1

Moville and Green Castle Proposed Sewage Treatment Plant

Considering Impacts on Sea grass Zostera marina

Karin Dubsky, BA, MSc Coastal Ecologist

Author:

Lecturer and scientific research staff, civil and env. eng. Trinity College Dublin and head of

the environmental group Coastwatch. Primary degree in Zoology, Masters in Environmental

Sciences with special focus on estuarine biology. Decades of coastal research, management

and site restoration experience in Ireland and abroad.

Report

This short report sets out the value of and likely damage to the sea grass beds in the area

where the proposed Moville and Green Castle sewage treatment plant outfall is to be sited.

It concludes with recommendations. Coastwatch work is based on large local participation

survey. Comments on the draft report and map information were by Trish Murphy and

Brian Wingham.

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Content:

1. Introduction

1.1 Zostera marina

Sea grass as species and habitat

Legal Status

1.2 Coastwatch Survey work and results

1.3 Goals of Sewage Treatment.

2. Sewage discharge pipe construction phase

2.1 Direct impact of digging the pipe trench

2.2 pipe trench spoil

2.3 Sediment plume from construct

3 Recovery from construction phase

4 Sewage treatment normal operation phase:

4.1 Warm treated fresh water plume fate on Zostera bed seaward edge

4.2 Nutrient enrichment and residues

5 Sewage treatment emergency overflows:

6.1 Raw discharge with sanitary material debris caught in Zostera

6.2 Oyster - L Ryan case

6. Conclusions

7. Recommendations

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1. Introduction

1.1 Zostera marina Sea grass as species and habitat

Zostera marina is a marine flowering grass, which forms dense beds, with trailing leaves swimming in the water column. The grass can be up to 1m long (up to 2 m in exceptional circumstances (Brittany France) (Hily et.al. 2003). Beds can be very long lived > 100 years. To develop and maintain itself the plants in a bed require shelter, the right sandy or muddy sand stable substrate, clean transparent water, yet enough nutrients. So we find it in sheltered bays and lagoons from the lower shore to about 5 m occasionally down to 10m depth. Ecological significance: Seagrass stabilises the substratum as well as providing shelter, a substrate and foraging area for many organisms. Organisms may be grazing on the blades or sheltering in grass or roots. Or hidden in the micro habitats around the rhizomes, roots and in the sediment. As recent example of species richness in Irish sea grass the National Parks and Wildlife Service Manual reports a Cork Kerry study of Zostera marina by UCC scientists, where a total of 124 species representing 81 families from six phyla were recorded from infaunal samples.Thirty-two of these species were only found at Barloge Creek, while 45 were only found at Ventry Bay and a further 47 were found at both locations. (Irish Wildlife Manual No 28: Dale, A. L., McAllen, R. & Whelan, P. (2007)

Management considerations for subtidal Zostera marina beds in Ireland. [2,008KB)

Distribution and Trends Zostera marina beds, bed sizes and health have declined over the last 80 years across

the world and in Europe. Sediment disturbance, siltation, erosion and turbidity resulting

from coastal engineering and dredging activities have been implicated in the decline of

seagrass beds world wide (Davison & Hughes 1998; Holt et al. 1997).

In Ireland it is officially known to occur in 19 bays. However Coastwatch volunteers have found further beds in at least 3 bays including the beds in Lough Foyle. The head marine biologist for NPWS, Dr. Eamon Kelly supplied the following most recent brief status information on Z marina stocks to the OSPAR Convention as published on their website: ‘The habitat is under threat in Ireland (Kelly, pers.com 07). Zostera beds, Seagrass beds - OSPAR Commission

www.ospar.org/html_documents/ospar/html/p00426post%20bdc%20version...And

P00426 Zostera beds - OSPAR Commission qsr2010.ospar.org/media/assessments/Species/P00426_Zostera_beds.pdf · PDF file

Halting and reversing that trend In line with Biodiversity Convention goals governments are looking at ways to protect, manage and restore this species – important in its own right and because of the many ecosystem services it provides to other species including man. The OSPAR Commission Zostera report notes: ‘While reductions may be rapid, re-colonisation may require long time periods. Once seagrass habitats are lost, restoration (if possible) is therefore likely to

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require considerable resources. Efficient management must therefore focus upon maintaining existing populations through protection of habitats (Krause-Jensen et al., 2004). Krause-Jensen, D, ED Almela, AH. Cunha and TM. Greve. 2004. Have seagrass distribution and abundance changed? In Borum J, CM Duarte, D Krause-Jensen and TM Greve eds. 2004. European Seagrasses: An introduction to monitoring and management. The M&MS project. ISBN: 87-89143-21-3. Internet version: http://www.seagrasses.org Legal Status Zostera marina is listed in the EU Habitats Directive as qualifying interest for Special Area of Conservation (SAC) site designation. Since 2004 the grass is also on the ‘List of Threatened and Declining Species and Habitats’ drawn up by the OSPAR Commission. Designation: Almost all of the known sea grass beds in Ireland are located in protected sites. However official Z marina records did not include Lough Foyle as a bed location and the species rich outer estuary is not designated as Natura 2000 site under the Habitats or Birds Directive. Problems of ownership and responsibility for biodiversity and Nature law enforcement in this cross border site would pose problems if the sublittoral was protected. Recent designations of Marine Protected Areas (MPA) under the OSPAR Convention would also have been a feasible way of increasing protection., but this was carried out without consultation and did not include this site.

1.2 Coastwatch Survey work and Results

The Western shores and shallow water of outer Lough Foyle were checked for Zostera

seagrass - from Quigley’s point in the mid lough northwards to Inishowen Head at the open

sea. The aim was to locate sea grass patches and beds; and if found, take simple recordings

as a first citizen science scoping exercise. The 2012 survey took place on suitable spring low

tide days between May and October 2012. A team of local divers and Coastwatchers with

traditional knowledge of the area participated, initially coordinated by Karin Dubsky, later

by the local Foyle Coastwatch group. Further records were gathered, during the autumn

2012 Coastwatch survey where blades of sea grass swept up and visible landward edges at

spring low water were noted.

Summary of Results: A string of Seagrass Zostera marina patches and beds were found

straddling the Lough Foyle Donegal coast from the Salt Pans (south of Carrickarory

Pier) to north of Glenburnie Bay just short of Greencastle. One may characterise the

distribution of the plant found so far as within a roughly 8 km length of shore in 4 distinct

beds, where plant density was > 30% of the seafloor. Beyond that outlying patches and

clumps were found. ( A fifth bed was located on the NI side of the Lough)

The beds straddling the Donegal shore were 30-80 m wide and 180 to almost 500m length,

occupying a band of sandy to sandy mud shell sediment, between ~0.4 and 1.4m deep

at mean low tide. Blades of dislodged grass and rhizomes were found in the same survey

area, as well as further south at Quigley’s Point and on Shroove beach at the open sea.

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One of the 4 Donegal beds fringes Carnagarve beach and extends into the path of the

proposed sewage discharge pipe. The landward boundary in waist deep water at low tide,

coming further inshore than indicated on the Natura map based on the 2006 survey. At the

beach rocky outcrop seaward end it is at its widest.

Google map: Showing provisional seagrass bed locations in outer Lough Foyle and their landward boundaries in 2012 Coastwatch Zostera marina citizen science survey. Map prepared by Brian Wingham. Proposed sewage discharge pipe bed highlighted by white overlay.

Limiting factors: The upper and lower limits appeared to be determined by depth of water,

as the sediment remained suitable above and below the band occupied. Plant exposure at

lowest spring tides may be causing desiccation and so determining the landward shallow

water limits, while deeper water may pose a transparency problem for photosynthesis and

or experience stronger currents.

Plant health varied from excellent quality with lush, dense clean dark green exceptional

long blades (some > 1.5m) in the seaward facing shelter of the old Moville pier, to healthy

looking ~ 0.5 – 0.8m high swart in the majority of the beds and patches, down to part

discoloured plants due to massive epiphyte cover converging into fast growing opportunist

eutrophication indicator Ectocarpus veils between plants in worst hit areas . Bright green

shoots growing among these were short and young, indicating potential for recovery. The

worst hit areas were in the bed in the shallow bay north of Moville around Carnagarve

beach. Bed quality improved again further north from Glenburnie.

Associated Biota: This initial scoping survey did not include scientific biota recording.

However it was noted – especially in the May and July surveys - that before even reaching

the beds and once the boat was above a bed that the seaward limit was full of small fish.

Juvenile fish also flushed from grass beds when approached from shore side and molluscs,

mainly winkles were gr\zing on the seagrass.

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Comparison with past records: Beds which were found occupied the same general locations

as pointed out by fishermen, divers, a lough pilot and elderly people asked to remember

the grass from swimming or boating in the area. Though several recollections suggest the

beds extended further seawards around and were larger in the past. Several locals

independently pointed out further beds which used to be in the Moville area, but though

the locations were well searched no trace of these beds were found.

Nutrient inputs: The area was searched for obvious local high nutrient level discharges

around the poor quality Carnagarve bed area, but there were neither high nitrate values in

discharge points, nor areas of extra lush grass in the hinterland, which could point to

episodes of high local nutrient input (e.g. excessive slurry spreading). However the Moville

raw sewage outfall plume was seen to move along shore on an outgoing tide in the seagrass

band line on one calm July day site research visit. Any light onshore wind would ensure the

fresh water plume would stay in the bay and feed seagrass and filamentous nutrients

released may be responsible for the observed seagrass bed eutrophication.

Survey Conclusions:

Parts of the Lough Foyle Donegal coast still contain extensive Zostera marina seagrass beds.

However going by local knowledge the range and hectares covered have reduced

significantly in the last few decades. Zostera grass was missing at Moville peer and just

north, with first location of the next bed north in poor condition with part smothered plants,

matching the descriptions of eutrophication impacts in the literature.

Given the value of the habitat it would be important to commence a more detailed

monitoring of this coastal area. Resources would be well spent if this could be done in

cooperation with the local committed public who all worked as volunteers on the scoping

survey. Further it is urgent to tackle the known source of nutrient enrichment – raw sewage

discharge at Moville peer and ensure that no other sources contribute.

Goals of Sewage Treatment: The primary goals of planning waste water treatment and

investing in the infrastructure is to remove the source of nutrient enrichment which is

damaging biota and coastal habitats and source of microbiological water pollution, threating

consumers of edible shellfish and swimmers in summer. Added impetus to carry out the

work is provided as it is urgent to become compliant with EU and national water legislation

and to encourage tourism activity.

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Sewage Treatment Plant proposal and impacts of the discharge pipe

2.1 Construction phase:

The pipe is to be set into the intertidal substrate which requires dredging an

underwater trench, or digging it at low tide. As the substrate is a coarse sand/shell

mix and the ground water table is near the surface, the trench wall gradient will be

a v shaped.

The method described in the EIS ( section 4.3) is:

The installation of the treated effluent outfall pipeline will be by open trenching overland (including the intertidal area), to a depth of 1m. However, once past the low water level, the pipe will be laid directly on the Lough bed.

The trench dimensions are given (section 5.2) ‘A pipe trench measuring approx. 1m in width

and 1.5m in depth will be excavated to accommodate the outfall pipe.

Finally the pipe is to be on the seabed – which is to be levelled – once it enters the

sublittoral. No information as to securing the pipe on the sea bed parallel to strong

tidal currents is provided.

The Natura map copied below shows the proposed path of the pipe from land through the

shore. The sea grass bed is roughly delineated by wide stripes rather than an actual bed

edge.

Concern with EIS data:

The trench dimensions are unrealistic for intertidal sandy shell sediment.

If the pipe is to be buried in a trench 1.5m deep then the trench width at the

intertidal surface could not possibly be 1 m unless they were planning to shutter it

which would be impossible if you intend to do it by barge at high tide. The trench

would have to be at least 4 m wide to hold. The fraction coefficient would be further

reduced by ground water which would turn the base of the trench into milkshake

like material, where the upper sand would just slump in under its own weight into

the 1.5 m deep hole.

There is no mention of where the spoil from pipe excavation in the intertidal is to be

stored. If on land that would entail moving machinery up and down the shore

damaging adjacent areas.

The seafloor is to be levelled where the pipe comes to the surface and travels out

in the sublittoral There is no mention of extend, or what that would do the seagrass

bed.

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2.2 An estimate of direct loss:

Seagrass beds are stable in their core, but can extend or contract in a given year as detailed

monitoring over 2 years by UCC in Cork and Kerry has shown. If we take the bed to be

crossed by the discharge pipe as approx. 60m with bed levelling involving only a 4 m wide

band - seen as very conservative going by marine discharge pipes laid in other sites - it

would already cause loss of approx. 240 sq m of Zostera marina habitat.

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2.3 Indirect loss

Sediment plumes from trench digging and infill as well as bed levelling during construction

are certain to move into the Zostera bed, especially the seaward end where the bed is at its

widest. This will cause increase in water turbidity, reduced light penetration impeding

photosynthesis which may be the tipping point causing bed loss as this seagrass bed is

already stressed.

The pipe is to go through that curtain and travel on the seafloor through the seagrass and

beyond. A long obstacle on the seafloor creates local changes in seafloor hydrology which

have not been assessed in the EIS. Other researchers have shown that ‘physical disturbance

and removal of plants can lead to increased patchiness and destabilization of the seagrass

bed’ (Davison & Hughes, 1998).

D.M.Davison, D.J.Hughes, 1998. Zostera Biotopes (volume I). An overview of dynamics and sensitivity characteristics for conservation management of marine SACs. www.ukmarinesac.org.uk/pdfs/zostera.pdf · PDF file

A review of Z marina sensitively to these and other factors was carried out in Plymouth

marine lab and used by Dr Harvey Tyler-Walters (20081) to create a sensitively key –

abridged version below).

The Table is interactive if viewed electronically. Full table includes further factors like noise

and chemical factors not included here. The sensitivities table also posted on the MARlin

website is used as guidance by government and researchers in the UK: see -

http://www.marlin.ac.uk/speciessensitivity.php?speciesID=4600

Based on that table and work planned there is a risk of complete loss of this seagrass

bed.

1 Zostera marina. Common eelgrass. Marine Life Information Network: Biology and

Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological

Association of the United Kingdom. [cited 05/11/2012]. Available from:

http://www.marlin.ac.uk/reproduction.php?speciesID=4600

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Click factor name to

view rationale Intolerance Recoverability Sensitivity

Substratum Loss High

Very High

Smothering High

Very High

Increase in suspended

sediment

Intermediate Moderate Moderate

Desiccation Intermediate High Low

Increase in emergence

regime

Intermediate High Low

Increase in water flow

rate

Intermediate Moderate Moderate

Increase in

temperature

Tolerant Not relevant Not sensitive

Increase in turbidity High

Very High

Increase in wave

exposure

High

Very High

Visual Presence Tolerant Not relevant Not sensitive

Abrasion & physical

disturbance

Intermediate Moderate Moderate

Displacement High Low High

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Irish recent example of observed impacts:

In summer 2011 Coastwatch surveyors noted areas of Zostera marina stress and dieback in

Tramore Backstrand Co Waterford. The tidal channel in which the seagrass was growing

had been exposed to silt plumes from lagoon works 300 m away. A second channel not

exposed to the silt load continued to have healthy seagrass.

3.Recovery from the construction phase

As mentioned above - if a marine habitat with significant structure and size is interfered

with – by cutting a gap, adjacent sediment is levelled and a pipe laid onto it, protruding

perpendicular to the main current over flat ground, the local hydrology will change.

The effect has not been modelled and we have virtually no experience of such post

construction Z marina bed restoration in Ireland and very little in Europe. It cannot be

assumed that this bed will repair. Research elsewhere has shown that.

It is more likely that plants will not be able to recolonize the newly made ground for some

time.

4. Sewage treatment operation phase:

Although the sewage discharge will have received secondary treatment it will still entail the

release of warm nutrient and chemical enriched fresh water.

Zostera marina is sensitive to heat, fresh water and nutrient enrichment. It is therefore of

critical importance to model how often the discharge plume would travel under different

tide and wind directions into the seagrass beds which are running behind and either side of

the discharge point

The EIS did not provide this information. It did not even map the sea grass beyond the

immediate outfall line.

5. Sewage treatment emergency overflows:

Emergency situations occur and the predictable risk needs to be taken into account. The

causes include malfunction of pumping station, blockage and toxic pollutants entering the

sewer and sewage treatment system, causing the microbs which treat the sewage to die off

on mass. Part or untreated sewage with or without added chemical contamination can

then be discharged.

If raw discharge with sanitary material debris is the problem then this can be caught in the

Zostera bed between plants and remain there for some time. Apart from smothering and

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high nutrient levels aiding local plankton blooms and opportunistic epiphyte growth it is

aesthetically extremely off putting.

If the problem is a release of chemicals – eg Creosote detected in Rings end on several

occasions, then the discharge could both kill or damage the Zostera bed and the species rich

biota associated with it.

Pipe Damage: One feature common to most sea outfalls is that they have a limited life span.

In this case the pipe is only protected while on land and the intertidal. Once below low

water, it is to be free standing, anchored to the sea bed, with currents running

perpendicular to the pipe. A discharge pipe set into the North Wexford coast at Tara Glen

in 2008 was lifted by storms in winter 2010.

Oyster The seaward line of the seagrass bed – that is the area between sea grass and

mouth of the proposed discharge - used to support a native oyster – Ostrea edulis bed until

15 – 20 years ago (Whiskey Rock fishermen including Paul Mc Laughlin - personal

communication) . Today only empty shells remain. While the cause it not known, I the fact

that the seagrass is in poor health inkeeping with nutrient enrichment here, may point to

one stress factor also affecting oysters.

If the Moville raw sewage outfall was removed it may be an area to priories for oyster bed

restoration. Especially as native oyster stock is still found in the lough and the species is

now red listed for protection and a species action plan has been drawn up in Northern

Ireland. In L Ryan UK, a planned sewage treatment plant discharge pipe was diverted from

the lough to the open sea after risks of pollution impacts in case of malfunction were

deemed too high. (Tristan Hugh Jones 2011)

6. Conclusions

The outer Lough Foyle Donegal coast has special high biodiversity quality including 4 shallow sublittoral seagrass beds. One of these forms an outer curtain around a shallow bay with Carargva beach as the most popular bathing water in the Donegal outer L Foyle area. While there are perhaps 3 or 4 other popular bathing waters with adjacent sublittoral seagrass beds in Ireland I do not know of one where the seagrass comes so far inshore that even a 10 year old can walk out to it at low tide. This provides extra educational value and chances for citizen involvement in protection. A sewage treatment plant is urgently needed for this area of the Inishowen peninsula and well overdue under EU law It is intended to reduce the lough water loading with nutrients, organic matter, chemicals and microbs. This will benefit direct human recreational use, quality of products from the sea , quality of shellfish water and benefit the biodiversity we depend on. High biodiversity value sensitive biota like the seagrass beds especially the bed at Carnagarve beach which is showing significant signs of stress from nutrient enrichment would benefit – assuming the treated sewage discharge is located in the right place and the plant is managed well.

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The proposed discharge pipe location at Carnagarve beach is not suitable due to the high

biodiversity value of the area and knowing:

- the damage which is certain to occur in construction to a Z. marina sea grass bed

- the lack of knowledge of seagrass biota in this area as no study was carried out

- the lack of sea grass restoration experience and lack of measures proposed

- the risk of total seagrass bed loss due to initial destabilisation and stress in the

construction phase followed by further stress every time the warm nutrient rich

fresh water backs up into the seagrass bed behind and beyond it on onshore winds.

Further treatment plant or pumping station malfunctioning has to be taken into account. If

that happens with onshore winds it would cause raw sewage with sanitary debris to be

discharged and lodged in the seagrass bed (if or while it still remains) .

Looking at the review and OSPAR conclusion of seagrass beds in Europe the conclusions

apply - While reductions may be rapid, recolonisation may require long time periods. Once

seagrass habitats are lost, restoration (if possible) is therefore likely to require considerable

resources.

7. Recommendations

The OSPAR Commission report on seagrass asks in section 7 ‘What action should be

taken measures at an OSPAR level (to protect, manage and restore seagrass)? The

guide which follows leads with one key point: Efficient management must focus

upon maintaining existing populations through protection of Zostera beds and

potential seagrass areas.

I recommend that this guidance be applied in all areas where seagrass can still be found in

Ireland. That is in less than 100km of >7000 km of our shallow intertidal shoreline. That

means urgent address of current raw sewage discharge problems and avoidance of bed

damage from any construction works.

The discharge for the planned treatment plant should be relocated to ensure it is also

suitable from a biodiversity point of view. There are low sensitivity locations, away from

valuable and threatened sea grass beds and prime restorable native oyster ground . Just

like the planning decision in Lough Ryan

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