Fen Management Handbook - Scottish Natural Heritage

Case Study 7.2
Fen Water Management
– Portmore Lough
Portmore Lough is a 1 m deep, 200 ha circular lough, situated on the south eastern
shore of Lough Neagh in Northern Ireland (grid reference J113690), surrounded by
a 100 m wide reedbed (the second largest in Northern Ireland), a 100 m fringe of
willow/alder carr, and on the western edge, a mosaic of lowland wet grassland and
ditches. It is this transition from open water to wet grassland that is one of the site’s
ASSI designation features.
Water quality and water levels on Portmore Lough are influenced by Lough Neagh
through two large interconnecting drainage channels. Water levels were 2.3
m higher and more extreme in the Lough Neagh basin 200 years ago. The last
lowering in 1959 allowed the fringe of willow/alder carr to develop at Portmore.
This layer of willow fringe was coppiced and in the short dry season lightly grazed.
The RSPB has focused on developing the adjoining lowland wet grassland at
Portmore to attract breeding waders, which is central to the south Lough Neagh
Lapwing Restoration Project. Lapwing have declined by 65% in 15 years in
Northern Ireland. A management regime of ‘cut, collect and graze’ for 15 years on
the meadow has produced a species rich sward enhanced by a bund isolating the
meadows from the eutrophic lough allowing only rain water to collect.
Removal of the willow/alder carr and restoration of the water fringe fen was critical
in increasing the invertebrate diversity. The carabid beetle Chlaenius tristis (RDB1)
found here is the first Northern Ireland record. Creating ‘openness’ and a more
diverse transition from open water also favours breeding waders and wildfowl.
Restoration of fen at Portmore preserves a once common, but now virtually extinct,
habitat around Lough Neagh.
Management objectives
Restoration of 9ha wet willow and alder carr to water fringe fen.
Management rationale
The key to the project is the suppression of reed canary grass (Phalaris
arundinacea) within the fen and the improvement in water quality of Portmore
Lough. Short of isolating Portmore Lough from Lough Neagh, water quality is a
regional problem and outside the scope of the RSPB.
The soil within the fen area is weakly consolidated silty clay sediment, with a fragile
supportive crust only 80 cm thick. This precluded the use of large machinery and
the removal of stumps. Frequent flooding and high winter water levels gave only a
short autumn window for mechanical operations.
Techniques
(a) Scrub control by herbicide injection
Willow/alder stems were injected with 10 ml undiluted glyphosate using a petrol
driven drill with 10 ml bit and a sheep dosing gun, which produced a 70% kill
of stems. The intention was to reduce moisture content in the resultant chip,
increasing its value to offset costs. The benefit however extended to reduced stump
regrowth and non-regeneration of submerged brash.
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