HEAVY METALS ARE LOWER IN
The United States Geological Survey has monitored
trends in metals concentrations at four locations in Boston Harbor.
This study showed that lead decreased approximately 50% in harbor
sediments, as did most other heavy metals at the sites sampled.
This is related to a decrease in metals inputs from many sources,
including sewage discharges.
USGS research showed a downward trend in
lead concentrations in surface sediments at four Boston
Harbor sites since the late 1970s.
(Bothner et al. 1998)
Bacteria and other organisms metabolize organic matter,
depleting oxygen. If the sediments use up oxygen too quickly,
it can mean that they are polluted by excess organic matter. In
the early 1990s, Boston Harbor sediments showed some of the highest
rates of oxygen use ever measured in any sediments! In the decade
since MWRA stopped discharging sludge, rates of metabolism in
the harbors sediments have dropped to levels that are more
typical of a healthy ecosystem.
SEDIMENT OXYGEN DEMAND IN BOSTON HARBOR
This graph shows the change in sediment oxygen demand from
1992-2000 near the former Nut Island discharge site. High
rates were recorded in 1993 and 1995, as burrowing and feeding
activities by benthic animals ventilated the sediments. Metabolism
rates declined in later years to normal levels. (Tucker et