Ferdinand Schanz

Two different methods of evaluating nutrient limitations of periphyton bioassays, using water from the River Rhine and eight of its tributaries

An investigation was untertaken to evaluate the nutrient status of the River Rhine (two stations) and eight of its tributaries (total of ten samplings). Determinations of the following inorganic substances were made: PO4−3-P; NO3−-N; NO2−-N; NH4+ -N and Cl−. In addition, pH and carbonate alkalinity were measured. Bioassays to obtain the algal growth potential (AGP) were carried out using periphyton from the River Rhine. A linear relationship could be established between NO3−-N and the AGP, while the AGP showed a non-linear dependence on the PO43−-P concentration. The critical N/P ratio for N or P limitation of the algal growth in bioassays was evaluated graphically and by calculation. The results of the two methods are in good agreement: N is the limiting factor at NO3−N/PO43−-P ratios less than 10, while P is limiting at ratios greater than 20. At values between 10 and 20 neither N nor P can be supposed with certainty to be limiting.

Lake shore deterioration, reed management and bank restoration in some Central European lakes

Abstract The causes of lakeshore deterioration and reed decline are concisely summarised, and demonstrated with examples of seven Central European lakes (Germany: Havel lakes, Lake Constance-Untersee, Lake Constance-Obersee; Switzerland: Lake Zurich, Lake Biel, Lake Neuchâtel, Lake Geneva). The main causes are assumed to be bank erosion, lake eutrophication, mechanical damage to the reeds, and recreational activities. Countermeasures can be grouped into: reed protection against mechanical load (fences), wave dissipative constructions (refilling of substrate, brushwood fascine), nutrient export from the reeds (winter mowing), and supplementary measures (reed plantations, prohibition of access for the public). Favourable issues and undesired results are discussed. It is stated that there is a need for fundamental research and scientific surveillance of the restoration measures to avoid ill effects in the future.

Limnological description of the Lakes Zürich, Lucerne, and Cadagno

Abstract: This introductory article of the special GAP issue gives an overview on general limnological characteristics of the prealpine Lakes Zürich and Lucerne and the alpine Lake Cadagno and reports on the specific situation of primary production parameters during the international GAP Workshop in mid September 1999. Furthermore, it describes methods used for water analysis and fieldwork in these lakes.¶A comparison of data related to primary production in the three lakes in September 1999 during stratification shows that (i) phytoplankton community structure varied considerably between the lakes. The dominating algae were Planktothrix rubescens in Lake Zürich, various chrysophytes and diatoms in Lake Lucerne, and Echinocoleum elegans in Lake Cadagno, (ii) the euphotic zone in Lake Lucerne was considerably deeper (app. 15m) than in the other two lakes (app. 10 m), (iii) chlorophyll a standing crop was highest in mesotrophic Lake Zürich (August: 121 mg m-2), followed by oligotrophic Lake Lucerne (August: 75, September: 34 mg m-2) and mesotrophic Lake Cadagno (August: 33, September: 25 and 14 mg m-2), and (iv) areal primary production was highest in Lake Zürich (August: 105, September: 124 mg C m-2 h-1), followed by Lake Cadagno (August: 102, September: 52 mg C m-2 h-1) and Lake Lucerne (August: 90, September: 52 mg C m-2 h-1). Physiological parameters, determined in situ from P versus I relationships, showed a lower initial slope α in Lake Lucerne (August: 0.03, September: 0.02 mg C mg-1 chl a h-1μmol-1 m2 s) than in the other two lakes (Lake Zürich in August: 0.05, in September: 0.11; Lake Cadagno in August: 0.05, in September: 0.11 and 0.28 mg C mg-1 chl a h-1μmol-1 m2 s). Lake Zürich showed the lowest ANmax (August: 2.6, September: 3.2 mg C mg-1 chl a h-1, as compared to 5.9 - 7.4 mg C mg-1 chl a h-1 in the Lakes Lucerne and Cadagno), while in Lake Cadagno the highest inhibitory effects of C-assimilation were found (highest slopes of inhibition β, 0.007-0.011, as compared to 0.0003-0.0026 in the other two lakes), due to a higher UV-exposure in this alpine lake.

The effects of diel changes in photosynthetic coefficients and depth of Planktothrix rubescens on the daily integral of photosynthesis in Lake Zürich

Abstract: In late summer and autumn, before the vertical circulation reaches the thermocline, the phytoplankton population of Lake Zürich is dominated by the red-coloured filamentous cyanobacterium Planktothrix rubescens, which stratifies in the metalimnion at depths close to the photosynthetic compensation point. The filament volume concentration reached a maximum of 12 cm3 m-3; the depth of the maximum varied from 10.5 to 12.5 m. Changes in the depth distribution were attributed to a combination of (1) seiche movements, which raised or lowered the thermocline by up to 2 m over 36 h, and (2) flotation by the buoyant filaments relative to the isotherms, by up 0.4 m d-1. These changes caused a 2-fold change in insolation at the Planktothrix peak. Estimates were made of the daily integral of photosynthetic O2-production, ΣΣ(NP), by the population of P. rubescens over a period of four cloudless days. The estimates were calculated from measurements of surface irradiance (at 5-min intervals), vertical light attenuation, temperature, filament volume concentration and the photosynthesis/irradiance (P/I) curves of filaments concentrated from the metalimnion. Despite the similar, high insolation on each of the four days, the calculated values of ΣΣ(NP) varied from 9 to 53 mmol m-2 d-1, owing to the changing depth distribution of the filaments. Measurements of P/I curves of lakewater samples incubated at a depth of 11 m showed changes in the photosynthetic coefficients during the day. These also generated large changes in calculated values of ΣΣ(NP). The computer spreadsheet used to calculate ΣΣ(NP) was modified to incorporate time-based changes in the photosynthetic coefficients and vertical distribution of the organism. These refinements provide a more accurate description of photosynthesis by the deep-living P. rubescens, which adjusts its position by buoyancy regulation to exploit the light field in the metalimnion, where it outcompetes other phytoplankton.

Light climate as the key factor controlling the spring dynamics of phytoplankton in Lake Zürich

During the spring seasons of 1983, 1986 and 1987 the development of phytoplankton in Lake Zürich was investigated (from February to May) using samples taken at short term intervals. The aim was to describe the effects of the short term dynamics of environmental factors on the algal growth. The results could then be used to discuss the existing theories to assess the start of phytoplankton growth pulses in spring.Only 7 to 10 days without wind driven vertical mixing were required in spring to start the first growth pulse, despite of a still very unstable water column (sometimes inverse thermal stratification). Mainly flagellates andStephanodiscus hantzschii increased their biomass and achieved net growth rates of 0.1 and up to 0.65 d−1 respectively. During such a phase the mixing depth was always smaller than the euphotic depth. Later on, at the start of the spring bloom (=last growth pulse in spring before the clear water stage), the intensity of vertical mixing as well as the mixing depth were markedly reduced due to an increase in heat input and low wind. Then flagellates dominated (contribution up to 75.5% of the areal biomass reaching 60 g fresh weight m−2) and the growth rate rose to a maximum of 0.65 d−1.Standard models of critical depth considers that there is only a biomass increase if the mixing depth is smaller than the depth of a water layer positive balanced between production and respiration. This model for determining the beginning of a phytoplankton growth pulse in spring takes no account of the favorable light conditions for phytoplankton cells at calm and sunny days in February and March. The newly developed threshold value model takes these situations into account: It assumes that the phytoplankton biomass increases when the calculated effective light climate is equal or greater than a previously fixed threshold. The calculations are based on the mean light intensity within the mixed layer at windy days or within the euphotic depth (zeu) at calm days. In Lake Zürich a minimum of 0.2 106 J m−2d−1 (=0.9 mol quanta m−2d−1) has to be reached or surpassed in at least 3 days before an exponential increase of algal biomass can occur. The value does not depend on short term fluctuations in neither radiation nor mixing depth. It seems that this value is rather low comparing with those of investigations in other water bodies (up to 0.8 106 J m−2 d−1) but high related to values from algal cultures (0.02 106 J m−2d−1). As the weather can only be forecasted a few days ahead with any certainty the period for a more or less accurate prediction of an algal bloom is restricted to about 1 to 5 days.

Changes in photosynthetic properties measured by oxygen evolution and variable chlorophyll fluorescence in a simulated entrainment experiment with the cyanobacterium Planktothrix rubescens

Abstract: The metalimnion of lake Zürich is dominated by the red coloured cyanobacterium Planktotrix rubescens, where it lives in an extremely low light environment. Photosynthesis of the organism was studied using oxygen evolution and variable fluorescence. After transfer to 2m depth in the epilimnion, simulating an entrainment event that normally occurs in late summer, photoacclimation was followed.¶ The metalimnetic population had a very high photosynthetic efficiency, and the minimum quantum requirement varied between 7-12 photons (mol O2)-1. Upon transfer to high light the quantum requirement increased, which was interpreted as inactivation of a number of photosystem II (PSII) units. At the first entrainment we observed only inactivation of PSII, causing a decrease in the slope of the photosynthesis light curve (both for oxygen evolution and photosynthetic electron transport by PSII (ETR)), without affecting the maximal rate of oxygen evolution (PBmax), suggesting no effect on CO2-fixation. During the 2nd entrainment experiment we observed both an inactivation of the number of PSII as well as a decrease in PBmax. In both cases the ETR-based estimates of oxygen evolution (PB) overestimated the measured rate of PB, indicating the operation of alternative electron sinks. Especially at high light respiratory processes were seemingly stimulated.

Influence of environmental factors on the phytoplankton spring bloom in Lake Zürich

The development of the phytoplankton spring bloom in Lake Zürich in 1983 was investigated using frequent sampling with short sampling intervals, which allowed the influence of short-term meteorological events on the bloom to be studied. The bloom can be divided into four distinct growth periods (March 1–April 28) and a period of collapse (April 29–May 16). During the four growth periods, growth pulses were found to be associated with high solar radiation, little wind and a shallow mixed layer, whereas stagnation or loss was associated with strong winds and a consequent deepening of the mixed layer, resulting in an unfavourable effective light climate. The population collapse was brought about by zooplankton grazing, possibly coupled with nutrient limitation and other factors.

Stability of toxin gene proportion in red-pigmented populations of the cyanobacterium Planktothrix during 29 years of re-oligotrophication of Lake Zürich

BackgroundHarmful algal blooms deteriorate the services of aquatic ecosystems. They are often formed by cyanobacteria composed of genotypes able to produce a certain toxin, for example, the hepatotoxin microcystin (MC), but also of nontoxic genotypes that either carry mutations in the genes encoding toxin synthesis or that lost those genes during evolution. In general, cyanobacterial blooms are favored by eutrophication. Very little is known about the stability of the toxic/nontoxic genotype composition during trophic change.ResultsArchived samples of preserved phytoplankton on filters from aquatic ecosystems that underwent changes in the trophic state provide a so far unrealized possibility to analyze the response of toxic/nontoxic genotype composition to the environment. During a period of 29 years of re-oligotrophication of the deep, physically stratified Lake Zürich (1980 to 2008), the population of the stratifying cyanobacterium Planktothrix was at a minimum during the most eutrophic years (1980 to 1984), but increased and dominated the phytoplankton during the past two decades. Quantitative polymerase chain reaction revealed that during the whole observation period the proportion of the toxic genotype was strikingly stable, that is, close to 100%. Inactive MC genotypes carrying mutations within the MC synthesis genes never became abundant. Unexpectedly, a nontoxic genotype, which lost its MC genes during evolution, and which could be shown to be dominant under eutrophic conditions in shallow polymictic lakes, also co-occurred in Lake Zürich but was never abundant. As it is most likely that this nontoxic genotype contains relatively weak gas vesicles unable to withstand the high water pressure in deep lakes, it is concluded that regular deep mixing selectively reduced its abundance through the destruction of gas vesicles.ConclusionsThe stability in toxic genotype dominance gives evidence for the adaptation to deep mixing of a genotype that retained the MC gene cluster during evolution. Such a long-term dominance of a toxic genotype draws attention to the need to integrate phylogenetics into ecological research as well as ecosystem management.

The effects of artificial ammonium enhancement on riverine periphytic diatom communities

An experiment to ascertain the influence of artificially enhanced ammonium concentrations on riverine periphytic diatom communities was conducted during an 80 day period in winter 1988/89 (temperature: 5°C). During an initial 47 day enrichment phase, ammonium chloride at different concentrations was added to O2-saturated river water in experimental channels. Compared to a control, the addition of 1.2 mg NH4+-N·l−1 resulted in only slight changes in the species composition of the diatom community. The addition of 5.1 mg NH4+-N·l−1 and more (≥60 µg NH3-N·l−1) resulted in a decrease in the biomass and a drastic change in the species composition. After the 42 day enrichment period, the diatom speciesFragilaria capucina var.vaucheriae, Navicula saprophila, Navicula atomus andGomphonema parvulum, all of which are known to be tolerant to organic pollution, were found with relative abundances of 44.8%, 35.6%, 2.3% and 1.5%, respectively. Changes in species composition of the periphytic diatom communities occurred within the first two weeks of the subsequent recovery phase. After a month of recovery, all periphytic diatom communities exhibited a high degree of structural similarity with the control.

Prediction of algal growth in batch cultures

The growth of algae in batch cultures is often well characterized by the logistic growth function. The equation used contents three parameters which have to be estimated. Two methods are presented: The linearizing procedure, and the direct method of least squares. We give an example for comparing several logistic growth curves.