We collected water samples from the river surface using a pre-rinsed HDPE 1 L bottle. The samples were filtered in the field with a GF/F-filter (0.7 μm nominal, precombusted at 500°C), using a Nalgene filter apparatus (Thermo Scientific). The filters with the suspended particulate matter were then frozen and transported in polyethylene cases to the Alfred Wegener Institute in Potsdam. After thawing and drying in a Memmert Modell 500 oven the filters were re-weighed with an analytical balance (Analytic AC 21 S, sartorius). Particulate organic carbon (POC) and the stable carbon isotope value of the POC (d13C-POC) were measured at the University of Basel, Department of Environmental Science. POC was measured using an aliquot of the GF/F filters and fumigated with concentrated hydrochloric acid (HCl 37 %) for 72 h to remove inorganic carbon, and subsequently dried at 50 °C for another 48 h following Lattaud et al. (2025) on an Elemental Analyzer (EA) interface coupled to a stable isotope analyzer (Thermo Scientific EA IsoLink IRMS System). The standard used to calculate TOC was ethylenediaminetetraacetic acid (EDTA, Sigma Aldrich). POC was blank corrected using a combusted GF/F filter, drift-corrected and calibrated using EDTA. Stable isotope values of particulate organic carbon were measured on an elemental analyzer coupled with an isotope ratio mass spectrometer. Measured values were corrected for size, blank and drift, and normalized to international standards (USGS64 and EDTA).