Preface: Waters are habitats!
A lake from the perspective of algae (Original title: ‘Ein See aus der Perspektive der Algen'), by Katrin Teubner:
The algae are seen in their microscopic form in front of the painting, as at this moment the water transparency is measured with a Secchi disk (see also the photo below). People are seen in the background leftside on a sampling boat on lake surface and are just putting down the disk on the rope.
As on the painting, the main focus of this website is on photosynthetic microbial organisms, which are algae and cyanobacteria. These primary producers play a key role in lakes and rivers.
Issues linked to algae and cyanobacteria discussed on this website are for example:
How do photosynthetic microbes utilize short-lived nutrient patches?
Why can a large nutrient input (eutrophication) rapidly change the colour of the water body?
Why may a lake restoration fail or why is this a long-lasting process that can take years?
Walking on the lake shore, how can we easily identify that the surface scum is mainly formed by cyanobacteria?
What are the climate responses on the lake and photosynthetic microbes?
How can natural and artificial freshwaters be assessed by their microbial community of algae and cyanobacteria?
How can we use microbes and algae to naturally clean up the swimming ponds and what are the key rules to maintain a swimming pond in good condition? Lakes and rivers are not just basins to retain or to facilitate the passage of water through the landscape – they are certainly much more. Water is life! The water in lakes and rivers is alive! Natural and artificial waters can be valuable habitats for many organisms, from an overwhelmingly large number of microscopic organisms to a variety of sizeable aquatic plants and animals. We may observe rare plants and animals on a boat trip. So whether it is the tropical looking water pineapple (Stratiotes aloides) and the spectacular antler freshwater sponge (Spongilla lacustris) in the shallow water or the exotic looking kingfisher (Alcedo atthis) in the reed belts of small lakes and rivers in the north temperate zone, we are fascinated. We are delighted about porpoises (Neophocaena phocaenoides) that are just seen in front of the boat, leaping in their natural habitat of subtropical great lakes. Many of the nature lovers are excited by detailed investigation of aquatic life. Creating a small pond in the wood or our garden has its own fascination. We remember ponds, lakes, streams and rivers that have attracted us in our childhood or where we like to go for a walk. Lakes and rivers are part of the life of people, cultural customs and traditions around the world.
Many healthy freshwaters are sustainably used as a valuable source for food and drinking water. Other freshwaters are heavily modified by constructions and serve for navigation or are used as reservoirs for flood control and drinking water basins. Environmental pollution of freshwaters gives another sign of human impact on these ecosystems and has also many consequences. One consequence is eutrophication where an artificially high input of main nutrient elements such as phosphorus and nitrogen affect an aquatic ecosystem. The concentrations of nutrients in an eutrophied lake or river are therefore, much higher than those found in the natural background of these ecosystems. High nutrient loads, e.g. by untreated waste-water inflow, generate an ‘extreme’ environment. Such nutrient enrichment is often associated with decreasing water transparency. The water body looks turbid. The water appears intensively coloured in yellow-green, dark-green or even Bordeaux-red, depending on which algae or cyanobacteria are most supported by an enhanced nutrient input. Lakes and rivers are then far from conditions of their ‘healthy ecosystem’ which are, for example, defined by a good or excellent ecological status according to national assessment measures (see alpine Attersee S and Traunsee S). In most cases, the reason of lake or river pollution is not found in the lake or in the river itself but is located in its huge catchment. In-lake restoration alone is hence not sufficient but needs to be accompanied by a successful restoration management in the catchment (details about an internal restauration see on the page about the urban oxbow lake Old Danube S).
Eutrophication of freshwaters is not a regional but a common phenomenon in urban regions worldwide. The health risks caused by a toxic scum, formed for example by the cyanobacteria Microcystis spp., Planktothrix rubescens, Cylindospermopsis raciborskii, Aphanizomenon spp. and Anabaena spp., are recognized in numerous countries around the globe (blooms of these cyanobacteria see on pages about Bergknappweiher S, Dianchi S, Grosser Mueggelsee S, Taihu S, Old Danube S, Ammersee S and Mondsee S). Lake and river monitoring and restoration programs are then often initiated to ensure an improvement of water quality. Photographs with a coloured water surface scum on this website may hence provide a historical view while these aquatic ecosystems are nowadays already successfully restored. Other heavily eutrophied inland-waters shown here still need an improvement of water quality. Even if much has already been done to achieve milestones of basic restoration for many lakes and rivers; other eutrophied inland waters are yet far from their ecological reference status. The success of restoration is usually mirrored by an increase of water transparency throughout growing season, mainly due to the avoidance of a further massive development of algae or cyanobacteria. The fundamental mechanisms behind such a basic restoration are quite well understood. Nutrient addition experiments in freshwaters, also called fertilizing experiments or nutrient addition bioassays were commonly applied to understand basically phytoplankton growth and species shifts within phytoplankton assemblages under nutrient-rich conditions. The restoration of highly eutrophic inland waters has been usually achieved by a drastic reduction of nutrient loading from the main external and internal sources and treatment by bio-manipulation. The costs of such a restoration program, which includes the management of the lake or river and its catchment, however, are substantial.
'Secchi disk' on lake shore; inset: Secchi
disk and light
meter in the lab:
The growth of photosynthetic microorganisms living in the water column depends on the underwater light conditions. Estimating underwater light climate hence is key to assess productivity of freshwaters. The simplest way to measure underwater light or water transparency is to use a Secchi disk. This disk is on a leash lowered down in the deep water until it is no longer visible. When pulling up the Secchi-disk back to the water surface, the water depth is measured, in which it is first seen again. This depth is called the Secchi depth (or Secchi depth transparency). In case of the alpine Lake Mondsee, the annual mean of Secchi depth is 3.3 m. Measuring the underwater light with a light meter, the annual mean of the depth where 1% of light is yet available for photosynthesis is about 11 m in Lake Mondsee. This illuminated depth layer is called euphotic zone where microbial community photosynthesis is predominant against microbial community respiration (see further the depth layers of 10-12% and 0.1% light for pronounced growth of photosynthetic microorganisms described for the two lakes Mondsee S and Ammersee S on this website). The euphotic depths and Secchi depths correspond well each other in a lake. The euphotic depth can be hence roughly estimated by Secchi depth. In Lake Mondsee the euphotic depth is on average 3.42 times deeper than Secchi depth during the growing season that is from late spring to early autumn in the temperate lakes. This factor may vary slightly among seasons and can be also moderately different among years in a one lake or among various lakes of the same lake type. In other freshwaters the control of cyanobacterial and algal blooms, however, has become more complex and still needs to be tackled to protect the freshwaters for next future generations. An ‘unexpected’ new mass development of photosynthetic microorganisms may occur even the lake restoration has previously been successfully implemented. The re-occurrence of blooms after basic lake restoration is then not due to large nutrient surplus as described in the previous paragraph but coincides with growth periods under nutrient limitation (!). Advanced ecosystem studies could show that rapid nutrient cycling counteracts the nutrient deficiency. As nutrient pools decrease, microbial loop and increased grazing pressure become important for an accelerated nutrient cycling. The nutrient elements are thus made re-available again sooner for phytoplankton growth than in nutrient-rich ecosystems. The effective nutrient cycling can be achieved by physiological responses on the nutrient-producer interface, e.g. by an enhanced release of extracellular enzymes from both algae and bacteria (see e.g. Fig.4 F in Teubner et al. 2003 R). In addition, on the producer-consumer interface, the coupling between biomass net changes of producers (phytoplankton) and consumers (zooplankton) becomes evident and becomes more closely correlated with increasing nutrient limitation. Simultaneously, the ratio of zooplankton carbon to producer carbon increases (see e.g. Fig.5 A and B in Teubner et al. 2003 R). An ‘ecosystem response’, as briefly described here for two interfaces, is actually the outcome of manifold interactions between living micro-organisms and their aquatic environment. While shifts in microbial communities are well described over large temporal and spatial scales (studies of freshwaters along transects around the world over months to many years, nutrient addition bioassay experiments assessing species shifts within microbial assemblages), the dynamic at short ecological scales most relevant for the life-time of small microbial organisms is less well known. We might even could say that focusing on studies, which are lasting over periods of several generations of micro-organisms, indeed obscure the view that ORGANISMS are being alive as they fail to capture the main intention of biologists, namely to understand how organisms cope with their ‘actual’ environment during their life-time. We assume that microbial primary producers live one day or a few days only under favourable growth conditions in a lake before they disappear or undergo a cell division. How do these microorganisms cope with their environment during their short lifetime of just a one day-night cycle? We need to better understand the biota-environment interactions in aquatic ecosystems lasting seconds to minutes or few hours to capture the ‘life’ of these short-living microorganisms. Indeed, a new perspective on the interaction of microorganisms with their environment in biologically relevant, spatially and temporally small scales comes from recent insights in microscale patchiness in aquatic environments. This perspective on small-scale phosphorus resources is most relevant for the growth of algae under phosphorus limitation in aquatic systems (and not for algal growth in nutrient-rich water basins where phosphorus is not the growth limiting factor for primary producers at all). In the following two aspects will briefly outline on why and how algae can efficiently utilize even small and short-lived phosphate sources.
One aspect relates to the patchiness of phosphate supply in the aquatic environment. Phosphate can be supplied simultaneously in a continuous and discontinuous way in aquatic systems. One of the main sources of phosphorus point concentrations is likely to be by excretion of aquatic animals. It is worth noting that the number of small-bodied animals such as flagellates and ciliates are much more abundant in aquatic ecosystems than large-bodied animals, e.g. mussels and fish. Hence we might expect an almost countless high frequency of small point source excretions (this frequency largely varies with the life-activity of these animals during day-night cycle) while the release of relative large concentrations by individual excretions will be less common. Experimental studies found evidence that rapid kinetic response enables photosynthetic microorganisms to exploit even small point phosphate concentrations as e.g. released by many zooplankton and all larger animals. These small amounts of phosphate can more rapidly incorporated by P-limited algae than these would be dissipated by physical processes as radial diffusion (Teubner et al. in prep.).
The second aspect refers closer to the nature of phosphorus uptake through the membranes of algae. Phosphate can be only incorporated by an active transport. The phosphate uptake is thus driven by metabolic energy, which can just be accomplished by entropy production and is accordingly quite different from the passive transport of ions or the typical situation for enzyme-substrate complexes. The uptake of SMALL portions of phosphate concentrations in the nanomolar range, which takes only few minutes, can be assumed to follow the thermodynamic flow-force relationship. The linear relationship between thermodynamic flow and force, which is resetting the uptake system to the stable steady state, follows the Prigogine's principle of MINIMUM entropy production (Glansdorff & Prigogine 1971). It is worth mentioning here that the P-uptake is not necessarily linked to growth (two compartment Droop-model, Droop 1973). It is thus different from all processes that are linked to build up NEW dissipative structures and that are when accomplished by rules of MAXIMUM entropy production, as discussed e.g. for ‘growth’ and ‘fitness’ in the literature (e.g. Glaser 2005). High-resolution time series measurements of the uptake responses to a series of nanomolar phosphate supply (lab experiments on superimposed and randomised sequences of P-supply) are aimed to mimic the exploitation of ephemeral phosphate patches by algae. Empirical evidence by such laboratory measurements suggests that the amount of small-portions of phosphate incorporated by P-limited algae can be the same, no matter whether phosphate is supplied by a number of small portions or by a few additions by larger concentrations (Teubner et al. in prep.). The uptake behaviour, however, results in the different effort per incorporated phosphate molecule. An amount of phosphate incorporated by successively added small portions results in a correspondingly lower entropy production than an incorporation after an addition of a few larger quantities (Teubner et al., in prep.). In other words, algae may, indeed, benefit from utilizing small-point phosphate sources that are supplied in form of sequences by the excretion of plenty of planktonic animals (see also above about the predominance of zooplankton with decreasing phosphorus pool after lake restoration). Algae are able to optimise their phosphate uptake kinetics in accordance to recent history of nutrient supply pattern (Teubner et al. in prep.). Such experiments provide evidence that small algal organisms are indeed able to adjust rapidly their phosphate uptake behaviour to the actual environment during their short life-span. The response of efficient P-acquisition by algae provides thus a further way, how biota is counteracting the nutrient deficiency in an aquatic system.
Studies on the dynamic at short ecological scales which are most relevant for the life-time of small microbial organisms are still rare. They would assist in determining why some long-term developments in lakes and rivers do not respond properly to restoration or why surface scum or blooms suddenly re-appear even when the water looks ‘crystal-clear’ most time the growing season. Water that is coloured by algae and suffers from dissolved components such as algal toxins or other algal compounds changing the taste and odor of water can be used neither as drinking water, nor does it meet the high standards of an attractive resort in tourist areas. In artificial water bodies in particular e.g., naturally landscaped swimming ponds, an unwanted development of algae and cyanobacteria at a relatively low nutrient level may occur under circumstances where the creation of such a pond was not sustainable undertaken. An ‘unexpected’ biomass development of algae and cyanobacteria can occur within the first season in a small pond and in about two to three years in a larger swimming pond system, respectively, after these water basins have been created. Artificial swimming ponds are commonly more vulnerable to even an even small nutrient input than ‘real’ ecosystems like lakes or ponds (see page swimming ponds S). Such nutrient-related issues and other aspects of the development of primary producers in freshwaters are described on this website in a more detail for different water types. A list of key words that is provided on the right-side column on the site about the author’s publications S, introduces in more detail the topics that are discussed on this website about lakes, rivers and other water basins.
cited References: preface to the website
Glaser, R. 2005. Biophysics. Springer Berlin Heidelberg New York , rev. 5th edition, pp 361.
Teubner, K., N. Crosbie, K. Donabaum, W. Kabas, A. Kirschner, G. Pfister, M. Salbrechter & M. T. Dokulil. 2003. Enhanced phosphorus accumulation efficiency by the pelagic community at reduced phosphorus supply: a lake experiment from bacteria to metazoan zooplankton. Limnol Oceanogr 48 (3): 1141-1149. Look-Inside OpenAccess
Droop, M.R. 1973. Some thoughts on nutrient limitation in algae. Journal of Phycology 9: 264-272.
Glansdorff, P. & I. Prigogine. 1971. Thermodynamic Theory of Structure, Stability and Fluctuations. Wiley-Interscience, New York, pp 306.
cited References: CV
↑ Teubner, K. 2004. More or less? Smaller or bigger? How relevant are relative changes in aquatic ecosystems? Habilitation thesis on Ecological Stoichiometry, Fac. of Sciences and Mathematics, Institute of Ecology and Conservation Biology University Vienna: 188 pp.
↑ Teubner, K. 1996. Struktur und Dynamik des Phytoplanktons in Beziehung zur Hydrochemie und Hydrophysik der Gewässer: Eine multivariate statistische Analyse an ausgewählten Gewässern der Region Berlin-Brandenburg. Ph.D thesis, Dept. Ecophysiology, Humboldt University Berlin: 232 pp. Look-Inside FurtherLink
↑ Pabst, K. 1985. Ökologische Untersuchungen als Grundlage für landeskulturelle Maßnahmen im Bereich der Michelner Teiche (Kreis Koethen). Diploma thesis on Vegetation Survey of reed belts of ponds, Dept. Biology and Chemistry, Teacher training college (Paedagogische Hochschule ‘W. Ratke’), Koethen / Sachsen-Anhalt, Germany: 60 pp. Look-Inside