Factors affecting light availability in some lakes of western Poland
JONIAK Tomasz
A. Mickiewicz University, Faculty of Biology, Department of Water Protection, Poland, Poznań 61-614
[email protected]
Abstract: The behavior of light in lake
has important ecological and water quality
implication. The depth of light penetration in
water is regulated by the water itself and by
various optically active substances, which
absorb or scatter the light. While the scattering
of light, which is a natural optical feature of
water, depends on the amount of light in water
environment, its incidence angle and the
amount of optically active substances which
cause a deeper light penetration, the absorption
completely attenuates the light radiation. The
analysis of the optical features of water in the
field of Secchi disc visibility permitted the
identification of a characteristic composition
of substances influencing the water
transparency in each of the lakes. The turbidity
and water opalescence generated by a high
content of autochthonous dissolved organic
substances was the main factor restricting the
light range in the eutrophic lake. In
mesotrophic lakes representing two different
types of mixis, the range of visibility depended
in one of them mainly on the concentration of
the suspended matter, and in the other one on
the dissolved optically active substances,
especially colour producing compounds. The
occurrence of the shallow-layer turbidity in the
bottom part of the euphotic zone was a
common property of dimictic lakes during the
summer stagnation.
Keywords: lake, light availability,
turbidity, water trophy.
1.
Introduction
Aquatic ecosystems are key components
of the Earth’s biosphere. They produce more
than 50% of the biomass on our planet and
incorporate at east the same amount of
atmospheric carbon dioxide as terrestrial
ecosystems [1]. Phytoplankton are by far the
major biomass producers in the inland water
and oceans, and form the basis of the aquatic
food webs. The behavior of light in water,
particularly its attenuation with depth, has
important ecological and water quality
implication. The limitation of nutrients, pH,
degree of adaptation and grazing pressure,
high levels of solar radiation inhibit
photosynthesis in species of different
taxonomic groups [2]. Besides optical
properties of natural waters are important for
many factors such as the heat budget of water
bodies, the depth distribution of submerged
macrophytes, productivity and species
composition of phytoplankton [3]. Light
attenuation is regulated by the composition
and concentration of various attenuating
constituents, which include water itself,
gelbstoff, tripton and phytoplankton [4].
Particulate
constituents
regulate
light
attenuation in the vast majority of inland
waters. The research on light conditions in
lakes and particularly on the impact that the
optically active substances have on the depth
of light transmission have so far been very rare
in Poland. In Polish lakes, the eutrofization
and the changes in the quality of lake water are
the most common reasons for the limitations in
the transmission of light [5].
Transformation of light energy flux
under influence of optically active substances
may cause its strong absorption or the
transmission to larger depths as scattered light.
As a result of eutrophication and the connected
degradation of lake waters the natural optic
features of water change, which leads to
numerous changes in the environment. A key
consequence of this is an acceleration of the
primary production of algae and as an effect
there is a considerable decrease of penetration
the solar radiation, which is mostly absorbed
in the shallow epilimnion [6, 7]. The aim of
1
this work was to characterize the factors
affecting of summer light availability in three
lakes of western Poland. A hypothesis was
proposed that the main magnitude factors for
the depth of the euphotic zone has a
concentration of dissolved and suspended
optically active substances connected with
occurrence of phytoplankton.
2.
Methodology
The objects of study were three postglacial lakes of different surface and
morphology of the basins, especially depth:
the dimictic Góreckie Lake, Kociołek Lake
and polymictic Wielkowiejskie Lake in the
area of the Wielkopolska National Park
(western Poland) (Tab.1). The Góreckie Lake
for over 20 years had been polluted with the
raw waste from the nearby sanatorium in
Jeziory. Although the sanatorium was closed
in 1990 and the point sources of pollution were
blocked, in the end of the 20th century the lake
was hypertrophic [8]. Most visible result of
lake degradation are yearly mass water blooms
of phytoplankton – from early spring to late
autumn.
Tab.1. Morphometrical parameters of study lakes
Góreckie
Kociołek
Wielkowiejskie
104.1
4.3
13.3
Max. depth (m)
17.2
7.8
4.3
Mean depth (m)
8.9
4.5
1.4
Elongation index
6.9
1.3
5.2
Expose index
11.7
1.0
9.5
Lake
Parameter
Surface (ha)
Kociołek Lake is a small, postglacial
mid-forest lake. Till a few years ago the lake
had been polluted with raw waste from the
sanatorium in the Ludwikowo, at present the
inflow of waste is blocked. The lake has been
for a long time treated as meromictic, although
this opinion has not been corroborated by
well-documented study. The most shallow
from three researched lakes is Wielkowiejskie
Lake. The lake is long and relatively shallow,
which at a high value of expose index
determines its polymictic character. Specific of
this lake is an extensive cover of various
macrophyte
associations
(macrophytedominated lake). Its whole basin is surrounded
by a belt of emergent macrophytes mainly
with Typha angustifolia L. and Phragmites
australis (Cav.) Steud. Chara spp. created
large beds, which occupied the greater part of
lake bottom.
The feature of lakes was a great
differentiation of susceptibility to influence of
climate factors, what displayed the large
difference of exposure index (Tab.1).
Sampling and field measurements were
conducted monthly in summer (June –
September) of 2008 at pelagic location of all
lakes. Five measurements were made routinely
for the study lake to characterize features of its
optical regime: water transparency SD (with
30 cm diameter white disk), unit m-1, turbidity
Tn (nephelometrically, Eutech Instr. TN-100),
unit NTU, total suspended sediments TSS
(after filtration through GF/F filter,
gravimetrical method), unit mg dm-3, inherent
water colour (spectrophotometrically at 420
nm), unit mg Pt dm-3 and OAS (optically
active substances, characterized by beam
attenuation coefficient of (GF/F) filtered water
at 380 nm measured spectrophotometrically),
unit m-1 [3]. The chlorophyll a concentration
was determined after extraction with ethanol.
Water trophy were assessed according to the
Carlson’s classification [10].
3.
Results
The Góreckie Lake in summer season
was characterized by eutrophy while the lakes
Kociołek and Wielkowiejskie by mesotrophy.
When analyzing the trophy state indexes (TSI)
in each of the lakes, it was found that
phosphorus had the main impact on the trophy
in the former lake, while in the latter two it
was the chlorophyll a (Tab.2). The most
favourable light conditions existed in the Lake
Wielkowiejskie, where the average value
Secchi disk visibility was 3.8 m. In Kociołek
Lake the range of light was much more limited
(2.5 m), yet the worst light conditions were
registered in the eutrophic Góreckie Lake (2.0
2
m). It was observed during the study that the
water transparency of Góreckie Lake improves
significantly during the summer months of
July and August (Fig.1).
Month
VI
VII
VIII
IX
Depth (m)
0
1
2
3
4
Góreckie L.
Kociołek L.
Wielkowiejskie L.
5
Fig.1 Summer dynamics of Secchi disk visibility
Although such a state is untypical for
eutrophic lakes, it has been already registered
in earlier studies and has been referred to as a
‘late clear water phase’ [11]. Nevertheless, it
has to be remarked that the water transparency
measured in 2008 in these summer months
was significantly lower than the water
transparency registered in the 1930s, when it
almost reached 5 m With regard to the water
trophy, this temporary improvement in light
conditions brought about the reduction of the
annual TSI values which base on water
transparency values (Tab.2).
Tab.2 Values of trophy state indexes of researched lakes
(summer 2008)
Lake
Góreckie
Kociołek
Wielkowiejskie
TSITP
TSIChl
TSISD
61.2
37.2
41.5
54.5
52.8
45.8
50.2
47.8
40.8
Trophy
status
eutrophy
mesotrophy
mesotrophy
The analysis of optical features in the
Secchi disc visibility zone revealed that in
each of the lakes a specific composition of
substances is responsible for the quality of
light in the euphotic zone. In the Góreckie
Lake, the turbidity (opalescence) of water was
the main factor that negatively impacted on
light quality, followed by the suspended matter
(Fig. 2). The turbidity and opalescence of
water were caused by a abundant development
of phytoplankton and the large release of
dissolved organic substances in form secretion
and excretion dissolved organic compounds
into the water. The composition of substances
causing the turbidity depends on the structure
of planktonic biocenosis and the quality of the
organic matter supplied by rainfalls and
surface run-off from the catchment area [5, 12].
Through the observations of the changes in the
visibility of the Secchi disk, horizontal
shallow-layer turbidity was registered. This
refers to a large concentration of fine organic
fractions that form a colloid phase with a
strong ability to attenuate and/or scatter the
light. The impact of the suspended matter on
the light penetration was significantly lower.
In the mesotrophic Kociołek Lake, the
water down to the depth of 1.5 m was crystalclear; below this depth, the light was more and
more absorbed by the growing concentrations
of the suspended matter and OAS. The water
colour was very low (<10 mg Pt dm-3) and did
not show any signs of fluctuation (Fig.2).
Because the water bloom did not take place, it
was not possible to study the water
opalescence. From the observations on the site,
it seems that the steep forested slopes of the
catchment area which protect the lake from the
winds and thus hinder the wind-induced
mixing of water, contributed greatly to the
formation of stable light conditions in the lake.
It seems that the long-term stability of the
vertical physical gradients and of the chemical
features of water (of the biogenic compounds,
among others) was the main reason for the
formation of these light conditions.
In the polymictic Wielkowiejskie Lake,
the second researched mesotrophic lake, the
optically active substances which influence the
light absorbency (by 380 nm), and the water
colour determined by humic substances were
the key determinants of the light quality in the
euphotic zone. The above mentioned water
features were characterized by a very low time
changeability, which indicates a stable and
undisturbed alimentation of the substances that
generate them (Fig.2). In the case of midforest lakes, the amount of precipitation has a
significant impact on the abundance of organic
matter (mainly organic carbon of humic acids)
3
In the case of Wielkowiejskie Lake, its entire
shoreline is covered by a broad belt of rush
vegetation, while the bottom is formed by
underwater meadows built by Characeae
phytocoenoses [17], whose high density
effectively blocking the resuspension of
bottom sediments [18].
and biogenic compounds [13]. From the other
site, in the lakes which are largely overgrown
with macrophytes, the inflow of autochtonic
substances produced by organisms as well as
by periphyton [14, 15, 16] is of major
importance. Further, the natural surrounding of
the lake has a significant influence on the
stabilization of the abiotic features of the lake.
30
Water colour (mg Pt/dm-3)
10
Turbidity (NTU)
8
6
4
2
0
20
15
10
5
0
GL
KL
WL
GL
KL
WL
GL
KL
WL
15
Suspended matter (mg/dm-3)
2,5
Optically active substances (m-1)
25
2,0
1,5
1,0
0,5
0,0
12
9
6
3
0
GL
KL
WL
Fig.2 The comparison of physical parameters of water in field of Secchi disk visibility of researched lakes – Góreckie (GL),
Kociołek (KL) and Wielkowiejskie (WL) (central point – mediana, frame – 25%-75%, line – min.-max.)
Consequently, the concentration of the
suspended matter in the water was
significantly lower than in other lakes, despite
its typical polymictic character.
4.
Conclusion
The depth of light penetration into water
and thus the productivity of water ecosystems
is determined by the optical properties of
water and content of mineral and organic
substances. The qualitative composition and
concentration of the components influencing
the access of light as well as the character of
processes affecting the spectrum of light
penetrating the water change among others
with the gradient of the water trophy. The
factors determining of Secchi disk visibility in
three lakes of different trophy and type of
mixis have been studied. Analysis of the
physical features of water in the field of Secchi
disk visibility has permitted identification of
4
characteristic
substances
blocking
the
penetration of light in each of the lakes. In the
eutrophic lake the main factor restricting the
access of light was the turbidity and
opalescence of water related to strong
blooming of the phytoplankton stimulated by
high trophy. In two mesotrophic lakes,
representing different types of mixis, the range
of visibility depended mainly on the
concentration of the suspended matter and
optically active substances, including colour
producing compounds.
Acknowledgement
The research work has been supported by the
Polish Ministry of Science and Education
within the project No N305 022 32/1103.
References
[1] R. G. Zepp, D. J. Erickson, N. D. Paul, and
B. Sulzberger, Interactive effects of solar
UV radiation and climate change on
biogeochemical
cycling,
Photochem.
Photobiol. Sci., vol. 6 (3), pp. 286-300,
2007
[2] B. M. Lafrancois, K. R. Nydick, B. M.
Johnson, and J. S. Baron, Cumulative
effects of nutrients and pH on the plankton
of two mountain lakes, Can. J. Fish. Aquat.
Sci., vol. 61, pp. 1153-1165, 2004.
[3] A. Reinart, A. Herlevi, H. Arst, and L.
Sipelgas, Preliminary optical classification
of lakes and coastal waters in Estonia and
south Finland, J. Sea Res., vol. 49, pp.
357-366, 2003.
[4] J. T. O. Kirk, Estimation of the absorption
and the scattering coefficients of natural
waters by use of underwater irradiance
measurements, Appl. Optic., vol. 33, pp.
3276-3278, 1994.
[5] T. Sobczyński, and T. Joniak, The water
chemistry variability in lake vertical
profile as the effect of biocenosis and
bottom sediments interactions, Ecology
and Technology, vol. XVI (4), pp. 170-176,
2008.
[6] M. M. Tilzer, C. R. Goldman, and E. de
Amezaga, The efficiency of photosynthetic
light
energy
utilization
by
lake
phytoplankton, Verh. Internat. Verein.
Limnol., vol. 19, pp. 800-807, 1975.
[7] T. Joniak, Annual dynamic of light
conditions and vertical gradient of
phytoplankton biomass in eutrophic lake,
in:
Anthropogenic
and
natural
transformations of lakes, vol. III, W.
Marszelewski, Ed., Toruń, Pol. Lim.
Society, pp. 117-121, 2009.
[8] T. Sobczyński, and J. Siepak, Speciation of
heavy metals in bottom sediments of lakes
in the area of Wielkopolska National Park,
Pol. J. Environ. Stud., vol. 10 (6), pp. 463474, 2001.
[9] A. Erm, H. Arst, T. Trei, A. Reinart, and M.
Hussainov,
Optical
and
biological
properties of Lake Ülemiste, a water
reservoir of the city of Tallinn I: Water
transparency and the optically active
substances in the water, Lakes and
Reservoirs, Research and Management, vol.
6 (1), pp. 75-84, 2001.
[10] R. E. Carlson, A trophic state index for
lakes, Limnol. Oceanogr., vol. 22, pp. 361369, 1977.
[11] E. Szeląg-Wasielewska, and J. Fyda,
Pelagic biocoenosis in a stratified
eutrophic lake: vertical variation in the
microbial loop and phytoplankton, Limnol.
Rev., vol. 6, pp. 269-276, 2006.
[12] T. Joniak, N. Kuczyńska-Kippen, and B.
Nagengast,
The
role
of
aquatic
macrophytes
in
microhabitatual
transformation
of
physical-chemical
features
of
small
water
bodies,
Hydrobiologia, vol. 584, pp. 101-109,
2007.
[13] T. Joniak, The dynamics of precipitation
and the abundance of biogenic compounds
and dissolved organic matter in mid-forest
lakes, Ecology and Technology, vol. XVII
(4), pp. 178-181, 2009.
[14] R. G. Wetzel, Death, detritus, and energy
flow in aquatic ecosystems, Freshwat.
Biol., vol. 33, pp. 83-89, 1995.
5
[15] R. Gołdyn, Changes in biological and
physico-chemical parameters of river water
quality as a result of its damming in
preliminary lowland reservoirs, AMU Press,
Poznań, 2000.
[16] T. Joniak, and N. Kuczyńska-Kippen, The
effect of aquatic macrophytes on water
trophy of lowland water bodies in aspect
their surface differentiation, TEKA Kom.
Ochr. Kszt. Środ. Przyr., vol. 5, pp. 47-52,
2008.
[17] N. Kuczyńska-Kippen, and B. Nagengast,
The influence of hydromacrophytes on the
structure of zooplankton communities in
Wielkowiejskie
Lake
(Wielkopolska
National Park), Morena, vol. 9, pp. 7-16,
2002.
[18] W. F. James, E. P. Best, and J. W. Barko,
Sediment resuspension and light attenuation
in Peoria Lake: can macrophytes improve
water quality in this shallow system?,
Hydrobiologia, vol. 515, pp. 193-201, 2004.
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