Impact of Crop Types and Locality of Farmlands on Pesticide Uses 42

The type and amount of the pests that occur in agricultural lands considerably change depending on the crop types. The agricultural crops can be a host for the different kinds of pests with their specific biological and chemical features. In this regard, the different types of crops are exposed to the different types of fungal diseases, weeds, and insects. While certain types of crops are susceptible to the various types of pests and require frequent spraying by pesticides, some of the crop types can have high resistance to the pests and do not require any pesticide usages. Hence, the type and dose of the pesticides applied on the different crop types are typically different. In

pollution strongly depends on the type of the cultivated crops, which determine the type and abundance of pests. Therefore, pesticide pollution sources should be investigated by evaluating each crop type separately.

The location of agricultural activities is another substantial factor that directly influences the type and amount of pesticide usage, and consequently, the degree of pesticide pollution in the river. Regarding spatial variability of agricultural activities, different localities have different agricultural issues. The factors like climate, geography, soil type, and topography, which determine the type of plant diseases, insects, and other crop disrupters, can considerably change depending on the location of the agricultural area. Regarding the degree of the impact of locality on agricultural activities in the Yeşilırmak River Basin, the agricultural profiles in the basin typically show variability at the district scale rather than the province scale. The different districts located in the same province can have considerably different pesticide usage profiles since one province can comprise various microclimates belonging to different districts. As a result, it can be concluded that pesticide usage pattern changes considerably depending on region; thus, pesticide contamination should be analyzed and evaluated to the extent of small localities that represent a specific agricultural pattern. Within the boundaries of the Yeşilırmak River Basin, the agricultural lands of each of the districts and provinces are exposed to the different types and amounts of pests for the same type of crops due to the different rain regimes, temperature, elevation, and humidity. Thus, within the scope of this thesis, the assessment and examination of the agricultural profiles and pesticide usage trends were performed separately for each of the districts or provinces in the basin by following the district and province oriented analysis approach.

3.2.2 The Fate of Pesticides from Agricultural Fields to the Freshwater Environment

The extent of agriculture-based pesticide pollution present in the freshwater environment depends on various factors like agricultural land use patterns, irrigation

strategies, physicochemical characteristics of the sprayed pesticides, and the localized climate, geography, and topography of territories where farming activities are carried out. After the application of pesticides in agricultural fields, pesticides are conveyed into river bodies by following different pathways. Spray drift, volatilization, surface runoff, soil erosion, and atmospheric deposition are the major entrance mechanisms of pesticides into the river bodies (Glinski, Purucker, Meter, Black, & Henderson, 2018; Brianda, Bertranda, Seuxa, & Millet, 2002). Glinski et al. (2018) stated that spray drift leads to the spread of pesticides by wind effect during pesticide application on agricultural fields. Spray drift carries pesticides from the target agricultural lands to the non-target environments. Volatilization and atmospheric deposition are other mechanisms that trigger the transportation of pesticides from agricultural areas to the freshwater environment. Volatilization of pesticides from agricultural fields can occur at different levels depending on the physicochemical properties of pesticides and climatic factors like temperature and humidity. According to Lenoir et al. (1999), the volatilization mechanism has the capacity to transport up to 90% of the sprayed pesticides from agricultural sites to non-target areas within a short period of time after application under certain conditions. Among the above-mentioned transportation mechanisms of pesticides, surface runoff is the most effective force that can severely drift pesticides from application zones to the freshwater environment. Richard et al. (1993) and Derbalah et al. (2003) emphasize that surface runoff is a fundamental force for the movement of pesticides from agricultural fields to freshwater environments. Surface runoff occurs under the effect of rain events, which wash the sprayed pesticides and drift them to the different environmental compartments. Duration and intensity of rainfall, land slope, and permeability of soil are major factors that significantly determine the degree of surface runoff. Purdue Pesticide Programs (PPP) (1995) stated that if soil binding strength (soil sorption capacity) of a pesticide is not strong enough then, pesticide entrance into freshwaters from application lands can happen in a few minutes or hours right after an intense rainfall event. In this regard, it can be

pesticide occurrence within the river basin can be notably short, even in minutes if driving forces and environmental conditions are sufficient to trigger pesticide movement. When the combination of volatilization, rainfall events, spray drift, and other driving forces are taken into account, it can be concluded that pesticide transport from application fields can quickly happen within a short period of time regardless of driving force intensity. This thesis has paid particular attention to the analysis of the relation between the pesticide application months specific to each district and the pesticide observation months at the sampling stations of the corresponding districts within the Yeşilırmak River Basin by taking into account the impact of the timing and amount of precipitation events.

3.2.3 Impact of Physicochemical Characteristics of Pesticides on Pesticide