Directions of Limnological Succession of Lobelia Lakes of Bory

Directions
of Limnological Succession of Lobelia Lakes of Bory Tucholskie
Limnological Review
7, 2: 79-85
79
Directions of Limnological Succession of Lobelia Lakes
of Bory Tucholskie
Karolina Pacewicz, Kamil Nowiński
University of Gdańsk, Faculty of Biology, Geography and Oceanology, Institute of Geography, Department of Lakeland Geography,
Dmowskiego 16a, 80-264 Gdańsk, e-mail: kmundo@wp.pl, geokamil@univ.gda.pl
Abstract: In August 2006 a series of the expeditionary field research was performed. 17 lobelia lakes situated, according to the borders
marked out by Kowalewski (2002), in the north-western part of Bory Tucholskie, were selected as the research subject. The selected
reservoirs are characterized by small areas, below 20 ha and depths up to 10 m. They are also characterized by small catchments and,
in terms of hydrology, they demonstrate an outflow-less character, with an exception of periodically flow-through Lake Kłodzko Małe.
The aim of the paper was an assessment of the current condition of their water environments as well as of the direction and rate of
limnological succession occurring in these small forest reservoirs. Measurements were made in places of maximum depths and covered
vertical distributions of: temperature, specific conductivity, oxygen saturation, relative irradiance, pH reaction and chlorophyll a.
Additionally, water transparency was measured using the Secchi disc, and water samples for laboratory analyses were taken in order to
determine main nutrients content. The obtained results were presented in the form of graphs and processed using the Carlson method
(TSI). On this basis, the following lakes were considered eutrophic: Kłodzko Małe, Moczydło, Nowoparszczenickie, Długie, Żabionek and
Trzemeszno Małe. The ß-mesotrophic status was assigned to lakes Zmarłe Duże, Linówko, Piecki, Kły, Sosnówek, Chińskie and Bardze
Małe. Level α-mesotrophy still occurs in lakes: Czarne near Zapceń and Sporacz, and oligotrophy level in Nawionek and Moczadło. In the examined group of the lobelia lakes of Bory Tucholskie it was established that, irrespective of the size of water tables, lakes of
maximum depth up to 6 m have already achieved the eutrophic stage, while these with depths above 6 m, reveal considerable trophic
diversity, dependent mainly on the size and the use of their catchments.
Key words: lobelia lakes, Bory Tucholskie, the limnological succession, Carlson, Trophic State Index
Introduction
Lobelia lakes are a small group of exceptionally
naturally valuable limnic systems, usually representing
the initial stage of limnological succession. In Poland
these reservoirs are distinguished on the basis of the
floristic and phytocenotic criterion, i.e. the occurrence
of at least one of three relict indicator plants: water lobelia (Lobelia dortmanna), lake quillwort (Isoëtes lacustris) and shoreweed (Littorella uniflora) (Szmeja 1996).
These species are regarded as phyto-indicators of lakes
with best preserved primeval natural value.
On the territory of Poland there are 175 documented lobelia lakes (Gos and Bociąg 2003), in majority situated in the Pomorskie Lakeland, of which
17 (Table 1), situated within Bory Tucholskie, were
selected as research objects. The aim of the paper was
an assessment of the current condition of their water
environments as well as of the direction and rate of
limnological succession occurring in these small, forest reservoirs.
In August 2006, during the summer thermaldensity stratification, a series of expeditionary field
research was carried out. Its purpose was the investigation of the internal structure of reservoirs and the
present trophic state. The measurements were made
from a pontoon boat, along columns corresponding
to maximum depths of lakes and their scope covered
vertical distributions of: temperature, specific conductivity, oxygen saturation, water lighting, pH reaction
and chlorophyll a. For comparative purposes, water
transparency was measured using the Secchi disc. Also
surface and near bottom water samples were taken for
laboratory analyses (nitrogen and phosphorus compounds). Additionally, land mapping was performed
together with a survey of possible pollution emitters.
80
Karolina Pacewicz, Kamil Nowiński
Table 1. Geographical situation and basic morphometric data of examined lakes
No
Name
φ
λ
Area
Depth
[°N]
[°E]
[ha]
[m]
1
Żabionek
53°50’
17°37’30”
7.0
2.4
2
Sosnówek
53°49’
17°37’10”
4.1
9.0
3
Długie
53°48’30”
17°37’30”
13.6
3.9
4
Moczadło
53°49’
17°38’
3.6
10.0
5
Trzemeszno Małe
6
Bardze Małe
53°50’
17°45’
2.3
4.9
53°46’10”
17°26’20”
6.0
8.2
7
Sporacz
53°46’50”
17°25’40”
11.5
6.1
8
Linówko
53°46’45”
17°22’
10.5
3.5
9
Kłodzko Małe
53°44’20”
17°22’
18.0
3.9
10
Piecki
53°54’50”
17°33’
6.0
6.6
11
Nawionek
12
Czarne n. Zapceń
13
Nowoparszczenickie
53°54’
17°32’
12.5
8.5
53°58’30”
17°28’
8.5
7.4
53°54’
17°28’
2.3
4.9
14
Zmarłe Duże
53°56’
17°48’
8.6
6.2
15
Kły
53°56’
17°47’
18.7
6.2
16
Moczydło n. Brusy
17
Chińskie
53°56’30”
17°47’
1.4
2.8
53°52’
17°50’
4.4
9.8
Fig. 1. Location of examined lakes. a – lakes, b – examined lobelia lakes, c – rivers, d – roads, e – railway line, f – border of the Bory
Tucholskie National Park , g – border of the Zaborski Landscape Park. Lakes’ numbers as in Table 1
Directions of Limnological Succession of Lobelia Lakes of Bory Tucholskie
Study area
17 lobelia lakes (Fig. 1) situated, according to
the borders marked out by Kowalewski (2002), in the
north-western part of Bory Tucholskie, within the Pomeranian province, were selected as the research subject. According to the physical-geographical division
of Poland by Kondracki (1994), the research area covers fragments of three mesoregions: Bory Tucholskie
(lakes: 3, 4, 5, 17), the Charzykowska Plain (lakes: 1, 2, 6,
7, 10, 11, 12, 13, 14, 15, 16, 17) and Krajeńskie Lakeland
(lakes: 8 and 9).
In hydrographic terms, all the lakes, apart from
No. 17 (Chińskie, also called Cyrkowe) situated in the
River Wda drainage basin, are located in the Brda
drainage basin. Both mentioned rivers are left-bank
tributaries of the Vistula River.
The research area is made of the Brda outwash
and patches of moraine plateaus (Nowaczyk 2006)
formed during the Pomeranian Stadial of the Baltic
Glaciation. The lake basins situated there demonstrate
a diversity of size and shapes, corresponding mainly to
their channel, melt-out or evorsion origin, and location
in hydrographical units differing in the water resources.
The investigated reservoirs have small areas (Table 1),
below 20 ha (the biggest lake Kły 18.7 ha) and depths
up to 10 m (Moczadło). Their catchments are also small,
because of the outflow-less character of the discussed
lakes (an exception is periodically flow-through Lake
Kłodzko Małe) and, except for the catchment of Lake
Kłodzko Małe, are in the 100% covered with forests,
mainly coniferous (Kraska 1994). Alimentation from
the catchment is in such conditions marginal and usually limited to a disorganized surface flow, slowed down
81
by forest covering of the land, and possibly groundwater drainage, which on the one hand is favourable for
the maintenance of the natural value of the explored
water environments, and on the other, hampers the
exchange of waters, which occurs here mainly in the
evaporation-precipitation way.
Results
In order to assess the current stage of the limnological succession, the results of author’s own research
results were used. They were presented, among others,
using the Carlson’s TSI method (Trophic State Index)
which takes into consideration such properties of the
water environment as: the scope of Secchi disc visibility, total phosphorus concentration and chlorophyll a
concentration. Reservoirs for which TSI value does
not exceed 30 are considered oligotrophic, whereas
the border between mesotrophy, and eutrophy is here
value 50 of the index.
The highest general TSI value (Fig. 2), of 61.6,
was observed in a relatively big and shallow Lake
Kłodzko Małe, the only flow-through reservoir in the
examined group, with a relatively large alimentation
area, including anthropogenic terrain. The value of the
remaining indicators also exceeds the eutrophy border here. Quite an advanced trophy is confirmed by
the extent of the photic zone reaching only 3 m (Fig.
5) and oxygen saturation distribution with supersaturation of about a dozen percent within the 2-metre
near-surface layer (Fig. 3). From 2 m of depth a rapid
decrease in oxygen saturation was observed to 2%
(0.19 mg l-1) above the bottom. Specific conductivity
of water also differs considerably here from the re-
Fig. 2. Trophic State Index according to Carlson. a – TSI (SD), b – TSI (Chl), c – TSI (TP), d – TSI
82
Karolina Pacewicz, Kamil Nowiński
Fig. 3. Vertical oxygen saturation distribution of examined lake waters
Fig. 4. Vertical distribution of chlorophyll a concentration
Directions of Limnological Succession of Lobelia Lakes of Bory Tucholskie
maining discussed lakes and is as high as 120 µS cm-1,
with about 20-40 µS cm-1 recorded in the majority of
lakes in the examined group.
The remaining lakes, for which general TSI
value was over 50, are characterized by depths to 5 m
and are classified as reservoirs with polymictic type
of mixing; these are: Trzemeszno Małe, Żabionek,
Długie, Nowoparszczenickie and Moczydło (an exception in this depth group is Linówko considered ßmesotrophic though close to eutrophy). Oxygen saturation distributions have a shape close to clinograde,
with small supersaturations mainly in the 3-metre
near-surface layer and with a rapid saturation decrease close to 0 at the bottom. The shallowest extent
of the euphotic zone, reaching slightly below 2 m, was
observed in Lake Żabionek. This was caused by a high
primary production, which is confirmed by TSI (Chl)
and vertical chlorophyll concentration distribution.
An influence on the considerable decrease in water
transparency of Lake Żabionek is also exerted by the
brownish colour of water caused by an inflow of humic substances from the catchment. Equally poor light
transmission occurred in acidic Lake Nowoparszczenickie and in Moczydło (No. 16), with a neutral reaction. In both lakes, relatively high total phosphorus
concentrations as well as chlorophyll a concentration
Fig. 5. Relative irradiance of examined lobelia lakes waters
83
were recorded. Lake Długie had the highest chlorophyll concentration among all the 17 examined reservoirs and consequently the highest TSI (Chl), and
its vertical distribution (Fig. 4) was characteristic of
eutrophic lakes (Kajak 2001).
Lakes in which the scope of Secchi disc visibility
is not over 2 m are also considered eutrophic. According to these characteristics, besides lakes mentioned
earlier, the following lakes were considered eutrophic
too: Bardze Małe and Kły (Fig. 6) which on the basis
of the general Carlson’s index were categorised as ßmesotrophic.
The remaining reservoirs, for which general TSI
value was between 40 and 50, are: Chińskie, Sosnówek,
Piecki, Linówko and Zmarłe Duże. They are still characterized by quite good conditions of water environment. The best oxygen conditions were observed in
Sosnówek where up to 8 m oxygen saturation was
over 100%, chlorophyll concentration distribution
indicated the succession stage on the level of early
α -mesotrophy, the same as TSI (SD) and TSI (TP),
whereas TSI (Chl) of eutrophy. Low trophy was here
confirmed by the extent of the euphotic zone reaching the bottom (9 m). Slightly shallower photic zones
covered 6 m in lakes Bardze Małe and Kły, 5 m in
Zmarłe Duże and Chińskie, and 4 m in Piecki. In the
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Karolina Pacewicz, Kamil Nowiński
last two, vertical chlorophyll distribution was close to
that characteristic of mesotrophic waters of dimictic
lakes (Kajak 2001), with the maximum of the primary
production in metalimnion, with the availability of
biogenic substances and good photic conditions.
Lakes Sporacz and Czarne near Zapceń, acidic
reservoirs of total depths between 6 and 8 m and areas
about 10 ha, on the basis of general TSI were classified as α -mesotrophic because of the complete lack
or scarce amounts of total phosphorus. In both cases
TSI (Chl) again indicates a higher succession stage,
however there are good photic conditions here and
their vertical chlorophyll concentration distributions
are characteristic of waters of low trophy.
The lowest degree of the advancement of limnological succession, on the oligotrophy level (according
to general TSI value), characterized lakes Moczadło
and Nawionek. The first is a lake of a very small area
(3.6 ha) and the largest depth (10 m) among the 17 examined lakes. Features of stratified dimictic lakes with
an exceptionally long circulation cycle as for such a
small, forest reservoir were observed here. The second
one is slightly shallower (8.5 m) and bigger (12.5 ha),
and polimictic. The oxygen saturation distribution
in both cases takes a form of positive heterograde
which indicates an intensified primary production
within the layer of the biggest thermal jump, with a
high water transparency allowing for photosynthesis
Fig. 6. Scope of Secchi disc visibility
Fig. 7. pH reaction of water of examined lobelia lakes
and consequently oxygen production. According to
Kajak (2001), such a situation is observed in oligo- or
mesotrophic reservoirs. Low trophy is confirmed by
a large extent of euphotic zone in Nawionek embracing the entire water mass, and in Moczadło reaching 9
m, as well as an even profile and very low chlorophyll
concentration in the entire water column. Specific
conductivity of water of Lake Moczadło was 35 µS
cm-1 and of Nawionek 73 µS cm-1, which confirms low
contents of all dissolved mineral compounds. Despite
establishing a good state of maintenance of primeval
limnological features of both reservoirs, again TSI
(Chl) value was here much higher than of the remaining indices.
In all the examined reservoirs low contents of
biogenic substances were recorded, which results from
their forest location and quite good isolation from areas transformed by man.
Recent transformations of limnic environments
proceed mainly in the direction of eutrophy, with a
relative balance of the influence of environmental
factors or of dystrophy, with a domination of some
components of the limnic system, e.g. humic acids
(Lange 1993). The location of the examined lakes on
postglacial formations and in majority among pine
forests, is theoretically favourable for maintaining
the pH advantageous for the growth and the life of
lobelia species, but in case of excessive, disturbing the
Directions of Limnological Succession of Lobelia Lakes of Bory Tucholskie
balance, inflow of humic substances, can lead to their
dystrophication.
On the basis of the data collected in summer
2006, it was established that 9 of the examined reservoirs had neutral pH reaction, i.e. from 6.5 to 7.5, and
8 had acidic reaction (Fig. 7). This can suggest that
lakes Żabionek, Sosnówek, Długie, Bardze Małe, Sporacz, Linówko, Czarne near Zapceń and Nowoparszczenickie are ageing disharmoniously and undergoing
dystrophication, whereas the remaining reservoirs are
progressing in the direction of eutrophy.
Conclusions
On the basis of the obtained results it is possible to state that the main factors influencing the
trophic state of the water environment of these lakes
are basin morphometry and the size and use of the
alimentation area. The slowest ageing occurs in lakes
with relatively large depths but also situated in catchments anthropogenically unchanged, only moderately
supplied with humic acids. In the examined group of
lobelia lakes of Bory Tucholskich it was established
that irrespective of the size of water tables, lakes with
the maximum depth up to 6 m have already achieved
the eutrophic stage, whereas those of depths over 6 m,
demonstrate a considerable trophic diversity dependent above all on the size and use their catchment, and
consequently on the supply of all substances hastening
the increase in trophy.
At present the biggest threat to the specificity
of lobelia lakes of Bory Tucholskie is their tourist exploitation which consists above all in trampling to the
ground and littering of shores, establishing bathing
beaches, which leads to an increase in the delivery
of biogenic substances, and consequently causes extinction of lobelia species. The presence of man also
contributes to mechanical damaging of these plants
occurring in shallow waters. The threats also come
from all other anthropogenic forms of transformation
in lakes’ surrounding, e.g. forest clearings, locating the
arable land or pastures, holiday cottages, camping sites
in their vicinity, fluctuations of water level caused by
artificial damming of outflow etc.
The increase in all forms of anthropopressure,
increases the burden of the reservoirs and threat of intensified eutrophication. For this reason, it is particularly important that the areas surrounding so valuable
limnic systems were used in a sustainable way, not
threatening with degradation.
85
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Karolina Pacewicz, Kamil Nowiński