208
In a mesocosm study involving the subsurface injection of Corexit 9527 dispersed Prudhoe Bay crude oil, Lee et al. (1985) noted the association of oil droplets
with biogenic material (phytoplankton and detritus) associated with a phytoplankton bloom, stimulatory effects on small zooflagellates, and increased mortality on
ciliates and appendicularians. Results further showed that Corexit and dispersed
Corexit stimulated bacterial productivity rates by serving as substrates and/or by
inducing the release of organic compounds from the indigenous microbial population. A mass balance for
14
C-hexadecane added to the test oil revealed that within
22 days, 3% was recovered in the suspended particulate fraction and 36% was
respired as CO 2 , 1% in the dissolved organic pool, and 10% as sedimentary
material.
Spatial gradients of MOSSFA are expected with distance from the predominant
river systems (nutrients, clay minerals, salinity) and the center of oil release (Daly
et al. 2016). Gradients in input parameters including flocculent thickness (Fig. 12.3a),
clay particles/minerals, algal and photoautotrophic bacterial communities and associated EPS/TEP, and oiled sediments (e.g., PAHs) control postdepositional response.
Natural spatial gradients exist in deltaic systems; however, MOSSFA inputs lead to
intensified postdepositional response in redoxcline, particulate organic carbon flux,
lithogenic flux, and benthic community impact and response. The formation of
MOSSFA is therefore not unique to the Deepwater Horizon oil spill and is likely to
occur in the event of any oil spill that occurs in an area that satisfies the aforementioned criteria.
12.7 MOS/MOSSFA: Modeling
Modeling of MOS formation during MOSSFA events and the processes affecting
these pathways can be used to predict the magnitude and duration of the downward
flux of oil. The DWH experience strongly indicates that MOSSFA events need to be
factored into the fate-and-effect models for future oil spills and targeted for field
measurements during response assessments and research. This is particularly important because surface oil budgets cannot be properly closed without an accurate,
quantitative estimate of the amount of oil leaving the surface waters as MOS or
OPAs.
Whereas MOS formed via bacterial exudate production or zooplankton activity
is driven by these biological processes, a large portion of MOS forms via the biologically mediated coagulation of smaller marine particles, like diatoms. Such
aggregates form through collision and adhesion of the component particles. Early
models concentrated on the important process of aggregation of oil droplets and
mineral or sediment particles, e.g., the formation of OMAs (Sterling et al. 2005;
Sun and Zheng 2009; Sun et al. 2013). Some of these models used conventional
aggregation theory (Burd and Jackson 2009) to predict the formation of oil-mineral
aggregates (OMAs). The numerical model A-DROP (Zhao et al. 2016, 2017) models the aggregation of oil droplets onto the surface of mineral particles and predicts
A. Quigg et al.
In a mesocosm study involving the subsurface injection of Corexit 9527 dispersed Prudhoe Bay crude oil, Lee et al. (1985) noted the association of oil droplets
with biogenic material (phytoplankton and detritus) associated with a phytoplankton bloom, stimulatory effects on small zooflagellates, and increased mortality on
ciliates and appendicularians. Results further showed that Corexit and dispersed
Corexit stimulated bacterial productivity rates by serving as substrates and/or by
inducing the release of organic compounds from the indigenous microbial population. A mass balance for
14
C-hexadecane added to the test oil revealed that within
22 days, 3% was recovered in the suspended particulate fraction and 36% was
respired as CO 2 , 1% in the dissolved organic pool, and 10% as sedimentary
material.
Spatial gradients of MOSSFA are expected with distance from the predominant
river systems (nutrients, clay minerals, salinity) and the center of oil release (Daly
et al. 2016). Gradients in input parameters including flocculent thickness (Fig. 12.3a),
clay particles/minerals, algal and photoautotrophic bacterial communities and associated EPS/TEP, and oiled sediments (e.g., PAHs) control postdepositional response.
Natural spatial gradients exist in deltaic systems; however, MOSSFA inputs lead to
intensified postdepositional response in redoxcline, particulate organic carbon flux,
lithogenic flux, and benthic community impact and response. The formation of
MOSSFA is therefore not unique to the Deepwater Horizon oil spill and is likely to
occur in the event of any oil spill that occurs in an area that satisfies the aforementioned criteria.
12.7 MOS/MOSSFA: Modeling
Modeling of MOS formation during MOSSFA events and the processes affecting
these pathways can be used to predict the magnitude and duration of the downward
flux of oil. The DWH experience strongly indicates that MOSSFA events need to be
factored into the fate-and-effect models for future oil spills and targeted for field
measurements during response assessments and research. This is particularly important because surface oil budgets cannot be properly closed without an accurate,
quantitative estimate of the amount of oil leaving the surface waters as MOS or
OPAs.
Whereas MOS formed via bacterial exudate production or zooplankton activity
is driven by these biological processes, a large portion of MOS forms via the biologically mediated coagulation of smaller marine particles, like diatoms. Such
aggregates form through collision and adhesion of the component particles. Early
models concentrated on the important process of aggregation of oil droplets and
mineral or sediment particles, e.g., the formation of OMAs (Sterling et al. 2005;
Sun and Zheng 2009; Sun et al. 2013). Some of these models used conventional
aggregation theory (Burd and Jackson 2009) to predict the formation of oil-mineral
aggregates (OMAs). The numerical model A-DROP (Zhao et al. 2016, 2017) models the aggregation of oil droplets onto the surface of mineral particles and predicts
A. Quigg et al.