The Oxidation of Hydrocarbons on Simple Oxide Catalysts

A simple practical scheme for prediction and control of short duration air pollution maxima from a single source is demonstrated for a particular source-site geometry. The method makes use of a number of traditional semi-empirical atmospheric turbulence and diffusion relations in a different application. The concepts stressed in the current example are: (1) the incorporation of interactions of high frequency turbulence and low frequency meandering of the wind into a concentration forecast and (2) the use of source-site geometry to simplify the practical problem as much as possible.     

Nutrient cycling by fish supports relatively more primary production as lake productivity increases

Animals can be important in nutrient cycling in particular ecosystems, but few studies have examined how this importance varies along environmental gradients. In this study we quantified the nutrient cycling role of an abundant detritivorous fish species, the gizzard shad (Dorosoma cepedianum), in reservoir ecosystems along a gradient of ecosystem productivity. Gizzard shad feed mostly on sediment detritus and excrete sediment-derived nutrients into the water column, thereby mediating a cross-habitat translocation of nutrients to phytoplankton. We quantified nitrogen and phosphorus cycling (excretion) rates of gizzard shad, as well as nutrient demand by phytoplankton, in seven lakes over a four-year period (16 lake-years). The lakes span a gradient of watershed land use (the relative amounts of land used for agriculture vs. forest) and productivity. As the watersheds of these lakes became increasingly dominated by agricultural land, primary production rates, lake trophic state indicators (total phosphorus and chlorophyll concentrations), and nutrient flux through gizzard shad populations all increased. Nutrient cycling by gizzard shad supported a substantial proportion of primary production in these ecosystems, and this proportion increased as watershed agriculture (and ecosystem productivity) increased. In the four productive lakes with agricultural watersheds (>78% agricultural land), gizzard shad supported on average 51% of phytoplankton primary production (range 27-67%). In contrast, in the three relatively unproductive lakes in forested or mixed-land-use watersheds (>47% forest, <52% agricultural land), gizzard shad supported 18% of primary production (range 14-23%). Thus, along a gradient of forested to agricultural landscapes, both watershed nutrient inputs and nutrient translocation by gizzard shad increase, but our data indicate that the importance of nutrient translocation by gizzard shad increases more rapidly. Our results therefore support the hypothesis that watersheds and gizzard shad jointly regulate primary production in reservoir ecosystems.     

Early Effects of Atmospheric Ammonia Deposition on Calluna Vulgaris (L.) Hull Growing on an Ombrotrophic Peat Bog

This paper reports data from a field study investigating the impacts of elevated ammonia (NH₃) deposition on Calluna vulgaris growing on an ombrotrophic peat bog in S.E. Scotland. Shoot extension, foliar N concentrations, chlorophyll concentration and chlorophyll fluorescence were measured during the second growing season of exposure to a gradient of ammonia concentrations. Results indicate that NH₃ increases growth between 150–200 kg N ha^–1y^–1 cumulative deposition. Foliar N content increased significantly in response to NH₃ cumulative deposition up to 400 kg N ha^–1 y^–1 whereas chlorophyll a content significantly decreased. Measurements of Fv/Fm suggest that although NH₃ exposure altered the growth and reduced chlorophyll a, the efficiency of photosystem II was insensitive to NH₃-N deposition at this stage.     

Dry Weather Water Quality Loadings in Arid,Urban Watersheds of the Los Angeles Basin,California, USA1

Abstract: Dry weather runoff in arid, urban watersheds may consist entirely of treated wastewater effluent and/or urban nonpoint source runoff, which can be a source of bacteria, nutrients, and metals to receiving waters. Most studies of urban runoff focus on stormwater, and few have evaluated the relative contribution and sources of dry weather pollutant loading for a range of constituents across multiple watersheds. This study assessed dry weather loading of nutrients, metals, and bacteria in six urban watersheds in the Los Angeles region of southern California to estimate relative sources of each constituent class and the proportion of total annual load that can be attributed to dry weather discharge. In each watershed, flow and water quality were sampled from storm drain and treated wastewater inputs, as well as from in‐stream locations during at least two time periods. Data were used to calculate mean concentrations and loads for various sources. Dry weather loads were compared with modeled wet weather loads under a range of annual rainfall volumes to estimate the relative contribution of dry weather load. Mean storm drain flows were comparable between all watersheds, and in all cases, approximately 20% of the flowing storm drains accounted for 80% of the daily volume. Wastewater reclamation plants (WRP) were the main source of nutrients, storm drains accounted for almost all the bacteria, and metals sources varied by constituent. In‐stream concentrations reflected major sources, for example nutrient concentrations were highest downstream of WRP discharges, while in‐stream metals concentrations were highest downstream of the storm drains with high metals loads. Comparison of wet vs. dry weather loading indicates that dry weather loading can be a significant source of metals, ranging from less than 20% during wet years to greater than 50% during dry years.     

Environmental chemistry of PCB-replacement compounds - VI - composition and metabolism of Wemcol ®, an isopropylbiphenyl formulation

Wemcol is a technical isopropylbiphenyl formulation that is used as a substitute for polychlorobiphenyl. According to the producer Wemcol is 4-isopropylbiphenyl, but we found our sample to consist of 60.3% 3-isopropylbiphenyl, 38.6% 4-isopropylbiphenyl and 3,5-, 3,3′-, 3,4′- and 4,4′-diisopropylbiphenyl in amounts of 0.3%, 0.4%, 0.2% and 0.1% respectively. The two major components of the mixture are metabolized in the rat by two routes : oxidation of the isopropyl group and hydroxylation of the aromatic nuclei. Rats fed the technical mixture retained 3- and 4-isopropylbiphenyl in a ratio 4.3 : 1 in their abdominal fat, whilst the ratio in the mixture is 1.6 : 1. One week after the simultaneous feeding of equal amounts of Wemcol, 4,4′-dichlorobiphenyl, 2,4′,5-trichlorobiphenyl and 2,2′,5,5′-tetrachlorobiphenyl, the isopropylbiphenyls, in contrast to the chlorobiphenyls, could no longer be detected in the abdominal fat of rats.     

Chemical contaminants in juvenile gray whales (Eschrichtius robustus) from a subsistence harvest in Arctic feeding grounds

Gray whales are coastal migratory baleen whales that are benthic feeders. Most of their feeding takes place in the northern Pacific Ocean with opportunistic feeding taking place during their migrations and residence on the breeding grounds. The concentrations of organochlorines and trace elements were determined in tissues and stomach contents of juvenile gray whales that were taken on their Arctic feeding grounds in the western Bering Sea during a Russian subsistence harvest. These concentrations were compared to previously published data for contaminants in gray whales that stranded along the west coast of the US during their northbound migration. Feeding in coastal waters during their migrations may present a risk of exposure to toxic chemicals in some regions. The mean concentration (standard error of the mean, SEM) of sigmaPCBs [1400 (130) ng/g, lipid weight] in the blubber of juvenile subsistence whales was significantly lower than the mean level [27,000 (11,000) ng/g, lipid weight] reported previously in juvenile gray whales that stranded in waters off the west coast of the US. Aluminum in stomach contents of the subsistence whales was high compared to other marine mammal species, which is consistent with the ingestion of sediment during feeding. Furthermore, the concentrations of potentially toxic chemicals in tissues were relatively low when compared to the concentrations in tissues of other marine mammals feeding at higher trophic levels. These chemical contaminant data for the subsistence gray whales substantially increase the information available for presumably healthy animals.