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Skład fizyczno-chemiczny wody w małej zlewni leśnej na Dolnym Śląsku

Pulikowski K., Palczyński M., Paluch J., Paruch A.

Czasopismo Techniczne. Środowisko

2002

R. 99, z. 4-Ś

95--104

Waters are this kind of environmental element, which is very susceptible to degradation and progressive development of human civilisation. The state of water pollution is a relative concept and require a point of reference. The best point of reference would be natural water, such which a composition does not change under influence of human activity. Maybe water in forest catchment areas could be a good point of reference, called "natural background", because of the fact that forest areas are treated as surroundings without anthropogenic changes. This paper describes a preliminary estimation of ground water composition in a small forest catchment area situated south-east of Milicz town, on the area of Landscape Park of Barycz Valley. The research involves exactly three catchment areas (Fig. 1): The first is a source area (F[I] = 0,230 km2), the second (F[II]=0,500 km2) include catchment area I. In cross-sections, which close both of the catchment areas (I and II), installations that delay and equalize the water run-offfrom catchment area were installed. The installations were called "run-off delayer". The third (F[III]=0,085 km2) is bordered on catchment area II and is useful for an estimation of water run-off equalization by means of using the run-off delayers. A hydrologic year described in this paper was classified as a wet year. Total annual precipitation amounted to as much as 778 mm, whereas multiannual total precipitation only 563 mm. By far the higher precipitation were noticed during the third quarter of 2001, e.g. in July was as much as 180 mm (Tab. 2). Also, mean annual air temperature (9,2 stopni C) was higher than mean multiannual and autumn-winter months (November, December, January) were definitely warmer (Tab. 3). The research involved a physical and chemical composition of groundwater and surface water. Groundwater was taken from two piezometer wells - P5, P6, and surface water from cross-sections, which close all catchment areas: I, II, II' (above run-off delayer a small reservoir has formed. It is filled up during high water stages, so above it water was also taken) and III. Depth to groundwater in the vicinity of piezometer P5 was between 108-136 cm, deeper than depth range 10-101 cm for piezometer P6. The pH scale of these tested waters ranged between 7,1 and 7,8 and was relatively stable regardless of sampling places (Tab. 4). This measured values are typical of most groundwater. A mean conductivity value of waters from both piezometers amounted to 278 miS x cm-1 for P5 and 415 miS X cm-1 for P6. This measured values vere relatively low and showed also a low concentration of mineral compounds. Values of oxygen demand indicators (BOD5, COD[Mn], COD[Cr] of water from P6 were higher than these values for water from P5, e.g.: a mean value of COD[Mn], amounted to only 4,4 mg O2xdm-3 in the water from P5 whereas value of it amounted to as much as 12,3 mg O2xdm-3 in the water from P6. A reason of such diversity could be a shallow groundwater in the vicinity of piezometer well P6 and direct contact with upper layer of forest soil, rrich in organic matter. In contrast to oxygen demand indicators, nitrogen concentration did not show such diversity between water samples from both piezometers. Concentration of mineral forms (ammonia and nitrate) was low. The measured concentrations were lower in comparison with values of this nitrogen forms in groundwater from lands for intensive agricultural activity or even in groundwater from tree-covered lands. Nitrogen in organic forms showed higher concentrations, which mean values in both cases amounted to 4,3 mg N[org] x dm-3. Phosphate concentrations was loww in the tested waters, but total phosphorus concentrations were higherr and amounted to 0,44 mg P x dm-3 in samples form P5 and 0,35 mg P x dm-3 in samples from P6. Concentration of alkali elements (Na, K, Ca, Mg) was low, but concentration of them except for potassium was higher in samples from P6 in comparison with samples from P5. The tested water showed quite high concentrations of irron and manganese (such as most groundwater on the area of Poland). Values of them changed in a wide range of concentrations. The mean values of manganese concentration were higher in the groundwater from P6 however iron showed an opposite trend. In samples of the tested groundwaters concentration of chlorides and sulphates was also low. Surface waters on the researched object i.e. watercourses arre classified as very small due to low mean flows in the cross-sections. Catchment areas of these are 100% forested, i.e. mixed forest where broad-leaved trees predominate except for catchment area I where coniferous trees predominate. A pH reaction of these tested waters showed a big diversity from an acid reaction (3,7 - 4,8 pH), in higher part of catchment area - cross-section I, to an alkaline reaction in others cross-sections (Tab. 5). Also, the lower value of conductivity but with the higher mean value of total solids was measured in cross-section I. The values of these indices and observations were done during taking the samples (i.e. water was brownish in this cross-section) can suggest that results obtained from laboratory testes were an effect of a considerable concentration of organic acids in the tested waters. These waters contained a smallquantity of total suspended solids. What interested is that the mean value of this indicator in the water from cross-section II was the biggest (25,4 mg x dm-3) and in the water from cross-section II was the smallest (12,3 mg x dm-3). It can show a good impact of reservoir which has formed above run-off delayer. The tested waters revealed a very high degree of oxygen saturation, except for a mean value for the water from cross-section II. A reason of that it could have been deoxidation of water stored in the reservoir above run-off delayer II, in May when temperatures were relatively high. In that time the amount of dissolved oxygen in water from cross-section II was only 0,5 mg O2 x dm-3 whereas in other cross-section from 7,8 to 8,0 mg O2 x dm-3. Mean and even maximum values of oxygen demand indicators (BOD5, COD[Mn], COD[Cr]) of the tested waters were relatively low except for water from cross-section I. Values of this indicators decreased regularly along with watercourse run from coss-section I and II' to II due to water inflowing which was less polluted with organic matters. Nevertheless, values coming from cross-section II were higher than values for water from cross-section III - i.e. control catchment area which was not supplied water polluted with organic matters. The tested waters showed low contents of mineral forms of nitrogen (ammonia and nitrate). They were also higher in water from cross-section I. Because of the fact that values of organic nitrogen were relatively high, content of total nitrogen was also high and amounted from 5,5 to 8,1 mg N[tot] x dm3. Phosphate contents were low but phosphorus concentration is a major problem for watercourse flowing out of the catchment area. The concentration in the tested samples changed in a wide range of values. A mean phosphorus concentration was similar for all cross-sections and amounted from 0,40 to 0,47 mg P x dm-3. A maximum phosphorus concentration amounted from 0,80 mg P x dm-3 for the waters from cross-section III to 1,40 mg P x dm-3 for the waters from cross-section II. Test of individual values of phosphorus showed general trend which is proved by well-known tendency: minimum contents were during summer/autumn period and maximum contents were in winter. Concentration of alkali elements was relatively low in the tested surface waters and did not show direct tendency. Contents of sulphates and chlorides were also low and were not connected with sampling places. Waters in forest catchment areas can be a comparison background useful in estimation of water on areas of human activity due to a natural composition. The tested groundwaters were classified as very pure, although quite high concentrations of iron and manganese (what is typical for groundwater of Poland) as well as organic nitrogen and some values of BOD5, COD[Mn]. The main environmental factor determining a composition of surface waters in forest catchment areas is a content of organic acids in these waters. Waters without pollution of such acids are also very pure and can be a comparison level for estrimation of surrface waters pollution. The tested surface waters (from all cross-sections) contained higher concentrations of phosphorus in relation to values of this indicator in the classification of purity of surface inland waters in Poland, but they contained relatively low concentration of other indices. Such relation between phosphorus and other indices can mean that classification criteria for established values of phosphorus concentration are too strict.