BfR-Wissenschaft 
27 
• Is it possible to mitigate the damage of oil pollution by using chemical dispersants 
as (part of) the response measures? 
(Hypothesis: If there is an increased degradation of oil and a decreased occurrence of oil 
slicks on the water surface, the ecological damage will be lower.) 
The coastal water of this area shows a wide range of salinity, turbidity and energy character 
istics: With increasing distance from the coast, depending on the tide especially in estuarine 
areas, the salinity changes from less than 5 %o to more than 30 %o. The gradient of turbidity is 
reverse but it is interrupted by high differences of about 80 to far more than 1000 ppm. The 
heterogeneity of wave energy on a small scale (some 100 m), caused by changing wind 
conditions, water depth and current speed in estuaries, tidal channels and creeks also de 
creases with distance from the coastline while the heterogeneity and number of sensitive 
tidal and subtidal habitats increases. Briefly: the effectiveness as well as the controlled appli 
cation of dispersants may be greater the further offshore they are applied (wave energy and 
salinity) but is very different on a small scale in nearshore areas (up to 25km wide), depend 
ing on currents and water depth - the danger to fundamental systems functions is greater if 
they are used nearshore (high adsorption rate of oil droplets to particles leads to increased 
microbial degradation and potentially detrimental to the oxygen balance). 
Additionally there are several nearshore phenomena of a high sensitivity to oil slicks: e.g. 
mussel beds, shell mounds, sea grass meadows, salt marshes and stocks of resting and 
moulting birds. For most of these phenomena an evaluation about the “good or bad” effects 
of chemical dispersant use also depends on the individual conditions of an accident. Howev 
er, a special case exists with regard to moulting and resting birds. In particular, moulting bird 
stocks are clearly much more vulnerable to untreated oil slicks in comparison to chemical 
dispersions. During one to two months in summer these birds are not able to fly because of 
changing their feathers. In distinct areas these stocks can reach far more than 100.000 indi 
viduals; just swimming or drifting on the water they are helpless in the face of being contami 
nated by oil slick residues. Their stock sizes and population dynamics are very well known 
and steadily monitored so that the degree of uncertainty in estimating damages to the popu 
lation level is comparably low. Although there may be no danger to the survival of their popu 
lation and role in systems functions, nevertheless a rough decrease of their local stock size 
has to be avoided for reasons of natural resource protection. 
Extracting the formulation of “endpoints” out of these roughly summarized conditions to de 
velop special strategies of oil pollution response, the resulting simplified scenarios would 
correspond as examples. 
Example 1: 
Moulting birds 
A drift model shows the probability of a high damage to moulting birds. As endpoint the de 
cision is: natural protection of local stocks is given higher priority than possible ecological 
consequences. Resulting from this statement, dispersants must be used in such a way that 
success is guaranteed as far as possible. Any half-hearted and ineffectual use will lead to 
damages in both directions and means a defeat of the strategy involved. 
Example 2 (Figure 5.2): 
A drift model shows: the oil remains in the „Jade“, a big tidal channel leading to the Jade- 
basin. The subtidal and adjacent intertidal of this channel is of minor sensitivity (Figure 5.2). 
Additionally the subtidal and the flats are accessible by foot and suitable vehicles. Effective 
cleaning is possible. As an endpoint may hold: because removal of oil is possible without 
greater harm to sub- and intertidal habitats and with focus on the sedimentation problems