Diversity of the TSI Indicators of the Middle-Forest Small Retention Reservoir

Studies upon the trophic status were carried out using water samples from a small retention reservoir Topiło located in a particularly valuable natural forests of Puszcza Białowieska. In order to assess the degree of Topiło reservoir contamination, three measurement and control points were selected for testing, which were situated near the inflow (point No. 1) and outflow (point No. 3) of river Perebel, as well as in the middle part of the reservoir (point No. 2). The selection and placement of measurement and control points on the reservoir was dictated by the ability to capture changes in the study object. Tests of water samples collected from the surface layer of the coastal zone, were carried out once a month during the period from April 2007 to March 2014. The following determinations in collected water samples were performed: total nitrogen, total phosphorus, chlorophyll “a”, and turbidity. The trophic level of Topiło reservoir was also assessed according to the concentration criteria and based on the trophic status indices (TSI) calculated after Carlson’s as well as Kratzer and Brezonik’s. Given the annual average value of overall trophic level (Trophic Sta-tus Index), the dominant role of the TSI (TP) during all years of research attracts some attention. The TSI index values ranged within 78.3–80.26, which allowed to classify the water of Topiło reservoir as hypertrophic. The research indicates an advanced and constantly progressive degradation of water quality in Topiło reservoir. Values of TSI (Chl) were in the range of 49.2–77.35 and therefore water status in winter can be defined as eutrophic indicating the hypertrophy in remaining periods under study. Additional investments planned for advance reclamation treatments should be necessarily taken into consideration at the stage of planning and design of new small water retention reservoirs. Topiło reservoir requires modernization and reclamation, it is also necessary to clean it up, especially the bottom pond, out of the stocked wood residues, as well as to remove the excess of sludge.