Browse History: Benthic Index of Biotic Integrity (2006) | Indicators (2006) | Methods (2006) | Dissolved Oxygen (2006)
Indicator Icon Dissolved Oxygen

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:





  Indicator Selection Diagram


Threshold Map

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Station Data
This map shows how often dissolved oxygen levels were above or below threshold levels between June and September 2006. Good water quality is characterized by having dissolved oxygen levels that are frequently above the threshold levels (indicated by shades of green), while poor water quality tends to have dissolved oxygen that is frequently below the threshold levels (indicated by shades of yellow and orange). In 2006, many regions of the Bay had dissolved oxygen levels that were frequently above the threshold level. Areas of the Bay that frequently had poor dissolved oxygen levels in relation to the thresholds include the mid reaches of the Bay's mainstem, the Patapsco River, the Lower Western Shore (MD) region and the Elizabeth River. Overall, dissolved oxygen threshold levels in 2006 were good compared to the high flow year of 2003 and the low flow year of 2002, perhaps because of the dry spring conditions.

Creating this map
Dissolved oxygen was measured at approximately 144 stations, 8 times between June and September 2006, 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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Station Data

This map shows average bottom dissolved oxygen levels for summer of 2006. The most extensive areas of low average dissolved oxygen generally 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 water and nutrients flowing out of the Susquehanna River during the preceding spring The volume of anoxic (oxygen depleted water) in 2006 was below the long-term average due to the dry spring conditions. (LINK to Summer Lookback).

Understanding this map
Dissolved oxygen was measured at approximately 144 stations, 8 times between June and September 2006, 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 Legend
 Score (%)
 0               20               40               60               80              100
  
Upper Western Shore  
James River  
Lower Bay  
Lower Eastern Shore (Tangier)  
Rappahannock River  
Choptank River  
Overall Bay  
Upper Bay  
Potomac River  
Upper Eastern Shore  
York River  
Mid Bay  
Patuxent River  
Elizabeth River  
Patapsco and Back Rivers  
Lower Western Shore (MD)  

This figure ranks each region from best to worst for the indicator dissolved oxygen. 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 do have dissolved oxygen levels below the threshold. The highest ranked regions in 2006 were the Upper Western Shore and James River Regions. The lowest ranked regions in 2006 were the Lower Western Shore (MD) and the Patapsco and Back Rivers.


Excel Spreadsheet

Threshold 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)