Ö Springer
Geo-Mar Lett (2017) 37:163-170
DOI 10.1007/s00367-016-0454-6
CrossMark
ORIGINAL
Effects of chemical dispersants on oil spill drift paths
in the German Bight—probabilistic assessment based
on numerical ensemble simulations
Fabian Schwichtenberg * 1 • Ulrich Callies 1 • Nikolaus Groll 1 • Silvia Maßmann 2
Received: 15 February 2016/Accepted: 7 June 2016/Published online: 21 June 2016
© The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract Oil dispersed in the water column remains sheltered
from wind forcing, so that an altered drift path is a key con
sequence of using chemical dispersants. In this study, ensem
ble simulations were conducted based on 7 years of simulated
atmospheric and marine conditions, evaluating 2,190 hypo
thetical spills from each of 636 cells of a regular grid covering
the inner German Bight (SE North Sea). Each simulation com
pares two idealized setups assuming either undispersed or
frilly dispersed oil. Differences are summarized in a spatial
map of probabilities that chemical dispersant applications
would help prevent oil pollution from entering intertidal coast
al areas of the Wadden Sea. High probabilities of success
overlap strongly with coastal regions between 10 m and 20
m water depth, where the use of chemical dispersants for oil
spill response is a particularly contentious topic. The present
study prepares the ground for a more detailed net environmen
tal benefit analysis (NEBA) accounting also for toxic effects.
Introduction
The intertidal sand and mud flats of the Wadden Sea cover an
area of about 4,700 km 2 along the Dutch, German and Danish
coasts (Reise et al. 2010). Their rich and biologically diverse
Responsible guest editor: C. Winter
G3 Fabian Schwichtenberg
fabian.schwichtenberg@hzg.de
1 Institute of Coastal Research, Helmholtz-Zentrum Geesthacht,
Max-Planck-Str. 1, 21502 Geesthacht, Germany
2 Bundesamt fur Seeschifffahrt und Hydrographic,
Bemhard-Nocht-Str. 78, 20359 Hamburg, Germany
ecosystem is a migration stopover and wintering site for many
birds (e.g. van Beusekom et al. 2012). Due to their proximity
to busy shipping lanes, some of the Wadden Sea habitats are
potentially endangered by nearshore oil spill incidents. Such
an accident already happened in October 1998, when the car
go vessel PALLAS ran aground close to the island of Ammm
(Reineking 1999). The subsequent oil spill affected about
12,000 sea birds residing in the North Frisian Wadden Sea
(Fig. 1).
So far, contingency planning for the German North Sea
coast considers only the use of mechanical devices because
of concerns regarding toxic effects of chemical dispersants.
Application of dispersants is regarded as a last resort response
option (EMSA 2014). If mechanical cleaning is not promis
ing, then dispersants could be applied without restriction in
areas deeper than 20 m, whereas it is strictly prohibited in
areas shallower than 10 m. At intermediate water depths
(10-20 m), dispersants might potentially be used depending
on the outcome of a case-specific assessment of environmen
tal damages and benefits. With today’s third-generation chem
ical dispersants being much less toxic (EMSA 2009), the op
tion of using them particularly in inshore zones needs to be
reassessed.
The advantages of using chemical dispersants are twofold;
in the first place, dispersants reduce the pollutant volume on
the water surface. In the second place, they facilitate biodeg
radation processes by increasing the reactive surface of the oil.
However, their effectiveness much depends on the kind of oil
spilled, its state of weathering (viscosity and degree of water
in oil emulsions) and the hydraulic energy in the polluted area.
Other factors of influence are salinity, turbidity and tempera
ture (EMSA 2009).
Initially, concentrations of dispersed oil may be quite
high before they get decreased by dilution and biological
degradation. Even when toxicity of the dispersant itself is