Investigstion of groundwater potential and quality of Kastamonu province, determination of water pollutant concentrations and evaluation of the suitability of groundwater for agricultural irrigation

Groundwater is the most serious source of fresh water after glaciers and snow waters. These resources are mostly consumed as irrigation water. The physico-chemical quality characteristics of the waters used are of great importance for good agricultural practices to become more efficient, effective and sustainable. Kastamonu province, which is the sub-basin of the Kızılırmak basin, has rich resources in terms of surface waters. However, access to surface waters is not distributed homogeneously and evenly on a provincial basis. In regions where access to surface waters is limited, it has become a necessity to meet the water needed for drinking-use and agricultural irrigation purposes from groundwater. In this study, groundwater quality characteristics of Kastamonu province were classified using internationally accepted classification systems in terms of agricultural irrigation use. Water samples taken from 27 points without access to surface water for 4 periods in Kastamonu Sub-Basin between 12/11/2020 -19/05/2022 were examined in terms of Irrigation water suitability criteria. In addition, the time-dependent variation of the irrigation water suitability assessment of the water samples taken from the wells of 6 observation stations in the dry and rainy periods (September – April) of 2018-2022 were evaluated. Parameter analyzes of pH, Electrical Conductivity EC, Anions F- Fluoride Cl⁻ ChlorideCl⁻SO₄²- Sulfate, Cations Na⁺, NH₄⁺, K⁺², Ca⁺², Mg⁺²Ca⁺² Carbonate Bicarbonate CO32-, HCO3-, Boron (B) were used. With these parameter values, irrigation water classification was made using Sodium Percentage (% Na), Sodium Adsorption Rate (SAR), Residual Sodium Carbonate (RSC) values, US salinity laboratory classification system, Wilcox (1948) graphic system. As a result of the study, in Kastamonu Sub-Basin, where most of the groundwater in the investigated area is suitable for irrigation water use, RSC. According to Wilcox diagrams, where the SAR and %Na values are not directly affected by the irrigation season, the waters in the basin are mostly in the "Very Good - Good" and "Good Usable" water class. USA Salinity Lab. According to the diagrams, it is seen that it is mostly in the "C2S1" and "C3S1" classes. In the long-term examinations, it was seen with the graphics that the time-dependent variation of the physicochemical parameters of the observation well samples was limited. Although the groundwater characteristics are close to each other in the study area, they differ in terms of chemical content. In irrigation using groundwater, together with the results of the analysis, the quality characteristics of the water of the plant to be cultivated, the effects of plant resistance and productivity potential should be taken into consideration.