The Yesilirmak River catchment is one of the twenty-six major basins in Turkey [29]. It is located in Northern Turkey and bounded by 39˚30′ and 41˚21′N, and 34˚40′ and 39˚48′E (Figure 1(a)). The catchment is 38,730 km² which covers approximately 5% of Turkey’s total area and is the third largest basin in Turkey [29]. The land falls from an altitude of 3000 m in the mountainous areas of the catchment to sea level (Figure 1(b)). The Yesilirmak River is approximately 519 km in length and flows through several major cities such as Tokat, Turhul, Amasya and Çarsamba, before discharging into the Black Sea (Figure 1(b)). The headwaters of the river and most of its tributaries originate in the mountains that form eastern and southern boundaries of the basin. The major tributaries to the Yesilirmak River are Kelkit river, Cekeret river (including Çorumriver) and Tersakan river (Figure 1(b)). The Kelkit river is the largest tributary and flows in the west direction and is mostly parallel to the Yesilirmak River. The annual streamflow varies with low flow between July and February and high flow between March and May as a result of seasonal rainfall, snowmelt and runoff [29]. The waters in the river system provide many ecosystem functions including public drinking water supply, industrial water supply, irrigation water for agriculture, cultural and sporting activities such as swimming and fishing and conservation value for wildlife habitats, fisheries and biodiversity.

General land use across the catchment is dominated by non-irrigated agriculture at 36%, irrigated agriculture at 10%, forest at 36% and mountain pasture at 18%. The uppermost catchment is mostly forest and pasture with a small component of agriculture (less than 20%). The land use changes to being more agricultural lower in the river system, as shown in Figure 2. Pasture land is located primarily around the catchment boundaries and in highland areas (Figure 2). At the base of the catchment, land use is largely dominated by agriculture, especially irrigated agriculture (Figure 2). The rock formations are

extensively faulted and folded due to the fault line located south of the river. In the basin, the bedrocks are mostly sandstones, claystones, andesite, volcanic bressica and tuff [29].

Population in the catchment was 3 million in the 2000 census with a population density of 83 per km² [30], which was slightly below the national average. Most inhabitants are employed in agriculture (personal communication). Water from the river is predominantly used for irrigation. Since the 1990s, the catchment has seen pronounced industrialization and urbanization leading to significant increases in runoff from wastewater discharge. There have been noticeable increases in the concentration of nutrients, biochemical oxygen demand (BOD) and turbidity [31], due to an intensified use of fertilizers and the fact that only 5% of the wastewater discharged into the river are treated [32]. Pollution from the river is potentially of concern to the whole of the Black Sea region [30], which is very sensitive to eutrophication [33].

The Yesilirmak River basin is located in a subtropical, semi-arid climate with extremes in temperature and rainfall that shows great spatial and temporal heterogeneity [34]. Average recorded temperature and precipitation in Amasya for 1967-1999 were 13.7˚C and 397 mm, respectively. The local climate regime in the area is characterized by the transition from the climate of the Middle Black Sea Region to that of Central Anatolia [35].

The catchment has been monitored for flow and water quality at over 60 monitoring stations for 30 determinands (Data source: DSI, State Hydraulic Works). Since 1995, samples at 33 sites have been collected regularly in January, April, July and October. Thus in our study, we used data from 1995 to 2008 (except for 1999—no samples were collected) at these 33 sites (Figure 1(c) and Appendix I). Water quality determinands presented in this paper are dissolved oxygen (DO), biological oxygen demand (BOD), ammonium (-N), nitrite (-N), nitrate (-N), orthophosphate (o-) as well as major dissolved ions, such as calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺) sulphate (), chloride (Cl⁻) and bicarbonate ()/hardness.

For spatial data analysis, average water chemistry was calculated from 1995 to 2008 data and mapped using ArcGIS 9.2. For temporal data assessment, time-series of chemical determinands and trend analyses were used to determine whether the concentrations have consistently increased or decreased during a particular time period. Moreover, average quarterly data from 1995 to 2008 were calculated in order to reveal seasonality.

Time series data are evaluated at five key monitoring stations on the Yesilirmak River, which cover upper, middle and base of the catchment. The uppermost water quality monitoring station selected is TokatÇikisi (Y1 in Figure 1(c)), close to city of Tokat. The second key station (Y2 in Figure 1(c)) is Sütlüce, close to city of Turhul. The third (Y3 in Figure 1(c)) is Durucasu, downstream of city of Amasya. The fourth (Y4 in Figure 1(c)) is SuatUgurluBarajÇikisi, at the outlet of the SuatUgurluBaraj lake. And the fifth (Y5 in Figure 1(c)) is ÇarsambaÇikisi, which is close to the river mouth and discharges to the Black Sea. Between Y2 and Y3, two tributaries, Cekeret (including Çorum) and Tersakanrivers, discharge into the main Yesilirmak River (Figures 1(b) and (c)). The largest tributary of the Yesilirmak River, Kelkit river, enters the main stream between Y3 and Y4 (Figures 1(b) and (c)). The trend analyses were performed for selected key determinands including BOD, nutrients (N and P) using standard statistical analysis software SPSS at these five locations along the Yesilirmak River. When the trend is statistically significant (p < 0.05), the direction is given as upward and downward.

The Turkish water classification system provides the main method of pollution control in Turkey and this is important from an EU perspective. Turkey is an EU accession country in that Turkey hopes to join the EU at some time in the future. One EU requirement is that the rivers in Turkey meet the EU Water Framework Directive in terms of water quality and ecology. In this paper we address this issue by comparing the water quality against both set of standards—the Turkish Water Classification system (Turkish Water Pollution Control Regulation— WPCR [36] and the EU Water Framework Directive (WFD) criteria (http://ec.europa.eu/environment/water/water-framework/).

In the case of the Turkish Legislation, the classification of in-land surface waters with respect to their quality are given below as four classes, namely: Class I: High quality water; Class II: Slightly polluted water; Class III: Polluted water; Class IV: Highly polluted water. Four water quality classes indicated above are considered for different water need. For example, to provide drinking water, class I water only required disinfection, while class II water requires advanced purification [36]. Appendix II summarizes the physical, organic and inorganic chemical standards for the Turkish classification system for the four classes and the EU WFD standards. In order to undertake a classification, the average water quality for each relevant parameter has been determined at each sampling site along the river using the data from 2004- 2008 to reflect the most recent water quality status. Data has then been compared to the four classes and an overall class has been given to each site and mapped using ArcGIS 9.2. Two categories of “pass” and “fail” were given when assessing water quality based on the EU standards. The results were then mapped using ArcGIS 9.2.

Average pH, TDS and major dissolved element contents of waters of 33 sites from 1995 to 2008 are summarized in Table 1. A minimum of three years data are utilized to calculate average values for each site.

For pH, values range from 7.27 - 8.44 with the mean value of 8.00 ± 0.23 (n = 33), which is slightly alkaline

and is fairly uniform across the catchment. The alkaline pH values reflect the occurrence of local mineralogy, such as calcite and dolomite. The value of total dissolved solids (TDS) vary from 97 to 902 mg/L with the mean of 343 ± 156 mg/L (n = 33). Ca²⁺ and Mg²⁺ are the dominant cations; and (hardness) are the dominant anions. The richness of Ca²⁺, Mg²⁺ and

in the area as well as their 1:2 stoichiometric ratio linear relationship of Ca²⁺ plus Mg²⁺ versus suggests that waters in the basin are mostly controlled by carbonate weathering, e.g. dolomite in bedrock (Figure 3). Components of Na⁺ and Cl⁻ do not fall on 1:1 stoichiometric ratio line and the excess of Na⁺ compared to Cl⁻ may indicate that there is another source of Na⁺ besides atmospheric deposition, which is possibly associated with anthropogenic source and local geological source (Figure 3).

For BOD, DO and nutrients concentrations (, , and o-), concentrations are also variable across the catchment which reflects point and nonpoint source pollution. BOD values range from 0.67 - 21.14 mg/L with the mean of 3.34 ± 3.65 mg/L (n = 29) and DO range from 6.45 - 10.79 with the mean of 9.38 ± 1.00 mg/L (n = 29). The mean concentrations of nutrients across the catchment are moderate to high with -N 0.69 mg/L, -N 1.62 mg/L and o- 0.36 mg/L

(Table 2). When compared to a range of average UK river baseflow chemistry, the nitrate levels in the Yesilirmak River waters are relatively low, corresponding to relatively undisturbed catchments, such as the River Swale and the Derwent (Table 2). However, ammonium concentrations are much higher than that of some major UK rivers (Table 2) and orthophosphate concentrations are similar to those rivers affected by point sources and agricultural diffuse inputs.

General chemistry (TDS, major cations and anions)

The pattern of average general water chemistry (e.g. TDS) from 1995 to 2008 across the basin is presented in Fig-

ure 4. TDS is variable with the lowest concentration at the headwater of Tersakan (Map ID29: DegirmendereSalipazariBarajiÇikisi) and the highest concentration at the mouth of the tributary Çorum before entering the main stream (Map ID 15: ÇorumÇayi-Seyhoglu) (Figures 1(c) and 4). Headwaters of the Yesilirmak River and its tributaries have less TDS than that of the downstream