Spectacular Underwater Landscapes of Arctic Lakes
By Ole Pedersen and Klaus Peter Brodersen
both associate professors at University of Copenhagen
First published April/June 2003, The Aquatic Gardener, Journal of the Aquatic
Gardeners Association
Aquarticles
Most people are familiar with the grand spectacle of tropical lakes and ponds mimicked in
the show aquarium. Few, however, are aware that many cold arctic lakes hold a rich
vegetation arranged in the most spectacular underwater landscapes, which just as well
could be the result of a talented artist.
The summers of South West Greenland are short but hectic. The lakes and ponds of the
Kangerlussuaq area (in older maps Søndre Strømfjord) are covered by meter thick ice most
of the year. But by the end of May, the sun is sufficiently powerful to melt the ice and
the aquatic vegetation now faces a season of three months to sprout, grow and reproduce.
This is only possible because light is available 24 hours a day during this period and
hence the total available light of the growth season can be almost as great as in
temperate regions of North Europe.
In contrast to most people’s belief, the lakes and ponds of South West Greenland are
not necessarily cold and unattractive biotopes unsuitable for submerged vegetation. The
area around Kangerlussuaq offers almost any type of biotope ranging in average summer
temperature from 5 to 15°C. The landscape is scattered with lakes and ponds with a
natural occurring climatic gradient starting from very cold and silty waters next to the
inland ice where the water temperature is only a few degrees above zero and with a
conductivity of less than 5 µS cm 1. Moving towards the west in the direction of the
fjord, the surface waters gradually become warmer and it is not unusual to find small and
sheltered ponds with a dense vegetation, which reach up to 15 to 20°C during July and
August.
Endless meadows of pondweeds in Lake Ferguson. This
lake hosts a great population of Potamogeton praelongus, which forms an
underwater landscape that just as well could be the landscape in the tropical sea.
Ponds
Many ponds are temporary biotopes that often dry out during the summer. They are mostly
shallow and warm up easily in the early summer months and the vegetation of these ponds is
not very different from the type of vegetation found in more temperate regions of North
Europe.
The dominating vegetation of the ponds is almost entirely made up by the perhaps most
common aquatic plant of the region, Hippuris vulgaris L. (see box). As an
amphibious plant it is perfectly adapted to the fluctuating water levels in many of the
temporary ponds. Early in the season, while the water level is still high, H. vulgaris
produces the most beautiful aquatic leaves, which do not resemble any other temperate
aquatic plant. Approaching the water surface, the plant starts to produce the emergent
leaves that at first sight may look quite similar to the emergent leaves of, for example, Myriophyllum.
H. vulgaris is very competitive and in previously water filled grooves of the
landscape it may still maintain a dense cover several weeks after the water has totally
evaporated.
In permanent ponds various species of Potamogeton become more frequent. In
particular, Potamogeton filiformis Pers. is abundant in certain ponds and this
tiny delicate plant is able to produce an inflorescence which reaches the water surface
from up to a depth of one meter. Species of Myriophyllum, Chara and Batrachium
may also be found here but they rarely comprise the majority of the vegetation.
Finally, the spectacular inflorescence of Menyanthes trifoliata (L.) is common by
mid July, where it may form a dense carpet of beautiful flowers that from a distance
resembles the inflorescence of Eichornia crassipes (Mart.) Solms-Laubach –
the water hyacinth.
Warm shallow lakes and lakes with thermoclines
A couple of interesting lakes are found in the vicinity of Kangerlussuaq, which is about
25 km west of the inland ice. Lake Ferguson is a relatively deep lake (more than 80 m)
that serves as the local water reservoir for the town. The lake is sufficiently sheltered
to develop a stable thermocline during the summer months and the epilimnion warms up to
about 12 °C, creating an ideal environment for the larger species of pondweed. Perhaps
the most common plant in this lake is Potamogeton praelongus Wulf. In Lake
Ferguson, it forms dense underwater meadows growing a few centimeters each day during the
season. P. praelongus may grow more than five meters tall but in arctic lakes it
rarely reaches more than a meter and a half.
Perhaps the most spectacular part of Lake Ferguson is the little shallow lagoon in front
of the run-off that feeds the beautiful waterfall falling the 80 meters down to the fjord.
The lagoon hosts a mixed meadow of Hippuris vulgaris, Potamogeton praelongus and
a few aquatic mosses that we have not identified yet (superficially, however, they
resemble species of Drepanocladus and Fontinalis). The rich aquatic
vegetation has overgrown the many remains from the American military airbase – oil
barrels, telephone poles, rims and tires are spread out over the entire area and all these
things left behind form an odd background for the stunning submerged vegetation.
Threespine stickleback (Gasterosteus aculeatus) and arctic char (Salvelinius
alpinus) are the only fishes in Lake Ferguson but they are present in high numbers.
Larvae of non biting midges (Chironomidae), water beetles (Dysticidae)
and Limnaea snails dominate the community of invertebrates and they all benefit
from the dense underwater vegetation creating a very high relative surface where the
nutritious biofilm forms a valuable basis of nourishment in addition to providing shelter.
A log is not necessarily the first thing you would expect to meet
underwater in Greenland. However, the Americans have used many of the lakes and ponds in
the area of Kangerlussuaq as the local dump. The plant is the submerged form of Hippuris
vulgaris and two species of aquatic mosses – photo from Lake Ferguson.
Some 15 km north west of Kangerlussuaq near Kelly Ville the relatively shallow Lake Jean
is found. Lake Jean also develops a stable thermocline but the lake is both smaller and
more sheltered than Lake Ferguson and therefore the epilimnion also becomes warmer during
the summer. The lake is slightly more nutrient-rich compared to Lake Ferguson and a rich
underwater vegetation is present here.
Below 9 meters at the profundal zone small chimneys formed by the chironomid larvae
dominate the underwater landscape, but the vegetation reaches down to a depth of 8 meters
where a belt of Chara sp. forms a dense meadow. The Chara zone is
replaced by various species of elodeid species such as Myriophyllum spicatum L.,
Potamogeton praelongus, Potamogeton pusillus (L.) Dandy & Thaylor, Potamogeton
filiformis and various species of aquatic mosses. They all form the most beautiful
underwater landscape, which is far from what most people connect with an arctic lake.
Underwater landscape in Lake Jean. This is the work
of nature – it is not made by a talented artist. At least four species are visible:
two species of aquatic mosses, Potamogeton filiformis and Hippuris vulgaris (the
long slender plants in the background).
Deep and cold nutrient poor lakes
Many of the lakes in the Kangerlussuaq area have not yet been named. One of the more
interesting of these ‘nameless’ lakes is a lake in the group of what the local
people call ‘The Long Lakes’. A few years ago, these lakes could only be reached
by means of helicopters. However, a new road has been built to service the test-lanes of
the German car manufacturer Volkswagen, which now makes them easier to access. As a
convenient working name, we named one of the lakes “Lake Niko” after Niko
Willemse, a Dutch scientist working on this lake some years ago. Lake Niko is deep and
cold and oriented from East to West, which is the prevailing wind direction of the area.
Therefore, it probably never develops a stable thermocline and the maximum summer
temperatures are around 5 °C. The lake is extremely nutrient-poor and the dominant
vegetation is a dense carpet of aquatic mosses at depths greater than 2 meters where the
ice does not scour during the winter. In more shallow water, sparse populations of Potamogeton
filiformis and the widespread Hippuris vulgaris are sporadically present but
mostly close to big boulders that provide some shelter from ice scouring.
Lake Niko hosts a dense population of the fairy shrimp (Branchinecta paludosa)
– a 1-centimeter large crustacean that swims the backstroke while filtering the
water. They are extremely abundant just above the bottom, which probably indicates that
Lake Niko does not hold a significant stock of either sticklebacks or arctic chars.
A quaint proof of the extremely nutrient poor conditions of the cold water of Lake Niko
is the vigorous growth of microalgae around reindeer remains left behind in the water by
hunters. After a successful shooting the deer is usually cut into pieces on location and
parts of no value are just left behind in the surroundings. The organic waste may end up
in the water, and it is able to stimulate the primary producers – mainly microalgae
– while the organic matter is decomposed and the nutrients are slowly released into
the surroundings.
The remains of a reindeer leg. The water of Lake
Niko is extremely nutrient poor and even during midsummer no significant biofilm develops
on stones and plant surfaces. In this case, however, inorganic nutrients are released when
the tissue decomposes and green microalgae thrives in the immediate vicinity of the bone.
The scarce vegetation of pondweed is dominated by Potamogeton filiformis.
Saline lakes
The area around Kangerlussuaq is well known for the oligosaline lakes formed by a negative
precipitation/evaporation balance. The lakes are often easily recognized by the fossil
shorelines with characteristic vegetation (e.g the cruciferous Braya linearis Rouy)
and a water conductivity between 2000-4000 µS cm 1. The lakes are permanently stratified
(meromictic) due to a strong chemo-thermocline and the lake bottom in the deep areas is
covered by purple sulfur bacteria well adapted to anoxic conditions of the bottom water.
Nevertheless, the lakes have recently been exposed to a significant rise in water
levels and this has caused a situation where the surface water is quite turbid due to the
decomposing terrestrial vegetation that has now been flooded. The bank is also seriously
eroding at several points, which also creates silty water when the fine clay particles are
suspended into the water column. One plant, however, benefits from the current situation
and that is the amphibious Triglochin palustris L., which, for example, around
Braya Sø forms a dense meadow starting at a depth of 30 cm and all the way up the shore
to 20 cm above the water level. The submerged leaves are much more sickle shaped and
softer than the emergent leaves and at very shallow water, even the submerged
population’s flowers. The true aquatic vegetation probably suffers from the
deteriorated light climate and only Myriophyllum spicatum forms a few stands at
shallow water.
In many of the lakes, the water is extremely clear. In this case,
the photo is from Lake Jean and it might just as well have been taken above the water
surface.
Kangerlussuaq is the gateway to Greenland as the locals like to express it. Going there
during clear weather conditions, you will notice that the whole area is scattered with
hundreds of ponds and lakes. At least three types of waters can be recognized from the air
without even going there with the test instruments and the underwater camera: the grey,
silty lakes close to the inland ice, the deep blue cold and clear lakes, and the greenish
ponds and lakes where the high summer temperatures allow a significant biomass of aquatic
autotrophs to develop. If you ever go to Greenland, do not miss the opportunity to stay a
few days in the area of Kangerlussuaq – and if you own an underwater camera, it
should always be part of the daypack…
This is probably as beautiful as it gets? A few
slender stems of Hippuris vulgaris intermingle elegantly with Potamogeton
praelongus on a dense carpet of aquatic mosses. A couple of threespined sticklebacks
are seen in the background. Photo from Lake Ferguson.
Hippuris vulgaris – Mare’s tail, the most common water plant
in Greenland
This very competitive plant is present in almost every water body in Greenland from the
coldest and milky waters at the foot of the glaciers to the warm and temporary ponds in
the low arctic. Part of the reason for being so ecologically successful is probably due to
the fact that Hippuris vulgaris is a genuine amphibious plant that thrives well
submerged as well as emerged. In the numerous temporary ponds they continue to grow when
the water evaporates during the summer. Closer to the ice sheet, the plant simply does not
develop the typical submerged leaves due to the very unfavorable light climate in the
silty and turbid water. Instead, the stiff emergent leaves are set with extremely long
internodes serving to lift the plant above the water level to the life-giving light as
fast as possible.
Emergent Hippuris vulgaris in bloom.
On the emergent shoots small and unimpressive flowers are formed at the axils. The
individual flowers are very small but a very dense emergent stand of H. vulgaris
may nevertheless appear beautifully red when the all the shoots flower in July and August.
Underwater photo of the green and red variety of Hippuris
vulgaris.
We found submerged H. vulgaris in two color varieties – a green and a red
variety. It is unclear whether the color has any ecological importance but it has been
speculated that the red color, which most probably is due to a high content of
antocyanins, may play an active role in absorbing harmful UV radiation present in high
amounts in the clear arctic atmosphere. We never observed any of the green forms in the
emergent populations, which actually indicate that the red form has a better survival rate
due to higher fitness in the terrestrial environment.
The authors
Ole Pedersen (opedersen@zi.ku.dk) works as associate professor at the Freshwater
Biological Laboratory (www.fbl.ku.dk), University of Copenhagen, where he works with the
ecology and physiology of aquatic plants. Klaus Peter Brodersen (kpbrodersen@zi.ku.dk) is
also associate professor at the Freshwater Biological Laboratory and works with paleo
limnology. At the current project in South West Greenland he uses the fossil remains in
lake sediments of the head capsule from non-biting aquatic midget larvae to estimate
climatic and ecological changes over time from the last ice age to present – a
scientific project funded by the National Danish Science Foundation.
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