Relating mineral magnetic measurements to sediment quality in a remediated, contaminated catchment: The significance of heavy metal delivery mode and water-sediment exchange dynamics in a small urban lake

Increased attention has focussed on using mineral magnetic measurements as a proxy for heavy metal related sediment quality since magnetic concentration often correlates with total heavy metal concentrations, thus providing rapid and non-destructive screening of contaminated samples. Mineral magnetic measurements are being used in the assessment of sediment quality in the Lower Swansea Valley (South Wales, UK) a uniquely contaminated environment with a legacy of 250 years of non-ferrous smelting. Fendrod Lake is an in-line flood detention lake (created in the mid-1980s) on the polluted Nant-y-Fendrod stream, which drains an area contaminated by atmospherically deposited heavy metals and metalrich smelter waste buried within the reclaimed and remediated valley floor. Heavy metals are accumulating in the lake sediment column. Positive correlations found between heavy metal (Zn and Pb) concentrations and magnetic susceptibility ($\chi$) in contaminated soils (mineral waste and aerial fallout) are not clearly observed in the lake sediment column (where the use of proxy measures of sediment quality is of greatest interest). Downcore profiles of $\chi$ and major and minor elements, and information on metal speciation, indicate two controlling factors: (1) sediment source and contaminant delivery mode and (2) water column sediment/contaminant interaction dynamics linked to lake productivity