## 1 Introduction  
Land-water interface zones are the junctions between the river and terrestrial ecosystems, and they have been emphasized in ecological and environmental fields in recent years because of their important roles in protecting biodiversity, intercepting and infiltrating ecological flows, such as material and energy flows, and purifying water bodies [1; 2; 3; 4; 5]. Overseas research on land-water interface zones has produced more in-depth results, e.g., in the Everglades National Park in Florida, USA, and the Laurentian Great Lakes in Canada. Natural and socio-economic vulnerability indices have been created via spatial modeling using geographic information systems (GISs). A multidisciplinary approach integrating geological, physical, and socio-economic vulnerability was synthesized to study the integrated vulnerability of the riverine and coastal land-water interface zones under different environmental factors. It was concluded that the spatial variability of the natural environment has a greater impact on ecosystems than temporal fluctuations [6; 7; 8; 9]. In China, research on land-water interface zones is focused on Dongting Lake [10], Chaohu Lake [11], Poyang Lake [12], and other important water bodies. The basic characteristics of the landscape pattern changes in the relevant study areas were explored; the landscape changes of different characteristics reflect different land use conditions, and the means and extent of the impact of human activities on the value of ecosystem services were revealed through land use. In the Pearl River Basin, studies on spatial and temporal changes in ecological land use and the evolution and value assessment of landscape patterns have been carried out [13], but there is a lack of research on the value of ecosystem services in the basin's land-water interface zones. Ecosystem services are the variety of resources and benefits that humans obtain from ecosystems or the direct or indirect contributions of ecosystems to human well-being and benefits [14], which can be categorized into provisioning services, regulating services, supporting services, and cultural services. The amount of goods and services that ecosystems create and provide in the form of economic benefits is called ecosystem service value (ESV). Market values can directly estimate the value of each individual ES using economic laws [15], and scholars have already used this method to study and achieve results in areas such as the San Antonio region of Texas in the USA [16], coastlines [17], and surface freshwaters [18]. Among the non-market values, the method used to evaluate the value equivalent factor per unit area and the INVEST model is the most widely used. INVEST (integrated valuation of ecosystem services and tradeoffs) is a modeling system that was developed by the US Natural Capital Project Team to assess the functional quantity of ecosystem services and their economic value and to support ecosystem management and decision-making, with the ability to simulate changes in the number of ecosystem services under different land cover scenarios and with an intuitive representation of the results of assessments [19]. Many scholars have conducted ESV assessments for important river basins [20; 21], forests [22], mangroves [23], coastal areas [24], and agricultural land [25] using the INVEST model method. The method used to evaluate the value equivalent factor per unit area is a dynamic valuation method for ES in China, proposed by [PERSON] [26], which has been widely used in studies of ecosystem service valuation in spatially heterogeneous ecosystems [27; 28]. In this study, the method allows for a more visual comparison of high and low ecosystem service values across gradient zones, which will be calculated based on a modified ESV equivalent scale.