Using Shallow-water Water Quality Data where Available. Because of 
these sources of variability, the use of midchannel data to evaluate the water-clarity 
criteria should be avoided whenever shallow-water data are available. Managers of 
tidal-water quality monitoring programs should consider the need for enhanced eval¬ 
uation of the shallow-water environment in future monitoring efforts and requests for 
funding. 
Guidance for Using Midchannel Data when Shallow-water Information 
Is Absent. When nearshore shallow-water monitoring data are not available, Karrh 
(1999) and Batiuk et al. (2000) provide guidance on the use of midchannel informa¬ 
tion. The findings published by Karrh (1999) and reported by Batiuk et al. (2000) 
were based on a comprehensive analysis of shallow-water and midchannel data in 
the Chesapeake Bay, which have been collected since 1983 to determine whether 
such data can be used to characterize shallow-water environments. Data for the 
Karrh (1999) study, obtained from state monitoring efforts, academic researchers 
and citizen monitors, were incorporated from the entire Chesapeake Bay and its tidal 
tributaries, including the upper Chesapeake Bay region; the Middle, Magothy, 
Rhode, Chester, Choptank, Patuxent, Potomac, Rappahannock, Poquoson, York and 
James rivers; and Mobjack Bay. 
These reports indicated that underwater bay grass habitat quality conditions (relative 
to attainment or nonattainment of the 1992 bay grass habitat requirements published 
by Batiuk et al. in 1992 and Dennison et al. in 1993) were comparable between 
nearshore and adjacent midchannel stations 90 percent of the time, when station 
pairs were separated by less than two kilometers. 
Midchannel and nearshore areas usually show similar attainment/nonattainment of 
the individual water quality parameters—IQ or Secchi depth, dissolved inorganic 
nitrogen, dissolved inorganic phosphorus, chlorophyll a and total suspended 
solids—published in 1992 as the original set of Chesapeake Bay underwater bay 
grass habitat requirements (Batiuk et al. 1992; 2000). These same water quality 
parameters are used in calculating percent light-at-the-leaf (PLL) and applying the 
supporting diagnostics tools (see Chapter VII). 
The Karrh (1999) study results also indicated that individual water quality parameter 
concentrations at many of the comparison sites differed significantly between shallow- 
water and midchannel areas, from a statistical standpoint. These differences suggest 
that although the attainment/nonattainment status may have been comparable, the 
magnitude of attainment/nonattainment and the diagnosis of the water quality factors 
involved between the shallow-water and midchannel areas could be affected. 
It should be noted that the comparisons made between shallow-water and 
midchannel areas may also have been affected by temporal factors, given that the 
pairs were not sampled on the same day. Water quality managers should also be 
aware that these reports were developed to support the application of nonregulatory 
bay grass habitat requirements and restoration goals, not regulatory aquatic life 
) 
chapter vi 
Recommended Implementation Procedures 
