When an organism is invaded by the contaminant and the adaptive responses are activated, the organism is considered to be in a state of environmental stress. If the quantity of contaminants exceeds the organism's ability to deactivate and excrete them, the contaminants or contaminant residues accumulate in the organism. The international academic community has developed efficient methods for investigating adverse effects at most organizational levels. In environmental impact studies, however, from a strictly biological point of view it is the population and not the individual that is important and it is argued that unless an effect has consequences at the population level it is insignificant, as McIntyre et al have asserted (WP-162). INSROP incorporates this point of view in its environmental impact assessment and has adopted it in its environmental impact assessment of offshore oil-field development in Norway.
To produce biological effects and environmental impact, impact factors such as contaminants and noise must have sufficient time to interact with ecosystem components. Impact factors and ecosystems are both temporally and spatially changing, in a state of contemporaneous disequilibrium. Environmental impact potential will therefore correspond to the state of the two parts at the moment of interaction. The impact is considered to continue as long as both parts coexist in a given area and as long as deviations are observed in environmental parameters between the influenced and the uninfluenced areas. To estimate the ultimate measure of damage, the following combined parameters should be taken into account in combination:
* Extent of damage
* Duration of damage
The immediate damage corresponds to the initial response when the ecosystem is exposed to the source of pollution. The duration of damage, also called the recovery period, is the period from maximum damage until the populations and community structures have reverted to a state similar to the uninfluenced system components in species composition and age distribution.
All kinds of biological resources have a potential role to play in the recovery of the environment, which can be understood in the functions of abiotic factors (type and fate of contaminants, exposure period and dosage, etc.) and biotic factors both intrinsic and extrinsic (physiological adaptive responses, tolerance and resistance, fecundity, reproduction strategy, food access, etc.). The intrinsic factors include specifics of species, population and community, as well as individual tolerance-sensitivity to the given contaminant based on these factors. In extreme situations of rapid population decrease, the population may lose its ability to restore itself or recover, leading to permanent decline in the population. When the physical and chemical properties or size of the habitat is altered or disturbed , the region may become unsuitable for the organisms. Vulnerability to hazardous substances and environmental stress indicate potential damage to a given ecosystem component, which could have been caused by an impact factor. In INSROP environmental impact assessments, the relative vulnerability of ecosystem components and main species was indicated on a scale by a set of indexes. As each ecosystem component refers to a particular type of environmental impact, each index is specific to a given impact factor.
(2) Evaluation of vulnerability and potential impact level
For each selected component in the ecosystem, impact hypotheses have been developed to suggest situations under which impact may occur. In Phase I of INSROP, for the selected Valued Ecosystem Components (VECs), a total of 59 impact hypotheses were identified. In Table 4.5-4, these hypotheses are correlated with a number of specific activities and the impact factors in the NSR operation. For each hypothesis, a schematic flowchart was drawn to illustrate the possible impact of the specific activities in relevant development on each VEC. Each hypothesis was classified as follows:
