Sediment Organic Carbon Concentration

What is organic carbon?

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.

what does it indicate?

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.

Data Note

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

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