The aim of this study is to determine the hydrochemical properties of water resources in the Seyfe Basin and to understand processes involving water chemistry using statistical techniques such as principal component analysis (PCA) and cluster analysis. Seyfe Lake closed basin is located west of Kirsehir (Turkey) in the Central Anatolia. Considering the importance of the Seyfe Lake Basin for its water resources potential and due to its fragile ecosystem, a detailed hydrogeological characterization of the basin has been undertaken. In order to characterize hydrogeological system accurately, water samples were collected from springs, wells, drainage channels during September and December 2019 field campaigns from the Seyfe basin. The temperature, pH, total dissolved solids (TDS) and specific electrical conductance (EC25°C) were measured at the field and spatio-temporal changes of major ions are evaluated. The waters have neutral to slightly alkaline character, and most of the water samples are saturated with calcite, dolomite and aragonite minerals. According to the results obtained from Gibbs, Piper plot, and PCA, the water-rock interaction takes place without any remarkable ion exchange reactions. Water facies identified with the Piper diagram; supports this view. Water types are determined as Ca-HCO3 for springs; Na-HCO3 for wells; Na-SO4 for drainage channel in the dry season and Na-Cl in the rainy season. In Ihe study area; ionic compositions of the springs are not affected by seasonal changes. The high sulfate concentration is probably related to the weathering of evaporitic rocks in the basin. The waters are grouped according to the results, and the difference observed within the groups are related to the lithology of aquifers and flow path of the waters. KEYWORDS: Hydrochemistry, Major ions, Kırsehir, Central Anatolia, Seyfe Closed Basin, Spatio-temporal Changes.

Lakes and wetlands are natural sources and have an important role for hydrological cycle. They are also affected by climate change and anthropogenic activities such as precipitation regime, diminishing water bodies, uncontrolled groundwater extraction, drainage and irrigation channels, agricultural activities and discharge of domestic and industrial waste. For this reasons monitoring the lake surface areas are very crucial. In this paper; the Seyfe Lake was selected as a case study. The study area is located at the southern part of the Seyfe basin with a catchment area of 1447 km2 in Central Anatolia. Seyfe Lake wetland is located in a closed basin. The lake area and its surroundings is a Ramsar site and have the status of Grade 1 Natural Site and Protected Natural Area. This study aimed to evaluate the spatio-temporal changes of the surface area of Seyfe Lake by using Geographical Information Systems (GIS) and remote sensing techniques. For this purpose Landsat (MSS, TM, ETM+, OLİ/TIRS) satellite images used for a period between 1987 and 2020. A total of 34 images were processed and, using unsupervised classification method, water body was extracted according to the spectral information of the image bands and the historical change of the lake surface area was calculated by using Image Analysis Function of ArcGIS 10.6.1 software. In addition to these satellite images, long-term hydrometeorological data and field observations were analyzed to determine the changes of the Seyfe Lake surface area and understand the effects of climate change and antropojenic activities. According to the old and recent satellite images of Seyfe Lake area, the persisting shrinkage of lake area and diminishing of the water resources over the years in the Seyfe Lake basin still continue. Maximum and minumum surface area of the lake was calculated 43 km2 and 18 km2 respectively during 1987-2020. In August 2008; the lake area is completely dried. Nowadays the 58% of the lake area is dried up. These variations could probably be related with the antropogenic effects and climatic changes in the study area. As a result, Satellite based techniques might provide a historical data to identify changes on the lake surface area. Remote sensing techniques are also effective to evaluate temporal and spatial changes on water resources resulted by human activities and local climate change. In-situ observation and hydrogeological monitoring are another important tools to support findings of remote sensing study. Keywords: Spatio-temporal change, Wetland, Seyfe Lake, Unsupervised Classification, Remote Sensing

Lakes are valuable and sensitive freshwater reservoirs with ecosystems that are highly vulnerable to many external threats. Specifically, changes in lake surface area and water level fluctuations are important parameters to detect changes in lake ecosystems. These fluctuations and shrinkage levels of the lake area occur due to both climatic and anthropogenic factors. Some examples of such include but are not limited to changes in meteorological factors, land use, potable water supply, water withdrawal for agricultural irrigation, and plant product pattern factors play an important role in the sustainability of the lake region and the water resources in the basin. In this paper, Seyfe Lake was selected as the primary research area. Seyfe Lake is located 30 km northeast of Kırsehir; the lake and its surroundings are a protected Ramsar site. The lake consists of a closed basin and the average area of the lake covers 35 km2, the calculation of which was obtained by interpretation of Landsat images and lake bathymetric studies. The average water depth of the lake is 1.65 m, with an elevation of 1110 m above sea level. The lake is recharged by rainfall, surface runoff, and underground flow. The discharge of the lake occurs via evaporation from the lake surface. The paper aims to evaluate the relationship between climatic and anthropogenic factors that caused the shrinkage of the Seyfe Lake surface area and water level changes in the lake to subsequently determine which factor predominantly posed a greater impact over three decades (1985-2020). Geological, hydrogeological, hydrological, and remote sensing surveys were carried out in the lake area and the basin. Furthermore, satellite images, meteorological data, lake bathymetric, and land cover maps were evaluated. It was determined that the lake surface area decreased from 66.87 km2 to 1.86 km2 and the lake area shrank by 93.78% between the years 1985 to 2020. In the period between 1990-2000, the total area of the lake was mainly controlled by climatic variations (precipitation and temperature). However, since the 2000s, there has been an increase in meteorological factors such as temperature and evaporation and contrastingly, a decrease in the amount of precipitation. When the land cover maps of the study area were evaluated, it was determined that rain-fed agriculture shifted to irrigated agriculture since 2006 within the lake basin. Additionally, it was concluded that the farmlands area increased and the transition to irrigated agriculture led to an increase in the amount of water used in agricultural irrigation with uncontrolled groundwater withdrawal from the wells in the lake basin. As a result of the research carried out in the study area, it was concluded that climatic and anthropogenic factors caused the decrease in the lake surface area and human activities impacted a greater share in the lake level change and shrinkage in the surface area in the last 15 years