A STUDY OF SURFACE WATER QUALITY IN MACEDONIA, GREECE: SPECIATION OF NITROGEN AND PHOSPHORUS D. VOUTSA1 , E. MANOLI1 , C. SAMARA1∗ , M. SOFONIOU2 and I. STRATIS2 1 Environmental Pollution Control Laboratory; 2 Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, Greece (∗ author for correspondence, e-mail:
[email protected])
(Received 13 July, 1999; accepted 3 July, 2000)
Abstract. A 2-yr (1997–1998) survey aiming at the establishment of national data bases concerning the quality of surface waters has been conducted in the major river systems of Macedonia, N. Greece. This paper presents the physicochemical parameters (pH, conductivity, total suspended solids, temperature and DO), the organic pollution parameters (BOD5 , COD) and the major N and P species − + (NO− 3 , NO2 , NH4 , organic N, orthophosphates and total P) determined at 25 sampling sites located on main rivers, tributaries, streams and ditches that drain the major rural, agricultural, urban and industrial areas of N. Greece. Use of multivariate statistics is also made to identify the principal factors which influence the chemistry of the water in individual river systems. The eutrophication status of the examined systems was evaluated by means of N/P ratios. Mean N/P ratios showed large variations among sampling sites ranging from potential N- to P-limitation conditions. N/P ratios at particular sampling sites showed also great temporal variability thus suggesting temporary states of N- or P- limitation. Most frequently, highest ratio values were observed during winter and early spring. Comparisons are made between data from this study region and literature on rivers elsewhere. Keywords: eutrophication, nitrogen, N/P ratio, nutrients, PCA, phosphorus, physicochemical parameters, rivers, surface water
1. Introduction The concentrations of biologically available nitrogen and phosphorus are well known to play a key role in determining the ecological status of aquatic systems (Jarvie et al., 1998). These nutrients in excess can lead to diverse problems such as toxic algal blooms, loss of oxygen, fish kills, loss of biodiversity, loss of aquatic plant beds and coral reefs etc. Nutrient enrichment seriously degrades aquatic ecosystems and impairs the use of water for drinking, industry, agriculture, recreation and other purposes (Carpenter et al., 1998). Eutrophication caused by overenrichment with N and P is a widespread problem in rivers, lakes, estuaries and coastal areas. Agricultural and urban activities are considered as being major sources of P and N to aquatic ecosystems. Atmospheric deposition further contributes as a N source since nitrogen containing gases can be released not only from agriculture (i.e. NH3 ) (Schlesinger and Hartly, 1992) but also from fossil fuel burning in thermoelectrical plants (Vitousek et al., 1997). These non-point inputs of nutrients are difficult to measure and regulate because Water, Air, and Soil Pollution 129: 13–32, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.
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they derive from activities dispersed over wide areas and vary significantly with time due to effects of weather (Carpenter et al., 1998). The concentrations of N, P as well as the ratio in which these two elements occur in the aquatic environment has become the subject of much research, since this ratio may influence the types of organisms occuring and whether or not individual species or whole communities are likely to be N- or P-limited. Recent studies on marine phytoplankton, lakes, and estuaries, have related N/P ratios to primary productivity and eutrophication (Magnien et al., 1992; Ebise and Inoue, 1991; Doering et al., 1995; Uhlmann and Paul, 1994). Although less research has been directed to the examination of nitrogen and phosphorus speciation and N/P ratios in river systems, a number of recent studies have been undertaken at small catchments and subcatchments (Ng et al., 1993), along river reaches (House et al., 1995), as well as in large river basins (Spahr and Wynn, 1997; Jarvie et al., 1998; Meybeck, 1998; Kim et al., 1998; Fisher et al., 1998). A 2-yr survey (February 1997–December 1998) aiming at the establishment of national data bases concerning the quality of surface waters has been conducted in the major river systems of Macedonia, N. Greece. The procedure established by the European Community to assess pollution levels in rivers and to lay down guidelines for the control of pollution and nuisance of the environment was followed (European Communities, 1977; European Communities, 1986). The particular objectives of this paper were to investigate the speciation of N and P in the examined water systems and also to evaluate eutrophication status of these water − + systems. The concentrations of nitrogen (NO− 3 , NO2 , NH4 and Kjeldhal nitrogen) and phosphorus species (orthophosphates and acid-hydrolysable phosphorus) concurrently obtained from 25 sampling sites located on main rivers, tributaries, streams and ditches within the study area are presented. Physicochemical parameters such as field pH, conductivity, temperature, Total Suspended Solids (TSS) and dissolved oxygen (DO), as well as Biological Oxygen Demand (BOD5 ) and COD (Chemical Oxygen Demand) are also given. Use of multivariate statistical analysis is made to identify the major factors influencing the chemistry of the water in individual river systems. To evaluate the eutrophication status the N/P ratios were calculated. Finally, the nutrient loads discharged into the sea were estimated. 2. Experimental 2.1. S TUDY AREA The study area covers a wide range of catchment and surface water types (rivers, streams, tributaries, ditches etc). The main river systems are Aliakmon, Axios, Loudias, Strymon and Gallikos. These rivers drain the major rural, agricultural, urban and industrial areas of N. Greece and discharge into the N. Aegean Sea (Figure 1).
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Figure 1. Map of the studied area.
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Aliakmon river is the longest river of Greece with a total length of about 310 km and mean flowrate 42 m3 s−1 (European Communities, 1997). It originates from northwestern Macedonia in Greece and after traversing a basin of about 5600 km2 that includes mountainous terrain, agricultural plains and urban areas, discharges into the Thermaikos Gulf (Figure 1). The major sources that can affect the quality of its water are the agricultural, animal husbandry, urban and industrial activities taking place in the area. Two thermoelectrical power plants are located in the northern region of this basin, whereas three hydroelectrical units and the corresponding artificial lakes interpose during the flow of the river, between the mountains. The artificial lake of Polyfytos is the larger water supply reservoir (74 km2 , maximum depth 91 m) causing an extended homogenisation of the river water. Some fish farming activities exist in the lake which, however, receives the domestic effluents from many neighbouring towns and villages. The other two water supply reservoirs are smaller (4.2 and 2.6 km2 ) and practically unaffected by any pollution sources. The quality of Aliakmon river water has been repeatedly examined during the last decade because it will be used as drinking water supply for the city of Thessaloniki (Mourkides et al., 1990; Kouimtzis et al., 1994; Voutsa et al., 1995). Significant pollution loadings are discharged into the lower part of Aliakmon river due to its confluence with Ditch-66. This ditch, which also receives water from smaller streams, is a major recipient for the effluents produced by a number of local industries, principally vegetable, fruit and juice canneries. The water of the ditch has been found highly polluted with organic compounds particularly during the processing period (unpublished results). Axios river originates from FYROM and flows into Thermaikos Gulf. Of its total length (∼300 km) only the lowest 75 km flow through Greece with a mean flowrate 65 m3 s−1 . The main pollutant loads include domestic wastewaters, agricultural runoff and industrial effluents from food processing, sugar and dairy industries (Fytianos et al., 1986). The estuaries of Axios river form an extended Delta that is protected by the Ramsar convention. Loudias river with a length of 38 km starts from the mountainous area of northern Greece and drains an intensively cultivated agricultural area with a flowrate of about 20 m3 s−1 . This river was found in the past relatively polluted by organic substances and heavy metals released from food processing, sugar and dairy industries (Fytianos et al., 1986; Voulgaropoulos et al., 1987). Strymon river originates from Bulgaria and flows into the northern Aegean Sea. The river has a total length of 330 km, of which 115 km flow through Greece. The mean flowrate is 28 m3 s−1 . It is used mainly for irrigation of an extensively cultivated plain, while it also receives agricultural, domestic and industrial effluents through a number of canals, streams and tributaries (Kilikidis et al., 1992). Gallikos river is characterized by very low flowrate ( Aliakmon > Loudias > Stymon, with Axios contributing almost 60% of the total. The nutrient loads annually discharged by Axios river are lower (by about 35%) than those reported for the period 1980–1989 (Antonopoulos and Tsiouris, 1991). This is mainly due to the high flowrate value used by these authors (137 m3 s−1 ). Indeed, flowrate of Axios in the period 1982–1986 was in the range 90–190 m3 s−1 , whereas in the period 1987–1992 it dropped in the range 40–90 m3 s−1 (European
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Figure 3. Annual nitrogen and phosphorus loads discharged to the sea.
Communities, 1997). Similar decrease in flowrate was also observed in the other Greek rivers.
4. Conclusions A considerable body of data concerning physicochemical parameters and nutrient speciation has been gathered for the surface waters (main rivers, tributaries, streams and ditches) draining Macedonia, Northern Greece. A large spatial and temporal variability in dissolved oxygen was identified which can probably be related to flow conditions, seasonal effects and anthropogenic impacts. BOD5 was at low levels in the majority of water bodies, however elevated BOD5 and COD values were observed at sampling sites influenced by wastes. A large variability in nutrient speciation for both nitrogen and phosphorus was found among different sites. The major factors influencing the speciation are suggested to be agricultural runoff, municipal and industrial effluents. Although at some sites a clear trend to either N- or P-limitation was observed, the majority of water systems showed time-variable nutrient limitation conditions. The total concentrations of nitrogen and phosphorus and N/P ratios in the ex-
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amined river systems have been found to lie in continuum with those of other European rivers.
Acknowledgements This project is financially supported by the Greek Ministry of the Environment, Physical Planning and Public Works.
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