Search

Since there is no life on earth without water, this opinion paper defines the likely consequences of a changing climate. Rise in global air temperature leads to increase in water temperature. Changes associated with precipitation, extreme events and catchment processes alter the hydrological cycle. Population growth increase water demand while climate warming enhances water scarcity leading to problems with water quantity, availability and water quality. Primary production by planktonic and sessile algae creates the basis for potential ecohydrological problems associated with the predicted changes in inland waters which are then outlined and discussed. Production and growth of algae also affects other trophic levels in the food web. Climate change will also promote non-native species to invade and occupy new previously unsettled ecosystems. To cope with these challenges, various efforts are needed based on ecohydrological principles. Some examples already under way are mentioned and some possible future trends are outlined. [ABSTRACT FROM AUTHOR]

Shallow polymictic lakes are very abundant in many regions of the world, they are more numerous than deep lakes and are of great importance especially in densely populated areas even when small. Their ecology differs from stratified lakes in many ways. During the eutrophication process, lakes may change from a clear water, macrophyte dominated state to an algal dominated state, a process known as the concept of `alternative stable equilibria'. The usefulness of this concept as a descriptor for the eutrophication process and as the basis for rehabilitation of lakes is tested on long-term data from two contrasting case study sites using a novel multivariate bubble-plot technique. In one case the concept proved to be useful and successful while it could not be applied to a large shallow turbid lake. The equilibrium concept is then generalised using further examples. Shallow lakes which are either macrophyte dominated or light limited because of high inorganic background turbidity have ratios of total phosphorus (TP) to algal Chlorophyll-a at or below 3:1. Deep oligotrophic or algal dominated lakes in contrast exhibit ratios between 3:1 and 1:1. Alternative stable equilibria of macrophyte or algal domination can occur within the same water-body at various locations, at different times of the year or during trophic development. [ABSTRACT FROM AUTHOR]

The vertical distribution pattern of algal species, chlorophylls and specific carotenoids present in the dimictic pre-alpine Ammersee (Bavaria, Germany) are given for the year 2001. A detailed taxonomic list of the phytoplankton species is recorded, along with light micrographs and detailed descriptions of the flagellates. A deep chorophyll maximum, mainly built by Planktothrix rubescens, was common in this deep mesotrophic lake. The three most dominant species among 83 identified taxa alternated seasonally and reached significant biovolumes in both the epi- and the metalimnion (Planktothrix rubescens > Ceratium hirundinella > unicellular centric diatoms > Asterionella formosa > Fragilaria spp. > Anabaena lemmermannii > Phacotus lenticularis and less frequent dominant was Rhodomonas minuta). We define a steady state phytoplankton assemblage in Ammersee as a stable community in terms of species composition and standing crop. The stability of species composition was measured by Bray-Curtis similarity between monthly samples and indicate the change of individual biovolumes of species from month to month. The stability of standing crop was evaluated by the net change of total biovolume for the same time intervals. Focussing on steady state phytoplankton assemblages we compared three spatially heterogeneous environments for vertical niche separation within the top 12 m: the euphotic epilimnion (2 and 5 m), the euphotic metalimnion (7 m) and the metalimnion below the euphotic zone with dim-light less than 1% (10 and 12 m). The definition of a steady state assemblage on both ends hold true only for metalimnetic layers at dim-light levels below 1% in Ammersee. At this metalimnetic layer more than 80% similarity in phytoplankton composition between successive monthly samples was reached, associated with almost zero net changes of total biovolume only. The greater the contribution of the three most dominant taxa to biovolume, the higher were the Bray-Curtis similarities at metalimnetic depths below the euphotic zone. Zooplankton biomass had very little effect on species assemblages in the metalimnion, while parameters related to stratification (Schmidt stability) as well as those of trophy (TP, Chl) correlated with species changes. The similarity values between successive monthly samples from all the euphotic layers never reached more than 60% and were usually significantly lower, even if biovolume net changes were around zero. Both the high fluctuations of the ratio of photosynthetic versus photo-protective carotenoids (PSC:PPC) and the statistical significance of correlations between the change of species and environmental-biotic parameters separate the euphotic layer of the top 7 m as a homogenous community from deeper strata. At all sampling depths within this euphotic zone the increase of sunshine duration was associated with an increase of the carotenoid ratio PSC:PPC, but no relationship was found for the deeper layers. The change of species in the euphotic layer was not significantly related to thermal stability, TP or the dominance structure of phytoplankton, but linked with the zooplankton biomass and therefore seemed to be top-down controlled. From our observations, we can conclude that only during stratification and only in the metalimnion below the euphotic zone steady state assemblages can be expected in the deep mesotrophic Ammersee. [ABSTRACT FROM AUTHOR]

The hypothesis that both photosynthesis and pigment pattern are more reflective of size related strategies than taxonomic composition of the assemblages was tested under natural conditions in alpine lakes during fall 1999. The small size fraction (< 10 μm) in Lake Lucerne, Mondsee and Traunsee and in an additional incubator experiment contributed 55-67 % to the total integral of chlorophyll-a and photosynthesis per m2. The photosynthetic depression induced by UV-A in Lake Lucerne, measured during the 7th GAP-workshop, markedly increased to 65 % with PAR up to 500 μmol m-2 s-1. At super-saturating light intensities near the surface, UV-A inhibition further increased marginally to 69 %. Effects of light acclimation and pigment adaptation on photosynthetic rates and efficiencies of phytoplankton indicated size related strategies that were more important than the taxonomic composition of the assemblage measured in Traunsee and Mondsee. Algal communities and small size fractions (<10 μm), that had a high maximum light utilisation coefficient ( $ \alpha $ *) were adapted to low light by high ratios of chlorophyll- a to photo-protective $ \beta $ -carotene. Algae at high solar radiation and of large size (>10 μm) were photosynthetically less efficient but high light adapted having low ratios of chlorophyll- a to $ \beta $ -carotene. In contrast to low light adapted small cells the high light adapted large-cells increased their relative proportion of photo-protective carotenoids above saturating light levels. At light limitation in deeper water layers lipophilic accessory photo-synthetic versus photo-protective pigments increased for all fractions. [ABSTRACT FROM AUTHOR]