Combined biotic and abiotic effects on FDOM composition dynamics

XX Seminario Ibérico de Química Marina (SIQUIMAR 2020) - XX Iberian Seminar on Marine Chemistry, 1-3 July 2020, Barcelona.-- 1 page

Fluorescent Dissolved Organic Matter (FDOM) composition is known to be subjected to modification by multiple processes, both biotic and abiotic. This work examines the combined effect of sunlight exposure and phytoplankton nutritional state on the evolution of FDOM composition along a 23-day mesocosm experiment, carried out at the University of Bergen Mesocosm Centre (Norway) during late spring 2018. The experiment setup consisted on seven 11 m3 bags, three of which were covered with a transparent plastic lid that limited UV-radiation. All bags were enriched with nitrate and phosphate at different ratios and frequency throughout the experiment and the surrounding fjord water was used as a control. Multiple optical parameters were examined daily along with various biogeochemical variables (Chlorophyll-a, DOC and nutrient concentration and phytoplankton composition). Thanks to the experimental design, we were able to attribute changes in FDOM composition to both biotic and abiotic effects. Photobleaching played a major role in the exposed bags, reducing significantly the humic-like components fluorescence (peaks A, C & M), while the production of protein-like components (peaks T & B) was mainly controlled by the nutritional state of the phytoplankton community. Phytoplankton responded to sunlight and nutrient limitation stress by increasing the production of humic-like components as a photoprotection strategy. These findings underline the importance of considering not only environmental and biological factors but also their possible synergetic effects to better understand the forces driving FDOM composition dynamics

We would like to thank all researchers that participated in the experiment, as well as the personnel of UiB mesocosm facility. This work was funded by the EU network Aquacosm under the Aquacosm - VIMS-Ehux project. The presenting author is funded by a predoctoral FPU grant from the Spanish Ministry of Education

Peer reviewed