EXPANDED APPLICATION OF DEEP-WATER AND DEEP-CHANNEL 
DESIGNATED USES 
A total of 13 Chesapeake Bay segments characterized with deep-water and deep-channel 
designated uses were published in U.S. EPA 2004 (Table II-1). In a number of segments 
classified as having the open-water designated use only applied year-round, dissolved oxygen 
criteria assessments through time provided evidence of persistent criteria non-attainment. In a 
select set of these same Chesapeake Bay segments, results from numerous Chesapeake Bay 
water quality/sediment transport model scenarios, simulating dissolved oxygen concentrations 
across a wide range of nutrient load reductions, suggested lack of dissolved oxygen responses to 
nutrient load reductions due to physical constraints to re-oxygenation. Segments not previously 
classified with the deep-water and (or) deep-channel designated uses in mesohaline salinities but 
showing both stratification (presence of a pycnocline) and persistent dissolved oxygen criteria 
non-attainment were reviewed for possible expanded application of deep-water and deep-channel 
designated uses. 
Review of Designated Use Definitions 
The 2003 Ambient Water Quality Criteria for Dissolved Oxygen , Water Clarity and Chlorophyll 
a for Chesapeake Bay and Its Tidal Tributaries highlights two relevant guidelines-stratification 
(presence of pycnoclines) and evidence of a physical barrier restricting reoxygenation-for 
determining the need to apply the deep-water and (or) deep-channel designated uses (U.S. EPA 
2003). Specifically, the following are published definitions for determining when and where the 
open-water, deep-water and (or) deep-channel designated uses apply within Chesapeake Bay 
tidal waters: 
Open-Water Designated Use 
“If the presence of a pycnocline prevents oxygen replenishment, the open-water 
fish and shellfish designated use extends only as far as the upper boundary of the 
pycnocline. If a pycnocline exists but other physical circulation patterns (such as 
the inflow of oxygen-rich oceanic bottom waters) provide oxygen replenishment 
to the deep waters, the open-water fish and shellfish designated use extends to the 
bottom water-sediment interface.” U.S. EPA 2003, Appendix A, page A-6. 
(Also see U.S. EPA 2007, pages 37-38, Dissolved oxygen assessments in shallow 
versus open waters, for details regarding the open water designated use definition 
beyond vertical water column structure.) 
Deep-Water Designated Use 
“Tidally influenced waters located between the measured depths of the upper and 
lower boundaries of the pycnocline, where a measured pycnocline is present and 
presents a barrier to oxygen replenishment from June 1 to September 30...the 
deep-water designated use extends from the upper boundary of the pycnocline 
down to the sediment/water interface at the bottom, where a lower boundary of 
the pycnocline is not calculated.” U.S. EPA 2003, Appendix A, page A-6. 
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