Seasonal exploration of water quality and bioindicators of an agricultural irrigation and drinking water reservoir: Armağan Dam Lake, Kırklareli, Türkiye

Armağan Dam Lake was established in 1986 on the Kocadere Stream, 26 km north of Kırklareli city center (Fig. 1). The dam lake has a lake area of 3 km², stores volume of approximately 52 hm³, and provides irrigation services to 5.623 ha. In this study, three stations that best represent the dam lake were selected (Station 1: the deepest point of the lake, Station 2: the middle of the lake, Station 3: the shallowest point of the lake; Fig. 1), and water samples were taken from these selected stations seasonally (spring summer, autumn, and winter). Additionally, phytoplankton, zooplankton, and benthic macroinvertebrate samples were collected simultaneously with water sampling at the stations. At the field area, temperature, pH, conductivity, salinity, total dissolved solids (TDS), and dissolved oxygen (DO) values were measured in the lake water using the ORION STAR S/N 610541(Thermo Scientific Orion Star A214) brand multiparameter device. The light permeability was determined with a Secchi disk (20 cm × 20 cm) at each station.

Figure 1

The sampling stations.

To measure the concentrations of chlorophyll-a, nutrient salts (nitrite nitrogen, nitrate nitrogen, phosphate, and sulfate), ions (fluoride, chloride, chlorate, chlorite, bromide, and bromate), and elements (B, Al, Cr, Mn, Co, Fe, Ni, Cu, Zn, As, Se, Cd, Ag, Pb, Na, Mg, K, and Ca) in the water from the three stations, water samples were taken with a Ruttner water collecting bottle (1.5 L capacity) seasonally for a year. The water samples were collected in light-proof glass bottles and transported to the laboratories of Trakya University Technology Research Development Application and Research Center (TÜTAGEM) for analysis. The ion and element analyses of the water taken from each station and each sampling period were measured in three repetitions in an Agilent Technologies (Tokyo, Japan) 7700 XX ICP-MS system according to EPA 200.8, and the average values were obtained (U.S. EPA, 1994). Water samples of 1 L were taken for chlorophyll-a determination and were filtered through a Whatman CF/C filter paper. The filter paper was dissolved in ethanol. The prepared sample was read in quartz glass cell cuvettes (1 cm) for spectrophotometric measurement. Chlorophyll-a was calculated using Nusch’s method on a Shimadzu U.V. 1240 model UV-Vis spectrophotometer (Shimadzu Corporation) (Nusch, 1980).

For qualitative sampling, a simple plankton mesh net (25 cm mouth diameter, 75 cm length, and 25-μm spacing), for quantitative sampling (up to the surface from the bottom), a Hensen-type plankton net (mesh size 55 μm, mouth diameter 15 cm, and length 75 cm) were used. The collected materials were put into 250 mL plastic bottles containing 4% formaldehyde, labeled, and brought to the laboratory. Edmondson’s (1959) method was used to count zooplankton samples. For this purpose, plankton samples in 250 mL plastic bottles were shaken well to make them homogeneous. Five milliliters of the sample was taken with a 10 mL pipette and was placed in the counting container. All organisms were counted under an inverted microscope. This process was repeated three times to determine the average number of individuals in 5 mL. The literature used for the zooplanktonic samples at the species level was Flössner (1972), Herzig (1987), Ejsmont-Karabin et al. (2004), Dussart and Defaye (2002, 2006), Segers (2008), and Błędzki and Rybak (2016).

Water samples were collected using a 2 L Nansen water sampler from the surface, 3 m, 5 m, 10 m, and 20 m depths at Stations 1 and 2, and from the surface, 3 m, 5 m, and 10 m depths at Station 3. The samples were transported to the laboratory in light-proof glass bottles. Plankton samples were also taken horizontally from each station using a plankton scoop with a mouth diameter of 25 cm and a pore size of 55 μm. The samples were first agitated, poured into 50-mL graduated cylinders, and allowed to settle for at least 24 hr. At the end of the settling period, 45 mL of water was aspirated from each graduated cylinder. The remaining 5 mL of water was poured into a small glass vial for microscopic analysis. The counts were made for the water in the counting tubes using an Zeiss Axio Observer 5 inverted microscope following standard protocols as described by Utermöhl (1958). Phytoplankton samples were identified with a light microscope, and their photographs were taken. The literature used for the phytoplanktonic samples at the species level was Anagnostidis & Komárek (1988), Hartley (1996), Krammer (2003), John et al. (2003), and Tsarenko et al. (2006).

Sediment samples taken using Van Veen Bager with an area of 260 cm² twice at each station were passed through a series of sieves with different mesh sizes (1.19, 0.595, and 0.297 mm, respectively). The material remaining on the sieve was fixed in 250 cc plastic containers containing 70% alcohol and brought to the laboratory. In addition to qualitatively determining the benthic macroinvertebrate fauna, mud samples were taken from random areas with hand-mud scoops and passed through sieves, and the resulting benthic material was fixed in 250 cc plastic containers containing 70% alcohol and brought to the laboratory. The samples were examined under a binocular microscope. The literature used for the macrozoobenthic samples at the species level was Soós (1968), Brinkhurst (1971), Pinder and Reiss (1983), Milligian (1997), Epler (2001), Schmelz and Collado (2010), Picazo et al. (2010), and Hacet et al. (2010).

The Shannon–Wiener diversity index was used to assess species diversity; the Bray–Curtis similarity index was used to compare sampling stations and seasons regarding physicochemical properties and the dynamics of zooplankton, phytoplankton, and benthic macroinvertebrates; canonical correlation analysis (CCA) was used to examine the correlation between zooplankton, phytoplankton, and benthic macroinvertebrates (most abundant species included in the CCA analyses for each group) and environmental factors. Heavy Metal Pollution Index (HPI; Mohan et al., 1996) and Metal Index (MI; Tamasi & Cini, 2004) were used to assess the impact of metal element pollution. To determine if the Armağan Dam Lake water is suitable for irrigation, the average concentrations of K, Mg, Na, and Ca over four seasons were analyzed. These averages were used to evaluate the lake’s suitability for irrigation based on sodium percentage (%Na), sodium absorption rate (SAR), magnesium rate (MgR), and Kelly index (KI) (Balamurugan et al., 2020; Madhav et al., 2018). Additionally, water suitability for drinking was assessed according to World Health Organization (WHO) standards (WHO, 2024), and water quality was classified according to the Surface Water Quality Management Regulation (SWQMR) standards (SWQMR 2015).

The analysis results of the water samples were averaged by station, and the values were evaluated according to water quality classes as outlined in the SWQMR (Turkish Regulations, 2015), as shown in Table 1. The values of pH (7.98), DO (8.18 mg · L⁻¹), conductivity (379.55 μS · cm⁻¹), TDSs (187 mg · L⁻¹), and water temperature (19°C) were found to be in Class I water quality; the salinity values were at permissible freshwater values (0.2‰–0.29‰) (Table 1). The nutrient salts, nitrate (0.95 mg · L⁻¹) and sulfate (7.01 mg · L⁻¹), were found to be in Class I water quality. However, nitrite (0.07 mg · L⁻¹) was in Class III water quality, and phosphate (0.33 mg · L⁻¹) was in Class II water quality (Table 1). All of the values belonging to the elements were recorded in Class I water quality values (B: 5.1 μg · L⁻¹; Al: 5 μg · L⁻¹; Cr: 0.1 μg · L⁻¹; Mn: 0.9 μg · L⁻¹; Fe: 3.9 μg · L⁻¹; Co: 0.04 μg · L⁻¹; Ni: 1 μg · L⁻¹; Cu: 1.5 μg · L⁻¹; Zn: 7.6 μg · L⁻¹; As: 1.3 μg · L⁻¹; Cd: 0.1 μg · L⁻¹; Se: 0.5 μg · L⁻¹; Pb: 0.9 μg · L⁻¹) (Table 1). The average chlorophyll-a value of the dam lake during the sampling period was measured as 2.23 μg · L⁻¹. Chlorophyll-a concentration is a parameter in classifying lakes according to their trophic level (Dillon & Rigler, 1974). According to the values of chlorophyll-a and light transparency (466.25 cm), Armağan Dam Lake was found to be a dam lake with an oligotrophic character (Turkish Regulations, 2015). The analysis results of the water samples were averaged by station, and the values were evaluated by the drinking water standards outlined by the WHO, as shown in Table 1. According to WHO standards, the values of physico-chemical variables were at the desirable levels for drinking water standards (WHO, 2024).

According to the suitability of irrigation water, the SAR and the MgR indices showed that Armağan Dam Lake was suitable for irrigation. However, the KI values were marginally suitable, and the %Na Index was unfit for irrigation (Table 1) (Balamurugan et al., 2020; Madhav et al., 2018). According to the WHO, the permissible ‘K’ value in drinking water is 12 mg · L⁻¹ (Table 1) (WHO, 2024). According to the results of this study, the value exceeded the permissible limit (18.88 mg · L⁻¹) (Table 1). In this context, the fact that it is not suitable for irrigation according to the %Na Index result suggests that it may be due to the ‘K’ value used in the index calculation.

The results of HPI showed that the water of the Armağan Dam Lake is safe for drinking and is not polluted with determined elements (Table 2). According to the MI, the dam water is at Class I (very pure) values in terms of heavy metals. However, in autumn, the water is at Class II (pure) level (Table 3).

The Bray–Curtis Similarity index results showed >80% similarity degree among the stations according to physicochemical features (Fig. 2). Accordingly, while Stations 2 and 3 were a cluster, Station 1 constituted the second cluster (Fig. 2). The reason for the difference is that Station 1 differs from the others because it accumulates behind the dam embankment.

Figure 2

The similarity dendrogram of the stations according to physicochemical features.

When studies on other dam lakes in the Thrace region are examined, the Armağan Dam Lake has cleaner water quality than the others. Tokatlı et al. (2017) studied at Sultanköy, Altınyazı, Süloğlu, and Kadıköy dams on physicochemical variables, and all the investigated reservoirs have Classes I–II. Class water quality in terms of electrical conductivity (EC), TDS, nitrate, sulfate, phosphate, and chemical oxygen demand (COD) parameters; Sultanköy, Altınyazı, and Kadıköy Dam Lakes have III. Class water quality in terms of nitrite parameter; Süloğlu and Sultanköy Dam Lakes have IV. Class water quality in terms of pH parameter; and Altınyazı and Kadıköy Dam Lakes have IV. Class water quality in terms of total organic carbon parameter (Tokatlı et al., 2017). Tokatlı (2020) determined the element pollution of Altınyazı, Karaidemir, Kayalıköy, Kırklareli, Sultanbey, and Süloğludams. As a result of the study, the ‘Se’ limit of the dams exceeds the acceptable limit (Tokatlı, 2020). Tokatlı (2021) studied irrigation water quality in Altınyazı, Karaidemir, Kayalıköy, Kırklareli, Sultanbey, and Süloğlu dams, and the investigated reservoirs were found to be suitable for use as irrigation water, in general.