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Dissolved OxygenDissolved 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.
Indicator Details:
Threshold Map
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Dissolved oxygen was measured at approximately 144 stations, 8 times between June and September 2007, 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.
Data Map
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This map shows average bottom dissolved oxygen levels for summer (June to September) 2007. The most extensive areas of low average dissolved oxygen occurred in the deeper channels of the mainstem Bay and lower Potomac River. However, small areas of low dissolved oxygen were also observed in the lower reaches of many smaller tributaries including the Patuxent, 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. The overall distribution of low dissolved oxygen levels in 2007 was very similar to that observed in 2006. 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, 8 times between June and September 2007, 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.
Ranking
| Score (%) | |
| 0 20 40 60 80 100 |
| Upper Western Shore | |
| Lower Bay | |
| James River | |
| Lower Eastern Shore (Tangier) | |
| Overall Bay | |
| Choptank River | |
| Upper Bay | |
| Upper Eastern Shore | |
| Rappahannock River | |
| Mid Bay | |
| Potomac River | |
| Elizabeth River | |
| Patuxent River | |
| Patapsco and Back Rivers | |
| York River | |
| Lower Western Shore (MD) |
This figure ranks each region from best to worst dissolved oxygen scores for 2007. 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 2007 were the Upper Western Shore and Lower Bay Regions. The lowest ranked regions in 2007 were the Lower Western Shore (MD) and York River regions.
Excel SpreadsheetTrends Graph
This graph is dynamic, you can check and uncheck regions (
checkboxes in legend), select year range (
click and drag), and export as an image (right click).
Editable Vector Version (SVG) Excel SpreadsheetThreshold Levels
| Designated Use | Season | Criteria Thresholds (mg L-1)‡ |
| Open Water | Jun-Sep | ≥5.0 |
| Deep Water | Jun-Sep | ≥3.0 |
| Deep Channel | Jun-Sep | ≥1.0 |
‡ U.S. Environmental Protection Agency (2003)
Additional Info
Relevant Web Sites
Chesapeake Bay Program - Bay Trends and Indicators
MD DNR - Eyes on the Bay
Virginia DEQ - Chesapeake Bay Monitoring Programs