Environmental letters最新文献

Although the exact mechanisms and factors of red tides are not fully understood, red tides are essentially a coastal phenomenon. The role of land drainage in the modification of coastal waters is discussed. The role of other factors (salinity, biologically active substances, etc.) that are altered by the process of land drainage is analyzed and correlated to experimental evidence derived from laboratory-grown dinoflagellate cultures.

Attempt has been made to asses quantitatively the magnitudes of both the gas-phase resistance and the surface resistance to the evaporation of droplets and to determine the transition point at which the evaporation changes from a diffusion-controlled to a surface-controlled process. This transition point is strongly dependent upon the ambient pressure and the droplet size. It is found that at atmospheric pressure the particle radius at which the transition takes place is in the range of 1 - 10mu for water, 0.1mu for n-dibutylphthalate, 0.1 - 1.0mu for mercury, and 0.001mu for liquid helium. Furthermore, we have found that the surface resistance and the gas-phase resistance vary with the size of the droplet in opposite direction, leading to the existence of a maximum rate of evaporation at a certain value of the droplet radius, this radius being dependent upon the characteristics of the liquid concerned. This conclusion may be useful in the search for an optimum and most efficient method of combustion of fuel sprays in automotive engines, gas turbines, and oil-burning power plants.

Drift loss rate was measured for three induced draft cooling towers by following the decrease in concentration of two conservative additives in the recirculating water during operation with no blowdown and normal makeup. The method described is simple and inexpensive and provides information essential in water use planning.

The marine blue green alga Trichodesmium sp is found in red-tide outbreaks in sub-tropical areas in the Pacific and Indian Oceans, the Arabian Seas and the equatorial currents of the Gulf of Mexico. Giberellic acid stimulated the growth of Trichodesmium cultures to a greater extent than in the diatom Melosira sulcata. While increasing either the nitrate or phosphate above the normal levels in the culture medium did not greatly stimulate the growth of this organism, Trichodesmium did thrive in nitrogen impoverished waters by nitrogen fixation. The relevance of these findings to the hydrological factors which favour red-tide outbreaks is discussed.

Infrared spectroscopy was used to follow the rates of the chemical changes in gaseous N(2)O(5)-SO(2) and N(2)O(5)-SO(2)-O(3) mixtures. Several results of interest to atmospheric scientists were obtained. (I) SO(3) was not a detectable product of these reaction systems, and no significant SO(2) removal occurred. From the kinetic treatment of these results, estimates were derived for the upper limits of the rate constants of the reactions 1 and 2: NO(3) + SO(2) leads to NO(2) + SO(3) (1); N2O5 +SO2 leads to N(2)O(4) + SO(3) (2); k(1) less than or equal to 4.2 1. mole-minus 1sec-minus 1; k(2) less than or equal to 2.5 x 10-minus 2 1. mole-minus1sec-minus 1 at 30 degrees C. These data suggest that reactions 1 and 2 are not important removal paths for SO(2) in the sunlight irradiated, NO(x)hydrocarbon polluted atmospheres. (II) The near ultraviolet absorption spectrum of pure N(2)O(5) has been determined. From these results and estimates of the actinic irradiance, it was shown that the rate of photochemical decomposition of N(2)O(5) by the absorption of solar light in the urban atmosphere is an unimportant factor among the reactions which establish the N(2)O(5) and NO(3) concentrations. (III) It has been observed that gaseous SO(3) and NO(2) react rapidly to form a relatively nonvolatile white solid. Preliminary data suggest a 1:1 mole ratio for this adduct. The significance, if any, of this and related compounds in urban aerosol formation must be evaluated.

Chloroform, bromodichloromethane, dibromochloromethane, bromoform, and dichloroiodomethane have been found in chlorinated drinking water. In addition to these five compounds, the other possible trihalomethanes (chlorodiiodomethane, bromochloroiodomethane, dibromoiodomethane, bromodiiodomethane, and iodoform) can also be formed by chlorination of surface water containing bromides and iodides. Mass spectra for each of these ten compounds were obtained.

Vertical migration as an accumulation mechanism in the formation of red tide models is discussed with reference to extant mathematical models. Its relationship to other biological and physical factors such as population density changes, tidal rhythms, nutrient limitation and light intensity is evaluated in terms of its possible causal role in red tides.

Chemicals which interfere with the growth and development of insects (morphogenetic agents) have been receiving major attention as potential means of selective insect control. Major advances in this field resulted from the identification of Juvenile Hormones -1, -2, and -3, and the discovery that various terpenoid and sesquiterpenoid derivatives were more potent morphogenetic agents than the three known Juvenile Hormones. Several highly active compounds have emerged from these research programs. Their field performance, problems, and prospects in selective insect control are considered here.