# Characteristics and Causes of Coastal Water Chemistry in Qionghai City, China
## 4 Discussion  
This study provides an in-depth analysis of the water chemistry characteristics of the main watersheds in the coastal zone area of Qionghai City and their causes. Using [PERSON]'s trilinear diagram, Gibbs diagram, and correlation analysis, this study drew significant conclusions about the water chemistry characteristics and sources in this region. The results show that the characteristics of water chemistry ion fractions in this region were similar to many other coastal zone regions.  
Firstly, the dominant cation was Na+, and the dominant anion was Cl-, which is consistent with the characteristics of being located in the coastal zone area. Secondly, the content of dominant cations showed Na+ > Ca2+ > Mg2+ > K+, while the content of dominant anions was Cl- > \(\text{SO}_{4}{}^{2-}\) > \(\text{HCO}_{3}{}^{-}\) > \(\text{CO}_{3}{}^{2-}\), and these results indicate that the influence of seawater was very significant in this region. In addition, the ion concentrations showed different trends in the water samples from different collection points, mainly because of the different sources of water and environmental factors.  
For example, the highest ion concentration in the water samples collected from the farming ponds, and the main water chemistry type, was Na-Cl, which might be related to the development of the surrounding farming industry, seawater backflow, and other factors. Therefore, measures must be taken to limit the scale of the farming industry and reduce the phenomenon of seawater backflow to reduce the risk of water pollution. On the contrary, the water samples collected in the river had the lowest ion concentration and the main water chemistry type was the Ca-Mg-HCO3 type; this is because water bodies in the area may be affected by factors such as rock weathering and atmospheric precipitation.  
[PERSON] et al. [37] studied the water chemistry characteristics of the southwest coastal zone area of Hainan Province and found that Na+ and Cl- were the main water chemistry ions and that water bodies in the area were influenced by human activities, with agricultural activities contributing more to \(\text{NO}_{3}{}^{-}\) and \(\text{SO}_{4}{}^{2-}\) ions in the water bodies. In addition, [PERSON] et al. [38] studied the water chemistry of groundwater in the east coastal zone area of Hainan Island and found that Ca2+ and Mg2+ were the main cations, \(\text{HCO}_{3}{}^{-}\) and Cl- were the main anions, and the water chemistry of the area was influenced by different hydrogeological conditions and human activities. These findings are consistent with the results of this paper.  
The results of this study also indicate that the sources of water chemical ions in the region resulted from various factors such as seawater, rock weathering, atmospheric precipitation, and evapotranspiration concentration effects. This conclusion provides a scientific basis for the development, utilization, and management of local water resources, which could help to protect water resources and the ecological environment of the region and promote the sustainable development of the area.  
However, due to the limited scope of this study, other possible factors were not explored in depth. Our future study will further expand this topic, collecting more water quality samples in Qionghai to explore the details and characteristics and possible spatial and temporal variability of the sources of water chemistry ions in the region.