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Page 1: Mark symons

Potential Ballast Water Movement

within the Fal Estuary

Authors:

Mr Mark Symons, (Student) Falmouth Marine School (University of

Plymouth) Fdsc Marine Science, Falmouth, Cornwall, United

Kingdom. 58 Manor Way, Helston, Cornwall, TR13 8LJ

[email protected]

Miss Louise Hockley, (Associate Lecturer) Falmouth Marine School,

Falmouth, Cornwall, United Kingdom. MSc Marine Science.

Abstract

The Fal Estuary a SAC under the E,U’s Habitats Directive but home to

a working docks, and invasive species. Its Hydrodynamic traits are

mainly unknown. Measurements of tidal flow in the dockland area

of the Fal are undertaken over an entire tidal cycle of

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February/March. This data plotted in vector graphs shows that the

mean movement of water is towards the docklands, and that

statistically there was no significant difference in direction between a

flooding and ebbing tide. Along with this the velocities were so slow

that the maximum any NIS would travel before the tidal current

reversed is 425.52m, thus negating the need to develop any

management strategies.

Introduction

Transportation of Non Indigenous Species (NIS) through the use of

ballast water in shipping is a well known problem and has been since

the technology was fully established in the 1950’s (Griffiths et al;

2009) (other transportation vectors do also exist such as hull fouling).

Though the use of ballast water has a negative effect on the

environment by introducing NIS, it plays a major role in keeping

vessels stable and improving manoeuvrability when free from cargo

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(Packard, 1984; Tsolaki, 2009; Zhang and Dickman, 1999). Tsolaki

(2009) states that “Shipping moves 80% of the world’s commodities

and transfers approximately 3-5 billion tonnes of ballast water

internationally”. This vast movement of ballast water has lead to the

introduction of over 1000 NIS in European coastal waters (Golasch,

2006); though it was the harmful affect to human health and the

economy that attracted the attention of scientists and professionals

to address the issue (Institute for European environmental policy

2008).

In 2004 the International Maritime Organisation organised a

convention for the management of ballast water and sediment in

ships. The convention came up with two strategies to combat the

problem.

1) They must have and implement a ballast water management

plan approved by the administration.

2) To have aboard a ballast water record book, recording when

ballast water is taken on board and when it is discharged, also

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any accidental or exceptional discharges must be recorded

(International Maritime Organisation, 2004).

The two most important regulations are D-1, Ballast water exchange

Ref (Matej, 2008), and D-2 which is a ballast water performance

standard which dictates the acceptable levels of organism allowed

within ballast water. A D-2 table of organism’s sizes and quantities

can be found in Tsolaki’s (2009) review of ballast water treatment.

Regulation D-1 is being phased out and after 2016 only ballast water

treatment systems will be utilised to comply with regulation D-2

(International Maritime Organisation, 2004). Therefore the ballast

water related industry is focused mainly on treatment of ballast

water, this maybe port based or ship based. Even with treatment

systems in place there is not a method which can remove 100% of

NIS (Tsolaki, 2009). The treatment systems do have their place and

should continue to evolve, however there maybe alternative

methods to manage NIS.

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This study is to investigate whether simple current modelling can

help to manage NIS within the Fal estuary, Falmouth, Cornwall.

When planktonic NIS is deposited with ballast water in the Fal it is at

the mercy of abiotic factors; Transportation will be controlled by the

estuaries hydrodynamic traits (Becker et al., 2010). The region of the

Fal estuary where the docks are located is macrotidal (Pirrie et al.,

2003) with the largest spring tides of 5.7m. The Fal possess a flood

dominant tidal flow, but low tidal currents (Stapleton and Pethick

1996) this means that settlement of sediment in lower half of the

estuary has been minimal which could have similar implications for

NIS. However geochemical data showing the distribution of

contaminates within the Fal suggests that it follows the dominant

tidal flow (Carrick Roads area) (Pirrie et al., 2003), this could also

have similar implications for NIS.

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Apart from the work by Stapleton and Pethic, I am only aware of one

physical study of the Fal performed by Matthew Le Maitre who

undertook a hydrographical survey for the Harbour Commission. The

survey was looking at the accuracy of tidal diamonds on admiralty

charts in comparison with real time data collected from in-situ

buoys. The current flow data was only undertaken for surface layers

and modelled in a programme known as PICES for mapping oil spill

distribution.

The Fal estuary is a special area of conservation under European

Habitats Directive, which aims to protect the site and stop any

Figure 1. Map showing dominant tidal flow in the Fal. Map A- 3 hours before high water.

Map B – 3 hours after high water. Courtesy of Stapleton and Pethic Institute of Estuarine

and Coastal Studies.

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degradation and obtain favourable conservation status of the

interest features across their bio- geographical ranges (Langston et al

2006) NIS would conflict with this. The Fal estuary is also a ria

making it one of the deepest natural harbours in the world. This

allows there to be a commercial docks run by A&P Ltd, again

conflicting with the special area of conservation principals. Although

export is low from Falmouth docks ,it still exists. Therefore ballast

water will be released into the estuary; the majority of ballast water

released in the docks is from vessels entering dry docks for repair

(Mike Pereir, A & P Ltd, Pers. Comm., January 14, 2011).

Species that have been recorded in the Fal are:

Crepidula fornicate,

Caprella mutica,

Styelea cava,

Crassostrea gigas,

Sargassum muticum,

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Watersipora subtorquata,

There is also no management in place by Cornwall council to deal

with invasive species. (Jenny Christie, Maritime Environment officer,

Cornwall Council. Pers. Comm., November 25th 2010). However both

the Environment Agency and Natural England “would be responsible

should an outbreak occur that could be contained or eradicated”

(Lisa Rennocks, Cornwall Wildlife Trust, Pers. Comm., May 04 2011)

There is a hotline for reporting NIS and each cased is judged on

whether action is needed.

Sampling area

The sampling area is shown in fig 2, the site was not the preferred

location but had to be used to coincide with the working

functionality of the docks. This site is however a good representation

for ballast water transport, as Duchy Wharf is one of the primary

wharfs used by A&P Ltd, thus NIS could potentially be released into

the recorded currents.

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The Hydrodynamic traits of this area are unknown, being affected by

natural fluxes and anthropogenic structures. These structures may

be permanent such as the wharfs, or mobile structures such as the

access barge and other vessels using the docks.

Wharf Destroyed in

Fire 2003.

Figure 2. This GiS Map shows the location of the sampling site, note anthropogenic structures that may

influence hydrodynamic traits. (a) Location was an access barge used for smaller vessels; this was constantly

in-situ.

(a)

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Methodology

The sampling was conducted using a Valeport 106 Current Meter. It

was used in self recording mode with the 10-way subconn connector.

Direct operation was not possible due to location. The current meter

was then lowered through the water column stopping at each 1m

interval for a period of two minutes allowing data collection. This

would be done each day over one entire tidal cycle, alternating daily

between flooding and ebbing tides. During spring and neap tides,

both the flooding and ebbing tide would be measured to give a tidal

flow for the extremes of the cycle.

As the 106 current-meter was used in self recording mode, the data

needed to be removed after each daily sample obtained. This is

done using Datalog (software provided by Valeport) and the Y lead to

connect the fish to the computer. Once the data had been removed

it is to be converted into an excel format and filtered (shading

alternative depths for clarity). Each depth’s flow and heading data

would be copied into a new spreadsheet (Flooding, Ebbing, Spring

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Flood, Spring Ebbing, Neap Flooding or Neap Ebbing): Sheets are

then separated into individual depths. Vectors would then be

converted into Cartesian coordinates and then averaged.

X= 𝑎 cos 𝑡ℎ𝑒𝑡𝑎

Y= 𝑎 sin 𝑡ℎ𝑒𝑡𝑎

(𝑎 = 𝑚𝑎𝑔𝑛𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑣𝑒𝑐𝑡𝑜𝑟)

(𝑡ℎ𝑒𝑡𝑎 = 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑣𝑒𝑐𝑡𝑜𝑟)

Once the data is averaged it is changed back to vector (polar)

coordinates using Atan2:

Atan2 = 2𝑎𝑟𝑐𝑡𝑎𝑛 (𝑦 ÷ √𝑥² + 𝑦² + 𝑥)

Hypothesis

H0–Mean directional flow of an ebbing tide is = mean directional flow

of a flooding tide.

H1 – Mean directional flow of an ebbing tide is ≠ directional flow of a

flooding tide.

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Observations

If vectors are

broken down

in ratio’s of

45 degrees Fig 3 shows 4:5:3:1 (0-90 : 90-180 : 180-270 : 270-360)

and that the highest velocities were recorded at 12 and 8 metres in

Ebbing Vector Graph

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.00.20.40.60.81.01.21.41.6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0

30

60

90

120

150

180

210

240

270

300

330

1M

2M

3M

4M

5M

6M

7M

8M

9M

10M

11M

12M

13M

Figure 3. Averaged Ebbing vector plot, taken from samples

between 04/02/2011- 22/03/2011 from location shown in

Fig 2. Each plot is representing metre depths see legend,

axis are cm/S.

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depth. 0-180 degrees holds the majority of the vectors from North

East to South South East in direction.

Flooding Vector Plot

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.00.20.40.60.81.01.21.41.61.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0

30

60

90

120

150

180

210

240

270

300

330

1M

2M

3M

4M

5M

6M

7M

8M

9M

10MVectors are

broken down into the same ratios as above, 1:5:4:0. 0-180 degrees

holds the majority of the vectors between North East and South East

Figure 4. Averaged Flooding vector plot, taken from

samples between 04/02/2011 – 16/03/2011 from

location shown in Fig 2. Each plot is representing

metre depths see legend, axis are cm/S.

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in direction. The highest velocities are found at 5 and 8 metres in

depth.

Vectors of ebbing and flooding tide, depths ignored to show an

easier graphical comparison of hydrodynamic traits of the two tidal

Ebbing vs Flooding

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.00.20.40.60.81.01.21.41.61.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0

30

60

90

120

150

180

210

240

270

300

330

Flooding

Ebbing Figure 5. Averaged vector plots, taken from samples between

04/02/2011 – 16/03/2011 from location shown in Fig 2. Axes are cm/S.

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flows. The graph indicates that the main vector headings are south

easterly and that flooding velocities are higher than ebbing.

With the coding for mean directional flow, anything above 0.5 would

be travelling in a Northward direction (>270-<90 degrees). Any value

below 0.5, would be travelling in a southward direction (>90-2<70).

Both Mean values for both tidal flows are below 0.5 so mean

directional flow in both cases, is more southerly than northerly. The

Depth (M) Flooding Ebbing Flooding Code Ebbing Code

1 201.6162306 106.4414867 0 0

2 38.84300014 181.0517796 1 0

3 183.2028478 224.6783325 0 0

4 183.2958067 190.2172458 0 0

5 138.8962462 98.70066586 0 0

6 266.7919884 163.2364974 0 0

7 116.4006659 23.34776993 0 1

8 116.9323133 50.28114248 0 1

9 131.320674 342.3382264 0 1

10 124.8657787 110.1098376 0 0

11 74.3705397 1

12 173.1563756 0

13 69.70374148 1

Mean Values 0.1 0.384615385

Critical Value 2.08

Test Value 0.134912594

Table 1. Coding of vector heading data for statistical unpaired t-test,

Table 1. Coding of the data: Any vector with a northward heading (270-90 degrees) was given

a score of 1. Any vector with a southward heading was given a score of 0.

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Test value is also far below the critical value for a two tailed test with

21 degrees of freedom. This suggests that there is no statistical

difference between the two input groups and so the Null Hypothesis

should be accepted. The difference could be a product of random

sampling variability.

Depth (M) Ebbing Velocities Flooding Velocities

1 0.81 1.21

2 0.60 0.92

3 0.46 0.84

4 0.75 0.10

5 1.11 1.97

6 0.85 0.42

7 0.23 0.55

8 1.62 1.42

9 0.36 1.02

10 0.77 0.79

11 0.59

12 1.49

13 0.86

Mean Values 0.81 0.92

Standard Deviation 0.41 0.53049043

Critical Value 2.08

Test Value 0.57

Table two shows that the flooding tide has a slightly higher mean

over all, however this is not statistically significant and could have

occurred through sampling variability.

Table 2. Unpaired t-test on ebbing and flooding tidal velocities, original and mean values

are in cm/S.

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Discussion

Vector heading analysis

Vector headings are not as expected with no statistical significant

difference in tidal flow direction (table 1) between the two tidal

states. This is very surprising as the sample location is macrotidal.

The majority of vector headings were in a mean southward direction

(Figure 5, Table 1) this would be characteristic of a flooding tide. A

more equal split between south/north directions was expected. The

ebbing tide is very variable over depth (Figure 3), and with only 5

vectors considered to be flowing outwardly in direction. These

depths are 7,8,9,11,13 (Figure 3). This could potentially be one of

following variables, anthropogenic obstructions or wind driven

mixing creating turbulent flow. Boats that docked at the wharfs

were recorded as was was wind speed and direction. However, as

the Flooding tide only had one anomaly in directional flow, 2M depth

(suggesting that this is wind interference), if wind was the variable

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effecting the ebbing tide, you would expect to see more anomalies in

the flooding tide. The vessel, Mounts Bay, was docked alongside

duchy wharf for 12 out of the 29 days so would influence the data a

great deal. It also had a depth of 5.2m, so would be affecting

movement of water to this depth. However this is not conclusive

and greater analysis would have to be undertaken comparing wind

vectors, obstructions and current vectors to come to a more

substantial conclusion.

Velocity analysis

As the Fal is flood tidal dominant in its hydrodynamic traits, you

would expect to see a stronger flooding current than ebbing. Whilst

this is the case for one off depths such as 5m (Figure 5), as a whole it

isn’t (Table 2) statistically significantly different. This may be due to

the sample location (Figure 2). If the data was collected from the

flooding channel, a difference in velocities may occur. The current

flow is slow as suggested. Again this is partly due to location with

maximum averaged velocity of 1.97cm/s. The velocities also don’t

have any correlation with depth, obstructions or wind vectors.

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Potential movement of NIS

NIS deposited within the ebbing tide mixing to the following depths

1,2,3,4,5,6,10,12 would stay within the area they are deposited

(Figure 2). The data suggests that if they were to colonise, it would

be within this area as they would be constricted by the solid wharf

structures which are rocky (potentially good substrates species

dependant). Whilst sampling, a vast number of anemones were

growing on the sides of the access barges. This may suggest settling

of planktonic larvae before the sessile stage of the life cycle would

begin. The depths 7,8,9,11,13 would carry planktonic larvae away

from the area and potentially stop colonisation within the sample

location, however, even travelling at the highest velocity, the

furthest the plankton would travel before the tide turns and it starts

travelling in a different direction is 394.92m. This slow velocity

means that plankton would not travel any further than the most

northern jetty (Figure 2), so it would be maintained within the

dockland area unless the velocity was to increase as moving away

from the sampling location.

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This is all similar for NIS deposited in a flooding tide; it possess a

higher chance of staying within the sampling area as only one vector

out of ten is travelling in a northward direction. Again the velocity

that the plankton would be travelling is so slow that it would only

reach a maximum of 425.52m. This would again keep it within the

dockland area unless affected by a change in the velocity or direction

of the vector.

Conclusion

Data of average vectors over a monthly tidal cycle cannot be

conclusive for NIS distribution. However Duchy wharf, south of the

sampling location, is on “stilts” and may provide suitable substrate

for colonisation of NIS; further biological investigation of this area

would help to prove or disprove the theory. The vector velocities

were so slow that any plankton deposited at this site would not

travel out of the dockland area, so colonisation (if necessary), would

occur within the dockland area for the species to progress through

its life cycle. This suggests that the evolution of management

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strategies would not be necessary as this would be impractical and

conflict with the docks.

Acknowledgments

Thanks to Harriet Knowles at Falmouth Harbour Commission for

support and helping networking with A&P Falmouth to gain access to

the docks. Mike Pereir for advice on potential sample locations

within the docks. Danielle Perrin & Amber Thornton for helping with

the physical act of sampling. Matt Le Maitre for help with vector

averaging and initial direction in methodology. Claire Eatock for

intial networking with Falmouth Habour Commission, to make

projects possible.

References

Becker, L.M, R. A. Luettich, and M.A. Mallin. 2010. Hydrodynamic

behaviour of the Cape Fear River and estuarine system: A synthesis

and observational investigation of discharge - salinity intrusion

relationships. Estuarine, Coastal and Shelf Science 88:407-418

International Maritime Organization, 2004. Convention for the

Management of Ballast Water and Sediment in Ships. International

Maritime Organization, London.

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Gollasch, S. 2006. Overview on introduced aquatic species in

European navigational and adjacent waters. Helgoland Marine

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Griffith, C.L., A. Mead, and T.B. Robinson.2009. A brief history of

marine bio-invasions in South Africa. African Zoology. 44(2):241-247.

Kettunen, M., P. Genovesi, S. Gollasch, S. Pagad, U. Starfinger, P.

Brink, and C. Shine. 2008. Technical support to EU strategy on

invasive species. 070307/2007/483544/MAR/B2. Institute for

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annexes.

Langston, W.J., B.S. Chesman, G.R. Burt, M. Taylor, R. Covey, N.

Cunningham, P. Jonas, and S.J. Hawkins. 2006. Characterisation of

the European Marine Sites in South West England:

the Fal and Helford candidate Special Area of Conservation.

Hydrobiologica 533:321-333.

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the ballast water issue. Marine Pollution Bulletin. 56:1966-1972.

Packard, W.V., 1984 Sea-Trading The Ships, Volume 1. Fairplay

Publications: Surrey.

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Butcher, P. Hughes. 2003. The spatial distribution and source of

arsenic, copper, tin and zinc within the surface sediments of the Fal

Estuary, Cornwall, UK. Sedimentology 50:579-595

Stapleton, C. and Pethick, J. (1996) The Fal Estuary: Coastal Processes

and Conservation. Report by the Institute of Estuarine and Coastal

Studies. University of Hull for English Nature

Tsolaki, E. and E. Diamadopoulos. 2009. Technologies for Ballast

water treatment a review. Journal of chemical technology and

Biotechnology 85:19–32.

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Zhang, F. and M. Dickman.1999. Mid-ocean exchange of container

vessels ballast water. 1: Seasonal factors affecting the transport of

harmful diatoms and dinoflagellates. Marine ecology progress series.

176:243-251


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