On the Flood Forecasting at the Bulgarian Part of
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
Influence Of The Main Tributaries On The Trophic State Of Lake Ohrid Suzana Patceva, Vasa Mitic, Momcula Jordanoski, Elizabeta Veljanoska - Sarafiloska Hydrobiological Institute Ohrid, Republic of Macedonia
Abstract With aim to determine the loading rate of the littoral region of Lake Ohrid caused by the influence of anthropogenic activities in its catchment area, were caried out investigations of the basic physic chemical parameters which are indicators of the water trophic state, spatial and temporal distribution of the phytoplankton community which is the most sensitive indicator of changes in aquatic ecosystems and its constitutional part, the chlorophyll a as biological indicator of the trophic state. Water samples were collected from the littoral region in front of the inflows of the following tributaries: River Velgoska, River Koselska, Sateska and Cerava. The results from the investigated parameters indicate that, the largest negative influence on the littoral region and in the same time the highest trophic state provokes the River Velgoska, and afterwards respectfully follows Cerava and Sateska, thus the lake water in the areas of their inflow has a mesotrophic state. Key-words: Lake Ohrid, littoral, phytoplankton, chlorophyll a, trophic state, nutrients
Introduction With the recent development of the human activities in the watershed of oligotrophic Lake Ohrid, which is the oldest lake in Europe, part of them have also negative impact on this unique lake's ecosystem. Especially large negative influence on the littoral zone of Lake Ohrid there are bigger tributaries. The littoral zone of a lake is affected both by the catchment area and by the water of the lake itself (Baffico 2000). The catchment area of Lake Ohrid counts over 40 rivers. However, most of them dry out during summer and are insignificant with respect to their discharge rate. Sateska, Koselska, Cerava and Velgoska are the only rivers with significant discharge rates flowing into the lake in the Macedonian part of Lake Ohrid. River Velgoska flows through the industrial Ohrid zone. Apart from the industrial wastewater, it also incorporates the communal sewage from the objects that are not included in the refining system. Although the River Velgoska has small quantities of flowing water, the inflow area and the quantities of matter that flow with it, have a considerable impact on the lake littoral loading. River Koselska flows through a predominantly rural area, which drainage waters through the river inflow into the lake carrying along the contaminants from the fertilizers used in the agricultural areas. Also, this river receives some communal and industrial wastewater. River Sateska, which was diverted into Lake Ohrid in 1962, flows through agricultural and urban areas. It is loaded with drainage water and communal wastewater and also this river carries a high load of alluvial sediment, which is deposited in the littoral zone of Lake Ohrid at the mouth of the river. River Cerava flows through two countries, Albania and Macedonia. It flows through mining regions (Albania) and through distinctly agricultural regions (Macedonia). The subject of the investigation was the littoral region of Lake Ohrid in front of the inflows of the main tributaries: River Koselska, Sateska, Cerava and River Velgoska. The purpose of this study is to describe influence of main tributaries of Lake Ohrid on trophic state of littoral region in front of their inflows.
Lakes
1
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
Material and methods Water samples were collected from littoral region of Lake Ohrid in front of the inflows of the main tributaries: River Koselska, Sateska, Cerava and River Velgoska, during the period from February 1999 to February 2000, with a monthly frequency of sampling The dissolved oxygen concentration was determined by the Winkler method. In the course of the investigation the ammonia, nitrates, nitrites and total nitrogen have been determined by Kjedahl, among the nitrogen compounds. The procedure for determining ammonia is performed by binding of the ammonia with hypochlorite in monochloramine, which in reaction with phenol gives p-aminophenol, which in reaction with natrium nitroprusside forms blue-coloured compounds. The values are read using Perkin-Elmer UV-VIS spectrophotometer, wavelength 640 nm. Nitrates are quantitatively reduced from the water to nitrites by a cadmium-copper couple (Strickland & Parsons 1968), and as nitrites bind with sulphanilic acid and N- (1-naphthyl ethylene diamine dichloride (III) in the shape of a very intensive diamine compound. The results are read on Specord S10 UV-VIS spectrophotometer, wavelength 530 nm. Total phosphorus - by acid digestion of persulphate all forms of phosphates are altered to orthophosphate, which with antimony-molybdate and antimonyl potassium tartarate form the complex antimony-phosphate-molybdate, which is reduced by ascorbic acid thus forming a blue molybdene complex whose intensity is in function of the quantity of total phosphorus. The results can be read on Specord S-10 UV-VIS spectrophotometer, wavelength 885 nm. Phytoplankton identification and counts were carried out in sedimentation chamber under an inverted microscope (Utermöhl 1958). The determination of chlorophyll a was carried out spectrophotometrically using Perkin Elmer UV VIS and calculated according to Strickland & Parsons (1968).
Results and discussion Disolved oxygen concentration is a very important indicator of a water body's ability to support aquatic life. During the study period, littoral zone was supplied with enough oxygen content. Values varied between 7.96 and 15.48 mg·l-1. In all investigated areas the highest values were recorded in February (Fig. 1). 1 5 .5 15 1 4 .5
-1
Disolved oxygen (mg l )
14 1 3 .5 13 1 2 .5 12 1 1 .5 11 1 0 .5 10 9 .5 9 8 .5 8 F '9 9
M
A V e lg o s k a
M
J
J K o s e ls k a
A
S
O S a te s k a
N
D
J
F '0 0
C e ra v a
Figure 1. Seasonal variation in dissolved oxygen concentration in the investigated areas Of the various nutrients known to limit algal production, phosphorus and nitrogen are most often implicated in fresh waters (Elser et al. 1990). Thus, the phosphorus and nitrogen concentrations will be used as indicators of eutrophication. Lakes
2
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
The phosphorus input into the lake stems partly from human activities (e.g. wastewater production, inadequate fertilizing and cultivation of land), and partly from natural sources. During the investigated period total phosphorus concentration in the littoral of River Velgoska varied between 5.3 and 68.82 µg•l-1, in the littoral of River Koselska between 3.07 and 26.66 µg•l-1, in the littoral of River Sateska between 4.03 and 79.05 µg•l-1 and in the littoral of River Cerava varied beetween 4.22 and 79.67 µg•l-1 (Fig. 2).
-1
Total phosphorus (g l )
0 .0 9 0 .0 8 0 .0 7 0 .0 6 0 .0 5 0 .0 4 0 .0 3 0 .0 2 0 .0 1 0 F'9 9
M
A
M
V e lg os k a
J
J
A
S
K o s e ls k a
O
N
D
S a tes k a
J
F'0 0
C e rava
Figure 2. Seasonal variation in total phosphorus concentration in the investigated areas In the littoral area of River Velgoska the highest phosphorus loading was registered, with annual average total phosphorus concentration of 31.57 µg•l-1, which have negative influence on water trophic state on this part of littoral zone and also in unity on Lake Ohrid. Then follow areas of Cerava (21.26 µg•l-1), Sateska (19.95 µg•l-1) and River Koselska (12.52 µg•l-1). The highest annual average total nitrogen concentration of 0.99 mg•l-1 in the littoral of River Cerava was observed and follows area of River Velgoska (0.80 mg•l-1). In the littoral of River Koselska and River Cerava was observed values of 0.63 and 0.62 mg•l-1, respectively. The highest total nitrogen concentration in the littoral of River Velgoska with value of 2.14 mg•l-1 was recorded in May, in River Koselska maximum total nitrogen concentration of 2.52 mg•l-1 was recorded in July and in River Sateska and River Cerava with value of 1.56 mg•l-1 and 2.15 mg•l-1 were recorded in February 1999 (Fig. 3). 3
-1
Total nitrogen (mg l )
2.5 2 1.5 1 0.5 0 F '9 9
M
V elgo ska
A
M
J
K o selska
J
A
S
O
S ateska
N
D
J
F '0 0
C erava
Figure 3. Seasonal variation in total nitrogen concentration in the investigated areas In addition to the level of nutrients in watershed waters, the N:P ratios are important factors enhancing eutrophication (Burt et al. 1993). Control of the nitrogen and phosphorus exported from the watersheds, as well as manipulation of the N:P ratio, may control algal growth (Rhee 1978, Kajak 1979, Burt et al. 1993). Lakes
3
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
N is considered to be limiting at ratios below 5 to 10 by weight while P is expected to be limiting at ratios above 10 to 17 (Schindler 1977, Chiandani and Vighi 1974, Tones 1987). Relative to the phosphorus concentrations, the nitrogen/phosphorus ratio, on average, decreases from more than 100 on the oligotrophic side to less than 10 on the eutrophic side. This can be interpreted as a tendency for lakes to shift from phosphorus dependency to nitrogen dependency with increasing trophy (OECD 1982). The TN:TP ratios in all investigated areas were above 10 (Tab. 1) which suggests that phosphorus is the nutrient which limits algal growth in the littoral zone of Lake Ohrid. Table 1. Seasonal variation in N:P ratio in the investigated areas F'99
M
A
M
J
J
A
S
O
N
D
J
F'00
Velgoska
10,24
16,07
51,74
31,02
19,1
30,33
13,74
35,61
28,76
102,62
38,9
37,2
18,88
Koselska
122,12
40,19
99,4
13,82
19,94
127,12
35,96
20,58
70,58
140,76
18,45
56,68
29,82
Sateska
68,76
60,22
138,21
65,63
53,23
33,79
43,39
68,89
29,77
382,49
40,86
15,13
16,89
Cerava
30,39
124,29 122,86
12,28
105,16 189,68
30,26
70,32
38,21
51,69
71,64
201,81
19,91
The highest mean N:P was found in area of River Cerava (82.19), and the lowest in River Velgoska (33.40). The mean N:P ratio in area of River Koselska and River Cerava was 61.19 and 78.25, respectively (Tab. 2). Table 2. Mean TN:TP ratio in the investigated areas River Velgoska-lit. River Koselska-lit. River Sateska-lit. River Cerava-lit.
33.40 61.19 78.25 82.19
Nutrient availability plays an important role in controlling structure and biomass of phytoplanktonic communities and species seasonal succession. Several studies have shown that there is no multiple nutrient limitation for phytoplankton growth. Algal growth is regulated by the single nutrient in shortest supply (Droop 1973, Rhee 1974) according to Liebig's law of the minimum. Phytoplankton is the most sensitive indicator of changes in the aquatic environment and a central feature of the trophic classification system. The other features of the system reflect the consequence of the degree of algal growth. Anthropogenic influences can alter the phytoplankton associations and the pattern of species succesion. Identified taxa in the investigated areas in the littoral zone of Lake Ohrid belong to the following groups of algae: Cyanophyta, Bacillariophyta, Chlorophyta, Chrysophyta, Pyrrophyta and Euglenophyta. In qualitative sense Bacillariophyta is the most represent group, followed by Chlorophyta. The percentage composition of the different algal group varied over time. During the winter and early spring when the temperature decreased (from December to the end of May) diatoms were dominant. In area of River Velgoska the highest species diversity and also the highest phytoplankton density was evidenced. The lowest phytoplankton density in area of River Koselska was evidenced. During the investigated period, in all investigated areas, the highest phytoplankton density was observed in June, due to increase of nutrient content in previous month. In this month green alga Pandorina morum which is exponent of mesotrophic water was the dominant species in the phytoplankton community. In areas of River Koselska and River Cerava Dinobryon bavaricum which is exponent of oligotrophic water was the second frequent species (Fig. 5, 7).
Lakes
4
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
450000 400000 350000
ind. l
-1
300000 250000 200000 150000 100000 50000 0 F'99
M
A
M
J
J
A
S
O
D
J
F'00
Chlorophyta Euglenophyta
Bacillariophyta Pyrrophyta
Cyanophyta Chrysophyta
N
Figure 4. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Velgoska 300000 250000
ind. l
-1
200000 150000 100000 50000 0 F'99
M
A
M
J
J
Cyanophyta Chrysophyta
A
S
O
N
Bacillariophyta Pyrrophyta
D
J
F'00
Chlorophyta Euglenophyta
ind.l
-1
Figure 5. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Koselska 5 0 00 00 4 5 00 00 4 0 00 00 3 5 00 00 3 0 00 00 2 5 00 00 2 0 00 00 1 5 00 00 1 0 00 00 5 00 00 0 F '99
M
C ya n o p h yta
A
M
J
B a c illa rio p h yta
J
A
S
C h lo ro p h yta
O
N
C h rys o p h yta
D
J
F '0 0
P yrro p h yta
Figure 6. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Sateska Lakes
5
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
1 6000 0 1 4000 0
ind.l
-1
1 2000 0 1 0000 0 8000 0 6000 0 4000 0 2000 0 0 F '99
M
A
M
J
J
C ya n o p h yta C h ryso p h yta
A
S
O
N
B a c illa rio p h yta P yrro p h yta
D
J
F '00
C h lo ro p h yta E u g le n o p h yta
-1
Chlorophyll a (g l )
Figure 7. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Cerava 20 18 16 14 12 10 8 6 4 2 0 F '9 9
M
A
V e lg o sk a
M
J
J
K o s e ls ka
A
S
O
S a te sk a
N
D
J
F '0 0
C e ra va
Figure 8. Seasonal variation in chlorophyll a content in the investigated areas During the rest of the year, relatively low nutrient concentration, restricts the development of green algae and representatives of Cyanophyta. Secondary peak was observed in March in the littoral of River Velgoska when Diatoma elongatum was the most frequent species, contributing 94% from total phytoplankton density (Fig. 4). At that time, in this area the lowest N:P ratio (10.24) was observed suggesting a balance between these nutrients (Tab. 1). During the summer period when the temperature increased total phytoplankton density began to decrease and the lowest phytoplankton density was evidenced in August. At that time phytoplankton community became dominated by Pyrrophyta. Peridinium cunningtonii was the most frequent species, followed by Ceratium hirundinella. Seasonal appearance of dinoflagelates is in accordance with its ecological features: preference for higher temperature and more intensive lighting (Heaney & Talling 1980). The population of the Chrysophyta group was dominant in October and main representative of this algal group was Dinobryon bavaricum. Dinobrion divergens was less represented species. Chlorophyll a is a photosynthetic pigment that serves as a measurable parameter for all phytoplankton production (Raschke 1993). This primary photosynthetic pigment in all algae is regarded as another indicator of the water trophic state. During the investigated period the chlorophyll a content in the littoral of River Velgoska ranged between 2.09 µg•l-1 (October) and 18.91 µg•l-1 (June), in the littoral of River Koselska ranged between 0.58 µg•l-1 (April) and 6.74 µg•l-1 (June), in Sateska - littoral between 1.27 µg•l-1 (April) and 16.29 µg•l-1 (June), and in Cerava - littoral between 1.79 µg•l-1 (November) and 5.25 µg•l-1 (July). In all investigated areas, except for littoral of River Cerava the highest chlorophyll a content was observed in June, when the highest phytoplankton density was recorded. Lakes
6
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
The highest annual average chlorophyll a content of 5.6 µg•l-1 was recorded in the littoral of River Velgoska, followed by littoral of River Sateska (3.65µg•l-1) and River Cerava (3.15 µg•l-1). In the littoral of River Koselska the lowest annual average chlorophyll a content of 2.43 µg•l-1 was recorded. According to chlorophyll a content as biological indicator of the water trophic state, litorall areas of River Velgoska, River Sateska and River Cerava are in mesotrophic state, while littoral of River Koselska is in oligotrophic state. Trophic classification of investigated regions basis of the OECD (1982) scheme, using mean total phosphorus, mean and maximum chlorophyll a values suggests that these should be classified as follows: littoral of River Velgoska, Sateska and Cerava mesotrophic and littoral of River Koselska oligotrophic/mesotrophic (Tab. 3). Table 3. A summary of the data on total phosphorus, total nitrogen, chlorophyll a for the investigated areas, used for determination of their trophic states Total phosphorus Locality (µg/l) Mean River Velgoska-lit. 31,57 River Koselska-lit. 12,52 Sateska-lit. 13,95 Cerava-lit. 21,26
Total nitrogen (mg/l) Mean 0.80 0.63 0.62 0.99
Chlorophyll a Chlorophyll a (µg/l) (µg/l) Mean 5,60 2,43 3,65 3,15
Max 18,91 6,74 16,29 5,23
Trophic category Mesotrophic Oligotrophic/mesotrophic Mesotrophic Mesotrophic
Summary In last several decades oligotrophic Lake Ohrid, is not exempt from general tendency of strength anthropogenic influence. Our data suggest that littoral regions of Lake Ohrid near the main tributaries are increasingly subject to a variety of anthropogenic impacts. The results from all of the investigated parameters indicate that, the largest negative influence on the littoral zone and in the same time the highest trophic state provokes the River Velgoska, as consequence of the insertion of large amount of industrial and communal waste waters in this littoral region with water from River Velgoska, and afterwards respectfully follows Cerava and Sateska, thus the lake water in the areas of their inflow has a mesotrophic state. From all of the investigated areas water of the littoral region of River Koselska had the best quality. In order to obstruct further negative influence of these tributaries on the trophic state of Lake Ohrid, it is necessary completely inclusion of waste waters in the sewerage system, respectively discharge outside of the watershed of Lake Ohrid. The results of this study indicated that in Lake Ohrid exists phosphorus limitation in terms of primary production, which indicates the necessity of reduction on phosphorus load in the lake. Reference Baffico, D. G., (2000) Periphyton community of Nahuel Huapi lake (Patagonia, Argentina) related to environmental factors. - Verh. Internat. Verein. Limnol. 27: 211-215. Burt, T. P., Heathwaite, A. I. & Trudgill, L. T., (1993) Nitrate (Processes, Patterns and Management). - John Wiley & Sons, Chichester. 444 pp. Chiandani, G. and M. Vighi (1974) The N:P ratio and tests with Selenastrum to predict eutrophication in lakes. Water Res. 8: 1063-1069. Droop, M. R., (1973) Some thoughts on nutrient limitation in algae. - J. Phycol. 9:264-272. Elser, J. J., Marzolf, E. R. & Goldman, C. R. (1990) Phosphorus and nitrogen limitation of phytoplankton growth in freshwaters of North America: a review and critique of experimental enrichment. - Can. J. Fish. Aquat. Sci. 47: 1468-1477. Heaney, S. I., Talling, J. F. (1980) Ceratium hirundinella - ecology of a complex, mobile, and successful plant. Ann. Rep. Freshwater biol. Ass. 48: 27-40. Lakes
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Ohrid, FY Republic of Macedonia, 25-29 May 2004
Kajak, Z., (1979) Eutrofikacja jezior (Eutrophication of lakes). - PWN, Warsaw, 233pp. OECD (1982) Eutrophication of Waters. Monitoring, Assessment, and Control. Organization for Economic C0-Operation and Development, Paris. 156p. Raschke, R. (1993) Guidelines for assessing and predicting eutrophication status of small southeastern piedmont impoundments. EPA-Region IV. Environmental Services Division, Ecological Support Branch. Athens, GA. Rhee, G. Y., (1974) Phosphate uptake under nitrate limitation by Scenedesmus sp. and its ecological implications. J. Phycol. 10: 470-475. Rhee, G. Y., (1978) Effects of N:P atomic ratios and nitrate limitation on algal growth, cell composition, and nitrate uptake. - Limnol. Oceanog. 23(1):10-25. Schindler, D. W., (1977) Evolution of phosphorus limitation in lake. - Science 195: 260-262. Strickland, H.D.J. and T.R. Parsons, (1968) A Practical handbook of Seawater Analysis. Bull.Fish.Res.Bd.Canada, 167: 311 pp. Tones, P. I. (1987) Evaluation of the effects of nutrients on the quality of flowing waters. Environment Canada. Conservation and Protection, Water Quality Branch. E-901-11-E-87. 76 pp. Utermöhl, H., (1958) Zur Vervollkommung der quantitativen Phytoplankton methodik. Mitt. Int. Verein. Limnol. 9, 1-38.
Lakes
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Ohrid, FY Republic of Macedonia, 25-29 May 2004
Influence Of The Main Tributaries On The Trophic State Of Lake Ohrid Suzana Patceva, Vasa Mitic, Momcula Jordanoski, Elizabeta Veljanoska - Sarafiloska Hydrobiological Institute Ohrid, Republic of Macedonia
Abstract With aim to determine the loading rate of the littoral region of Lake Ohrid caused by the influence of anthropogenic activities in its catchment area, were caried out investigations of the basic physic chemical parameters which are indicators of the water trophic state, spatial and temporal distribution of the phytoplankton community which is the most sensitive indicator of changes in aquatic ecosystems and its constitutional part, the chlorophyll a as biological indicator of the trophic state. Water samples were collected from the littoral region in front of the inflows of the following tributaries: River Velgoska, River Koselska, Sateska and Cerava. The results from the investigated parameters indicate that, the largest negative influence on the littoral region and in the same time the highest trophic state provokes the River Velgoska, and afterwards respectfully follows Cerava and Sateska, thus the lake water in the areas of their inflow has a mesotrophic state. Key-words: Lake Ohrid, littoral, phytoplankton, chlorophyll a, trophic state, nutrients
Introduction With the recent development of the human activities in the watershed of oligotrophic Lake Ohrid, which is the oldest lake in Europe, part of them have also negative impact on this unique lake's ecosystem. Especially large negative influence on the littoral zone of Lake Ohrid there are bigger tributaries. The littoral zone of a lake is affected both by the catchment area and by the water of the lake itself (Baffico 2000). The catchment area of Lake Ohrid counts over 40 rivers. However, most of them dry out during summer and are insignificant with respect to their discharge rate. Sateska, Koselska, Cerava and Velgoska are the only rivers with significant discharge rates flowing into the lake in the Macedonian part of Lake Ohrid. River Velgoska flows through the industrial Ohrid zone. Apart from the industrial wastewater, it also incorporates the communal sewage from the objects that are not included in the refining system. Although the River Velgoska has small quantities of flowing water, the inflow area and the quantities of matter that flow with it, have a considerable impact on the lake littoral loading. River Koselska flows through a predominantly rural area, which drainage waters through the river inflow into the lake carrying along the contaminants from the fertilizers used in the agricultural areas. Also, this river receives some communal and industrial wastewater. River Sateska, which was diverted into Lake Ohrid in 1962, flows through agricultural and urban areas. It is loaded with drainage water and communal wastewater and also this river carries a high load of alluvial sediment, which is deposited in the littoral zone of Lake Ohrid at the mouth of the river. River Cerava flows through two countries, Albania and Macedonia. It flows through mining regions (Albania) and through distinctly agricultural regions (Macedonia). The subject of the investigation was the littoral region of Lake Ohrid in front of the inflows of the main tributaries: River Koselska, Sateska, Cerava and River Velgoska. The purpose of this study is to describe influence of main tributaries of Lake Ohrid on trophic state of littoral region in front of their inflows.
Lakes
1
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
Material and methods Water samples were collected from littoral region of Lake Ohrid in front of the inflows of the main tributaries: River Koselska, Sateska, Cerava and River Velgoska, during the period from February 1999 to February 2000, with a monthly frequency of sampling The dissolved oxygen concentration was determined by the Winkler method. In the course of the investigation the ammonia, nitrates, nitrites and total nitrogen have been determined by Kjedahl, among the nitrogen compounds. The procedure for determining ammonia is performed by binding of the ammonia with hypochlorite in monochloramine, which in reaction with phenol gives p-aminophenol, which in reaction with natrium nitroprusside forms blue-coloured compounds. The values are read using Perkin-Elmer UV-VIS spectrophotometer, wavelength 640 nm. Nitrates are quantitatively reduced from the water to nitrites by a cadmium-copper couple (Strickland & Parsons 1968), and as nitrites bind with sulphanilic acid and N- (1-naphthyl ethylene diamine dichloride (III) in the shape of a very intensive diamine compound. The results are read on Specord S10 UV-VIS spectrophotometer, wavelength 530 nm. Total phosphorus - by acid digestion of persulphate all forms of phosphates are altered to orthophosphate, which with antimony-molybdate and antimonyl potassium tartarate form the complex antimony-phosphate-molybdate, which is reduced by ascorbic acid thus forming a blue molybdene complex whose intensity is in function of the quantity of total phosphorus. The results can be read on Specord S-10 UV-VIS spectrophotometer, wavelength 885 nm. Phytoplankton identification and counts were carried out in sedimentation chamber under an inverted microscope (Utermöhl 1958). The determination of chlorophyll a was carried out spectrophotometrically using Perkin Elmer UV VIS and calculated according to Strickland & Parsons (1968).
Results and discussion Disolved oxygen concentration is a very important indicator of a water body's ability to support aquatic life. During the study period, littoral zone was supplied with enough oxygen content. Values varied between 7.96 and 15.48 mg·l-1. In all investigated areas the highest values were recorded in February (Fig. 1). 1 5 .5 15 1 4 .5
-1
Disolved oxygen (mg l )
14 1 3 .5 13 1 2 .5 12 1 1 .5 11 1 0 .5 10 9 .5 9 8 .5 8 F '9 9
M
A V e lg o s k a
M
J
J K o s e ls k a
A
S
O S a te s k a
N
D
J
F '0 0
C e ra v a
Figure 1. Seasonal variation in dissolved oxygen concentration in the investigated areas Of the various nutrients known to limit algal production, phosphorus and nitrogen are most often implicated in fresh waters (Elser et al. 1990). Thus, the phosphorus and nitrogen concentrations will be used as indicators of eutrophication. Lakes
2
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
The phosphorus input into the lake stems partly from human activities (e.g. wastewater production, inadequate fertilizing and cultivation of land), and partly from natural sources. During the investigated period total phosphorus concentration in the littoral of River Velgoska varied between 5.3 and 68.82 µg•l-1, in the littoral of River Koselska between 3.07 and 26.66 µg•l-1, in the littoral of River Sateska between 4.03 and 79.05 µg•l-1 and in the littoral of River Cerava varied beetween 4.22 and 79.67 µg•l-1 (Fig. 2).
-1
Total phosphorus (g l )
0 .0 9 0 .0 8 0 .0 7 0 .0 6 0 .0 5 0 .0 4 0 .0 3 0 .0 2 0 .0 1 0 F'9 9
M
A
M
V e lg os k a
J
J
A
S
K o s e ls k a
O
N
D
S a tes k a
J
F'0 0
C e rava
Figure 2. Seasonal variation in total phosphorus concentration in the investigated areas In the littoral area of River Velgoska the highest phosphorus loading was registered, with annual average total phosphorus concentration of 31.57 µg•l-1, which have negative influence on water trophic state on this part of littoral zone and also in unity on Lake Ohrid. Then follow areas of Cerava (21.26 µg•l-1), Sateska (19.95 µg•l-1) and River Koselska (12.52 µg•l-1). The highest annual average total nitrogen concentration of 0.99 mg•l-1 in the littoral of River Cerava was observed and follows area of River Velgoska (0.80 mg•l-1). In the littoral of River Koselska and River Cerava was observed values of 0.63 and 0.62 mg•l-1, respectively. The highest total nitrogen concentration in the littoral of River Velgoska with value of 2.14 mg•l-1 was recorded in May, in River Koselska maximum total nitrogen concentration of 2.52 mg•l-1 was recorded in July and in River Sateska and River Cerava with value of 1.56 mg•l-1 and 2.15 mg•l-1 were recorded in February 1999 (Fig. 3). 3
-1
Total nitrogen (mg l )
2.5 2 1.5 1 0.5 0 F '9 9
M
V elgo ska
A
M
J
K o selska
J
A
S
O
S ateska
N
D
J
F '0 0
C erava
Figure 3. Seasonal variation in total nitrogen concentration in the investigated areas In addition to the level of nutrients in watershed waters, the N:P ratios are important factors enhancing eutrophication (Burt et al. 1993). Control of the nitrogen and phosphorus exported from the watersheds, as well as manipulation of the N:P ratio, may control algal growth (Rhee 1978, Kajak 1979, Burt et al. 1993). Lakes
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BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
N is considered to be limiting at ratios below 5 to 10 by weight while P is expected to be limiting at ratios above 10 to 17 (Schindler 1977, Chiandani and Vighi 1974, Tones 1987). Relative to the phosphorus concentrations, the nitrogen/phosphorus ratio, on average, decreases from more than 100 on the oligotrophic side to less than 10 on the eutrophic side. This can be interpreted as a tendency for lakes to shift from phosphorus dependency to nitrogen dependency with increasing trophy (OECD 1982). The TN:TP ratios in all investigated areas were above 10 (Tab. 1) which suggests that phosphorus is the nutrient which limits algal growth in the littoral zone of Lake Ohrid. Table 1. Seasonal variation in N:P ratio in the investigated areas F'99
M
A
M
J
J
A
S
O
N
D
J
F'00
Velgoska
10,24
16,07
51,74
31,02
19,1
30,33
13,74
35,61
28,76
102,62
38,9
37,2
18,88
Koselska
122,12
40,19
99,4
13,82
19,94
127,12
35,96
20,58
70,58
140,76
18,45
56,68
29,82
Sateska
68,76
60,22
138,21
65,63
53,23
33,79
43,39
68,89
29,77
382,49
40,86
15,13
16,89
Cerava
30,39
124,29 122,86
12,28
105,16 189,68
30,26
70,32
38,21
51,69
71,64
201,81
19,91
The highest mean N:P was found in area of River Cerava (82.19), and the lowest in River Velgoska (33.40). The mean N:P ratio in area of River Koselska and River Cerava was 61.19 and 78.25, respectively (Tab. 2). Table 2. Mean TN:TP ratio in the investigated areas River Velgoska-lit. River Koselska-lit. River Sateska-lit. River Cerava-lit.
33.40 61.19 78.25 82.19
Nutrient availability plays an important role in controlling structure and biomass of phytoplanktonic communities and species seasonal succession. Several studies have shown that there is no multiple nutrient limitation for phytoplankton growth. Algal growth is regulated by the single nutrient in shortest supply (Droop 1973, Rhee 1974) according to Liebig's law of the minimum. Phytoplankton is the most sensitive indicator of changes in the aquatic environment and a central feature of the trophic classification system. The other features of the system reflect the consequence of the degree of algal growth. Anthropogenic influences can alter the phytoplankton associations and the pattern of species succesion. Identified taxa in the investigated areas in the littoral zone of Lake Ohrid belong to the following groups of algae: Cyanophyta, Bacillariophyta, Chlorophyta, Chrysophyta, Pyrrophyta and Euglenophyta. In qualitative sense Bacillariophyta is the most represent group, followed by Chlorophyta. The percentage composition of the different algal group varied over time. During the winter and early spring when the temperature decreased (from December to the end of May) diatoms were dominant. In area of River Velgoska the highest species diversity and also the highest phytoplankton density was evidenced. The lowest phytoplankton density in area of River Koselska was evidenced. During the investigated period, in all investigated areas, the highest phytoplankton density was observed in June, due to increase of nutrient content in previous month. In this month green alga Pandorina morum which is exponent of mesotrophic water was the dominant species in the phytoplankton community. In areas of River Koselska and River Cerava Dinobryon bavaricum which is exponent of oligotrophic water was the second frequent species (Fig. 5, 7).
Lakes
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BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
450000 400000 350000
ind. l
-1
300000 250000 200000 150000 100000 50000 0 F'99
M
A
M
J
J
A
S
O
D
J
F'00
Chlorophyta Euglenophyta
Bacillariophyta Pyrrophyta
Cyanophyta Chrysophyta
N
Figure 4. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Velgoska 300000 250000
ind. l
-1
200000 150000 100000 50000 0 F'99
M
A
M
J
J
Cyanophyta Chrysophyta
A
S
O
N
Bacillariophyta Pyrrophyta
D
J
F'00
Chlorophyta Euglenophyta
ind.l
-1
Figure 5. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Koselska 5 0 00 00 4 5 00 00 4 0 00 00 3 5 00 00 3 0 00 00 2 5 00 00 2 0 00 00 1 5 00 00 1 0 00 00 5 00 00 0 F '99
M
C ya n o p h yta
A
M
J
B a c illa rio p h yta
J
A
S
C h lo ro p h yta
O
N
C h rys o p h yta
D
J
F '0 0
P yrro p h yta
Figure 6. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Sateska Lakes
5
BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
1 6000 0 1 4000 0
ind.l
-1
1 2000 0 1 0000 0 8000 0 6000 0 4000 0 2000 0 0 F '99
M
A
M
J
J
C ya n o p h yta C h ryso p h yta
A
S
O
N
B a c illa rio p h yta P yrro p h yta
D
J
F '00
C h lo ro p h yta E u g le n o p h yta
-1
Chlorophyll a (g l )
Figure 7. Participation of different groups of algae in the total phytoplankton density of the littoral region of Lake Ohrid in front of the inflow of River Cerava 20 18 16 14 12 10 8 6 4 2 0 F '9 9
M
A
V e lg o sk a
M
J
J
K o s e ls ka
A
S
O
S a te sk a
N
D
J
F '0 0
C e ra va
Figure 8. Seasonal variation in chlorophyll a content in the investigated areas During the rest of the year, relatively low nutrient concentration, restricts the development of green algae and representatives of Cyanophyta. Secondary peak was observed in March in the littoral of River Velgoska when Diatoma elongatum was the most frequent species, contributing 94% from total phytoplankton density (Fig. 4). At that time, in this area the lowest N:P ratio (10.24) was observed suggesting a balance between these nutrients (Tab. 1). During the summer period when the temperature increased total phytoplankton density began to decrease and the lowest phytoplankton density was evidenced in August. At that time phytoplankton community became dominated by Pyrrophyta. Peridinium cunningtonii was the most frequent species, followed by Ceratium hirundinella. Seasonal appearance of dinoflagelates is in accordance with its ecological features: preference for higher temperature and more intensive lighting (Heaney & Talling 1980). The population of the Chrysophyta group was dominant in October and main representative of this algal group was Dinobryon bavaricum. Dinobrion divergens was less represented species. Chlorophyll a is a photosynthetic pigment that serves as a measurable parameter for all phytoplankton production (Raschke 1993). This primary photosynthetic pigment in all algae is regarded as another indicator of the water trophic state. During the investigated period the chlorophyll a content in the littoral of River Velgoska ranged between 2.09 µg•l-1 (October) and 18.91 µg•l-1 (June), in the littoral of River Koselska ranged between 0.58 µg•l-1 (April) and 6.74 µg•l-1 (June), in Sateska - littoral between 1.27 µg•l-1 (April) and 16.29 µg•l-1 (June), and in Cerava - littoral between 1.79 µg•l-1 (November) and 5.25 µg•l-1 (July). In all investigated areas, except for littoral of River Cerava the highest chlorophyll a content was observed in June, when the highest phytoplankton density was recorded. Lakes
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BALWOIS 2004
Ohrid, FY Republic of Macedonia, 25-29 May 2004
The highest annual average chlorophyll a content of 5.6 µg•l-1 was recorded in the littoral of River Velgoska, followed by littoral of River Sateska (3.65µg•l-1) and River Cerava (3.15 µg•l-1). In the littoral of River Koselska the lowest annual average chlorophyll a content of 2.43 µg•l-1 was recorded. According to chlorophyll a content as biological indicator of the water trophic state, litorall areas of River Velgoska, River Sateska and River Cerava are in mesotrophic state, while littoral of River Koselska is in oligotrophic state. Trophic classification of investigated regions basis of the OECD (1982) scheme, using mean total phosphorus, mean and maximum chlorophyll a values suggests that these should be classified as follows: littoral of River Velgoska, Sateska and Cerava mesotrophic and littoral of River Koselska oligotrophic/mesotrophic (Tab. 3). Table 3. A summary of the data on total phosphorus, total nitrogen, chlorophyll a for the investigated areas, used for determination of their trophic states Total phosphorus Locality (µg/l) Mean River Velgoska-lit. 31,57 River Koselska-lit. 12,52 Sateska-lit. 13,95 Cerava-lit. 21,26
Total nitrogen (mg/l) Mean 0.80 0.63 0.62 0.99
Chlorophyll a Chlorophyll a (µg/l) (µg/l) Mean 5,60 2,43 3,65 3,15
Max 18,91 6,74 16,29 5,23
Trophic category Mesotrophic Oligotrophic/mesotrophic Mesotrophic Mesotrophic
Summary In last several decades oligotrophic Lake Ohrid, is not exempt from general tendency of strength anthropogenic influence. Our data suggest that littoral regions of Lake Ohrid near the main tributaries are increasingly subject to a variety of anthropogenic impacts. The results from all of the investigated parameters indicate that, the largest negative influence on the littoral zone and in the same time the highest trophic state provokes the River Velgoska, as consequence of the insertion of large amount of industrial and communal waste waters in this littoral region with water from River Velgoska, and afterwards respectfully follows Cerava and Sateska, thus the lake water in the areas of their inflow has a mesotrophic state. From all of the investigated areas water of the littoral region of River Koselska had the best quality. In order to obstruct further negative influence of these tributaries on the trophic state of Lake Ohrid, it is necessary completely inclusion of waste waters in the sewerage system, respectively discharge outside of the watershed of Lake Ohrid. The results of this study indicated that in Lake Ohrid exists phosphorus limitation in terms of primary production, which indicates the necessity of reduction on phosphorus load in the lake. Reference Baffico, D. G., (2000) Periphyton community of Nahuel Huapi lake (Patagonia, Argentina) related to environmental factors. - Verh. Internat. Verein. Limnol. 27: 211-215. Burt, T. P., Heathwaite, A. I. & Trudgill, L. T., (1993) Nitrate (Processes, Patterns and Management). - John Wiley & Sons, Chichester. 444 pp. Chiandani, G. and M. Vighi (1974) The N:P ratio and tests with Selenastrum to predict eutrophication in lakes. Water Res. 8: 1063-1069. Droop, M. R., (1973) Some thoughts on nutrient limitation in algae. - J. Phycol. 9:264-272. Elser, J. J., Marzolf, E. R. & Goldman, C. R. (1990) Phosphorus and nitrogen limitation of phytoplankton growth in freshwaters of North America: a review and critique of experimental enrichment. - Can. J. Fish. Aquat. Sci. 47: 1468-1477. Heaney, S. I., Talling, J. F. (1980) Ceratium hirundinella - ecology of a complex, mobile, and successful plant. Ann. Rep. Freshwater biol. Ass. 48: 27-40. Lakes
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Ohrid, FY Republic of Macedonia, 25-29 May 2004
Kajak, Z., (1979) Eutrofikacja jezior (Eutrophication of lakes). - PWN, Warsaw, 233pp. OECD (1982) Eutrophication of Waters. Monitoring, Assessment, and Control. Organization for Economic C0-Operation and Development, Paris. 156p. Raschke, R. (1993) Guidelines for assessing and predicting eutrophication status of small southeastern piedmont impoundments. EPA-Region IV. Environmental Services Division, Ecological Support Branch. Athens, GA. Rhee, G. Y., (1974) Phosphate uptake under nitrate limitation by Scenedesmus sp. and its ecological implications. J. Phycol. 10: 470-475. Rhee, G. Y., (1978) Effects of N:P atomic ratios and nitrate limitation on algal growth, cell composition, and nitrate uptake. - Limnol. Oceanog. 23(1):10-25. Schindler, D. W., (1977) Evolution of phosphorus limitation in lake. - Science 195: 260-262. Strickland, H.D.J. and T.R. Parsons, (1968) A Practical handbook of Seawater Analysis. Bull.Fish.Res.Bd.Canada, 167: 311 pp. Tones, P. I. (1987) Evaluation of the effects of nutrients on the quality of flowing waters. Environment Canada. Conservation and Protection, Water Quality Branch. E-901-11-E-87. 76 pp. Utermöhl, H., (1958) Zur Vervollkommung der quantitativen Phytoplankton methodik. Mitt. Int. Verein. Limnol. 9, 1-38.
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