UKCCSC
Benthic Mesocosm Experiments
Steve Widdicombe with
Amanda Beesley, Mary Brinsley, Sarah Dashfield, Chris Gallienne Carolyn Harris,
Mike Kendall, Malcolm Liddicoat, David Lowe, Louise McNeill, Hazel Needham, Phil
Nightingale, Christine Pascoe, Ken Perrett, Andy Rees, Fred Staff, Tony Staff,
Malcolm Woodward.
The Sediment Environment
Mud
Sand
Muddy sand
1
0
-1
-2
-3
-4
-5
-6
-7
-8
1
0
-1
-2
-3
-4
-5
-6
-7
-8
1
0
-1
-2
-3
-4
-5
-6
-7
-8
6
7
8
9
6
7
8
9
6
7
8
9
Control
7.7
Control
7.7
Control
7.7
7.3
6.5
7.3
6.5
7.3
6.5
Large pH changes can be seen in the sediment environment.
The nature of pH depth profiles depend on the sediment type.
Sediment type is important in determining the strength and direction of
nutrient flux as is the faunal community structure.
Nereis v Brissopsis
High tolerance to seawater
acidification
Highly vulnerable to
seawater acidification
Increases uptake of nitrate
Decreases uptake of nitrate
Increased release of silicate Increased release of silicate
No impact on phosphate
flux
Increased release of
phosphate
Impact on nitrite and
ammonium flux
No impact on nitrite and
ammonium flux
S. Widdicombe & H.R. Needham. In press. Impact of CO2 induced seawater
acidification on the burrowing activity of Nereis virens (Sars 1835) and
sediment nutrient. Marine Ecology Progress Series
J.I. Spicer A. Raffo, & S. Widdicombe In press. Influence of CO2-related
seawater acidification on extracellular acid-base balance in the velvet
swimming crab Necora puber. Marine Biology
H. Miles, S. Widdicombe, J.I. Spicer, & J. Hall-Spencer, 2007. Effects of
anthropogenic seawater acidification on acid-based balance in the sea
urchin Psammechinus miliaris. Marine Pollution Bulletin 54:89-96.
UKCCSC
Modelling
Jerry Blackford
Nancy Jones
Carbon Capture and Storage
What are the potential impacts of a leak?
Parameterising a leak
Parameterising the rate and duration of a leak event is speculative;
apart from the stochastic nature of such an event there is little
information available to guide us towards realistic scenarios.
Klausman (2003) reports preliminary estimates of seepage from a
terrestial EOR – sequestration project in Colorado, USA of < 3800
tonnes CO2.a-1 over an area of 78 km2 with subsequent C14
measurements indicating rates of < 170 tonnes CO2.a-1. These
estimates equate to 0.14 – 3.0 mmols C.m-2.d-1 which are the unit
relevant to the model system.
This compares with a typical DIC concentration of 2100 mmols
C.m-3.
The typical capacity of the pipelines used to deliver CO2 to well
systems, 100-250 mmscfd (million metric standard cubic feet per
day). This equates to ~0.27 x 1012 mmols carbon .d-1
The second issue, principally relating to fast-rate leak events is
the behaviour of the resulting high pressure gas jet; it’s rate of
travel to the surface, subsequent direct gassing to the
atmosphere and the portion of gas that dissolves in the water
column.
There is evidence from natural shallow (<20m) high pressure
gas seeps that the majority of CO2 can transfer to the water
column. Hence we assume for simplicity all CO2 from a leak is
dissolved.
For low pressure seepages we assume all gas is dissolved in the
bottom layer, for high pressure leaks we assume an equal
distribution of CO2 input through out the water column.
Scenarios:
1. Diffuse seepage: We assume a constant low level seepage
of CO2, spread homogeneously across the area of one model
box (49 km2), representing a notion of porosity in geological
formations. We employ two seepage rates, 0.5 mmol C.m-2.d-1
representing the Colorado data and a x100 treatment of 50.0
mmol C.m-2.d-1.
2. Long term well head failure: We assume an unmitigatable
fault in the well casing resulting in a catastrophic outgassing
of ~5 million tonnes CO2 over one year, five times the input
rate at Sleipner, or 5 years worth of sequestered CO2.
3. Pipeline fracture: We assume a fracture in a pipeline that
persists for one day. We use an injection of 150 000 tonnes
CO2, approx 10 times a typical pipeline capacity and 50x the
mean Sleipner injection.
i.e. worst case scenarios
Assume that the point source leaks disperses instantaneously
into a model 7km x 7km box. Clearly this is a weakness
although the tidally driven horizontal mixing processes in the
region are strong and would be capable of achieving this
mixing within a few days.
All modes of release were simulated at two sites,
North (57.75N, 1.00E), approximating to the Forties oil field
•water column depth of 138m
•strongly stratified during the summer
South (53.5N, 1.0E), representative of the Viking group of
oilfields.
•depth of 28m
•mixed throughout the year.
The pipeline failures were simulated at four times during the
seasonal cycle on julian days 11, 101, 191 and 281.
We report the pH anomaly caused by each leak event.
Much research is currently ongoing into the precise nature of
ecosystem response to high CO2 but because of the complexity
this is as yet unquantifiable
In order to give some guidance the pH anomalies might have the
following effects, it should be noted that this is subjective and
qualitative.
<0.1:
Perturbation probally insignificant.
0.1-0.2: Minimal likely effect, perturbation less than natural variability.
0.2-0.3: Perturbation ~ natural variability, potentially some impacts.
0.3-0.4: Some species experiencing moderate to significant impacts.
>0.4:
More wide ranging and significant to severe effects predicted.
Diffuse seepage of 0.5 mmol C.m-2.d-1 (~ Colorado data)
Results in no discernable impact
Diffuse seepage 50.0 mmol C.m-2.d-1 (x100 Colorado data)
North
South
Continuous
leak
South
North
South
North
~5 million
tonnes CO2
over one
year
Not masked
Masked (<0.02)
Note: different colour scale
-0.02
Sea bed
Surface
N.b. Anomalies less than 0.02 pH units masked
-0.02
Temporary pipeline blowout, 150 000 tonnes CO2
x10 pipeline capacity, ~x50 Sleipner injection rate
North
South
Comparison with atmospherically driven acidification
Summary
•Blackford, J.C., Gilbert, F.J., 2007. pH variability and CO2 induced acidification
in the North Sea. Journal of Marine Systems 64. 229-241.
•Initial results suggest that leaks from CCS will not have a major ecological
impact on the regional scale, but would probably have localised significant
effects.
•The general international consensus is that we simply do not yet know enough
about mechanisms and effects to be confident in model predictions of
ecological effects, although contemporary and paleo- evidence indictate
significant / catastrophic impacts.
Model of small scale leak dispersal
Nested set of water columns with turbulent mixing
parameterised
10 metres
1 kilometre
Model of small scale leak dispersal
Diffusion and mixing of a point source.
9
1m
2m
5m
10m
20m
50m
100m
200m
500m
1000m
CO2 concentration
8
7
6
5
4
3
2
0
0.5
1
Hours
1.5
2