Assessment of Temporal Occurrence Trend of the Pesticide Pollution

The temporal occurrence pattern of the pesticides in the river basin considerably depends on the timing of the pest infestations, which occur in specific periods for each crop type raised in the agricultural lands of each district in the river basin.

Within the scope of this section, the time-dependent distribution of the pesticides across the river basin was analyzed in order to determine the basin-wide temporal occurrence profile of the pesticide pollution. In this regard, the observation months of the pesticide concentrations above their EQS values were identified for each of the sampling stations. The months that are responsible for the most frequent pesticide occurrences in the river basin were identified for the insecticide, herbicide, and fungicide observations.

Precipitation plays a functional role by triggering the runoff and spread of the pesticides from their application sites to the freshwater environment. In this respect, the precipitation trend across the river basin was identified by calculating the average of monthly precipitation amounts of the Gümüşhane, Giresun, Sivas, Yozgat, Tokat, Amasya, Çorum, and Samsun provinces where the water quality sampling stations are located, unlike for the other provinces of the river basin. The precipitation data of these eight provinces were obtained from the Turkish State Meteorological Service (TSMS). The monthly precipitation amounts of the particular region of the

boundaries’ were compared to the pesticide detections observed at the corresponding months. In this context, the impact of the precipitation events on the wash and spread of the sprayed pesticides were also evaluated by analyzing the frequencies of the pesticide occurrences above their EQS values.

3.3.4 District-Specific Identification of the Agricultural Sources for 16 Pesticides

For the achievement of the target-oriented source identification of the pesticide pollution observed in the river basin, the localized geographic and climatic conditions, which create a terrain-specific agricultural profile, should be taken into account individually for each of the districts. In order to fulfill this goal, first of all, the information on the type, spraying frequency, and spraying timing of the agrochemicals against the district-specific and crop-specific pests was obtained by individually contacting the agricultural engineers of the District Directorates of Agriculture and Forestry of the 26 districts that locate water quality sampling stations in their boundaries. Within the light of the site-oriented expert knowledge regarding district-based agricultural practices, the elaborative and detailed investigation was performed by gathering and compiling information on district-specific agricultural characteristics and the localized and time-integrated insecticide, herbicide and fungicide usage schedules of each crop type raised in each district. In this context, the comprehensive and detailed inventories, which encompass insecticide, herbicide, and fungicide spraying schedules of each crop type and typical agricultural practices, were prepared for each district where sampling stations are located. These district-specific inventories were used as the baseline for the identification of the pesticide pollution in the river basin. Furthermore, Corine 2018 agricultural land use data for the provinces located within the boundaries of the Yeşilırmak River Basin were examined in order to observe the exact distance between the agricultural field of each crop raised in each district and the water quality sampling stations located in corresponding districts. In this respect, the water quality sampling stations and

Corine 2018 land use data were integrated into the Yeşilırmak River Basin map in order to depict the general distribution of the agricultural lands throughout the river basin, which is provided in Figure 3.1. However, as it can be seen in Figure 3.1, Corine 2018 agricultural land use data enable a general overview of the spatial distribution of agricultural lands across the basin without specifying the type of the agricultural crops. More specifically, the Corine 2018 land use map provides only the location data of the major land cover groups like arable lands, fruit trees, and pastures rather than the crop-specific sub-groups like apple trees, tomato fields, etc.

In order to accomplish elaborative and precise identification of the agricultural sources of pesticide pollution, each type of agricultural crop should be evaluated separately because the application period of the pesticides considerably differs for the different types of crops. Since Corine 2018 land use map only provides a general overview about the distribution of agricultural lands rather than crop-specific detailed data, within the context of this thesis, Corine 2018 land use data were not involved in the source identification study. In this thesis, the source identification of the pesticide pollution was employed by assessing the insecticide, herbicide, and fungicide spraying schedules of each crop type of each district separately.

Figure 3.1 Map of the Corine 2018 Agricultural Land Use and the Water Quality Sampling Stations within the Boundaries of the Yeşilırmak River Basin

As a preliminary step for the source identification of the pesticides, the determination of dominant crops was performed in order to identify the crops that have high potential to contribute to the pesticide pollution in each district. The agricultural sources of the pesticides observed at the sampling stations of each district will be selected among the pre-determined dominant crops; therefore, the dominant crops can be defined as the candidate crops to be a source of the pesticides detected at the sampling stations of each district. The contribution degree of the farmlands of each crop to the pesticide pollution depends on the size of the crop cultivation area, which determines the amount of agrochemical sprayed on the cropland; therefore, the percentages of the areal shares of each crop type raised in each district were calculated for the identification of the dominant crops. Since the abundance of the pests that attack the crops occupying large cultivation areas will be high, the crops that cover the large farming areas in the districts will be exposed to more intense agricultural protection practices compared to the crops covering the small farming area. In this regard, the dominant agricultural crops cultivated in each of the 26 districts were determined by calculating the percentage shares of the crop areas both among the areas of other types of crops raised in the host district and among the areas of the same crop types raised in the other districts of the basin. By taking into account these two percentages, the extent of the farming activities for each crop type is aimed to be determined both at the basin scale and district scale. For the calculation of the areal shares, the data of crop-based and district-specific agricultural areas were obtained from the Turkish Statistical Institute (Turkstat). The percentages of the areal shares of the crops at the basin scale and district scale were defined as the indication of the degree of their possible contribution to the agrochemical pollution in the river basin. In this context, the crops that have areal share above 5% in all types of total crop areas in the district and above 5% in the same type of crop areas in the other districts of the basin were determined as the dominant crops of the districts. The exceedance of 5% by at least one of these two percentages was determined as selection criteria for the dominant crop identification. After the selection of the

exceeded their EQS values at the sampling stations of each district were analyzed and determined by following district-specific assessments. For the identification of the degree of district-based pesticide pollution, the pesticides that exceeded at least one of their MAC-EQS and AA-EQS values at the sampling stations located in the boundaries of each district were determined, and their detection frequencies at corresponding sampling stations were calculated for each district.

After the preparation of the inventories on district-specific agricultural profiles, the determination of the dominant crops, and the identification of the type and degree of pesticide pollution in the boundaries of the districts, the temporal correlations between the agricultural activities and the pesticide occurrences were established for each district. More specifically, the temporal correlation between the EQS exceedance months of each pesticide at sampling stations of each district, and the insecticide, herbicide, and fungicide spraying schedules of each of the pre-determined dominant crops raised in each district were analyzed and pre-determined.

Based on the analysis of temporal correlations established for each district, district-specific precipitation trends, and also physicochemical properties of each pesticide, the district-based and crop-specific agricultural sources of each pesticide observed at each sampling station in the Yeşilırmak River Basin were identified within the scope of this thesis.

3.4 Results and Discussion

3.4.1 Data Compilation and Selection of the Concerning Pesticides for the