Practically no information exists on the impact of human trampling on tropical rain forest vegetation. We studied three trails
with varying periods of use and recovery in a tropical rain forest in Costa Rica. Human impact on trailside plants was curvilinearly
related to use, as found by other workers in temperate zone vegetation. Recovery in a period of two years and eight months
had been rapid, and herbs and seedlings were more abundant along the recovering trail than in undisturbed forest. The results
imply that a shifting mosaic of trails, analogous to the mosaic created by light gaps, may be the best management technique
to minimize the impact of human visitors in tropical rain forests. 相似文献
ABSTRACT: A study of residential canal system on the Mississippi Gulf Coast and adjacent natural water bodies was conducted to determine the relationship in flushing characteristics between man-made and natural systems. The comparison was based on measurements of temperature, salinity, conductivity, coliform, pH, transparency, biological oxidation demand, dissolved oxygen, bathymetry, tides, water velocity, and Rhodamine dye concentrations. The results indicate that coliform bacteria increase with increasing distance of stations from St. Louis Bay and dissolved oxygen decreases in a similar manner. Biological oxidation demand was low at all stations; showing no differences between natural and man-made systems. The canal system Studied was shallower than adjacent water bodies and water velocities in the canal system are a function of tidal amplitude while velocities in the river are affected by both tides and runoff. The other parameters measured show little or no differences between natural and man-made systems, but reflect overall seasonal changes. Flushing rates between the residential canal systems and an adjacent natural system are equivalent on the basis of decline in dye concentrations measured over a five-day period. 相似文献
Structurally based ultraviolet (UV)-reflective plumage parts can be important cues in mate choice. However, it remains largely
unknown if UV plumage variation can also function as a signal of social status during competitive interactions. In blue tits
(Cyanistes caeruleus), the UV-reflective crown plumage functions as a female mate choice cue that probably indicates male quality, as males with
higher UV reflectance have been shown to have better chances of over-winter survival. Possibly, the UV crown plumage acts
as a status signal in the competition over scarce food sources during winter. To test this idea, we related dominance of individuals
at an artificial food source during adverse winter conditions to spectrophotometric measurements of their crown plumage. However,
while controlling for the confounding effects of sex, age, and distance from territory, we found no significant effect of
crown UV reflectance on dominance. Consistent with this result, we also found no relation between crown UV reflectance and
over-winter survival. We conclude that the structurally based UV reflectance of the blue tit crown feathers plays little role
in competition between individuals during winter despite its importance as a cue in mate choice. 相似文献
A theoretical and experimental study of bisphenol A (BPA) degradation by the UV/H2O2 process in water is presented. The effects of the H2O2 concentration and the specific rate of photon emission (EP,0) on BPA degradation were investigated. A kinetic model derived from a reaction sequence was employed to predict BPA and hydrogen peroxide concentrations over time using an annular photochemical reactor in batch recirculation mode. The local volumetric rate of photon absorption (LVRPA) inside the photoreactor was computed using a Line Source with Parallel Plane emission model (LSPP). From the proposed kinetic model and the experimental data, the second order rate constants of the reactions between hydroxyl radicals and the main reacting species (H2O2 and BPA) were estimated applying a nonlinear regression method. A good agreement between the kinetic model and experimental data, for a wide range of operating conditions, was obtained. For BPA, H2O2, and TOC concentrations, the calculated root means square errors (RMSE) were 2.3?×?10??2, 9.8?×?10??1, and 9.0?×?10??2 mmol L??1, respectively. The simplified kinetic model presented in this work can be directly applied to scaling-up and reactor design, since the estimated kinetic constants are independent of the reactor size, shape, and configuration. Further experiments were made by employing low BPA initial concentration (100 μg L??1) in water and real wastewater. A lower degradation rate of BPA was observed in the real wastewater, although the UV/H2O2 process has also been able to completely degrade the target pollutant in less than 1 h.
Environmental Fluid Mechanics - We report novel results of a numerical experiment designed for examining the basin-scale hydrodynamics that control the mass, momentum, and energy distribution in a... 相似文献
Environmental Fluid Mechanics - The water waves resulting from the collapse of a dam are important unsteady free surface flows in civil and environmental engineering. Considering the basic case of... 相似文献
Environment, Development and Sustainability - Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is one of the biggest public health issues in the last years. The WHO has... 相似文献
Dry and wet deposition fluxes of the PCDD/F substituted congeners were measured at two different sites (Clinton Drive and Lang Road) in Houston, TX between December 2003 and April 2004. Average total dry deposition fluxes of 351 and 125pgm(-2)d(-1) were found at Clinton Drive and Lang Road, respectively. A wet deposition flux of 2.873pgm(-2)d(-1) was measured at the Clinton Drive site. The results indicated that the dry deposition process exhibited spatial variability. In addition, the results also demonstrated that precipitation, although intermittent, is the most important mechanism for the removal of dioxins from atmosphere in the area of study. Combining the contributions of the dry and wet deposition processes at Clinton Drive resulted in a total bulk deposition flux of 527pg m(-2)d(-1). The total dry and wet deposition fluxes were dominated by OCDD followed by 1,2,3,4,6,7,8-HpCDD at both sites. Overall average dry deposition velocities of 0.35 and 0.15cms(-1) were calculated at Clinton Drive and Lang Road sites, respectively. While these velocities were similar to velocities observed in other geographical areas, the contribution of OCDD to the total deposition flux in Houston was significantly higher, probably reflecting the unique nature and character of Houston dioxin sources. The results also showed that lower chlorinated congeners, primarily present in the gas phase, are more likely to be removed from the atmosphere by precipitation. Relationships between the detected congeners in the dry deposition samples and other routinely measured air pollutants/meteorological parameters were found. The results showed that in general, the dry deposition of these congeners was consistently negatively correlated with SO(2) and NO(x) concentrations in the air and positively correlated with relative humidity. However, more research is needed to ascertain those correlations. 相似文献