INPUT AND DYNAMIC BEHAVIOR OF THE ORGANIC POLLUTANTS TETRACHLOROETHENE, ATRAZINE, AND NTA IN A LAKE - A STUDY COMBINING MATHEMATICAL-MODELING AND FIELD-MEASUREMENTS

The dynamic behavior of tetrachloroethene (PER), atrazine, and nitrilo triacetate (NTA) in a small lake in Switzerland has been evaluated qua ntitatively using field data and a simulation software (MASAS) for mod eling organic pollutants in lakes. For PER, atrazine and NTA, the inpu t and the seasonal variation in the vertical distribution could be des cribed successfully by applying simple box models as well as a one-dim ensional vertical model. In the case of PER, it was possible to recons truct the input history for a long time period (9 years), and it was f ound that the stagnant boundary layer model was well suited for estima ting the average gas exchange rate of this volatile compound between t he lake and the atmosphere. Atrazine showed, except for a short time p eriod during the summer, a very conservative behavior in the lake. For NTA, an average in situ rate constant of 0.035 d(-1) was determined f or its elimination from the water column. The elimination was attribut ed primarily to biodegradation. The results of this study demonstrate nicely the power of the combined use of mathematical models, including computer simulations, and field measurements for assessing the enviro nmental behavior of organic pollutants.