Ice breakup dates from 196 8 to 19 8 8 were examined for 20 Wisconsin lakes to determine whether consistent interannual and long-term changes exist. Each ice record had a trend toward earlier breakup dates, as demonstrated by a negative slope with time, indicating a recent warming trend. The average change in breakup dates was 0.82 d earlier per year for the lakes in southern Wisconsin, which was more extreme than that for the northern Wisconsin lakes (0.45 d yr-I). Interannual variation in breakup dates was related to the warm phase of El Nina/Southern Oscillation (ENSO) episodes. El Niiio events occurred five times during this period (1965, 1972, 1976, 1982, and 1986). Average breakup dates were significantly earlier than average (5-14 d) during the mature phase of El Nifio. This variability was affected by the location of the lake: El Nine-related variation was more evident for the southern lakes than the northern lakes. This difference was caused by the average date of breakup for the southern lakes being in late March directly following the period when air temperatures were strongly related to El Nifio events, whereas the average dates of breakup of the northern lakes was in mid-to late April following a period when air temperatures were not significantly related to El Nina events. Overall, the interannual and long-term patterns across Wisconsin were relatively consistent, indicating that recent warming and El Nina-related variation are regional climatic responses.
Metal ion binding to biomaterials derived from cultured antheral cells of Datura innoxiu has been investigated as a function of solution pH. Specifically, the binding of Ba2+, Cd2' , Cu2+, NiZ+, and SrZ+ was studied at pH 1-6, inclusive, in 0.1 M MES solutions. For 10 mg.L-' metal ion solutions, maximum binding was observed for solutions at pH 5 . The dependence of metal ion binding on solution pH was studied for the biomass both free in solution and immobilized in a polysilicate matrix. A significant change in the pH-dependent binding of each of these metals was observed when the cell material was immobilized. These variations in the impact of metal solution pH could not be explained by the Lewis acidity of the metal ions. The involvement of conformational changes of the macromolecular components of the material for the formation of metal-selective coordination sites is postulated.
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