Impact of microphytobenthos on the sediment biogeochemical cycles: A modeling approach

In marine biogeochemical modeling, the sediment is usually represented by diagenetic models, but in shallow ecosystems these models are incomplete, because they do not take into account the benthic primary production. While microphytobenthos (MPB) is known to strongly impact mineralization pathways and nutrient fluxes, MPB is rarely integrated as an explicit variable. To investigate the impact of microphytobenthos on early diagenesis in sediment, we built a fine-scale dynamic model, based on the diagenetic model OMEXDIA and including MPB and associated processes. The model outputs were similar to a data set of MPB-colonized sediment sampled in Florida Bay, suggesting that the model can recreate a realistic situation. The model showed that MPB activities induced a strong diurnal rhythm on concentration profiles, fluxes, and mineralization processes. When MPB was present at the sediment surface, the total mineralization was strongly enhanced thanks to the supply of labile organic matter. In contrast, coupled nitrification–denitrification was inhibited by a factor of 3.8. This inhibition can be explained by the competition for nitrate and ammonium between MPB and bacteria. Nitrogen uptake of MPB represented 96% of the daily supply of dissolved inorganic nitrogen. This was more than 50 times greater than N consumption by denitrification. With MPB, sediment nitrogen flux to the water column was reduced by a factor of 70, suggesting that sediment colonized by MPB represents a minor source of nutrients for phytoplankton and bacterioplankton. Results showed that current diagenetic models are not well-suited for shallow ecosystems with significant MPB primary production.     

Life cycle assessment of nutrient remediation and bioenergy production potential from the harvest of hydrilla (Hydrilla verticillata)

Hydrilla (Hydrilla verticillata) is one of the world’s most problematic invasive aquatic plants. Although management of hydrilla overgrowth has often been based on use of chemical herbicides, issues such as the emergence of herbicide-resistant hydrilla biotypes and the need for in situ nutrient remediation strategies have together raised interest in the use of harvester machines as an alternative management approach. Using a life cycle assessment (LCA) approach, we calculated a range of net energy and economic benefits associated with hydrilla harvests and the utilization of biomass for biogas and compost production. Base case scenarios that used moderate data assumptions showed net energy benefit ratios (NEBRs) of 1.54 for biogas production and 1.32 for compost production pathways. NEBRs for these respective pathways rose to 2.11 and 2.68 when labor was excluded as a fossil fuel input. Base case biogas and compost production scenarios respectively showed a monetary benefit cost ratio (BCR) of 1.79 and 1.83. Moreover, very high NEBRs (3.94 for biogas; 6.37 for compost) and BCRs (>11 for both biogas and compost) were found for optimistic scenarios in which waterways were assumed to have high hydrilla biomass density, high nutrient content in biomass, and high priority for nutrient remediation. Energy and economic returns were largely decoupled, with biogas and fertilizer providing the bulk of output energy, while nutrient remediation and herbicide avoidance dominated the economic output calculations. Based on these results, we conclude that hydrilla harvest is likely a suitable and cost-effective management program for many nutrient-impaired waters. Additional research is needed to determine how hydrilla harvesting programs may be most effectively implemented in conjunction with fish and wildlife enhancement objectives.     

Age Dependence of Female to Male Fatality Risk in the Same Crash: An Independent Reexamination

A 1988 study reported that females are more likely than males to be killed by the same physical insult. This was determined by analyzing 1975–1983 data. The present study revisits this question using 123,678 fatalities from 1984–1996 data. As none of these data contributed to the earlier study, the present investigation is therefore independent of the earlier one. Female to male fatality risk ratios are calculated for 14 categories of vehicle occupants, including six light truck occupants (belted and unbelted drivers and right front passengers, and unbelted left and right rear passengers). The earlier study did not include light trucks. Close agreement is found between the results of the present and prior studies, thus solidifying the interpretation that findings are of a general nature and not dependent on specific data sets. Except at ages less than about 10 years, or older than about 55, females are more likely to be killed than males. While obtained using traffic data, the results are interpreted to reflect fundamental differences in human physiological response to blunt trauma in general, and are expected to apply to blunt trauma from falls, being struck by objects, etc.     

Views of the City: Multiple pathways to sustainable transport futures

In this paper we look behind the notion of sustainable transport and highlight the tensions and contradictions between the different ways of achieving this. The paper examines transportation plans for a major UK city and describes how these develop the idea and practice of sustainable transport and demand management along three quite distinct trajectories. By focusing on both the technological and the institutional dimensions of three different routes to sustainable transport, the analysis explicates the different ways in which the urban transport problem is framed, the different socio-technical logics of demand management embodied in the plans and the differing ways in which institutional relationships are (re)constituted. A key finding is that technological and institutional innovations are inversely related so that radical technological innovation often serves to reinforce existing social relations of power and exclusion. The conclusion drawn is that the choice is not just between a sustainable and an unsustainable transport future, but also between different forms of sustainability.     

Influence of atmospheric dispersion and new particle formation events on ambient particle number concentration in Rochester, United States, and Toronto, Canada

Continuous measurements of particle number concentrations were performed in Rochester, NY, and Toronto, Ontario, Canada during the 2003 calendar year. Strong seasonal dependency in particle number concentration was observed at two sites. The average number concentration of ambient particles was 9670 +/- 6960 cm(-3) in Rochester, whereas in Toronto the average number of particles was 28,010 +/- 13,350 cm(-3). The particle number concentrations were higher in winter months than in summer months by a factor of 1.5 in Rochester and 1.6 in Toronto. In general, there were also distinct diurnal variations of aerosol number concentration. The highest weekdays/weekends ratio of number concentration was typically observed during the rush-hour period in winter months with a ratio of 2.1 in Rochester and 2.0 in Toronto. The correlation in the total particle number concentrations between the two urban sites was stronger in winter because of the common urban traffic patterns, but weaker in summer because of local sulfur dioxide (SO2)-related particle formation events in Rochester in the summer. Strong morning particle formation events were frequently observed during colder winter months. Good correlations between particle number and carbon monoxide (CO) as well as temperature suggested that motorvehicle emissions lead to the formation of new particles as the exhaust mixes with the cold air. Regional nucleation and growth events frequently occurred in April. Local SO2-related particle formation events most frequently occurred in August. SO2 and UV-B were highly correlated with particle concentration, suggesting a high association of photochemical processes with these local events. A high directionality in a northerly direction was observed for particle number and SO2, indicating the influence of point sources located north of Rochester.     

The influence of geographic location on population exposure to emissions from power plants throughout China

This analysis seeks to evaluate the influence of emission source location on population exposure in China to fine particles and sulfur dioxide. We use the concept of intake fraction, defined as the fraction of material or its precursor released from a source that is eventually inhaled or ingested by a population. We select 29 power-plant sites throughout China and estimate annual average intake fractions at each site, using identical source characteristics to isolate the influence of geographic location. In addition, we develop regression models to interpret the intake fraction values and allow for extrapolation to other sites. To model the concentration increase due to emissions from selected power plants, we used a detailed long-range atmospheric dispersion model, CALPUFF. Primary fine particles have the highest average intake fraction (1 x 0(-5)), followed by sulfur dioxide (5 x 10(-6)), sulfate from sulfur dioxide (4 x 10(-6)), and nitrate from nitrogen oxides (4 x 10(-6)). For all pollutants, the intake fractions span approximately an order of magnitude across sites. In the regression analysis, the independent variables are meteorological proxies (such as climate region and precipitation) and population at various distances from the source. We find that population terms can explain a substantial percentage of variability in the intake fraction for all pollutants (R(2) between 0.86 and 0.95 across pollutants), with a significant modifying influence of meteorological regime. Near-source population is more important for primary coarse particles while population at medium to long distance is more important for primary fine particles and secondary particles. A significant portion of intake fraction (especially for secondary particles and primary fine particles) occurs beyond 500 km of the source, emphasizing the need for detailed long-range dispersion modeling. These findings demonstrate that intake fractions for power plants in China can be estimated with reasonable precision and summarized using simple regression models. The results should be useful for informing future decisions about power-plant locations and controls.     

Assessing the risk to firefighters from chemical vapors and gases during vehicle fire suppression

Despite the frequent occurrence of vehicle fires, very few studies investigating firefighters' potential inhalation exposures during vehicle fire suppression have been conducted. In this paper, we present an assessment of firefighters' health risk from vehicle fire suppression that accounts for the mixture of gases and vapors likely to be found in these fires. Summa canisters were used to collect emissions from the engine and cabin fires of a single vehicle and were analyzed for 75 volatile organic compounds (VOCs). Firefighters' breathing zone concentrations (BZCs) of aromatic hydrocarbons, aldehydes, isocyanates, and carbon monoxide were measured during the suppression of three vehicle fires. The Summa canister and BZC data were used to develop a simple model for predicting BZCs for the compounds that were not measured in the firefighters' breathing zones. Hazard quotients (HQs) were calculated by dividing the predicted and measured BZCs by the most conservative short-term exposure limits (STELs) or ceiling limits. Hazard indices (HIs) were determined by adding HQs for compounds grouped by the target organ for acute health effects. Any HIs above unity represented unacceptable risks. According to this mixture analysis, the estimated 95(th) percentile of the exposure distribution for the study population represents ≥ 9.2 times the acceptable level of risk to the respiratory tract and eyes. Furthermore, chemicals known or reasonably anticipated to be human carcinogens contributed to > 45% of these HIs. While STELs are not usually based on carcinogenicity, maintaining exposures below STELs may protect individuals from the biological stress that could result from short-term exposures to carcinogens over time. Although vehicle fires are suppressed quickly (<10 min), this assessment suggests that firefighters have the potential to be overexposed to acute toxins during vehicle fire suppression and should therefore wear self-contained breathing apparatus at all times during vehicle fire response.