Experiences with qualitative monitoring of small water resources in forested catchments

Comprised in monitoring of forest ecosystems from the viewpoint of human nutrition chain, in 2000 - 2003 the assessment of small resources and streams was carried out related to chemical composition of water. Samples from 267 localities were analyzed within 37 forest areas distributed all over the territory of the Czech Republic. One of the assessed coefficients was water acidity. Values of pH for 75.3 % of samples ranged between 6.5 - 9.5, 24.7 % of samples had pH lower than 6.5 (minimal value pH 3.83). Occurrence of low pH values is principally significant and in many cases corresponds with high content of aluminium. The most critical acidity was in the forest area Jizerske Mts. (94.1 % of samples with pH lower than 6.5 and average pH value only 5.82). Most samples with pH lower than 6.5 also overrun the limiting value for aluminium (0.2 mg. l(-1)). Totally the limiting value for Al exceeded 20.2 % of samples. The values for magnesium (Mg) are very low. The average real value of concentrations is only 5.36 mg. l(-1). Totally 82.4 % of samples show Mg concentrations lower than minimal 10 mg. l(-1). The lowest average concentrations are in the forest area Novohradske Mts. (average 1.236 mg. l(-1)) and Sumava Mts. (average 1.305 mg. l(-1)), average concentrations are also very low in the forest areas Jizerske Mts., Luzicka Sandstones, Cesky les, Krkonose Mts., and Jihoceske basins. Values of calcium did not reach the minimal limiting value of 30 mg. l(-1) and were found in 77.2 % of samples, mainly also in the forest areas of the Bohemian boundary mountains. The area of south-eastern Moravia showed to be the most favourable. Also here, similarly as at magnesium, mineral parent rock and soil influence the water. Of other elements coefficients of iron overrun the standard in much lower extent (18.4 %). Values of sodium, manganese, copper and sulphates did not overreach the limiting values in any case. Only in one case the value of fluorides was over the limit defined by the instruction.