Suspended sediment and particulate phosphorus in surface waters of the upper Thames Basin, UK

Abstract

Summary Suspended sediment (SS) and particulate phosphorus (PP) concentrations in surface waters of the upper Thames Basin are reported for the main stem of the River Thames, several of its tributaries, the Cherwell, Dun, Lambourn, Pang and Thame, the Kennet and Avon Canal (that drains to the Dun and Kennet) and an artificial supply reservoir (Wilton Water). For the rivers which are mainly supplied from Chalk aquifer sources, SS and PP concentrations are poorly correlated with flow and there are issues of both biological and inorganic production of SS and PP during the spring and summer months. SS and PP are better correlated with flow when the antecedent conditions are taken into account. Thus, if flows had increased the previous day, then SS and PP concentrations are augmented. Wilton Water and the Kennet and Avon Canal have, on average, higher SS and PP concentrations than the nearby Chalk fed rivers and this probably reflects increased effects of biological activity and calcite (CaCO3) precipitation under more stagnant conditions. For the rivers draining less permeable (clay dominated) catchments, then there is clearer linkage between flow and SS and PP concentrations. This feature reflects the more responsive influence of runoff from the land surface without the confounding issues of seasonally-varying groundwater discharges, intersection of groundwater levels with the ground surface and overland flow that may well characterise the permeable Chalk catchments. SS and PP are linearly correlated across the catchments. For the Chalk catchments and the associated Wilton Water and Kennet and Avon Canal, the PP:SS ratios are similar, ranging typically between 2 and 4 μg/mg. For the clay dominated catchments, the ratios are typically higher at 3–7 μg/mg. The results are considered in the light of process understanding, farming, climate change/climate-variability and the Water Framework Directive.