In the presence of a pycnocline, the deep-water designated use will also apply to the Magothy 
River and South River mesohaline segments in the June 1 through September 30 time period. 
The application of the deep-water designated use to these two segments is fully consistent with 
previously published procedures which called for: 
1. the physical exchange of higher oxygenated waters from the upper water-column is much 
reduced by density stratification, and 
2. pycnocline waters are not reoxygenated by riverine or oceanic bottom waters 
in order to apply the deep-water designated use (U.S. EPA 2003). 
Previously, such segments including the deep-water designated use were only thought to be 
"located principally in the river channel at the lower reaches of the major rivers and along the 
spine of the middle mainstem of the Bay” (U.S. EPA 2003). These analyses conducted in 
support of the development of this addendum have demonstrated the deep-water designated use 
can occur in smaller tidal tributaries segments receiving limited freshwater flow from their 
surrounding watershed. 
Given the South River segment has a lower pycnocline and 19 of 43 depth profiles (44%) over 
the 1991-2000 data record, consideration was given to whether a deep-channel designated use 
should apply to this segment as well as a deep-water designated use. The published procedures 
for delineating a deep-channel designated use included: 
1. The very deep water-column and adjacent bottom surficial sediment habitats located 
principally in the river channel at the lower reaches of the major river and along the spine 
of the middle mainstem of the bay; 
2. At depths below which seasonal anoxic to severe hypoxic conditions routinely set in and 
persist for extended periods of time under current conditions; and 
3. At depths greater than the lower boundary of the pycnocline (U.S. EPA 2003). 
The South River segment does not contain a "very deep water-column” given a total maximum 
depth of 5 meters and the segment does not have conditions where "seasonal anoxic to severe 
hypoxic conditions routinely set in and persist for extended periods of time under current 
conditions”. Therefore, even in the presence of a lower pycnocline, a deep-channel designated 
use will not be applied to this segment. 
The initial review of stratification and dissolved oxygen data from the eight remaining segments 
identified in Table 11-2 did not provide immediate evidence of where stratification appeared to be 
limiting oxygen replenishment. A more in-depth review of water column stratification conditions 
and identification of any needs for further adjustments to the applicable designated uses for the 
remaining segments is planned for completion prior to the 2012 303(d) listing cycle. 
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