Bilans wodny oraz dynamika zmian wybranych zanieczyszczeń zbiornika Dzierżno Duże w warunkach silnej antropopresji

Abstract

Silesian Upland and its borders (Fig. 1) belongs to the most anthropogenically transformed areas in Poland and reasons of this state should be found in the exploitation of raw resources, causing not only the intensive development of industry but also massive population inflow. Owing to high degree of urbanisation and industrialisation, the natural environment of the area discussed underwent wide transformation, which spectacular example is the catchment of the Klodnica together with Dzierżno Duże water reservoir (Fig. 2). It is located in north-eastern part of Racibórz basin and its catchment - of area amounting near to 530 km2 - is located almost completely in an area of Katowice Upland, that is identified with the largest industrialisation and urbanisation within borders of Silesian Province. Identification of research problems allows determining the range of elaboration and putting into words the purposes of work, which especially refer to: a) estimation of quantitative differentiation of reservoir water balance elements in the light of natural and anthropogenic environmental conditions; b) the importance of reservoir in the shaping of physico-chemical properties of surface- and underground waters of the neighbourhood; c) estimation of degree of pollutants cumulative effectiveness in the reservoir; d) estimation of eutrophication intensity and variability of thermal-oxygen conditions in strongly polluted limnic waters; e) determination of limnological separateness of Dzierżno Duże water reservoir against a background of lakes and other artificial water reservoirs of Poland. The geological basal complex in the area discussed is composed of the Devonian-Carboniferous deposits, creating widespread basin, lying discordantly at the Cambrian deposits and possibly in some place at the Ordovician and Silurian ones. At partly folded and cut by numerous faults Carboniferous deposits, the Triassic formations, occurring under the cover of the Tertiary deposits, lie (Fig. 3). Varigrained fluvioglacial sands with addition of gravels and clays (Fig. 4) as well as Holocene material, represented by deluvial, fluvial, lacustrine and peat deposits lie higher. In the area discussed the Klodnica valley reaches the width of about 400 m up to 1.5 km. Many lateral valleys of basin shape divide it. The relief of valley was considerably transformed owing to human activity what the occurrence of numerous anthropogenic relief forms betokens (Fig. 5). In the neighbourhood of Dzierżno Duże water reservoir the mean annual air temperatures and precipitation sums were characterised by the wide range of fluctuations (Fig. 6). The most frequent winds blew from SW, NW, W and S directions (Fig. 7). Wind of velocity up to 2 m/s and from 2.0 to 5.0 m/s predominated, whereas calms made 16.3% of observation. Surface waters in an area discussed (Fig. 8) are an evident example of human activity influence on the water environment, which is revealed among others by the anthropogenisation of runoff (Fig. 9), changes in surface hydrographic net arrangement (Tab. 1) and degradation of surface waters quality (Tab. 2). Post-exploitation-dam water reservoir of Dzierżno Duże (Fig. 10), which was functioning in the middle part of the Kłodnica catchment since 1964 year is characterised by the total capacity amounting to 93,5 hm\ maximal depth reaching over 20 m and area exceeding 6 km2- at maximal level of damming (203,5 m. a.s.l.). This reservoir is used to improve conditions of inland navigation at Gliwice canal and the Oder, purification of strongly polluted Kłodnica river waters and the prevention against flood. It is characterised by significant and unusually dynamic fluctuations of water states (Fig. 11), rarely met in other objects of this type. They stimulate the development of littoral processes and considerably are the implicators of filtration processes, which occur in the reservoir neighbourhood, conditioning frequent changes in character of connection of surface waters with water-bearing horizon. The occurrence of underground waters in the area discussed is mostly connected with deposits as follows: the Quaternary. Tertiary, Triassic (I'ig. 12) and Carboniferous. The existing reservoirs of underground waters (Tab. 3) are characterised by the varied yield and quality of exploited waters, to ti varied degree undergoing the process of drainage by coal mining. Balance calculations were carried out for hydrological period 1975-1996 (Tab. 4; Fig. 13-17, 22 and 23). In total sum of both surface alimentation and alimentation of reservoir by waters originating from atmospheric precipitation. 98.2% falls for surface inflow but atmospheric precipitation makes only 1.8%. The dominating position in water balance at the side of losses is surface runoff; evaporation from the reservoir area is of marginal importance. The difference balance, which can be identified with the balance of water interchange with subsurface catchment (Fig. 17), shows water escapes from reservoir, making almost 30% of surface inflow. It is confirmed by existence of many hydrophysical and hydrochemical premises, e.g. a) slope of underground waters table in the direct neighbourhood of reservoir, estimated on the base of piezomctric and well measurements (Fig. 18; Tab. 5); b) neighbourhood of hydrogeological window (Fig. 3 and 4); c) location of basin of limited possibilities of silting in the permeable Quaternary deposits, filling the fossil valley of the Kłodnica; d) physicochemical properties of underground waters in reservoir neighbourhood (Fig. 19 and 20); e) water balance for difference catchment of Kłodnica limited by profiles Gliwice and Łany Małe, prepared with regard to the quantity of water, drained by Gliwice Canal (Fig. 21). Water quality in the neighbourhood of Dzierżno Duże water reservoir is mostly determined by the occurrence of allochthonous pollutants, delivered from above-located strongly urbanised and industrialised parts of catchment (Fig. 24-31). In relation to the hydrochemical composition of autochthonous waters in reservoir neighbourhood, waters delivered from western part of Katowice Upland arc characterised by total mineralisation, which is even above ten times higher. Formation of Dzierżno Duże reservoir in post-sand excavation and directing to it waters originating from the drainage of western part of Katowice Upland - despite the significant improvement of quality in some parameters of potamic waters (Fig. 24-31) - does not solve problem of pollution at below-located parts of the Kłodnica catchment and the Oder, fed by it. It is connected with the problem of so- -called chemical retention in lakes and water reservoirs, which importance is possible to estimate in the context of contamination (Fig. 24-31; Tab. 6) and substances loads (Fig. 32-36; Tab. 7), analysed in system of inflow-outflow. On this base it was ascertained, that Dzierżno Duże water reservoir, not causing essential changes in surface waters purity classes, plays a role of contamination reductor and loads cumulator (e.g. suspensions or substances, which cause salinity). But there are cases (biogenic substances) when it is the source of secondary water pollution. One should acknowledge it for the especially harmful process in relation to the present alimentation of underground waters - the Triassic and Quaternary water-bearing deposits - by limnic waters of low quality. Rubble material accumulated in the reservoir is significantly polluted, what is confirmed e.g. by the content of heavy metals, corresponding with quantities determined for differently anthropogenically transformed areas and - in many cases - exceeding the levels, which are typical for natural, i.e. geochemical background. Hydrochemical researches, applying the existing poor network of working piezometers and wells (Fig. 18) confirm the infiltration of water from the reservoir and facilitate the determination of some directions of polluted limnic waters migration as well as the supposed ranges of negative influence of their retention. The reservoir surface influence on the changes in physico-chemical properties of waters of the first water-bearing horizon - automatically connected with the lowering in their usable values - is clearly visible in the distance of 1 km to the west from reservoir (Tab. 8). One should suppose that the zone of Dzierżno Duże water reservoir influences on the shaping of physico-chemical properties of the first water - bearing horizon reaches slightly far to the west. Premises of these supposes are results of research on Plawniowice water reservoir (Fig. 19 and 20). Many research-workers connect successively decreasing quality of water resources of the Triassic underground waters reservoir with inflow of pollutants, originating from potamic and limnic waters. Spectacular differences in underground waters quality occur in relation to some from tens intakes (Tab. 9). Especially low usable values and disadvantageous physico-chemical properties have underground waters in this part of the Triassic underground water reservoir, which is located in direct neighbourhood of hydrogeological window, prepared in the Tertiary deposits (Tab. 9). The sign of high degree of water pollution in Dzierżno Duże water reservoir is eutrophication. The deciding role in the process of reservoir waters alimentation by biogenic substances plays the catchment and the delivery of nutrients from bottom deposits. The loading of reservoirs by phosphorous and nitrogen loads is an indicator of this object high trophy (Tab. 10; Fig. 37-39). Owing to large quantity of substances, being stimulators of biogenic life, in the summer half-year the massive development of phytoplancton occurs in the reservoir (so-called “water-blooms”), which consequence is the increased outflow of suspensions in the summer-autumn period. Bioindicator of high nitrophilinity is also vegetation, covering the littoral zone, although its development is importantly limited (phytotoxic properties of substratum, fluctuation of water state, littoral processes). Processes of eutrophication additionally modify the distribution of oxygen content in water mass and they are reflected in 24 hours’ fluctuations of oxygenation in epilimnion waters. Therefore, the eutrophication makes the important exploitation, reclamation and protection problem, all the more so as the inflow of allochthonous pollutants essentially influences the shaping of thermal-oxygcn conditions as well as lightness of water mass. The occurrence of two periods of water circulation have been stated in the reservoir, i.e. the period of spring homothermy and longer-lasting autumn homothermy. In the summer period the shaping of normal water stratification in the reservoir (anothermy) takes place, whereas in winter the opposite stratification circuit (katothermy) occurs. Very important is the fact of limnic waters loading by thermal pollutants (Fig. 40-42). It is documented by mean annual temperature of waters alimentating Dzierżno Duże water reservoir, which exceeds of about 3°C the mean annual temperature of atmospheric air and about 1,6°C the mean annual temperature of waters in streams inflowing to other water reservoirs (Przeczyce, Kozłowa Góra, Pogoria III, Plawniowice), being to decidedly smaller degree under the human impact. One should pay attention to the separate thermal regime of the eastern and western parts of the reservoir (Fig. 40 42; Tab. 11), which is documented by the occurrence of horizontal thermal gradients, typical for reolimnic objects and conditioned - to a small degree - by inflow to reservoir of waters of anthropogenically increased temperature. Strong pollution of limnic waters is the determinant of their oxygenation (Fig. 43 and 44), which rarely has the features of supersaturation or the full saturation, most often shaping itself at the borderland of normal and deficit saturation. Especially during summer stratification the oxygen conditions should be acknowledged as exceptionally disadvantageous (e.g. even tens days-lasting lack of oxygen in hypolimnion, leading to the exhaustion of sulphur hydrogen, superoxygenation of waters of strongly eutrophiced epilimnion). High load of reservoir by allochthonous pollutants essentially influence the shaping of oxygen conditions - profiles located in the eastern part of basin arc characterised by decidedly more disadvantageous oxygenation and the improvement of oxygen condition goes to the west direction. Nevertheless, even there they are far from state typical for objects devoid of pollutants. Despite the disadvantageous oxygen conditions in reservoir the surface runoff waters contain decidedly more oxygen (on average 3.3 mg O2/dm ') than waters of its tributaries. Only alarming is the fact that the increase of oxygenation in potamic waters below the reservoir results mostly from the development of limnic eutrophication processes. Reservoir waters transparency (Fig. 45) is also important for eutrophic lakes and it is located within the ranges of transparency, which is most often met in waters of lowland lakes. Wide range of this elaboration is specified in the widespread synthesis, containing the estimation of area investigated state, referring to more important limnological typologies as well as to published and unpublished results of research on natural and artificial water reservoirs (Fig. 46-48; Tab. 12-20). The separateness of Dzierżno Duże water reservoir against a background of lakes and other artificial water reservoirs is appeared by the largest degree of anthropogenisation of particular elements of water balance and extremely rarely met level of pollution. It creates the possibility to predict the course of degradation processes in limnic waters quality in objects functioning now under conditions of incomparable lower environment transformation.