Eden Estuary Salt Marsh Restoration
Project No. RA005-016 (Report 2011 – 2012)
University of St. Andrews (Sediment Ecology Research Group)
Scottish Oceans Institute, East Sands, St. Andrews
Background
Saltmarsh is a priority BAP habitat, and is important as a wildlife resource and for coastal
defence purposes. Therefore the halt of its decline is urgently required. Unfortunately, the
saltmarsh on the Eden Estuary is classed as ‘unfavourable’ by Scottish Natural Heritage
(SNH), as former pollution and fragmentation and burial under hard sea defences have
taken their toll. Climate change and rising sea levels now mean that without intervention, its
future is uncertain.
Successful trials in the estuary, using native species, showed that saltmarsh
restoration through direct planting is a viable management option, and have led to a marsh
recreation project in two particularly degraded sections of the estuary’s upper mudflats: at
the bases of a seawall on the south shore and a disused rubble tip on the north shore.
The planting this year was undertaken on the south shore by a student taskforce
from St. Andrews University and Links Trust personnel, while on the north shore the site
was planted by an RAF conservation team, in addition to help from students. Though
planting of the marshes at the degraded sites began during 2010 to 2011, this report
illustrates the work undertaken during the second year of funding (2011 – 2012).
Recap on the work completed during 2010 – 2011
The two images below (1 & 2) show the marshes immediately post planting in front of the
seawall and the rubble tip at the end of the last financial year (March, 2011). Sea club rush
(Bolboschoenus maritimus, known previously as Scirpus maritimus) is a perennial marsh
plant and as such the stems die-back during winter, while the roots and buds are dormant
until a temperature rise during springtime triggers bud development. Planting therefore has
to take place before bud development, but after the worst of the winter storms, to avoid
uprooting by tides until the plants have established (i.e., anchored by roots).
(1) South shore seawall, March 2011.
(2) North shore rubble site, March 2011.
Work undertaken and completed during 2011 – 2012
The sections of new marsh shown above (planted 2010 – 2011) were monitored and their
establishment ensured during the summer of 2011. The plants in these sections were
flourishing by May and June (2011), as the images (3 & 4) show below. The number of stems
that emerged from each plant was the result of the large size of sprig used (a sprig being the
basic planting unit) which incorporates a maximum number of buds and a large root mass
and rhizome system (rhizomes are the food store that enable bud elongation until the
shoots can photosynthesize).
(3) South shore seawall, May 2011.
(4) North shore rubble site, June 2011.
One particular section on the south shore site did not perform so well (5), which was
anticipated given the drier and sandier nature of the sediment. However, plant growth in
this area will accelerate over subsequent years as water-retaining silts and clays are trapped
by the vegetation, and organic matter accumulates, to generate a marshier sedimentary
environment.
(5) A dry and sandy section of the south shore site.
The accumulation of algae (Enteromorpha spp.) on the estuary’s mudflats can be
problematic during summer when high tides wash up algae that can smother the young
plants (6). The algae become entangled around the vulnerable stems which are then
uprooted by the dragging motion of subsequent tides. Observation of older trial plots show
that the impact has minimal effect as the plant stems grow taller and the underground parts
connect to increase plant resistance to drag, but can be detrimental to young shoots.
(6) Enteromorpha spp. smothering the young plants on the north shore site, July 2011.
In the meantime, the way around the impact is to remove the algae by hand (7).
Help was given to this task on the north shore in the summer of 2011 by an RAF
conservation team, who have also offered assistance this coming summer. The south shore
marsh was kept clear of algae by members of the project team (SERG).
(7) The RAF conservation team removing algae from the young plants, July 2011.
The last section of seawall at the south shore site was replaced by the Links Trust
prior to planting, and rocks on the upper mudflats that have accumulated over previous
years from failing gabion baskets were removed. The image below (8) shows the gabion wall
being constructed and also one of the beds of rocks prior to removal.
(8) Replacing the seawall and the bed of rocks prior to removal, Nov. 2011.
Links Trust staff also helped out by removing approximately 10 – 12 tonnes of rocks
from the mudflats (9), because not only was further planting at the seawall site impeded by
the rocks, but their movement by the tide are damaging habitat in the vicinity, not to
mention the young and vulnerable marsh. As part of a co-ordinated effort between the Links
Trust and project staff, more stones will be removed next year from another section of the
seawall site prior to the planting.
(9) Links Trust staff clearing the mudflats at the south shore site, Dec. 2011 (Links Trust).
The planting target was exceeded this year as the team size was larger on some days,
and the weather was more favourable than in previous years. The number of plants
removed from the donor marsh was also increased this year; monitoring over the last two
years of the effects of harvesting showed that in the subsequent summer the donor marsh
made a full recovery.
The table shows a breakdown of the planting programme. The new section of marsh
planted on the south shore was doubled in width compared to last year; while the entire
length of the rubble tip on the north shore (already planted) was increased by two metres.
Eden seawall (300m)
RAF rubble tip (250m)
2010 - 2011
2011 - 2012
2012 - 2013
100m x 2m
250m x 2m
100m x 4m
250m x 2m
100m x 4m
0
Total area to
be planted
1000m2
1000m2
The increased planting width will speed up the establishment process and it is hoped
the increase in size can be maintained in next years’ planting, provided the donor marshes
make another full recovery.
The image below (10) is the 100 m section planted last year in front of the south
shore seawall, followed by an image (11) of the adjacent section planted this year (100 m),
which means that the new marsh is now linked to the end of the fragmented marsh
(illustrated on the map). Images (12 – 14) show digging at the donor site, preparation of the
sprigs and planting the marsh.
(10) South shore seawall, April 2011.
(11) South shore seawall, Feb. 2012.
(12) Students digging up donor marsh during the Feb. 2012 planting session (M. Macdonald,
University of St. Andrews).
(13) Links Trust staff separating plugs of marsh into sprigs prior to planting.
(14) Planting at the seawall site, Feb. 2012 (M. Macdonald, University of St. Andrews).
Work planned during 2012 – 2013
The next year (2012 – 2013) will be busy. The increase in the size of area planted mean
many more days will be spent this summer removing algae from the young marshes.
However, help has been offered from the RAF conservation team for the north shore, while
the Links Trust staff, students from St. Andrews and the project team will ensure the south
shore site is kept clear. Monthly sediment bed levels for each site are also recorded and
changes should occur during the coming third year. Another large mudflat section at the
south shore seawall will be planted, and gaps at the north site filled.
If the nine year old trial plots (15) are anything to go by, the newly planted areas will
make a difference to the Eden Estuary, as a stabilising buffer to its degraded upper shore
and by reversing the loss of a valuable coastal habitat. The partnership between SEPA, the
University of St. Andrews, the Links Trust, RAF Leuchars, Scottish Natural Heritage and Fife
Coast & Countryside Trust has proved to be a good example of how integrated coastal zone
management can work to everyone’s benefit to improve an estuarine environment.
(15) A stand of Sea Club Rush on the south shore, planted in March 2003.