Abstract. Concentrations of in-situ-produced cosmogenic 10Be in river sediment are widely used to estimate catchment-average denudation rates. Typically, the 10Be concentrations are measured in the sand fraction of river sediment. However, the grain size of bedload sediment in most bedrock rivers covers a much wider range. Where 10Be concentrations depend on grain size, denudation rate estimates based on the sand fraction alone are potentially biased. To date, knowledge about catchment attributes that may induce grain-size-dependent 10Be concentrations is incomplete or has only been investigated in modelling studies. Here we present an empirical study on the occurrence of grain-size-dependent 10Be concentrations and the potential controls of hillslope angle, precipitation, lithology, and abrasion. We first conducted a study focusing on the sole effect of precipitation in four granitic catchments located on a climate gradient in the Chilean Coastal Cordillera. We found that observed grain size dependencies of 10Be concentrations in the most-arid and most-humid catchments could be explained by the effect of precipitation on both the scouring depth of erosion processes and the depth of the mixed soil layer. Analysis of a global dataset of published 10Be concentrations in different grain sizes (n=73 catchments) – comprising catchments with contrasting hillslope angles, climate, lithology, and catchment size – revealed a similar pattern. Lower 10Be concentrations in coarse grains (defined as “negative grain size dependency”) emerge frequently in catchments which likely have thin soil and where deep-seated erosion processes (e.g. landslides) excavate grains over a larger depth interval. These catchments include steep (> 25∘) and humid catchments (> 2000 mm yr−1). Furthermore, we found that an additional cause of negative grain size dependencies may emerge in large catchments with weak lithologies and long sediment travel distances (> 2300–7000 m, depending on lithology) where abrasion may lead to a grain size distribution that is not representative for the entire catchment. The results of this study can be used to evaluate whether catchment-average denudation rates are likely to be biased in particular catchments.

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Abstract. Concentrations of in situ-produced cosmogenic 10Be in river sediment are widely used to estimate catchment-average denudation rates. Typically, the 10Be concentrations are measured in the sand fraction of river sediment. However, the grain size of bedload sediment in most bedrock rivers cover a much wider range. Where 10Be concentrations depend on grain size, denudation rate estimates based on the sand fraction alone could potentially be biased. To date, knowledge about catchment attributes that may induce grain size-dependent 10Be concentrations is incomplete or has only been investigated in modelling studies. Here we present an empirical study on the occurrence of grain size-dependent 10Be concentrations and the potential controls of hillslope angle, precipitation, lithology and abrasion. We first conducted a study focusing on the sole effect of precipitation in four granitic catchments located on a climate-gradient in the Chilean Coastal Cordillera. We found that observed grain size dependencies of 10Be concentrations in the most-arid and most-humid catchments could be explained by the effect of precipitation on both the scouring depth of erosion processes and the depth of the mixed soil layer. Analysis of a global dataset of published 10Be concentrations in different grain sizes (n=62 catchments), comprising catchments with contrasting hillslope angles, climate, lithology and catchment size revealed a similar pattern. Lower 10Be concentrations in coarse grains (defined as negative grain size dependency) emerge frequently in catchments which likely have thin soil and where deep-seated erosion processes (e.g. landslides) excavate grains over a larger depth-interval. These catchments include steep (>25°), arid (<100 mm yr−1) and humid catchments (>2000 mm yr−1). Furthermore, we found that an additional cause of negative grain size dependencies may emerge in large catchments with long sediment travel distances (>2300–7000 m, depending on lithology) where abrasion and sediment provenance may lead to a grain size distribution that is not representative for the entire catchment. The results of this study can be used to evaluate whether catchment-average denudation rates are likely to be biased in particular catchments.

&lt;p&gt;Rivers transport large amounts of fine mineral and organic matter in suspension from their sources to the ocean. Suspended solids, which also bind contaminants and nutrients, therefore, affect river morphodynamics, water quality and ecosystem functioning. A detailed understanding of suspended solid dynamics is urgently needed to improve suspended sediment monitoring and management around the world.&lt;/p&gt;&lt;p&gt;Sediment rating curves (SSC=aQ&lt;sup&gt;b&lt;/sup&gt;) describe the relation between suspended solid concentrations (SSC) and river discharge (Q) and are frequently used to study suspended sediment dynamics at specific location in a river. In this formula, &lt;em&gt;a&lt;/em&gt; and &lt;em&gt;b&lt;/em&gt; are regression coefficients that depend on river basin characteristics. The &lt;em&gt;a&lt;/em&gt;-parameter is an indicator of the erosion severity and the &lt;em&gt;b&lt;/em&gt;-parameter reflects the erosion reactivity with respect to changing discharge. To date, a few studies have compared the rating parameters (&lt;em&gt;a&lt;/em&gt; and &lt;em&gt;b&lt;/em&gt;) to catchment characteristics, however, these studies only focused on specific regions on earth. A global study is required to better understand suspended sediment dynamics along a wide range of catchments characteristics.&lt;/p&gt;&lt;p&gt;In this study, we compiled available SSC and Q data from 176 rivers that are located in various regions around the world. The majority of the SSC and Q data have been collected from the GEMStat and the Global Runoff Data Centre (GRCD) databases, but we also included data from the USGS and SO-HYBAM datasets. The compiled dataset ranges from small basins (~50 km&lt;sup&gt;2&lt;/sup&gt;) to large basins (~190,000 km&lt;sup&gt;2&lt;/sup&gt;), with medium-sized river basins (~1000-10,000 km&lt;sup&gt;2&lt;/sup&gt;) being most dominant. Furthermore, the dataset contains basins that are located in various climate regions, ranging from semi-arid to humid climate, and includes both upland and lowland rivers. We only included river monitoring stations with &gt;50 overlapping SSC and Q data points (i.e., SSC and Q data measured on the same day). We parameterized the rating curve between the SSC and Q data and compared the &lt;em&gt;a-&lt;/em&gt; and &lt;em&gt;b&lt;/em&gt;-parameters to topographic, lithologic, climatic and land cover-related catchment characteristics using simple and multiple linear regressions.&lt;/p&gt;&lt;p&gt;The first results reveal that the &lt;em&gt;b&lt;/em&gt;-exponent and, thus, the suspended solids variability, shows a fairly good relationship with catchment steepness and basin size. The data suggests that climatic and land use parameters play an insignificant role, however, when combining all parameters in a multiple linear model, climate seems to have a secondary effect on top of topographic parameters. The erosion severity (&lt;em&gt;a&lt;/em&gt;-parameter) is most strongly controlled by climatic and land cover parameters. The results of this study can be used to infer for suspended sediment dynamics in ungauged catchments, which is relevant for implementing sediment monitoring and management in these regions on earth.&lt;/p&gt;