MERCURY LOADING ALONG THE CONNECTICUT RIVER: SEDIMENT RECORDS FROM BARTON COVE, MA

Barton’s Cove lies 110 miles north of the mouth of the Connecticut River. This low energy water body, cut off from the main channel, houses a number of plunge pools making it an ideal sink for the settlement of heavy metals, organic matter and fine-grained sediments. Using a piston coring rig, a 10 meter deep core was recovered from a plunge pool near the eastern edge of the cove. The top 9 meters consist of dark, organic rich, fine grained mud with the bottom meter being fine to medium grained sand. Mercury content was determined at 1cm intervals for the top 60 cm, 5 cm intervals for the next 40 cm, and 10 cm intervals for the remainder. Mercury concentrations rise from 166 ppb at the sediment water interface to a high of 1006 ppb approximately 23 cm down the core. At one meter mercury levels are down to 90 ppb and by two meters concentrations remain below what is considered pre-anthropogenic levels at less than 60 ppb. The shape of the mercury spike, along with initial concentrations of 150-200 ppb, is similar to six previously studied off-river embayments along the Connecticut. Lead 210 results for these other sites date the peak mercury concentration occurring at approximately 1960 for each. If this holds true for the spike at Barton’s Cove the resultant sedimentation rate would be ~ 0.5 cm yr^-1. This would continue the trend found amongst the now 7 sites under study of increasing sedimentation rates as you head towards the mouth of the river. These rates increase from the ~0.5 at Barton’s Cove to near 4.5 cm/yr at Hamburg Cove, close to the Long Island Sound. Total Organic Content (TOC), obtained through loss on ignition, increases from 20% for depths 0-50 cm to 50-60% for meters 2 through 8 after which levels return to 15-20% as the sandy intervals are reached. When normalizing mercury concentrations with TOC, a profile similar to non-normalized mercury content emerges. This very similar mercury record is also apparent 30 miles south at Oxbow Lake, another off-river embayment. Ongoing research will complement existing data on mercury loading along the Connecticut River, and illuminate how factors, such as grain size, control the housing and sequestering of mercury in riverine environments.