Nature and Intensity of Effects.

determinative according to EPA (1998), from which much of the following

discussion is taken. Important factors that should be considered include:

Nature and intensity of effects.

Spatial and temporal scale of effects.

Potential for recovery from effects.

Nature and Intensity of Effects. Distinguishing important effects from those

of little importance requires consideration of the nature and extent of effects. For

example, effects on growth are less likely to be reflected in population changes

than effects on survival or reproduction. Large reductions in survival of offspring

are more likely to result in measurable population effects than small reductions. A

statistically significant 1-percent decrease in fish growth may not be ecologically

relevant at the population level. A 10-percent decline in reproduction may be

more significant for a population of a slowly reproducing species than for a

rapidly reproducing species.

Spatial and Temporal Scale of Effects. Important considerations include the

extent and pattern of effects in space and time as well as the context of the effects

in the surrounding area over time. The size of the affected area is important. A

larger affected area may be subject to a greater number of other stressors,

increasing the complications from stressor interactions. A larger area may be more

likely to contain sensitive species or critical habitat, and may be more susceptible

to ecosystem-level changes because multiple communities may be altered.

However, a smaller area may not necessarily mean a lower likelihood of the need

for management actions. The extent to which critical habitats may be affected

compared to the larger landscape of interest is important. The function of an area

within the larger landscape may be more important than the absolute size of the

area.

Some important population, community, and ecosystem features operate on

short-time scales and others on very longtime scales. Hence, the time scale of

stressor-induced changes should be considered in the context of the time scales of

the multiple natural processes within which they operate. For example, effects of

COC should be considered in the context of natural variability and cycles in

populations, communities, and ecosystems. Temporal considerations for COC

include the time scale of exposure, including repetitive exposures, and the rate at

which COC may be accumulated and depurated from tissues. These scales should

be considered relative to the time scale on which important population,

community, and ecosystem features operate.

Potential for Recovery from Effects. Consideration of potential recovery is

a logical extension of consideration of temporal scales. Recovery is the rate and

extent of return of a population, community, or ecosystem to some aspect of its

condition prior to the action being evaluated. Because populations, communities,

and ecosystems are dynamic and continually change under natural conditions, it is

unrealistic to expect them to remain static or return to the original state before the

action being evaluated (Landis et al. 1993). However, the return to a state within

2-12

Chapter 2 Structure and Approach of the UTM