Paper No. 5
Presentation Time: 10:00 AM
METAL POLLUTION IN COVES ALONG THE CONNECTICUT RIVER
The Connecticut River stretches over 655 km from source to its mouth in Long Island Sound. Small coves with narrow inlets occur along the river, and these are especially efficient traps for fine clastic sediment in the tidally active river segment south of Hartford. Sediment from the Oxbow Lake near Northhampton (MA) shows low levels of pollutants (up to 500 ppb Hg), whereas the coves south of Hartford show much higher pollutant concentrations. Wethersfield Cove near Hartford was studied in detail, and shows maximum concentrations of 2800 ppb Hg, 350 ppm Cu, 600 ppm Zn, 330 ppm Pb, 360 ppm Cr, and 190 ppm V (DMA and WD-XRF). The sediments in the pond are also rich in organic carbon (3-4 % Corg), which, based on their C/N values, is predominantly of terrestrial origin. Southeast of Wethersfield, Keeney Pond has up to 700 ppb Hg, whereas coves further south have 1000 ppb Hg to a ‘high spike’ of 2600 ppb Hg in Hamburg Cove. There are several possible sources for Hg and the other metals in these river coves. A power plant operated from 1928-1961 on the South Meadows lands of Hartford that used mercury as its working fluid (mercury boiler). Historical records of this plant show evidence for substantial Hg losses (>30,000 pounds), especially during the 1930s; this is corroborated by preliminary dating of the Wethersfield Cove cores that indicates the highest Hg levels during the 1930s and a steeply decreasing trend since 1960. Wethersfield Cove has a connection to a Storm Water Overflow from the Hartford waste water treatment plant. Sewage treatment plant effluents are rich in these metals as well, and part or most of the pollutants may stem from this source. In the relatively small Wethersfield Cove (~0.3 km2 surface area), cove-wide excess metal inventories are 300 kg Hg, 27 tonnes Cu, 68 tonnes Zn, 34 tonnes Pb and 21 tonnes Cr. Excess metal concentrations were calculated relative to Th, a non-pollutant, and analytical data were corrected for the “natural pollutant burden” of each element. The excess Zn/Cu in Wethersfield Cove is 2.5, similar to excess Zn/Cu in lower Connecticut River Estuary embayments, but much higher than excess Zn/Cu in muds from Long Island Sound. Detailed dating, d15N and organic geochemical data of cove sediment will be presented for fingerprinting the metal sources of these coves along the Connecticut River.