Overview of endmember samples collected along the Río Bermejo

To document distinct sources of particulate organic carbon (POC) to the Río Bermejo, we collected 15 soil and 13 leaf litter samples from the local floodplain, and 10 bedrock (predominantly outcroppings of fine-grained sedimentary bedrock) and 2 soil samples from the Río Bermejo headwaters. Leaf litter and soil were oven-dried at 40°C for >48 hours. We shredded leaf litter in an industrial blender, homogenized soil samples in an agate mortar and manually removed root and plant debris >1 cm, and pulverized bedrock samples to <63 µm.