Dissolved oxygen is critical to the survival of Chesapeake Bay's aquatic life. The amount of dissolved oxygen needed before aquatic organisms are stressed, or even die, varies from species to species.
Chesapeake Bay - Indicator Details:
Dissolved oxygen was measured at approximately 144 stations, 8 times between June and September 2010, using a water quality probe positioned just above the bottom. The proportion of time that dissolved oxygen was below the threshold at each station was calculated and then interpolated to provide estimates between the stations.
This map shows average bottom dissolved oxygen levels for summer (June to September) 2010. The most extensive areas of low average dissolved oxygen occurred in the deeper channels of the mainstem Bay and lower Potomac River. Unlike other years, however, there was not a sharp decline from good oxygen to no oxygen (which would be indicated by red). Rather, there is a wider than average band of low dissolved oxygen (1-2 mg l-1) that continues from the mainstem into the Potomac River. Small areas of low dissolved oxygen were also observed in the lower reaches of many smaller tributaries including the Chester, Patapsco, and Choptank Rivers.
Low dissolved oxygen in the Bay's mainstem is controlled primarily by the quantity of organic matter and nutrients flowing out of the Susquehanna River during the preceding spring. While this map provides a broad-level assessment of dissolved oxygen in the Bay, it does not accurately capture small and short-term low dissolved oxygen events that are often attributed to causing fish kills.
Dissolved oxygen was measured at approximately 144 stations, up to 6 times between June and September, using a water quality probe positioned just above the bottom. Average dissolved oxygen levels at each station were calculated and levels between stations estimated using spatial interpolation software.
Comparison of Bay Health Index scores for 2010 () compared to ()
|0 20 40 60 80 100|
|Upper Western Shore|
|Lower Eastern Shore (Tangier)|
|Upper Eastern Shore|
|Lower Western Shore (MD)|
|Patapsco and Back Rivers|
This figure ranks each region from best to worst dissolved oxygen scores for 2010. As the number of sampling times and locations that dissolved oxygen is below the threshold is relatively few, the scores for most regions are relatively high. However, as shown on the threshold map, many regions of the Bay have dissolved oxygen levels that are frequently below the threshold. The highest ranked regions in 2010 were the Upper Western Shore and James River regions. The lowest ranked regions in 2010 were the Patapsco and Back Rivers and Elizabeth River regions.
This graph is dynamic, you can: a) show and hide items by clicking them in the legend, b) select year range (click and drag), and c) export as an image.
|Designated Use||Season||Criteria Thresholds (mg L-1)‡|
‡ U.S. Environmental Protection Agency (2003)