Photos of the Long Island Sound

Status and Trends: LISS Environmental Indicators

Type of Indicators: Health/Condition Response/Performance Socio-Economic Historical/Background

Sediment Delta 15N

Sediment Delta 15N

Source: Johan Varekamp, Wesleyan University.

What is Sediment delta 15?

Delta 15N (δ15N) is a nitrogen isotope whose abundance in benthic sediment is used to determine the contribution of wastewater and sewage to total nitrogen.  Anthropogenic nitrogen loadings from wastewater have higher δ15N levels relative to natural sources.  Scientists can use sediment cores to look back in time at changes in δ15N levels and make inferences about historical conditions in Long Island Sound.

What does this indicate?

δ15N levels indicate the concentration of nitrogen loading in a sediment sample. Higher  δ15N levels indicate a greater concentration of nitrogen loading than what would be found in natural sources, thus indicating the presence of high amounts of sewage-related nitrogen from wastewater treatment plant discharges.


The chart above depicts δ15N values over the last 1000 years in Long Island Sound. The increase in sediment δ15N values around 1800 reflects an increase in sewage and wastewater treatment plant discharges into Long Island Sound.

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