VERTICAL DISTRIBUTION OF HEAVY METALS IN SPRINGWOOD LAKE SEDIMENTS, RICHMOND, INDIANA

Lake sediments are increasingly recognized as an integrated “memory” of pollutant introductions to watersheds. Springwood Lake (SWL) is a small (~ 20 acre), shallow reservoir owned by the City of Richmond, Indiana. SWL is the site of a municipal park, and is frequented by anglers. The SWL catchment is located in an industrialized area that has been subjected to numerous uncontrolled releases of hazardous materials, including heavy metals, since the late 1940s. In order to provide a basis for assessing potential public health risks, we studied the archive of anthropogenic metal inputs preserved in SWL sediments.

In January of 2003, we collected 8 bottom cores (average recovery of 0.93 m) through the frozen lake surface with a Wildco gravity corer and a tractor jack. All of the cores revealed a pronounced textural (gyttja to silt and sand) and color (reduced to oxidized) transition from shallow to deeper taken to indicate the 1930 flooding surface. Two cores, selected for detailed chemical analyses, were sub-sampled at 2 cm intervals. The sub-samples were frozen, lyophilized and microwave digested in concentrated nitric acid (EPA SW-846 Method 3051). Sediment digests were then quantitatively analyzed in triplicate for Cd, Cr, Cu, Ni, Pb, and Zn using a Perkin Elmer Optima 4100 DV ICP-AES. Samples were validated by comparison against a NIST standard reference material (Montana Soil 2711).

Heavy metal concentration profiles for each core reveal background concentrations at depth that are overprinted by significant anthropogenic increases in younger strata. Observed concentration ranges for the heavy metals (all in mg/kg or ppm) are: Cd (1.12 to 169.9); Cr (7.77 to 297.41); Cu (6.86 to 503.98); Ni (1.63 to 49.60); Pb (4.98 to 1732.1) and Zn (9.75 to 2845.5).

Metal concentration trends are consistent with point source loading via the lake's inlet channel. Estimated core chronology (based on avg. sedimentation rates from the 1930 flooding surface) reveals a peak loading interval of ~1964-1971. Despite a significant decline in anthropogenic metals loading since ~1971, metals concentrations in SWL remain an order of magnitude above baseline concentrations. Our investigation suggests a more comprehensive assessment of metals concentrations to predict potential metals remobilization and related risks to biota and to human health.