Temporal Analysis of Ammoniacal Nitrogen and Chloride Concentrations on River Tees at Bran Sands (2012–2021)

Bran Sands, situated within the Tees Estuary, has been significantly impacted by decades of industrial activity, including steel production, shipbuilding, and chemical manufacturing. Which have contributed to substantial changes in water quality and sediment composition due to the continuous discharge of millions of litres of industrial wastewater into the estuarine ecosystem. This study assesses long-term trends in key water quality parameters, such as ammoniacal nitrogen, pH, chemical oxygen demand (COD), and biochemical oxygen demand (BOD), in the Bran Sands, between 2012 and 2021. The analysis utilises descriptive statistics to summarise and interpret the pollution loads from the Bran Sands sewage treatment works, and time-series graphs to evaluate the effectiveness of wastewater treatment improvements over time. Results indicate significant reductions in pollution levels, with ammoniacal nitrogen, BOD, COD, and pH concentrations frequently exceeding compliance limits at the inlets, particularly at the Wilton Complex Main Effluent and Bran Sands inlets, but remaining within permissible thresholds at the outlets. Temperature and salinity at river Tees also maintained within acceptable limits. However, Chlorine was measured above compliance limits at both inlets and outlets monitored sites, with an inclining trend throughout the study period. Chlorine reacts with organic and inorganic compounds, forming persistent chlorinated by-products that affect freshwater and marine organisms. Chronic exposure to residual chlorine has been linked to growth inhibition, reproductive impairment, and mortality in fish and invertebrates. These findings warrant continuous monitoring and adaptive management to sustain water quality improvements and protect aquatic ecosystems.