The hyperturbid mesotidal Guadalquivir estuary during an extreme turbidity event: Identifying potential management strategies

Abstract

The Guadalquivir estuary (SW Iberian Peninsula) is a mesotidal system within a Mediterranean climatic region. It experiences severe and persistent hyperturbid conditions during the wet and cold season, significantly impacting both the ecosystem and various economic activities. During an investigation of an extreme turbidity event, suspended particulate matter (SPM) concentrations exceeding 30 g/L were found near the salt intrusion limit, with a 45 km stretch showing a depth-averaged SPM concentration greater than 10 g/L. Throughout this event, the estuary can accumulate more than 900,000 tonnes of SPM, leading to severe surface light blockage, with the euphotic layer remaining shallower than 10 cm in most areas. Additionally, hypoxia develops in the zone of maximum turbidity, near the bottom. These extreme turbidity events are linked to short-duration freshets that discharge a large amount of sediment from a highly erodible catchment area, followed by a significant reduction in river flow, primarily due to strong water regulation. However, hyperturbid conditions never extend into the summer in this estuary, indicating a non-negligible capacity to clear the SPM. Considering these findings, several recommendations are proposed. First, establishing a monitoring programme for extreme turbidity processes can aid in implementing necessary management actions. Second, it is crucial to develop an optimal protocol for water discharges from the network of dams to maximise sediment export to the sea, minimise plankton washout, and prevent excessive freshwater loss.