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BISSINGER, V.; TITTEL, J.: Process rates and growth limiting factors of planktonic algae (Chlamydomonas sp.) from extremely acidic (pH 2,5 - 3) mining lakes in Germany ; BORK, H.-R. et al.: Erodierte Autos und Brunnen in Oregon, USA ; BRONSTERT, A. et al.: Bewirtschaftunsmöglichkeiten im Einzugsgebiet der Havel ; JELTSCH, F. et al.: Beweidung als Degradationsfaktor in ariden und semiariden Weidesystemen ; JELTSCH, F. et al.: Entstehung und Bedeutung räumlicher Vegetationsstrukturen in Trockensavannen: Baum-Graskoexistenz und Artenvielfalt ; JESSEL, B. et al.: Bodenbewertung für Planungs- und Zulassungsverfahren in Brandenburg ; JESSEL, B.; ZSCHALICH, A.: Erarbeitung von Ausgleichs- und Ersatzmaßnahmen für die Wert- und Funktionselemente des Landschaftsbildes ; RÖßLING, H. et al.: Umsetzung von Ausgleichs- und Ersatzmaßnahmen beim Ausbau der Bundesautobahn A 9 ; SPINDLER, J.; GAEDKE, U.: Estimating production in plankton food webs from biomass size spectra and allometric relationships ; TIELBÖRGER, K. et al.: Sukzessionsprozesse in einem Sanddünengebiet nach Ausschluß von Beweidung ; TIELBÖRGER, K. et al.: Populationsdynamische Funktionen von Ausbreitung und Dormanz ; TIELBÖRGER, K. et al.: Raum-zeitliche Populationsdynamik von einjährigen Wüstenpflanzen ; TITTEL, J. et al.: Ressourcennutzung und -weitergabe im planktischen Nahrungsnetz eines extrem sauren (pH 2,7) Tagebausees ; WALLSCHLÄGER, D.; WIEGLEB, G.: Offenland-Management auf ehemaligen und in Nutzung befindlichen Truppenübungsplätzen im pleistozänen Flachland Nordostdeutschlands: Naturschutzfachliche Grundlagen und praktische Anwendungen ; WEITHOFF, G.; GAEDKE, U.: Planktische Räuber-Beute-Systeme: Experimentelle Untersuchung von ökologischen Synchronisationen
Water column mixing is known to have a decisive impact on plankton communities. The underlying mechanisms depend on the size and depth of the water body, the nutrient status, and the plankton community structure and they are well understood for shallow polymictic and deep stratified lakes. Two consecutive mixing events of similar intensity under different levels of herbivory were performed in enclosures in a shallow, but periodically stratified, eutrophic lake, in order to investigate the effects of water column mixing on bacteria abundance, phytoplankton abundance and diversity, and rotifer abundance and fecundity. When herbivory by filter-feeding zooplankton was low, water column mixing provoking a substantial nutrient input into the euphotic zone, led to an intense net increase of bacteria and phytoplankton biomass. Phytoplankton diversity was lower in the mixed enclosures than in the undisturbed ones owing to the larger contribution of a few fast-growing species. After the second mixing event at high biomass of filter-feeding crustaceans, the increase of phytoplankton biomass was lower than after the first mixing, and diversity remained unchanged as the enhanced growth of small fast-growing was prevented by zooplankton grazing. Bacteria abundance did not increase after the second mixing, when cladoceran biomass was high. Rotifer fecundity indicated a transmission of the phytoplankton response to the next trophic level. Our results suggest that water column mixing in shallow eutrophic lakes with periodic stratification has a strong effect on the plankton community by enhanced nutrient availability rather than resuspension or reduced light availability. This fuels the basis of the classic and microbial food chain via enhanced phytoplankton and bacteria growth, but the effects on biomass may be dampened by high levels of herbivory.
Planktische Räuber-Beute-Systeme : experimentelle Untersuchungen von ökologischen Synchronisationen
(2000)
Phytoplankton dynamics in a shallow eutrophic lake were investigated over a 3-year period with respect to environmental forces which drive species composition and diversity. Diversity was calculated on the basis of species as well as on the basis of their functional properties (the C-R-S-concept). Stratification and water column mixing had a strong impact on phytoplankton composition. Application of a similarity-diversity model revealed that a high diversity was a transient non-stable state, whereas drastic changes or long-lasting stable environmental conditions are characterized by low diversity. This effect was more pronounced when the diversity was calculated on the basis of the phytoplankton species functional properties. Thus, this functional approach supports the intermediate disturbance hypothesis from field data.
In recent years most studies of the benthic microbial food web have either been descriptive or were restricted to the measurement of within sediment process rates. Little is known about benthic-pelagic coupling processes such as recruitment. We, therefore, developed an ex situ core incubation procedure to quantify the potential for microbial recruitment from the benthos to the pelagic in an acidic mining lake, Mining Lake 111 (ML 111; pH 2.6), in eastern Germany. Our data suggest that considerable zooplankton recruitment from the benthos takes place. Heliozoan and rhizopod recruitment in both summer and winter sediment cores was highest when they were incubated at 20°C. Maximum heliozoan recruitment was 23 (± 9 s.e.) individuals cm-2 d-1 (40% initial standing stock daily) in the winter 20°C incubation. Maximum rhizopod recruitment was 6 (± 2 s.e.) individuals cm-2 d-1 in the summer 20°C incubation. Little or no recruitment was apparent for either taxa when winter cores were incubated at 5°C, implying a temperature cue. Conversely, the rotifer, Cephalodella hoodi, exhibited a maximum recruitment of 6 (± 2 s.e.) individuals cm-2 d-1 during the winter 5°C incubation, representing 30% of initial standing stock daily, but little recruitment when incubated at 20°C. Cephalodella may have responded to an increased winter benthic food supply; in situ winter Chl a concentrations in the benthos were 3.4 times higher than those in the summer. The importance of this was reinforced by the poor pelagic food supply available in ML 111. In situ, Heliozoa, rhizopods and Cephalodella were first observed in the epilimnion of ML 111 in spring or early summer, suggesting active or passive recruitment following lateral transport from littoral sediments. Benthic-pelagic coupling via recruitment is potentially important in understanding the pelagic food web in ML 111 and warrants further investigation in this and other aquatic environments.
A characteristic vertical sequence of phytoplankton populations was observed below the metalimnetic oxycline of a stratified, mesotrophic lake. Ceratium spp., Closterium acutum and Aphanizomenon flos- aquae were present in the epilimnion but had distinct population maxima in the microaerobic chemocline. Below these populations, Cryptomonas phaseolus, Planktothrix clathrata, Pseudanabaena catenata and Limnothrix sp. followed each other in the transition zone between the chemocline and the sulphide-containing hypolimnion. The dominating populations of P. clathrata and P. catenata caused a deep chlorophyll maximum. Phytoplankton structure was determined by the vertical gradients of sulphide and light. Compared with the epilimnion, nutrient availability was not fundamentally better below the oxycline but the algae might have benefited from reduced grazing pressure in their habitat.
1. This is a discussion of the applicability to the phytoplankton of the concepts of 'Plant Functional Types' (PFTs) and 'Functional Diversity' (FD), which originated in terrestrial plant ecology. 2. Functional traits driving the performance of phytoplankton species reflect important processes such as growth, sedimentation, grazing losses and nutrient acquisition. 3. This paper presents an objective, mathematical way of assigning PFTs and measuring FD. Ecologists can use this new approach to investigate general hypotheses (e.g. the intermediate disturbance hypothesis (IDH), the insurance hypothesis and synchronicity phenomena), since, for example, in its original formulation the IDH makes its predictions based on FD rather than species diversity.