Atmospheric dimethyl sulfide (DMS) and sulfur dioxide (SO2) concentrations were measured at Baring Head, New Zealandduring February and March 2000. Anti-correlated DMS and SO2 diurnalcycles, consistent with the photochemical production of SO2 from DMS, were observed in clean southerly air off the ocean. The data is used to infer a yield of SO2 from DMS oxidation. The estimated yields are highly dependent on assumptions about the DMS oxidation rate. Fitting the measured data in a photochemical box model using model-generated OH levels and the Hynes et al. (1986) DMS + OH rate constant suggests that theSO2 yield is 50–100%, similar to current estimates for the tropical Pacific.However, the observed amplitude of the DMS diurnal cycle suggests that the oxidation rate is higher than that used by the model, and therefore, that theSO2 yield is lower in the range of 20–40%. 相似文献
A two-dimensional global climate model is used to assessthe climatic changes associated with the new IPCC SRES emissions scenarios and to determine which kind of changes in total solar irradiance and volcanic perturbations could mask the projected anthropogenic global warming associated to the SRES scenarios. Our results suggest that only extremely unlikely changes in total solar irradiance and/or volcanic eruptions would be able to overcome the simulated anthropogenic global warming over the century. Nevertheless, in the critical interval of the next two decades the externally-driven natural climate variability might possibly confuse the debate about temperature trends and impede detection of the anthropogenic climate change signal. 相似文献
The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens
floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so
the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer
modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled
using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following
hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of
sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward
the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The
model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head
values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered
despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge,
and the well-developed karst system of the region has a very high hydraulic conductivity.
Electronic Publication 相似文献
. Groundwater sampling and geophysical methods determined a serious contamination problem associated with refilled exploitation sites at the Cal Dimoni area, Llobregat delta, Barcelona, Spain. To characterise this process, hydrogeochemical analyses were performed and showed the following modifications to groundwater chemical composition: increasing pH values, changing redox conditions, significant increases in total organic carbon (TOC) and certain trace elements, and high groundwater conductivity values. Major ion content accumulations were found under the refilled area. In contrast, elements involved in the oxidationreduction processes, such as iron, manganese and nitrates, clearly diminished. Electromagnetic prospecting methods were also performed and delineated the contamination plume extent. These methods also showed separate sources of contamination, one clearly related to the groundwaterrefilled zone leachate interaction, another as a consequence of the manureaccumulation surface site. Geochemical and geophysical methods have shown similar results for locating groundwater contamination sources, and for determining leachate generation mechanisms and flow paths. 相似文献
Apatite fission track analysis was performed on 56 samples from central Spain to unravel the far field effects of the Alpine plate tectonic history of Iberia. The modelled thermal histories reveal complex cooling in the Cenozoic, indicative of intermittent denudation. Accelerated cooling events occurred across the Spanish Central System (SCS) from the Middle Eocene to Recent. These accelerated cooling events resulted in up to 2.8±0.9 km of denudation in the western Sierra de Gredos and 3.6±1.0 km in the central and eastern Gredos (assuming a paleogeothermal gradient of 28±5 °C and a surface temperature of 10 °C). The greatest amount of denudation (5.0±1.6 km) occurred in the Sierra de Guadarrama. Accompanying rock uplift was 4.7±1.0 and 5.9±1.6 km in the eastern Gredos and Guadarrama, respectively. Most denudation in the Gredos occurred from the Middle Eocene to the Early Miocene and can be related to the N–S stress field, induced by the Pyrenean compression. In the Guadarrama, the greatest denudation was Pliocene to Recent of age and seems related to the ongoing NW–SE Betic compression. The fact that the formation of the E–W trending Gredos coincides with the N–S Pyrenean compression and the creation of the present day morphology of the NE–SW trending Guadarrama with the younger NW–SE Betic compression, indicates that they record the far field effects of Alpine plate tectonics on Iberia. The trend of pre-existing lineaments was of major importance in influencing the style and magnitude of these of far field effects. 相似文献
As a result of the collapse of the Aznalcollar mine tailings dam, a large extension of the Guadiamar valley in SW Spain was covered with a layer of pyrite sludge. Although most of the sludge was removed, a small amount remains in the soil, constituting a potential source of water pollution. A column experiment was carried out in order to determine the rate of sludge oxidation in the soil, and the existence of metal retention processes. The column was filled with a mixture of sludge and a sandy soil common in the region. At different time intervals, the column was leached with water and the resulting solution analysed.
The pH of the water dropped to values around 2 after 260 days and then remained constant due to the buffering role of silicate dissolution. The concentration of Zn, Cd and Co in the leachates matched the expected values from flow-through experiments at atmospheric oxygen pressure. This indicates that oxygen diffusion in the pores was complete. Moreover, no efficient processes existed for retaining Zn, Cd and Co, which formed soluble salts and were entirely incorporated into the infiltrating water. During the first 2 months of the experiment, when pH was higher than 4.5, the concentrations of Fe and Al were very low. Saturation indices showed that the solution was in equilibrium with amorphous Fe(OH)3 and Al(OH)3. Subsequently, at lower pH values, jarosite [(Na,K)Fe3(SO4)2(OH)6] formed. This solid phase was identified by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Jarosite was also responsible for the depletion of As, Pb, Sb and probably Tl in the water resulting from infiltration. 相似文献
The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary. 相似文献