Assessing the susceptibility of two UK estuaries to nutrient enrichment

• The approach to the study is based on measured data and the application of a model.
• Severn was less susceptible to nutrient enrichment compared to the Solva.
• Turbidity, tidal currents and mixing exert a control on the response in the Severn.
• Response in Solva is mediated by water exchange rate and consistent rapid flushing.
• Sensitivity test identified key system-specific parameters for the model predictions.

The susceptibility of two UK estuaries, the Severn and Solva Estuaries to the risks and impacts of nutrient enrichment was investigated in this study by examining nutrients, dissolved oxygen (DO) and turbidity concentrations in the estuaries and applying a risk assessment model based on the UK׳s Comprehensive Studies Task Team (CSTT) modelling approach. Both estuaries were found to be nutrient enriched. However, there was no evidence of oxygen depletion in the Severn and algal blooms were not observed due to high turbidity, strong tidal currents and tidally induced vertical mixing conditions in the estuary. Although algal blooms were observed in the Solva Estuary, the estuary was well-oxygenated due to the relatively high water exchange rate and consistent rapid flushing in the estuary. The conditions in the Solva Estuary were predicted to be favourable for phytoplankton productivity and the wider potential implications for future water quality protection strategies in the Solva were discussed.