## 1 Introduction  
As matter transport systems, rivers can be proxy indicators of many landscape and catchment processes. Before water reaches the stream, it moves from precipitation through many different river basin features, such as vegetation, soil, and geology. The water may dissolve substances from soil and rocks during this movement or transport matter. As a kind of archive, the sediments in the river itself, along its banks, and the whole floodplain can be used to determine relationships and interactions between processes such as land cover change, runoff formation, and soil erosion [1, 2]. Sediments can function as matter sinks for different materials and chemicals. Depending on conditions, this function can be reversed. The same sediments can become sources, releasing accumulated materials back into the river water [3, 4]. Many chemicals and elements are transported in rivers and accumulated or released from river sediment. Among them are those considered harmful to the environment and humans, such as specific metals. Many rivers are affected by heavy metal concentrations that exceed natural background levels [5, 6]. This can lead to adverse health effects for humans and aquatic life [7, 8, 9], and in areas where drinking water for human consumption is extracted from rivers, heavy metals and other pollutants can be severely harmful, especially under long-term exposure [10]. Therefore, identifying the specific factors that affect metal concentrations in river sediments can be essential for strategy and policymaking and protecting human and animal health. Factors at different scales that affect chemical concentrations in river sediment to some degree are land cover, hydrology, human activity, geologic setting, and climate [11; 12; 13; 14; 15; 16]. Many scientific studies have dealt with pollution in soils, river water, and sediments [17; 18; 19]. Most of these studies focused on individual heavy metals, sites, or processes, which is essential for understanding detailed causes and relationships. However, it was also found that the overall variation in water quality was better explained by basin-scale land cover than by smaller-scale variables [20; 21]. Larger-scale landscape patterns have been linked to river water quality, and landscape pattern-slope interactions were found to explain part of the variability of soil contamination [22; 23]. Nevertheless, there is still a lack of understanding of the differing importance of factors affecting metal accumulation at a basin scale. Thus, it is necessary to identify the most important basin-scale factors that determine river sediment metal concentrations and, thus, pollution potential. Factors in this context are individual parameters, such as specific vegetation types, but also categorical terms, such as land cover. The basin scale here can be understood as an aggregated characteristic of the whole basin, in contrast to the point- or regional scale. Data describing important factors at this scale is often readily available for most of the planet's surface from surveys and satellite imagery, while measured chemical data is relatively rare. Therefore, a deeper understanding of the large-scale factors could support estimating metal pollution potential at the basin scale for areas without direct measurements. To achieve this goal, it is essential to study whether the information content at the basin scale is high enough to determine metal concentrations and thus pollution potential. This study focuses on the importance of basin-scale factors of river sediment metal concentrations. The goal will not be to explain the behavior of individual metals in detail but to discover the general effect of basin-wide characteristics on different metals. The study is performed for the contiguous USA. The reason for this is, on the one hand, the excellent data availability. Large amounts of data collected by many government agencies are available to the public, including physical spatial data and geochemical data.