Evaluating dissolved organic matter loads in tropical alpine rivers using FDOM measurements

Abstract

Peru is home to about 70% of the world’s tropical glaciers. However, due to climate change mainly, they have lost 40% of their surface area since the 1970s. This retreat has been decreasing the meltwater contribution to the streams especially in the dry season, which increases the concentration of contaminants. Dissolved organic matter (DOM) is an indicator of water quality as it is influenced by natural as well as by anthropogenic activities. Quantifying and characterizing DOM is challenging because of its complexity. Recent technological development allows us to quantify and/or qualify fluorescent dissolved organic matter (FDOM), the fraction of DOM that has fluorescence properties, by employing portable fluorometers or benchtop measurements of fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). The objective of this research was to evaluate the evolution of FDOM measurements throughout two glacierized tropical alpine watersheds in Peru: the Shullcas and the Upper-Santa. Using a portable fluorometer equipped with a CDOM/FDOM sensor and a portable multimeter, 38 on-site measurements of FDOM, pH and turbidity were completed. Simultaneously 38 samples were taken to be analyzed with fluorescence spectroscopy followed by parallel factor analysis. FDOM results performances were compared with Dissolved Organic Carbon (DOC) measurements using high-temperature catalytic oxidation used as a reference method. Our results show that the portable fluorometer readings are limited to the portion of fluorescent dissolved organic matter that corresponds to humiclike substances due to the narrow bandwidth of the sensor used. The fluorescence spectroscopy coupled with PARAFAC was the only method able to both differentiate between potential sources of DOM and estimate relative concentrations of different organic substances types. The ability of the method to provide accurate estimations of the total FDOM load at the watershed scale remains, however, to be proven. Among others, this study shows cities have a strong impact on the water quality of studied catchments, mainly due to the absence of proper sewage systems.

Date	21 Oct 2019
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Michel Baraër (Supervisor)