Myvatn-Laxá Ramsar Site + a Case of Integrated Monitoring

9 Pages·1994·0.75 MB·English

by  Einarsson, Arni

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MYVATN-LAXA RAMSAR SITE -
A CASE OF INTEGRATED MONITORING
Ärni Einarsson
Abstract
Waterfowl populations at Lake Myvatn and River Laxä, Iceland, have been monitored since 1975. A hypothesis
that the local populations of breeding waterfowl are determined by the food supply on the breeding grounds sti-
mulated monitoring of the most abundant food species. Chironomid midges have been monitored since 1977. The
record of two duck species, the Wigeon (Anas penelope) and Common Scoter (Melanitta nigra) and a critical
food, chironomid midges, is used to illustrate how analyses of time lags can generate hypotheses about the causes
of population changes in waterfowl. The records of waterfowl numbers, and also the catch of Brown Trout
(Salmo truttd), suggest a close relationship with food conditions. A record of egg harvesting, going back to 1901,
also indicates a close link with food conditions on the breeding grounds. By employing palaeolimnological me-
thods it has been possible to gain a better historical perspective and assess the stability of the ecosystem.
Einarsson, Ä.: Myvatn-Laxä RAMSAR Gebiet - ein Fallbeispiel für integriertes Monito-
ring
Monitoring von Wasservogelpopulationen wird am Myvatn-See und am Laxä-Fluß seit 1975 durchgeführt. Auf-
grund der Hypothese, daß die lokale Brutpopulation der Wasservögel vom Nahrungsangebot an den Brutplätzen
bestimmt wird, begann man mit Monitoringstudien an den abundanten Nahrungsarten. Seit 1977 findet Monito-
ring an Chironomiden statt. Daten über zwei Entenarten, Pfeifente (Anas penelope) und Trauerente (Melanitta
nigra) und über Chironomiden als Nahrung, sollen illustrieren wie die Analyse von Zeitverschiebungen zu Hypo-
thesen über die Ursachen von Populationsschwankungen bei Wasservögeln führt. Angaben über Wasservogelbe-
stände und Forellenfangergebnisse (Salmo trutta) lassen einen engen Zusammenhang zu den Nahrungsbedingun-
gen vermuten. Daten über die Ernte von Eiern, die bis 1901 zurückreichen, zeigen ebenfalls enge Beziehungen zu
den Nahrungsgrundlagen an den Brutplätzen. Durch palaeolimnologische Methoden wurde es möglich, eine bes-
sere historische Einsicht zu gewinnen und die Stabilität des Ökosystems zu erfassen.
Einarsson, Ä.: Ramsarska lokalita Myvatn-Laxä - pfiklad integrovaneho monitoroväni
Populace vodniho ptactva na jezefe Myvatn a fece Laxä na Islandu jsou monitoroväny od roku 1975. Hypoteza,
ze mi'stni populace hnizdfciho vodniho ptactva jsou zävisle na zdroji potravy na hnfzdistfch, byla podnetem k
monitoroväni nejrozsffenejsi'ch druhü potravy. Populace pakomärü jsou monitoroväny od roku 1977. Analyzy
populacnfch dat dvou druhü kachen hvfzdäka (Anas penelope) a turpana cemeho (Melanitta nigra) a jejich
zakladnf potravy larev pakomärü jsou zäkladem hypotez o pffcinäch populacnfch zmen vodniho ptactva. Pocty
vodnfch ptakü i ülovky pstruha (Salmo trutta) ukäzaly tesnou zävislost na potrave, stejne jako üdaje o sberu va-
jec, ktere se datujf od roku 1901. Paleolimnologicke analyzy poskytly pfesnejsf historicke üdaje a tak umoznily
zhodnocenf stability ekosysttmu.
211
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INTRODUCTION monitoring. At the same time, all the now
familiar questions about the purpose and
Lake Myvatn is a large (37 km2), shallow, limitations of monitoring have emerged, -
eutrophic lake in a region of active volca- if not in the beginning then in retrospect.
nism in Iceland. The landscape is shaped In this paper I should like to use examples
by volcanism and the present lake was from our monitoring programme and rela-
created only about 2300 years ago by a ted research to illustrate how monitoring
volcanic eruption which poured large vo- data can be used to gain insight into the
lumes of lava over the district. The lake processes at work within the ecosystem.
rests in a shallow depression in the lava-
field. The lake and its outflowing river -
the Laxä - have a worldwide reputation as AIMS AND PRINCIPLES
a breeding and moulting place for water-
fowl, especially ducks. Iceland is situated
Monitoring has been defined in various
on biogeographical crossroads, between
ways (cf. GOLDSMITH, 1991 and
North America and Eurasia, and the Arctic
SPELLERBERG, 1991) but here I shall use a
and the Boreal regions. This results in a
definition which suits the Myvatn situati-
unique species composition of waterfowl at
on: "Monitoring is a long-sighted, syste-
Myvatn. Larvae of Diptera constitute the
matic and repeated documentation of popu-
most important food for the ducks and the
lations and their habitats." This definition
local fish populations. In the lake chiro-
is population oriented, rather than focusing
nomids dominate, but in the river Simulium
on environmental quality as displayed by
is the dominant food species. The name
chemical and physical parameters.
"Myvatn" literally means "lake of midges"
There are two main aims of monitoring.
and reflects the large amounts of these flies
One is to aid conservation, the other to
on the banks (see JÖNASSON, ed., 1979).
promote understanding of the ecosystem.
The lake and the river were protected by
These two aims interact: better understan-
law in 1974, and in 1978 designated on the
ding of the ecosystem helps conservation.
RAMSAR list of wetlands of international
Collection of data may, however, be done
importance. Large changes had been ob-
purely out of academic interest. The aims
served in populations of both the vertebra-
of monitoring can be defined further:
tes and the invertebrates in the preceding
years, and there were fears that recent in-
a. To be an alarm bell, i.e. to give early
dustrial development (mining of the lake
notice that unwanted changes may be
sediment for diatomite production, com-
taking place.
mencing in 1967) was harming the ecosy-
b. To provide information on base line va-
stem. A research station was established in
riation in the ecosystem.
1974 and among its earliest aims was to
c. To observe how perturbations travel
monitor the animal populations. The cur-
through the ecosystem in order to high-
rent monitoring programme started with
light hypotheses about causal links.
bird censuses in 1975, but more animal
d. To assess the efficiency of management
populations were included later. The pro-
measures.
gramme developed hand in hand with our
knowledge of the ecosystem which in-
The aims may vary from place to place,
creased considerably during the first years.
depending on the characteristics of the eco-
Academic interest in the lake is high and
system, the type of threat, if any, and the
interaction between the monitoring and
political environment. The usefulness and
academic research activities has played a
limitations of monitoring for detecting en-
crucial role in the development of the
vironmental stress in natural populations
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has been discussed by UNDERWOOD Why do these changes occur? At the outset
(1989); see also CARPENTER (1988) for there were indications that recent changes
discussions about temporal variability in in the duck populations were linked with
freshwater ecosystems. food abundance in the lake. Older histori-
cal data suggested that this might be the
rule. Chironomid midges were known to be
EXAMPLES OF MONITORING the most important food (BENGTSON 1971,
GARDARSSON 1979). The Common Scoter,
like most other diving ducks, takes the chi-
When monitoring of animal populations
ronomid larvae on the bottom of the lake or
started in 1975 there were clear signs of a
picks the flies from the surface when they
poor situation in the waterfowl populati-
emerge. The Wigeon has to rely on flies on
ons. Waterfowl has a relatively high con-
the water surface or larvae washed up on
servation value, and seems suitable as an
the shore with vegetation. Although the
indicator of the general situation of the
Wigeon is to a large extent a herbivore,
area because there are many species with
midges comprise an important source of
different requirements. Also, waterfowl
protein for the laying female and small
can be counted rather easily. So when
young. Midge larvae in Myvatn can be
comparing cost and efficiency, waterfowl
divided into two groups. There is a group
was the obvious choice for starting a moni-
of infaunal species, with larvae living in
toring programme. As examples I should
the bottom mud. These are the most abun-
like to take the Common Scoter (Melanitta
dant ones, represented by Tanytarsus and
nigra) and the Wigeon (Anas penelope), a
Chironomus species. The other group of
diving duck and a dabbling duck (Fig. 1).
species has epifaunal larvae, crawling upon
The numbers in spring of these two species
the bottom and moving about in vegetati-
vary about 2-3 fold. Periods of increase
on. The epifaunal larvae are preferred by
may last 6-8 years, decreases seem to take
the diving ducks, probably because of
a shorter time. The variation is large
greater accessibility.
enough to conceal a long term trend, if it
exists.
2000H 600
MELANITTA NIGRA
500
1600-
CO
LLI
< 400-
AA
1200-
u. w
0 300-
tr
m 600-
s 1 200
400-
100-
0
1975 1980 1985 1990 1975 1980 1985 1990
YEAR YEAR
Fig. 1.: Numbers of male Wigeon (Anas penelope) and Common Scoter (Melanitta nigra) in
spring in the Lake Myvatn area.
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Monitoring of midges started in 1977. As a dependent variable, we use the change
Specially designed window traps have be- that had occurred in duck numbers since
en employed to catch flying insects the previous year. As independent varia-
(JONSSON et al. 1978). The traps are emp- bles, we use the catch of chironomid mid-
tied at 7-10 day intervals in the summerti- ges in the year (t) and the production of
me. About 50 different species of chiro- young in the previous year (t-1), two years
nomid midges have been recorded, about earlier (t-2) and three years earlier (t-3).
10 of which play a significant role in terms Analyzing longer time lags is hardly worth
of abundance. The total catch of chirono- while in this case because too many data
mid midges (Fig. 2) in 1977-89 shows points will be lost.
fluctuations which suggest a link between The duck populations studied did not show
the food supply and the duck populations significant correlations with the numbers
(GARDARSSON & EINARSSON, in press). of chironomid midges in the same year.
We wanted to consider the question whe- This means that in spring the ducks do not
ther the duck numbers respond directly to react directly to the food supply. Both the
the food situation or whether the response Common Scoter and Wigeon numbers cor-
is through the production of young. In related with the number of young produced
other words: do duck numbers increase the year before. In the case of the Wigeon
because adults become attracted to richer this is understandable because yearlings
food supplies or because they produce mo- return to the breeding grounds. The re-
re young? By analysing time lags between sponse of the Common Scoter is more sur-
changes in the food situation and changes prising because their young do not return
in the duck populations we may learn to the breeding grounds until later. The
which process is the more important. If the one- year lag suggests that the adult birds
response is slow (long time lags) it be- "remember" the situation from last year.
comes more likely that the population is Good food conditions the previous summer
reacting by increased production. Multiple may encourage the birds to return to
regression analysis makes it possible to Myvatn rather than going somewhere else.
analyze the importance of several indepen- Perhaps they simply survive better.
dent variables simultaneously.
25<h 1CH
83 8^
S *
< 4-
O
•
f 2
V
(H-r-
1978 1980 1982 1984 1986 1988 1978 1980 1982 1984 1986 1988
YEAR YEAR
Fig. 2: Catches of adult chironomid midges in flytraps at Lake Myvatn. A: all chironomids; B:
chironomid midges whose larvae are epifaunal. (Data from GARDARSSON & EINARSSON, in
press)
214
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3.0n
Anas penelope Melanitta nigra
r = 0.80 " r = 0.89 ••••
4.0 2.5-
o
3.5 2.0
i
o
u.
O
3.0- <r 1.5-
m I
D
Z
2.5- 1.0
2.0 0.5
3.5 4.0 4.5 5.0 5.5 3.5 4.0 4.5 5.0 5.5
NUMBER OF RJES (log) NUMBER OF FUES (log)
Fig. 3. Production of Wigeon (Anas penelope) and Common Scoter (Melanitta nigra) young
in relation to the total catch of chironomid midges in fly traps. The data point in parenthe-
ses is excluded from the analysis. It is from 1983, when counting methods differed and re-
sulted in an overestimation of production. (Data from GARDARSSON & EiNARSSON, in
press)
The young of the Common Scoter do re- the previous year indicates a significant
turn later, and a significant correlation oc- relationship (Fig. 4) (GISLASON, in press).
curs between the change in spring numbers
and the production of young three years
earlier (GARDARSSON & EINARSSON, in 5000n
press).
We are aware of the pitfalls involved in
correlating time series and also in relying
too heavily on the results of multiple re-
gression analyses. Our intention is to sort
out the relationships which seem to be the
most significant in order to get a better
focus for future research.
The link with food can be further clarified
by analyzing the relationship between the
food situation and the production of young.
The relationship is statistically significant
50 100 150 200 250 300
for both species (Fig. 3). THOUSANDS OF FLIES
The Brown Trout (Salmo trutta) in the Ri-
Fig. 4.: Catch by rod fishing of Brown
ver Laxä is another example of how moni-
Trout (Salmo trutta) in the River Laxä
toring of different trophic levels can be
in relation to the previous year's catch of
useful. Catch statistics (from angling) are
blackflies (Simulium) in flytraps.
available from 1976 onwards. The main
(Redrawn from GISLASON, in press).
food of the Brown Trout, the blackfly
(Simulium vittatum), has been monitored
The relationship is curvilinear: the total
with fly traps since 1977. A regression of
catch of Brown Trout seldom exceeds 4500
the catch of trout on the food situation in
fishes. This is probably because of catch
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restrictions, or alternatively, because at diatoms, chrysophyceans as well as plant
high food levels other environmental fac- pigments (e.g. HA WORTH & LUND, 1984;
tors than food may become limiting. GRAY, 1988). This kind of information is
In this example we can go further down the useful in revealing the conditions in a
food chain. The blackfly larvae are filter wetland before, e.g. the industrial revoluti-
feeders and planktonic algae (mostly Ana- on or forest clearance, and also gives an
baena flos-aquae) and detritus drifting indication of the long term stability of the
from the lake comprise their main food. ecosystem. Some of the microfossils in the
The drift of algae varies considerably bet- sediment are derived from species which
ween years. A multiple regression analysis are important in the food web, such as the
reveals a significant relationship between chironomid midge Psectrocladius barbi-
blackfly numbers and both drift of Ana- manus and the cladoceran Eurycercus la-
baena and water temperature (GiSLASON, mellatus (Fig. 6). In Lake Myvatn, both
in press). species are associated with filamentous,
mat-forming green algae (Cladophora ae-
gagropild) on the bottom of the lake. Pa-
laeolimnological studies indicate that in
HISTORICAL PERSPECTIVE
Lake Myvatn these species have been more
common in the last 270 years than earlier
Very few biological monitoring program-
in the history of the lake, which spans
mes have been running for more than
about 2300 years. This has been linked
twenty years. This number of data points is
with a corresponding increase in Clado-
minimal if we want to detect long term-
phora (EINARSSON & HAFLIDASON, 1988;
trends, given the variation in the data. A
EiNARSSON et al., 1993).
search for historical data may be fruitful.
Most often such information is based on
harvest figures: fishing or hunting, and can
be difficult to interpret because of varying DISCUSSION
and often unknown intensity of harvesting.
At Myvatn we have fishing data from 1900
Monitoring is, strictly speaking, an endless
to the present day, also figures about har-
process and because of financial con-
vesting of duck eggs from 1901 to 1957
straints we have to be selective about what
(GUDMUNDSSON, 1979). The similarity of
to monitor and about the methods em-
the harvest figures of Common Scoter
ployed. We have to make efforts to combi-
{Melanitta nigra) and Long-tailed Duck
ne low cost and high efficiency, and have
(Clangula hyemalis) eggs is interesting
to be certain that our methods will be valid
(Fig. 5) (see GARDARSSON et al. 1988). for a long time. At the same time, we
The similarity cannot be explained by
should make efforts to identify the most
changes in harvesting practice. The two
important factors in the ecosystem, and I
duck populations have different wintering
have demonstrated how a monitoring pro-
grounds, and these data indicate that chan-
gramme may be useful in this process, al-
ges in duck numbers at Myvatn are pri-
though by no means sufficient. I would like
marily governed by local processes rather
to stress the importance of having well
than processes operating on the wintering
formulated hypotheses, preferably more
grounds (GARDARSSON, 1979). than one, about the crucial factors deter-
The historical perspective can be improved
mining the populations in question, be it
considerably by employing palaeolimno-
animals or plants. Equally important is to
logical methods. A number of techniques
formulate hypotheses about the impact of
are available, which allow tracing the hi-
man-induced changes.
story of, e.g., chironomids, cladocerans,
216
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3000-]
Melanrtta nigra
Clangula hyemalis
2500-
g 2000-
u.
o
a: 1500-]
UJ
03
= 1000-
500-
1900 1910 1920 1930 1940 1950 1960
Fig. 5. Harvest of eggs of Long-tailed Duck (Clangula hyemalis) and Common Scoter
(Melanitta nigra) at Myvatn 1901-1957. Three years running averages. (Data from
GUDMUNDSSON, 1979).
Psectrocladius barbimanus
DEPTH (m) IN SEDIMENT
Fig. 6.: A palaeolimnological record of 2300 years of the chironomid Psectrocladius and the
cladoceran Eurycercus from the Lake Myvatn sediment. The location of two dated volca-
nic ash layers (A.D. 1477 and A.D. 150) is also shown. The densities are thousands of
fragments per g organic sediment. Redrawn from EINARSSON & HAFLIDASON (1988).
217
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The problem most of us are faced with is by interested scientists, carrying out well
the lack of baseline data. The need for designed research projects.
monitoring a piece of wetland does not The food web is a fundamental feature of
become generally recognized until after the the ecosystem. When unexpected changes
threat is there and after symptoms have occur in an animal population, changes in
emerged. We normally do not know the so- the food situation should be suspected.
called natural variation in the ecosystem or Monitoring different trophic levels at Lake
the variation that existed before the most Myvatn and River Laxä has been especial-
recent threat was realized. The frequent ly rewarding in this respect. Statistically
lack of control is also frustrating: quite significant relationships within the food
often we are dealing with some precious web, like the ones I have presented here,
piece of wetland, and there is no other La- are stimulating, because they suggest that
ke Myvatn to compare with. And even we might be on the right track. But the lack
though there was a similar lake, because of of significant relationship between two
cost considerations we have to choose time series is equally important, especially
whether to spread the effort and run a in the light of hypothesis testing. Food web
parallel monitoring programme in the con- studies are gaining more attention because
trol lake or whether we should concentrate of recent crystallization of theories about
on our own lake that we know so much the controlling factors of lake communities
about already. There is no golden rule. ("top down" and "bottom up") (see
Each case is in some way special and what KERFOOT & SIH, 1987; MCQUEEN et al.,
we do depends on the local situation and 1989). I would not like to say that we
the hypotheses posed. should concentrate all our effort on food
Each wetland has its characteristics and webs. By doing so we may miss other im-
ecological principles can only be applied in portant parameters. But omitting the study
a rather general way. Therefore we must of the food web seems to be unwise.
formulate hypotheses about the dynamics
of the specific wetland we are interested in. ACKNOWLEDGEMENT
Hypotheses, as a tool of science, have an
important property: they have to be falsi-
Prof. Arnthor Gardarsson read the ma-
fiable, and furthermore, every effort should
nuscript and suggested a number of impro-
be made to prove them wrong. What then
vements which are gratefully acknowled-
is the value of letting hypotheses govern
ged.
our choice about what to monitor if we run
the risk of spending time and money for
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© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at
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