A baywide assessment could not be completed in 2012 due to an incomplete data set. In 2011, 56 percent of the Bay’s surface waters met the phytoplankton goal.
Water clarity is currently too poor and pollution levels too high to consistently support healthy phytoplankton communities. Algae blooms are still frequent, harmful species of algae are often abundant, and algae cells show signs of stress.
Phytoplankton (Index of Biological Integrity) (2012) Annual Average Score by Sampling Station Apr 22 2013 / Download
Phytoplankton (Index of Biological Integrity) (2012) Percent of Goal Achieved Apr 22 2013 / Download
Phytoplankton (algae) are the critical base of most Chesapeake food webs. Moderate, stable phytoplankton levels are needed for healthy bottom-dwelling species, which support larger species such as fish and birds.
However, too much or the wrong type of algae can be detrimental to the overall health of the Bay by decreasing oxygen, blocking sunlight and harming aquatic life. In some cases, algae blooms can also harm human health.
Phytoplankton serve as an excellent indicator of the health of the Bay’s surface waters because they are especially sensitive to changes in pollution, water clarity, temperature and salinity.
The health of phytoplankton is measured on a scale of 1 (very degraded) to 5 (least impaired). The goal is for all scores to be at least a 3.
Note: Since a baywide assessment could not be completed in 2012 (due to lack of Maryland data in 2012), trends are reported through 2011.
Long-term Trend (1986-2011)
There is no discernable baywide trend because of too many extreme wet and extreme dry years. Goal achievement has averaged 50 percent and has ranged from 36 percent to 74 percent. Beginning in 2010, the number of sampling events was reduced to once monthly and this may have impacts on comparisons to data from 1986 through 2009.
Short-term Trend (10-year trend)
There is no discernable baywide trend. Goal achievement averaged 52 percent during the most recent 10-year period (2002-2011). Beginning in 2010, the number of sampling events was reduced to once monthly and this may have impacts on comparisons to data from 2002 through 2009.
Change from Previous Year (2010-2011)
The score Bay-wide increased slightly from 54.7 percent to 55.9 percent of goal achieved.
Discussion of 2012 Data in Virginia’s Tidal Waters
Conditions improved in the James and Elizabeth rivers. Conditions declined slightly in all other Virginia tributaries. Conditions in the mainstem lower-bay area declined to levels approaching the long term average value for the region after reaching an all time high in 2011.
Overall Status of Phytoplankton
Water column clarity is currently too poor and nutrient levels too high to support healthy phytoplankton communities in the Bay. The overall status of the phytoplankton community is:
An earlier downward trend in phytoplankton status in low-salinity waters has leveled off.
Phytoplankton Indicator
A measurement called the Index of Biotic Integrity is used to rate the health of phytoplankton on a scale of 1 to 5. Scores are generated using monthly samples taken from 31 stations during the spring and summer. The goal is for all scores to be at least a 3.
This indicator is area-weighted and thus heavily influenced by conditions in the larger mesohaline (moderately salty) and polyhaline (salty) segments, which tend to be better than those in low-salinity segments of the tidal tributaries and upper Bay.
Jackie Johnson
Interstate Commission on the Potomac River Basin (ICPRB)
(410) 267-5729
