## 1 Introduction  
Heavy metal pollution in freshwater ecosystems is a universally pressing concern, with the ramifications being especially pronounced in regions undergoing rapid industrial and agricultural expansion. Despite their natural existence in the environment, these freshwater ecosystems serve diverse functions, including water supply, agricultural irrigation, flood control, climate regulation, aquaculture, tourism, and biodiversity preservation [1]. Despite exponential economic growth, China faces escalating heavy metal concentrations in its freshwater sources, primarily attributed to urbanization, industrial activities, and modern agricultural practices [2; 3].  
Historically, natural traces of heavy metals in Chinese freshwater systems have been attributed to the country's rich and diverse geological features. However, research has highlighted that, in contemporary times, several water bodies are recording concentrations that dangerously surpass national safety thresholds [4; 5]. Such alarming trends are not isolated but echo across industrial hubs, such as the Yangtze River Economic Belt and the Pearl River Delta. Here, industries, agriculture, and expanding urban sprawls intersect, producing a cocktail of pollutants that find their way into the aquatic systems [6; 7; 8].  
China's extensive network of lakes and rivers, spanning 82,642 km\({}^{2}\), intertwines with the nation's socioeconomic and cultural fabric, serving agricultural, industrial, and recreational purposes. However, heavy metal discharges, intensified by agricultural activities, pose a significant threat. Chemical fertilizers, pesticides, and herbicides contribute to metal leaching into water systems, with Cadmium from phosphate fertilizers and Arsenic from pesticides being prominent concerns [9; 10; 11; 12]. These contaminants, upon entering water bodies, often undergo intricate interactions. Research has shown that they can bind with organic runoffs from agricultural landscapes, potentially amplifying their toxicity and influencing their behavior in aquatic habitats [13; 14; 15]. Multiple researchers have outlined that peak agricultural seasons, coinciding with monsoons, can substantially influx these metals into rivers and lakes, creating episodic challenges for water management systems [16; 17].  
The complexity deepens as heavy metal dynamics in freshwater systems are non-linear, involving intricate interactions with organic runoffs and seasonal variations, particularly during peak agricultural seasons and monsoons. The Chuhe River in Nanjing exemplifies these challenges, as it experiences periodic heavy metal concentrations surging amidst urban and agricultural landscapes, reflecting the broader issues that Chinese rivers face [6; 18; 19; 20].  
In this context, we conducted an investigation into eight specific heavy metals--Arsenic (As), Mercury (Hg), Chromium (Cr), Nickel (Ni), Copper (Cu), Zinc (Zn), Cadmium (Cd), Lead (Pb), and Manganese (Mn)--in the surface water and sediment of the tributary connecting the Chuhe River and the Changjiang River. This study had three primary objectives: firstly, to elucidate the distribution patterns of these heavy metals within the water and sediment; secondly, to assess the extent of pollution and ecological risks associated with these heavy metals in the aforementioned aquatic environments; thirdly, to determine the relationship between the heavy metals and physicochemical parameters to identify the potential sources of the heavy metals. These comprehensive analyses and assessments are pivotal in showcasing this tributary's heavy metal pollution and ecological risk index issues.