Polish Journal of Environmental Studies Vol. 12, No. 1 (2003), 111-117 Changes in Water Chemistry Along the Course of Two Rivers with Different Hydrological Regimes P. Zieliñski*, A. Górniak, T. Suchowolec Department of Hydrobiology, Institute of Biology, University of Bia³ystok, ul. wierkowa 20 B, 15-950 Bia³ystok, Poland Received: 5 August, 2002 Accepted: 6 September, 2002 Abstract Chemical composition of water and dissolved organic carbon (DOC) levels were investigated over three years, along two large rivers in NE Poland, with different hydrological regimes. One river was from lakeland and the second a typical lowland river with forests and high contributions of peatlands in the catchment. The study involved hydrological (specific runoff, river discharge) effects on the variability of water chemistry and DOC concentrations. Specific runoff and discharge influence on DOC level and water quality. DOC concentrations and chemical water parameters were highest in the upper part of the lowland river and lowest in the upper course of the lakeland river. A two times lower DOC concentration was observed in the river draining lakeland with high values of specific runoff than in the lowland river. In typical lowland rivers organic compounds (mainly natural humic substances) intensified water eutrophication along the river course. Keywords: river, DOC, water chemistry, hydrology. catchment to rivers [5]. Numerous data clearly show the Introduction important effect of the river basin character on carbon concentrations and their losses [6]. The influence of the Numerous lowland rivers in Europe are contaminated hydrological parameters of rivers on water chemistry and and loose their characteristic biodiversity [1]. Chemical its changes along the river course has not yet been changes of their waters are brought about by different comprehensively studied, especially in Poland [7, 8]. causes such as the inflow of wastes, nutrients, and pesticides The aim of the present study was to examine the spatial from urban and agricultural areas or nutrients and dissolved and seasonal variation of DOC and water chemistry in two forms of organic carbon from drained organic soils [2]. Polish rivers with contrasting basins, river flow, and Dissolved organic carbon plays an important role in varied catchment land-use. biogeochemical cycles. Nutrients and metals such as DOC- mineral complexes, can migrate in fresh water [3]. Study Area and Methods Dissolved forms of organic carbon are a source of energy for stream ecosystems [4]. Recent reports have shown concern of the intensification of DOC export from The Narew River (NR) (the largest in NE Poland) and the Czarna Hañcza River (CHR) in northeastern Poland *Corresponding author, e-mail: [email protected] were selected for investigation as relatively undisturbed river 112 Zieliñski P. et al. ecosystems of lowland and lakeland areas (Fig. 1). The annual spring rise of waters and several lakes in the river region has scarce industrial development and low human system. The mean river discharges in Poland do not exceed density. The aim of the regional policy is to preserve these 10 m3/s, but the specific runoff from the catchment is almost undisturbed conditions. In the catchment of the Vistula two times higher then that from the Narew River catchment, River, the Narew River is the largest in NE Poland while the respective values being 6-10 and 4-6 dm3/s km-2. The the catchment of the Czarna Hañcza River is a part of the CHR catchment area is dominated by extensive agriculture, Niemen River basin, lying chiefly in Lithuania. a small degree of forestation, and high denivelations to 170 m. The investigated rivers represent two geographic In May, July and October (3 times a year in 1996-1998) regions with similar annual precipitation of 550-770 mm water samples were collected from 12 stations located along and a vegetation season of 190-200 days. The lowland the Narew River (7 stations) and Czarna Hañcza River (5 Narew River drains a periglacial sandy-loam catchment stations) (Fig. 1, Table 1). The samples were taken from with a different percentage of forests and wetlands the upper water layer, in places with maximum velocity of (undisturbed by human activity). Multiannual discharge the water flow. At each sampling station water temperature, of the Narew River varies from 5 m3/s in the upper course pH and electrical conductivity were measured. On the same to 150 m3/s in the lower course. The catchment of the day chemical parameters of the water were determined Czarna Hañcza River in the Lithuania Lake District covers using standard methods. DOC concentrations were sediments from the last glaciation. It is characterized with measured using a Shimadzu TOC-5050 A analyser in samples previously filtered through 0.45mm Nalgene SFCA filters and acidified to pH = 2. The quality of DOC Czarna was determined on the basis of spectrophotometric data as Ha ñcza SUVA (specific ultraviolet absorbance) calculated with the ratio of absorbance 260nm (1cm of filtered water, natural pH) x 1000 to DOC concentration. The hydrological data Czarna (multiannual river discharge from 1981 to 1990 were taken Ha ñcza from the Biaùystok Institute of Meteorology and Water Management (unpublished data). Statistical analyses, Biebrza ANOVA rang test, and discriminant analyses, were carried Narew out using Statgraphics and Statistica 5.0. Narew Results and Discussion Narew Bug Throughout the entire study period mean concentrations of most parameters investigated in the two rivers were Fig. 1. Location of investigated rivers and sampling stations. significantly different except for conductivity, potassium Table 1. Characteristic of sample stations on Narew River (a) and Czarna Hañcza River (b). River length Catchment area Discharge Specific runoff a Sample station [km] [km2] [m3/s] [dm3/s km2] 1 52.3 1 050 5.6 5.30 2 74.0 1 978 9.9 5.00 3 99.9 2 538 13.9 5.50 4 181.8 4 302 20.4 4.75 5 238.1 14 308 70.2 4.81 6 303.7 20 106 100 4.97 7 367.2 24 433 141 5.77 River length Catchment area Discharge Specific runoff b Sample station [km] [km2] [m3/s] [dm3/s km2] 1 8.8 40.0 0.16 4.00 2 45.2 203.2 1.50 7.38 3 54.9 504.2 3.82 7.58 4 78.8 821.2 5.99 7.29 5 105.8 883.2 6.00 6.79 Changes in Water Chemistry... 113 and ammonia ions (Table 2). For most parameters the contained large quantities of aliphatic organic compounds. mean concentrations determined in the Narew River Hence in the initial river sector the SUVA parameter was markedly exceeded those found in the Czarna Hañcza River. smaller (Fig. 4a). In the river course bacteria selectively Comparison of the mean water specific runoff in both utilize dissolved organics. UV radiation penetrating the investigated rivers showed that in the case of the Czarna upper water layer also plays an active role in its Hañcza River catchment the mean specific runoff is one transformation [13], affecting the biogenic spiralling of third greater than that from the Narew River basin. nutrients [4]. In this case the poorly decomposable dissolved However, the DOC load reaching the Czarna Hañcza River organic matter of intensified aromaticity (SUVA exceeding is much smaller than that recorded in the Narew (Figs 30) prevails. The microbiological decomposition of organic 2a,b). The increased annual export of DOC is associated matter is probably affected by the length of time the flowing with the leaching of dissolved organic matter from the water remains in the riverbed; so the correlation coefficient peat-covered catchment [9]. The intensified DOC export between the water retention time in the Narew River channel is connected with large loads of organics immobilised in and DOC is r= –0.98 (p<0.001). In the entire investigated peat soils with high intensity. This particularly concerns sector of the Czarna Hañcza River the SUVA index phosphorus and ammonia ions [10], which get to waters constantly shows high values. Higher velocity, stony-gravel chiefly in the form of mineral-organic complexes [11]. bottom, and rich water oxygenation characterizing the river The average DOC concentrations gradually decrease with are favourable for the rapid microbiological utilization of the course of the Narew River (Fig.3a). This record is in organic matter originated from syrton or peryphyton (Fig. agreement with the data reported by Radwan et al. from 4b). This confirms the higher oxygen saturation of waters the Krutynia River [7]. A negative correlation (r= -0.97, in the Czarna Hañcza River in comparison with the Narew p<0.001) was determined between the average DOC (Table 2). concentration at different sample stations and the Narew In the waters of the Narew River the concentrations of River length. In NR decreases in DOC concentration occur analysed nutrients, i.e. nitrogen and phosphorus forms, were owing to its gradual utilization by aquatic micro-organisms considerably higher than in the Czarna Hañcza River (Table and because DOC export from middle and lower course II). The mean concentrations of P-PO4 and Ptot in NR are of the river is very low. These results correspond with two times higher than in CHR. The main and reach source River Continuum Concept [12]. In the Czarna Hañcza of phosphorus for NR is the hypertrophic Siemianówka Dam River the concentrations of dissolved organic carbon Reservoir (SDR), situated in the upper part of the Narew slightly increase (Fig. 3b) owing chiefly to the autochthonous River, where cyanobacteria blooms are observed [9]. No production of DOC in lakes lying in the river course. point sources of pollution are found in the entire upper sector The quality of organic matter exported by the two rivers of the Narew River, though the investigated parameters is quite different.