Data gathered during the summer months between 2011 and 2013 indicate that 34 percent of the combined volume of the Chesapeake Bay’s open water, deep water and deep channel habitats met dissolved oxygen standards during this time.
What is dissolved oxygen? Laura Fabian from the Maryland Department of Natural Resources (DNR) explains why oxygen is so important to underwater life and how it is used to measure water quality in the Chesapeake Bay.
Like animals on land, living creatures in the Chesapeake Bay need oxygen to survive. In the water, oxygen is present in dissolved form. Without adequate concentrations of dissolved oxygen, the Bay’s ability to support aquatic life is compromised.
Dissolved oxygen concentrations are an important indicator of nutrient pollution. This is because low dissolved oxygen levels are often the result of nutrient-fueled algae blooms. When algae blooms die and undergo bacterial decomposition, these bacteria use up oxygen in the water, leaving little for fish and shellfish and creating what are known as “dead zones.” Increased nutrient pollution leads to larger algae blooms, which in turn create more dead zones.
Over time, large-scale reductions in the amount of nutrients flowing into the Bay will help improve low-oxygen conditions.
In 2014, the Chesapeake Bay Program adopted a goal to reduce pollution and achieve the water quality necessary to protect human health and support the region’s underwater resources. Our partners are working to bring 100 percent of the Bay and its tidal tributaries up to dissolved oxygen standards.
Long-term trend (1985-2013)
Statistically rigorous long-term trend analyses of this data set have not been recently conducted. During the summer months between 1985 and 2013, an average of 41 percent of the Chesapeake Bay’s open water, deep water and deep channel habitats met dissolved oxygen standards. Goal achievement ranged from 27 percent to 68 percent during this time.
Short-term trend (2004-2013)
Statistically rigorous short-term trend analyses of this data set have not been recently conducted. During the summer months between 2004 and 2013, an average of 37 percent of the Bay’s open water, deep water and deep channel habitats met dissolved oxygen standards. Goal achievement ranged from 32 percent to 42 percent during this time.
Change from previous reporting period (2010-2012 to 2011-2013)
Results of the 2011-2013 assessment period indicate that 34 percent of the combined volume of the Bay’s open water, deep water and deep channel habitats met dissolved oxygen standards during this time. These results are not significantly different from those of the previous assessment period (2010-2012), in which 35 percent of the combined volume of the Bay’s open water, deep water and deep channel habitats met dissolved oxygen standards.
Water quality standards for dissolved oxygen
Because the amount of dissolved oxygen required to thrive varies by aquatic species, season and location within the Chesapeake Bay, state standards for dissolved oxygen vary with water depth, season and duration of exposure.
To meet state regulations, data gathered within each tidal river and Bay segment must meet required dissolved oxygen concentrations based on a combination of interpolation and cumulative frequency distribution (CFD) analyses. These analyses allow for some temporal and spatial exceedences of dissolved oxygen criteria. However, if the designated use of a Bay segment has concentrations that exceed the permitted temporal or spatial allowances, the entire volume of water for that designated use in the given segment is considered out of attainment.
To adjust for annual weather-driven fluctuations, data is reported in three-year assessment periods.
Chesapeake Bay Program