detect changes related to management strategies to reduce nutrients and sediments 
on a tributary to baywide level. Traditional monitoring programs have collected peri¬ 
odic data at a small number of fixed sampling locations, often in the deeper 
midchannel areas. These measurements provide a good baseline for watershed 
assessment and long-term trends, but may miss small-scale gradients in tidal water 
quality and neglect critical shallow-water habitats. 
In the past, intensive water quality monitoring of these shallow-water habitats has 
been time-intensive and cost-prohibitive. The advent of a new suite of technologies 
known as the DATAFLOW water quality monitoring system, however, has brought 
intensive monitoring of shallow-water habitats into reach (http://mddnr. 
chesapeakebay.net/sim/index.html). DATAFLOW is a system of shipboard water 
quality probes that measure spatial position, water depth, water temperature, salinity, 
dissolved oxygen, turbidity (a measure of clarity of the water) and chlorophyll a 
from a flow-through stream of water collected near the water body’s surface. The 
system allows data to be collected rapidly (approximately every four seconds) and 
while the boat is traveling at speeds up to 25 knots. Because the DATAFLOW system 
is compact, it can be housed on a small boat, enabling sampling in shallow water and 
the ability to map an entire small tributary in less than a day. Typical DATAFLOW 
research cruise sampling paths traverse shallow and channel areas to obtain a full 
characterization of a tributary’s water quality. 
The discussion below focuses on migratory spawning and nursery, open-water, deep¬ 
water and deep-channel designated uses. The DATAFLOW system is the only viable 
option for monitoring water quality conditions in the shallow-water designated use. 
The high temporal and spatial variability expected in shallow-water areas implies 
that intensive data collection would be required for any assessment to have credi¬ 
bility. A probability-based approach was considered as a less expensive approach for 
shallow-water monitoring, but the cost savings were not sufficient to justify the 
reduced amount of information that this approach would provide. The only option 
for reduced costs in shallow-water monitoring is to limit the amount that is 
conducted during any one year. 
DISSOLVED OXYGEN CRITERIA ASSESSMENT 
'Recommended' Level of Monitoring 
Monitoring for dissolved oxygen criteria attainment should address all four frequen¬ 
cies of dissolved oxygen criteria: 30-day mean, 7-day mean, 1-day mean and 
instantaneous minimum. The current fixed-station monitoring program is designed 
to provide a long-term record of dissolved oxygen concentrations that reflect 
seasonal and interannual variation. For that reason, even though instantaneous meas¬ 
urements are collected, the current monitoring is best suited for assessing the 30-day 
mean dissolved oxygen criteria component and poorly suited for assessing the 7-day, 
1-day mean and instantaneous minimum criteria components. To address the need 
for data that will address the 7-day, 1-day mean and instantaneous minimum criteria 
chapter vi • Recommended Implementation Procedures 
