-
4
Lakes
Streams
12
3
4
6
19 9 8
1011
12
1718
13
14
1516
7
2221
20
1. Loch Coire nan Arr2. Allt a'Mharcaidh3. Allt na Coire nan
Con4. Lochnagar5. Loch Chon6. Loch Tinker7. Round Loch of
Glenhead8. Loch Grannoch9. Dargall Lane10. Scoat Tarn11. Burnmoor
Tarn12. River Etherow13. Old Lodge14. Narrator Brook15. Llyn
Llagi16. Llyn Cwm Mynach17. Afon Hafren18. Afon Gwy19. Beagh's
Burn20. Bencrom River21. Blue Lough22. Coneyglen Burn
5
Site Summaries
■ 37
Chris Evans , Don Monteith,Bi l l Beaumont, Roger F lower,&
Jul ie Winterbottom
Figure 4.1.1 Location ofUKAWMN sites
-
38 ■
Chapter Four Site Summaries
-
4.1 Loch Coire nan Arr
■ Site ReviewLoch Coire nan Arr is the most northerly of
allUKAWMN sites. As atmospheric pollution loads atthe site were
known to be low and the waterchemistry relatively well buffered,
the site wasinitially considered as a potential control for
theother more impacted regions to the south.However,
palaeoecological studies have sincesuggested that the loch has
undergone very slightacidification in recent years (Patrick et
al.,1995).In 1991 a temporary dam was placed on the lochoutflow as
a means of conserving the water supplyto a fish farm located
beneath the site. Morerecently a permanent structure with sluice,
hasreplaced this. The dam has raised mean water levelat the site by
at least 0.5 m loch shoreline. Thewater level change has clearly
reduced the extentof emergent macrophyte stands at the site
(seebelow).
0 1 km
Loch Coire nan Arr
Contours in metres
Allt Coire nan Arr
500
600
700
200
300
400
500
500
600
700
200
300
400
500
Figure 4.1.1 Loch Coire nanArr: catchment
Table 4.1.1 Loch Coire nan Arr: site characteristics
Grid referenceLake altitudeMaximum depthMean depthVolumeLake
areaCatchment area (excl. lake)Catchment: Lake area ratioCatchment
GeologyCatchment Soils Catchment vegetation
Net reliefMean annual rainfall 1996 deposition Total Snon-marine
S Oxidised NReduced N
NG 808422125 m12.0 m4.8 m
5.6 x 105 m3
11.6 ha897 ha
77.3Torridonian Sandstone
peat moorland 99%
conifers
-
40 ■
Chapter Four L. Coire nan Arr
■ Water Chemistry(Figure 4.1.2,Table 4.1.2-3)
Although potentially susceptible to acidification,with a
ten-year mean Ca concentration of just 43µeq l-1, Loch Coire nan
Arr receives low levels ofanthropogenic S and N deposition and is
notacidic. Mean pH is 6.39 and mean alkalinity 38µeq l-1, with
labile Al concentrations at or closeto detection limits. Non-marine
SO4 con-centrations reflect the low deposition, with a tenyear mean
of 13.5 µeq l-1. NO3 concentrationshave remained below 10 µeq l-1
throughout themonitoring period, although some seasonality
isobserved with concentrations above detectionlimits during all
winter periods (Figure 4.1.2e).
The proximity of this site to the coast results inlarge marine
ion inputs, and Na and Clconcentrations at the loch are therefore
high (10year means 203 µeq l-1 and 258 µeq l-1respectively). Both
ions show a pronouncedseasonal cycle, with winter peaks resulting
fromlarge frontal storms at this time. Marine iondeposition events
have been shown to causeepisodic acidification through the
‘sea-salteffect’ (Wright et al., 1988; Langan, 1989)whereby marine
cations temporarily displace H+
from soil exchange sites. This natural process isevident in pH
and alkalinity minima that occurconcurrently with marine ion maxima
(Figure4.1.2a,b). Some temporary retention of marineSO4 may also
occur (Evans et al., in press;Section 5.3), leading to reduced or
even negativexSO4 concentrations (Figure 4.1.2d).
In accordance with the continuously low
pollutant deposition at the site, no significanttrends were
observed for pH, alkalinity, basecations or mineral acid anions.
There are also noidentifiable changes in chemistry following
therise in water level in 1991. However, large andhighly
significant increases were observed overthe last decade for both
DOC and non-labile Al(Table 4.1.3). LOESS curves suggest that
theseincreases took place fairly steadily between1988-1996, but may
have levelled off in recentyears. The SKT estimated total increase
over thedecade of 2.5 mg l-1 represents a major change inwater
chemistry given a mean concentration inthe first year of sampling
of just 1.0 mg l-1.Organically complexed non-labile Al shows aclear
correlation with DOC, suggesting thatconcentrations are determined
by the availabilityof complexing ligands (Driscoll et al.,
1984).Since almost all Al present is in non-labile form,total
soluble Al exhibits similar behaviour(Figures 4.1.2j,k). The issue
of DOC trends isdiscussed in detail in Section 5.2.3.
■ Epilithic diatoms(Figure 4.1.3,Table 4.1.4)
The epilithic diatom flora of Loch Coire nan Arrdemonstrates
marked inter-annual variation overthe past decade. Samples are
dominated byTabellaria flocculosa, (pH optima 5.4)Brachysira vitrea
(pH optima 5.9) andAchnanthes minutissima(pH optima 6.4),
T.flocculosa was most abundant between 1989-1991, gradually
declined until 1997 andincreased again in 1998. These changes
havebeen largely reciprocated by A. minutissima.Similar patterns in
species variation have
Table 4.1.3Significant trends in chemical determinands (June
1988 - March 1998)
Determinand Units Annual trend (Regression) Annual trend
(Seasonal Kendall)
DOC mg l -1 +0.21*** +0.25**
Non-labile Al µg l -1 +1.13** +1.00*
* Trend significant at p < 0.05; ** trend significant at p
< 0.01; *** trend significant at p < 0.001
-
■ 41
L. Coire nan Arr Chapter Four
Figure 4.1.2Loch Coire nan Arr:summary of
majorchemicaldeterminands (July 1988 - March 1998)
Smoothed linerepresents LOESScurve (Section 3.1.2)
•
•
•
•
••
•
•
•
•
• •• •
• •
•
•
•
•
• •
• •
• • •
•
• •
••
•
•
•
•
• ••
•
1989 1991 1993 1995 1997
6.0
6.5
7.0(a) pH
•
••
•
•
•
•
•
•
•
• •
••
••
•
•• •
• •
• •
• ••
•
•
•
••
•
•
•
•
•
•
•
•
1989 1991 1993 1995 1997
20
40
60
80
(b) Alkalinity
•
•
••
•
••
••
•
• •• •
• • •
••
•• •
••
•• • • • • •
••
•
••
• • ••
1989 1991 1993 1995 1997
-20
0
20
40
60
-20
0
20
40
60
(c) Sulphate
•
••
•
• • •
••
•• •
••
• • • • ••
•• •
•• • •
•
• • • • • • ••
•• •
•
1989 1991 1993 1995 1997
(d) Non-marine Sulphate
•
•
•
•
•
•
•
•• •
•
•
• •
• •
• ••
•
•
••
•
••
••
•
•
•
•
• •
•
••
•
•
•
1989 1991 1993 1995 1997
2
4
6
8
(e) Nitrate
•••
•
•
••
•
•
•
••
•
•
• ••
••
•
•
•
•
•
•• •
•
• • •
• •
•
•
•
•• •
•
1989 1991 1993 1995 1997
200
400
600
(f) Chloride
•
•
•
•
•
•
• •
•
•
• ••
•• •
•
••
••
••
•• • • • •
•
•
• •
••
•
••
••
1989 1991 1993 1995 1997
20
40
60
(g) Calcium
••
•
•
•
••
•
•
•
• • ••
• • •
••
•
•
•
•
•
•• •
•
• ••
• •
•
•
•
•• •
•
1989 1991 1993 1995 1997
200
300
400
500
(h) Sodium
•
• •
•
• • • • •
•
• ••
• • • •
•
• • • •
•
• ••
• • • • • • • • • • • • • •
1989 1991 1993 1995 1997
0
2
4
6
8
10
(i) Labile Al
•
••
•
•
•
••
•
•
•
•
•
•
•
•
•
••
• • •
••
•
•
•
•
• ••
•
•
•
•
••
•
••
1989 1991 1993 1995 1997
(j) Non-labile Al
•• •
•
••
••
•
•
•
•
••
•
•
•
• •
• • •
•• •
•
•
•
• • •
•
•
•
•• •
•
• •
1989 1991 1993 1995 1997
10
20
30
40
10
20
30
(k) Total Soluble Al
•• •
•
••
•• •
•
• • •
•
• • •
•
••
•
• •
•
•
•
•
•
••
•
•
•
•
•
•
•
•
•
•
1989 1991 1993 1995 1997
0
1
2
3
4
5
pHµe
q l-1
µeq
l-1µe
q l-1
µg l-
1µg
l-1
µeq
l-1
µ eq
l-1µ e
q l-1
µ eq
l-1µ
g l-1
mg
l-1
(l) Dissolved Organic Carbon
-
Chapter Four L. Coire nan Arr
42 ■
INDICATOR SPECIESNitella flexilis1 2 3 3 3 3 3 1 1Myriophyllum
alterniflorum2 3 3 3 3 3 3 2 2Utricularia sp.2 2 3 3 2 2 0 2
2Callitriche hamulata3 2 3 3 3 3 3 3 3Sphagnum auriculatum4 0 1 1 1
1 1 1 1Juncus bulbosus var. fluitans4 5 5 5 5 5 4 4 4OTHER
SUBMERGED OR FLOATING LEAF SPECIESBatrachospermum sp. 1 1 0 0 0 0 1
0Filamentous green algae 1 2 3 1 1 1 1 1Fontinalis sp. 1 1 1 0 0 0
0 0Rhytidiadelphus sp. 0 1 1 1 0 1 0 1Lobelia dortmanna 3 3 4 4 3 3
3 3Isoetes lacustris 4 4 4 4 4 3 3 3Littorella uniflora 3 3 4 4 4 3
3 3Subularia aquatica 0 0 0 0 0 0 0 1Potamogeton natans 4 4 4 4 4 2
2 4Potamogeton polygonifolius 0 0 1 1 0 1 1 1Sparganium
angustifolium 1 2 2 2 2 1 2 2EMERGENT SPECIESEquisetum fluviatile 2
2 2 2 2 1 2 0Ranunculus flammula 2 2 3 3 3 2 3 1Carex nigra 1 2 2 2
2 1 2 1Carex rostrata 0 0 1 1 0 0 0 0Eleocharis multicaulis 2 2 1 1
1 0 0 0Glyceria fluitans 1 1 1 1 1 0 1 0Juncus
acutifloris/articulatus 1 3 2 2 2 1 0 0Juncus effusus 1 1 1 1 1 1 1
1
TOTAL NUMBER OF SPECIES 20 22 23 22 19 18 19 18
Table 4.1.4Loch Coire nan Arr: trend statistics for epilithic
diatom, macrophyte and macroinvertebrate summary data (1988 -
1998)
Total sum Number Mean N2 λ1RDA/λ2RDA λ1RDA/λ1PCAof squares of
taxa diversity
Variance p
explained (%) within year between years linear trend
unrestricted restricted
Epilithic diatoms 49.9 50.1 7.0 0.01 0.24Macrophytes * *
30.1
-
occured in sediment trap samples from the lochwhich have been
collected since 1991 (Figure4.1.6). As the sediment traps should
provide anintegrated annual sample, it would seem that theepilithon
data are generally representative of thediatom crop for the full
growing season. Thevarying proportion of A. minutissimaand
T.flocculosaappear to indicate fluctuating levels ofacidity and
this is also shown by the diatominferred pH derived from pH
weighted averagingapplied to the whole assemblage (Figure
7.3a)which suggests a gradual increase in pH between1990 and 1996.
Although these inferences arenot strongly supported by changes in
waterchemistry, low pH was recorded in the spring of1990, 1997 and
1998, apparently associated withhigh rainfall and Cl
concentrations. The floristicsimilarity between 1998 samples and
those of1989-1991 appear to rule out any long termtrend. RDA shows
time to be insignificant as alinear variable at the 0.01 level
using therestricted permutation test. The extent to whichspecies
variation may be influenced by ‘natural’oscillations in acidity
will require verification byongoing monitoring.
■ Macroinvertebrates(Figure 4.1.4,Table 4.1.4)
The macroinvertebrate benthic fauna ismoderately diverse and
dominated byChironomidae and the acid tolerant mayflyfamily
Leptophlebiidae. Several mayfly specieshave been recorded
throughout the study period.The acid sensitive Baetis spp. has
appearedintermittently since 1991, Siphlonurus lacustrishas been
recorded in all years except 1990 and inmost recent years
Centroptilum luteolumreplaced the acid tolerant Leptophlebiidae as
thedominant mayfly. In studies of Finnishfreshwaters C. luteolumhas
a pH preference ofapproximately 6.0 (Hämäläinen &
Huttunen,1996). The acid tolerant caddisfliesPlectrocnemiaspp. and
Polycentropusspp. wererecorded throughout most of the
monitoringperiod, being most abundant in 1995 and 1993respectively.
However, Plectrocnemiaspp. hasbeen absent since 1996. RDA shows a
significantlinear trend at the 0.01 level. The shift in
speciesrelative abundance, and in particular the decrease
in the relative adundance of acid tolerantLeptophlebid mayflies
and the appearance of C.luteolum since 1996 is indicative of
animprovement in conditions.
■ Fish(Figure 4.1.5)
The outflow of Loch Coire nan Arr was firstfished in 1989. Trout
density is intermediate forUKAWMN sites. There are no significant
lineartrends in density, mean condition factor orcoefficient of
variance of condition factor foreither age group over the last nine
years.However, general declines in density of bothgroups are
apparent since 1991, possiblyreflecting an influence of the outflow
dam on thestream population. In common with many of theother
Scottish sites, very high recruitmentoccured in 1991. Mortality of
this cohorthowever appears to have been high as there is noevidence
of higher than average trout densitiesprogressing through the
subsequent year groups.Poorest recruitment occurred in 1992 and
1996.
■ Aquatic macrophytes(Table 4.1.4-5)
The aquatic macrophyte flora of Loch Coire nanArr is typical of
non-acid oligotrophic lakes. Thesubmerged community is dominated by
theisoetids, Isoetes lacustris, Lobelia dortmannaand Littorella
uniflora. The acid sensitivecharophyte species Nitella flexilis,
and otherspecies intolerant of acidity levels at the moreacid
UKAWMN lake sites (i.e. Myriophyllumalterniflorum and Utricularia
sp.) are alsopresent.
The installation of a dam, and the consequentincreases in mean
water level and levelfluctuations, appear to have led to a
substantialreduction in the abundance of some submergedspecies. In
particular N. flexilis, which waswidespread during the first few
years ofmonitoring, is now considered rare. Conversely,Potamogeton
natans, which forms floatingleaved beds in moderately deep water,
appears tohave increased. Assessment of cover of
L. Coire nan Arr Chapter Four
■ 43
-
Chapter Four L. Coire nan Arr
44 ■
Figure 4.1.3Loch Coire nan Arr:summary ofepilithic diatomdata
(1988 - 1998)
Percentagefrequency of all taxaoccurring at >2%abundance in
anyone sample
Euno
tia pe
ctina
lis va
r. ve
ntrali
s
Gomp
hone
ma in
tricatu
m
Euno
tia sp
.
Navic
ula su
btilis
sima
Frag
ilaria
vire
scen
s var
. exig
ua
Cymb
ella m
icroc
epha
la
Euno
tia rh
ombo
idea
Euno
tia pe
ctina
lis va
r. mi
nor
2040
60
Tabe
llaria
flocc
ulosa
Achn
anthe
s sp.
20
Frus
tulia
rhom
boide
s var
. sax
onica
20Br
achy
sira b
rebis
sonii
Achn
anthe
s alta
ica
20
Achn
anthe
s sco
tica
Pero
nia fib
ula
Gomp
hone
ma gr
acile
Cymb
ella l
unata
Syne
dra a
cus
Euno
tia in
cisa
Gomp
hone
ma an
gusta
tum
Euno
tia pe
ctina
lis va
r. mi
nor f
. impr
essa
2040
60
Brac
hysir
a vitre
a
Nitzs
chia
perm
inuta
Syne
dra m
inusc
ula
Frag
ilaria
vauc
heria
e
Euno
tia na
egeli
i
Navic
ula le
ptostr
iata
2040
60
Achn
anthe
s minu
tissim
a
Euno
tia ex
igua
Syne
dra r
umpe
ns
Nitzs
chia
grac
ilis
year
88 89 90 91 92 93 94 95 96 97 98
% fr
eque
ncy
of ta
xa in
eac
h sa
mpl
e
-
L. Coire nan Arr Chapter Four
■ 45
submerged species has been hampered by theproblem of precise
re-location of transects nowthat the characteristics of the lake
perimeter havechanged. It is highly likely that the
water-levelchange has also been responsible for the loss ofemergent
stands of Equisetum fluviatile, Carexrostrataand Eleocharis
multicaulis. It is unlikelythat these species could become
re-established atthe site unless water level management were
tocease for a considerable period. “Sample year” issignificant as a
linear trend according to RDAand restricted permutation tests but
this almostcertainly results from the effects of water
levelchange.
■ SummaryDespite geological sensitivity, Coire nan Arrreceives
very low levels of pollutant inputs, andhas remained unacidic for
most of the monitoringperiod. Episodic pH and alkalinity reductions
area feature of the site, due to large winter inputs ofmarine ions
and high rainfall, and it is possiblethat these have influenced the
inter-annualdifferences in species assemblages of diatomsand
macroinvertebrates. However, negativealkalinities, have not been
recorded at any timeduring the study period. Given the low levels
ofpollutant deposition, loch chemistry appearsgenerally stable over
the last ten years, butsignificant increases have been recorded
forDOC and non-labile Al. A rise in water levelfollowing damming,
and subsequent water levelmanagement since 1991, has led to
considerableinundation of the loch’s former shoreline. Theincreased
DOC at this site could therefore resultfrom peat erosion. However,
similar trends areobserved at many other sites in the
Network,suggesting a more general pattern of rising DOC.This issue
is discussed in detail in Section 5.2.3.Changes in water level have
almost certainly leadto a reduction in the representation of
emergentmacrophytes (through loss of habitat), while out-flow
regulation may have had an impact on thetrout density of the
outflow burn
-
Chapter Four L. Coire nan Arr
46 ■
Figure 4.1.4Loch Coire nan Arr:summary ofmacroinvertebratedata
(1988 - 1998)
Percentage frequency of taxa inindividual samples
Lymn
aea p
ereg
ra
20
Pisid
ium sp
.
2040
OLIG
OCHA
ETA
20
Glos
sipho
nia sp
.
Helob
della
stag
nalis
20
40
Siph
lonur
us la
custr
is
20
Amele
tus in
opina
tus
Baeti
s sp.
2040
60Ce
ntrop
tilum
luteo
lum
20
Centr
optilu
m pe
nnula
tum
Hepta
genia
later
alis
2040
6080
LEPT
OPHL
EBIID
AE
Amph
inemu
ra su
lcico
llis
Nemo
ura s
pp.1
Siph
onop
erla
torre
ntium
Arcto
coris
a ger
mari
Potam
onec
tes de
pres
sus
Hydr
opor
us pa
lustris
Oulim
nius t
uber
culat
us
20
Plec
trocn
emia
sp.
20
Polyc
entro
pus s
p.
Holoc
entro
pus s
p.
LIMNE
PHILI
DAE
unde
t.
20
Limne
philu
s sp.
Seric
ostom
a per
sona
tum
TIPU
LIDAE
CULIC
IDAE
CERA
TOPO
GONI
DAE
2040
6080
CHIR
ONOM
IDAE
20
EMPI
DIDA
E
200
400
600
TOTA
L NO
. IND
IVID
UALS
Yea
r
88 89 90 91 92 93 94 95 96 97 98
% fr
eque
ncy
of ta
xa in
eac
h sa
mpl
e
-
L. Coire nan Arr Chapter Four
■ 47
Figure 4.1.5Loch Coire nan Arr:summary of fishdata (1988 -
1997)(a) Trout
populationdensity for 0+and >0+ ageclasses(individuals 100
m-2)
(b) Mean conditionfactor (withstandarddeviation) of thetrout
populationand itscoefficient ofvariation(histogram)
(a) Density
0
5
10
15
20
25
30
35
40
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
no
. in
ds.
100
m-2
Dens ity 0+ Density >0+
(c) Condition (>0+)
0
2
4
6
8
10
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
cv(h
isto
gra
m)
0.8
1.0
1.2
me
anco
nd
itio
nfa
cto
r
(b) Condition (0+)
0
5
10
15
20
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
cv(h
isto
gra
m)
0.8
1.0
1.2
me
anco
nd
itio
nfa
cto
r
notfished
notfished
notfished
-
Chapter Four L. Coire nan Arr
48 ■
Figure 4.1.5Loch Coire nan Arr:summary of fishdata (1989 -
1997)(c) Trout length
frequencysummaries (1989 - 1998)
1989
0
20
40
60
1990
0
20
40
60
1991
0
20
40
60
1992
0
20
40
60
1993
0
20
40
60
1994
0
20
40
60
1995
0
20
40
60
1996
0
20
40
60
1997
0
20
40
60
0 50 100 150 200 250 300
length (mm)
-
L. Coire nan Arr Chapter Four
■ 49
Figure 4.1.6Loch Coire nan Arr:summary ofsediment trap datafor
diatoms andcarbonaceousparticles
Relative frequency of diatom taxa (>2% inat least one sample)
at time of trap retrievaland estimatedcarbonaceous particleflux
(no. trap-1 day-1) for preceding year
Achn
anthe
s pse
udos
wazi
20
Achn
anthe
s minu
tissim
a
Achn
anthe
s mar
ginula
ta
Achn
anthe
s sax
onica
Achn
anthe
s mod
estifo
rmis
20
Brac
hysir
a vitre
a
Brac
hysir
a bre
bisso
nii
Cymb
ella p
erpu
silla
Cymb
ella m
inuta
Cymb
ella l
unata
Euno
tia pe
ctina
lis
Euno
tia pe
ctina
lis va
r. mi
nor
Euno
tia pe
ctina
lis va
r. ve
ntrali
s
Euno
tia pe
ctina
lis va
r. mi
nor f
. impr
ess
Euno
tia ex
igua
Euno
tia rh
ombo
idea
20
Euno
tia in
cisa
Euno
tia na
egeli
i
Euno
tia sp
.
Frag
ilaria
vire
scen
s var
. exig
ua
Frag
ilaria
vauc
heria
e
Frus
tulia
rhom
boide
s var
. sax
onica
Gomp
hone
ma an
gusta
tum
Nitzs
chia
perm
inuta
Pero
nia fib
ula
20
Tabe
llaria
flocc
ulosa
20
CARB
ONAC
EOUS
PAR
TICL
E FL
UX
Yea
r
1991
1992
1993
1994
1995
1996
1997
1998
-
Chapter Four L. Coire nan Arr
50 ■
-
Allt a’Mharcaidh Chapter Four
4.2 Allt a’Mharcaidh
■ Site ReviewThe Allt a’Mharcaidh, in the western Cairngormsof
northeast Scotland, is a well buffered mountainstream which is
subject to occasional acidepisodes. No physical changes have been
observedin the study catchment since the onset ofmonitoring in
1988. The Allt a’Mharcaidh wasstudied as part of the SWAP project
(e.g. Ferrier &Harriman, 1990). It is one of the two British
sitesrepresented in the UNECE Integrated MonitoringProgramme (UNECE
- IMP) and is also afreshwater site in the UK Environmental
ChangeNetwork (ECN).
■ Water Chemistry(Figure 4.2.2,Table 4.1.2-3)
The Allt a’Mharcaidh has a relatively well bufferedchemistry,
with a 10 year mean pH of 6.45.Although the site can be considered
acid-sensitive,with a mean Ca of 42 µeq l-1, S and N depositionare
low. Mean xSO4 is 33 µeq l-1, whilst virtuallyall incoming N is
retained; NO3 concentrations in88% of samples collected were below
detectionlimits, and the maximum recorded was 5 µeq l-1.
The Allt a’Mharcaidh is however subject to acidicepisodes, in
which alkalinity falls to around zeroand pH to
-
52 ■
Chapter Four Allt a’Mharcaidh
regression analysis. However the same increaseis not found using
SKT, and the time series plot(Figure 4.2.2) suggests that this
trend may be theresult of a small number of high DOC samples
inrecent years rather than a genuine and sustainedincrease.
■ Epilithic diatoms(Figure 4.2.3,Table 4.2.4)
The epilithon of Allt a’Mharcaidh is dominatedby Synedra
minuscula, Achnanthes minutissimaand Fragilaria vaucheriae, species
typical ofmildly acidic softwater streams. These taxa have
shown marked variation in their relativeabundance between years,
A. minutissimashowing relatively high abundances from 1991-1992 and
1994-1995. F. vaucheriaeand rare taxa,including Gomphonema
angustatum[agg.] andDiatoma hyemale var. mesodon, have undergonea
decline in relative abundance since the onset ofmonitoring, while
Achnanthes modestiformishasincreased slightly. The species
assemblage in1998 samples was particularly unusual, withrelatively
high representation of Brachysiravitrea, B. brebissonii, Frustulia
rhomboides var.saxonica and Achnanthes marginulata. Thesespecies
have relatively low pH optima and theirincrease is likely to
reflect a sustained period ofdepressed pH over the summer of 1998
resultingfrom unusually high flow conditions (see Section7.4.1).
RDA analysis shows time as an explana-tory variable to be
insignificant at the 0.01 leveland no trend is apparent in diatom
inferred pHfor the site.
■ Macroinvertebrates
(Figure 4.2.4,Table 4.2.4)
The macroinvertebrate community of Allta’Mharcaidh is diverse
and dominated through-out the monitoring period by the acid
sensitivemayfly Baetisspp.. Several other acid sensitivemayflies
are also present in lower numbers,including Rhithrogena
semicolorata andHeptagenia lateralis. The site also contains
adiverse assemblage of stoneflies of whichLeuctra inermis is most
abundant, while othercommon taxa include Brachyptera
risi,Protonemura spp., Amphinemura sulcicollis andthe predatory
species Isoperla grammatica and
Table 4.2.3Significant trends in chemical determinands (July
1988 - March 1998)
Determinand Units Annual trend (Regression) Annual trend
(Seasonal Kendall)
DOC mg l -1 +0.11*** -
* Trend significant at p < 0.05; ** trend significant at p
< 0.01; *** trend significant at p < 0.001
Table 4.2.2 Allt a’Mharcaidh: summary of chemicaldeterminand,
July 1988 - March 1998
pH 6.45 7.08 5.12Alkalinity µeq l-1 44.2 91.0 -4.0Ca µeq l-1
42.0 60.5 4.5Mg µeq l-1 29.2 50.0 16.7Na µeq l-1 135.2 213.0 91.3K
µeq l-1 7.4 12.8 2.6SO4 µeq l-1 44.4 72.9 29.2xSO4 µeq l-1 32.9
57.9 18.3NO3 µeq l-1 1.4 5.0 < 1.4Cl µeq l-1 110.1 259.2
56.3Soluble Al µg l-1 35.7 166.0 < 2.5labile Al µg l-1 6.7 46.0
< 2.5Non-labile Al µg l-1 29.8 150.0 < 2.5DOC mg l-1 2.3 12.1
< 0.1Conductivity µS cm-1 24.0 38.0 14.0
Determinand Mean Max Min
-
■ 53
Allt a’Mharcaidh Chapter Four
Figure 4.2.2Allt a’Mharcaidh:summary of
majorchemicaldeterminands(April 1988 - March 1998)
Smoothed linerepresents LOESScurve (Section 3.1.2)
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(e) Nitrate
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(f) Chloride
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(g) Calcium
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(h) Sodium
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(i) Labile Al
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(j) Non-labile Al
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(k) Total Soluble Al
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(l) Dissolved Organic Carbon
pHµe
q l-1
µeq
l-1µe
q l-1
µg l-
1µg
l-1
µeq
l-1
µ eq
l-1µ e
q l-1
µ eq
l-1µ
g l-1
mg
l-1
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Chloroperla tripunctata.The macroinvertebratecommunity remains
relatively persistent with nomarked changes in either species
abundance orcomposition. Time as a linear trend is notsignificant
at a 0.01 level, using RDA andassociated permutation tests.
■ Fish(Figure 4.2.5(i), (ii))
Trout densities at this site are the third highest ofthose found
in the Network sites. Although
Chapter Four Allt a’Mharcaidh
54 ■
(% cover of 50 m survey stretch)Year 88 89 90 91 92 93 95 96
97
INDICATOR SPECIESLemanaea sp.1 0.0 0.4 0.0 1.4 0.0 0.0 0.4 0.0
0.4Brachythecium plumosum1
-
Allt a’Mharcaidh Chapter Four
■ 55
Figure 4.2.3Allt a’Mharcaidh:summary ofepilithic diatomdata
(1988 - 1998)
Percentagefrequency of all taxaoccurring at >2%abundance in
anyone sample
Gomp
hone
ma cl
avatu
m
Gomp
hone
ma ac
umina
tum
2040
Hann
aea a
rcus
Diato
ma hy
emale
var.
meso
don
Euno
tia pe
ctina
lis va
r. mi
nor
20
Achn
anthe
s deth
a
Diato
ma hy
emale
2040
Frag
ilaria
vauc
heria
e
Gomp
hone
ma in
tricatu
m
Gomp
hone
ma an
gusta
tum
Euno
tia [s
p. 1
0 (m
inim
a)]
Euno
tia pe
ctina
lis
2040
6080
Achn
anthe
s minu
tissim
a
Achn
anthe
s sax
onica
2040
60
Syne
dra m
inusc
ula
20Ta
bella
ria flo
cculo
sa
Frus
tulia
rhom
boide
s var
. virid
ula
Frag
ilaria
vire
scen
s
Gomp
hone
ma co
nstric
tum
Achn
anthe
s mod
estifo
rmis
Euno
tia va
nheu
rckii v
ar. in
terme
dia
Achn
anthe
s aus
triaca
var.
helve
tica
Euno
tia pe
ctina
lis va
r. ve
ntrali
s
Frus
tulia
rhom
boide
s var
. sax
onica
Euno
tia in
cisa
Syne
dra u
lna
Cymb
ella l
unata
Achn
anthe
s helv
etica
var.
mino
r
20
Achn
anthe
s mar
ginula
ta
20
Brac
hysir
a vitre
a
Brac
hysir
a bre
bisso
nii
Achn
anthe
s alta
ica
Yea
r
88 89 90 91 92 93 94 95 96 97 98
% fr
eque
ncy
of ta
xa in
eac
h sa
mpl
e
-
population densities of 0+ trout show somevariation over the ten
years of monitoring, thereis no apparent trend in this fluctuation.
Mostyears show good recruitment with 1991, 1996and 1997 showing the
highest densities.Population densities of >0+ trout are more
stableand show a significant (p =
-
Allt a’Mharcaidh Chapter Four
■ 57
Figure 4.2.4Allt a’Mharcaidh:summary ofmacroinvertebratedata
(1988 - 1998)
Percentagefrequency of taxa inindividual samples
Amele
tus in
opina
tus
2040
60
Baeti
s sp.
Rhith
roge
na se
mico
lorata
20Br
achy
ptera
risi
Proto
nemu
ra sp
.
20
Amph
inemu
ra su
lcico
llis
2040
Leuc
tra in
ermi
s
Leuc
tra hi
ppop
us
20
Isope
rla gr
amma
tica
Chlor
oper
la trip
uncta
ta
Oreo
dytes
sanm
arkii
Elmi
s aen
ea
Rhya
coph
ila sp
.
TIPU
LIDAE
2040
CHIR
ONOM
IDAE
2040
60
SIMU
LIIDA
E
EM
PIDI
DAE
500
1000
1500
2000
TOTA
L NO
. IND
IVID
UALS
Yea
r
88 89 90 91 92 93 94 95 96 97 98
% fr
eque
ncy
of ta
xa in
eac
h sa
mpl
e
-
Chapter Four Allt a’Mharcaidh
58 ■
Figure 4.2.5 (i)Allt a’Mharcaidh:summary of fishdata (1988 -
1997)(a) Trout population
density for 0+and >0+ ageclasses(individuals 100 m-2)
(b) Mean conditionfactor (withstandarddeviation) of thetrout
populationand itscoefficient ofvariation(histogram)
(a) Density
0
20
40
60
80
100
120
140
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
no
. in
ds.
100
m-2
Density 0+ Density >0+
Condition (>0+)
02468
101214
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
cv(h
isto
gra
m)
0.8
1.0
1.2
1.4
me
anco
nd
itio
nfa
cto
r
(b) Condition (0+)
0
5
10
15
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
cv(h
isto
gra
m)
0.8
1.0
1.2
1.4
me
anco
nd
itio
nfa
cto
r
-
Allt a’Mharcaidh Chapter Four
■ 59
1989
0
20
40
60
1990
0
20
40
60
1991
0
20
40
60
1992
0
20
40
60
1993
0
20
40
60
1994
0
20
40
60
1995
0
20
40
60
1996
0
20
40
60
1997
0
20
40
60
0 50 100 150 200 250 300
length (mm)
1988
0
20
40
60 Figure 4.2.5 (i)Allt a’Mharcaidh:summary of fishdata (1988 -
1997)(c) Trout length
frequencysummaries(1988 - 1997)
-
Chapter Four Allt a’Mharcaidh
60 ■
0
5
10
15
20
25
30
35
40
45
50
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
no
.in
ds.
100
m-2
1988
0
10
20
30
1989
0
10
20
30
1990
0
10
20
30
1991
0
10
20
30
1992
0
10
20
30
1993
0
10
20
30
1994
0
10
20
30
1995
0
10
20
30
1996
0
10
20
30
1997
0
10
20
30
0 50 100 150 200 250 300
(b)
(a)
length (mm)
Figure 4.2.5 (ii)Allt a’Mharcaidh:summary of fishdata
(1988-1997)(a) Mean site density
of salmon (allage classes)
(b) Salmon lengthfrequencysummaries(1988-1997)
-
Allt na Coire nan Con Chapter Four
4.3 Allt na Coire nan Con
■ Site ReviewAllt na Coire nan Con, in the Strontian region
ofnorthwest Scotland, is a fast flowing stream withina partially
forested catchment. The bulk of thecatchment was planted
(predominantly with spruceand larch) around 1970. Grazing on the
upperslopes is confined to deer. Considerable felling andsome
re-planting has been carried out, particularlyover the last 5 years
(see Figure 4.3.1), includingareas close to the survey and sampling
stretches.
■ Water Chemistry
(Figure 4.3.2,Table 4.3.2-3)
Mean pH (5.85) and alkalinity (22 µeq l-1) aresomewhat lower
than at Loch Coire nan Arr, theother northwest Scotland site, and
mean xSO4 (30µeq l-1) substantially higher. A number of acidic
episodes have been recorded, with pH fallingbelow 5.0 and
alkalinity becoming negative duringthe most severe events. Sea-salt
inputs areextremely high, since the catchment is very close tothe
west coast. As winter sea-salt deposition events
�
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����
�����
�
������
���
��
�
��
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�planted pre 1988
felled and re-planted post 1988
felled since 1988
500500
500
600
700
500
600
700
400
300
200
100
400
300
200
100
400
300
200
100
Contours in metres
0 500 m
Allt na Coirenan Con
Figure 4.3.1 Allt na Coire nanCon: catchment
Table 4.3.1 Allt na Coire nan Con: site characteristics
Grid referenceCatchment areaMinimum catchment altitudeMaximum
catchment altitudeCatchment GeologyCatchment Soils
Catchment vegetation
Mean annual rainfall 1996 deposition Total Snon-marine S
Oxidised NReduced N
NM 793688790 ha
10 m756 m
schists and gneisspeaty podsols,
peaty gleys, peats conifers 42%
recently felled 4% moorland 54%
2582 mm
22 kg ha-1 yr-1
12 kg ha-1 yr-1
5 kg ha-1 yr-1
6 kg ha-1 yr-1
Table 4.3.2 Allt na Coire nan Con: summary ofchemical
determinands,June 1988 - March 1998
pH 5.85 6.70 4.96Alkalinity µeq l-1 21.6 98.0 -11.0Ca µeq l-1
57.5 107.5 22.5Mg µeq l-1 67.5 175.0 25.0Na µeq l-1 262.2 569.6
152.2K µeq l-1 9.0 18.5 2.6SO4 µeq l-1 61.3 110.4 35.4xSO4 µeq l-1
30.2 81.5 -7.7NO3 µeq l-1 4.3 17.1 < 1.4Cl µeq l-1 296.3 816.9
126.8Soluble Al µg l-1 65.7 131.0 12.0Labile Al µg l-1 17.4 98.0
< 2.5Non-labile Al µg l-1 48.5 110.0 10.0DOC mg l-1 3.9 10.0
< 0.1Conductivity µS cm-1 46.3 108.0 20.0
Determinand Mean Max Min
■ 61
-
Chapter Four Allt na Coire nan Con
tend to coincide with periods of high rainfall, it islikely that
the major winter acid episodes resultfrom the net effects of marine
ion displacementof H+ ions and base cation dilution. NO3,although
still low (mean 4.3 µeq l-1), is present atmeasurable
concentrations during winter periods,suggesting the commencement of
nitrogensaturation. Since estimated moorland S and Ndeposition are
similar at the two north westernsites (Tables 4.1.1 and 4.3.1), the
more impactednature of Allt na Coire nan Con may result
fromelevated dry deposition inputs to the large area ofconiferous
forest.
SKT analysis suggests a decrease in Cl over thestudy period, but
this is not detected usingregression. Since the only significant
source ofCl is marine, it is likely that any apparent trend inthis
anion is the result of natural climaticvariation. This is supported
by the time seriesdata and LOESS fit (Figure 4.3.2f) showing
aperiod of raised Cl during the early part of therecord.
Both trend detection methods indicate highlysignificant
increases in DOC over the monitoringperiod, which appears to have
taken place at anapproximately constant rate (Table 4.3.3,
Figure4.3.2). The total estimated increase of 2.8 mg l-1
over the ten years is similar to that at Loch Coirenan Arr, but
from a higher initial value. Anassociated increase is also apparent
for non-labileAl. The issue of DOC trends is discussed inSection
5.2.3.
■ Epilithic diatoms
(Figure 4.3.3,Table 4.3.4)
The epilithic diatom flora of Allt na Coire nanCon shows
considerable inter-annual variability.Samples from the early years
of monitoring weredominated by Achnanthes saxonica(pH optima5.7).
This species was less abundant between1993 - 1997, when Synedra
minuscula,A. minut issima and Brachysira v i t rea(a l l o f wh ich
have slightly higher pHpreferences) increased, but it became
dominantagain in 1998. The acidophilous speciesTabellaria
flocculosawas the dominant taxa in1993. Diatom inferred pH values
correlateclosely with summer rainfall totals for the
nearbyMeteorological Station (Inverailort), suggestingthat the
species assemblage has been stronglyinfluenced by natural pH
variations linked tovarying summer flow conditions (see
section7.4.1). “Sample year” is insignificant as a lineartrend
using RDA and restricted permutation test.
■ Macroinvertebrates
(Figure 4.3.4,Table 4.3.4)
The macroinvertebrate fauna is typical of amildly acid
oligotrophic stream, and ischaracterised by chironomidae, Simulidae
and adiverse fauna of both mayflies and stoneflies.The acid
sensitive mayfly Rhithrogenasemicoloratadominated the first seven
years of
Table 4.3.3Allt na Coire nan Con: significant trends in chemical
determinands(June 1988 - March 1998)
Determinand Units Annual trend (Regression) Annual trend
(Seasonal Kendall)
C1 µeq 1-1 - -7.65*
DOC mg 1-1 +0.21*** +0.25**Non-labile Al µg 1-1 +1.13**
+1.00*
* Trend significant at p < 0.05; ** trend significant at p
< 0.01; *** trend significant at p < 0.001
62 ■
-
■ 63
Allt na Coire nan Con Chapter Four
Figure 4.3.2Allt na Coire nanCon: summary ofmajor
chemicaldeterminands (June 1988 - March 1998)
Smoothed linerepresents LOESScurve (Section 3.1.2)
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1989 1991 1993 1995 1997
5.0
5.5
6.0
6.5
(a) pH•
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1989 1991 1993 1995 1997
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20
40
60
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(b) Alkalinity
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1989 1991 1993 1995 1997
0
50
100
(c) Sulphate
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1989 1991 1993 1995 1997
0
50
100
(d) Non-marine Sulphate
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1989 1991 1993 1995 1997
5
10
15
(e) Nitrate
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1989 1991 1993 1995 1997
200
400
600
800
(f) Chloride
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1989 1991 1993 1995 1997
20
40
60
80
(g) Calcium
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1989 1991 1993 1995 1997
200
500
300
400
(h) Sodium
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1989 1991 1993 1995 1997
0
20
40
60
80
100
100
(i) Labile Al
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1989 1991 1993 1995 1997
20
60
80
40
100
(j) Non-labile Al
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1989 1991 1993 1995 1997
50
100
(k) Total Soluble Al
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1989 1991 1993 1995 1997
0
2
4
6
8
10
(l) Dissolved Organic Carbon
pHµe
q l-1
µeq
l-1µe
q l-1
µg l-
1µg
l-1
µeq
l-1
µ eq
l-1µ e
q l-1
µ eq
l-1µ
g l-1
mg
l-1
-
the study period, while Baetisspp. was presentthroughout and
showed an increase in numbers in1996. Siphlonurus lacustrisappeared
in 1993and Heptagenia lateralis, which first appeared in1992, has
shown an increase in abundance in thelatter years of the study. The
stonefly communityincludes the detritivores Brachyptera
risi,Leuctra inermisand Amphinemura sulcicollisas
well as predators Isoperla grammatica andChloroperla
tripunctata. Several ‘new’ species ofcaddisfly were recorded after
1992, among themChaetopteryx villosa, Silo pallipes andLepidostoma
hirtum, the latter intolerant of veryacid conditions. Moderately
acid sensitiveColeoptera Hydraena gracilis and Elmis aeneawere
first recorded in 1994. 1990 was a very poor
Chapter Four Allt na Coire nan Con
64 ■
(% cover of 50 m survey stretch)Year 88 89 90 91 92 93 95 96
97
INDICATOR SPECIESHygrohypnum ochraceum1 16.0 16.2 16.6 9.4 3.7
1.5 0.2 0.4 0.1Hyocomium armoricum1
-
Allt na Coire nan Con Chapter Four
■ 65
Figure 4.3.3Allt na Coire nanCon:summary ofepilithic diatomdata
(1988 - 1998)
Percentagefrequency of all taxaoccurring at >2%abundance in
anyone sample
Frus
tulia
rhom
boide
s var
. virid
ula
20
Euno
tia ex
igua
2040
6080
Achn
anthe
s sax
onica
E
unoti
a sp.
Frag
ilaria
vauc
heria
e
2040
6080
Tabe
llaria
flocc
ulosa
Eun
otia r
homb
oidea
20
Gomp
hone
ma an
gusta
tum
2040
Syne
dra m
inusc
ula
20
Euno
tia in
cisa
2040
60
Achn
anthe
s minu
tissim
a
Frus
tulia
rhom
boide
s var
. sax
onica
20
Brac
hysir
a vitre
a
Gomp
hone
ma co
nstric
tum
Gomp
hone
ma co
nstric
tum va
r. ca
pitatu
m
20
Euno
tia pe
ctina
lis va
r. mi
nor f
. impr
ess
Navic
ula le
ptostr
iata
Brac
hysir
a bre
bisso
nii
Yea
r
88 89 90 91 92 93 94 95 96 97 98
% fr
eque
ncy
of ta
xa in
eac
h sa
mpl
e
-
year both in number of species and abundance.Time as a linear
trend accounts for 15.8% of thetotal variance and is significant at
the 0.01 level.There is some indication of an improvement
inconditions as species richness has increased inthe second half of
the study period, although thiscould be linked to a decline in
spring flowconditions (Section 7.4.2).
■ Fish
(Figure 4.3.5)
Trout densities at this site are intermediate forthose found on
the Network. Mean populationdensities of both 0+ and >0+ trout
show no trendsover the ten years. However, in common withseveral
other Scottish sites, densities of 0+ fishshowed a peak in 1991,
and higher than averagerecruitment also occurred in 1990 and 1995.
Verylow densities of >0+ fish were recorded in threeconsecutive
years between 1992-1994 despite thehigh recruitment observed in
1991. Significantnegative linear trends are apparent in
thecoefficient of variation of CF for the 0+ group(p0+ group (p
-
Allt na Coire nan Con Chapter Four
■ 67
Figure 4.3.4Allt na Coire nanCon:summary ofmacroinvertebratedata
(1988 - 1998)
Percentagefrequency of taxa inindividual samples
OLIG
OCHA
ETA
20
Siph
lonur
us la
custr
is
Amele
tus in
opina
tus
2040
Baeti
s sp.
2040
Rhith
roge
na se
mico
lorata
20
Hepta
genia
later
alis
Ecdy
onur
us sp
.
LEPT
OPHL
EBIID
AE
20
Brac
hypte
ra ris
i
20
Proto
nemu
ra sp
.
2040
Amph
inemu
ra su
lcico
llis
Nemo
ura s
pp.1
Nemo
ura s
pp.2
2040
Leuc
tra in
ermi
s
Leuc
tra hi
ppop
us
Leuc
tra ni
gra
20
Isope
rla gr
amma
tica
20
Siph
onop
erla
torre
ntium
20Ch
lorop
erla
tripun
ctata
2040
Oreo
dytes
sanm
arkii
Hydr
aena
grac
ilis
20
Limniu
s volc
kmar
i
Rhya
coph
ila sp
.
Plec
trocn
emia
sp.
Polyc
entro
pus s
p.
LIM
NEPH
ILID
AE u
ndet
.
Silo
pallip
es
Lepid
ostom
a hirtu
m
TIPU
LIDA
E
CULI
CIDA
E
2040
60
CHIR
ONOM
IDAE
2040
6080
SIM
ULIID
AE
200
400
600
TOTA
L NO
. IND
IVID
UALS
Y
ear
88 89 90 91 92 93 94 95 96 97 98
% fr
eque
ncy
of ta
xa in
eac
h sa
mpl
e
-
Chapter Four Allt na Coire nan Con
68 ■
Figure 4.3.5 (i)Allt na Coire nanCon:summary of fishdata (1988 -
1997)(a) Trout population
density for 0+and >0+ ageclasses(individuals 100 m-2)
(b) Mean conditionfactor (withstandarddeviation) of thetrout
populationand itscoefficient ofvariation(histogram)
(a) Density
0
5
10
15
20
25
30
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
no
. in
ds.
100
m-2
Density 0+ Density >0+
Condition (>0+)
0
5
10
15
20
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
cv(h
isto
gra
m)
0.8
1.0
1.2
1.4
me
anco
nd
itio
nfa
cto
r
(b) Condition (0+)
0
5
10
15
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
cv(h
isto
gra
m)
0.8
1.0
1.2
1.4
me
anco
nd
itio
nfa
cto
r
-
Allt na Coire nan Con Chapter Four
■ 69
1989
0
5
10
15
1990
0
5
10
15
1991
0
5
10
15
1992
0
5
10
15
1993
0
5
10
15
1994
0
5
10
15
1995
0
5
10
15
1996
0
5
10
15
1997
0
5
10
15
0 50 100 150 200 250 300
length (mm)
1988
0
5
10
15 Figure 4.3.5 (i)Allt na Coire nanCon: summary offish data
(1988 -1997)(c) Trout length
frequencysummaries(1988 - 1997)
-
Chapter Four L. Coire nan Arr
70 ■
0
20
40
60
80
100
120
140
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
no.
inds
.100
m-2
1988
0
20
40
60
1989
0
20
40
60
1990
0
20
40
60
1991
0
20
40
60
1992
0
20
40
60
1993
0
20
40
60
1994
0
20
40
60
1995
0
20
40
60
1996
0
20
40
60
1997
0
20
40
60
0 50 100 150 200 250 300
length (mm)
(b)
(a)Figure 4.3.5 (ii)Allt na Coire nanCon: summary of fishdata
(1988-1997)(a) Mean site density
of salmon (all ageclasses)
(b) Salmon lengthfrequencysummaries
-
Lochnagar Chapter Four
4.4 Lochnagar
■ Site ReviewAt an altitude of 785 m in the Grampian Mountainsof
northeast Scotland, Lochnagar is the highest ofthe UKAWMN lakes.
Palaeoecological pHreconstruction indicates that Lochnagar
acidifiedfrom around pH 5.6, in the mid-nineteenth century,to
around pH 5.0 by the 1940s (Patricket al.1989,Patrick et al. 1995).
Although prone to aconsiderable duration of ice cover during
somewinters, the extent of the freezing period has beenhighly
variable over the past decade, with ice onlypresent for a few days
during the winter of 1997-1998. Scientific work at Lochnagar has
increasedsince its inclusion in the EU funded mountain
lakesprojects AL:PE, MOLAR, CHILL and, mostrecently, EMERGE, in
addition to a DETR study ofthe impact of heavy metals deposition
andadditional sampling carried out for theEnvironmental Change
Network. There have beenno physical disturbances in the catchment,
otherthan occasional scree falls from the corrie back-wall, since
the onset of monitoring in 1988.
Contours in metres
0 500 metres
Lochnagar800
90010001100
800
90010001100
Figure 4.4.1 Lochnagar:catchment
Table 4.4.1 Lochnagar: site characteristics
Grid referenceLake altitudeMaximum depthMean depthVolumeLake
areaCatchment area (excl. lake)Catchment: Lake area ratioCatchment
GeologyCatchment Soils Catchment vegetation
Net reliefMean annual rainfall 1996 deposition Total Snon-marine
S Oxidised NReduced N
NO 252859785 m26 m8.4 m
8.2 x 105 m3
9.8 ha91.9 ha
9.37granitepeats
alpine - moorland100%
370 m1536 mm
16 kg ha-1 yr-1
13 kg ha-1 yr-1
6 kg ha-1 yr-1
8 kg ha-1 yr-1
■ 71
Table 4.4.2 Lochnagar: summary of chemicaldeterminands, June
1988 - March 1998
pH 5.33 5.81 4.95Alkalinity µeq l-1 0.6 12.0 -10.0Ca µeq l-1
29.0 50.0 21.5Mg µeq l-1 33.3 58.3 25.0Na µeq l-1 93.9 173.9 69.6K
µeq l-1 7.4 12.8 2.6SO4 µeq l-1 57.7 85.4 45.8xSO4 µeq l-1 48.3
74.4 35.4NO3 µeq l-1 15.7 30.7 < 1.4Cl µeq l-1 89.3 166.2
50.7Soluble Al µg l-1 41.8 147.0 4.0Labile Al µg l-1 25.5 137.0
< 2.5Non-labile Al µg l-1 16.5 41.0 < 2.5DOC mg l-1 1.1 3.4
0.2Conductivity µS cm-1 21.8 35.0 4.0
Determinand Mean Max Min
-
72 ■
Chapter Four Lochnagar
■ Water Chemistry
(Figure 4.4.2,Table 4.4.2-3)
Lochnagar is acidic with a ten year mean pH of5.33 and a mean
alkalinity of 0.6 µeq l-1. Unlikethe other sites in northern
Scotland, mean labileAl concentrations exceed those of non-labile
Al.Much of the Lochnagar catchment comprisesbare granite or thin
soils, resulting in a verylimited buffering capacity (mean Ca=29
µeq l-1)and therefore high sensitivity to acid deposition.The mean
xSO4 concentration of 48 µeq l-1 ishigher than at the other
northern Scotland sites,and NO3 is also moderately high with a mean
of15.7 µeq l-1. It is probable that, due to the sparsesoil and
vegetation cover, and low ambienttemperature, the catchment has
little ability toimmobilise incoming N deposition, and hastherefore
reached a more advanced stage of Nsaturation than lower altitude
catchments in thesame region. Marine ion concentrations arelower
and less variable than at west coast sites,and in general it
appears that the site is notsubject to major episodic variations,
with rangesof pH (4.95 to 5.81) and alkalinity (-10 to 12 µeql-1)
among the lowest in the Network. Seasonalvariations are also weak
or absent, perhapsreflecting the low level of biological
activitywithin the catchment.
Trend analyses (Table 4.4.3) indicate that thechemistry of
Lochnagar has changedsubstantially over the last decade. Both SKT
andregression suggest that xSO4 has fallen slightly
(5 or 8 µeq l-1 respectively), whilst NO3 has risenover the same
period (11 or 14 µeq l-1). Thecombined effect of these trends
should be areduction in pH and alkalinity, and a decliningtrend is
indeed observed for pH using regression,although not SKT.
Examination of time seriesand LOESS plots confirm that a
reasonablylinear xSO4 decline has taken place over the lastten
years. However the increase in NO3 andassociated decrease in pH
appear to haveoccurred during a short period, from 1992-1995,since
when concentrations have remained fairlystable. The possibility
that the NO3 increasereflects a short term climatic
fluctuation,possibly due to climatic variability, cannottherefore
be ruled out at this stage; furthersampling should help to clarify
this issue. As atmost other UKAWMN, regression analysissuggests
that DOC has risen during the last tenyears, in this case by
approximately 0.8 mg l-1.
■ Epilithic diatoms
(Figure 4.4.3,Table 4.4.4)
The epilithic diatom flora of Lochnagar isrelatively diverse and
dominated by acidophiloustaxa. Achnanthes marginulata(pH optima
5.2) isgenerally the most abundant species, althoughTabellaria
flocculosa(pH optima 5.4) was moreabundant in 1991 and more
recently in 1997-1998. Eunotia incisa (pH optima 5.1) wasrelatively
abundant from 1990-1992 but hassince declined. Diatom inferred pH
(derivedfrom weighted averaging) demonstrates that the
Table 4.4.3Significant trends in chemical determinands ( July
1988 - March 1998)
Determinand Units Annual trend (Regression) Annual trend
(Seasonal Kendall)
pH -0.020* -SO4 µeq l-1 -0.94* -0.52*xSO4 µeq l-1 -1.00**
-0.67**NO3 µeq l-1 +1.43*** +1.13*DOC mg l-1 +0.08* -
* Trend significant at p < 0.05; ** trend significant at p
< 0.01; *** trend significant at p < 0.001
-
■ 73
Lochnagar Chapter Four
Figure 4.4.2Lochnagar:summary of
majorchemicaldeterminands(September 1988 -March 1998)
Smoothed linerepresents LOESScurve (Section 3.1.2)
••
•• •
• •
••
•
•
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•
•
•
•
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•
• •
••
•
•
•
•
••
•
• •
••
1989 1991 1993 1995 1997
5.0
5.4
5.8
(a) pH
• •
•• •
• •
••
• • ••
•
••
•
•
•
•
•
•
••
• •
•
••
••
• • • ••
•
• •
1989 1991 1993 1995 1997
-10
0
5
-5
10
(b) Alkalinity
••
•
•• • • • •
•• • •
•
•
• •• • • •
••• •
•
• • •
• •• •
••
• ••
•
1989 1991 1993 1995 1997
40
60
80
(c) Sulphate
••
•
• • • • • •• •
• ••
•
• ••
• • ••
• • ••
•• •
• •• •
• • •• •
•
1989 1991 1993 1995 1997
40
60
80
(d) Non-marine Sulphate
•
•
••
• ••
•
••
•
••
•
••
••
••
••
•
• • ••
••
•
•
••
•
••
•• •
1989 1991 1993 1995 1997
10
0
20
30
(e) Nitrate
• •
•
•• •
•
•• •
•
•• • • • • •
•
• ••
•
•• •
•
•• •
• • • ••
• •
••
1989 1991 1993 1995 1997
60
80
100
120
140
160
(f) Chloride
• •
•
••
• •
•
•
•
•
• • •• • •
• • •• •
••
•• • •
••
•
•
• •
••
•
•
1989 1991 1993 1995 1997
30
40
50
(g) Calcium
• •
•
• ••
• • • ••
• • • • •• •
•
• • •
•
• ••
•
• • •
• • • ••
• •• •
1989 1991 1993 1995 1997
80
120
140
100
160
(h) Sodium
•
•
••
• • •
•
•• • • •
••
•• •
•
• •
•
•
•• •
•• •
•
•
•
• • •
• •• •
1989 1991 1993 1995 1997
0
50
100
(i) Labile Al
•
•
•
••
••
•
•
••
••
•
•
•• • •
• •
•
• •
• •
••
•
••
•• •
• ••
•
•
1989 1991 1993 1995 1997
10
20
30
40
(j) Non-labile Al
•• •
•
•
• •• •
••
••
•
•
•• •
•
• •
••
••
•
•• •
••
•
• • •
• •
••
1989 1991 1993 1995 1997
0
50
100
150
(k) Total Soluble Al
••
•
• • ••
•
••
•
••
••
•
•
••
••
•
••
••
• •
•
•
• • •• •
•
• ••
1989 1991 1993 1995 1997
1
2
3
(l) Dissolved Organic Carbon
µeq
l-1µe
q l-1
µeq
l-1µe
q l-1
µeq
l-1
µeq
l-1µg
l-1
µg l-
1µe
q l-1
µeq
l-1pH
mg
l-1
-
assemblage reflects the deterioration in pHevident from water
chemistry samples since1993. Despite this, RDA and associated
restrictedpermutation test show no significant linear timetrend
over the full period, at the 0.01 level. Thesediment trap record
for Lochnagar only began in1991 and the sample for 1992 was lost
(Figure4.4.6). No trends are evident in this limiteddataset,
although there are clear similarities inspecies representation with
the epilithon.
■ Macroinvertebrates
(Figure 4.4.4,Table 4.4.4)
The impoverished macroinvertebrate fauna istypical of a
moderately acidic, high altitude lake.The fauna is dominated by
chironomids and thestonefly Capnia spp., which is patchy in
itsoccurrence (only one individual was recorded in
Abundance Taxon Year 88 89 90 91 92 93 95 97
INDICATOR SPECIESSphagnum auriculatum4 3 3 3 3 3 3 3 3Juncus
bulbosus var. fluitans4 1 2 2 2 2 2 2 3OTHER SUBMERGED
SPECIESFilamentous green algae 1 3 0 2 1 1 2 1Fontinalis
antipyretica 1 0 1 1 1 1 1 1Racomitrium aciculare 0 0 1 0 0 0 1
1Cephalozia connivens 0 0 1 0 0 0 0 0Marsupella emarginata 0 0 0 0
1 0 0 0Nardia compressa 1 1 3 2 3 2 2 2Plectocolea obovata 0 1 1 0
0 0 0 0Scapania undulata 3 3 3 3 3 3 3 3Isoetes lacustris 2 2 2 2 2
2 2 2
TOTAL NUMBER OF SPECIES 7 7 9 7 8 7 8 8
Chapter Four Lochnagar
74 ■
Table 4.4.4Lochnagar: trend statistics for epilithic diatom,
macrophyte and macroinvertebratesummary data (1988 - 1998)
Epilithic diatoms 481 145 7.2 0.26 0.26Macrophytes 18 11 6.5
0.32 0.30Invertebrates 871 25 2.5 0.52 0.40
Variance pexplained (%) within year between years linear trend
unrestricted restricted
Epilithic diatoms 56.3 43.7 5.2 0.06 0.44Macrophytes - - 15.8
0.34 0.12Invertebrates 43.0 57.0 10.4 0.00 0.00
Total sum Number Mean N2 λ1RDA/λ2RDA λ1RDA/λ1PCAof squares of
taxa diversity
Table 4.4.5Lochnagar: relative abundance of aquatic macrophyte
flora (1988 - 1997)(see Section 3.2.3 for key to indicator
values)
-
Lochnagar Chapter Four
■ 75
Figure 4.4.3Lochnagar:summary ofepilithic diatomdata (1988 -
1998)
Percentagefrequency of all taxaoccurring at >2%abundance in
anyone sample
Aulac
oseir
a sp.
Euno
tia pe
ctina
lis va
r. mi
nor
Achn
anthe
s minu
tissim
a
Tabe
llaria
kuetz
ingian
a
Aulac
oseir
a dist
ans v
ar. a
lpige
na
Euno
tia pe
ctina
lis
Euno
tia sp
.
Euno
tia te
nella
Frag
ilaria
vire
scen
s var
. exig
ua
Euno
tia pa
ludos
a
Achn
anthe
s sp.
Achn
anthe
s helv
etica
var.
mino
r
2040
Euno
tia in
cisa
20
Euno
tia rh
ombo
idea
Frus
tulia
rhom
boide
s var
. sax
onica
Brac
hysir
a vitre
a
Aulac
oseir
a alpi
gena
Euno
tia m
inutis
sima
Achn
anthe
s sco
tica
20
Brac
hysir
a bre
bisso
nii
Achn
anthe
s deth
a
Aulac
oseir
a dist
ans v
ar. n
ivaloi
des
2040
60
Achn
anthe
s mar
ginula
ta
Achn
anthe
s alta
ica
Frus
tulia
rhom
boide
s var
. virid
ula
20
Euno
tia va
nheu
rckii v
ar. in
terme
dia
20
Euno
tia de
nticu
lata
Cocc
oneis
plac
entul
a
Navic
ula kr
assk
ei
Tabe
llaria
quad
risep
tata
20
Achn
anthe
s aus
triaca
var.
helve
tica
20
Aulac
oseir
a dist
ans v
ar. n
ivalis
Pinn
ularia
subc
apita
ta va
r. hil
sean
a
Pero
nia fib
ula
2040
60
Tabe
llaria
flocc
ulosa
20
Achn
anthe
s alta
ica va
r. mi
nor
Navic
ula m
edioc
ris
20
Euno
tia na
egeli
i
Cymb
ella p
erpu
silla
Aulac
oseir
a per
glabr
a
Tabe
llaria
bina
lis f.
ellipt
ica
20
Euno
tia [te
nella
/palud
osa]
Aulac
oseir
a dist
ans v
ar. te
nella
2040
60
Euno
tia ex
igua
20
Euno
tia [v
anhe
urck
ii var
. 1]
Aulac
oseir
a lira
ta va
r. alp
igena
Yea
r
88 89 90 91 92 93 94 95 96 97 98
% fr
eque
ncy
of ta
xa in
eac
h sa
mpl
e
-
1994). Several other species of stonefly arepresent including
Diura bicaudata andSiphonoperla torrentium. Acid
tolerantstonefliesNemurella pictetii and Protonemuraspp. appeared
after 1991. Other common taxainclude the water beetle, Oreodytes
davisii, andmembers of the caddisfly family, theLimnephilidae, and
the Tipulidae. Time as alinear trend is significant at the 0.01
level. Theapparent shift in stonefly species, from Nemouraspp. to
Nemurella picteti, the increase in therelative abundance of
Plectrocnemiasp. andPolycentropussp., and the general decline
inspecies richness, are all indicative of increasingacidity.
■ Fish
(Figure 4.4.5)
The outflow stream of Lochnagar has been fishedsince 1989. The
electrofishing site issignificantly downstream of the water
chemistrysampling point and it is likely that geologicalbuffering
results in less acid conditions thanthose experienced at the actual
outflow. Thiscould explain why, when the Loch troutpopulation is
believed to be impoverished,densities within the fishing stretch
are high, andindeed the highest found in the Network.Densities of
0+ group fish were relatively low forthe site in 1993, 1996 and
1997, but no trends areapparent over the nine years of data.
Densities of>0+ group are variable, three years (1990, 1991&
1996) being significantly above average.Condition factor and the
coefficient of variationof the condition factor for both age groups
alsoshow no time trends. Length frequency graphsindicate a healthy
population structure, althoughnumbers of larger fish (>100 mm)
are relativelylow in certain years. This feature does not seemto be
linked to the recruitment reductionsmentioned above.
■ Aquatic macrophytes
(Tables 4.4.4-5)
The impoverished macroflora of Lochnagarreflects the extreme
altitude and acidity of thesite. Isoetes lacustrisand Juncus
bulbosusvar.
fluitans are the only vascular species whichappear able to
withstand a combination ofadverse factors including low
nutrientavailability, the effects of ice scouring, lowambient
temperature and strong wave action. TheLoch is dominated by
liverworts, and particularlyNardia compressa, while the moss
Fontinalisantipyreticais present in a few isolated locations.The
cover of Juncus bulbosusvar. fluitansalongtwo of
