However, the interpretation of d15N data can often be challenging, as the isotope values
fractionate substantially due to preferential retention and uptake by biota.
There is a growing
body of evidence that carbon isotopes may be a useful alternative indicator for eutrophication,
as they may be sensitive to changes in primary production that result from anthropogenic
nutrient inputs. We provide three examples of systems where d13C values sensitively track
phytoplankton production. First, earlier (1980s) mesocosm work established positive
relationships between d13C and dissolved inorganic nitrogen and dissolved silica concentrations