Heavy metals partitioning in a stream receiving urban runoff

Water, sediment, detritus, caddisflies, snails, and crayfish were collected from Bull Run between July 31 and October 2, 1977 and analyzed for Fe, Mn, Ni, Pb, Cd, Zn, Cr, and Cu by atomic absorption spectrophotometry after appropriate digestion and extraction procedures. The samples were collected from six sampling stations along Bull Run which received sewage effluent, urban runoff, and stormwater drainage from the Manassas area. Sampling stations included an upstream control located well above the urban area, four stations located immediately above and below suspected stormwater inputs, and a station sufficiently removed from direct stormwater input.

Concentrations of Pb and Cu in water, sediment, detritus, and caddisflies increased with increasing distance downstream and were significantly (0.95 level) greater in these components immediately below the stormwater input than at the upstream control. Concentrations of Pb in sediment collected at a downstream station were significantly greater than those at the control station even though the control sediment characteristics favored metal retention more than the downstream sediment characteristics. Mean Cu concentrations in sediments at this station were greater (but not significantly) than at the upstream control station while all other metals were concentrated the least in sediment at the downstream station. Significant (0.95 and 0.99 level) linear correlation coefficients among a majority of stream components were found for Pb and Cu. It appears that urban runoff and stormwater drainage contributed sufficient quantities of Pb and Cu into Bull Run such that these metals accumulated greater in stream components below the Manassas urban area.