Photos of the Long Island Sound

Research & Monitoring


The Long Island Sound Study has launched a new version of the Environmental Indicators section. The data below may be out of date. Please visit and bookmark the new section here to see the most recent data.

Status and Trends: LISS Environmental Indicators

Sediment Organic Carbon Concentration

Johan Varekamp, Wesleyan University.


Organic carbon refers to the portion of total carbon that comes from living (and formerly living) organisms. Organic carbon in Long Island Sound can come from land sources (including leaves, grasses, soils and even wastewater treatment plants) that run off into local waters, as well as carbon produced in the marine environment by plants such as phytoplankton and seaweeds.


Measurements of organic carbon concentration in sediment cores can be used to reconstruct a historical record of organic carbon in Long Island Sound. These measurements can identify carbon from runoff as well as carbon that came from algal growth. High sediment organic carbon concentrations are indicative of eutrophication in the Sound.


The first peak in organic carbon in the chart above was in the early 18th century, and coincides with an increase in carbon supply from the land as forests were cleared for farming. The second increase, that began 1800 and continues to present, was driven instead by increased algal production within Long Island Sound. These data suggest that the eutrophication of the Sound dates back to the 19th century.

what are historical/legacy indicators?

Some of our indicators are categorized as either historical or legacy indicators. The Organic Carbon 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. A legacy indicator might also be replaced by a more effective indicator or may not need to be updated because the goal has been met. We continue to present these legacy indicators because they can still provide baseline information on conditions in the Sound if the sampling programs resume.


Samples collected off Norwalk coast as part of a LISS-funded study by Johan Varekamp, Wesleyan University.

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