S. Hilger et al., Size fractionation of phosphorus (dissolved, colloidal and particulate) intwo tributaries to Lake Lugano, AQUAT SCI, 61(4), 1999, pp. 337-353
An in-situ fractionation mainly consisting of continuous flow centrifugatio
n and cross-flow-ultrafiltration was used to separate a particulate (partic
le diameter > 1 mu m), a colloidal (particle diameter < 1 pm and molecular
weight > 10 kD) and a dissolved fraction (molecular weight < 10 kD) of tota
l phosphorus in river water. A similar fractionation pattern is observed in
function of discharge in two tributaries to Lake Lugano, the rivers Cassar
ate and Vedeggio. In Cassarate river 31% of the total P is particulate, 10%
colloidal and 59% dissolved at low discharge, whereas at high discharge 73
% is particulate, 10% colloidal and 17% dissolved. 19% of the total P is pa
rticulate, 12% colloidal and 69% dissolved at low discharge in Vedeggio riv
er, and at high discharge 19% of the total P is dissolved, 8% colloidal and
73% particulate. Release of ortho-phosphate (o-P) from Cassarate and Vedeg
gio colloids was observed at pH 10, and by the enzyme alkaline phosphatase
in laboratory experiments. Calculations of a model based annual P-load into
Lake Lugano showed an average total P-distribution with 60% particulate P,
10% colloidal P and 30% dissolved P in Cassarate and Vedeggio river for 19
96 and 1997.