Beryllium-7 as a tracer to study mechanisms and rates of metal scavenging from lake surface waters

The removal of Be-7 from lake surface waters (Lake Lugano, Switzerland/Ital y) was studied from September 1995 to May 1996. During this period the atmo spheric input and sedimentary flux of Be-7, as well as concentrations of di ssolved (<10 kD), colloidal (10 kD-1 mu m), and particulate (>1 mu m) Be-7 in the epilimnion were measured. The separation of dissolved, colloidal, an d particulate fractions of Be-7 was carried out using continuous how centri fugation (CFC) and tangential flow filtration (TFF) techniques. Lacustrine colloids (log K-c approximate to 6) were shown to be much more efficient so rbents for Be-7 than the suspended particles (log K-p 4-5). Particle concen trations C-p ranged from 0.5 to 2 mg/L. The ratio of colloid (>10 kD) to pa rticle concentration C-c/C-p was close to 0.09 during winter months when de trital inputs are dominant, but was higher (0.16) in summer and in spring a fter an algal bloom. The Be-7 data were used to estimate coagulation rates of colloids. The highest coagulation rates (lambda(coag) approximate to 0.4 d(-1)) along with the lowest K-c (log K-c approximate to 5.2) were found a fter an algal bloom in spring. Copyright (C) 1999 Elsevier Science Ltd.