POTENTIALS OF PHOTOLYTIC RHODAMINE WT AS A LARGE-SCALE WATER TRACER ASSESSED IN A LONG-TERM EXPERIMENT IN THE LOOSDRECHT LAKES

The disperal of 0.13 kg of water-tracer rhodamine WT in the Loosdrecht lakes was surveyed during 19 months. Solid-phase extraction and liqui d chromatography were used to measure the very low concentrations of r hodamine WT in the experiment. The detection limit was approximately 2 x 10(-11) kg m-3. The photolysis constant of rhodamine WT was measure d in a laboratory experiment. A numerical model for hindcasting the di lution of a photolytic tracer in the lake system was developed. Model results compare well with observations showing that rhodamine WT is we ll suited for tracer experiments on large time and space scales, provi ded that photolysis is taken into account.