153 Hydrochemical evaluation of dystrophy of the water bodies in the Łęczna and Włodawa area ... Limnological Review 9, 4: 153-158 Hydrochemical evaluation of dystrophy of the water bodies in the Łęczna and Włodawa area in the years 2000-2008 Stanisław Chmiel Maria Curie-Skłodowska University in Lublin, Institute of Earth Sciences, Department of Hydrography, ul. Akademicka 19, 20-033 Lublin, Poland, e-mail: stanislaw.chmiel@poczta.umcs.lublin.pl Abstract: In the present paper, an evaluation of the level of dystrophy of 74 water bodies in the Łęczna and Włodawa area is presented, which was prepared based on the studies on physical and chemical characteristics of their water from the years 2000-2008. Water dystrophy was evaluated using the HDI index (Hydrochemical Dystrophy Index) which comprises the following indicators: water pH, speciic electrolytic conductivity, dissolved organic carbon (DOC) concentration and dissociated inorganic carbon (DIC) concentration. In the collected material, the evaluation of the status/level of water dystrophy in particular lakes was made based on the minimum HDI values obtained in the study period. he dystrophy index (HDI) of the lake waters was within a range of 4.1-76.9. he index values above 50, considered to be the indication of water dystrophy, were noted periodically only in several lakes. Key words: water dystrophy, hydrochemistry, Łęczna-Włodawa area water bodies Introduction Dystrophic lakes (also called humic lakes) belong to water bodies with inharmonious sequence of succes- sion, water rich in humic acids, acidic pH, brown colour, exhibiting low biological productivity (Hansen 1962; Kajak 1994). hese are generally small lakes, surround- ed by peatland adjoining a forest; they are characterized by a high degree of naturalness and are distinguished by their exceptional ecological values (Hutorowicz et al. 1999; Radwan ed. 2002). Due to this uniqueness, in Poland they are most frequently protected as nature reserves, sites within national parks, or as ecological lands. In addition, such habitats are protected under the Natura 2000 network as “natural dystrophic water bod- ies, code 3160”. Dystrophic lakes are included in the group of “ex- treme” habitats, since they are very sensitive to changes, in particular eutrophication (Hutorowicz 2004; Strategy …). he main reasons for the degradation of this group of lakes are most frequently associated with a decrease in groundwater levels and in lake surface level, drain- age of the adjacent peatland, the ishery use of the re- spective water body (Hillbricht–Ilkowska et al. 1998; Chmiel and Urban 1995; Wojciechowski 1999; Huto- rowicz and Hutorowicz 2002). During the irst stage, the change in the trophic nature of a lake is manifested through physico-chemical characteristics of the water, in particular: an increase in its pH, the disappearance of the brown colour of the water, an increased pool of biogenic and mineral compounds. In the second stage, the appearance of lora and fauna species characteris- tic of eutrophic environment is observed. herefore, hydrochemical studies are an essential diagnostic tool for quick evaluation of dystrophy of lake waters and for monitoring their evolution. To evaluate lake dystrophy using hydrochemi- cal methods, the HSI index is used most frequently (Håkanson and Boulion 2001), which includes water colour and chlorophyll, and/or the HDI index (Górniak 2006), which includes water pH, speciic electrolytic conductivity (SEC), dissolved organic carbon (DOC) concentration and dissociated inorganic carbon (DIC) concentration.