Phytoplankton Index of Biotic Integrity for Chesapeake Bay

Interstate Commission on the Potomac River Basin

Phytoplankton are microscopic algae that float freely in the water.  In an effort led by ICPRB staff, a phytoplankton index of biotic integrity (PIBI) was developed for the Bay in 2005/6 and re-validated with new data in 2013.

Community-level phytoplankton metrics (e.g., chlorophyll, diatom biomass, dinoflagellate biomass) are calculated from water quality and phytoplankton data, and scored to create the index. The index helps characterize balanced, “healthy”, desirable phytoplankton populations for different seasons and salinity zones. It is used by resource managers to track progress in Bay restoration.


The following publications describe the PIBI development and applications in more detail. They are available upon request.

  • Buchanan, C., R. V. Lacouture, H. G. Marshall, M. Olson, and J. Johnson.  2005.  Phytoplankton reference communities for Chesapeake Bay and its tidal tributaries.  Estuaries 28(1):138-159.
  • Lacouture, R. V., J. M. Johnson, C. Buchanan, and H. G. Marshall.  2006.  Phytoplankton index of biotic integrity for Chesapeake Bay and its tidal tributaries.  Estuaries 29(4):598-616.
  • Marshall, H. G., R. V. Lacouture, C. Buchanan, and J. M. Johnson.  2006.  Phytoplankton assemblages associated with water quality and salinity regions in Chesapeake Bay, USA.  Estuarine Coastal and Shelf Science 69:10-18.
  • Johnson, J. M., and C. Buchanan. 2013. Revisiting the Chesapeake Bay phytoplankton index of biotic integrity. Environmental Monitoring and Assessment. doi 10.1007/s10661-013-3465-z.

Phytoplankton Taxonomic Index

ICPRB used a similar approach to develop a Phytoplankton Taxonomic Index (PTI) based on seventy-seven taxa, or groups of closely related taxa, found in high salinity waters of Chesapeake Bay.  The PTI can augment the PIBI results in high salinity waters. More information about the project and the final report are available.