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Further long-term changes in the submerged macrophyte vegetation of the eutrophic Lake Mikolajskie (North Poland)
Aquatic Botany, 46 ( 1993 ) 341-345
341
0304-3770/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Short Communication Further long-term changes in the submerged macrophyte vegetation of the eutrophic Lake Mikolajskie (North Poland) Andrzej Kowalczewski*, Teresa Ozimek Department of Hydrobiology, ZoologicalInstitute, Universityof Warsaw, Nowy Swiat 67, 00-046 Warsaw, Poland (Accepted 3 June 1993)
Abstract
On the basis of quantitative sampling of submerged vegetation, repeated in Lake Mikolajskie a further 10 years after the last survey, and compared with 1980, 1971 and 1963, continuing changes are reported. There was a further decrease of the depth range and thus of the colonized area. The frequency and percentage contribution of some formerly abundant species diminished, as the submerged vegetation continued to change to a Myriophyllum-Potamogetonassemblage.
Introduction
There are very few accurate data on long-term changes of submerged macrophytes in lakes. Some authors (Dambska, 1976; Schiemer, 1979; Orth and Moore, 1983; Ozimek and Kowalczewski, 1984; Toivonen, 1985) present sound data on this subject but, in general, knowledge on the subject is based on isolated or occasional observations. The general time changes of submerged vegetation are known mainly from the comparison of the flora of lakes at various stages in their evolution. The influence of environmental conditions of eutrophying lakes for the aquatic vegetation was reviewed by De Nie (1987), who showed various reasons for the decreasing biomass of submerged vegetation. The long-term changes in the submerged vegetation in Lake Mikolajskie have already been described, and discussed by the present authors on the basis of 1963, 1971 and 1980 data (Ozimek and Kowalczewski, 1984). Over this period, macrophytes decreased their depth range, biomass and species composition; changing from Chara to Potamogeton domination. Lake Mikolajskie is undergoing further eutrophication, 1% of surface light is found in summer at a depth of about 2.5 m (A. Kowalczewski, *Corresponding author.
342
A. Kowalczewski, T. Ozimek / Aquatic Botany 46 (1993) 341-345
unpublished observation, 1992). Consequently it seemed valuable to trace further changes of submerged vegetation after another 10 years and compare them with the existing data. Studies of long-term changes of aquatic macrophytes seem to be the best way to understand the changes in the lake littoral caused by lake eutrophication. Area and methods The eutrophication of Lake Mikolajskie is progressing. The means of spring and summer data for chlorophyll concentrations raised from below 20/zg 1-1, in 1984-1985 to about 45 in 1990, the Secchi depth stayed at about 1.3 m. The lake production is phosphorus limited. The method of sampling was the same as described previously (Ozimek and Kowalczewski, 1984). For the present study, performed in the first days of August 1990, we decreased the number of transects sampled to 50, evenly distributed along the lake littoral. A total of 130 samples was collected. Results and discussion The frequency of occurrence of submerged macrophytes changed in comparison with earlier years. It was now highest at a depth of 1.5 m, a pattern similar to, but more pronounced than that in 1980 (Fig. 1 ). It did not show the similarly high values for 0.5 m depth observed in 1980. The maximum depth of occurrence decreased by 0.5 m, now reaching only 3.0 m. This furF r e q u e n c y ~o I0 20 30
40
o
I-
4- /"
/I
---'1971 - - 1990
5I
6 Fig. 1. Frequencyvalues for submergedmacrophytesat various depths of Lake Mikolajskiein 1990 as comparedwith 1971 and 1980 data (frequency= percentageof occurrencein the total number of samples).
A. Kowalczewski, T. Ozimek /Aquatic Botany 46 (1993) 341-345
343
ther reduction of the depth range of submerged plants suggests that if no technical means against eutrophication of the lake are applied, macrophytes may become even more restricted. However, it should be noted that the depth of maximum frequency has stayed the same for the last 10 years and has changed only slightly in 20 years. The frequency of particular species also changed in many cases (Table I ). The most striking are changes of frequency values of Characeae (now represented only by Nitellopsis obtusa ), Ceratophyllum demersum and Fontinalis antipyretica, which show a continuing decrease over the whole 20 years. The frequencies of Potamogeton obtusifolius and Lemna trisulca have also decreased over the last 10 years. Three species disappeared completely: Potamogeton gramineus, Utricularia vulgaris and Sagittaria sagittifolia. But there were species which showed a significant rise in their frequencies of occurrence: Myriophyllum spicatum, Potamogeton perfoliatus and Batrachium circinatum. Other species did not change much in numbers. The above changes were associated with alternation in the depth distribution of plant biomass (Fig. 2 ). The biomass maximum now occurred at 1 m depth, within the general maximum depth range for 1980, but decreased Table 1 Frequencies of species and their percentage contribution to the total biomass of submerged macrophytes in the littoral zone of Lake Mikolajskie in 1990, as compared with 1971 and 1980 data (Ozimek and Kowalczewski, 1984) Taxa
Frequencies (%)
Contribution (%)
1971
1980
1990
1971
1980
1990
Characeae ( Nitellopsis obtusa (Desvaux) J. Groves+ Chara) Fontinalis antipyretica L. Ceratophyllum demersum L. Elodea canadensis Michx. Lemna trisulca L. Batrachium circinatum (Sibth.) Fr.
55.3 47.8 40.6 37.3 22.1 18.8
Potamogeton perfoliatus L.
10.8
39.0 39.3 30.7 32.0 41.9 13.5 18.1 2.8 25,6 2.3 3.7 30.7 0.9 1.9 0.5
11.61 2.9 10.7 34.9 3.9 18.4 29.1 38.8 10.0 2.6 12.6 29.1 -
43.5 7.6 23.5 14.9 1.6 1.2 4.1 2.0 0.22
24.8 10.2 5.6 12.5 6.0 1.8 10.0 0.3 3.0 0.1 5.2 19.0 0.1 1.3 0.1
7.0 l 0.5 1.4 12.3 0.1 6,9 20,9 38,2 0,6 0,1 7,9 3.9 -
Myriophyllum spicatum L. P. obtusifolius Men. et Koch P. cornpressus L. P. lucens L. P. pectinatus L. Utricularia vulgaris L. Stratiotes aloides L. Sagittaria sagittifolia L. P. gramineus L. P. crispus L.
8.7 7.72 2.3 2.0 1.3 1.0 0.5 -
0.52
0.5
0.3 0.3 0.1 0.7 0.1 _ -
0.12
0.2
~In 1990 - - only Nitellopsis obtusa.
2p. obtusifolius and P. compressus in 1971 and P. gramineus and P. crispus in 1980 were treated jointly.
344
A. Kowalczewski, T. Ozimek / Aquatic Botany 46 (1993) 341-345
Dry w e i g h ! .
t
.
.
I
.
,
50
I.
11
.1
44, "~ S"
.
.
.
g . m -2 lOO
; I ,
.
.
.
.
15o,
$/ .-
',
,
.
./..--'"
.;
I t
,
- - -1,971 -'-1980
~
--1990
Fig. 2. Dry weight (mean data) distribution with depth for the submerged macrophytes in Lake Mikolajskie in 1990 as compared with 1971 and 1980 data. Table 2 The occurrence of submerged macrophytes in the littoral zone of Lake Mikolajskie in 1990 as compared with 1963, 1971 and 1980 data (Ozimek and Kowalczewski, 1984) Year
Maximum depth (m)
Colonized area (ha)
Dry weight (t ha-1 ) colonized area
1963 1971 1980 1990
6.0 5.5 3.5 3.0
48.0 44.0 30.0 about 28.0
2.1 0.6 0.2 0.4
sharply in both shallow and deeper water. This distinct maximum results from the abundance of M. spicatum and B. circinatum at this depth, these species having characteristically high biomasses per unit area of the littoral zone. The contributions of particular species in the total biomass (Table 1 ) changed similarly to the frequencies of species occurrence. The main difference was that the contribution ofP. pectinatus, which had become abundant in the lake by 1980, was not sustained to 1990. Thus, the dominant contributors to the total biomass of submerged plants were now M. spicatum, P. perfoliatus and E. canadensis, with the latter being a relatively steady, major component of the submerged flora throughout the period 197 l-1990. Summarizing the results now obtained and comparing them with earlier ones (Table 2 ) show that submerged macrophytes of Lake Mikolajskie have undergone progressive changes: their depth ranges have diminished and hence so has the colonized area. Three species, previously present in small quantities, disappeared completely. However, apart from the changes in the im-
A. Kowalczewski, T Ozirnek /Aquatic Botany 46 (1993) 341-345
345
portance of particular species, the total biomass for the colonized area has not changed significantly over the last 20 years. This suggests that in a lake undergoing eutrophication, changes in the species composition of the submerged vegetation can be quite considerable, in our case from a Chara-type through a Potamogeton-type to a Myriophyllum-Potamogeton-type, but that the biomass supported by the area accessible for colonization can remain quite stable. Acknowledgements The authors wish to express their thanks to Wacek Turlaj for his technical assistance with macrophyte sampling. Comments and text improvement by referees are also acknowledged.
References Dambska, I., 1976. Zmiany we florze roslin naczyniowych Jeziora Goslawickiego na przestrzeni 17 lat w zwiazku z uzytkowaniem tego jeziora. (Changes of the vascular plants of Lake Goslawickie related to the utilization of the lake water during 17 years). UAM, Poznan, Ser. Biol., 6: 13-16. De Nie, H.W., 1987. The decrease in aquatic vegetation in Europe and its consequences for fish populations. Occasional Paper No. 19. European Inland Fisheries Advisory Commission, Rome. Orth, R.J. and Moore, H.A., 1983. Chesapeake Bay: An unprecedented decline in submerged aquatic vegetation. Science, 222:51-53. Ozimek, T. and Kowalczewski, A., 1984. Long-term changes of the submerged macrophytes in eutrophic Lake Mikolajskie (North Poland). Aquat. Bot., 19:1-11. Schiemer, F., 1979. Submerged macrophytes in the open lake. Distribution patters, production and long-term changes. In: E.H. L6ffier (Editor), Neusiedlersee: The Limnology of a Shallow Lake in Central Europe. Monogr. Biol., 37: 235-250. Toivonen, H., 1985: Changes in the pleustic macrophyte flora of 54 small Finnish lakes in 30 years. Ann. Bot. Fenn., 22: 37-44.
341
0304-3770/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Short Communication Further long-term changes in the submerged macrophyte vegetation of the eutrophic Lake Mikolajskie (North Poland) Andrzej Kowalczewski*, Teresa Ozimek Department of Hydrobiology, ZoologicalInstitute, Universityof Warsaw, Nowy Swiat 67, 00-046 Warsaw, Poland (Accepted 3 June 1993)
Abstract
On the basis of quantitative sampling of submerged vegetation, repeated in Lake Mikolajskie a further 10 years after the last survey, and compared with 1980, 1971 and 1963, continuing changes are reported. There was a further decrease of the depth range and thus of the colonized area. The frequency and percentage contribution of some formerly abundant species diminished, as the submerged vegetation continued to change to a Myriophyllum-Potamogetonassemblage.
Introduction
There are very few accurate data on long-term changes of submerged macrophytes in lakes. Some authors (Dambska, 1976; Schiemer, 1979; Orth and Moore, 1983; Ozimek and Kowalczewski, 1984; Toivonen, 1985) present sound data on this subject but, in general, knowledge on the subject is based on isolated or occasional observations. The general time changes of submerged vegetation are known mainly from the comparison of the flora of lakes at various stages in their evolution. The influence of environmental conditions of eutrophying lakes for the aquatic vegetation was reviewed by De Nie (1987), who showed various reasons for the decreasing biomass of submerged vegetation. The long-term changes in the submerged vegetation in Lake Mikolajskie have already been described, and discussed by the present authors on the basis of 1963, 1971 and 1980 data (Ozimek and Kowalczewski, 1984). Over this period, macrophytes decreased their depth range, biomass and species composition; changing from Chara to Potamogeton domination. Lake Mikolajskie is undergoing further eutrophication, 1% of surface light is found in summer at a depth of about 2.5 m (A. Kowalczewski, *Corresponding author.
342
A. Kowalczewski, T. Ozimek / Aquatic Botany 46 (1993) 341-345
unpublished observation, 1992). Consequently it seemed valuable to trace further changes of submerged vegetation after another 10 years and compare them with the existing data. Studies of long-term changes of aquatic macrophytes seem to be the best way to understand the changes in the lake littoral caused by lake eutrophication. Area and methods The eutrophication of Lake Mikolajskie is progressing. The means of spring and summer data for chlorophyll concentrations raised from below 20/zg 1-1, in 1984-1985 to about 45 in 1990, the Secchi depth stayed at about 1.3 m. The lake production is phosphorus limited. The method of sampling was the same as described previously (Ozimek and Kowalczewski, 1984). For the present study, performed in the first days of August 1990, we decreased the number of transects sampled to 50, evenly distributed along the lake littoral. A total of 130 samples was collected. Results and discussion The frequency of occurrence of submerged macrophytes changed in comparison with earlier years. It was now highest at a depth of 1.5 m, a pattern similar to, but more pronounced than that in 1980 (Fig. 1 ). It did not show the similarly high values for 0.5 m depth observed in 1980. The maximum depth of occurrence decreased by 0.5 m, now reaching only 3.0 m. This furF r e q u e n c y ~o I0 20 30
40
o
I-
4- /"
/I
---'1971 - - 1990
5I
6 Fig. 1. Frequencyvalues for submergedmacrophytesat various depths of Lake Mikolajskiein 1990 as comparedwith 1971 and 1980 data (frequency= percentageof occurrencein the total number of samples).
A. Kowalczewski, T. Ozimek /Aquatic Botany 46 (1993) 341-345
343
ther reduction of the depth range of submerged plants suggests that if no technical means against eutrophication of the lake are applied, macrophytes may become even more restricted. However, it should be noted that the depth of maximum frequency has stayed the same for the last 10 years and has changed only slightly in 20 years. The frequency of particular species also changed in many cases (Table I ). The most striking are changes of frequency values of Characeae (now represented only by Nitellopsis obtusa ), Ceratophyllum demersum and Fontinalis antipyretica, which show a continuing decrease over the whole 20 years. The frequencies of Potamogeton obtusifolius and Lemna trisulca have also decreased over the last 10 years. Three species disappeared completely: Potamogeton gramineus, Utricularia vulgaris and Sagittaria sagittifolia. But there were species which showed a significant rise in their frequencies of occurrence: Myriophyllum spicatum, Potamogeton perfoliatus and Batrachium circinatum. Other species did not change much in numbers. The above changes were associated with alternation in the depth distribution of plant biomass (Fig. 2 ). The biomass maximum now occurred at 1 m depth, within the general maximum depth range for 1980, but decreased Table 1 Frequencies of species and their percentage contribution to the total biomass of submerged macrophytes in the littoral zone of Lake Mikolajskie in 1990, as compared with 1971 and 1980 data (Ozimek and Kowalczewski, 1984) Taxa
Frequencies (%)
Contribution (%)
1971
1980
1990
1971
1980
1990
Characeae ( Nitellopsis obtusa (Desvaux) J. Groves+ Chara) Fontinalis antipyretica L. Ceratophyllum demersum L. Elodea canadensis Michx. Lemna trisulca L. Batrachium circinatum (Sibth.) Fr.
55.3 47.8 40.6 37.3 22.1 18.8
Potamogeton perfoliatus L.
10.8
39.0 39.3 30.7 32.0 41.9 13.5 18.1 2.8 25,6 2.3 3.7 30.7 0.9 1.9 0.5
11.61 2.9 10.7 34.9 3.9 18.4 29.1 38.8 10.0 2.6 12.6 29.1 -
43.5 7.6 23.5 14.9 1.6 1.2 4.1 2.0 0.22
24.8 10.2 5.6 12.5 6.0 1.8 10.0 0.3 3.0 0.1 5.2 19.0 0.1 1.3 0.1
7.0 l 0.5 1.4 12.3 0.1 6,9 20,9 38,2 0,6 0,1 7,9 3.9 -
Myriophyllum spicatum L. P. obtusifolius Men. et Koch P. cornpressus L. P. lucens L. P. pectinatus L. Utricularia vulgaris L. Stratiotes aloides L. Sagittaria sagittifolia L. P. gramineus L. P. crispus L.
8.7 7.72 2.3 2.0 1.3 1.0 0.5 -
0.52
0.5
0.3 0.3 0.1 0.7 0.1 _ -
0.12
0.2
~In 1990 - - only Nitellopsis obtusa.
2p. obtusifolius and P. compressus in 1971 and P. gramineus and P. crispus in 1980 were treated jointly.
344
A. Kowalczewski, T. Ozimek / Aquatic Botany 46 (1993) 341-345
Dry w e i g h ! .
t
.
.
I
.
,
50
I.
11
.1
44, "~ S"
.
.
.
g . m -2 lOO
; I ,
.
.
.
.
15o,
$/ .-
',
,
.
./..--'"
.;
I t
,
- - -1,971 -'-1980
~
--1990
Fig. 2. Dry weight (mean data) distribution with depth for the submerged macrophytes in Lake Mikolajskie in 1990 as compared with 1971 and 1980 data. Table 2 The occurrence of submerged macrophytes in the littoral zone of Lake Mikolajskie in 1990 as compared with 1963, 1971 and 1980 data (Ozimek and Kowalczewski, 1984) Year
Maximum depth (m)
Colonized area (ha)
Dry weight (t ha-1 ) colonized area
1963 1971 1980 1990
6.0 5.5 3.5 3.0
48.0 44.0 30.0 about 28.0
2.1 0.6 0.2 0.4
sharply in both shallow and deeper water. This distinct maximum results from the abundance of M. spicatum and B. circinatum at this depth, these species having characteristically high biomasses per unit area of the littoral zone. The contributions of particular species in the total biomass (Table 1 ) changed similarly to the frequencies of species occurrence. The main difference was that the contribution ofP. pectinatus, which had become abundant in the lake by 1980, was not sustained to 1990. Thus, the dominant contributors to the total biomass of submerged plants were now M. spicatum, P. perfoliatus and E. canadensis, with the latter being a relatively steady, major component of the submerged flora throughout the period 197 l-1990. Summarizing the results now obtained and comparing them with earlier ones (Table 2 ) show that submerged macrophytes of Lake Mikolajskie have undergone progressive changes: their depth ranges have diminished and hence so has the colonized area. Three species, previously present in small quantities, disappeared completely. However, apart from the changes in the im-
A. Kowalczewski, T Ozirnek /Aquatic Botany 46 (1993) 341-345
345
portance of particular species, the total biomass for the colonized area has not changed significantly over the last 20 years. This suggests that in a lake undergoing eutrophication, changes in the species composition of the submerged vegetation can be quite considerable, in our case from a Chara-type through a Potamogeton-type to a Myriophyllum-Potamogeton-type, but that the biomass supported by the area accessible for colonization can remain quite stable. Acknowledgements The authors wish to express their thanks to Wacek Turlaj for his technical assistance with macrophyte sampling. Comments and text improvement by referees are also acknowledged.
References Dambska, I., 1976. Zmiany we florze roslin naczyniowych Jeziora Goslawickiego na przestrzeni 17 lat w zwiazku z uzytkowaniem tego jeziora. (Changes of the vascular plants of Lake Goslawickie related to the utilization of the lake water during 17 years). UAM, Poznan, Ser. Biol., 6: 13-16. De Nie, H.W., 1987. The decrease in aquatic vegetation in Europe and its consequences for fish populations. Occasional Paper No. 19. European Inland Fisheries Advisory Commission, Rome. Orth, R.J. and Moore, H.A., 1983. Chesapeake Bay: An unprecedented decline in submerged aquatic vegetation. Science, 222:51-53. Ozimek, T. and Kowalczewski, A., 1984. Long-term changes of the submerged macrophytes in eutrophic Lake Mikolajskie (North Poland). Aquat. Bot., 19:1-11. Schiemer, F., 1979. Submerged macrophytes in the open lake. Distribution patters, production and long-term changes. In: E.H. L6ffier (Editor), Neusiedlersee: The Limnology of a Shallow Lake in Central Europe. Monogr. Biol., 37: 235-250. Toivonen, H., 1985: Changes in the pleustic macrophyte flora of 54 small Finnish lakes in 30 years. Ann. Bot. Fenn., 22: 37-44.