An investigation into nutrient fluxes in a lowland, pumped-storage reservoir during ferric sulphate dosing

This study (between August 1992-May 1994) of the impact of ferric sulphate dosing, examined phosphorous and nitrogen inputs and outputs, nutrient fluxes within the water column, and phosphorus sediment-water interactions in Rutland Water. Rutland Water, a lowland, eutrophic pumped-storage reservoir in the UK experienced severe cyanobacterial blooms and scums during the late summer of 1989 which received national media attention. In response to this, from June 1990, ferric sulphate was added to the reservoir with the pumped input from the rivers Nene and Welland to attempt to precipitate phosphorus to the sediments to limit phytoplankton abundance.;The seasonality of phosphorus and nitrogen loadings influenced in-lake nutrient concentrations and subsequent phytoplankton biomass. The pumped input was the dominant source; the natural inflows were insignificant. Ferric sulphate did not influence nutrient temporal and spatial patterns, although the decline in in-lake phosphorus concentrations between 1990 and 1991 was related primarily to the decline in the annual phosphorus loading during drought conditions and also to the large quantities dosed.;Wind-generated mixing, together with the effect of the jetted input were sufficient to prevent the development of full stratification, although at the deepest site slight dissolved oxygen stratification developed during summer. Nutrient depth variation was attributed to sedimentation and subsequent decomposition of organic matter in the bottom waters. Ferric sulphate increased phosphorus sedimentation, which was the dominant downward flux.;Ferric sulphate floc increased the sediment redox potential, lowered pH and increased the phosphorus-binding capacity of the sediments, although the high ratio of total iron:total phosphorus already present was inferred as governing the strong phosphorus-binding capacity. Although no sediment phosphorus release was detected under the redox-driven mechanism, any potentially released phosphorus influenced by microbiological actions was reprecipitated to the sediments due to the maintenance of relatively aerobic conditions in the water column.