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Sediment flux of lowland rivers is dominated by suspended transport, but data is often sparse and analysis largely relies on rating relationships. However, suspended sediment concentration is by no means constant in both, space and time. Here we analyse the variability of sediment rating curves and the seasonality of suspended sediment concentration in German waterways, as recorded by 10 gauging stations with catchment areas between 2600 - 22000 km2. Our data reveal a distinct break in power-law scaling relationships for all stations, with increased scaling exponents above threshold discharges close to the geometric mean. We attribute this mainly to the activation of sediment sources that resist mobilisation at lower flows. Furthermore, all stations show a counter-clockwise hysteresis effect throughout the year, where summer discharges have a higher sediment load than comparable winter discharges. Though the reasons for this pattern need further investigation, preliminary results show a strong correlation with rainfall erosivity and land-use parameters.