ON THE USE OF UV SPECTROPHOTOMETRY TO ASSESS DISSOLVED ORGANIC-CARBONORIGIN VARIATIONS IN THE UPPER RHONE RIVER

To detect temporal changes and the origin of the refractory dissolved organic matter in the Upper Rhone River, UV light absorbance (A) at 28 5 nm and quantitative dissolved organic carbon (DOC) measurements were carried out. Data from 63 visits to the main channel ove a period of two years and from visits to different waterbodies in the alluvial pla in before and after a flood are presented. There was a good correlatio n between A (0.019-0.160) and the DOC content (1.40-9.81 mg/L) for the waterbodies, but not for the river axis with lower A (0.013-0.044) an d DOC content (1.13-2.20 mg/L). Due to this good correlation, the DOC content could be quantified for the waterbodies by absorbance measurem ents only. For the river water this indirect determination of the DOC content was not possible. However, the A/DOC ratio showed changes in t he composition of DOC of river water and provided indications about th e origin of the dissolved organic matter in the Upper Rhone River.