The water quality of the River Trent: from the lower non-tidal reaches to the freshwater tidal zone

The water quality of a major river system, the River Trent, which flows into the Humber estuary and drains large centres of population and industry in central England, is examined in terms of trace element, nutrient, major-ion, suspended sediment and carbon concentrations and set within the context of the transition from non-tidal to the tidal freshwater reaches. Detailed investigation of the water quality variability in the non-tidal river Trent has revealed mainly simple patterns in dissolved chemical concentrations, controlled largely by hydrology and the mixing of baseflow and stormflow endmember chemistries. However, silicon, carbon and nitrate show much more complex behaviour, as concentrations of these chemical determinands are regulated by in-stream biological processes. Major increases in concentrations of suspended solids and acid-available particulate AAP. trace elements are shown to be linked to tidal mobilization of sediment and the location of the ‘turbidity maximum’. Reductions in the concentrations of AAP trace elements per gram of suspended sediment suggest the mobilization of a different sediment type with a lower trace element content, which may result from: i. a secondary sediment source; or ii. mobilization of coarser-grained sediment under the stronger tidal hydrodynamic forces. Increased correlations for AAP-trace element interrelationships downstream suggest increasing simplicity of mixing relationships.