In 2011, salinity was very low after Hurricane Irene (27 August 2011) and Tropical Storm Lee (7 September 2011). 
Because of very low salinity at some sampling sites but similar species composition at these sites relative to 
previous years, a salinity class correction was necessary for making the BIBI more comparable to previous years. 
Box plots of bottom salinity for all THE RANDOM sites, 1995-2010, were constructed. Five years for which the 
salinity was clearly too high or too low (1995, 1996, 1999, 2002, and 2004) were removed. Using GIS, the 
bottom salinity values of the remaining years were mapped and the 2011 sites were superimposed on the map. 
The salinity class of the 2011 sites was then re-assigned to reflect the predominant salinity class of the 
average year. Some of the 2011 sites did not need re-assignment because their salinity, although low (e.g., 6 ) 
was still within the salinity class of the average year (e.g., 5-12). Affected sites included many of the sites 
in the Upper Bay and Upper Maryland Western Tributaries strata; some of the sites in the Maryland Eastern 
Tributaries stratum and the Maryland Main Stem; and some of the sites in the Patuxent River. Sites sampled 
prior to the storms were not evaluated nor were their salinity class re-assigned.

In 2018, salinity was very low in summer because of high precipitation in the Chesapeake Bay region. The species
composition of the 2018 random sites was compared with the species composition of nearby sites sampled in 2017.
Species composition was similar in both years. However, because of habitat salinity class differences, the B-IBI was
quite different when calculated on the lower salinity classes of 2018. A salinity habitat class correction was necessary
for making the B-IBI more comparable to previous years, and was conducted as described above for 2011. Affected
sites included sites in each of the Maryland and Virginia sampling strata.