Author(s): Eva Fenrich; Reza Ahmadian; Bettina Bocklemann-Evans; Walter Marx; Silke Wieprecht; Roger Falconer
Keywords: Severn Estuary; Water quality; Food web; Habitat; Input-output model; DIVAST
Abstract: Estuaries are very unique habitats. Physical parameters as well as chemical parameters like nutrients or salinity are interlinked with the ecosystem’s food web. The Severn Estuary and some of its tributaries, e. g. the rivers Severn, Wye and Usk, have been recognised as internationally and nationally important and are designated under the Habitats and Birds Directives and Ramsar Convention, as well as being “Sites of Special Scientific Interest” (SSSIs). A combination of immense tidal range and the classic funnel shape make the Severn Estuary unique in the UK and rare worldwide. As there is an ever present need in the UK to find renewable sources of energy and reduce CO2 emissions, tapping into the vast tidal resource as a means to produce carbon neutral energy has come yet again into focus. These tidal energy schemes could at the same time help mitigate against negative impacts from climate change, e. g. act as flood protection schemes with regards to both sea level rise, as well as the increasing risk of surges from the Atlantic. To gain a better understanding of the linkages between the different trophic stages within the estuarine habitats and the physio-chemical environment, an input-output model of the ecosystem, including: hydraulics, bed and suspended sediment transport, water quality, fish species and energy output parameters, was set up which could then be used to analyse the effects of different proposed tidal energy schemes. The ecosystem networks were integrated with input-output models for different tidal energy schemes. The two-dimensional hydrodynamic and water quality model DIVAST (Depth Integrated Velocities And Solute Transport) was used to investigate the hydro-environmental impacts of a number of marine renewable energy projects in the Severn Estuary. Water quality parameters investigated in this study included: available nutrients and other physio-chemical parameters. An extensive set of field and laboratory velocity, nutrient and bed and suspended sediment data have been used to calibrate the hydrodynamic / water quality model. With this approach it was possible to study connections between more localized and global effects of tidal energy devices. Such an approach can help to reduce any negative effects, optimize mitigation measures, and improve operation schemes for different tidal power devices, as well as help to communicate the variety of linkages to different stakeholders.