Applying turbidity as a witness of the vulnerability of a ria to meteorological changes and anthropogenic interventions

In this paper, turbidity in the interior of a ria with reduced exchange with the ocean is studied to know the relative weight of each of its components and to infer the vulnerability of the ecosystem to anthropogenic and meteorological changes. Two components or groups of variables related to turbidity have been identified: a biological one, related to phytoplankton through nutrients and solar irradiation, and a hydrodynamic one related to wind, precipitation and tide. The results show that both components are related, given the influence of wind on nutrient dynamics. It has been impossible to apply the obtained model to infer turbidity in the recent past because the anthropogenic and meteorological changes recorded suggest very different conditions from the present ones. These changes include modifications of anthropogenic origin, such as the significant reduction in wastewater inputs and the narrowing of the outer part of the ria due to the construction of a harbour. The changes are also related to meteorological conditions, such as the lack of north and north-westerly winds. Thus, the paper demonstrates the need to understand and consider medium-term local changes when studying the local influence of broader-scale changes. It also highlights the usefulness of turbidity as a measure of the system's vulnerability, given its relationship with a wide range of environmental variables.