Coastal Realignment at RSPB Nigg Bay Nature Reserve. Steph Elliott Site Manager, Central Highland Reserves

Transcription

1 Coastal Realignment at RSPB Nigg Bay Nature Reserve Steph Elliott Site Manager, Central Highland Reserves September

2 Contents 1. Summary Introduction The Nigg Bay Coastal Realignment Site The Nigg Bay Coastal Realignment Project Key Events History of Monitoring Vegetation Development Benthic Invertebrates Use by Wintering Waterbirds Sedimentation, Geomorphology & Sea Wall Condition References Acknowledgements Appendix

3 1. Summary Background The RSPB s Nigg Bay nature reserve in the Cromarty Firth is the location of Scotland s first ever managed coastal realignment, undertaken in February A 25ha field known locally as Meddat Marsh on the edge of Nigg Bay was the site and was reconnected to the sea for the first time since the 1950s. Two breaches were dug into the existing sea wall allowing the tide to enter the field which had been used as rough grazing and never ploughed. The aim was to allow the tide to re-establish saltmarsh habitat in the area to replace habitat lost in the past and prepare for future losses as a result of sea level rise. The works cost 47,480 and was funded by the Heritage Lottery Fund, SNH, SEPA and the RSPB. A programme of monitoring the site has gone on for 15 years from before the breach to the present day. Results Six months after the seawall was breached 3 saltmarsh plant species had colonised the site. By year 3 saltmarsh plants dominated and by 2011 (9 years after breach) all monitoring plots bar one were saltmarsh. This colonisation has been quicker than expected and the new saltmarsh is now of the same composition as the surrounding areas. Very little saltmarsh has been lost outside the managed realignment site so any negative impact of the work has been small. However, the project has increased the area of saltmarsh habitat in Nigg Bay by 23%. It has also added nearly a km of new saltmarsh edge and 5 hectares of intertidal mudflat all very important for foraging birds. Four surveyed species of mud-dwelling invertebrates (snails, worms and shrimps) were found on the site in the first winter after the tide flooding in, much quicker than expected. These are key food for waterbirds. In the first winter after the breach, 3 waterbird species used the site but this jumped to 19 species in the second winter and now stands at 25 species. The managed realignment site is one of the last areas in the whole of Nigg Bay to be covered by seawater on the incoming tide. It provides valuable extra feeding areas as the tide comes in and safe roosting areas at high tide. During windy conditions and in high spring tides it is an essential refuge for up to 2,000 waterbirds. Over the 10 years there has been 20-30cm of sedimentation in some parts of the site and saltmarsh creek systems have developed. The new sea defence around the site remains strong and provides greater protection to inland areas than the original sea wall. 10 years on from Scotland s first ever managed realignment project the results show that the project has been a success. The saltmarsh habitat returned more quickly than expected, as did the marine animal life. As a result the many species of waterbirds use the area and it has become an essential feeding roosting and refuge are in Nigg Bay. 3

4 2. Introduction The RSPB s Nigg Bay nature reserve in the Cromarty Firth is the location of Scotland s first coastal realignment, undertaken in This technique for creating or restoring new intertidal habitats involves breaching the defences of an area of land currently separated from the sea in order to allow tidal conditions to (re)establish. Over the past few centuries, significant areas of intertidal habitats have been claimed from the sea around the coasts of Britain to provide agricultural ground for grazing and crop production. This was done through a combination of sea wall defences and drainage. In February 2003, after several years of planning and studying the potential realignment site, two 20m breaches were dug into the existing sea wall at the field known locally as Meddat Marsh in Nigg Bay, allowing the tide to enter the field for the first time since the 1950s. One of the main reasons for creating new saltmarsh at Nigg Bay was to mitigate for past and future losses of saltmarsh and other intertidal habitats due to climate changes and sea level rise. These habitats are important for the nationally and internationally important passage and wintering birds that Nigg Bay that use the bay and wider estuary. A study of the changes in saltmarsh habitat in Nigg Bay (Johnstonova & Cowie 2001) showed that 39.4ha were lost between 1946 and 1997, representing a 36% loss. A further 93ha of intertidal mudflat was claimed for the building of an oil terminal and fabrication yard between 1970 and The Nigg Bay Coastal Realignment Site The coastal realignment site (referred to in this report as Nigg Bay CRS) is a 25ha field on the northern side of Nigg Bay (Figure 1). It was chosen as a suitable site for coastal realignment for a number of reasons, the most important being that until relatively recently it had been under tidal influence, and that it is adjacent to areas currently used by large numbers of wintering waterbirds. The field was the last part of Nigg Bay to be claimed from the sea in the 1950s. It can be seen from the 1872 Ordnance Survey map that there appears to have been some mudflat as well as saltmarsh (shown as liable to floods on the map) present in the field at that time (Figures 2 and 3). The wall that was built in the 1950s, therefore, had little or no saltmarsh in front of it to protect it, and thus the wall was constantly being eroded by wave action. The field was also difficult to keep dry enough for agricultural purposes and was only used for rough grazing.. At one stage, diesel pumps were employed to drain this low-lying area of marsh, but this was eventually abandoned. As it had not been ploughed, much of the topography (including relict saltmarsh creeks) was still present in the field when the coastal realignment was undertaken. Figure 1 Location of Nigg Bay Coastal Realignment Site (CRS) RSPB nature reserve Coastal realignment site 4

5 Figure 2 Comparison of Ordnance Survey mapping Modern 1:25,000 Ordnance Survey map 1872 Ordnance Survey map Figure Ordnance Survey map showing the locations of sea defences built in the 1950s (dashed line) A Design and Impacts study was commissioned from Babtie Group by RSPB in 2002, to look at all the factors and consequences of undertaking a realignment project at this location, and to identify the most appropriate design for promoting the development of intertidal habitats. Subsequent ecological monitoring has included studying vegetation development, colonisation by benthic invertebrates and use by wintering waterbirds, and to a lesser extent, sedimentation development. 5

6 4. The Nigg Bay Coastal Realignment Project In 1997, RSPB made initial approaches to a neighbouring landowner about the possibility of purchasing additional intertidal land to add to its nature reserve at Nigg Bay. It was at that stage that RSPB were asked if they would also like to purchase the Meddat Marsh field. As the issue of sea level rise was coming further up the agenda in Scotland, it was realised that this field may be a good location to restore intertidal habitats through coastal realignment. Negotiations started, and purchase of the coastal realignment site and adjacent intertidal land was completed in March Most of the sea walls in Nigg Bay were in good condition, but the sea wall at Meddat Marsh was in poor condition due to erosion. A secondary defence around the outside of the field already existed from previous reclamation schemes (this defence can be seen already in existence on the 1872 Ordnance Survey map). Consultations with statutory bodies and local communities about the potential realignment began shortly after the site was purchased. Whilst an Environmental Impact Assessment was not required for this project, a Design and Impacts study (a feasibility study) was commissioned from Babtie Group. This was completed in August The Design and Impacts study showed that coastal realignment at Nigg Bay CRS was feasible, and that intertidal habitats (saltmarsh and intertidal mudflats) were predicted to develop. The study modelled flooding of the site under various tidal conditions, and also showed that the project would have a negligible effect on the tidal regime and coastal processes of Nigg Bay and the Cromarty Firth. The study modelled different engineering options - a single breach, two breaches or completely removing the sea wall. Hydraulic modelling informed the decision that two 20m breaches, lining up with the relic drainage channels, was the preferred design. This design provided sufficient inundation by the tide, whilst affording relatively sheltered conditions for the establishment of vegetation and maintaining sufficient velocity to allow creek redevelopment. The study also gave specifications for the other required engineering works, specifically the blocking of culverts to a drainage channel behind the sea wall, and the strengthening of the secondary defences to 1 in 50 year predicted storm surge height. The study also modelled the likely zonation of saltmarsh communities within the coastal realignment site, using the elevations of the site. This showed that there was sufficient topographical variation for a full zonation of saltmarsh communities to be restored without further engineering works (Figure 4). 6

7 Figure 4 Predicted zonation of saltmarsh communities post breach (from Design & Impacts study) mudflat and pioneer saltmarsh mid saltmarsh high saltmarsh Following the completion of the Design and Impacts study, a contract for the required engineering works was put out to tender and a contractor appointed. The removal of material to create two 20m breaches in the sea wall was undertaken over two days in February Photo 1 Digging the breaches 7

8 Photo 2 Blocking culvert to ditch behind old sea wall Photo 3 Building up northern secondary defence 8

9 Permissions, licences & consents Various permissions, licences and consents were required from statutory bodies in order to undertake the coastal realignment project at Nigg Bay. At the time of planning the Nigg Bay project, several coastal realignments had already been undertaken in England and the suite of consents required there had become well known. However, the Nigg Bay project was the first of its kind in Scotland and therefore there was no experience of the consents required, or the processes required for securing those consents, under the Scottish system. Consequently, the RSPB drew up a long list of potential regulations affected and the relevant agencies were consulted. A full commentary on these regulations and agencies is presented in the Lessons Learned (Chisholm, Kindleysides & Cowie 2004) report, and are summarised below. Planning Permission Town and Country Planning (Scotland) Act (1997) SSSI Consent Wildlife and Countryside Act (1981) Appropriate Assessment Habitats Regulations (1994) Environmental Impact Assessment (EIA) Environmental Impact Assessment (Scotland) Regulations (1999) Consent for coastal protection works Coastal Protection Act (1949) part I (coastal protection) Consent re marine transport & navigation Coastal Protection Act (1949) part II (marine transport and navigation) Flood Prevention (Scotland) Act (1961) (as amended by the Flood Prevention and Land Drainage (Scotland) Act 1997) and Land Drainage Act (Scotland) (1958) FEPA licence Food and Environment Protection Act (1985) Not required. (May be required elsewhere) Required & granted. Required & granted. Not required*. (May be required elsewhere) Required & granted. Not required. Not highlighted as an issue by any consultees during consultation process. Required & granted. * although an EIA was not required, RSPB commissioned the Design and Impacts study which included modelling of potential impacts to the wider estuary etc, as well as various realignment design scenarios. Project Costs Table 1Costs of the initial phase of the coastal realignment project, excluding land purchase Expenditure Cost, Design and Impacts study 22,400 Secondary defence upgrade 2,100 Digging of breaches; culvert blocking 1,470 Tree removal from sea wall 1,100 Fencing 8,450 Topping 1,350 Survey & monitoring (pre-breach & PhD) 8,500 Promotional Video 1,400 Launch event 600 FEPA licence 110 TOTAL COST 47,480 Staffing costs for the duration of the project implementation phase (March 2001 to March 2003) were estimated to be FTE, although this was covered by various members of staff. The site manager for the reserve took on the role of project management. Other staff involved included the reserve ecologist, land agent, assistant warden, marine policy officer and communications/pr staff. 9

10 Other potential costs: Design & Impacts study RSPB provided the topographic data and undertook all the consultation. If these works were undertaken by the consultant, the costs of the D&I Study would have been greater. Secondary Defences there was already a secondary defence surrounding the coastal realignment site, and so the only works required were to strengthen these to the required flood protection standard. Completely new secondary defences would have cost considerably more. Profiling no engineering works to profile new creek systems or variable topography were required. Schemes where the site has been isolated from the sea for a long time, or with a history of cultivation, may require this at potentially considerable cost. Surveys and monitoring whilst some work was contracted out, the initial post-breach vegetation, invertebrate and sediment monitoring was carried out through a PhD study, and all of the bird monitoring has been undertaken by RSPB staff and volunteers. Funding The project was part funded by Heritage Lottery Fund and Scottish Natural Heritage. A small grant was also received from Scottish Environment Protection Agency, through the SEPA Habitat Enhancement Initiative. A legacy from the Miss EMP Scott Will Trust was also received. 10

11 5. Key Events Dec 2000 Feb 2001 Mar 2001 May Oct 2001 Jun 2001 Aug 2001 Dec 2001 Feb 2002 Mar 2002 Funding sought and gained for the project CRS purchased Local community consultation CRS re-fenced, topped and then grazed with cattle Project management team formed; first planning meeting held Statutory Authorities & Scottish Executive Departments initial consultation sent out Historical changes in saltmarsh at Nigg Bay published (Johnstonova & Cowie 2001) Baseline NVC vegetation and invertebrate surveys (McHaffie 2002) Baseline topographic survey Design & Impacts (feasibility) Study specification drawn up & sent out to tender D&I Study tenders received. Babtie Group appointed. Visit to Essex coastal realignment sites by Project Team, SNH staff and Community Council chair. Extra funding required sought & received. Aug 2002 Design & Impacts study completed. (Babtie Group 2002) Statutory consultation & local consultation undertaken. Aug Oct 2002 Nov 2002 Dec 2002 Feb 2003 Licences and consents processed. Contract for CRS engineering works put out to tender and contractor appointed. PhD to study physical & biological responses to coastal realignment started, in conjunction with University of Stirling. Engineering works undertaken secondary defences built up & culverts blocked 11 th & 12 th Feb 2003 Sea wall breached with two 20m breaches Feb Mar 2003 Feb 2003 onwards Aug 2003 Media and local launch events held Post breach monitoring started, through PhD study 3 saltmarsh plant species had colonised the realignment site Feb 2004 Lessons Learned report produced. (Chisholm, Kindleysides & Cowie 2004) Oct 2004 Bird monitoring - 10 waders,9 wildfowl species using the realignment site Sep 2007 PhD on ecological development completed. (Crowther 2007) 2008 Decision made to cease grazing whilst saltmarsh vegetation develops Coastal realignment site entered into SRDP Management of Wetland option 2009 Vegetation and invertebrate monitoring repeated (Kennerley 2009) RSPB hosts BTCV Saltmarsh Apprentice, used realignment site for training in vegetation and invertebrate monitoring (Foot & Elliott 2012) Nov 2013 Autumn years on presentation compiled & given to RSPB, SNH etc. 12 years on report published 11

12 6. History of Monitoring RSPB recognised early in the project the importance of monitoring the ecological development of Scotland s first coastal realignment. With the site being geographically remote from many other sites, such as those in East Anglia, the composition of the vegetation, invertebrate and bird communities are slightly different. Monitoring can be categorised into four main sections: - Vegetation: the colonisation by saltmarsh plants, and development of saltmarsh communities - Benthic invertebrates: particularly of species important as food sources to wintering waterbirds - Use by wintering waterbirds - Sedimentation & geomorphology Pre-breach monitoring focussed on setting up vegetation, sedimentation and intertidal invertebrate monitoring plots. This work is detailed in McHaffie (2002). Monitoring in the initial four years after breaching the sea wall was undertaken by a PhD study, carried out by Amy Crowther and supervised by University of Stirling and RSPB s Reserves Ecology department. After this initial intensive period of monitoring, the frequency of monitoring was reduced due to lack of resources and requirement. Since the production of the PhD study in 2007, the vegetation and invertebrate monitoring has been repeated twice using a contract ecologist (Kennerley 2009) and a partnership apprenticeship (Foot & Elliott 2012). Some work on geomorphology has also been undertaken by MSc students (Tawse 2014, Rawlinson 2014), and there is further scope for this type of project. Formal bird monitoring has been supplemented by regular monitoring of wintering waterbirds via the Wetland Bird Survey (WeBS) scheme and ad-hoc informal monitoring by reserves staff (e.g. collecting records during site visits). Table 2 History of biological monitoring at Nigg Bay CRS Seasons since breach* Year / Month Monitoring S / Aug Vegetation (1) W0 2001/02 Birds - WeBS 2002 (no monitoring) W0 2002/03 Birds - WeBS S / Sep Vegetation (2) / Benthic invertebrates (2) W1 2003/04 Birds intensive monitoring (2) Birds breeding survey & WeBS S / Jun Vegetation (2) / Benthic invertebrates (2) W2 2004/05 Birds intensive monitoring (2) Birds breeding survey & WeBS S / Jun Vegetation (2) / Benthic invertebrates (2) W3 2005/06 Birds intensive monitoring (2) Birds breeding survey & WeBS S / Jun Vegetation (2) / Benthic invertebrates (2) W4 2006/07 Birds intensive monitoring (2) Birds breeding survey & WeBS S (no monitoring) W5 2007/08 Birds breeding survey & WeBS S (no monitoring) W6 2008/09 Birds breeding survey & WeBS S / Aug Vegetation (3) / Benthic Invertebrates (3) W7 2009/10 Birds breeding survey & WeBS 12

13 S (no monitoring) W8 2010/11 Birds breeding survey & WeBS S / Aug Vegetation (4) / Benthic invertebrates (4) W9 2011/12 Birds monitoring through tidal cycle (4) Birds breeding survey & WeBS S (no monitoring) W /13 Birds breeding survey & WeBS S (no monitoring) W /14 Birds breeding survey & WeBS S Vegetation (5) / geomorphology (5) W /15 Birds breeding survey & WeBS * S = spring/summer season; W = autumn / winter season (1) McHaffie (2002). Baseline survey and monitoring of change to saltmarsh and wet grassland communities prior to removal of the sea wall at Meddat Marsh. RSPB Internal Report (2) Crowther (2007). The restoration of intertidal habitats for non-breeding waterbirds through breached managed realignment. PhD, University of Stirling. (3) Kennerley (2009). Nigg Bay Coastal Realignment 7 years on. RSPB Internal Report. (4) Foot & Elliott (2011). Monitoring of ecological development at the coastal realignment site, Nigg Bay. RSPB Internal Report. (5) 2014 MSc student reports 13

14 7. Vegetation Development Vegetation Communities The development of saltmarsh habitat (along with intertidal mudflats) is one of the key aims of the Nigg Bay CRS. This habitat provides both feeding and roosting opportunities to internationally important numbers of wintering waterbirds in the UK, as well as providing wider benefits such as sea wall protection and flood protection. Some evidence suggests that development of recognisable saltmarsh communities may take 5-6 years, and that relatively natural communities may take years to develop (Babtie, 2002). Sixty vegetation monitoring plots were set up prior to breach. These plots cover a range of elevations and positions in the tidal frame. The development of the vegetation communities, using the National Vegetation Classification, has been monitored six times post breach, with baseline monitoring completed in 2001 prior to breach. Figure 5 Map showing locations of vegetation monitoring plots Prior to breaching the sea wall in 2003, the Meddat field had been used for rough grazing. This was reflected in the vegetation types found in the field pre-beach, with mesotrophic grasslands and rush pasture being the dominant vegetation type. This community is found on a wide range of soils, and is typical of rough grazings in western Britain and north-east Scotland. A total of 37 plant species were found in the field prior to breach, and no rare species were found. It was expected that species diversity would decline post-breach, as the number of species tolerant to tidal conditions ( halophytes ) is low. In the first years following breach it was difficult to assign vegetation communities. This is because the National Vegetation Classification is based on mature vegetation communities, and following the reintroduction of tidal conditions the vegetation communities were in a state of transition. However, when post-breach monitoring was done in S7 and S9 the vegetation communities were mature enough to assign NVC communities. The following chart groups the NVC communities into broad vegetation types in order to show the transition from rush dominated pastures prior to breach to saltmarsh communities nine seasons after breach. 14

15 Figure 6 Change in vegetation types from S0 to S9 In the immediate period of time following breaching of the sea wall, there was a rapid transition of vegetation types from terrestrial mesotrophic grasslands to halophyte-dominated saltmarsh communities. In the first monitoring seasons following breach there many plots were covered by bare mud, as the terrestrial vegetation died and intertidal sediments were deposited due to exposure to tides. By 2009 (seven seasons after breach) rush pastures no longer formed a constituent of the vegetation in the CRS. By 2011 (nine seasons after breach) 56 of the 60 vegetation monitoring plots were saltmarsh, with only one plot now bare mud. 15

16 Figure 7 Maps of vegetation change in monitoring plots Summer 0 (pre-breach 2001) Summer 1 (post-breach 2003) Summer 2 (2004) Summer 3 (2005) Summer 4 (2006) Summer 7 (2009) Key Summer 9 (2011) rush pastures mud grass-dominated inundation saltmarsh 16

17 Table 3 NVC classification by season since breach, in order of elevation (highest to lowest) Quadrat Elevation (m) Prebreach S1 S2 S3 S4 S7 S MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG6 MG11 SM16d MG9 MG10 MG6 MG10 MG10 MG6 MG6 MG11 (MG13) MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG6 MG11 (MG11) MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG6 MG11 SM16d MG10 MG10 MG6 MG10 MG10 MG6 MG6 MG10 (MG11) MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG6 SM16 SM16d MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG6 SM16 SM16d MG9 MG10 MG6 MG10 MG10 MG6 MG6 SM16 SM16d MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG6 SM16 SM16d MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG11 SM16 SM16d MG9 MG10 MG6 MG10 MG6 MG10 MG6 MG11 SM16 SM16d MG10 MG10 MG10 MG10 MG6 MG11 SM16 SM16d MG9 MG10 MG6 MG6 MG10 MG11 MG11 MG11 SM MG10 MG10 MG6 MG6 MG10 MG11 MG11 MG11 SM16d MG9 MG10 MG6 MG6 MG10 MG11 MG11 SM16 SM12a MG10 MG10 MG6 MG10 MG11 MG11 SM16 SM16d MG10 (SM) MG10 MG11 MG11 SM16 SM16d MG9 MG10 MG6 MG6 MG10 17 MG10 MG6 MG11 MG11 SM12a MG10 (SM) (SM) (SM) (SM) SM13a SM12a MG10 (SM) (SM) (SM) (SM) SM13a SM MG10 (SM) (SM) (SM) (SM) SM13 SM13a MG9 MUD MUD (SM) (SM) SM12 SM MG9 MUD (SM) (SM) (SM) SM13 SM12a MG10 MUD (SM) (SM) (SM) SM13a SM13a MG10 MUD MUD (SM) (SM) SM13a SM MG10 (SM) (SM) (SM) (SM) SM13a SM MG9 MUD MUD (SM) (SM) SM12 SM13a MG10 MUD MUD (SM) (SM) SM13a SM13a MG9 MUD (SM) (SM) (SM) SM13a SM13a MG9 MUD MUD (SM) (SM) SM16 SM MG9 MUD (SM) (SM) (SM) SM13 SM MG10 MUD MUD (SM) (SM) SM13a SM13a MG10 (SM) (SM) (SM) (SM) SM13a SM MG10 MUD MUD (SM) (SM) SM13a SM13a MG10 MUD MUD (SM) (SM) MUD SM12a MG10 (SM) MUD (SM) (SM) SM13 SM13a MG10 (SM) (SM) (SM) (SM) SM12 SM13

18 Quadrat Elevation (m) Prebreach S1 S2 S3 S4 S7 S MG10 MUD (SM) (SM) (SM) SM13a SM MG10 (SM) (SM) (SM) (SM) SM13a SM12a MG10 MUD MUD (SM) (SM) SM13a SM12a MG10 MUD (SM) (SM) (SM) SM13a SM MG10 MUD MUD (SM) (SM) SM13a SM MG10 MUD (SM) (SM) (SM) MUD SM MG9 MUD MUD (SM) (SM) MUD SM MG9 MUD MUD (SM) (SM) SM13 SM MG9 MUD MUD (SM) (SM) SM8 SM MG10 MUD (SM) (SM) (SM) SM8 SM MG9 MUD MUD (SM) (SM) SM8 SM MG9 MUD MUD (SM) (SM) MUD SM MG9 MUD MUD (SM) (SM) MUD SM MG9 MUD MUD (SM) (SM) SM8 SM MG10 MUD MUD MUD (SM) MUD SM MG10 MUD MUD (SM) (SM) SM8 SM MG10 MUD MUD (SM) (SM) SM13 SM MG10 MUD MUD (SM) (SM) SM8 SM MG9 MUD MUD (SM) (SM) MUD SM MG10 MUD MUD (SM) MUD SM8 SM MG9 MUD MUD MUD (SM) SM8 SM MG10 MUD MUD MUD MUD SM8 MUD MG10 MUD MUD (SM) (SM) SM8 SM13 Notes: Brackets indicate transitional communities that did not match defined NVC communities particularly well. MG9 (Holcus lanatus - Deschampsia cespitosa grasslands) and MG10 (Holcus lanatus - Juncus effusus rush-pasture) are both communities associated with poorly drained soils MG6 (Lolium perenne - Cynosurus cristatus grassland) is associated with well drained permanent pasture, and here is found at higher, better drained elevations. MG11 (Festuca rubra - Agrostis stolonifera - Potentilla anserina grassland) and MG13 (Agrostis stolonifera - Alopecurus geniculatus grassland) are two of three types of grass-dominated inundation community often associated with saltmarshes. SM8 annual Salicornia saltmarsh and SM13 Puccinellia maritima saltmarsh are both lower saltmarsh communities. SM16 Festuca rubra saltmarsh is a middle saltmarsh community. All three of these communities are well represented on reference saltmarshes in Nigg Bay.SM12 is the NVC community dominated by rayed Aster tripolium. MUD denotes monitoring plots that were completely covered by mud, with little or no vegetation present. 18

19 Although saltmarsh plants will colonise coastal realignment sites relatively quickly, even after 100 years there are differences in species richness, composition and structure from reference saltmarshes (Garbutt & Wolters 2008). At Nigg Bay, comparison to the reference saltmarsh outside the Meddat sea wall has shown that by 2012 the newly-created saltmarsh is made up of the same types of NVC communities as found nearby, with a very good goodness-of-fit (a match coefficient of 75 or greater). The PhD study found the main NVC communities found on the reference saltmarshes outside the CRS were SM8 annual Salicornia saltmarsh, SM13 Puccinellia maritima saltmarsh and SM16 Festuca rubra saltmarsh. Species Diversity It was expected that species diversity would decline after the reintroduction of tidal conditions. The number of species that are tolerant of saline conditions is far lower than the total number of terrestrial plant species. Indeed, those plant species that make up saltmarsh vegetation are adapted to live in saline conditions, rather than tolerate those conditions. Overall, the species diversity of plants has fallen from 37 species pre-breach to 27 species by S9 post breach. Due to the variation in topography, some plots (in particular, those plots containing MG11 vegetation) are above Mean High Water Springs (MHWS) and therefore only being inundated on Highest Astronomical Tides (HAT). These plots have a higher species diversity than those at lower elevations where tidal conditions are more frequent. As can be seen in Figure 8, overall species diversity initially decreased with the reintroduction of saline conditions to the CRS. The number of herbs, grasses, rushes and sedges decreased but the number of saltmarsh species increased. The same saltmarsh species found on the reference saltmarsh outside the CRS are now also found within the CRS. All the herb species that are no longer present in the CRS are common and widespread species. Figure 8 Changes in diversity of plant type over time Changes to the existing saltmarshes in Nigg Bay The seaward edge of the reference saltmarsh along the CRS sea wall was mapped prior to breach with a GPS. This exercise was repeated in 2015 to detect any changes. The saltmarsh edge was defined as two types the edge of the solid saltmarsh, and the edge of hummocky saltmarsh. It is known from previous modelling of the Cromarty Firth that this part of Nigg Bay is an erosion zone 1 and it is therefore likely that some erosion would have taken place anyway. The reference saltmarsh is mostly of the NVC community SM13 (Puccinellia maritima saltmarsh), with some SM8 (annual Salicornia saltmarsh). 1 Institute of Estuarine and Coastal Studies, University of Hull (from Babtie Group, 2002) 19

20 Table 4 Changes in extent of reference saltmarsh between 2001 & 2015 Habitat Type Area in 2001 Area in 2015 Change Solid Saltmarsh 1.90 ha 1.73 ha ha Hummocky Saltmarsh 0.73 ha 0.77 ha ha Total 2.63 ha 2.50 ha ha The extent saltmarsh within the CRS was 20 ha by Accounting for the losses directly on the outside of the CRS, the net gain of saltmarsh was ha. It is likely that there was no loss of sediments, as those eroded on the outside of the site would have deposited within the CRS or elsewhere in Nigg Bay. Figure 9 Changes in extent of saltmarsh at the Nigg Bay CRS solid saltmarsh 2001 solid saltmarsh As shown in Figure 9, there has been some erosion of the solid saltmarsh on the outside of the CRS between 2001 (pre-breach) and 2015 (12 years post-breach). There has also been some small areas of accretion in the monitored area outside the CRS. However, this has been more than compensated for by the creation of 20ha saltmarsh within the CRS. Some of this is upper saltmarsh and inundation grassland communities, habitats that are rare elsewhere in Nigg Bay. The remaining 5ha are intertidal mudflats and sparser saltmarsh vegetation. 20

21 8. Benthic Invertebrates Initially, research into benthic invertebrates at the CRS focussed on colonisation of the new intertidal habitats, as well as comparing the invertebrate community with a reference mudflat and assessing whether the invertebrates available are profitable prey for waterbirds. Later studies have focussed on the latter two questions, as the initial colonisation period had passed. Key bird food species studied at Nigg Bay CRS Mudsnail or laver spire shell Hydrobia ulvae Baltic tellin Macoma balthica (a mollusc) Mud shrimp - Corophium sp. Ragworm - Hediste diversicolor Colonisation by Benthic Invertebrates Unlike some other coastal realignment sites, colonisation by benthic invertebrates was relatively rapid at Nigg Bay. For example, all four study species were found in the CRS during the first winter following breach, including mature individuals that were of a size that provide a suitable food source for wintering waterbirds. It is likely that this is in part due to the large-scale sediment transport that occurs within Nigg Bay, enabling benthic invertebrates to rapidly colonise the newly-created habitat. Other sites may rely on the settlement of planktonic larvae, which means that colonisation by mature-sized individuals takes longer. Comparison with Reference Site Comparisons to the reference intertidal flats have been attempted during various studies, but conclusions are difficult to draw due to differences in particle size between the CRS and reference intertidal flats, and the mobility of the different life stages of different species of benthic invertebrates. In some ways, comparisons with existing intertidal habitats is not necessary as the desired outcome for the CRS is to create suitable habitats for wintering waterbirds in its own right. Profitable Prey for Waterbirds Intertidal invertebrates that are profitable prey for wintering waterbirds are those species and sizes of prey that provide the highest net rate of energy return. Profitable-sized mudsnail and Baltic tellin were found in the CRS within the first year following realignment. Profitability of some benthic invertebrates such as mudsnail and Baltic tellin is usually measured using size classes (see Figure 10). Other species profitability is assessed by measuring the mass. It is important to have a benthic invertebrate population that comprises small size classes as well as larger size classes. This is because the small individuals are the big ones of the future! A site may contain lots of individuals of a particular species, but if they are mostly small individuals this does not yet represent a good feeding resource for wintering waterbirds. Therefore it is important to look at numbers within size classes over a number of seasons, as this gives a better indication of the development of the bird feeding resource. 21

22 Figure 10 Size classes (width) of Baltic tellin Macoma balthica in the CRS in The size classes preferred by knot are within the black box. Baltic tellin are an important food resource for wintering knot (Calidris canutus), which eat the mollusc whole and crush the exterior shell with their specially-adapted strong gizzard. The preferred prey size classes for knot are 8-16mm (with anything over 25mm being too big). Figure 10 demonstrates that profitable-sized Baltic tellin (total number of individuals across all sampling points) were found in the CRS within 10 years of breach, with the majority of individuals being the preferred 8mm or greater (Foot & Elliott 2012). 22

23 9. Use by Wintering Waterbirds As one of the reasons for undertaking this habitat creation project was to provide habitat for wintering waterbirds, several aspects of use by these species have been studied since the sea wall was breached in The PhD study looked in depth at some aspects of the use by wintering waterbirds in the first four seasons following the reintroduction of intertidal conditions. Subsequently, data on wintering waterbird use has been collected by reserve staff and the British Trust for Conservation Volunteers Saltmarsh Apprentice post hosted and mentored by the RSPB s Central Highland Reserves team. The PhD study looked at the following aspects of use by wintering waterbirds: species & numbers of birds areas used use for feeding and/or roosting patterns of usage regular use by individual birds age structure use during the tidal cycle and differing weather conditions Subsequent data collection has focused on use through the tidal cycle, and use during extreme tide and/or weather conditions. Prior to breaching the sea wall, the field at Meddat Marsh was rush-dominated rough grazing of limited use to wintering waterbirds. Ad-hoc records show that small numbers of mallard, teal, snipe and curlew used the field on occasion. Monitoring of birds began after the reintroduction of tidal conditions in February 2003, with wader diversity increasing almost immediately. Redshank was one of the first species to respond to the creation of the new habitat and have been a common presence as a wintering species in the realignment site ever since. This species was chosen by the PhD researcher as the study species. Habitat Availability Two features of saltmarsh are important from a bird roosting point of view the total area and the length of seaward edge. Creeks and muddy edge are also important for feeding. By undertaking the coastal realignment project we have added 20ha of saltmarsh, 5ha of intertidal mudflat and 900m saltmarsh edge to Nigg Bay. Table 5Habitats in the CRS Habitat Feature Saltmarsh Area Saltmarsh Seaward Length Intertidal (between MLWS and MHWS) Feature importance Area available to birds as high tide roost sites Length available to birds as high tide roost sites Area available to roosting birds at low water on a spring tide Nigg Bay (excluding CRS) CRS in 2006 CRS in 2012 Percentage of Nigg Bay habitat in CRS in ha 6.0ha 20 ha 23% 6.7 km 1.2km 0.9 km 12 % 1063 ha 9.7ha 5.0 ha < 1% MLWS Mean Low Water Spring tides MHWS Mean High Water Spring tides Species A total of 14 wader and 21 wildfowl species were recorded on the Nigg Bay WeBS counts (Oil Terminal to Tarbat sections) since the coastal realignment was undertaken in Of these, 12 wader and 13 wildfowl species have been recorded within the CRS since breach. The number of waterbird species using the realignment was low (3 species) in the first winter following breach, but increased to 19 species in the second winter. This has subsequently risen to 25 species of waders and wildfowl recorded during monitoring 23

24 by winter 2012/13. Grey heron and little grebe were also recorded during monitoring, but are not included in counts of waders and wildfowl. The waterbird assemblage that now uses the CRS is typical of a sanddominated estuary. Species recorded in the wider Nigg Bay area, but not within the CRS since the sea wall was breached are mostly species that (i) are recorded on WeBS counts in low numbers; or (ii) winter in specific parts of Nigg Bay on habitats that have not been created within the CRS. No waterbird species has been recorded in the CRS that has not also been recorded during WeBS counts across the rest of Nigg Bay. Other species recorded within the CRS during ad-hoc site visits include skylark, meadow pipit and twite. Table 6 Wildfowl and wader species recorded during winter WeBS counts in Nigg Bay 03/04 to 12/13 Wildfowl Mute Swan Whooper Swan Pink-footed Goose White-fronted Goose Greylag Goose Canada Goose Barnacle Goose Brent Goose Shelduck Wigeon American Wigeon Teal Mallard Pintail Shoveler Tufted Duck Scaup Eider Long-tailed Duck Goldeneye Red-breasted Merganser Waders Oystercatcher Ringed Plover Golden Plover Grey Plover Lapwing Knot Dunlin Snipe Black-tailed Godwit Bar-tailed Godwit Curlew Redshank Greenshank Turnstone Species recorded in the Nigg Bay CRS since restoration in February 2003 are in bold and blue. Tidal Cycle and Weather Coastal realignment can be used to restore or create new upper intertidal mudflats (for foraging habitat) and saltmarsh (for high tide roosting sites). The CRS is one of the last areas of Nigg Bay to be covered by seawater on the incoming tide (and therefore one of the first exposed areas on the outgoing tide), as it is higher up the tidal frame than the majority of Nigg Bay. More birds use the CRS when water is present (from midway through the tidal cycle to high water and reverse) than at low tide. Peak usage of the site has been shown to be in cold, windy conditions (typically strong, north-westerly wind) and/or on the highest spring tides (and storm surge tides when barometric pressure causes tides to be higher than predicted). In these conditions, up to 2000 waterbirds will use the CRS for roosting, representing 20% of the peak waterbird assemblage of Nigg Bay. For example, the peak curlew roosting flock recorded in the CRS is 800. The CRS is principally used as a high tide roost site, but is also used for top-up feeding by some individual waterbirds when the intertidal mudflats are covered by the tide elsewhere in Nigg Bay. Patterns of Usage The PhD study showed that spatial distribution of wintering waders in the CRS is affected by landscape features such as elevation, vegetation cover, creeks and proximity to the breaches and embankments. Many waders tended to (and still do) feed near to the breach gaps, probably because this provides the greatest field of view for detecting predators. Areas of the site closest to the secondary defence embankments area are avoided by feeding and roosting birds. The main area used for roosting by wintering waterbirds is an area of saltmarsh in the north-western part of the site. This area has short vegetation, is well away from embankments and fences, and has good visibility across the rest of the site. 24

25 As redshank was one of the first species to regularly use the CRS, this species was selected for colourringing and radio-tracking work to further identify patterns of usage by individuals. A total of 126 redshank were caught in the Nigg Bay area and colour-ringed by Highland Ringing Group between October 2004 and December 2005, with the scheme identifier being a single yellow ring on either the right or left tarsus (depending on whether the bird already had a metal BTO ring or not). Each individual was identified by a unique combination of colour rings, two on each tibia. Of these, 88 redshank were re-sighted during the PhD study period within the Moray Firth area and, of those, 85 birds were re-sighted in Nigg Bay. Two birds were re-sighted outside the Moray Firth area, one at Montrose Basin, and one at Den Helder Kooysluis, North Holland! As has been shown in other studies, these redshank were faithful to their wintering sites throughout the season, with birds caught and colour-ringed during the winter at Meddat then subsequently re-sighted in the same area. Of those birds that were colour-ringed at Nigg Bay in winter 2004/05 and then subsequently re-sighted in winter 2005/06, 100% were re-sighted within Nigg Bay, again showing a high degree of winter site fidelity. About 20% of the birds colour-ringed for this part of our studies were subsequently re-sighted within the CRS, suggesting that, even only two years after the reintroduction of tidal conditions, the site had become important for at least part of the wintering Redshank population of Nigg Bay. Both adults and juveniles used the CRS, possibly indicating that, at that time, the feeding habitat was not good enough for adults to defend against juveniles. It may be interesting to repeat this study, to see if this age structure has changed now that the habitats have developed. Importance of CRS to wintering waterbirds As stated in Table 3, the CRS created an additional 23% of saltmarsh and 12% of saltmarsh seaward edge by Depending on tides and weather conditions, the CRS may hold up to 20% of Nigg Bay s wintering waterbirds. The CRS, therefore, proportionally more important to wintering waterbird numbers than other parts of Nigg Bay. It is particularly important on the highest spring tides and storm surge tides, when other roosting habitat in the bay becomes unavailable due to being covered by sea water. The CRS is higher up the tidal frame than other parts of Nigg Bay, so it is covered by the incoming tide later than other parts of the bay. Unlike other parts of Nigg Bay, which form part of the Cromarty Firth Special Protection Area (SPA), the CRS is not designated but the newly-created habitats are now important for the internationally important wintering waterbird population in Nigg Bay. A fence, roughly following MHWS within the CRS bisected the site until The fence was formerly used to prevent grazing animals from wandering through the breaches and therefore into the wider estuary, when animals were present the first few years following breach. However, the fence acted as a trap for natural and man-made marine debris, making it a very visible obstacle (sometimes resembling a seaweed drying line!). It was observed that it seemed to form a barrier to bird use of the newly-created upper marsh areas, as roosting flocks could not edge up the marsh as they are pushed by the tide. Roosting flocks were observed to leave the CRS when they were pushed towards the fence, rather than fly over it. Hence the management decision was taken to remove the fence to allow birds to naturally move up the marsh with the incoming tide. If the decision is taken to reinstate grazing, a solution such as invisible fencing will be employed. This should enable larger numbers of wintering waterbirds to use the CRS. 25

26 10. Sedimentation, Geomorphology & Sea Wall Condition Sedimentation Sedimentation was initially studied as part of the PhD study. Sediment traps (metal plates) were installed near the vegetation monitoring plots (see Appendix), with a cane used to probe through the ground cover to measure the depth of sediment accumulated. Monitoring in the initial year following breach showed that there had been little accumulation of sediments at that point. However, subsequently there was some difficulty relocating the sediment traps, even with a metal detector. In 2011, it was found that there had been 20-30cm of sediment accumulation in some parts of the site (found by digging down to the original vegetation layer). Lidar data covering the CRS was collected in 2005 as a baseline, and repeating this exercise will allow us to detect changes in sediment volume over time. Geomorphology Partial mapping of the development of the creek system within the CRS was done in This showed that since breach, a complex system of saltmarsh creeks has developed. Figure 11 Map showing creeks within part of the coastal realignment site in 2013 creek bed pools low saltmarsh Sea Wall Condition The secondary defences (Figure 12) at the CRS were required to be built up to defend against predicted 1 in 50 year storm surge levels m AOD with a 500mm freeboard (additional sea wall crest height above still water). Many of the neighbouring sea walls in Nigg Bay are lower than this height. The secondary defence was strengthened to this crest height prior to breach. It was recommended in the Design & Impacts study, and a condition of planning consent, that the condition of the secondary wall should be monitored every 5 years. Monitoring of the wall has been carried out by reserve staff inspecting the wall on site visits, with no problems noted. In 2014, an MSc student was able to accurately monitor the height of the wall using differential GPS (DGPS). Again, no problems were noted. 26

27 The width of the breaches have been measured several times since breach. The two breaches in the southern embankment were both 20m wide in 2003 when the realignment was done. Both breaches are now more than 50m wide. The breaches have both eroded more in the eastwards direction, which is to be expected as tides move in a clockwise direction with the greatest pressure on the breached wall being on the incoming tide. Figure 12 Location of secondary sea wall defences 27

28 11. References Babtie Group Nigg Bay Coastal Realignment Project Design and Impacts Study. Report to RSPB. Chisholm, K., Kindleysides, D. & Cowie N Identifying, developing and implementing coastal realignment projects in Scotland: Lessons learned from Nigg Bay, Cromarty Firth. RSPB Internal Report. Crowther, A The restoration of intertidal habitats for non-breeding waterbirds through breached managed realignment. PhD University of Stirling. Elliott, S Wintering Waterbirds on Restored Saltmarsh at Nigg Bay RSPB Nature Reserve. In Highland Bird Report. Foot, C. & Elliott, S Survey and monitoring of change to saltmarsh communities eight winters after the removal of the sea wall at the Nigg Bay Coastal Realignment Site. RSPB Internal Report. Garbutt, A. and Wolters, M. (2008), The natural regeneration of salt marsh on formerly reclaimed land. Applied Vegetation Science, 11: doi: / Johnstonova, A. & Cowie, N The effect of sea level change on the saltmarsh habitat in Nigg Bay, Cromarty Firth. RSPB Internal Report. Kennerley, R Nigg Bay Coastal Realignment 7 years on. RSPB Internal Report. McHaffie, H Baseline survey and monitoring of change to saltmarsh and wet grassland communities prior to removal of the sea wall at Meddat Marsh, Nigg Bay. RSPB Internal Report. Nottage, A. & Robertson, P The saltmarsh creation handbook: a project manager s guide to the creation of saltmarsh and intertidal mudflat (Chapter 4 Case Studies 7 Nigg Bay, Highlands). The RSPB, Sandy and CIWEM, London. Rowlinson, H Nigg Bay Coastal Realignment. An analysis of success in terms of biological and geomorphological functions. MSc University of Glasgow. Tawse, P Rates of change at the Meddat managed realignment site: establishing baseline conditions for future surveys. MSc University of Glasgow. 12. Acknowledgements Many staff within the RSPB have been involved in the project. In particular, Dr Pete Mayhew, Senior Conservation Manager, and Kenna Chisholm, then Ross-shire and Moray Firth Officer (now Conservation Manager) instigated the project, with Kenna project managing the operation to breach the sea wall. Dr Neil Cowie of the Reserves Ecology department has provided valuable ecological advice throughout the project, including the supervision of the PhD studies. Jim Densham, Dave Jones, Neil Cowie and Chris Bingham provided many useful comments on earlier drafts of this report. 28

29 13. Appendix Location of post and orientation of other associated monitoring points 29