Using δ 15N in Fish Larvae as an Indicator of Watershed Sources of Anthropogenic Nitrogen: Response at Multiple Spatial Scales

Joel C. Hoffman, John R. Kelly, Greg S. Peterson, Anne M. Cotter, Matthew A. Starry, Michael E. Sierszen

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


There is growing interest in applying δ15 N in biota as an indicator of anthropogenic nutrient inputs to coastal environments because changes in δ15 N correlate to inputs of land-based nutrients. In complex coastal receiving waters, however, land-use effects on biota δ15 N may be masked by local hydrologic processes, especially exchange with coastal waters of different geochemical character. We examined δ15 N differences among larval fish, a novel biotic indicator, in coastal receiving waters at both among and within watershed scales. Our goal was to characterize how hydrologic processes within coastal river mouths and embayments mediate the effect of land-based N sources on larval fish δ15 N. We sampled three Lake Superior river-embayment systems from watersheds that span a large population density gradient. Over all stations, mean fish δ15 N ranged from 2.7 ‰ to 10.8 ‰. Within each system, we found a different pattern in δ15 N across the river–lake transition zone. Correlations between fish δ15 N and water quality, particularly NH4 + and total nitrogen, were highly significant and corresponded to known differences in sewage waste water inputs. A multivariate model that included both watershed-based population density and NH4 + was found to provide the best fit to the δ15N data among a series of multi- and univariate candidate models. These results demonstrate that: (1) fish larvae δ15 N responded at within watershed scales, and (2) within coastal receiving waters, fish larvae δ15 N was related to waste water inputs at the watershed scale; however, expression at specific locations within a coastal system was strongly influenced by local hydrologic processes.

Original languageEnglish (US)
Pages (from-to)1453-1467
Number of pages15
JournalEstuaries and Coasts
Issue number6
StatePublished - Nov 1 2012


  • Eutrophication
  • Great Lakes
  • Monitoring
  • Nitrogen stable isotopes
  • Sewage waste water


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