Fluorescence behaviour of Zn and Ni complexes of humic acids from different sources

Conventional fluorescence spectroscopy in the excitation, emission and synchronous scan modes and three-dimensional fluorescence spectroscopy in the form of an excitation-emission matrix (EEM) of fluorescence intensity as a function of excitation and emission wavelengths have been applied to the study of three humic acids (HAs) extracted from soil (SHA), peat (PHA) and compost (CHA) and their interaction products with Zn(II) and Ni(II) ions. Fluorescence spectra of HAs appear to be related to the nature and origin of the sample. A strong reduction of intensity of all peaks is observed in the spectra of HAs-metal complexes as compared to those of untreated HAs. Ni(II) exhibits greater quenching ability than Zn(II). Fluorescence quenching measured for complexes of HAs at increasing Ni(II) concentrations was linearly correlated with metal ion concentration. The different capacity to interact with metal ions showed by various HAs is attributed to their different molecular complexity.     

Extinction Measurements for Sensitive Assessment of Air Quality

Measures of horizontal extinction were initiated at the Lowell Observatory at Flagstaff, Arizona In January of 1972, and by October of 1973 an instrumental accuracy compatible with the best observing conditions was achieved. Excellent data obtained in a horizontal direction during a seven night run are compared with long term highly standardized astronomical measures of extinction obtained at Flagstaff during the period 1955–1972. The data obtained both vertically and horizontally suggest that the extinction and scattering due to aerosols were at times as low as 10% of that caused by molecular (Rayleigh) scattering alone. The vertical extinction seems to correspond (with several months lag) to rough estimates of volcanic loading; the effect of the March 17, 1963 outburst of Mount Agung, a volcano on the island of Bali, very probably caused abnormally high extinction in late summer of that year. A generally high extinction level was observed throughout 1964-1965 with a rather slow decay to a “normal” level showing up by 1966. The very high level of transparency and abnormally blue sky found in 1961 was again observed in 1972. These data strongly suggest that man-made aerosols are not yet the major contributor to the particulate matter in the upper atmosphere.     

A Sediment Budget for an Urbanizing Watershed, 1951‐1996, Montgomery County, Maryland,U.S.A.1

Abstract: Despite widespread interest, few sediment budgets are available to document patterns of erosion and sedimentation in developing watersheds. We assess the sediment budget for the Good Hope Tributary, a small watershed (4.05 km²) in Montgomery County, Maryland, from 1951‐1996. Lacking monitoring data spanning the period of interest, we rely on a variety of indirect and stratigraphic methods. Using regression equations relating sediment yield to construction, we estimated an upland sediment production of 5,700 m³ between 1951 and 1996. Regression equations indicate that channel cross‐sectional area is correlated with the extent of development; these relationships, when combined with historical land use data, suggest that upland sediment yield was augmented by 6,400 m³ produced by enlargement of first‐order and second‐order stream channels. We used dendrochronology to estimate that 4,000 m³ of sediment was stored on the floodplain from 1951‐1996. The sediment yield from the watershed, obtained by summing upstream contributions, totals 8,100 m³ of sediment, or 135 tons/km²/year. These results indicate that upland erosion, channel enlargement, and floodplain storage are all significant components of the sediment budget of our study area, and all three are approximately equal in magnitude. Erosion of “legacy” floodplain sediments originally deposited during poor agricultural practices of the 19th and early 20th Centuries has likely contributed between 0 and 20% of the total sediment yield, indicating that these remobilized deposits are not a dominant component of the sediment yield of our study area.