close

Вход

Забыли?

вход по аккаунту

?

The effect of catchment liming on bryophytes in upland Welsh streams with an assessment of the communities at risk.

код для вставкиСкачать
AQUATIC CONSERVATION: MARINE A N D FRESHWATER ECOSYSTEMS, VOL. 4, 297-306 (1994)
The effect of catchment liming on bryophytes in upland
Welsh streams, with an assessment of the communities at risk
S. M. WILKINSON and S . J. ORMEROD*
Catchment Research Group, School of Pure and Applied Biology, University of Wales Cardiff, PO Box 915,
Cardiff CFI 3TL, UK
ABSTRACT
1 . The effects of catchment liming, used to restore acidified streams, are still only partially known.
In particular, the impact on aquatic bryophytes remains unappraised.
2. Six upland streams were surveyed for aquatic bryophytes from 1987-93, and three of their
catchments limed experimentally in 1987-88 so that the resulting changes in the abundance and
distribution of common bryophyte taxa could be assessed. A n additional nine streams were surveyed
during 1987-89, 1992 and 1993 using the same methods to give a wider indication of the bryophyte
communities in streams where liming might occur.
3. Twenty-nine bryophyte species were recorded from the wetted margins of these 15 upland streams.
Percentage cover by individual species varied markedly, and was highest in Nardia compressa (up
to 71%). Cover by most other species was limited t o less than 5%.
4. Total bryophyte cover, and cover by Scapaniu undulata fluctuated from year to year so that
no responses t o liming could be detected. However, cover by Nardia compressa declined significantly
from 39% t 21 070 SD to 5% ? 2Vo SD in treated streams following lime addition. Reference streams
showed no such change, and no other taxa increased in abundance to replace the lost Nardia in the
5 years after liming.
5 . Changes of this type, and their possible ramifications for invertebrates, will have to be considered
where catchment liming is planned.
INTRODUCTION
Until recently, conservation of bryophytes in Great Britain had received scant attention, with many important
sites only receiving protection indirectly in areas notified for other taxa and communities (Hodgetts, 1992).
Riverine species are among those often dispersed in habitats outside areas formally notified for their
conservation value, leaving some populations at risk from the wide range of environmental changes which
occur in river systems. So far, however, there are few systematic data on how such changes affect bryophytes,
even though many survey data have revealed marked differences in species richness and community
composition between rivers of different conservation quality (e.g. Slater et a/., 1987).
Aquatic bryophytes occur predominantly in fast-flowing streams, where suitable substrata provide
attachment points and where there is sufficient free carbon dioxide in solution to permit photosynthesis
(Hynes, 1970). Functionally they are important producers, fixing nutrients, accumulating detritus, and
providing sites for periphyton or invertebrate colonization and shelter (Suren, 1991 ; Suren and Winterbourn,
1992; Steinman and Boston, 1993). This means that any change among aquatic bryophytes, in addition
to direct conservation impacts, might have ecological consequences for other organisms.
*Correspondence
Received 5 January 1994
Accepted 1 April 1994
CCC 1052-761 3/94/040297-10
01994 by John Wiley & Sons, Ltd.
121.1
298
S. M. WILKINSON AND S. J . ORMEROD
Some of the most widespread ecological changes affecting upland regions in recent decades have been
due to acid deposition (Usher and Thompson, 1988). In this case, not only are there conservation ramifications
arising from the initial problem, but also from some of the management options which have been suggested
in the shorter term (Hildrew and Ormerod, in press). In particular, the spreading of limestone onto catchment
wetlands as a treatment for symptoms has probably led to reductions in Sphagnum cover, with associated
knock-on effects on other organisms (Mackenzie et al., 1990). At the same time, the need for such measures
to protect fisheries is being increasingly emphasized. While there is widespread recognition that emission
reductions would bring benefits over extensive areas, the scale of reduction required to protect and restore
all sensitive habitats is liable to be substantial and costly (e.g. Reynolds and Ormerod, 1993). Moreover,
neither the implementation of control technologies, nor the chemical recovery of affected systems, can be
immediate (e.g. Ormerod et al., 1988), so that environmental managers need to consider the options available
more readily at the local scale.
Experimental applications of limestone have already been made to headwater catchments and surface
waters in the British uplands to assess the effectiveness of liming (Diamond et al., 1992; Donald and
Stoner, 1992). So far, most considerations of its effects have been restricted to fish and invertebrates.
However, recent qualitative evidence suggested that there may be adverse changes among some aquatic
bryophytes (Weatherley and Ormerod, 1987; Rundle et al., in press). Hitherto, however, there has been
no quantitative assessment of such changes, nor any assessment of the wider communities that might be
at risk.
This paper investigates changes in the cover by aquatic bryophytes in upland Welsh streams draining
a base-poor area which occurred following replicated experimental catchment liming. It also records the
wider riparian bryophyte community potentially at risk from chemical change.
STUDY AREA AND METHODS
The second-order streams under study are located adjacent to the Llyn Brianne reservoir in the catchment
of the upper River Tywi, mid-Wales (see Stoner et al., 1984; Rutt et al., 1989). All drain base-poor soils
overlying shales, mudstones and grits of Ordovician and Silurian origin, giving rise to soft waters susceptible
to acidification (total hardness 3.9-18.8mg CaC03 L-'; Rutt et al., 1989).
Experimental manipulation
Three stream catchments were treated with CaC03 between autumn 1987 and summer 1988 (C2, C5 and
L4, the limed group; see Ormerod et al., 1990 for treatment details), while three adjacent streams were
monitored as acidic reference sites (Cl, C3, L1; acid group). Cover and species composition of bryophytes
in the wetted zone of each stream were assessed during July and August for 1987-93 following the method
of Rutt et al. (1989): a 0.5 x 0.5 m quadrat divided into 25 sub-quadrats (0.1 x 0.1 m) was placed randomly
on the left, right or mid-channel at 20 points, on a stratified random basis, over a 200m reach of stream.
The number of sub-quadrats occupied by each taxon was recorded and from this their percentage cover,
and the total percentage cover of all bryophytes, were derived. Other taxa observed in the 200m reach
but not within the quadrats were assigned a nominal 0.01 To cover value. Voucher specimens were collected
for subsequent identification and verification in the laboratory.
Using the same quadrat method, the physical composition of each stream bed was assessed for the
percentage cover of seven defined types of substratum (Table 1). In addition, calcium, aluminium,
conductivity, pH and dissolved organic carbon (DOC) were measured as weekly spot samples throughout
the period (see Weatherley and Ormerod, 1987, for details). However, only data from the 12-month
post-liming period are used here, these providing a typical period from which subsequent years have not
departed strongly (Rundle et a/., in press).
LIMING AND AQUATIC BRYOPHYTES
299
Table 1. Substratum categories used in habitat survey
(size categories according to Wentworth Scale).
Category
Size (mm)
Bedrock
Boulders
Cobbles
Pebbles
Gravel
Sand
Silt/mud
> 256
> 64-256
> 16-64
>2-16
> 0.0625-2
C0.0625
General bryophyte distribution
Nine additional streams in the Llyn Brianne area were surveyed for bryophytes and physico-chemical
variables, using the same methods, during 1987-89, 1992 and 1993 in order to provide data on typical
bryophyte communities from a wider array of upland streams.
Analysis
Prior to any statistical analysis, all data were transformed (loglo ( x + 1) or arcsin square root (percentage
cover) ) to normalize distributions. Percentage cover by all bryophytes, and by selected common species,
were compared between streams, groups of streams (limed versus unlimed) and years using a crossed
multifactorial analysis of variance (ANOVA) based on the general linear model (GLM, Ryan et al., 1985).
Correlations between cover values and physico-chemical variables were calculated to investigate possible
relationships (Spearman-ranked correlations; Sokal and Rohlf, 1981).
RESULTS
General bryophyte distribution and abundance
Twenty-nine bryophyte species, including four unconfirmed, were recorded during the survey from the 15
streams (Table 2). Percentage cover by each species within the wetted margin vaned markedly between streams:
most were present at very low cover, with only five species covering more than 10% of any stream bed. Nardia
compressa exhibited the greatest cover in any one stream (71Yo), followed by Rhynchostegium riparioides
(440/0),Polytrichum commune (26Vo), Scapania undulata (23%), and Hygrohypnum ochraceum (16%).
Streams fell into three well-defined groups according to pH (‘acid’: mean pH = 5.23 f 0.38 SD, n = 9;
‘circumneutral’: mean = 6.79 f0.43, n = 3; and ‘limed’: mean = 6.12 f0.67, n = 3). Nine taxa were common
to all (Table 2, pre-treatment data for limed streams omitted), with N . compressa occurring on 40 of 51
(78%) sampling occasions in acid streams, but on only 6 of 15 (40%) sampling occasions in circumneutral,
and 6 of 18 (33%) in limed streams (post-liming). Five taxa were restricted to acid streams alone, a further
eight occurred solely in circumneutral streams, whilst another seven were present in both circumneutral
and acid streams.
Nardia cover tended to decrease in pebble-rich streams, although this trend was not formally significant
(Table 3). Instead, cover by Nardia was correlated negatively with stream pH (mean r = - 0.7197, ~ ~ 0 . 0 1 ;
Table 3), and positively with aluminium concentration (mean r = 0.6255, p<0.05).
Experimental streams: liming effects
Acid streams contained significantly less dissolved calcium than limed streams (acid mean = 1.59 _+ 0.73
SD mg L- l , limed mean = 4.61 f 1.69 mg L- l ; one-way ANOVA, Fl,5= 10.25, p = 0.003). Otherwise,
300
S. M. WILKINSON AND S. J . ORMEROD
Table 2. Major brvouhyte species recorded from 15 upland streams in mid-Wales, 1987-93.
Speciesa
=Nardiacompressa S. Gray
‘Scapania undulata Dum.
‘Sphagnum lescurii Sull.
ePellia epiphylla Corda
eHyocomium armoricurn Wijk & Marg.
‘Polytrichum commune Hedw.
CRacomitriumaciculare Brid.
dSphagnum papillosurn Lindb.
dSphagnum cuspidatum Ehrh. ex Hoffm.
‘Dichodontium pellucidurn Schimp.
CHygrohypnumochraceum Loeske
‘Rhynchostegium riparioides Card.
dMnium hornum Hedw.
dBrachytheciurn rivulare B., S. & G.
dCinclidotusfontinaloides P. Beauv.
‘Gymnocolea inflata Durn.
dDicranum scoparium Hedw.
dHomalothecium sericeum B., S. & G.
eDicranum majus Sm.
dRacornitrium aquaticum Brid.
CThamnobryumalopecururn Nieuwl.
dLeucobryum glaucum Angstr.
cNardia scalaris S . Gray
R hytidiadeiphus loreus War nst .
dThuidium tamariscinum B., S . & G.
Preferred
habitat
Aquatic
Aquatic
Semi-aquatic
Semi-aquatic
Semi-aquatic
Semi-aquatic
Aquatic
Semi-aquatic
Semi-aquatic
Semi-aquatic
Semi-aquatic
Aquatic
Moorland
Aquatic
Semi-aquatic
Semi-aquatic
Moorland
Moorland
Moorland
Semi-aquatic
Semi-aquatic
Moorland
Moorland
Moorland
Moorland
9 acid streams 3 circumneutral streams 3 limed streamsb
(15 samples)
(18 samples)
(51 samples)
mean
mean
mean
occurrence cover occurrence
cover occurrence cover
(Too)
(70)
(To)
(Too)
(To)
(To)
<1
<I
78.4
68.6
51.0
35.3
33.3
17.6
17.6
13.7
7.8
5.9
5.9
3.9
3.9
3.9
2.0
2.0
2.0
2.0
<I
5.9
10.8
3.0
<1
<I
<I
<I
<1
<I
<1
<I
<1
<1
<I
<I
<I
<I
-
-
-
-
-
-
<I
<I
<I
<1
<I
<I
<1
<I
<1
40.0
73.3
6.7
40.0
40.0
26.7
46.7
6.7
6.7
-
-
1.9
9.1
6.7
93.3
-
-
<I
13.3
-
-
<1
<1
<I
<1
<1
<I
<I
<I
<I
<1
<1
<1
<1
<1
<I
<I
<1
-
33.3
50.0
72.2
27.8
33.3
11.1
5.6
5.6
-
-
13.3
20.0
20.0
-
6.7
6.7
6.7
6.7
6.7
“Source of nomenclature: Grolle (1983) and Corley et al. (1981).
bPre-liming data (1987) omitted.
‘Pre-1993 record.
d1993 record.
eBoth 1993 and pre-1993 record.
Table 3. Mean ( 5 years) Spearman-ranked correlation coefficients between percentage cover values for dominant bryophyte species
and physico-chemical variables (12 sites).
To
To
To
To
To
To
Bedrock
Boulder
Cobble
Pebble
Gravel
Mud
PH
Conductivity
A1u mini u m
Calcium
Nardia (To)
Scapania (To)
0.3705
-0.1557
- 0.1974
- 0.5392
- 0.0440
- 0.3679
- 0.7197**
0.2175
0.6255*
-0.1974
0.1596
0.0520
0.0030
0.1993
- 0.2784
- 0.1664
- 0.3443
0.2098
0.4738
0.0280
Total bryophytes (To)
0.3435
- 0.0709
-0.1244
- 0.3636
0.0480
- 0.3346
-0.1868
0.2858
0.0749
0.0080
Transformations prior to correlation: arcsin. square root (percentage values); otherwise Log,, (x). Mean correlation coefficients derived
by averaging z-transformation of individual year’s coefficients (Sokal and Rohlf, 1981).
*Significant at 5 % , **significant at 1%.
301
LIMING AND AQUATIC BRYOPHYTES
between group differences were limited to pH (one-way ANOVA, Fl,5= 15.08, p=O.OOl). All physicochemical data are given in Appendix 1 .
Statistical comparisons of bryophyte cover between years and groups (limed versus acid) were limited by
data availability to N. compressa, S. undulata, and total bryophyte cover (Table 4). Over the 7 years of
the study, Nardia cover varied significantly between streams and years principally due to greater values
in acid streams (Figure 1). On exclusion of the data for the three 'limed' streams pre-liming (1987), or all
data for 1987, the significant between-year effect disappeared. This indicated that the differences in Nardia
cover between limed and acid streams, and between years, were due to changes in treatment streams that
accompanied liming. Despite a near-absence pre-liming (0.01 (70cover) in one limed stream, time-series analysis
confirmed marked reductions in Nardia cover in the limed group: it was originally very common in two
streams (41%-77% in 1987) where it fell to 7% and zero respectively (1988).
Like Nardia, S. undulata cover over 7 years was significantly greater in acid streams than in limed.
However, unlike Nardia there were no year to year effects related to liming, nor any evidence that this
species declined post-liming (Figure 2). In other words, post-treatment differences for Scapania between
limed and acid streams were probably unrelated to liming since they also occurred prior to treatment.
Nardia made an important contribution to bryophyte cover in experimental streams (up to 98% of the
total) and, as a result, total bryophyte cover varied significantly between years and streams (Figure 3). On
removal of Nardia from the total cover values, no significant differences between years or streams arose,
suggesting that this species was responsible for these patterns.
DISCUSSION
The 15 second-order streams at Llyn Brianne supported 29 bryophyte species in total, although most were
scarce. This is a small number of species compared with other sites in Wales (e.g. Slater eta/., 1987), reflecting
the concentration of our efforts in or near the stream wetted perimeter. It also reflects the exposed nature
of many of the sites in our study. The most prolific species was the liverwort Nardia compressa, whose
presence increased with stream acidity. Experimental evidence highlighted a clear decline in its abundance as
Table 4. Percentage cover differences between bryophytes in acid streams (n = 3) and limed streams (n = 3) (GLM analysis).
Data
Total To cover by all bryophytes
All years
Excluding 1987
Excluding 1987 limed sitesa
Vo cover by Nardia compressa
All years
Excluding 1987
Excluding 1987 limed sitesa
070
cover by Scapania undulata
All years
Excluding 1987
Excluding 1987 limed sitesa
"Excludingpre-liming data from limed sites only.
Effect
Stream
Year
Stream
Year
Stream
Year
Stream
Year
Stream
Year
Stream
Year
Stream
Year
Stream
Year
Stream
Year
df
F
P
5
8.27
4.28
1 1.56
2.69
11.98
2.62
16.97
3.67
30.36
1.24
30.19
1.67
4.04
0.71
7.67
1.08
4.55
0.73
0.001
0.003
6
5
5
5
6
5
6
5
5
5
6
5
6
5
5
5
6
O.OO0
0.044
O.OO0
0.039
0.000
0.008
O.Oo0
0.318
O.Oo0
0.166
0.006
0.643
O.Oo0
0.395
0.004
0.626
302
S. M. WILKINSON A N D S. J . ORMEROD
!
87
88
89
90
91
92
93
Year
Figure 1. Mean percentage cover (with SE) of Nardiu compressa in three acid streams ( A ) and three limed streams (0)over 7 years.
Liming occurred in autumn 1987 or spring 1988 (see text).
a response to catchment liming in three streams. No other taxa increased in abundance to replace it as
the dominant large plant. At the same location, year to year changes in the abundance of Scapania undufufa,
although evident, were not necessarily a response to liming. No other species was present in sufficient
abundance to allow any assessment of change due to liming, although the bryophyte community in and
around the base-poor streams indicates that there is scope for such effects to occur.
Causal mechanisms
Assuming the decline in Nardia was a real response to liming, what mechanisms might be responsible? The
inability of aquatic bryophytes to photosynthesize hydrogen carbonate ions directly is well known, and
means that they depend on dissolved, free C 0 2 as a source of photosynthetic carbon (Gessner, cited from
Hynes, 1970). Since C 0 2 gas diffuses through water lo5 times slower than air, the availability of free C 0 2
to aquatic plants is markedly reduced (Hynes, 1970). This problem is exacerbated in calcareous streams,
where HCO; is the dominant form of inorganic carbon, resulting in loss of C 0 2 from solution. Changes
87
88
89
90
91
92
93
Year
Figure 2. Mean percentage cover (with SE) of Scupania undulutu in three acid streams ( A ) and three limed streams (0)over 7 years.
303
LIMING AND AQUATIC BRYOPHYTES
a7
aa
89
90
91
Year
Figure 3. Mean percentage cover (with SE) of all bryophytes in three acid streams
92
(A )
93
and three limed streams ( 0 )over 7 years.
such as this in the HCO; /COz equilibrium have important consequences for those bryophyte species
present (Bain and Proctor, 1980). In this study, the addition of lime to acidic streams is liable to
have caused a shift towards HCO; as the dominant form of inorganic carbon, mimicking more closely
the situation in calcareous streams. Chemical conditions conducive to this altered equilibrium have persisted
for at least 6 years following liming at Llyn Brianne (Rundle et ul., in press) during which time the most
prolific species, Nurdiu compressu, has been all but eliminated. Although we have no information on the
sensitivity of this species to altered C 0 2 concentrations, reductions in its abundance following liming are
consistent with its scarcity in circumneutral streams (Hill, 1988), and consistent also with effects by the
above mechanism. However, the effects of liming on stream PCOz are far from clearly known (C. Neal,
personal communication), and other chemical effects on Nurdiu cannot yet be ruled out.
Ecological significance
Whereas aquatic bryophytes are likely to support a range of epiphytic organisms, including diatoms,
their value as habitat for invertebrates has been more fully documented (Eglund, 1991; Suren and
Winterbourn, 1991, 1992; Steinman and Boston, 1993). Within bryophytic mats, water velocity is
reduced, and large quantities of periphyton and detritus can accumulate; two corrolaries are the
provision of shelter and food for associated organisms. Greatly enhanced invertebrate densities occur
probably as a result (Suren, 1991), although some invertebrates also utilize bryophytes directly as a
food source (Suren and Winterbourn, 1992). At Llyn Brianne, however, no gross change in invertebrate
abundance occurred as a result of liming (Rundle et ul., in press) and so the consequences of reduced
Nurdiu cover appeared unimportant to such organisms at the stream level. However, the effects of
liming on relationships between Nurdiu and invertebrates at the micro-habitat level have not yet been
investigated.
304
S . M. WILKINSON AND S . J . ORMEROD
Nature conservation importance
In this study, many of the species recorded can be described as common, at least regionally in Wales
(Nardia compressa, Scapania undulata, Sphagnum cuspidatum; Hill, 1988), although some of them are
restricted to acidic habitats. In the case of Nardia, effects by limited liming would be unlikely to have
major implications for gross range and abundance, but would nevertheless represent a local change in a
representative community. Other, less frequent species in the aquatic community at Llyn Brianne (e.g.
Racomitrium aquaticum) were too sparse to allow any assessments of effects by liming; this feature may
repeatedly prevent the detection of changes amongst such rare taxa generally unless future work involved
mapping in fixed quadrats in which they were known to occur. In fact, one lesson of hindsight from this
study was that only such a method would have detected change among these rarer taxa. Given that many
bryophyte species have restricted range, and often highly specific habitat requirements, such a targeted
methodology might be profitably employed in future studies where the aim is to detect change due to
environmental perturbation.
The wider effects of most of the strategies aimed at reducing surface water acidification are as yet
unclear, or are known solely from modelling studies (Ormerod et a/., 1990). This is unfortunate,
precluding a rigorous environmental cost-benefit appraisal of any individual option (Hildrew and
Ormerod, in press). In the case of liming, effects on aquatic invertebrate assemblages have been
minimal (Rundle et a/.,in press), and the water quality conditions created by liming do not represent those
which occurred prior to acidification (Ormerod et al., 1990). Fish species richness tends not to increase
(Degerman and Appelberg, 1992), but there have sometimes been benefits to salmonid density (Weatherley,
1988 cf Diamond et a/., 1992) and the quality of water supplies. As a result, both water undertakings and
conservation agencies have prescribed liming to protect fish populations that are valuable in economic and
conservation terms (e.g. Farmer, 1992; see EU Directive 92/43/EEC). At the same time, some conservationists
have drawn attention to the possible adverse consequences of lime additions to terrestrial ecosystems which
are naturally oligotrophic, base-poor, and contain resources of intrinsic conservation value (Woodin and
Skiba, 1990; Farmer, 1992). The response of an important and widespread bryophyte in upland acid streams,
Nardia compressa, must now be considered as a further environmental cost in any future appraisals of
lime additions.
Appendix 1. Physico-chemical data for the 12-month post-liming period. Unless otherwise stated, all values are in mg L-I, except
pH and conductivity (pS cm-I).
Stream
L1
L2
L3
L4*
L5
L6
L7
L8
c1
c2*
c3
c4
c5*
uc4
G1
*Limed.
Bedrock Boulder Cobble Pebble Gravel Mud
Dissolved
(Vo)
(Yo)
(Vo)
(Yo) (Yo)
(Yo) pH Conductivity Calcium Aluminium organic carbon
26.0
33.8
23.2
3.2
4.0
14.0
6.8
5.5
8.2
8.7
15.1
0.0
0.9
0.0
31.7
4.8
6.6
5.3
0.5
2.5
12.3
9.8
8.4
5.4
0.5
0.5
0.4
0.6
16.1
1.3
28.3
27.8
39.3
40.8
31.9
40.1
41.7
52.5
46.1
42.0
34.2
52.1
22.2
38.7
29.3
19.8
20.8
29.2
46.4
37.8
24.2
27.8
30.0
26.8
36.5
39.9
44.2
31.3
36.5
36.1
5.2
9.5
3.0
7.2
9.6
9.4
13.2
3.6
10.7
2.3
4.6
1.4
18.1
7.6
1.6
0.0
0.0
0.0
1.6
14.2
0.0
0.0
0.0
0.0
0.0
0.0
1.9
5.0
1.0
0.0
4.71
4.78
5.05
6.43
5.84
6.93
7.13
5.27
5.12
5.35
5.26
5.30
6.57
5.74
6.31
48.0
51.8
55.4
64.0
36.0
48.3
60.5
36.4
34.5
46.1
31.9
36.4
45.7
30.3
41.2
1.40
1.59
2.36
6.41
1.46
3.27
5.39
3.20
0.96
3.06
1.05
1.13
4.35
1.17
2.03
0.470
0.645
0.357
0.074
0.056
0.059
0.038
0.204
0.095
0.155
0.140
0.154
0.052
0.074
0.046
0.88
1.26
1.26
0.98
0.45
1.12
1.30
3.60
3.52
3.48
3.62
4.91
3.45
5.17
3.48
LIMING AND AQUATIC BRYOPHYTES
305
ACKNOWLEDGEMENTS
Thanks are due to G. P. Rutt, E. C. Lloyd, H. Thomas, M. Jenkins and Drs K. Davies, N. S. Weatherley, S. D. Rundle
and N. Stringer for assistance with fieldwork and bryophyte taxonomy. Financial assistance was provided by the Welsh
Office, the National Rivers Authority and the Department of the Environment. This study formed part of the Llyn
Brianne Project.
REFERENCES
Bain, J. T. and Proctor, M. C. F. 1980. ‘The requirement of aquatic bryophytes for free CO, as an inorganic carbon
source: some experimental evidence’, The New Phytologist, 86, 393-400.
Corley, M. F. V., Crundwell, A. C., Dull, R., Hill, M. 0. and Smith, A. J. E. 1981. ‘Mosses of Europe and the Azores’,
Journal of Bryology, 11, 609-689.
Degerman, E. and Appelberg, M. 1992. ‘The response of stream-dwelling fish to liming’, Environmental Pollution,
78. 149-155.
Diamond, M., Hirst, D., Winder, L., Crawshaw, D. H. and Prigg, R. F. 1992. ‘The effect of liming agricultural land
on the chemistry and biology of the River Esk, north-west England’, Environmental Pollution, 78, 179-185.
Donald, A. P. and Stoner, A. S. 1992. ‘Acid waters in upland Wales: causes, effects and remedies’, Envir~nmental
Pollution, 7 8 , 141-148.
Eglund, G. 1991. ‘Effects of disturbance on stream moss and invertebrate community structure’, Journal of the
North American Benthological Society, 10, 143-153.
Farmer, A. M. 1992. ‘Catchment liming and nature conservation’, Land Use Policy, January 1992, 8-10.
Grolle, R. 1983. ‘Hepatics of Europe including the Azores: an annotated list of species, with synonyms from the recent
literature’, Journal of Bryology, 12, 403-459.
Hildrew, A. G.and Ormerod, S. J. in press. ‘Surface water acidification: consequences and solutions’, in Harper, D.,
Ferguson, A. and Edwards, R. W. (Eds), The Ecological Basis of River Management, John Wiley, Chichester.
Hill, M. 0. 1988. ‘A bryophyte flora of North Wales’, Journal of Bryology, 15, 377-491.
Hodgetts, N. G. 1992. ‘Measures to protect bryophytes in Great Britain’, Biological Conservation, 52, 259-264.
Hynes, H. B. N. 1970. The Ecology of Running Waters, Liverpool University Press, Liverpool.
Mackenzie, S. M., Lee, J. A. and Wright, J. M. (1990). EcologicalImpact of Liming Blanket Bog. Report to the Nature
Conservancy Council, Peterborough.
Ormerod, S. J., Weatherley, N. S., Merret, W. J., Gee, A. S. and Whitehead, P. G. 1990. ‘Restoring acidified streams
in upland Wales: a modelling comparison on the chemical and biological effects of liming and reduced sulphate
deposition’, Environmental Pollution, 64, 67-85.
Ormerod, S. J., Weatherley, N. S., Varallo, P. V. and Whitehead, P. 1988. ‘Preliminary empirical models of the historical
and future impact of acidification on the ecology of Welsh streams’, Freshwater Biology, 20, 127-140.
Reynolds, B. and Ormerod, S. J. 1993. A Review of the Impact of Current and Future Acid Deposition in Wales.
Report to the Welsh Office and the Countryside Council for Wales, Institute of Terrestrial Ecology, Bangor.
Rundle, S. D., Weatherley, N. S. and Ormerod, S. J. in press. ‘The effects of catchment liming on the chemistry and
biology of upland Welsh streams: testing predictions from empirical models’, Freshwater Biology.
Rutt, G. P., Weatherley, N. S. and Ormerod, S. J. 1989. ‘Microhabitat availability in Welsh moorland and forest streams
as a determinant of macroinvertebrate distribution’, Freshwater Biology, 22, 247-261.
Ryan, B. F., Joiner, B. L. and Ryan, T. A. 1985. MINITAB Handbook, 2nd edn, PWS-Kent Publishing Company,
Boston.
Slater, F. M., Curry, P. and Chadwell, C. 1987. ‘A practical approach to the evaluation of the conservation status
of vegetation in river corridors in Wales’, Biological Conservation, 40, 53-60.
Sokal, R. R. and Rohlf, F. J. 1981. Biometry, Freeman, San Francisco.
Steinman, A. D. and Boston, H. L. 1993. ‘The ecological role of aquatic bryophytes in a woodland stream’, Journal
of the North American Benthological Society, 12, 17-26.
Stoner, J. H., Wade, K. R. and Gee, A. S. 1984. ‘The effects of acidification on the ecology of streams in the upper
Tywi catchment in west Wales’, Environmental Pollution (Series A), 35, 125-157.
Suren, A. M. 1991. ‘Assessment of artificial bryophytes for invertebrate sampling in two New Zealand alpine streams’,
New Zealand Journal of Marine and Freshwater Research, 25, 101-112.
Suren, A. M. and Winterbourn, M. J. 1991. ‘Consumption of aquatic bryophytes by alpine stream invertebrates in
New Zealand’, New Zealand Journal of Marine and Freshwater Research, 25, 331-343.
Suren, A. M. and Winterbourn, M. J. 1992. ‘The influence of periphyton, detritus and shelter on invertebrate colonisation
of aquatic bryophytes’, Freshwater Biology, 27, 327-339.
306
S. M. WILKINSON AND S. J . ORMEROD
Usher, M. B. and Thompson, D. B. A. Eds. 1988. Ecological Change in the Uplands. Blackwell Scientific Publications,
Oxford.
Weatherley, N. S. 1988. ‘Liming to mitigate acidification in freshwater ecosystems: a review of the biological consequences’,
Water, Air and Soil Pollution, 39, 421-437.
Weatherley, N. S. and Ormerod, S. J. 1987. ‘The impact of acidification on macroinvertebrate assemblages in Welsh
streams: towards an empirical model’, Environmental Pollution, 46, 223-240.
Woodin, S. J. and Skiba, U . 1990. ‘Liming fails the acid test’, New Scientist, 1707, 50-53.
Документ
Категория
Без категории
Просмотров
3
Размер файла
644 Кб
Теги
effect, welsh, liming, stream, communities, assessment, upland, risk, bryophyta, catchment
1/--страниц
Пожаловаться на содержимое документа