appendix ^51 
Procedure for 
Assessing Dissolved Oxygen 
Criteria Attainment 
30-day Criterion, Including 
Plotting a Bioreference Curve 
Currently, dissolved oxygen is assessed using the monthly mean criterion (i.e., 30- 
day) for the open-water designated use, the monthly mean criterion for the 
deep-water designated use, and the instantaneous minimum criterion for the deep- 
channel designated use. The following step-by-step procedure is used to assess the 
status of Chesapeake Bay waters with respect to dissolved oxygen. 
STEP 1. COMPILING AND FORMATTING THE DATA SET 
A three-year dissolved oxygen dataset is compiled (most recently, the 2008 eval¬ 
uation used the 2004-2006 assessment period) with georeferenced stations for 
Chesapeake Bay Program mainstem and tributary tidal waters, and included the 
date sampled, and coincidently measured water temperature (°C) and salinity 
(ppt) covariates. Ancillary data for the same parameters were added by the state 
of Virginia where applicable, collected from their benthic monitoring program 
and the Alliance for the Chesapeake Bay’s Virginia volunteer monitoring 
program. 
A FORTRAN computer program was developed to reformat this flat file into a 
“d3d file” —a format that could be input into the Chesapeake Bay Program Inter¬ 
polator. 
STEP 2. INTERPOLATION OF WATER QUALITY MONITORING 
DATA 
For the Chesapeake Bay and its tidal tributaries and embayments, a three-dimen¬ 
sional grid-based spatial interpolator was developed to provide a common spatial 
framework for spatial extrapolation of georeferenced water quality monitoring 
data (Bahner 2001). Spatial interpolation is conducted using an inverse distance 
weighting algorithm that extrapolates point data between itself and its nearest 
appendix a 
Procedure for Assessing Dissolved Oxygen Criteria Attainment 
