Polyhumous Dystrophic Pit Lakes: Hydrographic and Hydrochemical Characteristics on the Example of Reservoirs in the Włoszczowska Basin, Central Poland

The article presents the hydrographic and hydrochemical characteristics of post-exploitation reservoirs formed in peat excavations. Two natural bog lakes were selected as the control objects for the study. The research indicated that both the waters of post-exploitation peat reservoirs and natural bog lakes show low electrolytic conductivity (<100 µS/cm) and acidic water reaction (pH < 5.5). The concentration of major cations and anions is also very low. The concentration of calcium and magnesium does not exceed a few mg/L. Hydrochemically, all post-exploitation peat reservoirs are bi-ionic sulphate–calcium (SO 4 2− -Ca 2+ ). This distinguishes post-exploitation peat reservoirs from natural bog lakes in which multi-ion waters were found, for example, sulphate–chloride–calcium (SO 4 2− -Cl − -Ca 2+ ) and sulphate–calcium–sodium (SO 4 2− -Ca 2+ -Na + ). The calculated water humic state index (HSI) allowed the classifying of the examined reservoirs as polyhumous. The value of this index, in all reservoirs, was >50. Based on the calculated hydrochemical dystrophy index (HDI), it was found that all post-exploitation peat reservoirs are dystrophic. So far, no such hydrochemical type has been found in other post-exploitation peat reservoirs. Therefore, the examined objects should be classified as unique post-exploitation peat reservoirs.