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 Dussuk@hotmail.com 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

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

(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

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.

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.

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.

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

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,

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.

Wharf Destroyed in Fire 2003.

(a)

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.

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.

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

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= đ?‘Ž cos đ?‘Ąâ„Žđ?‘’đ?‘Ąđ?‘Ž Y= đ?‘Ž sin đ?‘Ąâ„Žđ?‘’đ?‘Ąđ?‘Ž (đ?‘Ž = đ?‘šđ?‘Žđ?‘”đ?‘›đ?‘–đ?‘Ąđ?‘˘đ?‘‘đ?‘’ đ?‘œđ?‘“ đ?‘Łđ?‘’đ?‘?đ?‘Ąđ?‘œđ?‘&#x;) (đ?‘Ąâ„Žđ?‘’đ?‘Ąđ?‘Ž = đ?‘Žđ?‘›đ?‘”đ?‘™đ?‘’ đ?‘œđ?‘“ đ?‘Łđ?‘’đ?‘?đ?‘Ąđ?‘œđ?‘&#x;) Once the data is averaged it is changed back to vector (polar) coordinates using Atan2: Atan2 = 2đ?‘Žđ?‘&#x;đ?‘?đ?‘Ąđ?‘Žđ?‘› (đ?‘Ś á √đ?‘ĽÂ˛ + đ?‘ŚÂ˛ + đ?‘Ľ)

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.

Observations

Ebbing Vector Graph

0 1.6 330

30 1.4 1.2 1.0

300

60

0.8 0.6 0.4 0.2

270

0.0 90 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.2 0.4 0.6 0.8

240

120

1.0 1.2 1M 2M 3M 4M 5M 6M 7M 8M 9M 10M 11M 12M 13M

1.4 210

150

1.6 180

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.

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

depth. 0-180 degrees holds the majority of the vectors from North East to South South East in direction.

Flooding Vector Plot 0 330

30

1.8 1.6 1.4 1.2

300

60

1.0 0.8 0.6 0.4 0.2

270

0.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

90

0.4 0.6 0.8 1.0

240

120

1.2 1.4 1.6 1M 2M 3M 4M 5M 6M 7M 8M 9M 10M

210

1.8

150 180

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.

Vectors 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

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

Ebbing vs Flooding

0 330

1.8

30

1.6 1.4 1.2 300

60

1.0 0.8 0.6 0.4 0.2

270

0.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

90

0.4 0.6 0.8 1.0

240

120

1.2 1.4 1.6 210

1.8

150

180

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.

Vectors of ebbing and flooding tide, depths ignored to show an easier graphical comparison of hydrodynamic traits of the two tidal

flows. The graph indicates that the main vector headings are south easterly and that flooding velocities are higher than ebbing.

Table 1. Coding of vector heading data for statistical unpaired t-test, Depth (M) 1 2 3 4 5 6 7 8 9 10 11 12 13

Flooding 201.6162306 38.84300014 183.2028478 183.2958067 138.8962462 266.7919884 116.4006659 116.9323133 131.320674 124.8657787

Ebbing 106.4414867 181.0517796 224.6783325 190.2172458 98.70066586 163.2364974 23.34776993 50.28114248 342.3382264 110.1098376 74.3705397 173.1563756 69.70374148

Flooding Code Ebbing Code 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 0 1 0 1

Mean Values

0.1 0.384615385

Critical Value Test Value

2.08 0.134912594

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.

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

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.

Table 2. Unpaired t-test on ebbing and flooding tidal velocities, original and mean values are in cm/S. Depth (M)

Ebbing Velocities 1 2 3 4 5 6 7 8 9 10 11 12 13

Mean Values Standard Deviation Critical Value Test Value

Flooding Velocities 0.81 0.60 0.46 0.75 1.11 0.85 0.23 1.62 0.36 0.77 0.59 1.49 0.86

1.21 0.92 0.84 0.10 1.97 0.42 0.55 1.42 1.02 0.79

0.81 0.41

0.92 0.53049043 2.08 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.

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

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 isnâ&#x20AC;&#x2122;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 donâ&#x20AC;&#x2122;t have any correlation with depth, obstructions or wind vectors.

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.

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 â&#x20AC;&#x153;stiltsâ&#x20AC;? 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

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.

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