Bromus tectorum invasion alters nitrogen dynamics in an undisturbed arid grassland ecosystem

The nonnative annual grass Bromus tectorum has successfully replaced native vegetation in many arid and semiarid ecosystems. Initial introductions accompanied grazing and agriculture, making it difficult to separate the effects of invasion from physical disturbance. This study examined N dynamics in two recently invaded, undisturbed vegetation associations (C3 and C4). The response of these communities was compared to an invaded/ disturbed grassland. The invaded/disturbed communities had higher surface NH4+ input in spring, whereas there were no differences for surface input of NO3-. Soil inorganic N was dominated by NH4+, but invaded sites had greater subsurface soil NO3-. Invaded sites had greater total soil N at the surface four years post-invasion in undisturbed communities, but total N was lower in the invaded/disturbed communities. Soil delta15N increased with depth in the noninvaded and recently invaded communities, whereas the invaded/disturbed communities exhibited the opposite pattern. Enriched foliar delta15N values suggest that Bromus assimilated subsurface NO3-, whereas the native grasses were restricted to surface N. A Rayleigh distillation model accurately described decomposition patterns in the noninvaded communities where soil N loss is accompanied by increasing soil delta15N; however, the invaded/ disturbed communities exhibited the opposite pattern, suggesting redistribution of N within the soil profile. This study suggests that invasion has altered the mechanisms driving nitrogen dynamics. Bromus litter decomposition and soil NO3- concentrations were greater in the invaded communities during periods of ample precipitation, and NO3- leached from the surface litter, where it was assimilated by Bromus. The primary source of N input in these communities is a biological soil crust that is removed with disturbance, and the lack of N input by the biological soil crust did not balance N loss, resulting in reduced total N in the invaded/disturbed communities. Bromus produced a positive feedback loop by leaching NO3- from decomposing Bromus litter to subsurface soil layers, accessing that deepsoil N pool with deep roots and returning that N to the surface as biomass and subsequent litter. Lack of new inputs combined with continued loss will result in lower total soil N, evidenced by the lower total soil N in the invaded/disturbed communities.     

Behavior of pesticides in sediment/water systems in outdoor mesocosms

The distribution of eight pesticides between sediment and water held in 1-m square outdoor stainless-steel mesocosms was studied, simulating both spring and autumn applications. Pesticide behavior was largely independent of rate of application, chosen in the first three experiments to be 4% or 40% of the normal field rate so as to simulate spray drift or partial overspray. Following application by spray to the water surface, all compounds were uniformly distributed in the 30 cm of overlying water within 24 h. The lipophilic pesticides (chlorpyrifos, pendimethalin, and permethrin) moved into the sediment within 30 d but with little penetration below 2.5 cm depth, and only chlorpyrifos persisted beyond 30 d. The mass balance of these lipophilic pesticides at 1 d was only 26.3% to 61%, with these initial losses attributed to processes such as volatilization. Isoproturon and chlorotoluron persisted for around 120 d, remaining largely in the overlying water with a maximum of 15% in the sediment. Permethrin and difenoconazole were much less persistent in these mesocosms, with very little ever found in the sediment in contrast to previous findings in laboratory-scale stirred systems as used in registration tests. The polar mecoprop remained almost entirely in the water phase and was rapidly degraded. Two further experiments examined also the influence of the submerged plant Lagarosiphon major in the mesocosms, the first experiment simulating a full-rate overspray with chlorpyrifos and linuron and the second a repeat in spring of the earlier main autumn experiment. Both chlorpyrifos and linuron applied in the autumn were quite persistent over the winter period, with about 20% still remaining after 152 d. Uptake into L. major was correlated with pesticide lipophilicity, but was only a small factor compared to uptake by sediment and degradation in these lightly vegetated systems.     

Yields of field-grown soybeans exposed to simulated acidic deposition

Rainfall acidity response functions for crop yield and growth are necessary to predict the overall impacts on crop yields of ambient and/or anticipated levels of acidic rain. The experiment described herein was performed at Brookhaven National Laboratory during 1984 and 1985 to determine the effects of simulated rainfalls of pH 5.6, 4.4, 4.1 and 3.3 on seed yields of four cultivars of field-grown soybeans (Glycine max Merrill). Soybeans were chosen because previous results suggested that certain varieties of this crop are sensitive to rainfall acidity and because they are an economically important crop in the USA. Sixteen plots per treatment were used. Plants were grown using standard agronomic practices under automatically movable exclusion shelters which minimize changes in the plant's microclimate. Analysis of variance of seed yields of the four cultivars showed significant treatments for all four cultivars. For all cultivars, seed yields were lower when exposed to simulated rainfalls of pH 4.4, 4.1 and 3.3 compared with rainfalls of pH 5.6. Compared with pH 5.6 rainfall (controls), yields of Amsoy exposed to pH 4.4, 4.1 and 3.3 were lower by 13, 11 and 12%, respectively. The percentage yield reductions for Asgrow, Corsoy and Hobbit were not as great as those of Amsoy. Averaged over all cultivars tested, there was a 9% seed reduction for plants exposed to simulated rain at pH 4.1 (comparable to ambient) compared with pH 5.6.     

Adaptation to air pollution

This study examines human adaptation to air pollution by comparing responses to photochemical smog of long-term residents and recent residents of the Los Angeles air basin. Long-term residents in comparison to recent migrants use a higher response criterion to identify smog in a visual signal detection task. There is no difference in visual sensitivity between the two residential groups in detecting the presence of air pollution in photographic slides. Thus for low levels of visual air pollution, both long-term residents of Los Angeles and new migrants are equally accurate in detecting the presence of smog. Long-term residents, however, are less likely to decide that smog is present in a scene. This response bias is interpreted in terms of adaptation level theory. Characteristics of the response bias differences between the two residential groups are examined in detail using signal detection procedures.     

Polychlorinated dibenzo-p-dioxins,dibenzofurans and polychlorinated biphenyls in polar bear,penguin and south polar skua

Concentrations of 2378-substituted polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (DFs) and non- and mono-ortho-substituted polychlorinated biphenyls (dioxin-like PCBs) were measured in livers of polar bears from the Alaskan Arctic and in eggs of Adelie penguin and south polar skua and weddell seal liver, fish and krill from Antarctica. This is one of the first reports to document the concentrations of PCDDs/DFs in polar bear livers from Alaska, and in penguin and skua eggs from Antarctica. Concentrations of total PCDD/DFs in livers of polar bears ranged from 8 to 66 (mean: 26) pg/g, on a lipid weight basis. Concentrations of total PCDD/DFs in Antarctic samples were in the increasing order on a lipid weight basis; weddell seal liver (8.9 pg/g) < fish (11-17 pg/g) < krill (27 pg/g) > penguin eggs (30 ng/g) > seal liver (57 ng/g) > fishes (6.2 ng/g) > krill (0.9 ng/g). Concentrations of 2378-tetrachlorodibenzo-p-dioxin equivalents (TEQs) calculated based on the WHO TEFs were higher in the eggs of polar skua (mean: 344: range: 220-650 pg/g, lipid wt.) from Antarctica than in polar bear livers from Alaska (mean: 120; range: 69-192 pg/g). In general, concentrations of PCDFs were greater than those of PCDDs in polar organisms. 23478-PeCDF is one of the dominant congener found in several samples. Concentrations of TEQs in polar bear livers and skua eggs were close to those that may cause adverse health effects. Dioxin-like PCBs, particularly, non-ortho coplanar PCBs were the major contributors to TEQ concentrations in penguin and skua eggs whereas mono-ortho PCBs accounted for a major portion of TEQs in polar bear livers.     

Aerosol laser ablation mass spectrometry of suspended powders from PM sources and its implications to receptor modeling

Primary sources of particulate matter (PM) were analyzed by suspending powdered samples into an aerosol laser ablation mass spectrometer (LAMS). PM sources studied included vehicle exhaust particulates, dust from a non-ferrous smelter, cement powder, incinerator fly ash, two coal fly ash samples, and two soils. Marker peaks signified certain PM source sectors: construction particles could be distinguished by abundant Ca and Ca compounds, fuel combustion was marked by elemental carbon clusters, and nonferrous industrial particles showed inorganic As, Cu, Pb, Zn, and SOx. In addition to the distinction between particles from these different source sectors, mass spectral results also showed that for a single source, different particle types existed, and among different sources within a sector, similar spectra were present. The aerosol LAMS results show the difficulty in differentiating among separate fly ash sources as well as among different soil samples. A particle class balance receptor model that measures the amount of specific particle types rather than the amount of a chemical component is suggested as a means of source apportionment when particle spectra with overlapping source possibilities occur. The assumptions and limitations of receptor modeling aerosol LAMS data are also described. In particular, methods need to be developed to account for the contribution of secondary sources.     

Cadmium accumulation in the freshwater isopod Asellus racovitzai: the relative importance of solute and particulate sources at trace concentrations

A stable isotope tracer technique was used to evaluate the relative importance of particulates and water as respective sources of cadmium (Cd) uptake in the freshwater isopod Asellus racovitzai (Isopoda, Crustacea). 113Cd(NO3)2 was applied to the sediment at a nominal concentration of 20.0 ng g-1, and 114Cd(NO3)2 was added to the overlying water (nominal concentration of 4.4 ng g-1), in the same test systems. Asellids added were either free-ranging on the sediment surface, where they were exposed to both particulate and water sources of Cd, or were enclosed in dialysis 'tubes', 10 cm above the sediment surface, and were therefore exposed to Cd in water only. By analysis of both isotopes, uptake vectors could be determined simultaneously. After 7 days of exposure, average 114Cd concentrations in 'free' asellids were 15.6 +/- 2.0 micrograms/g, compared with 10.4 +/- 1.8 micrograms/g in 'tube'-held asellids (P < 0.05), i.e. at least 60% of accumulated 114Cd was from water. Furthermore, water-spiked 114Cd was accumulated in asellids to tissue concentrations that were more than four-times greater than sediment-spiked 113Cd. When the sediment organic content was increased (20% peat moss), total Cd concentrations in both overlying water and asellids were significantly lower (P < 0.01), compared with the mineral sediment treatments, and Cd accumulation in tube and free asellids was similar. This study shows that water is an important vector of Cd accumulation in A. racovitzai, and factors that lower Cd concentrations in solution (such as increased organic content of sediment), decrease Cd bioaccumulation.     

Dioxin incinerator emissions exposure study Times Beach, Missouri

PURPOSE: To determine whether living in the vicinity of a hazardous waste incinerator that was burning material contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increased TCDD and toxicity equivalencies (TEQ) in individuals living near the incinerator. METHODS: Participants were randomly chosen from an area close to the incinerator and compared to participants outside of the exposure area. TCDD and related compounds were measured in blood serum before incineration, four months after incineration started, and at the end of incineration. RESULTS: Lipid adjusted serum levels of TCDD and TEQ decreased from pre-incineration to four months after incineration, and decreased further by the end of incineration. CONCLUSION: Incineration of TCDD did not result in any measurable exposure to the population surrounding the incinerator.