# Characteristics and Causes of Coastal Water Chemistry in Qionghai City, China
## 1 Introduction  
In recent years, water quality studies for the coastal zone area of Qionghai City have gradually increased, including the monitoring and analysis of seawater, river water, lake water, and other water bodies. Some bays and estuaries in the region have water pollution problems, mainly from agricultural, industrial, and urban sewage sources. Water chemistry plays an important role in ecological environmental protection, water resource utilization, water pollution control, and water safety assurance. The water chemistry of watersheds can reflect the effects of rock weathering, atmospheric deposition, and human activities in the watershed [1]. By analyzing the characteristics and spatial and temporal changes inriver water chemistry, the basic processes that proceed from water chemistry component formation could be effectively discerned [2]. In addition, the analysis of the water chemistry characteristics of coastal zone water bodies is a very critical part of the evaluation of the quality of water resources in the basin, which has non-negligible value for the scientific development and natural protection of water resources in the basin [3]. The water chemistry composition characteristics of watershed water bodies are mainly influenced by physical geography [4]; however, more and more studies show that the water chemistry composition of watershed waters is also influenced by human activities and has become an important issue affecting human survival and social development [4; 5; 6]. For the above-mentioned studies, many results have been achieved both in China and abroad, and research methods tend to be diversified [7; 8]. Since the middle of the 20 th century, a large amount of theoretical knowledge and a great number of technical means have been used to study the characteristics and evolution of the chemistry in both surface water and groundwater. Among them, there are many mathematical methods to deal with water quality data, generally including cluster analysis, principal component analysis, correlation analysis, factor analysis, etc. [9; 10]. Based on the analysis of water quality data and the further use of piper trilinear plots [11], [PERSON] [12], the water quality simulation method, the isotope analysis method [13; 14], etc., investigations into the ion chemical characteristics of rivers and the influence of major weathering processes in watersheds have been undertaken [15]. Following this, the GIS visualization function appeared as a clear display of water quality results [16]. [PERSON] analysis of the water chemistry components of various global water bodies (precipitation, seawater, lakes, and rivers) suggests that rock weathering, atmospheric precipitation input, and evapotranspiration-crystallization are the three major controlling factors of global surface water chemistry components [12]. [PERSON]'s analysis of the water chemistry of the Eulphrates River in Syria showed that the ionic fraction in the river was influenced by the dissolution of rock weathering, water temperature, and evaporation [17]. Different study areas were located in different environmental contexts, including a variety of factors such as geological formations, climate, and human activities. These factors affect the ion concentrations and chemical composition of water bodies, resulting in significant differences in the water chemistry characteristics of different regions. Therefore, when conducting water resources management and environmental protection, the influence of these factors needs to be fully considered when developing management measures that are appropriate for the region [18; 19; 20]. Qionghai City, located on the east coast of Hainan Island, is a coastal city with rich coastal ecological resources. The quality of the water environment in the area is important for maintaining the local ecological environment and developing tourism [21].