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Changes in chemism of the Łabuńka river..

the Topornica (Fig. 1), water samples for laboratory analyses were taken every 2 weeks. Among other things, I determined to tal solute concentration conductometrically, pH value potentiometrically, and the concentration of macrocomponents by the standard methods according to M. Markowicz and M. Pulina (1979). I also took into consideration the results of sample analyses of river waters madę once a month from 1980—1992 at 3 measurement points of the Provincial Inspectorate of Environment Protection in Zamość (on the Łabuńka river in Krzak, its tributary the Czarny Potok in Sitaniec and the Topornica in Zamość). For these points the concentration of dissolved oxygen, phosphates and ammonium nitrogen were also taken into consideration, as well as the content of organie substances (BOD₅ index). From this Inspectorate, I also obtained data on the amount of sewage discharged into surface waters in the years 1989-1992.

From these data a relatively detailed picture of the different hydro-chemical conditions of the discussed catchment, and changes caused by wastewater, was obtained.

HYDROLOGICAL CHARACTERISTICS OF THE ŁABUŃKA RIVER CATCHMENT

The Łabuńka river is the biggest right tributary of the upper Wieprz river, with a length of 34.4 km, and a catchment area of 513.5 km². Its two bigger tributaries are: on the left — the Topornica on the 22.5 km of its course, and on the right — the Czarny Potok on the 13 km of its course. The studied catchment up-stream of the gauging station at Krzak (the 4.2 km of its course) is 416 km² in size, which constitutes 81% of the Łabuńka river catchment.

The Łabuńka river catchment up-stream of the gauging station at Krzak largely comprises the area of the Zamość Basin, partially the Middle Roztocze and the Grabowieckie Heights (Fig. 1). Upper Cretaceous marls predominate in the substratum; marły and typical opokas occur in places. Of Quaternary formations, mineral-organic ones lining the valley bottom of the Łabuńka river and its tributaries, are the most widely-distributed. Loesses occur on the Grabowieckie Heights and in Roztocze as well as in watershed zones in the Zamość Basin.

My studies were carried out in much warmer and drier years than average, i.e. at much lower flows. The mean annual air temperaturę was 8.2°C in Zamość in the years 1989-1992 and was almost one degree higher than the average of the years 1951—1980 (7.2°C). The mean annual precipitation was 567 mm in Zamość in those years and was lower by 3.1% than that of 1951-1980 (585 mm). The Łabuńka river discharges were also Iow; at Krzak the mean annual discharge in the years 1989-1992 was 1.16 m³s^-1, thus as lower as 40% of the average for the years 1951-1980.