Photos of the Long Island Sound

Research & Monitoring

Status and Trends: LISS Environmental Indicators

Heavy Metals in Sediment

Wesleyan University and USGS Woods Hole Field Center

Heavy Metals in Sediment
Depth (cm) HG PPB CU PPM ZN PPM
0 1997
0.1 1996 313 94 153
0.8 1992
2.8 1988 300 92 150
5.3 1984 307 105 153
7.8 1975 339 121 151
10.3 1965 417 110 160
12.8 1955 472 117 160
15.3 1940 351 92 148
17.8 1910 432 36 126
20.3 1880 320
22.8 1850 180
25.3 1837 73 17 71
27.8 1820 58 14 64
30.3 1754 31 9 56
33.3 1695 13 69
35.3 1652
37.8 1594 24 10 66
40.3 1530 11 13 69
42.8 1462
45.5 1382 11 9 64
47.8 1311
50.3 1229 19 13 64
52.8 1141
55.3 1049 39 29 70
57.8 951

WHAT ARE HEAVY METALS IN THE SEDIMENT?

During the 19th and early and mid-20th centuries, industries discharged large amounts of heavy metals into the Sound and its tributaries as byproducts of manufacturing processes.  While large-scale industrial release of heavy metals has been reduced, other modern sources still exist.  Atmospheric deposition into the Sound directly and into the larger watershed can be a source of heavy metals, as well as particles discharged from wastewater treatment plants.

WHAT DOES THIS INDICATE?

Data from sediment cores is an indicator of trends in heavy metal contamination of Long Island Sound over the last thousand years.

STATUS

The chart above uses data collected from a core sample taken off Norwalk Harbor. It represents a historical record of heavy metal concentrations in a formerly industrial area of Long Island Sound.  Concentrations of mercury, copper and zinc began to increase during the Industrial Revolution.  Although concentrations have begun to decrease in the most recent decades, overall concentrations are still far above the pre-industrial baseline.

what are historical/legacy indicators?

Some of our indicators are categorized as either historical or legacy indicators. Heavy Metals in Sediment indicator is a historical indicator. This type of indicator provides perspective on past environmental conditions in Long Island. It is not measured periodically like our other indicators. Many indicators of this type use sediment core samples to measure how conditions in the Sound have changed over hundreds to thousands of years.

A legacy indicator is another type of indicator that is no longer actively tracked by the Long Island Sound Study. This is often due to lack of funding or termination of field sampling programs, but also sometimes because we have developed more effective indicators to replace them. We continue to present these legacy indicators because they can still provide baseline information on conditions in the Sound if the sampling programs resume.

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