Periphytic primary production during spring. A sink or source of oxygen in the littoral zone?

Limnologica 30 (2000) 169-174 http://www.urbanfischer.de/journats/limno

LIMNOLOGICA © by Urban & Fischer Verlag

Institut ftir Hydrobiologie und Fischereiwissenschaft, Hydrobiologische Abteilung, Universit~it Hamburg, Hamburg, Germany

Periphytic Primary Production during Spring. A Sink or Source of Oxygen in the Littoral Zone?* UTE MI)LLER With 5 Figures and one Table Key words: Periphyton, chlorophyll a, net and gross production of oxygen, PB rate, oxygen deficit

Abstract The vertical distribution of gross primary production rates of periphyton communities was determined based on changes in the oxygen concentration. The gross primary production conformed to the colonization pattern of the epiphytic algae on submerged shoots of Phragmites australis. The algae produced the most on stem sections that grew from 0.2 to 0.5 m deep in the littoral zone. The PB rates, however, decreased on these middle sections of the stems due to increasing self-shading by the periphyton. Although high gross oxygen production rates were determined during the hours of incubation, an oxygen deficit was calculated for the full 24 hours periods on all days of the investigations at the time the algae peaks occurred during the spring.

Introduction The littoral zones are regarded as the most productive areas of aquatic ecosystems, and periphytic algae can be an important contributer to organic matter production (WETZEL 1964, 1990). The contribution of aufwuchs algae toward the total littoral primary production ranged between 5.5 and 71% (WETZEL 1964; PIECZYNSKA& SZCZEPANSKA1966; ALLEN 1971; KOMARKOVA & KOMAREK 1975; KOWALCZEWSKI1975; Ho 1979), and it amounted to 5.7% in dense stands of Phragmites australis in the eutrophic Lake Belau (GESSNERet al. 1996). The periphyton on emergent macrophytes forms coatings several millimeters thick (MESCHKAT 1933; MEULEMANS& ROOS 1985). The epiphytic algae are part of a very heterogeniously structured community, which contains consumers and decomposers as well as primary producers. During spring, Bacillariophyceae are most abundant and form several layers on the substrate which display a complex architec* This paper is dedicated to Prof. Dr. HARTMUTKAUSCHon the occasion of his 60 th birthday.

ture (MEucHE 1939; JORGENSEN1957; MEULEMANS& ROOS 1985). Following the period of diatom abundance, chlorophytes predominated the epiphyton in Lake Belau and formed filaments extending into the surrounding water. The most abundant invertebrates that graze on aufwuchs are oligochaetes, nematodes, molluscs, rotifers, insect larvae, and crustaceans (MEUCHE 1939; GLOWACKAet al. 1976). Heterotrophic bacteria colonize on algae, in the periphytic matrix and directly on the reed, and chytrids parasitize on several species of Bacillariophyceae (Roos 1983). Primary production by periphytic communities on emergent macrophytes, determined from the changes in the oxygen concentration in light and in darkness, can produce high daily rates of oxygen release (ASSMAN 1953; STRASKRABA 1963; PIECZYNSKA& SZCZEPANSKA1966; SPODNIEWSKAet al. 1975). The amount of dissolved oxygen released by periphytic communities depends on the light intensity and varies from day to day (SOMMER 1976; SAND-JENSENet al. 1985; CARLTON& WETZEL 1987). In spite of the periodic release of large quantities of oxygen, net production rates cannot eliminate oxygen deficiency when the periphyton biomass has rapidly decreased or when irradiance is reduced by seasonal change or increased shading by a canopy of macrophytes (SOMMER 1976; MEULEMANS1988). Production rates do not increase linearly with the chlorophyll a concentration (PIECZYNSKA& SZCZEPANSKA1966). Self-shading inside the periphyton layer limits the photosynthetic activity of epiphytic algae (STRASKRABA& PIEZCYNS1970; SZCZEPANSKA1968) since the photic zone is usually restricted to a few outer millimeters of the periphyton (MEULEMANS 1987; DODDS 1992). Production of oxygen reaches optimal rates, while supersaturation occurs only in the outermost layer. In deeper layers, the oxygen concentration is significantly lower (CARLTON& WETZEL 1987). 0075-9511/00/30/02-169 $12.00/0

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In Lake Belau, self-shading in the middle of the submerged part of the Phragmites stems reduced algal activity, and the PB rates or chlorophyll specific rate of photosynthesis decreased as the periphyton biomass increased (MOLLER 1995). During the earlier investigation, the biomass and production rates were determined by the z4C-method on different stems. To examine the effect of self-shading on the photosynthetic activity of the epiphytic community in the present investigation, the primary production was determined from changes in the dissolved oxygen concentration. This method allows both net production rates and chlorophyll a concentrations to be determined in the same periphytic biocoenosis. Furthermore, the net primary production rates indicate whether photoautotrophic processes occur more rapidly than heterotrophic metabolism during spring, when submerged sections of Phragmites are covered by dense periphytic layers.

Material and Methods Material and location The oxygen concentrations were determined of the periphyton colonizing Phragmitesaustralis (CAv.) TRIN. ex STEUDEL.This investigation was proposed by ASSMAN(1953), who investigated intact periphytic communities remaining on their substrate. The Phragmites plants were collected along the western shore of Lake Belau, a eutrophic hardwater lake in Northern Germany, the littoral zone of which was described previously by MOLLER(1994). The stems were harvested one day before the incubation was begun in the laboratory. The investigation began in February, when the Phragmites stems were nearly almost completely dead througout their entire lengths, and only short green sections remained alive just above the sediment. By the end of May, the stems from the previous year were too short to be used for determinations. They were decomposing from the broken off emergent part down to submerged sections.

Incubation procedures For the incubation the submerged shoots were cut into eight sections 0.07 to 0.08 m long. The sections were exposed in 0.120 1 glass bottles filled with a modified mineral nutrient solution enriched with silicon (KUHL & LORENZEN1964). Ammonium was substituted for nitrate to avoid oxygen release from the nitrate (WILLIAMS et al. 1979). The bottles rotated in an incubator for 3 hours while illuminated by fluorescent lamps with a photon flux density (PFD) of 180 pmol m -2 s 1. The ambient water temperature was maintained at 11.2 °C -+0.4 °C, while the littoral temperature was 3.9, 4.6, 5.5, 7.0 and 10.9 °C on the sampling days. The oxygen concentrations on each two parallel stem sections were determined polarographically using a microprocessor oximeter (WTW Oxi 2000). After the oxygen determinations, the periphyton was scraped off onto WHATMAN GF/C glassfiber filters using a scalpel. This material was used for the spectrophotometric determination (ZEISS PMQ II) of the chlorophyll a concentration according to the method of NUSCH (1980). After grinding the filters in a cell mill, the pigments were extracted in ethanol for 18 hours in the dark. Chlorophyll a concentrations were corrected for phaeophytin. The algae species composition was observed on selected stems. 170

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Calculation of the net production per day The estimation of the net daily oxygen production was based on a PI curve plotted from in-situ >C primary production determinations carried out from October to April of the years 1988 through 1991 (MOLLER 1996). The BLACKMANmodel was applied for calculating the onset of light saturated photosynthesis (Production [pg C cm-2 h-1] = 0.00762 PAR [~mol m-2 s-l]; n = 27; r = 0.840 _ r~26;000~= 0.588; light saturation onset parameter (Ik) = 313 pmol m-2 s<; P~,x = 2.39 pg C cm 2 h-~). When the light was limiting the production rates determined in the incubator were calculated as a linear function of the irradiance, and at light saturation independent production rates were assumed. Calculating the photosynthetically active radiation (PAR) at 0.35 m, the mean solar radiation during the weeks of the experiments, recorded with a Licor-quantum sensor by the Deutscher Wetterdienst Quickborn, was corrected for the shading by the canopy, which amounted to 42.2, 38.9, 37.4, 35.8 and 35.2% on the sampling days from February through May. The decrease in PAR by shading was estimated from ten measurements with a sphaericaI quantum sensor (QSP-170) at the sampling site in the littoral zone. To calculate the light attenuation under water, five measurements were made at 0.10 m depth intervals. The vertical attenuation coefficient of the PAR depends not only on the phytoplankton density but also on the amount of resuspended sediment generated by wind induced wave action. To compensate this short-term effect on the sampling day, the constant attenuation coefficient of 1.696 m -1 was used as an average during the investigation period. Respiration was assumed to be constant for the entire 24 hours. The conversion of the oxygen production per cm 2 of substrate into a production per m; of the littoral zone was based on the following assumption: 60 reed stems 0.7 m long and with a mean surface area of 120 cm 2 are present in each m 2 of the littoral zone.

Results Chlorophyll a concentration and dominant algae on Phragmites during spring The experiments were carried out while the periphyton biomass was characteristic of the spring period of growth (Fig. 1). During the first spring maximum, which occurred in March, the algal species belong mainly to the Bacillariophyceae. They included Cymbella spp., Fragilaria spp., Gomphonema spp. and Cocconeis placentula var. euglypta (EHRENBERG) GRUNOW. The chlorophyte, Ulothrix tenuissima K~TZING, which preferred to colonize the upper stem sections, was less abundant as was the cyanobacterium, Geitlerinema splendidum (GREY. ex GOMONT) ANAQNOSTIDES, which occurs above the sediment. At the end of April, the Bacillariophyceae were replaced by the filamentous chlorophytes, Oedogonium spp., Mougeotia sp. and Spirogyra spp., which produced a second chlorophyll m a x i m u m in June. On the days of the experiments the chlorophyll a concentration ranged between 1.4 and 67.8 pg cm -2. M a x i m u m amounts of chlorophyll a were found at the middle of the submerged stems, whereas on the upper and lower sections, only low concentrations were determined (Fig. 2).

Oxygen production and respiration rates The hourly gross production rates of the periphyton ranged between 1.6 and 17.8 pg O2 cm -2 h -1 and correspond closely to the vertical distribution of the chlorophyll a concentrations (Fig. 3). On average, 53.4% of the gross production on

the entire stems was consumed by metabolic processes of the periphyton as well as the macrophyte (s.d._+ 25.2%; range: 6.3-126.5%; Fig. 4). Net oxygen production peaked in February and May, when the biomass of diatoms and filamentous chlorophytes was increasing. However, during the interim the respiration processes consumed more than 50% of the material produced.

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Fig. 3. Vertical distribution of the gross production rate (solid line) and the respiration rate (dotted line) of periphyton on Phragmites australis. The curves represent the average of two parallel determinations. The values in the figures are the mean gross production rates in pg 02 cm -2 h-~ on the entire stems.

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Limnologica 30 (2000) 2

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A net gain in the production of oxygen was determined on nearly all sections of the stems in the vertical profile. There were exceptions when decomposition processes by the macrophyte tissue consumed more oxygen than the amount produced by the epiphytes. This occurred in March on the sections of the stem above the sediment, where there were senescent leave sheaths. It occurred again in May just below the water surface, where the stem was decomposing.

PB rate The epiphytes produced the highest PB rates on the stem sections from just below the water surface, and on the sections just above the sediment, where the stems were colonized by thin periphytic coatings (Fig. 5). When the chlorophyll a concentration on the middle stem sections was increasing, a decrease was observed in the PB rates indicating reduced photosynthesis activity due to intensive self-shading by the periphyton. Exceptionally high PB rates were determined when the net production rates were negative due to high respiration rates on the lowest stem section in March and on the uppermost stem section in May.

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Net daily oxygen

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During spring, the periphyton metabolism consumed oxygen from the ambient water in the littoral zone and did not supply oxygen. The daily net production was always negative and 172

Limnologica 30 (2000) 2

Table 1. Daily oxygen deficit per unit area on Phragmitesand in the

littoral zone. Date

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ranged between -5.84 and -48.14 ~ag 0 2 cm -2 d -~ on Phragmites (Table 1), which was equivalent to-60.05 and 4 9 5 . 1 1 ~tg O21 1d L As the PAR increased during spring, the oxygen deficit was reduced. However, when the periphytic layers increased in density during March and April, the oxygen consumption on the stems increased•

Discussion During spring 1992, the chlorophyll a concentrations and species present among the epiphytic algae on Phragmites austraIis were similar to those observed during previous years (Mt2LLER 1994, 1995), although the very intensive solar radiation during May and June caused an extraordinarily high maximum density of filamentous chlorophytes. Primary production determinations using the oxygen method for intact periphytic communities remaining on Phragmites plants account for oxygen release and respiration rates by the periphyton biocoenosis and in the substrate. Although the proportion of the dissolved oxygen production contributed by the macrophytes can be high in comparison to that of the periphyton (ASSMAN 1953; SAND-JENSEN et al. 1985), it can be generally neglected in this case, because the Phragmites stems were almost completely dead by February. Hourly rates of net oxygen were in the same order of magnitude as those determined on periphyton in situ (SzcZEPANSKI ~; SZCZEPANSKA 1966; SOMMER 1976). In Lake Belau gross oxygen production rates were converted to carbon without using any correction factor. They were equal to 97.8 through 126.7% of those rates as determined by 14C assimilation hz situ around midday (MULLER, unpubl, results). These determinations were carried out one day before the incubations were begun in the laboratory. However, on April 21 and 22, oxygen production was three times greater than ]4C production because silicon concentrations in the littoral zone were a limiting factor for cell division by diatoms (WERNER 1978), which were still predominant in the periphyton during that period. Much of the released oxygen is immediately consumed by the algae themselves but as well as by heterotrophic organisms in the intact periphyton layers (ASSMAN 1953; KO-

MARKOVA ~2 MARVAN 1987). In Phragmites stands in the Neusiedlersee, heterotrophic activity produced an oxygen deficiency following periods of maximum development by periphyton communities. Such deficiencies were recorded in autumn when the PAR decreased (SOMMER 1977). In Lake Belau, the animals found on the stems which contributed to the spring oxygen deficiency included the snail, Acroloxus lacustris LINNI~, the nematodes, Punctodora ratzeburgensis LINSTOW and Chromadorina cf. viridis, and the oligochaetes Nais spp., Chaetogaster diastrophus GROITHUISEN and Stylaria lacustris L1NNI~. The nematodes became most abundant during and the oligochaetes following the development of the algae during spring (Lt3HLEIN 1996, 1998). Insect larvae became abundant in May and were therefore only observed near the end of the investigation (OTTO 1991). Bacteria and fungi, the decomposers of dead macrophytes, were responsible for almost equal proportions of oxygen consumption (MASON 1976). However, great epiphytic algae abundance favours the growth of bacteria biomass because they depend on extracellular organic carbon released during photoautotrophic production (NEELY 1994, 1995). Vertical distribution of the PB rates coincided with that determined by in situ 14C assimilation methods during previous years, as well as with those determined one day before the incubation in the laboratory (Mt)LLER 1995, unpubl, results). At the light intensities prevailing in the incubator, which reach all stem sections equally, the PB rates on the middle stem sections were less than those found during in situ exposure. The increase in the PB rate toward the sediment is related to the small periphyton biomass and not to the adaptation processes of epiphytic algae communities to lower PAR above the sediment. The vertical distribution of the PB rates calculated from the oxygen and the 14C-method were similar, supporting the assumption that there is considerable selfshading inside the periphytic layer on Phragmites stems. This is valid, although the determination of the net oxygen production rates and respiration rates still have to be carried out on different sections of the stems. The I k of 313 pmol m -2 s : used for the calculations of the daily oxygen production was calculated from the amount of production during winter and spring, when the periphyton architecture was very complex with multistorey layers. The I k describes the irradiance outside of the periphyton and is more than twice as high as the values from 105 to 135 laE m -2 s-1 determined for periphyton communities on Potamogeton crispus L~YNE by using microprofiles (SAND-JENSEN et al. 1985). Although the high Ikvalue for the periphyton in Lake Belau would indicate that the gross oxygen production rates were high, the calculated daily oxygen deficit was similar to those recorded for periphyton communities of the Neusiedlersee during autumn at decreasing biomass (SOMMER1977). The periphyton forms a sink for oxygen in the littoral zone of Lake Belau from the end of February through early

May. It can be assumed that its respiratory activity consumes more oxygen than the periphytic autotrophs produce throughout the year because its biomass is very small during summer and autumn due to grazing by Acroloxus lacustris and insect larvae (AsSHOFF 1990; OTTO 1991). Oxygen is not only consumed by the aquatic invertebrates but also by the bacteria that consume the dead leaves and leaf sheaths and the fungi which attack the growing parts of the plants as soon as they emerge above the surface of the water. However, the impact of the oxygen deficit on the waters of the littoral zone is slight, and the oxygen concentration in these waters during 1992 ranged between 6.2 to 14 mg 1-1, which was 53 to 130% of saturation.

Acknowledgement: I offer my sincere thanks to M. ZIEMERfor technical assistence.The investigation was supported by the BMBF as part of the project "Okosystemforschung im Bereich der BornhOveder Seenkette". The manuscript was prepared using the programme HSP III of the University of Hamburg. C. HECKMANcorrected the English manuscript.

References ALLEN, H.L. (1971): Primary productivity, chemo-organotrophy, and nutritional interactions of epiphytic algae and bacteria on macrophytes in the littoral of lakes. Ecol. Monogr. 41: 97-127. ASSHOFF,M. (1990): Die Mollusken des Belauer Sees und seines Abflusses (Schleswig-Holstein) unter Berticksichtigung produktionsbiologischerAspekte. Diplomarbeit, Kiel, 141 pp. ASSMAN,A.V. (1953): Rol vodoroslevykh obrastanii v obrazovanii organicheskogo veshchestva v Glubokom ozere. Trudy vsesoyuz. gidrobiol. Oshch. 5: 138-157. CARLTON,R.G. & WETZEL, R.G. (1987): Distribution and fates of oxygen in periphyton communities. Can. J. Bot. 65: 1031-1037. DODDS, W.K. (1992): A modified fiber-optic light microprobe to measure spherically integrated photosynthetic photon flux density: characterization in periphyton photosynthesis-irradiance patterns. Limnol. Oceanogr. 37:871-878. GESSNER, M.O., SCHIEFERSTEIN,B., MOLLER,U., BARKMANN,S. & LENFERS,U.A. (1996): A partial budget of primary organic carbon flows in the littoral zone of a hardwater lake. Aquatic Botany 55: 93-105. GLOWACKA,I., SOSZKA,G.J. & SOSZKA,H. (1976): Invertebrates associated with macrophytes. In: E. PIECZYNSKA(ed.), Selected problems of lake littoral ecology, pp. 97-122. Warsaw. Ho, S.-C. (1979): Structure, species diversity and primary production of epiphytic algal communities in the Schthsee (Holstein) Westdeutschland. Thesis, University of Kiel, 306 pp. JORGBNSEN, E.G. (1957): Diatom periodicity and silicon assimilation. Dansk Bot. Ark. 18 (1): 1-54. KOMARKOVA,J. & KOMAREK,J. (1975): Comparison of pelagial and littoral primary production in a South Bohemian Fishpond (CzechoslovaNa). Symp. Biol. Hung. 15: 77-95. - & MAaVAN,R (1987): The role of algae in the littoral zone of carp ponds. Arch. Hydrobiol., Beih. 27: 239-249. KOWALCZEWSKI,A. (1975): Periphyton primary production in the zone of submerged vegetation of Mikolajskie Lake. Ecol. Polska 23: 509-543. Limnologica 30 (2000) 2

173

KUHL, A. & LORENZEN,H. (1964): Handling and culturing of Chlorella. In: D.M. PRESCOTT(ed.), Methods in cell physiology. Vol.1, pp. 159-187. New York and London. LOHLEIN, B. (1996): Seasonal dynamics of aufwuchs Naididae (Oligochaeta) on Phragmites austral& in a eutrophic lake. Hydrobiologia 334: 115-123. (1998): Nematoden und Oligochaeten im Aufwuchs auf Schilf eines eutrophen Sees: Okologie, Populationsdynamik und die Rolle im trophischen Geftige. EcoSys Suppl. 24, 132 pp. MASON,C.E (1976): Relative importance of fungi and bacteria in the decomposition of Phragmites leaves. Hydrobiologia 51: 65-69. MESCHKAT,A. (1933): Vorlfiufige Mitteilungen fiber die Ergebnisse quantitativer hydrobiologischer Untersuchungen in den Phragmitesbestfinden des Balatonufers. Arb. Ungar. Forschungsinst. Tihany 6: 93-103. MEUCHE, A. (1939): Die Fauna im Algenbewuchs. Nach Untersuchungen im Litoral ostholsteinischer Seen. Arch. Hydrobiol. 34: 349-520. MEULEMANS,J.T. (1987): A method for measuring selective light attenuation within a periphytic community. Arch. HydrobioL -

1

0

9

:

1

3

9

-

1

4

5

.

(1988): Seasonal changes in biomass and production of periphyton growing upon reed in Lake Maarsseveen I. Arch. Hydrobiol. 112: 21-42. - & Roos, P.J. (1985): Structure and architecture of the peripbytic community on dead reed stems in Lake Maarsseveen. Arch. Hydrobiol. 102: 487-502. MOLLER, U. (1994): Seasonal development of epiphytic algae on Phragmites australis (CAv.)TRIN. ex STEUD.in a eutrophic lake. Arch. Hydrobiol. 129: 273-292. (1995): Vertical zonation and production rates of epiphytic algae on Phragmites australis. Freshwater Biol. 34: 69-80. (1996): Production rates of epiphytic algae in a eutrophic lake. Hydrobiologia 330: 37-45. NEELY, R.K. (1994): Evidence for positive interaction between epiphytic algae and heterotrophic decomposers during the decomposition of Typha latifolia. Arch. Hydrobiol. 129: 443457. (1995): Simultaneous use of ~4C and 3H to determine autotrophic production and bacterial protein production in periphyton. Microbial. Ecol. 30: 227-237. NUSCH, E.A. (1980): Comparison of different methods for chlorophyll and phaeopigment determination. Arch. Hydrobiol., Beth. Ergebn. Limnol. 14: 14-36. OTTO, C.-J. (1991): Benthonuntersuchungen am Belaner See (Schleswig-Holstein): Eine 6kologische, phaenologische und produktionsbiologische Studie unter besonderer Berticksichtigung tier merolimnischen Insekten. Thesis, University of Kiel, 139 pp. -

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PIECZYNSKA,E. & SZCZEPANSKA,W. (1966): Primary production in the littoral of several Mazurian lakes. Verh. Internat. Verein. Limnol. 16: 372-379. Roos, P.J. (1983): Dynamics of periphytic communities. In: R.G. WETZEL (ed.), Periphyton of freshwater ecosystems, pp. 5-10. The Hague. SAND-JENSEN, K., REVSBECH,N.P. & JORGENSEN,B.B. (1985): Microprofiles of the oxygen in epiphyte communities on submerged macrophytes. Mar. Biol. 89: 55-62. SOMMER, U. (1976): Untersuchungen tiber den Zusammenhang zwischen Periphytonproduktion und Schilfdichte. Sitzungsberichte Osterr. Akademie der Wissenschaften, mathem.-naturw. KI., Abt.1,185, H. 8-10, S. 250-258. - (1977): Produktionsanalysen am Periphyton im Schilfgtirtel des Neusiedler Sees. Sitzungsberichte 0sterr. Akademie der Wissenschaften, mathem.-naturw. KI., Abt.1,186, H. 6-10, S. 219-246. SPODNmWSKA,I., PIECZYNSKA,E. & KOWALCZEWSKI,A. (1975): Ecosystem of the Mikolajskie lake, primary production. Pol. Arch. Hydrobiol. 22: 17-37. STRASKRABA,M. (1963): Share of the littoral region in the productivity of two fishponds in southern Bohemia. Rozpr. Cesk. Akad. Ved. Rada Mat. Prir. Ved. 73 (13): 1-64. - & PIECZYNSKA,E. (1970): Field experiments on shading effect by emergents on littoral phytoplankton and periphyton production. Rozpr. Cesk. Akad. Ved. Rada Mat. Prir. Ved. 80 (6): 7-32. SZCZBPANSKA,W. (1968): Vertical distribution of periphyton in the Lake Mikolajskie. Pol. Arch. Hydrobiol. 15: 177-182. & SZCZEPANSKA,W. (1966): Primary production and its dependence of the quantity of periphyton. Bull. Acad. Pol. Sci., C1 I114: 45-50. WERNER, D. (1978): Regulation of metabolism by silicate in diatoms. In: G. BENDZ& I. LUNDQVIST(eds.), Biochemistry of silicon and related problems, pp. 149-176. New York. WETZEL, R.G. (1964): A comparative study of the primary productivity of higher aquatic plants, periphyton, and phytoplankton in a large, shallow lake. Int. Rev. ges. Hydrobiol. 49: 1-61. (1990): Land-water interfaces: Metabolic and limnological regulators. Verh. Internat. Verein. Limnol. 24: 6-24. WmL:AMS, RJ.LEB., RA:NE, R.C.T. & BRYAN,J.R. (1979): Agreement between the :4C and oxygen methods of measuring phytoplankton production reassessment of the photosynthetic coefficient. OceanoL Acta 2: 411416. -

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Author's address: Dr. UTE MULLER,Institut ffir Hydrobiologie und Fischereiwissenschaft, Hydrobiologische Abteilung, Universit~it Hamburg, Zeiseweg 9, D - 22765 Hamburg, Germany; e-mail: Utemueller @uni-hamburg.de