A recent study shows that nitrogen isotopes in chlorophyll could be used to understand nutrient utilization in both modern and ancient lake environments. Chlorophyll is produced by all photosynthetic organisms on Earth, making is a useful target in studies of phytoplankton. Phytoplankton refers to autotrophic, aquatic algae, which are primary producers and the base of the food chain in Earth’s ocean, sea, and freshwater ecosystems. Phytoplankton communities are composed of organisms that are primarily single-celled; and includes both eukaryotes and cyanobacteria.

In laboratory studies, a team of researchers found that differences in the nitrogen (N) isotope ratio of chlorophyll and the N isotope ratio for biomass can be tied to the taxonomy of phytoplankton members. Recently, the team performed studies during the annual cyanobacterial bloom in Lake Erie, USA, to see if similar results could be achieved in the natural environment. The results from Lake Erie were consistent with laboratory studies, and show that N isotope ratios could be a useful means of determining the contributions of cyanobacteria and eukaryotic algae to primary production in lake environments. This method could be used to examine both modern systems and ancient environments that have left their mark in Earth’s rock record.

The study, “Chlorophyll nitrogen isotope values track shifts between cyanobacteria and eukaryotic algae in a natural phytoplankton community in Lake Erie,” was published in the journal Organic Geochemistry. The work was supported by NASA Astrobiology through the Exobiology Program.