Citation:

Pruell, R., B. Taplin, A. Oczkowski, J. Grear, W. Mendoza, A. Pimenta, Alana Hanson, AND K. Miller. Nitrogen isotope fractionation in a continuous culture system containing phytoplankton and blue mussels. MARINE POLLUTION BULLETIN. Elsevier Science Ltd, New York, NY, 150:110745, (2020). https://doi.org/10.1016/j.marpolbul.2019.110745

Impact/Purpose:

Nutrient contamination is a widespread problem in aquatic systems and the element of nitrogen is generally found in two form (called isotopes). The nitrogen isotopes are often used to identify the sources of nitrogen inputs to these systems. This manuscript describes the results of an experiment designed to examine how nitrogen isotope ratios can be influenced by biological processes (such as photosynthesis and predation) in the environment. These processes must be considered when interpreting the results of isotopic measurements as indicators of man-made nitrogen inputs. This information is important to the Agency because it advances our understanding of methodology that is often used to monitor nutrient inputs to aquatic systems.

Description:

An experiment was conducted to examine the fractionation of nitrogen stable isotopes in a continuous culture system containing field collected estuarine phytoplankton and blue mussels, Mytilus edulis. Nitrate and phosphate were added to culture vessels at concentrations above ambient levels and nitrogen isotope ratios (δ15N) were measured in particulate matter (PM) and blue mussels over the course of the 15-day experiment. The added nutrients resulted in large productivity and chlorophyll increases in the system. Study results indicate that rapid and significant nitrogen isotope fractionation can occur during incorporation by phytoplankton grown under conditions of excess dissolved inorganic nitrogen, as shown by δ15N values depleted by as much as 9‰ in PM from the higher nutrient treatments. These lower δ15N values were also reflected in mussels exposed to culture vessels effluents. Therefore, nitrogen concentration needs to be considered when using δ15N values in biota as indicators of anthropogenic nitrogen inputs.

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