Responses to projected changes in climate and UV-B at the species level

Environmental manipulation experiments showed that species respond individualistically to each environmental-change variable. The greatest responses of plants were generally to nutrient, particularly nitrogen, addition. Summer warming experiments showed that woody plant responses were dominant and that mosses and lichens became less abundant. Responses to warming were controlled by moisture availability and snow cover. Many invertebrates increased population growth in response to summer warming, as long as desiccation was not induced. CO2 and UV-B enrichment experiments showed that plant and animal responses were small. However, some microorganisms and species of fungi were sensitive to increased UV-B and some intensive mutagenic actions could, perhaps, lead to unexpected epidemic outbreaks. Tundra soil heating, CO2 enrichment and amendment with mineral nutrients generally accelerated microbial activity. Algae are likely to dominate cyanobacteria in milder climates. Expected increases in winter freeze-thaw cycles leading to ice-crust formation are likely to severely reduce winter survival rate and disrupt the population dynamics of many terrestrial animals. A deeper snow cover is likely to restrict access to winter pastures by reindeer/caribou and their ability to flee from predators while any earlier onset of the snow-free period is likely to stimulate increased plant growth. Initial species responses to climate change might occur at the sub-species level: an Arctic plant or animal species with high genetic/racial diversity has proved an ability to adapt to different environmental conditions in the past and is likely to do so also in the future. Indigenous knowledge, air photographs, satellite images and monitoring show that changes in the distributions of some species are already occurring: Arctic vegetation is becoming more shrubby and more productive, there have been recent changes in the ranges of caribou, and "new" species of insects and birds previously associated with areas south of the treeline have been recorded. In contrast, almost all Arctic breeding bird species are declining and models predict further quite dramatic reductions of the populations of tundra birds due to warming. Species-climate response surface models predict potential future ranges of current Arctic species that are often markedly reduced and displaced northwards in response to warming. In contrast, invertebrates and microorganisms are very likely to quickly expand their ranges northwards into the Arctic.     

Model Assessment of Air-Pollution in Prague

Results of relatively simple gaussian dispersion model are presented. This model, developed in the beginning of this decade, is suitable mainly for determination of spatial distributions of annual mean concentrations of such kinds of air-pollution as sulphur dioxide (SO₂), mixture of nitrogen oxides (NO_x) or suspended particulate matter (SPM) from all types of emission sources located within the city - point sources, line sources and area sources. Model has been used in years 1994, 1996 and 1998 to assess the air-pollution distributions of the above mentioned kinds in the Prague area and the development of the air quality state. It contributed to the decision making process when possible impact of some changes in traffic system or in system of domestic heating, for example, has been investigated. In this contribution, behaviour of sulphur dioxide (SO₂) and mixture of nitrogen oxides (NO_x) ground concentration distributions are analyzed with respect to changing emission situation in Prague in recent years. Results show that SO₂ ground concentration level decreases mainly due to changes in local heating methods and type of fuel used. Different trend can be seen in NO_x ground concentrations thanks to rapid increase in the traffic density.     

Determination of primary and secondary sources of organic acids and carbonaceous aerosols using stable carbon isotopes

Stable carbon isotope ratio (δ¹³C) data can provide important information regarding the sources and the processing of atmospheric organic carbon species. Formic, acetic and oxalic acid were collected from Zurich city in August–September 2002 and March 2003 in the gas and aerosol phase, and the corresponding δ¹³C analysis was performed using a wet oxidation method followed by isotope ratio mass spectrometry. In August, the δ¹³C values of gas phase formic acid showed a significant correlation with ozone (coefficient of determination (r²) = 0.63) due to the kinetic isotope effect (KIE). This indicates the presence of secondary sources (i.e. production of organic acids in the atmosphere) in addition to direct emission. In March, both gaseous formic and acetic acid exhibited similar δ¹³C values and did not show any correlation with ozone, indicating a predominantly primary origin. Even though oxalic acid is mainly produced by secondary processes, the δ¹³C value of particulate oxalic acid was not depleted and did not show any correlation with ozone, which may be due to the enrichment of ¹³C during the gas - aerosol partitioning.The concentrations and δ¹³C values of the different aerosol fractions (water soluble organic carbon, water insoluble organic carbon, carbonate and black carbon) collected during the same period were also determined. Water soluble organic carbon (WSOC) contributed about 60% to the total carbon and was enriched in ¹³C compared to other fractions indicating a possible effect of gas - aerosol partitioning on δ¹³C of carbonaceous aerosols. The carbonate fraction in general was very low (3% of the total carbon).     

Impact of varying soil structure on transport processes in different diagnostic horizons of three soil types

When soil structure varies in different soil types and the horizons of these soil types, it has a significant impact on water flow and contaminant transport in soils. This paper focuses on the effect of soil structure variations on the transport of pesticides in the soil above the water table. Transport of a pesticide (chlorotoluron) initially applied on soil columns taken from various horizons of three different soil types (Haplic Luvisol, Greyic Phaeozem and Haplic Cambisol) was studied using two scenarios of ponding infiltration. The highest infiltration rate and pesticide mobility were observed for the Bt₁ horizon of Haplic Luvisol that exhibited a well-developed prismatic structure. The lowest infiltration rate was measured for the Bw horizon of Haplic Cambisol, which had a poorly developed soil structure and a low fraction of large capillary pores and gravitational pores. Water infiltration rates were reduced during the experiments by a soil structure breakdown, swelling of clay and/or air entrapped in soil samples. The largest soil structure breakdown and infiltration decrease was observed for the Ap horizon of Haplic Luvisol due to the low aggregate stability of the initially well-aggregated soil. Single-porosity and dual-permeability (with matrix and macropore domains) flow models in HYDRUS-1D were used to estimate soil hydraulic parameters via numerical inversion using data from the first infiltration experiment. A fraction of the macropore domain in the dual-permeability model was estimated using the micro-morphological images. Final soil hydraulic parameters determined using the single-porosity and dual-permeability models were subsequently used to optimize solute transport parameters. To improve numerical inversion results, the two-site sorption model was also applied. Although structural changes observed during the experiment affected water flow and solute transport, the dual-permeability model together with the two-site sorption model proved to be able to approximate experimental data.     

Methanotrophic activity in a diffusive methane/oxygen counter-gradient in an unsaturated porous medium

Microbial methane (CH4) oxidation is a main control on emissions of this important greenhouse gas from ecosystems such as contaminated aquifers or wetlands under aerobic onditions. Due to a lack of suitable model systems, we designed a laboratory column to study this process in diffusional CH4/O2 counter-gradients in unsaturated porous media. Analysis and simulations of the steady-state CH4, CO2 and O2 gas profiles showed that in a 15-cm-deep active zone, CH4 oxidation followed first-order kinetics with respect to CH4 with a high apparent first-order rate constant of approximately 30 h(-1). Total cell counts obtained using DAPI-staining suggested growth of methanotrophic bacteria, resulting in a high capacity for CH4 oxidation. This together with apparent tolerance to anoxic conditions enabled a rapid response of the methanotrophic community to changing substrate availability, which was induced by changes in O2 concentrations at the top of the column. Microbial oxidation was confirmed by a approximately 7 per thousand enrichment in CH4 stable carbon isotope ratios along profiles. Using a fractionation factor of 1.025+/-0.0005 for microbial oxidation estimated from this shift and the fractionation factor for diffusion, simulations of isotope profiles agreed well with measured data confirming large fractionation associated with microbial oxidation. The designed column should be valuable for investigating response of methanotrophic bacteria to environmental parameters in future studies.     

The role of hydrodynamics, matrix and sampling duration in passive sampling of polar compounds with Empore SDB-RPS disks

There is an increasing need to monitor concentrations of polar organic contaminants in the aquatic environment. Integrative passive samplers can be used to assess time weighted average aqueous concentrations, provided calibration data are available and sampling rates are known. The sampling rate depends on environmental factors, such as temperature and water flow rate. Here we introduce an apparatus to investigate the sampling properties of passive samplers using river-like flow conditions and ambient environmental matrices: river water and treated sewage effluent. As a model sampler we selected Empore SDB-RPS disks in a Chemcatcher housing. The disks were exposed for 1 to 8 days at flow rates between 0.03 and 0.4 m s(-1). Samples were analysed using a bioassay for estrogenic activity and by LC-MS-MS target analysis of the pharmaceuticals sulfamethoxazole, carbamazepine and clarithromycin. In order to assess sampling rates of SDB disks, we also measured aqueous concentrations of the pharmaceuticals. Sampling rates increased with increasing flow rate and this relationship was not affected by the environmental matrix. However, SDB disks were only sampling in the integrative mode at low flow rates <0.1 m s(-1) and/or for short sampling times. The duration of linear uptake was particularly short for sulfamethoxazole (1 day) and longer for clarithromycin (5 days). At 0.03 m s(-1) and 12-14 degrees C, the sampling rate of SDB disks was 0.09 L day(-1) for clarithromycin, 0.14 L day(-1) for sulfamethoxazole and 0.25 L day(-1) for carbamazepine. The results show that under controlled conditions, SDB disks can be effectively used as passive sampling devices.     

Meteorological Factors of Ozone Predictability at Houston,Texas

ABSTRACT

Several ozone modeling approaches were investigated to determine if uncertainties in the meteorological data would be sufficiently large to limit the application of physically realistic ozone (O₃) forecast models. Three diagnostic schemes were evaluated for the period of May through September 1997 for Houston, TX. Correlations between measured daily maximum and model calculated O₃ air concentrations were found to be 0.70 using a linear regression model, 0.65 using a non-advective box model, and 0.49 using a three-dimensional (3-D) transport and dispersion model. Although the regression model had the highest correlation, it showed substantial underestimates of the highest concentrations. The box model results were the most similar to the regression model and did not show as much underestimation. The more complex 3-D modeling approach yielded the worst results, likely resulting from O₃ maxima that were driven by local factors rather than by the transport of pollutants from outside of the Houston domain. The highest O₃ concentrations at Houston were associated with light winds and meandering trajectories. A comparison of the gridded meteorological data used by the 3-D model to the observations showed that the wind direction and speed values at Houston differed most on those days on which the O₃ underestima-tions were the greatest. These periods also tended to correspond with poor precipitation and temperature estimates. It is concluded that better results are not just obtained through additional modeling complexity, but there needs to be a comparable increase in the accuracy of the meteorological data.