Characterisation of the phytoplankton community of the Urdaibai estuary: influence of anthropogenic nutrient loadings and analysis of monitoring techniques

Abstract

This thesis aims to obtain a more complete and updated description of the phytoplankton community of the Urdaibai estuary, using different monitoring techniques, to determine the potential effect of the cessation of wastewater discharges from the Gernika wastewater treatment plant and evaluate the usefulness of the different monitoring techniques. The study integrates data from phytoplankton monitorings conducted during the wastewater discharges (2019-2020) and after sewerage works (2021 and 2022), where both environmental variables and the phytoplankton community were analysed, using three different techniques for the latter, i.e., microscopy, pigment analysis and eDNA metabarcoding. The results obtained in the present study might be useful as a baseline for future studies in the area, especially for phytoplankton research focused on ecological goals and the impact of management actions, but also for other interdisciplinary research that require updated data on the phytoplankton biomass and community composition of the Urdaibai estuary. Additionally, this thesis provides novel information on the species richness of the Urdaibai estuary, due to the application of metabarcoding as a monitoring tool for the first time in the area, and proposes and applies a new tool for phytoplankton monitoring (PIGMENTUM), based on pigment analyses, that might be applicable in future water quality management and/or in long-term ecological phytoplankton monitoring programs.