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Abstract: The chemical response of 20 headwater lakes in Nova Scotia to reduced acid deposition was investigated using trend analysis, and the need for further reductions was assessed using two [...]

A stopped-flow technique and three-dimensional excitation emission (Ex/Em) fluorescence spectrophotometer were used to detect the full fluorescence spectral kinetic changes that occurred during the complexation between fulvic acid (FA) and several metals [Cu(II), Ni(II), Co(II), Cd(II) and Ca(II)]. The study was carded out with a fulvic acid isolated from Cavan Bog, Canada. At pH 7, the FA reacted rapidly with all metals studied. Two major kinetically distinguishable binding sites on FA ('fast' and 'slow'), having reaction half-lives of 1.3- 3.9 and 34.7-69.3 s, respectively, were identified using pseudo-first-order kinetic plots. Kinetic changes of Ex and Em wavelengths of the fluorescence maximums also indicate two major binding sites. For the fast-reacting binding site, the rate constant and the site relative contribution were as follows, [Cu.sup.2+] > [Ni.sup.2+] > [Co.sup.2+] > [Cd.sup.2+] > [Ca.sup.2+], which agrees with the Irving Williams series, indicating that complexation kinetics are affinity dependent. Within each kinetic phase, both Ex and Em wavelengths of fluorescence maximums increased with time, indicating the occurrence of structural changes during the binding process. Based on the results obtained, the use of full fluorescence spectra appears to be a promising tool for further understanding metal-FA complexation mechanisms.

Levels of acidic deposition from the atmosphere have fallen during the 1980s and 1990s over large areas of North America and Europe. This is believed by many to have led to observed reversals in surface-water acidification. Regional trends between 1980 and 1995 in indicators of acidification were examined and lak and stream sulphate concentrations were found to have fallen in all areas apart from Great Britain. However regional falls in lake and stream nitrate concentrations were rare, and if seen, were very small.

This paper explores the relationship between thermal energy and fresh water recoveries from an aquifer storage recovery ( ASR) well in a brackish confined aquifer. It reveals the spatial and temporal distributions of temperature and conservative solutes between injected and recovered water. The evaluation is based on a review of processes affecting heat and solute transport in a homogeneous aquifer. In this simplified analysis, it is assumed that the aquifer is sufficiently anisotropic to inhibit density-affected flow, flow is axisymmetric, and the analysis is limited to a single ASR cycle. Results show that the radial extent of fresh water at the end of injection is greater than that of the temperature change due to the heating or cooling of the geological matrix as well as the interstitial water. While solutes progress only marginally into low permeability aquitards by diffusion, conduction of heat into aquitards above and below is more substantial. Consequently, the heat recovery is less than the solute recovery when the volume of the recovered water is lower than the injection volume. When the full volume of injected water is recovered the temperature mixing ratio divided by the solute mixing ratio for recovered water ranges from 0.95 to 0.6 for ratios of maximum plume radius to aquifer thickness of 0.6 to 4.6. This work is intended to assist conceptual design for dual use of ASR for conjunctive storage of water and thermal energy to maximize the potential benefits. [ABSTRACT FROM AUTHOR]