SPATIAL VARIABILITY OF Fe, Mn, Zn AND Cu IN SOILS OF BÜYÜK MENDERES DELTA IN WESTERN TURKEY

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1 SPATIAL VARIABILITY OF Fe, Mn, Zn AND Cu IN SOILS OF BÜYÜK MENDERES DELTA IN WESTERN TURKEY Ercan Yeşilırmak *, Levent Atatanır 2, Alper Yorulmaz 2, Gönül Aydın 2 and Cafer Turgut 3 Department of Agricultural Structures and Irrigation, Faculty of Agriculture, Adnan Menderes University, Aydın, Turkey 2 Department of Soil Science and Plant Nutrition, Faculty of Agriculture, Adnan Menderes University, Aydın, Turkey 3 Department of Plant Protection, Faculty of Agriculture, Adnan Menderes University, Aydın, Turkey ABSTRACT The purpose of this study was to investigate the spatial distribution of micronutrients (Fe, Mn, Zn and Cu) in soils of Büyük Menderes Delta, Western Turkey. Soil samples were taken at 0-30 cm and cm depths on grid nodes ( by km), 59 samples (in total) for each depth. Spherical model is best fitted to the experimental models for Fe at two depths, Mn at 0-30 cm depth, Zn at cm depth and Cu at 0-30 cm depth, while the experimental semivariograms for Mn at cm depth, Zn at 0-30 cm depth and Cu at cm depth showed pure nugget effect model. Then, point kriging was employed to get soil micronutrient values at unsampled locations. Spatial distribution maps of each micronutrient attained in this study are considered to be beneficial for refining agricultural management practices. KEYWORDS: Micronutrient, Büyük Menderes Delta, geostatistics, spatial variability, Turkey. INTRODUCTION The availability of micronutrients in the soil can strongly affect the production and quality of crops []. Soils vary widely in their micronutrient contents and their ability to supply sufficient micronutrients for optimal crop growth []. Surveys and maps illustrating the geographic distribution of soil micronutrient availability would provide guidance for proper management of nutrients in soils, and are necessary for a better understanding of the nature and extent of micronutrient deficiencies and toxicities in plants, livestock and humans [2]. In Turkey, many local and regional studies were conducted to determine the micronutrient status of soils. The most comprehensive one was conducted by the General Directorate of Rural Services to determine micronutrient *Corresponding author status of soils in Turkey [3]. Besides, some local studies were conducted to delineate the micronutrient status of soils in various regions of Turkey, for example in Karadeniz [4], Marmara [5, 6], Aegean [7] and Eastern Anatolia [8]. Büyük Menderes River, located in Western Turkey, is an important river system which includes wetland areas, such as Lake Işıklı, Lake Bafa and the delta of Büyük Menderes River. Büyük Menderes Delta which covers an area of 6,690 ha was incorporated into Dilek Peninsula National Park in 994. This area hosts many endangered and endemic species, and is protected through international conventions. However, agricultural activities are carried out in the Delta, and the required irrigation water is supplied mostly from nearby drainage canals. Büyük Menderes River and its tributaries have long been considered as receiving water body for disposal of industrial and municipal wastewaters [9]. Not only pollutants but also (micro)nutrients carried by irrigation return flows contribute to soils in the Delta. Understanding of the spatial variabilities and distribution patterns of soil micronutrients and detecting areas where micronutrient fertilization or soil remediation are required are essential for a proper agricultural management. Therefore, this study was carried out to assess the spatial distribution of Fe, Mn, Zn and Cu in soils of Büyük Menderes Delta located in Western Turkey using geostatistical approach which is widely applied for delineating the spatial distribution of soil heavy metals [0-2]. 2. MATERIAL AND METHODS Büyük Menderes Basin and Büyük Menderes Delta are located in the western part of Turkey (Fig. ). Büyük Menderes River, with a length of 584 km, drains an area of about 24,873 km 2 which corresponds to 3.2 % of Turkey [3]. It rises near Dinar county of Afyon province and discharges into Aegean Sea within the boundaries of Aydın province, creating the delta [3]. Typical Mediterranean climate is dominant in the Delta, with dry and hot summers as well as wet and mild winters. Annual average temperature is 7. C, and mean annual rainfall is about 608 mm at the nearest meteorological station in Kuşadası. 30

2 FIGURE - Study area and sampling locations. Soil samples were taken at 0-30 cm and cm depths on grid nodes ( by km), 59 samples (in total) for each depth. Then, soil samples were brought to the laboratory and analyzed for Fe, Mn, Zn and Cu. The concentrations of Fe, Mn, Zn and Cu were determined using AAS after extraction with DTPA [4]. Soil characteristics z ( x i ) may vary considerably over small distances, and a geostatistical treatment quantifies this variation in the semivariogram, a function which measures the spatial correlation between data pairs as a function of the displacement between the pairs [5]: N ( h) 2 ˆ( γ h) = [ z( xi ) z( xi + h) ] 2N ( h) i= where N (h) is the number of pairs of data separated by a lag distance h. Then, the prediction of soil characteristics at any unsampled location is the linear weighted average of observations in the neighborhood of the unsampled location x 0 : n 0 ) = i z( x i ) i= zˆ ( x λ where λ i is the weight obtained from the ordinary kriging system [6]. In this study, the spatial patterns of Fe, Mn, Zn and Cu in soils of Büyük Menderes Delta were determined by geostatistical methods. Semivariograms were constructed using GS+, while kriging and mapping were done using geostatistical analyst extension of ArcGIS RESULTS AND DISCUSSION The summary statistics for the variation of Fe, Mn, Zn and Cu levels in soils of Büyük Menderes Delta are presented in Table. The results showed that the spatial variability of soil micronutrients was considerably large for all depths, with the coefficient of variation ranging between and Geostatistics provides descriptive tools, such as semivariograms, to characterize the spatial pattern of continuous and categorical soil attributes [7]. A semivariogram can be described with three parameters: nugget, sill and range. Semivariance ideally increases with distance between 3

3 TABLE - Descriptive statistics of soil micronutrients at 0-30 and cm depths. Item Fe Mn Zn Cu Mean (ppm) Min (ppm) Max (ppm) SD CV Skewness Kurtosis sample locations, or lag distance ( h ), to a more or less constant value (the sill or total variance) at a given separation distance, called the range of spatial dependence [8]. The nugget which is the semivariance at h = 0 is a measure of the amount of variance due to errors in sampling, measurement and the other unexplained sources of variation [9]. In semivariogram modeling, firstly, an experimental semivariogram was constructed using available data, then a theoretical semivariogram was fitted using an authorized model. Commonly used theoretical models are exponential, spherical and linear ones. In this study, spherical model was best fitted to the experimental models for Fe at two depths, Mn at 0-30 cm depth, Zn at cm depth and Cu at 0-30 cm depth among the candidate models as shown in Fig. 2 and Table 2. However, the experimental semivariograms for Mn at cm depth, Zn at 0-30 cm depth and Cu at cm depth showed pure nugget effect model (Table 2). Pure nugget effect model indicates that sampled property has very little spatial structure or varies randomly [9]. The ratio of nugget to sill ( C 0 /( C + C0 ) ) is used to quantify the degree of spatial dependence of soil variables. If the ratio is less than or equal to 25%, the variable is considered to be strongly spatially dependent; if the ratio is between 25 and 75%, the variable is considered moderately spatially dependent; and when the ratio is greater than 75%, the variable is considered to be weakly spatially dependent [8]. Semivariograms indicated strong spatial dependence for Fe at 0-30 cm layer, Zn at cm layer and Cu at 0-30 cm layer. Strongly spatially dependent properties may be controlled by intrinsic factors, such as soil formation [0, 8]. The rest of measured properties, Fe at cm layer and Mn at 0-30 cm layer, exhibited moderate spatial dependence, indicating that the anthropogenic factors changed their spatial correlation [0]. In order to gain insight into the spatial distribution of soil micronutrients, ordinary kriging interpolation was employed for Fe at 0-30 and cm layers, Mn at 0-30 cm layer, Zn at cm layer, and Cu at 0-30 cm layer based on semivariogram models/parameters as shown in Table 2. Fe showed more or less similar spatial patterns at both layers, with lower contents in northern and southern parts while higher contents in central part of the study area (Figs. 3 and 4). Mn at 0-30 cm layer exhibited lower concentrations in central and southern parts compared to eastern and northern parts of the study area (Fig. 3). Zn at cm depth showed higher contents in central part of the study area (Fig. 4). Cu at 0-30 cm layer exhibited lower concentrations in southern part than the other parts (Fig. 3). On the other hand, no spatial correlation was found for Mn at cm layer, Zn at 0-30 cm layer, and Cu at cm layer, and the semivariogram model was pure nugget effect (Fig. 2). Therefore, kriging maps were not produced for them. A pure nugget effect model entails a complete lack of spatial correlation; the data value at any particular location bears no similarity, even to very nearby data values [20]. General Directorate of Rural Services of Turkey conducted a comprehensive survey to determine the micronutrient status of soils in Turkey [3]. The survey revealed that national averages of Fe, Zn, Cu and Mn are.62, 0.78, 2.7 and ppm, respectively, for 0-25 cm soil layer. For the evaluation of the results, they used critical values proposed by Viets and Lindsay [2]. These critical TABLE 2 - Theoretical semivariogram models for soil micronutrients in the studied area and the corresponding model parameters. Soil Variable Fe Mn Zn Cu Depth Model C 0 C 0 +C A 0 C 0 /C 0 +C R 2 (cm) (Nugget) (Sill) (Range) (%) 0-30 Spherical Spherical Spherical Pure nugget effect 0-30 Pure nugget effect Spherical Spherical Pure nugget effect 32

4 FIGURE 2 - Experimental semivariograms of soil micronutrients with fitted models. 33

5 FIGURE 4 - Spatial variability of Fe and Zn at cm depth in the study area. FIGURE 3 - Spatial variability of Fe, Mn and Cu at 0-30 cm depth in the study area. values are 4.5 ppm, 0.5 ppm, 0.2 ppm and.0 ppm for Fe, Zn, Cu and Mn. According to the results, the major potential deficiency problems are with iron (Fe) and zinc (Zn) % and 26.87% of the Turkish soils are deficient in Zn and Fe contents. Only 0.70% of the soils are deficient in Mn content, and there is no Cu deficiency in the soils of Turkey. When considering top layer of soils, Zn and Cu contents (0.70 and 2.26 ppm, respectively) of soils in Büyük Menderes Delta are very close to national averages (0.78 and 2.7 ppm, respectively) of Turkish soils (Table ). On the other hand, while average Fe concentration (28.3 ppm) of soils in Büyük Menderes Delta is greater than the national average (.62 ppm), average Mn content (6.47 ppm) is lower than the national average (25.84 ppm). The results of this study show that there is almost no deficiency problem for either micronutrient studied in 34

6 Büyük Menderes Delta (Figs. 3 and 4). But rather, micronutrient contents largely seem to be higher than critical levels. Therefore, toxicity rather than deficiency may occur in the study area. Although Cu, Fe, Mn, and Zn are essential micronutrients, when present at high concentrations, micronutrients can also result in phytotoxicity [, 22]. In case of toxicity, various methods, such as phytoremediation, are available to remove excess levels of heavy metals from soils [23, 24]. Besides, zeolite and humic acids are also considered as important remediation agents for the immobilization of heavy metals in soils [25, 26]. 4. CONCLUSIONS Based on the experimental semivariograms, the sampling distance ( km) was sufficient to depict the spatial variation of Fe at both 0-30 and cm depths, Mn at 0-30 cm depth, Zn at cm depth and Cu at 0-30 cm. Therefore, produced interpolation maps for these soil attributes at given layers may be used for environmental and agricultural purposes. On the other hand, the sampling distance was found to be insufficient to depict the spatial correlation structure for Mn at cm depth, Zn at 0-30 cm depth and Cu at cm depth. Therefore, a shorter sampling distance should be used for them to characterize their spatial variability in a future study in the same area. Since micronutrient contents in soils of Büyük Menderes Delta are generally higher than the critical levels, no micronutrient fertilization is needed. Instead, it may be required to remediate soils of Büyük Menderes Delta using an appropriate remediation method. ACKNOWLEDGEMENT This research was funded by Adnan Menderes University (Project No: ZRF-07025). REFERENCES [] Shi, J., Xu, J. and Huang, P. (2008) Spatial variability and evaluation of status of micronutrients in selected soils around Taihu Lake, China. Journal of Soils and Sediments. 8, [2] Liu, X., Xu, J., Zhang, M., Si, B. and Zhao, K. 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