Deciphering patterns and inferring processes in multicausal floodplain river ecosystems is a challenge in river science. The effects of larger-scale top-down constraints and smaller-scale bottom-up influences on the spatial patterns of nutrient concentrations across multiple inset-floodplain surfaces was studied in a large dryland floodplain river (Barwon-Darling River, south-east Australia). The distribution of sediment-associated carbon, nitrogen, and phosphorus was primarily related with significant differences in the textural character of the different floodplain surfaces. Elevation of the different floodplain surfaces above the active channel was a secondary influence on the distribution of carbon and phosphorus. Combined, these factors produce a spatial patch mosaic of sediment associated carbon, nitrogen, and phosphorous across these floodplain surfaces.