3.3 Surface Compartment Calculations
41
• T exp is exposure time of oil thicker than TH
• p beh is the probability of encountering an area with surface oil (sea surface)
• p phy is the probability of lethal effects given encountering with oil above TH
An alternative equation has been derived for oil drift models that do not estimate
the exposure time. This equation will result in lower impact than (Eq. 3.2) if T exp
> 1 day and it is therefore recommended to use an oil drift model that estimates
exposure time in the cell.
3.3.2 Time Factors and Recovery Modelling
The impact time in sea surface is set to 1 year, i.e. full impact is expected to be seen
within one annual cycle including a breeding season. Contamination of shoreline
habitats and breeding sites used by the surface VECs may have long-term consequences that may inhibit or prolong the recovery of the population, e.g. following
the Deepwater Horizon incident (In ERA Acute, this is incorporated by using the
lag-time calculated in the shoreline compartment (t lag,sh Natural Resource Damage
Assessment Trustees 2016; National Research Council (US) 2003), the relative abundance data of the species in habitats (N hab ) and a resource-specific sensitivity factor
(SF r ) for the resource (r). The calculations are summarized in Eq. 3.3.
t lag,su =
∞
i=1
N hab i × t lag,sh i × SF r
(3.3)
The restoration time is calculated based on the population loss from Eq. 3.2,
using a discrete logistic growth model (Maynard-Smith and Slatkin 1973). The model
estimates the relative population size N in generation t + 1 as a function of the number
of individuals in the previous generation. A generic look-up table of the fundamental
net reproductive rate (R) for seven wildlife groups is used to determine the growth
rate and the vulnerability of the population. See Supplementary Information 1 Table 3
which includes references for the values.
N t+1 =
N t R
1 + (aN t )
b
(3.4)
• R = the fundamental net reproductive rate.
• a = (R–1)/K, where K is the carrying capacity
• b = a factor determining the density dependence type.
The restoration time factor is defined as the period from restoration starts until
the population is restored to a pre-defined level of its pre-spill baseline.
The total recovery time (t rec ) is the sum of impact (t imp ), lag (t lag ) and restoration
time (t res ). Together with RDF su for the sea surface it is illustrated in Fig. 3.2. For
the sea surface compartment, the RDF SU is calculated by Eq. 3.5:
41
• T exp is exposure time of oil thicker than TH
• p beh is the probability of encountering an area with surface oil (sea surface)
• p phy is the probability of lethal effects given encountering with oil above TH
An alternative equation has been derived for oil drift models that do not estimate
the exposure time. This equation will result in lower impact than (Eq. 3.2) if T exp
> 1 day and it is therefore recommended to use an oil drift model that estimates
exposure time in the cell.
3.3.2 Time Factors and Recovery Modelling
The impact time in sea surface is set to 1 year, i.e. full impact is expected to be seen
within one annual cycle including a breeding season. Contamination of shoreline
habitats and breeding sites used by the surface VECs may have long-term consequences that may inhibit or prolong the recovery of the population, e.g. following
the Deepwater Horizon incident (In ERA Acute, this is incorporated by using the
lag-time calculated in the shoreline compartment (t lag,sh Natural Resource Damage
Assessment Trustees 2016; National Research Council (US) 2003), the relative abundance data of the species in habitats (N hab ) and a resource-specific sensitivity factor
(SF r ) for the resource (r). The calculations are summarized in Eq. 3.3.
t lag,su =
∞
i=1
N hab i × t lag,sh i × SF r
(3.3)
The restoration time is calculated based on the population loss from Eq. 3.2,
using a discrete logistic growth model (Maynard-Smith and Slatkin 1973). The model
estimates the relative population size N in generation t + 1 as a function of the number
of individuals in the previous generation. A generic look-up table of the fundamental
net reproductive rate (R) for seven wildlife groups is used to determine the growth
rate and the vulnerability of the population. See Supplementary Information 1 Table 3
which includes references for the values.
N t+1 =
N t R
1 + (aN t )
b
(3.4)
• R = the fundamental net reproductive rate.
• a = (R–1)/K, where K is the carrying capacity
• b = a factor determining the density dependence type.
The restoration time factor is defined as the period from restoration starts until
the population is restored to a pre-defined level of its pre-spill baseline.
The total recovery time (t rec ) is the sum of impact (t imp ), lag (t lag ) and restoration
time (t res ). Together with RDF su for the sea surface it is illustrated in Fig. 3.2. For
the sea surface compartment, the RDF SU is calculated by Eq. 3.5: