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The extensive character of this economy is accounted for by the fact that the ąuality of water started to improve after the change of the social-political system in the 90’s. The increasing improvement, despite the short period of observations, has already been signalled in some papers of this volume.

The problem of anthropogenic impact on water conditions in Poland is presented using the examples of a few selected areas (catchments). The first two papers refer to the Vistula River catchment. The influence of hydro-technical works on sediment transport is presented by A. Łajczak; he has found that Vistula channel regulation works caused increased sedimentation rates of the suspended load in recent decades. The balance and structure of the solute yield in the Vistula River basin is presented by H. Maruszczak and M. Wilgat, who found that during the last several dozen years the amount of "synthetic" substances (introduced to circulation by man) has increased several times. The authors of the other two papers present changes of water conditions in the past in the areas of old, big town centres existing sińce the early Middle Ages: Poznań in Wielkopolska — in the western part of the Middle Polish Lowlands (A. Kaniecki), and Lublin in Małopolska — in the eastern part of the South Polish Uplands (Z. Michalczyk and M.J. Łoś). A research group of Prof. T. Wilgat have described the Łęczna-Włodawa Lakę Region, where the natural water conditions were rather well-preserved till the middle of the 20th century, and then changed rapidly and deteriorated due to unreasonable drainage works, intensified recreational utilization and the digging of mines in the new coal basin at the border of this region. A.T. Jankowski has studied the great increase in the dissolved load supplied to rivers with minę wastewaters from the old coal basin in Upper Silesia; in the late 80’s and early 90’s about 35% of sulphates and 50% of chlorides transported by Polish rivers came from this coal basin. The paper by A. Świeca gives information about rapidly-increasing pollution of a smali river with wastewaters from Zamość — a middle-sized town, with fast development of the administrative centre of the new district established in 1975.

Henryk Maruszczak

Leszek Starkel