seasonality, biomass and primary productivity of epipelic algae in a shallow lake (neusiedlersee,...

Acta hydrochim. hydrobiol. 18 (1988) 5, 499-515

M. KHORDKER and M. DOKTJLIL*

University of Dhakar, Dhakar; *Institut fur Limnologie, Mondaee

Seabonality, Biomass and Primary Productivity of Epipelic Algae in a Shallow Lake (Neusiedlersee, Austria)'

Summary: The seasonal fluctuation, biomass and productivity of epipelic algae in the shallow Neusiedlersee (Austria) were studied from 1981 t o 1983. The seasonality of epipelic algae, dominated by diatoms (70 0/0 of the total population), showed a pattern of variable winter growth coupled with a moderate spring and summer maximum. The number of mud dwelling species remained the same as shown in previous studies (LOUB; HUSTEDT 1959a, b), but only twoof them, namely Surirella peiaonie Pmtocsekand Campylodiecua clypeua Ehr., were not abundant. The Di- versity Index (H') varied between 1.0 and 2.86. Specific Biovolumen (i.=47 m 10'2 pm3m2) and potential of production (Z=22.75 mg/m2 - h C) showed a positive correlation with the cell number (5=0.165 10'O/m2). The average chlorophyll-a content of 20.51 mg/m2 is comparable t o that of the Wadden Sea (COLIJN and DIJKEMA), Schohsee (IIO) and Lake Chilwa (Moss 1979). The average activity coefficient (P/B, mg C per mg chlorophyll-a and hour) varied between 0.10 ... 1.93 and the maximum value is only 29 O/,, of that of the phytoplankton. No significant correlation between the algal populations and the ionic concentration of the overlying water could be found because the populations are limited by light intensity.

Introduction

The importance of epipelic algae in shallow lakes has been well established by many authors (WETZEL; Moss 1968, 1969; HARGRAVE; HICKMAN 1971, 1974, 1976; HICKMAN and ROUND; URUENDLING; MOORE 1974a, b). Investigations on the population dynamics, biomass and production of epipelic algae suggest that they might a t times exceed total phytoplankton production and therefore cannot be neglected when the total primary production of aquatic ecosystems is assessed (MOSS 1969; STANLEY; CADEE and HEGEMAN 1974, 1977; ASMUS).

The Neusiedlersee, one of the largest shallow lakes (area 300 kmz) in central Eu- rope provides a large habitat for epipelic algae in its reed and bay sediments. Until recently, research on non-planktonic algae of this lake was rather limited (SOMMER; KUSEL-FETZMANN 1979 and SCHIEMER), describing the primary productivity of periphyton in the reed belt, and species composition and cell volume of epipelic algae. Much of the information about the dynamics of the lake has been accumulated in a recent monograph (LOFFLER). The role of epipelic algae in the nutrient dynamics, benthic food web, and oxygen conditions under the winter ice cover has been re- peatedly raised (HACKER; SCAIEMER; NEUHTJBER and HAB~MEB and DOKULIL 1973, 1979b), but no detail investigation on this biocoenosis has been undertaken until now. 1 Part of the Ph. D. thesis submitted by the first author.

500 KHONDKEB, M., M. DOKULIL, Epipelic Algae in il Shallow Lake

Materials and methods

The Neusiedlersee is located 50 km south east of Vienna a t 47'50" and 16O43E. In terms of surface area it is one of the largest water bodies of Austria, having a length of 32 km and a maximum width of 16 km. About 66 '1,; of its total area is covered with dense stands of Phragmites communia TRIN. The lake is extremely shallow (z = 1.3 m, zmaX = 2 m) and alkaline. Tab. 1 summarizes some of the physico- chemical features.

The saniples were collected between 1980 and 1983 a t monthly or sometimes closer intervals. Sediments from two bay stations, namely Neusiedl and the mouth of the river Wulka (hereafter abbreviated as NS and WE, respectively), and a winter traJ1- sect were collected by using a Gilson corer with a plexiglass tube 5 cm wide and 50 cm long. The uppermost 0.5cm of the soft sediment was washed with lake water into plast,ic boxes. Each time 2 ... 10 samples were placed in an ice box and transported to the laboratory. The vertical distribution of chlorophyll-a was determined from 2 cm thick sections of seiliments.

111 the laboratory the samples were illuminated from above for 5 hours, so that the epipelic algae which are phototactic could appear 011 the surface (EATON and Moss; HICKMAN 1969). After that, the overlying water was sucked out with a peristaltic pump. The harvestiiig of epipelic algae was followed by the tissue trapping technique of EATON and MOSS. Three different sizes of lens tissue (47 cmz, 10 cmj and 1 cm2, Kodak and Whatman 105 grade) were laid on the sediment surface and peeled off regularly after 12 ... 14 hours overnight (EATON and MOSS; ROUND aiid EATON; ROUND arid HAPPY).

After cleaning (ZOTO, DILLON and SCHLIEHTINC ; SHERMAN and YIIINNEY) all the epipelic diatoms were identified to the species level. Fresh samples were counted using the UTERM~HL technique (LUND, KIPLING and LECREN). The cell volumes calculated for each species fell into the range described in MOORE (1981a). Algal volumes determined by M. PROSSER (unpublished) or DOKULIL (1679b) were directly used. The results are expressed as mean per unit area (ma) of the lake bottom.

The bigger tissue (47 cma) was used for chlorophyll-a and productivity analyses. The 10 cm:! and 1 cma tissues were used for diatom identification and counting, respectively. Chl-a and phaeopigment were determined aft,er HOLM-HANSEN and RIE- MANN with methanol as an extracting medium. Both the 14C and O2 methods were used to determine the primary productivity of epipelic algae (HICKMAN 1969 and STRICKLAND and PARSONS). The O2 values were converted to carbon values by multiplying by 0.32 (AsMus). An incubation chamber was constructed using plexiglass 830 (STANLEY and DALEY) to determine the production a t six different light levels (100 %, 14 o/o, 3 "/o, 1 (J/o, 0.5 o/o of ambient light = 75 pE/mzs, and in complete darkness). The daily production was estimated according to HUNDINQ. The underwater light (PhAR) measurement was performed with a Lambda meter (LICOR 185) and a boxed mercury thermometer was used t o measure the bottom temperature. Dissolved silicate from pore and interstitial water samples was determined according to GOLTERMAN, CLYMO and OHNSTAD.

Acta hydrochim. hydro:biol. 16 (1988) 5. 501

Results

Major parts of the bottom sediments of the open lake are frequently stirred by wind action (60 are =-lo km/h, DOKULIL 1984) and hence are inhabitable to epipelic algae for most times of the year. Soon after ice formation in winter underwater light intensities become relatively better, because of reduced turbidity, and the sediment surface is stabilized due to the elimination of wind affects. These conditions in turn allow benthic algal growth on much larger sediment areas. Fig. 1 summa-

Fig. 1 . Inshore-offshore distribution of epi- pelir chlorophyll-ii from a transect near NS under winter ire cover Abb. 1. Verteilung von epipelischem Chloro- phyll-a in Uferniihe und Uferferne RUS einer Schnittlinie in drr Nahe von NS unter der Wintereidecke

0

40

E -1

N

z . 2 0

.10

0 23.1.81 28.12.81 13.~82 2% 1.82 12.82

D a t e

b 18.2.82

rizes the chlorophyll-a concentration (at 0, 500 and 1000 m away from t,he shore) of the lake along winter transects. The average value a t points 500 m and lo00 m away represeilt only one-fourth of the bay values. Similar results were obtained by M. PROS- SER (SCHIEMER). The almost bare and hard sediment surface a t the lake centre does not favour the growth of epipelic algae and was found insignificant for further studies. Thus, concentrating more on the bay stations (NS and WE), a distinct temporal and spatial variation of epipelic algae has been noticed.

Temperuture und light

The temperature of the sediment surface varied between 10 ... 23 "C in summer and 0.2 ... 3.7 "C in winter. I t s annual fluctuation is similar to that of water temperature, i.e. increasing in spring and decreasing in autumn with a summer maximum and a winter minimum (Fig. 2). A longer duration of the ice cover, also indicated in Fig. 2, is more favourable for epipelic algal growth.

Underwater light conditions vary greatly throughout the year depending on the concentration of suspended sediments (DOKULIL 1979a). Fig. 3 represents measurements of the underwater PhAR-attenuation a t stations NS and WE. The scatter of individual data sets is by far greater a t NS compared to the shallow ( z = 3 2 cm) and more sheltered situation a t WE.

Dissolved silicu and other chemical variubles

The silicate concentrations are relatively high both in the lake water and in the sediment porewater. In the water i t varied from 4 ... 10 mg/l SiOz and in sediment from 10 ... 50 mg/l SiO, (Fig. 4) and hence was never likely to limit growth.

502 KHONDKER, M., M. DOKULIL: Epipelic Algae in a Shallow Lake

L .- " J A S O N D J F M A M J J A S O N D J F M A M J J A S ~ H D J F M A M J J A S

1 9 8 0 1 9 8 1 7 9 8 2 1 9 8 3

Fig. 2. Seasonal chiinges of bottom temperature, epipelic algal number, biovolume, chlorophyll a, phaeopigment and productivity from NS (-) and WE (- - - - )

Abb. 2. Jahreszeitliche Veranderungen der Grundtemperatur, der epipelischen Algenzahl, des Biovolumens, Chlorophyll a, Phaeopigments und der Produktivitiit von NS (-) und W E (- - - -)

Nutrient concentrations together with a few other chemical parameters are summa- rized in Tab. 1. A high load of nitrogen and phosphorus is observed at the entry of the river Wulka (WE) compared to the other station (NS). Concentrations of N03-N

Table 1. Range of physico-chemical variables from two sampling points (NS and WE) 3f the Neu- siedlersee. Data on water chemistry from LOFFLER et al. (1982). P,: soluble phosphorus, P,: total phosphorus Tabelle 1. Bereich der physikochemischen Variablen von zwei Probenahmestellen (XS und WE) des Neusiedlersees. Wasserchemische Daten von LOFFLER et al. (1982). P,: loslicher Phosphor, P,: Gesamtphosphor _____

Parameter KS WE

z cm t "C (bottom)

Alkal. meq/l PH

NO2 -N yg/l NO3 -N POI-P pg/l p* Pidl pt Izdl

80 ... 120 0.20 ... 22.70 8.25 ... 9.20 9.00 ... 10.90 0.60 ... 12.00

10 ... 206 2.90 ... 40

13 ... 117 50 ... 518

20 ... 60

7.40 ... 9.025 7.00 ... 10.32 0.40 ... 185

0 ... 2075 14.50 ... 210

27 ... 304 54 ... 390

-

Acta hydrochim. bydrobiol. 16 (1988) 5. 503

Light . intensity

P /

p'

N S /

/ /

80 $ Q QJ m

100 cm 2 120 P

Fig. 3. Semilogarithmic plots of light penetration versus depth as percentage of indicent light Abb. 3. Halblogarithmische Diagramme der Eindringtiefe des Lichtes iiber der Tiefe als Prozent- satz des einfallenden Lichtes

and PO,-P usually show a peak during high tourist activity in summer. The pH value varied between 8.25 and 9.20 a t NS and 7.40 and 9.05 at WE. The overall water quality of the lake is directly related to tourism (FEDRA).

Seasonal changes of the epipelic standing crop

At NS, the epipelic algae were mainly dominated by diatoms. Three species, namly Cyclotella meneghiniana KUTZ., Fragilaria brevistriata GRUN. and Nitzschia tryblionella var. levidensis (W. SM.) GRUN. dominated the flora all year round. With the exception of December 1980 C . meneghiniana was present throughout the study (Fig. 5) . From March to December 1981 their numbers varied between 1.1 * 10s and 10 . 108/m" similar to F. brevistriuta which reached cell numbers of (10.1 ... 50) 108/m2 in July 1981. N . tryblionella var. levidensis showed several peaks in 1981.

A profuse growth of epipelic algae was observed during the winter ice cover of 1980/81 (Fig. 2) reaching 698. 109 pm3/mz. At that time Nitzschia acicularis var. closterioides Grun. dominated the mud surface as a dark brown easily recognizable layer. This species showed two other successive peaks in the spring and summer accounting for 507 . 109 and 118 - l o 9 pm3/ms before it disappeared. Among other Bacillariophyceae, Synedra fasciculata K ~ ~ T z . , Nawicula cryptocephla KUTZ., Gyro- s@ma acuminatum KUTZ. RABH. were common. Chlorophyceae were represented by 37 Acta hydrochim., Bd. 16, H. 5

504

-8 cm -6

-4

-2

0

2 c 2 4 a O 6

8

10

12

14

16 cm 78

KEONDKEE, M., M. DOKULIL: Epipelic Algae in a Shalow Lake

Fig. 4. Isopleths of dissolved silicate concentration (mg/l SiO,) determined from interstitial and overlying water at NS. Dots represent depth and time of sampling Abb. 4. Isoplethen der Konzentration des gelosten Silikats (mg/l Si02) nach der Bestimmung von Porenwasser und dariiber befindlichem Wasser bei NS. Die Tiefe und die Probenahmezeit sind durch Punkte dargestellt

the occasional appearance of Oocystis solitaria WITTR. and Crucigenia tetrupediu (KIRCHN.) West et West. Among Euglenoids, Euglem~ oxyuris SCHM. and Phacus pusilus LEMM. were frequent (Fig.).

The sediment of station WE was mostly dominated hy Gyrosiymw m c r u m (W. S M . ) Griff. et Henfr. and N. sigma (KUTZ.) W. SM. (Fig. 6). I n mmmer Oscillatwia tenuis KUTZ. and Spirulinu major KUTZ. appeared as a mat on the sediment surface which later became detached by gas bubbles and floated on the water surface. This sediment was found to be very rich in Unicellular flagellate organisms. The diversity index varied between 1 and 2.86 bits/individual and the species number between 2 and 10. The maximum number of epipelic algae was recorded in September and October 1982. The biovolume varied in the range of (3.24 ... 32.9) * 1012 prn?/mma (Fig. 6).

I'

I

I

I'

I I

I I

I I

I I

/I

1 J I I

[I I I!! I

I 'I

I,' 1 I

I

I' I

11

I

I II I 'I 11

31 JUL 80 12 AUG 80 04 SEP 80 26 SEP 80 14 OCT 80 27 OCT 80 13 NOV 80 03 DEC 80 19 DEC 80 30 DEC 80 18 JAN 81 23 JAN 81 30 JAN 81

20 FEB 81 05 MAR 81

08 FEE ei

26 MAR ei 03 APR 81 15 APR 81 05 MAY 81 05 JUN 81 16 JUN ei 19 JUN 81 03 JUL ei 10 JUL 81 11 AUC 81 24 AUG 81 09 SEP 81 15 SEP 81 04 NOV 81 11 NOV 81 03 DEC 81 ze DEC 81 13 JAN e2

05 FEB e2 18 FEB e.2 25 MAR 82

25 MAY ez 02 JUL e2

27 JAN 82

08 APR 82

D?. AUC 82

506 KHONDICER, M., M. DOICUML: Epipelic Algae in ti Shallow Lake

Oscillatoria tenuis Kiitz. 'Wndana major Kii tz. Cyclotella meneghiniann Kutz. Bagilaria brevistriata Grun. Navicula c q i d a t a var. ambigua (Ehr.) Cleve N. halophila (Grun.) Cleve Gyrosigma acuminatum (Kiitz.) Rabh. C. macnrrn (W.Srnith) Grif f .e t Henlr. Amphora ovalis var. pediculus Kiitz. Mzschia accicularis var. clostarioides Grun. M z . sigma (Kutz.) W.sm. Nitz. tlyblinnella Hantzsch Mz. tlyblinnella var. levidensis (W.Srn.) Grun. Bacillariaparadoza Gmelin ,%rireUa peisonis Pantocsek Cuglena deses var. intermedia Nebs E. ehrenbergii Klehs E. o w & Schrnarda

i r - L

I- tm 1

I t

--- B

I

I

Fig. 6. Comparison of the biovolume of different epipelic species between NS and WE (*Calculated per average filament length) Abb. 6. Vergleich des Biovolumens verschiedener epipelischer Arten zaischen NS und W E (* berechnet je durchschnittlicher Faserliinge)

2

4

6

8

10 z c

-o ,2 11 25.03.82 1 08.04.82 25.05.82 u 2 14

6 2 E

- 4

6 cm 8

01 1' 25.08.82

Fig. 7. Vertical distribution of chlorophyll-a in sediment cores f r x n the sampling point NS Abb. 7. Vertiknle Verteilung des Chlorophyll a in Sedimentkernen von der Probenahmestelle NS

Acta hydrochim. hydrobiol. 16 (1988) 5 507

The specific mass of chlorophyll-a a t the station NS was between 4 and 53 mg/m2 with an average value of 14.47mg/m? The highest value of 53mg/ma was measured during the peak growth of N.acicularis var. closterioides under the winter ice cover of 1980/81. It decreased gradually towards 1983 without any further peak in the following winter (Fig. 2). Additional small peaks occurred in July 1981, March and October 1982. Higher values of specific chlorophyll-a mass (21 ... 60mg/ms, Fig. 2) were observed a t station WE. The average of 40.5 mg/m2 is nearly three times higher than for NS.

The relative chlorophyll-a content of the biovolume was 0.62 ... 1.49 o/,, at station NS because of the dominance of diatoms. At station WE values were lower (0.13 ... 0.57 ",',J, because of blue-green algal dominance. Phaeopigments were equal in the chlorophyll-a concentration at certaiii times (Fig. 2).

The vertical distribution of the pigment content within a sediment core showed highest concentrations at the mud surface, decreasing gradually down to 8 cm depth (Fig. 7). 011 only one occasion was chlorophyll detectable at depths greater than 8 cni. On 8.4. 1982 the maximum value of chlorophyll-a was measured a t 4 cm sediment depth and not a t the surface.

Pote 11 tiul primwr y production

Since n~easurements of photosynthetic rates were carried out in the laboratory, data represent potential productivity rather than actual ,,in situ" photosynthesis ( HICRMAN and ROUND ; HUNDING ; GARGAS). Measurements of potential productivity are good estimators of primary production in the field in the case of epipelic algae, because benthic algae yield maximal photosynthesis over a wide range of light intensities ( HUNDING).

111 the present investigation the potential production a t NS varied between 0.6 and 23.0 mg/m' h C aiid that of station WE between 25 ... 116 mg/m? - h C (Fig. 2). The epipelic population a t WE had higher average activity coefficients of 1.17 mg C per mg vhlorophyll-a and hour than station NS which had 0.48.

Assuming in s i tu productivity to be 50 o/u of the potential measurements (ORBNT- VED), estimated daily production amouiits to 0.0004 ... 0.2750 g/m2 - d C.

Discussion

Similar t,o other findings, the epipelic algae of the Neusiedlersee are dominated by diatoms (HICKMAN 1971, MOORE 1974a, b ; MOORE 1980; ROUND 1957a, b ; ROUND 1960). From the work of LOUB and HUSTEDT (1959a, h) a change in the species composition over the past decades can be deduced. The two previously recorded, most common mud dwelling species, Surirella peisonis and Campylodiecus clypeus, were rare in the present investigation. The newly recorded diatom species Gyrosigma inacruin (KUSEL-FETZMANN 1973) is now abundant in the WE sediments. DOKULIL (1979b) also found a shift i n the species composition of phytoplankton from diatoms towards green algae, which he attributed to the influence of increasing eutrophication (LOFFLER 1979).

One important aspect of the benthic diatom distribution in the Neusiedlersee is its frequent intermixing with phytoplankton. DOKULIL (1975) reported five species of

608 KHOBDKEB, M., M. DOKULIL: Epipelic Algae in a Shallow Lake

diatoms in a phytoplankton sample which seemed to have originated from the sediments as a result of wind affecting the surface of the sediment in that shallow lake. Similar observations are reported from Lake Myvhtn (JONASSON), Lacke Vechten (GONS) and Lake Michigan (STEVENSON and STBEOMER).

Data on abundance, biovolnme and productivity of the present study are sumnia- rized in Tab. 2.

Table 2. Observed ranges of epipelic algal variables in the years 1980 ... 1983 Tabelle 2. Beobachtete Bereiche von Variablen epipeliecher Algen in den Jahren 1980 ... 1983

Parameter NS WE

Total cells lOfO/m2 .009 ... .547 .065 ... 1.27 Total cell volume 1012 ym''/rnn .004 ... 6.98 3.24 ... 32.97 Chlorophyll-a rnglrnn 4 ... 53 21 ... 60.0 Productivity mg/ms h C .6 ... 1.27 25 ... 116.0 P/B mg/mg C/Chl.-a .10 ... 1.27 .76 ... 1.93 Diversity index (H') 0.92 ... 2.86 .22 ... 2.27

Biovolumes reported in this study can be compared with information about t h e seasonality of this biocoenosis from the past obtained by M. PROSSER (SCHIEMEB). His two years study (May 1971 to June 1973) shows three distinct growth peaks. The specific biovolume started to increase in Sept. 1971 and reached a peak of 8 0 . 1011 pm3/mz in Jan. 1972. It fell until Aug. 1972 and then reached a smaller peak during May. A high biovolume of 40 - 1012 ym3Jmz was observed in Oct. 1972. At NS a high growth was obtained in February 1981, followed by a medium growth in June of the same year. No further peak except a little rise in May 1982 (Fig. 2) was found. In the WE areadetached masses of epipelic bluegreen algae were seen floating on the water surface in July and September 1983. KUSEL-FETZMANN (1979) reported the similar occur- rence of epipelic algae from other parts of the lake in the month of September. Sum- marizing these observations it can be said that the epipelic algae of the Neusiedlersee from an early-to-late-winter peak (which again might vary according to the duration of the ice cover), a moderate spring peak and a late-summer-to-early-autumn peak. This obviously deviates from the generalized trend for temperate lakes as observed by ROUND (1960, 1964) where the ,,growth commences in the earlyspring and reaches a maximum in April to May, after which it declines to a mid summer minimum prior to a small maximum that is over by November" (HICKBUN 1978a).

The average cell number (1.6 - 10VrnZ) recorded for the Neusiedlersee seems to be quite low when compared to other ecosystems (Tab. 3). Higher @ell numbers were reported from the Alaskan tundra ponds (STAKLEY 1980), Lake Chilwa (MOSS 1979) and the ponds and rivers of Baffin Island (MOORE 1974a, b). ROTKACAOUX found an extremely high epipelic standing crop (100 * lOiO/rn*) from Lac Pavin. The densities of epipelic algae from Great Slave Lake and Lake Gordon (MOOBE 1980,1981 b) are com- paratively low. The average total biovolume crop exprerrsed as cell volume (44.7 * lop1

pms/m2) is within the range recorded for thelakes in northern latitudes and a t the arctic circle (MOORE 1979, BJORK-RAMBERG; Tab. 3). PFEIFEB obtained a similar value from an alpine lake of Austria. The biomass of Lake Mikolaijakie is extraordirlarily high


Table. 3. A comparison of cell number, cell volume and chlorophyll-a from different ecosystems Tabelle 3. Ein Vergleich der Zellzahl, dee Zellvolumens und des Chlorophyll-a von verschie- denen Okosystemen

Ecosystem Cell number Cell volume Chl. a Author 1010/mz 1012 pm3/m2 mg/m?-

Lake Chilwa 0.90-8.50

Rivers, Baffin Island 13 Ponds, Baffin Island 40 Arctic Lake - Great Slave Lakes 0.58 Lake Gordon 0.35 Five lakes in Canada - Three lakes in Canada -

Tundra ponds 2-4

Shear Water

Abbots Pool Priddy pool and Abbots pond Lake Mikolajskie

Wadden Sea

Wadden Sea

Lake Vechten Lac Pavin Lake Mgvatn Gardsjon Lake Gunillajaure

Suomun jiirvi Schohsee Finstertalersee Neusiedlersee Neusiedlersee

- - 110 520 1547.5 1 .R .39 - - -

-

- 1410

-

-

- - 160 - 5.6-20.1

- - 45.3 12.7 44.7

15.6-56.5 - - - - - - 13.06 17.00 3.74

7.60

4.65 -

-

20-100

17 300

35 -

-

114 6.87-42.13 146

20.51 -

Moss 1979 S T A N L E Y ~ ~ ~ ~ MOORI~ 1974a MOORE 1974 b MOORE 1979 MOORE 1980 MOORE 1981 b HIUKMAN 1978a HICKMAN 1978 b HICKMAN and ROUND 1970 Moss 1969

HICKMAN 1971 KOWALCZEW- SKI and PIEC- Z Y ~ S R A 1976 COLIJN et al. 1976 COLIJN and DIJKEMA 1981 GONS 1982 ROMAGOUX 1979

LAZAREK 1980 BJORK-RAM-

SORSA 1979 Ho 1979 PPEIPER 1974 SCHIEMER 1979 Present investi- gat ion

J6NASSON 1979

BERG 1983

(KOWALCZEWSKI and PIECZYNSKA). A four times smaller average biovolume value (12.7 * 1012 pmJ/m2 recorded by M. PROSSER (SCH~MER)) for the Neusiedlersee is due to the fact that M. PROSSER did not include the most eutrophicated part (WE) of the lake. The average chlorophyll-a value of 20.61 mg/m2 fell within the range reported the Wadden-Sea (COLIJN and DIJKEMA), Schohsee (Ho) and Lake Chilwa (MOSS 1979) whereas higher pigment concentrations were observed in the Finstertalersee (PFEIFER), Suomunjarvi (SORSA) and Lac Pavin (ROIKAGOUX). Lakes of Canada and England are low in epipelic chlorophyll-a (HICKMAN 1971, 1978a, b ; HICKMAN and ROUND; Moss 1969).

Regarding the primary productivity Tab. 4 summarizes the results obtained from

610 KHONDKER, M., M. DOKULIL: Epipelic Algae in a Shallow Lake

Table 4. A comparison of daily epipelic primary productivity from different ecosystems Tabelle 4. Ein Vergleich der tiiglichen epipelischen Primiirproduktion verschiedener Okosysteme

Lake Productivity Type of Author g/m2. d C measurement

Tahoe 0.01 11 -0.01 71 in situ FLINT et 01. 1977 Tundra ponds 0.0274 estimated STANLEY 1980 lkroavik 0.0063 estimated STANLEY 1976 a Tundra ponds 0.0258 simulated STANLEY 1976b Long Island Sound 4-5 estimated BURKHOLDER et al.

Borax 0.7300 - Marion 0.1096 in s i tu HARQRAVE 1969 Marion 0.1205 in uitu GRUENDLINQ 1971 Mikolajskie 0.3370 unknown KOWALCZEWSKI and

P I E C Z Y ~ K A 1976 Mivatn 0.1370 11 n kno w n J~NASSON 1979 Gunillajaure 0.0077-0.01 10 in situ BJORK-RAMBERQ

Fureso 0.8137 potential HUNDINR 1971

Paajiirvi 0.0300 in situ KAIRESALO 1977 Suomunjarvi 0.0005 in u i t u SORSA 1979 Dutch Wttdden Sea 0.2740 in situ CADEE and Hege-

Dutch Wadden Sea 0.2329 in situ CADEE and HEQE-

1965 W E T Z E L ~ ~ ~ ~

1983

Fureuo 0.3918 cstimitted HUNDING 1971

MAN 1974

MAN 1977 Vechten 0.3000 in situ GONS 1982 Lac Pavin 0.0466 in situ ROMAQOUX 1980 Schohsee 0.1980 estimated Ho 1979

Neusiedlersee 0.1010 potential Present investiga-

Neusied lersee 0.0500 estimated, in uitu Present investiga-

Wadden Sea 0.1863 in situ -4SMUS 1982

tion

tion

* In caue of yearly data the daily production was calculated by dividing by 36.5.

different lakes together nit11 that from Neusiedlersee. The estimated in situ productioti (0.05 g/mj * d C) of Neusiedlersee could be conipared to the values recorded from Lake Pavin (ROMAGOUX 1980), Paajarvi (KAIRESALO 1976, 1977) and Tundra Pond ecosystems (STANLEY 1980). The productivity of Lake Marion is 50 0; higher than that of the Neusiedlersee (HARGRAVE; GRUENDLING). Some of the Swedish and Finnish lakes (BJORK-RAMBERC ; SORSA) and the Lake Ikroavik from Alaska (STANLEY 1976a) show lower rates of epipelic productivity (Tab. 4). A very high rate of production ($ ... 5 g/mr * d C) was reported by BURKHOLDER et al. from the Long Island Sound.

Unstable sediment surface arid wind-induced turbidity reducing the underwater light penetration (Fig. 3) are responsible for low biomass and productivity of the epipelic algae i n the Neusiedlersee. Below the winter ice cover the sediment surface remains stable, the suspended material settles and improves the light penetration.


These conditions favour winter growth, if the ice-cover exists for a sufficiently long period of time. Years with short ice-duration are unfavourable for benthic algal growth. (Fig. 2). NEUHUBER and HAMMER stated that the photosynthesis of epipelic algae under a relatively long winter ice cover might be the reason why the sediment surface can remain aerobic. Similar situations should also occur in other wind influenced shallow temperate lakes (e.g. Lake Balaton, Steinhuder Meer etc.), but until now no information is available.

Similar to many other examples (WESTLARE), light is an important factor controlling the growth of the epipelic algae in the Neusiedlersee. The low light intensities at the sediment surface (0.3 ... 3 o/o, Pig. 3) indicate light limitation. Experimental data, however, do not confirm any adaptation to low light intensities. HuNDINa and STAN- LEY and DahY reported saturation of photosynthesis between 60 and 200 yE/mz s for epipelic algae. According to HUNDINC, the maximum photosynthethic efficiency of epipelic algae lies within a wide range of light intensities, while OARGAS found a significant adaptation of the epipelic algae to low light intensities.

Many authors (HICRMAN 1971, 1974, 1975, 1976; 1978a, b; Moss 1969; MOORE 1980, 1981a) have tried to establish a relationship between the epipelic algae and the overlying water chemistry. The results of their attempts varied over a wide range and mostly depended upon the magnitude of nutrient concentrations i n the pelagic water. HICKMAN (1976) found very little relationship between the epipelic algae and the water chemistry as was observed in the present investigation. Higher biomass and productivity a t station WE are to some extent a reflection of the 3 to 8 times higher nutrient concentration there.

Moss (1969) and HICKMANN (1978a) established a direct relationship between bi- carbonate ions and the epipelic algae. In the Neusiedlersee, the concentration of bi- carbonate and silicate are high (Tab. 1) and, therefore, their role appears to be insignificant for the population dynamics.

Table 5. Primary production by different biococnoses of the Neusiedlersee Tabel le 5. Primiirproduktion vertichiedener Biozonoscn des Neusiedlersees

BiocoenoRes Produrtioii g/m?. d C

Phytopl ankton (open lake) 0.2350

Periphyton (on the reeds)l 0.0116 Phytopl ankton (reed belt) 0.0200

Epipelic algae 0.0500 Submerged macrophytrs 2 0.0120 (other than Ulricukariu sp.) Utricularia spp:' 0.2424 P . coinmuniv Trin. 2.7400

Percent age I1 /"

Source

7.10 0.60 0.35 1.51 0.36

7.32 82.75

DOKUIJL 1984 DORUJJL 1975 SOMMER 1977 Present investigation SCHIEMER 1979

MAIER 1979 (Pig. 21.3) SIEUHARDT pers. comm.

1 E from potiitions I , 11, and I11 (annual total m-2 water surface) 2 E from the imnunl total of 1971 and 1972. 50 o/l, of the dry weight was considered as the value

of ctirbon. 3 5 from the commiinities of open water and reeds. The monthly averag? was back calrulated

and then divided by 30. Thc conversion of annual total to daily rate was done by dividing by 365.

61% KIKONDKEB, M., M. DOKULIL: Epipelic Algae in a Shallow Lake

Table 5 summarizes the average daily production for different communities in the Neusiedlersee. Although epipelic algae contribute as little as 1.61 "/o to the total daily primary production their importance for the benthic food chain is large because they contribute with 8.8 o/" to the submerse production. Many maom- and meiobenthic species, e.g. dlonhystera mucramphi8 FILIPJEV, Chaetogaeter hngi BRET. H y p e a i m augusti (J. MUBRAY) and Tanypus punctipennds (MEIG), feed on benthic algae. Diatoms such a8 Q. aouminatum, N . tryblionella and S. peisoni8 are preferred by chi- ronomids (SCHIEMER). HACKER was able to show that 40 (\,',, of t.he gut content of a fish (Blicoa bjirrkna L.) consists of epipelic algae. Grazing might thus be another important factor controlling epipelic algal biomass (SCHIEMEB).

Although low in biomass and productivity for most time of the year, epipelic dgae are second in importance among algal communitieR and prove to be of great significance for the ecosystem as a whole.

During the tenure of this project the first author was holding a scholarship from The Afro-Asiatic Institute in Vienna, Austria. The authors greatly acknowledge the corrections and helpful com- ments made by Prof. WOOD, University of Ulster and an unknown referee on earlier versions of the manuscript.

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Anschrift der Verfasser: M. KEONDKER, Department of Botany, University of Dhaka, Dhaka-2, Bangladesh; Doz. Dr. M. DOKULIL, Institut fur Limnologie der osterreichischen Akademie der Wissenschaften, Abt. Mondsee, A-5310 Mondsee, Gaisberg 116, Austria.

seasonality, biomass and primary productivity of epipelic algae in a shallow lake (neusiedlersee,...

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