Introduction

The number of societies facing water shortages is increasing as the level of the ground water table decreases as a consequence of excessive usage and the level of pollution of surface and groundwater resources increases due to environmental impacts. For this reason, there have been many studies on water quality in various parts of the world (Srivastava et al. 1988; Beler Baykal et al. 2000; Olajire and Imeokparia 2001; Mladenov et al. 2005; Jaji et al. 2007; Tayfur et al. 2008; Moskovchenko et al. 2009).

Like all Eastern Black Sea Regions, Trabzon has numerous streams but ground water is limited in this region because of the rock type and morphology. Water from the alluvial gravels is used as drinking/potable water in all the towns but this is unlikely to be sufficient as the population increases. In addition to the small industrial facilities in the alluvial areas, which cause surface and ground waters to be contaminated by heavy and poisonous metals, there are large tea farms and hazelnut production is significant in the basin. Fertilizers and pesticides used in agriculture reach the main stream quickly in the generally wetter northern part of the area.

Some of the river basins in Trabzon have been investigated by such researchers as Gültekin et al. (2005), Verep et al. (2005). Kanca (1995) states that the Trabzon city drinking water (Değirmendere raw water) and treated drinking water (clean water) are in accordance with Turkish drinking water standards and fall into the 1st Class for quality according to the water pollution regulations. Based on analyses of 12 parameters at 16 sampling stations, Dayı (1996) ascertained that the level of pollution of Değirmendere is very low for a distance of some 45 km from the sea, although the amounts of sulphate, nitrate, phosphate and heavy metals increase towards the sea.

Mutlu (1996) reported the analyses of 11 physical and chemical parameters in water samples obtained from 18 river basins in Trabzon. The levels of sulphate, phosphate and nitrate indicated these river waters would fall into the 3rd and 4th quality Classes and pose a threat to environmental health. Boran and Sivri (2001) measured the amounts of average nitrate, nitrite, ammonium, phosphate, oxygen, pH and suspended solid substances in the Solaklı and Sürmene Rivers and reported that the water was of high quality in terms of the amount of oxygen, but whereas the Solaklı River was 1st Class as regards quality, the Sürmene River was only 3rd Class in terms of pH values. Both rivers are classified as high quality in terms of the amounts of nitrate and phosphate and the water quality as 3rd Class in terms of nitrite and ammonium concentrations.

The objective of this study was to determine spatial changes in stream water and groundwater quality and the relationships between quality and sources of contamination in the Solaklı Basin, a 760 km2 area to the east of Trabzon (Fig. 1). The Solaklı River commences at some 2,000 m asl and runs in an almost triangular basin, narrowing towards Of, a coastal town on the Black Sea. As seen in Fig. 1, there are several towns in the basin, the waste from which is discharged into the side valleys which recharge the basin or into the main valley. Uzungöl Lake, a significant local tourist attraction, is located in the upper part of the basin.

Fig. 1
figure 1

Location of the study area (Trabzon, Turkey)

Full size image

Solaklı Basin has different climatic characteristics related to the gradually increasing elevation. The annual average temperature in the northern part of the basin is 14.1 °C and the average rainfall 1,685 mm. However, in the southern part of the basin the annual average temperature decreases to 12 °C and the rainfall to 942 mm (Akkaş 1990). In the southern region most of the rainfall occurs during the spring and fall but the northern region is wet all year round. According to the data prepared by the 22nd Regional Directorate of State Hydraulic Works in 2004, the annual flow rate of the Solaklı River is 17 m3/sn, the precipitation area is 760 km2 and the annual rainfall 587 hm3.

Materials and methods

Field study

Water samples were collected from two ground water stations and 31 surface water stations in the wet season (May 2009), in order to conduct major anion–cation, pollution parameter concentration and trace element analyses. The surface water samples were collected from the main and side streams in order to ensure the whole basin was represented. Two of these samples were collected from Uzungöl. The ground water samples were collected from bores drilled to provide potable water for the town of Of. Following TS 266 (2005), 1 l polyethylene bottles were used in the sampling process for the major anion–cation and pollution parameter concentration analyses while 100-ml polyethylene bottles were used for trace element analyses. The bottles were initially rinsed with nitric acid, tap water and pure water before being dried and subsequently rinsed at least three times with the water to be sampled. Temperature (T), pH, electrical conductivity (EC) and dissolved oxygen (DO) values at the sampling stations were measured using a Horiba U-10 and the amount of total dissolved solids (TDS) by a Hanna multi-parameter measurement device.

Laboratory study

Prior to analysis, the surface water samples were filtered in a vacuum filtration system to remove any solid substances. The major anions (Cl−, SO4 2−, HCO3, CO3 2−) and pollution (PO4 3−, NO2 −, NO3 −, NH4 +, COD, F−, Cl2, CN−) analyses were carried out within a maximum of 6 h after collection. Major anion and pollution parameter concentrations were determined by photometer. Alkalinity (HCO3 − and CO3 2−) was analyzed by the standard titrimetry method. Major cation (Ca, Mg, Na, K) and trace element (Fe, Al, Cu, Pb, Mn, Ni, Co, Cd, Be, As, Ba, Bi, Mo, Sb, W, V) analyses were carried out with the ICP/OES (inductively coupled plasma–optical emission spectrometry; the ionic balance for the analyses is within ±5 %).

Geology and hydrogeology

The upper part of the Solaklı Basin is formed of basalt, andesite and pyroclastics of Liassic age (Güven 1993) with interbedded sandstone, siltstone and limestone into which there is a Palaeocene granitic intrusion (Fig. 2). In the lower part of the basin there are Upper Cretaceous basalt, andesite, dacite and pyroclastic deposits with interbedded sandstone and mudstone (Güven 1993). Alluvial deposits are present in the northern part of the basin with an average width of 500 m and a length of 5 km, narrowing inland. Aktaş and Yılmaz (1993) report that the thickness of the alluvium ranges between 23 and 42 m.

Fig. 2
figure 2

Geology of the study area and its surroundings (modified after Yılmaz et al. 1998)

Full size image

The primary permeability of the volcanic rocks is low although crack and fault systems allow secondary permeability.

GIS mapping

GIS is widely used for the assessment of water quality and developing solutions for water resource-related problems (Chaudhary et al. 1996; Fukushima et al. 2000; Shomar et al. 2010) and was also used in the present study. The working maps were prepared from 1:25,000 scale topographic paper maps which were scanned and digitized to generate a digital output using Arc/Info GIS software.

The sampling locations were integrated with the surface water data for the generation of spatial distribution maps of selected water quality parameters including pH, EC, TDS, total hardness, NO3 −, NO −22 , DO, COD, F−, total Fe, total Al, total Mn; the ground water data were disregarded. The water data were linked to the sampling locations using the basic database creation function of ArcGIS 9.3 software. The chemical results were analysed and concentration curves prepared assuming every sample point represents its own small basin.

Results and discussion

The results of the chemical analyses and the types of surface and ground water identified are given in Table 1; samples SOL-7 and SOL-8 were collected from Uzungöl and SOL-18 and SOL-19 from wells. The trace element results are given in Table 2. The major ions of the surface and ground waters are shown in the Piper triangle and Schoeller diagrams (Figs. 3, 4) and the trace elements in Fig. 5. All the water samples showed similar characteristics in terms of cations, but the Cl− and SO4 2− values were higher in the ground water than in the surface water samples (Table 2).

Table 1 Chemical properties of water in the Solaklı Basin
Full size table
Fig. 3
figure 3

Piper diagram to show the distribution of surface and groundwater in the study area

Full size image
Fig. 4
figure 4

Chemical analysis of surface and groundwater plotted on a Schoeller diagram

Full size image
Fig. 5
figure 5

Distribution of trace elements in surface and groundwater (GW) samples

Full size image
Table 2 Trace element results for water in the Solaklı Basin (concentrations in ppb)
Full size table

As seen in Fig. 6a, the EC values generally increase downstream and are higher in the tributaries where the pH values are more alkaline (Fig. 6b). While the TDS values of the surface water in the side streams ranged between 35 and 56 ppm, in the main river they were as high as 156 (Fig. 6c). The water hardness of the Solaklı River and its side streams was less than 100 mg CaCO3/l (Fig. 6d).

Fig. 6
figure 6

a Spatial distribution of EC, b spatial distribution of pH, c spatial distribution of TDS, d spatial distribution of hardness in the Solaklı River water

Full size image

The results of the pollution parameters (NO2 −, NO3 −, PO4 3−, chemical oxygen demand (COD), cyanide (CN−) and total suspended solids) are given in Table 3. The NO2 − and NO3 − values ranged between 0.07 and 0.12 mg/l for the main river and 0.5–2 mg/l for the side streams (Fig. 7a); the NO3 − values increasing towards the north of the basin (Fig. 7b). The PO4 3− values were below 0.5 mg/l while the DO values were between 8.9 and 10.3 mg/l (Fig. 7c). The COD values ranged between 14 and 68 mg/l (Fig. 7d) throughout the basin, probably because of intense development, but the concentrations were lower in the south-east.

Table 3 Pollution parameters of waters in Solaklı Basin (concentrations in mg/l)
Full size table
Fig. 7
figure 7

a Spatial distribution of NO2, b spatial distribution of NO3, c spatial distribution of DO, d spatial distribution of COD in the Solaklı River water

Full size image

As seen from Table 2, the Fe, Al, Mn and Cu concentrations range between 2–115 ppb, 17–175 ppb, 71–119 ppb and 57–61 ppb, respectively, with Fe, Al and Mn values increasing at the discharge location of the stream (SOL-27, SOL-28 SOL-30 SOL-33); see Fig. 5. The map of Fe concentration (Fig. 8a) shows that most of the surface samples have low values. The concentrations of fluoride in the Solaklı River varied between 0.03 and 0.9 mg/l (Fig. 8b), generally increasing towards the west. The highest Al values were from the Dernekpazarı Town area (Fig. 8c), indicating that the volcanic rocks are leached by surface water. The As, Cd and Pb values were below the measurement limit in most of the side streams and where measurable were 2 ppb for As, <3 ppb for Cd and Co and between 3 and 20 ppb for Pb. Again, the Ni concentration was below the measurement limits at most sampling locations, although some values of up to 51 ppb were recorded (Table 2). The trace element concentrations were similar for both ground and surface water. The Fe and Al values were generally lower in the surface water samples, but the Mn was as high as 116 ppb (Fig. 5).

Fig. 8
figure 8

a Spatial distribution of Fe, b spatial distribution of F, c spatial distribution of Al in the Solaklı River water

Full size image

According to the Water Pollution Control Regulation of the Turkish Republic (1988) and Criteria for Inland Surface Water Classification (2004), the surface waters in the bas are classified as:

  • 1st class (high quality) in respect of T, pH, DO, TDS, Na+, Cl−, F−, CN−, Fe, Al, Pb, Co, Cd, As, Cr and Ba;

  • 2nd class (slightly polluted) in respect of PO4 3−;

  • 3rd class (polluted) in respect of Cu; and

  • 4th class (highly polluted) in respect of NO2 −.

The ground water used in the town of Of was also evaluated with respect to WHO (2006) and TS 266 (2005) in terms of drinking–potable water specifications. The Mn and Ni values exceeded the limits in TS 266. According to WHO, all of the inorganic parameters analyzed in the ground water are below the limits given in the standard.

Conclusions and recommendations

The Solaklı Basin is a long, narrow basin composed of generally very low permeability rocks hence surface streams predominate. Due to the dispersed settlement in the basin, characteristic of the Black Sea Region, each of the side streams from the main Solaklı River is contaminated by domestic waste.

Samples were taken from 33 locations considered to provide a representative indication of the water characteristics throughout the basin. The sampling was deliberately carried out during the wet season when the concentrations of pollutants were likely to be at their lowest.

The analyses were considered in terms of the Water Pollution Control Regulation of the Turkish Republic (1988), Criteria for Inland Surface Water Classification (2004) TS 266 (2005) and WHO (2006). The results indicated that in some respects the water was polluted or highly polluted (Cu; and NO2 −) and slightly polluted in respect of PO4 3−. Although overall the quality of the Solaklı River water was considered to be of 2nd or 3rd Class, the results highlighted the need for tests to be carried out at regular intervals and measures taken to protect the limited resources of good quality water in this area.