This paper presents a comprehensive study of spatial and temporal patterns of water chemistry (1995-2008) in the Yesilirmak River catchment in Northern Turkey. Biological oxygen demand (BOD), dissolved oxygen (DO) and nutrient concentrations (nitrogen and phosphorus) are variable across the catchment because the upland areas are relatively undisturbed, and the lower catchment is dominated by urban, industrial and agricultural inputs. Seasonally, high nutrient concentrations occur in winter possibly due to flushing from the soil zone. Low summer flow and reduced dilution lead to high orthophosphate concentrations. However, denitrification seems to be more significant than dilution processes and this generates low nitrate concentrations in summer. Nutrient levels since 1995 do not show a significant upward trend. The current water quality status indicates that the river system is in poor condition. The majority of sites fall in the Turkish water classification class II-III and more than half fail the EU standards because of high nutrient concentrations. In order to improve the status of water quality to achieve good chemical and ecological status, there is clearly a need to improve pollution control within the river system by installing waste water treatment plants, while keeping the agricultural pollution to a minimum in the system.
Nutrients; Nitrate; Orthophosphate; Agriculture; Wastewater; Waste Water Treatment Plants1. Introduction
Fresh water in large river systems is an essential natural resource, providing drinking water, irrigation water for agriculture and power from hydroelectric power stations. However, water quality in many large river waters has deteriorated significantly worldwide due to anthropogenic activities in the past two-three decades [1]. Pollution entering the rivers from agricultural runoff has caused significant increases in nutrient concentrations such as nitrogen (N) and phosphorus (P) [2-4]. It is also widely accepted that wastewaters from treatment plants supply significant amounts of P to rivers, particularly in populated urban areas [5,6]. Nutrient enrichment can result in excessive growth of aquatic plants, algae productivity and reductions in dissolved oxygen in rivers [7,8].
A new human induced environmental change affecting fresh water systems is from climate change, which may have significant impacts on the water cycle and water quality [9-13]. The projected future increasing temperatures and decreasing flows in summer are the main concerns in the UK and Europe [14,15]. This is because intensive water resource use is often constrained by the lack of natural low flow, and low flow rivers are more affected by effluent discharges from cities, industries, and agriculture. For example, effluent from sewage treatment works can contribute significant inputs of nutrients to lowland rivers in the UK and nutrient concentrations are high during the summer low flow months, when dilution is at its lowest and biological activity is at its highest [16-18].
Turkey provides an extremely interesting case study as it is a country where water quality is expected to come under serious threat in future years due to a combination of factors. According to recent reports of the OECD (Organization for Economic Co-operation and Development), Turkey presents one of the strongest economic growth rates with around 7.5% of yearly average growth since 2002 as well as one of the fastest growing populations among OECD countries in recent years [19]. Although agricultural intensity is still fairly low, pressures from agriculture on the environment are rising as production along with irrigated land area are increasing steadily [20]. These characteristics make Turkey a country where, similarly to other rapidly developing economies such as Brazil [21] and China [22], the nutrient cycle is increasingly controlled by human activities as opposed to natural processes. Furthermore, Turkey is situated in the Eastern Mediterranean, an area where according to the latest IPCC report, annual mean temperatures are likely to increase more than the global mean and annual precipitation is very likely to decrease [23]. A recent modelling study in the area [24] showed that under combined climate change and other environmental changes, such as land use change, in-stream nitrogen concentrations in Yesilirmak River are likely to increase significantly in future years. Solutions to these problems could come from the fact that Turkey is a candidate country for the EU. Candidate countries must complete the necessary procedures for the implementation of the EU Water Framework Directive (WFD), which Turkey plans to meet by 2025. The aims of the WFD of the EU are to improve surface, coastal, transitional and groundwater quality to a “good ecological and chemical status” across Europe [25]. The focus on maintaining good water quality in water bodies gives Turkey the unique opportunity to ensure that the quality of its waters will not be severely affected by land use changes and climate change [26]. Turkey is still engaged in its “hydraulic mission” characterized by intensive dam and irrigation canal constructions [27] because water resource management is still at an early stage. The WFD is also likely to bring monetary support for improving the country’s water infrastructure and pollution prevention measures [28]. The EU could, therefore, provide added support and motivation to finance and construct waste water treatment plants (WWTWs), control fertilizer application and to adapt to climate change, in order to ensure that problems of nutrient pollution in aquatic systems like those experienced in the developed world are prevented.
The study by Hadjikakou et al. showed the importance of nutrient loading to the Black Sea. It also suggested that climate change and land use change in future years will make the pollution worse with increases in nutrient loading [24]. In order to reverse the negative trends due to pollution from large catchment areas from countries around the Black Sea, including the Yesilirmak, it is so crucial to understand the current state of the water quality and sources of pollution in the Yesilirmak River basin. This paper presents the first comprehensive analysis of water quality data including major dissolved solutes, nutrients, BOD and DO in the Yesilirmak River basin and identifies spatial and temporal patterns in water quality from 1995 to 2008. It provides some insight into the patterns and broad scale controls on river water chemistry in the Yesilirmak catchment. Our specific objectives are 1) to understand the major sources for general water quality determinands and nutrients in the catchment; 2) to assess the overall state of water quality for the basin and explore its implications.
2. Study Area and Methods2.1. Study Area
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].
2.2. Chemistry Data and Analysis
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.
2.3. Water Classification
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.
3. Results and Discussion3.1. Summary of Average Water Chemistry
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
Summary of average pH, TDS and major element contents of waters from 1995-2008 for each monitoring sites (TDS: total dissolved solid; TH: total hardness)
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.
3.2. Spatial Pattern in Average Water Chemistry
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
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