Water Quality Management - River Dynamics and Integrated River Management - page 576

determination of impaired water bodies as per Section 303D of the CWA, allowance is made for the
randomness in nature when assessing whether the DO (or other constituent) standard is met at all times.
For example, in the waste-load allocation process compliance with the standard usually is assessed for a
design low-flow condition. In the U.S., this condition is the 7-day, 10-year low flow, Q 7,10 , which is the
average flow over a 7-day period for which such average 7-day flows are smaller than Q 7,10 only once on
average in 10 years. In the Regional Water Quality Management Plan Update for Southeastern Wisconsin
if DO (or other constituent) concentrations met the appropriate standard at least 85% of the time, DO (or
other constituent) was considered in compliance at that location (SEWRPC, 2007). Finally, in many
States if DO (or other constituent) concentrations meet the appropriate standard at least 90% of the time,
DO (or other constituent) is considered in compliance and the water body is not put on the 303D list of
impaired waters for that constituent (Smith et al., 2001).
Biology-based criteria —By the mid-1980s the U.S. Environmental Protection Agency (USEPA)
completed an exhaustive survey of the research on DO requirements for various, mainly “sportfish,” fish
species. This survey was used to develop National DO Criteria on the basis of DO requirements of fish
that could be used by States as guidance for development of DO standards that could result in biological
integrity of the fish community. The focus on sportfish resulted because the National DO Criteria were
established to protect more sensitive species within the fish community. The National DO Criteria
established by the USEPA (1986b) are listed in Table 9.6.
The National DO Criteria Document subdivides fish species into salmonid and nonsalmonid fish.
Salmonid fish are coldwater fish. Nonsalmonid fish include many other coldwater and coolwater fish plus
all warmwater fish (USEPA, 1986b, p. 2). The warmwater fish species are dominated by centrarchid fish.
The National DO Criteria Document also notes that there is little published data on the DO requirements
of most nonsalmonid species (USEPA, 1986b, pp. 2 and 12). The published data on the following DO
sensitive species are the basis of the National DO Criteria recommended for nonsalmonid fish: largemouth
bass, smallmouth bass, channel catfish, sunfish, black crappie, white sucker, white bass, northern pike,
walleye, among others. The effects of various DO concentrations on the well-being of aquatic organisms
have been studied more extensively for fish of the family Salmonidae (including various species of
Salmon and trout) than for any other family of organisms (USEPA, 1986b, p. 4). Nearly all these studies
have been conducted under laboratory conditions, simplifying cause and effect analysis, but eliminating
or minimizing other possibly important environmental conditions, such as chemical and physical stresses
associated with non-optimal water quality, as well as competition, behavior, and other related activities.
These studies are the basis of the National DO Criteria for Salmonid fish.
Table 9.6 National water quality criteria for ambient dissolved oxygen concentration (after USEPA, 1986b, p. 34)
Coldwater criteria Warmwater criteria
Time Period Early life stages 1,2 Other life stages Early life stages 2 Other life stages
30 day mean NA 3 6.5 NA 5.5
7 day mean 9.5 (6.5) NA 6.0 NA
7 day mean minimum NA 5.0 NA 4.0
1 day minimum 4,5 8.0 (5.0) 4.0 5.0 3.0
1 These are water column concentrations recommended to achieve the required intergravel DO concentrations shown in
parentheses. The 3 mg/L differential is discussed in USEPA (1986b). For species that have early life stages exposed
directly to the water column, the figures in parentheses apply.
2 Includes all embryonic and larval stages and all juvenile forms to 30-days following hatching.
3 NA means “not applicable”.
4 For highly manipulatable discharges, further restrictions apply (USEPA, 1986b, p. 37).
5 All minima should be considered as instantaneous concentrations to be achieved at all times.