Spatial–temporal dynamics of wastewater effluent in a tidal river system: the lower River Tyne, UK

Wastewater effluent can introduce nutrients that drive eutrophication and oxygen depletion in river systems, impacting their chemical and ecological status under the Water Framework Directive. Microbial degradation of effluent can also generate indirect greenhouse gases, which are increasingly relevant for meeting Net Zero goals. Understanding effluent behaviour in tidal rivers, where transport and mixing are complex, is therefore critical for effective catchment management. This study investigates the spatial and temporal dynamics of effluent discharge in the lower River Tyne, which receives continuous treated wastewater from Howdon Sewage Treatment Works, by applying a multi-phased approach that combines geospatial analysis, hydrodynamic modelling, and field measurements. Historical datasets have been analysed to characterise patterns and variability in effluent discharge, highlighting the need for targeted monitoring to capture biogeochemical hotspots. Two- and three-dimensional hydrodynamic simulations will be used to explore effluent transport and mixing under varying tidal and flow conditions and will be validated against in situ observations. Ongoing field campaigns monitor several water quality parameters, alongside Acoustic Doppler Current Profiler surveys to resolve flow structure and stratification. Model outputs will be integrated with observed data to identify zones of minimal and maximal effluent impact and to estimate indirect greenhouse gas emissions. Overall, this research will enhance our understanding of effluent dynamics in aquatic systems, providing insights for monitoring strategies and catchment management under current and future environmental conditions.