Vegetation, water beetles and habitat isolation in abandoned lowland bog drains and peat pits

Copyright # 2005 John Wiley & Sons, Ltd. Received 6 May 2004Accepted 25 September 2004

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS

Aquatic Conserv: Mar. Freshw. Ecosyst. 15: 175–188 (2005)

Published online 14 January 2005 in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/aqc.668

Vegetation, water beetles and habitat isolation in abandonedlowland bog drains and peat pits

ALAN COOPERa,*, THOMAS McCANNa, ROBERT DAVIDSONb and GARTH N. FOSTERc

aSchool of Environmental Sciences, University of Ulster, Coleraine, Northern Ireland, UKbEnvironment and Heritage Service, Department of the Environment for Northern Ireland, Belfast, UK

cSAC Research and Development Division, Auchincruive, Ayr KA6 5HW, Scotland, UK

ABSTRACT

1. Multivariate analysis of vegetation and water beetles recorded in the abandoned drains andflooded workings of a cut-over lowland Irish raised bog, Montiaghs Moss, shows that water depthand trophic status are key predictors of plant species composition and that vegetation communitystructure significantly explains water beetle composition.2. The spatial distribution of secondary and tertiary drains and peat pits influences species

composition indirectly, through trophic status, by connecting habitats with primary agriculturaldrains passing through the bog.3. Habitat isolation and the cessation of drain management promote change in the submerged

aquatic vegetation, emergent-swamp and poor-fen habitats recorded by facilitating vegetationdevelopment and surface acidification.4. The ecological consequences are likely to be a reduction in the area of open-water habitats, the

development of poor-fen vegetation and the subsequent loss of high conservation value species ofplants and beetles.5. Management for biodiversity conservation should initially address water quality, for example,

through the European Union (EU) Water Framework Directive, followed by restoration to promotestructural and spatial heterogeneity of drain and peat-pit habitats.6. At a landscape scale, implementing ditch and peat-pit management across abandoned cut-over

lowland raised bog habitats in the farmed Northern Ireland countryside, through EU CommonAgricultural Policy agri-environment schemes, would give regional gains.Copyright # 2005 John Wiley & Sons, Ltd.

KEYWORDS: agri-environment; DCA; emergent swamp; landscape ecology; Montiaghs Moss; peat cutting; poor

fen; raised bog; water beetles; Water Framework Directive

INTRODUCTION

In Britain, emergent herbaceous vegetation (swamp) occurs at the margins of freshwater bodies, in thewetter parts of floodplains, valley mires and along rivers and streams (Rodwell, 1995). Spatial transitions in

*Correspondence to: A. Cooper, School of Environmental Sciences, University of Ulster, Coleraine BT521SA, Northern Ireland, UK.E-mail: [email protected]

species composition from swamp to periodically inundated fen are determined by gradients of water depth,frequency and extent of flooding, water trophic level and water base-richness. Temporal transitions fromswamp to fen are described from studies of peat stratigraphy or inferred from contemporary vegetationzonations (chronosequences). Vegetation development from fen to poor fen and subsequently toombrotrophic bog is classically understood to depend on isolation of the mire surface from mineral-richwater, by processes of root mat formation and peat accumulation (Kulczynski, 1949). Colonization bySphagnum promotes the development of a low surface pH (Clymo, 1964) and facilitates the transition frompoor fen to bog.

The spatial structure and temporal development of the semi-aquatic vegetation of abandoned peatcuttings (peat diggings) is less well understood. This habitat is particularly important in the lowlands ofnorth-west Europe, where rich fens are mainly restricted to peat pits with a lateral influx of base-richsurface water or upwelling groundwater (van Diggelen et al., 1996). Giller and Wheeler (1988) showed thatisolation from inundation by flood water results in the establishment of Sphagnum communities fromfloating mire developed in peat pits.

Under stable hydrological conditions, the time scale for poor-fen development from open water(terrestrialization) can be centuries (Walker, 1970; Succow, 1988). Semi-aquatic and fen vegetationdevelopment in peat pits can, however, occur rapidly. Bakker et al. (1994) concluded that, in theNetherlands, vegetation succession from open water to groundwater-fed floating rich fen in peat cuttingstakes about 35 yr and develops to carr woodland in a further 17 yr. They also emphasized that the rate ofchange is affected greatly by vegetation management and hydrological regime. Van Wirdum (1995)described the almost complete replacement of rich fen by embryonic bog vegetation in abandoned peat pitswithin 27 yr. Van Diggelen et al. (1996) estimated that rich fen with a 40 cm floating root mat can decalcifywithin 30 yr when isolated from alkaline surface water. Such rapid rates of vegetation transition areassociated with hydrological conditions altered by land use.

The ecology of fen and bog invertebrate assemblages is not as well developed as it is for vegetation, butwater beetle assemblages have been classified within Ireland (Foster et al., 1992) and elsewhere, with amajor divide between the faunas of standing and running waters. Studies of water beetle assemblagesfrequently indicate the apparent importance of acidity, but Juliano (1991), in a detailed study of thedistribution of Hydroporus species along a pH gradient, demonstrated clear inconsistencies from this.Water permanence is generally accepted to be important because temporarily flooded sites are largely freefrom fish predators. Other site characteristics, such as the extent of shading and the density of vegetation,are often important in standing waters (Foster and Eyre, 1992).

In Northern Ireland, there are large areas of peat cuttings in lowland raised bog (Murray et al., 1992).The associated drainage ditches, which usually consist of a regular system of linked primary, secondary andtertiary drains (White, 1930), often have semi-aquatic, swamp or fen vegetation. Because hand peat-cuttingis no longer carried out, drains are currently maintained only where they have an agricultural function. Incommon with many European lowland wetlands, peat cuttings in Ireland occur as fragmented habitats inagricultural landscapes subject to recent land-use intensification and hydrological change, which has alteredthe trophic status and depth or frequency of winter flooding. The ecological consequences of reducedvegetation management and altered hydrological conditions to prevent winter flooding are the focus of thisstudy.

Studies of peat-pit ecology have relied primarily on mapping changes in vegetation distribution andpatterns with time, sampling the species composition of vegetation and the aquatic environment, andinferring the ecological mechanisms of change with a space–time substitution approach. This researchapplies stratified random sampling and multivariate statistical techniques to analyse spatial relationshipsbetween species composition and environmental variables in a cut-over raised bog and to assessrelationships between vegetation and water beetle assemblages. This provides the potential for usingvegetation as an indicator of beetle assemblages.

A. COOPER ET AL.176

Copyright # 2005 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 15: 175–188 (2005)

METHODS

Site description

The study site was the Montiaghs Moss, a cut-over raised bog with peat pits linked by a system of drains. Itis a statutory Area of Special Scientific Interest (Countryside and Wildlife Branch, 1985). The basis ofdesignation is an assemblage of wetland plants, water beetles and dragonflies with regional, national andEuropean conservation value. In the west, the site is bordered by drumlins derived from basalt glacial drift,with peat reclaimed as farmed grassland on all other sides. The dome of the bog was eradicated last centuryby hand peat-cutting and the site now consists largely of wet heath, with areas dominated by Moliniacaerulea. Characteristic species of the now eradicated minerotrophic lagg are present in the largelyabandoned peat pits and drains constructed for peat extraction.

The vegetation of the drain and peat pit complex consists of submerged aquatic, emergent-swamp, rich-fen and poor-fen communities in which Carex rostrata, Equisetum fluviatile and Potamogeton polygonifoliusare key species. Locally rare species include Baldellia ranunculoides, Carex lasiocarpa, Cicuta virosa,Eleocharis multicaulis, Hydrocharis morsus-ranae, Oenanthe fistulosa, Oenanthe aquatica, Utriculariavulgaris, Sparganium minimum and Drosera anglica. Some 58 water beetle species have been recorded, ofwhich several are uncommon in Ireland and one (Gyrinus natator) is considered to be extinct in GreatBritain (England, Scotland and Wales) and declining in Europe (Foster et al., 1992).

Regional water catchment management, particularly over the last 50 yr, has lowered water levels andreduced the incidence of landscape-scale flooding (Davidson, 1993). Land cover in the catchment is mainlyintensively managed grassland with high nutrient loadings to main agricultural drains connected to the bog(McAllister et al., 1977). Major land drains, maintained by the Department of Agriculture and RuralDevelopment for Northern Ireland, pass through the site to discharge into the now eutrophic Lough Neagh(Figure 1). They prevent the regular winter flooding of the bog surface which occurred before Lough Neaghwater levels were lowered and stabilized in 1959 (Davidson, 1993). Secondary, largely unmanaged, drainsconnect with the main drains and are linked with tertiary drains, representing former peat cuttings. Somepeat pits are isolated from the system of drains.

Past peat-cutting

Ordnance Survey maps dated 1729 show no roads or drains across the Montiaghs Moss bog. Intensive peatcutting was in progress by 1836 (Anon., 1836), when the road and pattern of main peat-cutting drains wasmuch the same as exists at present. The bog was being cut extensively for fuel by hand up to the 1940s(James Mulholland, pers. comm.). Aerial photographs indicate less cutting during the 1960s, and in 1992cutting was restricted to 10 small locations (pers. obs.). The traditional method of peat cutting was for twomen to extract from parallel cuttings 2.25–2.4m wide and up to 200m long, each separated by a bank 0.6mwide. If one man was working alone, cuttings were narrower (1–2m). The long cuttings were dividedtransversely into 4.5m sections by uncut partitions to control flooding during peat digging.

Surface vegetation was removed before peat extraction and either burned as low-grade fuel or throwninto flooded, worked-out sections. Peat was extracted by churning it in a working section, to a semi-liquidstate. It was then spread onto the bog surface, left to lose water for a few days, then cut into bars ready forstacking and drying for fuel. The depth of cutting was to a maximum of 1.5m. At certain locations cuttingpartitions were removed to gain more peat, leaving wider flooded areas. To control water movement intoworking sections, notches were removed from partitions or plugged with peat. It was common for water toburst up through the floor of a cutting, making further extraction impossible.

WATER BEETLES AND HABITAT ISOLATION 177


Field sampling and physico-chemical analysis

Drain and flooded peat-pit sample sites were selected following stratification based on isolation and depth.There were four categories of isolation: main drain, secondary drain, tertiary drain and unconnected peatpit. There were three categories of depth (1:510 cm; 2: 11–50 cm; 3: >50 cm). The sampling strategy was torecord three sample sites from each of the 12 stratum permutations, thus representing the range of variablesof interest. In practice, some stratum permutations did not occur, e.g. shallow main-drains, shallow peatpits, and deep secondary drains.

At each of the resulting 23 sample sites, plant species cover and water beetle species presence wererecorded. Sample quadrats (1m� 4m), whose size was determined by pilot studies to define a minimal area,were positioned randomly in each site. Plant species cover and the area of open water in each quadrat wasassessed on the Domin scale (Mueller-Dombois and Ellenberg, 1974), a method shown by Brakenhielm andQinghong (1995) to perform well in comparison with objective quantitative measures. Vascular plantspecies nomenclature follows Stace (1991). Bryophyte nomenclature follows Smith (1993).

Adult water beetles were recorded by repeatedly dip-netting (1mm mesh size) throughout the watercolumn over a standard 10min period in each quadrat. Beetle species were recorded in 18 quadrats. Fieldwork was carried out from mid-June to mid-July 1992. Beetle nomenclature follows Nilsson (2001) forDytiscidae and Hansen (1999) for Hydrophiloidea.

Surface water samples from each quadrat were taken on a single sampling occasion in June 1992. Watersamples were stored overnight in a refrigerator (548C) and filtered prior to laboratory analysis (Chapman

Figure 1. Location map of the Montiaghs Moss cut-over raised bog showing agricultural main drains.

A. COOPER ET AL.178


et al., 1962). Water conductivity and pH were determined with electronic meters, and hardness wasmeasured by EDTA titration. Ammonia-nitrogen was determined by reaction with Nessler’s reagent afterpreliminary distillation with magnesium carbonate. Nitrate-nitrogen was measured by reducing nitrate tonitrite with hydrazine in alkaline solution and then determining total nitrate by a modified Griess–Ilosvayreaction. Water-soluble orthophosphate was measured colorimetrically with the molybdenum blue method.Water depth in late June (minimum level) and late September (maximum level) was recorded on agraduated 1.5 cm diameter rod pushed into the quadrat to a firm surface. The range of water level variationwas determined from these measures.

Multivariate analysis

Vegetation samples were classified with two-way indicator species analysis (TWINSPAN), a hierarchicaldivisive classification (Hill, 1994). The TWINSPAN program parameters were set so that pseudospeciescut-levels corresponded with the Domin values 1, 2, 3, 4, 5, 6 and 7–10 to downweight the influence of less-common and dominant species. The stopping criterion of the classification was a minimum group size ofthree.

Ordinations were carried out with CANOCO version 3.15 (ter Braak and Smilauer, 1998). For vegetationordinations, Domin cover values were analysed without further transformation. Detrended correspondenceanalysis (DCA) gave gradient lengths of greater than four standard deviations, indicating unimodal speciesresponse curves in all vegetation and beetle analyses. Environmental variables were plotted passively ontothe vegetation and beetle DCA axes as intra-set correlations. Canonical correspondence analysis (CCA)with forward selection of environmental variables was used to analyse species–environment relationships. AMonte Carlo permutation test (p50.05, 999 permutations) was used to determine the significance ofordination axes. Because the area of open water was inversely related to vegetation cover it was notincluded in the canonical ordination.

Environmental variables were log-transformed prior to analysis if their distribution was skewed. Thequantitative variable isolation was derived by allocating the value 1 to a main drain, 2 to a secondary drain,3 to a tertiary drain and 4 to a peat pit. Two peat pits had no beetles and four had only one species, giving asample size of 16 in the beetle ordination. Eighteen beetle species with only one record in the samples wereomitted from the ordination to reduce the influence of sampling error.

RESULTS

Classification of the 23 vegetation quadrats, containing 31 plant species, produced four groups (Table 1):a floating-aquatic group with Lemna minor, Spirodela polyrhiza and Riccia fluitans; a submerged aquaticgroup, characterized by Myriophyllum spicatum; an emergent-swamp group, characterized by C. rostrataand E. fluviatile; and a poor-fen group, characterized by the oligotrophic bog species Myrica gale,Eriophorum angustifolium and Molinia caerulea. Common species in all three semi-aquatic vegetation types(submerged aquatic, emergent-swamp and poor fen) were C. rostrata, E. fluviatile and P. polygonifolius.

Water samples from the floating-aquatic vegetation group had higher mean concentrations of ammoniaand phosphate (Table 2) and higher conductivity and hardness values than the three semi-aquaticvegetation types. Nitrate concentration across all groups was low and close to the limits of detection. Thefloating-aquatic vegetation samples were confined to the main drains (Table 3). Submerged aquaticvegetation occurred mainly in tertiary drains, emergent-swamp occurred mainly in peat pits and tertiarydrains, and poor fen occurred more in secondary drains. Water depth decreased from floating-aquatic topoor-fen vegetation types. The range of water level fluctuation was greatest in the floating aquatic



Table 1. Plant species composition of TWINSPAN classification groups. Percentage frequency and mean percentage cover (bracketed)are given (+: 50.5%)

Poor fen Emergent swamp Submerged aquatic Floating aquatic

Cicuta virosa 60 (51)Menyanthes trifoliata 60 (20)Eleogiton fluitans 20 (1)Sphagnum auriculatum 40 (2)Agrostis canina 20 (51)Alnus glutinosa 20 (1)Carex panicea 20 (+)Juncus articulatus 20 (1)Myrica gale 80 (23) 13 (51)Potentilla erecta 20 (+)Potentilla palustris 40 (51)Salix cinerea 20 (+)Molinia caerulea 80 (2) 13 (+)Eriophorum angustifolium 80 (4) 38 (7)Hydrocotyle vulgaris 60 (51) 25 (8) 14 (+)Calliergon cuspidatum 13 (51)Galium palustre 13 (51)Lycopus europaea 20 (+) 13 (1)Myosotis secunda 13 (1)Pseudobryum stellatum 13 (+)Eleocharis multicaulis 20 (1) 25 (1)Carex rostrata 100 (14) 100 (9) 57 (14)Equisetum fluviatile 80 (10) 100 (15) 43 (13)Potamogeton polygonifolius 100 (15) 88 (8) 57 (6)Scorpidium scorpioides 20 (1) 14 (+)Juncus bulbosus 13 (+) 14 (+)Myriophyllum spicatum 100 (23)Utricularia vulgaris 25 (+) 43 (51)Lemna minor 20 (+) 25 (51) 57 (1) 100 (17)Spirodela polyrhiza 14 (+) 67 (29)Riccia fluitans 33 (6)

Mean number of species 10.0 5.3 4.1 2.0Number of samples 5 8 7 3

Table 2. Mean values of water chemistry attributes of TWINSPAN classification groups. Standard deviation in parentheses

Attribute Poor fen Emergent swamp Submerged aquatic Floating aquatic

Ammonia (mgL�1) 0.09 (0.04) 0.05 (0.01) 0.06 (0.04 0.88 (0.96)Conductivity (mS cm�1) 81.6 (9.9) 96.0 (34.4) 92.7 (24.1) 170.7 (29.0)Hardness (mgL�1 CaCO3) 27.0 (8.7) 38.0 (17.0) 26.2 (5.2) 87.3 (17.2)Nitrate (mgL�1) 0.06 (0.03) 0.05 (0.04) 0.05 (0.04) 0.05 (0.03)pH 5.6 (0.2) 6.1 (0.5) 5.8 (0.4) 6.4 (0.1)Phosphate (mgL�1) 0.08 (0.03) 0.03 (0.03) 0.06 (0.08) 0.31 (0.19)

Number of samples 5 8 7 3

A. COOPER ET AL.180


vegetation of the main drains and least in the emergent-swamp vegetation of the tertiary drains and peatpits. Open water was recorded in all samples and was highly variable within each vegetation group.

The first two axes of a DCA ordination of the 23 vegetation samples accounted for 33% of the speciesvariation. The first axis (Figure 2(a)) separated quadrats 8, 13 and 23, with their floating-aquaticvegetation, along a gradient corresponding to water trophic status (exemplified by high water conductivity,phosphate concentration and ammonia concentration) and water depth (Figure 2(b)). Species on the left ofaxis 1 (Figure 2(c)), e.g. Menyanthes trifoliata and Sphagnum auriculatum, are indicative of oligotrophic,shallow-water conditions, whereas species on the right, e.g. L. minor, are indicative of open water andhigher nutrient concentrations. The environmental variable isolation occurs on the left of axis 1.

The second axis separated samples along a gradient corresponding primarily to the area of open waterrecorded. Submerged aquatic vegetation samples, with a greater area of open water and characterized byM. spicatum and U. vulgaris, were separated along this axis, from emergent-swamp vegetation samplescharacterized by C. rostrata and E. fluviatile, and from samples characterized by poor-fen species such asM. gale, M. caerulea and E. angustifolium.

CCA ordination of the vegetation samples selected water depth and water hardness as significantvariables (p50.05), accounting for 24% of the species variation. This compares favourably with 33% of thevariation accounted for by the first two axes of the DCA ordination, an indication that water depth andhardness are reliable explanatory variables. CCA carried out with the floating-aquatic samples of the mainagricultural drains (8, 18 and 23) omitted showed that water depth and hardness were still the onlysignificant variables, accounting for 20% of the sample variation.

Forty-one beetle species were recorded in the samples, of which 17 occurred only once (14%). The mostfrequent species were Noterus crassicornis and Hygrotus inaequalis (26%). Hydroporus palustris, Haliplusruficollis and Agabus bipustulatus (22%) also had a high frequency. Despite small sample numbers andqualitative beetle records (presence/absence), the DCA ordination of the 16 beetle samples (Figure 3) wassimilar to the vegetation ordination.

The first two axes of the beetle ordination accounted for 27% of the species variation. Axis 1(Figure 3(a)) separated samples with a large area of open water (e.g. 1, 11 and 9) from samples associatedwith more developed vegetation (e.g. 10 and 7) and samples from the main agricultural drains (8, 23 and13). Axis 2 represents a gradient of trophic status related to isolation (Figure 3(b)), with samples of lowernutrient status more isolated. Passive overlay on the first two axes of the vegetation DCA onto the beetlesordination (Figure 3(b)) showed that axis 2 of the vegetation DCA was equivalent to the first axis of thebeetle DCA and that axis 1 of the vegetation DCA was equivalent to the second axis of the beetle DCA.

The distribution on the ordination of beetle species with well-known habitat preferences showed beetlesof species-rich, open vegetation on the left (Figure 3(c)). N. crassicornis, in particular, is often associated

Table 3. Frequency of drain and peat-pit attributes and hydrological structure attributes of the TWINSPAN classification groups(standard deviation in parentheses)

Attribute Poor fen Emergent swamp Submerged aquatic Floating aquatic

Main drain – – – 3Secondary drain 3 1 2 –Tertiary drain 1 3 5 –Peat pit 1 4 – –Mean water depth (cm) 0.23 (0.17) 0.41 (0.36) 0.64 (0.31) 0.90 (0.82)Mean water level range (cm) 12.8 (3.4) 8.9 (2.7) 12.3 (2.6) 17.3 (1.2)Open water Domin (min–max) 2–7 1–10 7–10 1–10

Number of samples 5 8 7 3



with emergent and floating vegetation with aerenchymatous tissues, such as M. trifoliata. Beetle speciesoften associated with leaf litter or mosses, such as in more developed semi-aquatic vegetation, occurred onthe right of the ordination. Rhantus grapii, for example, is usually found in shaded habitats, often inassociation with Suphrodytes dorsalis. The second axis had a species typical of low pH water: Hydroporusgyllenhalii at the bottom of the ordination and Laccobius minutus, a species of open, base-rich sites, at thetop. Many of the remaining species are characteristic of base-rich ponds.

Axis 1

Axis 2

-2.0 +7.0-1.5

+4.0

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+4.0

Q23Q13

Q08

Q11

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Q02

Q06

Q15

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Axis 1

Axis 2

Conductivity

Depth

Hardness

pH

PhosphateWater range

Ammonium

Open water

Nitrate

Isolation

(a)

(b)

Figure 2. DCA ordination of 23 vegetation samples. Model parameters for axes 1, 2 and 3 are as follows. Eigenvalues. 0.78, 0.35 and0.17; cumulative percentage of species variance. 24.3, 35.1 and 40.3. (a) Quadrats. Vegetation group names: open square, floating-aquatic; open circle, submerged-aquatic; triangle, emergent-swamp; filled square, poor fen. (b) Environmental attributes. The length ofarrow symbols represents the magnitude of correlation. The direction of an arrow symbol represents correlation with axes and othervariables. Axes are scaled by 7. (c) Species. Species codes: Agrocapi: Agrostis capillaris; Alnuglut: Alnus glutinosa; Bryupseu: Bryumpseudotriquetrum; Carepani: Carex panicea; Carerost: Carex rostrata; Callcusp: Calliergon cuspidatum; Cicuviro: Cicuta virosa;Eloemult: Eleocharis multicaulis; Eleoflui: Eleogitan fluitans; Equifluv: Equisetum fluviatile; Erioangu: Eriophorum angustifolium;Galipalu: Galium palustre; Hydrvulg: Hydrocotyle vulgaris; Juncarti: Juncus articulatus; Juncbulb: Juncus bulbosus; Lemnmino: Lemnaminor; Lycoeuro: Lycopus europaea; Menytrif: Menyanthes trifoliata; Molicaer: Molinia caerulea; Myossecu: Myosotis secunda;Myrigale: Myrica gale; Myrispic: Myriophyllum spicatum; Potanata: Potamogeton natans; Poteerec: Potentilla erecta; Potepalu:Potentilla palustris; Riccflui: Riccia fluitans; Salicine: Salix cinerea; Scorscor: Scorpidium scorpioides; Sphaauri: Sphagnum auriculatum;

Spirpoly: Spirodela polyrhiza; Utrivulg: Utricularia vulgaris.

A. COOPER ET AL.182


A beetle samples CCA carried out with sample scores from the vegetation DCA used as explanatoryvariables accounted for 17% of the beetle species variation. Forward selection showed that the firstcanonical axis corresponded to axis 2 of the vegetation DCA and was significant (p=0.01). The secondcanonical axis, corresponding to axis 1 of the vegetation DCA, was also significant (p=0.02).

DISCUSSION

The semi-aquatic vegetation of the Montiaghs Moss peat pits and drains is related to British plantcommunities described by Rodwell (1995). The submerged aquatic vegetation has some affinity with S9Carex rostrata swamp (Menyanthes trifoliata–Equisetum fluviatile sub-community) of the NationalVegetation Classification (NVC) of Britain; emergent-swamp corresponds broadly to S27 Carexrostrata–Potentilla palustris tall-herb fen (Carex rostrata–Equisetum fluviatile sub-community) (Rodwell,1995); and poor fen corresponds to M9 Carex rostrata–Calliergon cuspidatum mire (Campylliumstellatum–Scorpidium scorpioides sub-community) (Rodwell, 1991). Abundant M. spicatum and a highfrequency of L. minor in the submerged aquatic vegetation, and a high frequency ofM. gale in the poor fen,differentiate the Montiaghs vegetation from swamp and mire communities of the NVC. In Irish andEuropean phytosociology, the semi-aquatic swamp and fen communities are related to the associationCaricetum rostratae (O’Connell et al., 1984).

McAllister et al. (1977) showed that catchment stream water linked to the main drains of MontiaghsMoss had high phosphate and ammonia concentrations, indicative of pollution by agricultural waste.Analysis of water samples associated with the vegetation of the main drains shows this currently to be thecase, with similar values of phosphate and ammonia concentrations recorded. Water phosphateconcentrations of the floating-aquatic vegetation were similar to the polder wetlands of north-westernOverijsell in the Netherlands (0.38� 0.57mgL�1) (Bootsma and Wassen, 1996), but lower compared withthe River Rhine irrigated turf-pond fens of the Vecht river plain in the Netherlands (0.94� 1.24mgL�1).Water samples associated with the semi-aquatic vegetation of the secondary and tertiary drains and peatpits were less nutrient-rich than the main drains.

-2.0 +7.0-1.5

+4.0

Axis 1

Axis 2

Spirpoly

Lemnmino

Myrispic

Utrivulg

MyossecuGalipalu

Lycoeuro

Equifluv

Potanata

Juncbulb

Hydrvulg

Carerost

SalicinePoteerec

Juncarti Scorscor

Potepalu

AgrocapiAlnuglut

Carepcea

Eleoflui

Myrigale

Menytrif

Sphasp.

Molicaer

Erioangu

Eleomult

Cicuviro

BryupseuCallcusp

Riccflui

(c)

Figure 2 continued.



Axis 1

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Nitrate

PhosphateAmmonium

HardnessConductivity

Isolation

Depth

pH

VegDCA2

Open_water

VegDCA1

(a)

(b)

Water_range

Figure 3. DCA ordination of 16 beetle samples. Model parameters for axes 1, 2 and 3 are as follows. Eigenvalues. 0.69, 0.46 and 0.22;cumulative percentage of species variance. 16.2, 26.9 and 32.0. (a) Quadrat ordination. Vegetation group names: open square floating-aquatic; circle, submerged-aquatic; triangle, emergent-swamp; filled square, poor fen. (b) Environment ordination. The length of arrowsymbols represents the magnitude of correlation. The direction of an arrow symbol represents correlation with axes and othervariables. VegDCA1 = first axis of the vegetation DCA; VegDCA2 = second axis of the vegetation DCA. Axes are scaled by 7.Species ordination. Species name codes: Agabbipu: Agabus bipustulatus; Ilybmont: Ilybius montanus; Agabstur: Agabus sturmii;Anacluti: Anacaena lutescens; Anaclimb: Anacaena limbata; Enoccoar: Enochrus coarctatus; Grappict: Graptodytes pictus; Halirufi:Haliplus ruficollis; Hydreryt: Hydroporus erythrocephalus; Hydrgyll: Hydroporus gyllenhalii; Hydrobsc: Hydroporus obscurus;Hydrpalu: Hydroporus palustris; Hydrplan: Hydroporus planus; Hydrpube: Hydroporus pubescens; Hygr inae: Hygrotus inaequalis;Hyphovat: Hyphydrus ovatus; Ilybquad: Ilybius quadriguttatus; Laccminu: Laccobius minutus; Notecras: Noterus crassicornis; Pohrlina:Poryhdrus linaeutus; Rhanexso: Rhantus exsoletus; Rhangrap: Rhantus grapii; Suphdors: Suphrodytes dorsalis; Species not included inthe ordination were: Agabus unguicularis; Anacaena globulus; Coelostoma orbiculare; Enochrus affinis; Enochrus ochropterus; Enochrustestaceus; Graptodytes pictus; Helophorus aequalis; Helophorus brevipalpis; Hydaticus seminiger; Hydrobius fuscipes; Hydroporus striola;

Ilybius aenescens; Hydroporus tessellatus; Nebrioporus assimilis; Stictonectes lepidus.

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The inferred chronosequence at Montiaghs Moss is that vegetation development from emergent-swampand submerged aquatic vegetation occurs by the formation of a root mat with subsequent development ofpoor fen. Key root-mat species are C. rostrata, E. fluviatile, P. polygonifolius and M. trifoliata. Colonizingpoor-fen species are M. gale, E. angustifolium, and M. caerulea. Terrestrialization is inferred to proceed bysurface acidification, ombrotrophic peat formation and the establishment of S. auriculatum. Thischronosequence is similar to that described in the Netherlands by van Wirdum (1995) for vegetationdevelopment in abandoned peat pits 10–50m wide, 10–100m long and 0.4–0.7m deep.

Van Wirdum (1995) attributed the initiation of change to the stabilization of water management practicesand assessed poor-fen development as taking about 30 yr. Also, under changed hydrological management,Beltman et al. (1995) showed that acidification of rich fen, with loss of species diversity, occurs quicklywhen peat drains are blocked. The mechanism is by formation of a rainwater lens on top of calcium-richwater, leading to colonization by Sphagnum species. Experiments on floating rich-fen peat pits isolated byuncut peat walls (Beltman et al., 1995) showed that surface water drainage to remove rain water wasessential to restore rich fen and that restoration by peat-pit creation without drainage was unsuccessfulregardless of pit size. Van Diggelen et al. (1996) recorded transitions between rich fen and embryonic bogthat take 20–30 yr where there is rain-water infiltration, but noted that when root mats stay in contact withbase-rich water, the fen can persist longer, probably more than 100 yr.

Observations by White (1930), that the effects of peat-cutting depth on peat-pit vegetation wereimportant 150 yr after a closed and relatively stable vegetation had developed, suggest that the time scale ofchange last century was slow. This may have been a function of low phosphate concentrations in the waterand less nutrient-rich agricultural drains. Currently, the potential rate of change is probably higher than inthe past because of the effects of water rich in phosphate (McAllister et al., 1977) promoting vegetationdevelopment in habitats influenced by agricultural drains.

Changes in the hydrological regime of Lough Neagh earlier last century involved lowering and stabilizingthe water level of Lough Neagh, most recently in 1959 (Davidson, 1993), and probably initiated the currentphase of vegetation development in the pools and drains at Montiaghs Moss. Succession to poor fen is

Axis 1

Axis 2

-2.0(c) +6.0

-1.5

+5.0Hydrpalu

Agabstur

Suphdors

Hydrgyll

Rhanexso

Hygrinae

Hydrplan

Anaclimb

Agabmela

Hydrpube

Hydrobsc

Hydreryt

Porhlina

Enocochr

Grappict

Halirufi

Anaclute

Ilybquad

HyphovatNotecras

Laccminu

Agabbipu

Rhangrap

Figure 3 continued.



probably facilitated in the more isolated parts of the site where there is reduced flooding. The relativelyrecent cessation of drain management has probably also promoted surface acidification. The ecologicalconsequences of this are a reduction in the area of open-water habitats, poor-fen development andsubsequent reduced biodiversity.

The DCA vegetation model suggests that the trophic status of the drainage water, water depth andvegetation development are the main variables influencing species composition. The high phosphate andammonia concentrations in the main drains are probably derived from farm wastes, as suggested byMcAllister et al. (1977). Farm wastes also contribute to the conductivity of the water, together withgroundwater solutes from the largely basaltic catchment. Differences in trophic status among the mainagricultural drains, secondary drains, tertiary drains and peat pits are related to the connected nature of thenow largely abandoned bog drainage system. While the main agricultural drains have an influence onthe trophic status of the secondary drain vegetation, they have less effect on the more isolated vegetation ofthe tertiary drains and peat pits. In these habitats, poor-fen development, probably influenced by nutrientinput from agricultural drains, is the main driver of change. The hydrotrophic variables selected by CCA assignificantly explaining variation in the vegetation are good indicators of water trophic status andvegetation development: water hardness is indicative of high measured values of phosphate and ammonia,and water depth is indicative of vegetation development.

The Montiaghs appears to be the most species-rich beetle site in Ireland, with 58 species recorded byNelson et al. (1997). Of the 20 water beetle species recorded at Montiaghs Moss by Nelson et al. (1997) asnationally notable (sensu Ball, 1986), 11 were recorded in our samples, distributed across the full range ofpeat-pit and drain habitats. Foster (1995) argues that habitat structure is the key factor influencing thewater beetle composition of peat-bog pools in a Scottish blanket mire catchment. The Montiaghs Mossseems to sustain such a high number of beetle species because of the diversity of drain and peat-pit habitatsavailable. The ecological consequences of current vegetation development to poor-fen vegetationdevelopment and the effects of nutrients from agricultural drains are, therefore, likely to have long-termeffects in reducing beetle species diversity. Cessation of hand peat-cutting in the last 25 yr has reduced theinitiation of areas of open water of different depths throughout the system, thus decreasing habitatstructural heterogeneity further. Plant species with a notable conservation status at Montiaghs Moss occuracross the range of emergent-swamp and poor-fen vegetation types of the drains and peat pits (Countrysideand Wildlife Branch, 1985). C. virosa, for example, was recorded in the poor-fen vegetation samples. Thisspecies is typical of base-rich fen and swamp in Ireland (Webb et al., 1996). Its occurrence in a poor-fensample is indicative of vegetation change to ombrotrophic conditions and the ecological consequences ofsuch change.

Bilton (1992) demonstrates the importance of small demic populations breeding separately from eachother in pool complexes. The effectiveness of vegetation composition gradients in predicting beetle speciesassemblages shows that vegetation composition is a reliable indicator of beetle species assemblages and can,therefore, be used to inform management decisions on beetle population conservation. There areinsufficient data, however, to determine management priorities for particular beetle species.

Under current conditions of relatively controlled water levels for agriculture, long-term managementintervention is probably essential if the present aquatic vegetation and water beetle species assemblages areto be retained and site conservation value maintained. Flooding has been proposed as a mechanism forpreventing fen acidification (Giller and Wheeler, 1988). This is not a practical option at the MontiaghsMoss, because nutrient concentrations in the main agricultural drain running through the site are high.When the site flooded regularly (over 50 yr ago), the water was base rich, but it probably had lowerconcentrations of nutrients such as phosphorus. This work suggests that restoring variation in the structureand spatial variation of drain and peat-pit habitats by peat-pit excavation and drain clearing, guided byhistorical patterns of drain connectivity and current variation in habitat water depth and trophic structure,is an ecologically sound management prescription. The isolation of peat pits from agricultural drains,

A. COOPER ET AL.186


however, needs to be maintained, with tertiary drains and peat pits maintained at a water pH between 5 and7 and with low concentrations of phosphate. If drain excavation is too extensive, then their resultingincreased trophic status is likely to have detrimental effects.

The Montiaghs Moss habitat complex is a cultural landscape created by historic land-use, with speciesassemblages highly dependent on land management practices. There are large numbers of other cut-overlowland raised bogs in the farmed Northern Ireland countryside (Murray et al., 1992), most of which areunmanaged for biodiversity conservation (Smith and Cooper, 1997). These areas and their associated semi-aquatic drain and peat-pit vegetation contribute greatly to the regional biodiversity of lowland Irishagricultural landscapes. The European Union (EU) Environmentally Sensitive Area (ESA) scheme and theCountryside Management Scheme (CMS) are the principal measures by which EU Common AgriculturalPolicy agri-environment legislation (CEC, 1992) is implemented in Northern Ireland. The schemes aim tomaintain farm economies and promote biodiversity and cultural landscapes, and they function by imposingenvironment prescriptions and compensating farmers for this. The Water Framework Directive (WFD)(CEC, 2000) addresses EU water policy through river basin management plans. A primary objective of theWFD is to protect and enhance the status of aquatic ecosystems and the terrestrial ecosystems and wetlandsdirectly dependent on them. The WFD requires member states to encourage interested parties in itsimplementation. The management of cut-over lowland raised bog for biodiversity conservation initiallyneeds to address water quality issues through river basin management plans. Peat-drain and peat-pithabitat rejuvenation and creation could then be addressed through agri-environment schemes withoutdetrimental effects of nutrient-rich drainage water occurring. This joint strategy has the potential to deliverregional biodiversity gains.

ACKNOWLEDGEMENTS

We wish to thank Brian Nelson of the Belfast Museum for identifying beetle species.

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Vegetation, water beetles and habitat isolation in abandoned lowland bog drains and peat pits