Water Quality
Ambient Water Quality Criteria for Dissolved
Oxygen
6.0 Research and Development Needs
Temperature
It is accepted that chronic toxicity
(e.g., growth impairment) from hypoxia is negatively affected
at higher temperatures. However, there continues to be sufficient
controversy, and inconsistency or lack of data, that additional
studies are needed. The majority of researchers have employed
a safety factor when deriving dissolved oxygen requirements
by utilizing high seasonal temperatures for the organisms under
study. Rombough's (1988) work shows promise that a temperature
component of oxygen criteria eventually may be possible for
individual
species and taxonomic groupings. In addition, few studies employ
cold-water test conditions (the other extreme, where criteria
are potentially over-protective); further work in this area
would be helpful.
Oxygen cycles
Typical dissolved
oxygen research reflects controlled conditions with constant
exposure levels over relatively
short time periods. More work is required on the effects of naturally
flucuating dissolved oxygen levels (it is known, for example,
that the reduced growth rate of fish during the depressed period
of a sinusoidal oxygen cycle is not compensated for during the
elevated period). While there is limited information on the effects
of daily oxygen cycles, there is even less known about irregular
oxygen cycles as may occur below controlled discharges from an
impoundment.
Interstitial oxygen
The assumed
3 mg O2/L differential between surface water and interstitial
water, adopted by the
US EPA (1986) and used in our own criteria, is based on only
two studies of natural redds. Additional effort is required to
further test the validity of this assumption. It may be that
the magnitude of variability could preclude the use of a standard
differential and that more efficient methods of monitoring oxygen
within the streambed are needed.
Narrow data
The literature
base on dissolved oxygen research is heavily biased to the
few economically important
salmonid species. Investigation needs to be expanded within groupings
such as freshwater invertebrates and marine species.
