unexpected, often causing a switch to very different ecosystem types. Many of these triggers for change are amenable to management, suggesting that our choice of policies in the coming decades will substantially influence the ecological and societal consequences of current climatic change.     

Nitrogen trace gas emissions from a riparian ecosystem in southern Appalachia

In this paper, we present two years of seasonal nitric oxide (NO), ammonia (NH₃), and nitrous oxide (N₂O) trace gas fluxes measured in a recovering riparian zone with cattle excluded and adjacent riparian zone grazed by cattle. In the recovering riparian zone, average NO, NH₃, and N₂O fluxes were 5.8, 2.0, and 76.7 ng N m⁻² s⁻¹ (1.83, 0.63, and 24.19 kg N ha⁻¹ y⁻¹), respectively. Fluxes in the grazed riparian zone were larger, especially for NO and NH₃, measuring 9.1, 4.3, and 77.6 ng N m⁻² s⁻¹ (2.87, 1.35, and 24.50 kg N ha⁻¹ y⁻¹) for NO, NH₃, and N₂O, respectively. On average, N₂O accounted for greater than 85% of total trace gas flux in both the recovering and grazed riparian zones, though N₂O fluxes were highly variable temporally. In the recovering riparian zone, variability in seasonal average fluxes was explained by variability in soil nitrogen (N) concentrations. Nitric oxide flux was positively correlated with soil ammonium (NH₄⁺) concentration, while N₂O flux was positively correlated with soil nitrate (NO₃⁻) concentration. Ammonia flux was positively correlated with the ratio of NH₄⁺ to NO₃⁻. In the grazed riparian zone, average NH₃ and N₂O fluxes were not correlated with soil temperature, N concentrations, or moisture. This was likely due to high variability in soil microsite conditions related to cattle effects such as compaction and N input. Nitric oxide flux in the grazed riparian zone was positively correlated with soil temperature and NO₃⁻ concentration. Restoration appeared to significantly affect NO flux, which increased ≈600% during the first year following restoration and decreased during the second year to levels encountered at the onset of restoration. By comparing the ratio of total trace gas flux to soil N concentration, we show that the restored riparian zone is likely more efficient than the grazed riparian zone at diverting upper-soil N from the receiving stream to the atmosphere. This is likely due to the recovery of microbiological communities following changes in soil physical characteristics.     

Volatile hydrocarbon emissions from a diesel fuel-contaminated soil bioremediation facility

Concerns have been expressed that emissions of volatile hydrocarbons (HCs) from bioremediation facilities containing soils contaminated with petroleum HCs may negatively impact regional air quality or human health. Little information is available regarding the emission of HCs from bioremediation sites, and few field studies have been performed during which the flux of HCs has been directly measured during bioremediation. To aid in answering questions about the impact of bioremediation facilities on the atmospheric environment, a two-part field study was conducted over summer 1996 at a remote landfarm in northern Ontario where diesel fuel-contaminated soil was undergoing bioremediation. Volatile total hydrocarbon (THC) atmospheric flux measurements were successfully taken over 18 days using a flux gradient micrometeorological technique incorporating a THC detector constructed in-house. Peak THC emissions reached 131 microg C/m2/sec shortly after implementation and tilling of the landfarm soil. The influence of soil temperature and tillage on THC emissions was examined. Off-site inhalation exposure was considered with the aid of an areal source model and results from speciated air samples collected on sorbent tubes and analyzed via gas chromatography/mass spectrometry (GCMS) techniques.     

The histology,histochemistry and ultrastructure of the cement apparatus of three adult sessile barnacles,Elminius modestus,Balanus balanoides and Balanus hameri

The histology, histochemistry and ultrastructure of the cement gland cells of 3 species of sessile barnacles are described. Cells of both Elminius modestus Darwin and Balanus balanoides (L.) (membranous bases) are similar histologically and ultrastructurally, and within the cells there are 2 distinct regions. One is the site of secretion accumulation, the other the site of secretion synthesis. In Balanus hameri Ascanius (calcareous base) the cells are different in that the cytoplasm is more homogeneous. In all 3 species protein is the final secretion product (cement) of the cement cells. The mode of discharge of secretion from the cells differs between the membrane based and calcareous based barnacles. In the former, there is a series of collecting canals within the cytoplasm of the cement cells (intracellular canals) which join with the larger extracellular cement ducts. Secretion passes into the intracellular canals and is moved along to the larger cement ducts, which have an inner chitin lining. In Balanus hameri (calcareous base) there are no intracellular collecting canals. Secretions are thought to pass from the cement cells into the cement duct cells direct. The cement ducts in this species are not chitin lined.     

The effects on welfare of the imposition of individual transferable quotas on a heterogeneous fishing fleet

This paper examines the determination of effort levels, the rental price of quotas and the number of participants in a fishery managed with a total allowable catch and individual transferable quotas. How these variables change is determined for three phases of the management process. Potential participants in the fishery are assumed to be heterogeneous in their catching capabilities so that almost all active fishers earn positive net profits from fishing activities. It is shown that these quasirents are reduced during any of the management phases considered here. The impact of free allocations of permanent quota rights on fishers’ welfare is also considered. This may increase the welfare of all fishers if the allocation is based on catch history. However, an example is provided where the welfare of some highliners is reduced when the allocation is based on effort history.