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A preface to the journal "Hydrobiologia" is presented.

The paper presents a new index for assessing water trophy and organic pollution. It is based on only true aquatic macrophytes – being calculated on species score, coefficient of ecological amplitude and degree of cover. The method was tested in an acidic lowland river and an alkaline mountain river, and is shown to be validated by bio-indication scales based on macrophyte communities. The practical interest is discussed regarding the Water Framework Directive. [ABSTRACT FROM AUTHOR]

The present paper reports the results on the occurrence and composition of steady state phytoplankton assemblages in the shallow water bodies of 18 Bulgarian natural wetlands. They all differ in their morphometry, hydrology and trophic state. Steady states were identified according to Sommer & Padisák (1993) when (i) 1, 2 or 3 species of algae contribute more than 80% of total biomass, (ii) their existence or coexistence persists for long enough (more than 1–2 weeks) and (iii) during that period the total biomass does not increase significantly. These situations were rare and were dominated by 7 stress-tolerant, colony-forming and ruderal disturbance-tolerant cyanoprokaryotes ( Microcystis aeruginosa, Microcystis wesenbergii, Anabaena spiroides, Anabaenopsis arnoldii, Aphanizomenon flos-aquae, Aphanizomenon gracile and Cylindrospermopsis raciborskii). The equilibrium states had been registered only during hypertrophic conditions in three stressed and frequently disturbed shallow water bodies and were related to the summer – late summer season. [ABSTRACT FROM AUTHOR]

This study tests if rainfall regime and estuary hydrodynamics affect ecological picocyanobacterial patterns. We statistically related rainfall with picocyanobacteria (flow cytometry) and water quality data from a seven-year-long survey of Guanabara Bay (GB). The quality of GB's water varies spatially, depending on pollution hotspots, tidal influence, and water circulation patterns. It also varies seasonally, depending on the rainfall regime. Our results showed that rainfall regularly makes water quality and microbiology of the inner estuarine regions more like the tributaries' environment. We found that phycocyanin-rich and phycoerythrin-rich picocyanobacterial abundances are associated with riverine and marine waters, respectively. Besides affecting GB's water quality, rainfall governs its picocyanobacterial distribution and ecology. Thus, climate changes may influence the balance of the picocyanobacterial groups in tropical estuaries. Furthermore, the omnipresence of picocyanobacterial groups found in GB, such as Synechococcus and Cyanobium, highlights their ecological role in tropical estuaries, as seen in the open ocean. [ABSTRACT FROM AUTHOR]

While the success of restoration efforts frequently depends on reconstructing ecological communities, time series observations of community structure over the course of restoration are rare. Here, frequent sampling of bacterioplankton, phytoplankton, planktonic protozoa (ciliates and testaceans), and zooplankton was done along with measurements of select physical and chemical parameters during the first year of ecological restoration of Thompson Lake (TL), an Illinois River floodplain lake not connected to the river. The primary objective was to describe the microbial composition, diversity, and seasonal dynamics in TL and compare these results to similar measurements made in a nearby reference lake, river flood-pulsed Lake Chautauqua (LC). Strong seasonal patterns in bacterioplankton diversity were observed for both lakes. While TL phytoplankton diversity was lower and blooms more erratic than in LC, ciliate richness and abundance patterns were similar in both lakes. Rotifers and microcrustaceans were about 5× more abundant in TL than LC, with copepods and cladocerans exhibiting a fall abundance peak only in TL. When compared to temporal patterns of planktonic microorganisms in the reference lake (LC), the microbial dynamics in a lake recovering from decades of agriculture and drainage (TL) reflect the instability associated with early stages of ecological restoration. [ABSTRACT FROM AUTHOR]

The nuisance diatom Didymosphenia geminata has recently increased in abundance worldwide and has spread through oligotrophic rivers in the South Island of New Zealand. However, it remains absent from the North Island. Its proliferation in oligotrophic environments has prompted work on phosphorus acquisition, but potential nitrogen acquisition pathways have received little attention. We partially sequenced the nifD gene, encoding a component of nitrogenase, from South Island samples containing D. geminata and compared its diversity with that of North Island sites independently ranked as high, medium and low risk for infestation. Godleyacean cyanobacteria were present in all four South Island provinces investigated, and also in three North Island sites rated medium or high risk. Most high-risk sites were dominated by Nostoc sequences, as were some infested South Island sites. Monte Carlo simulations and the weighted UniFrac metric showed that nifD diversity in low-risk North Island sites differed significantly from sites rated medium and high risk, and from infested South Island sites; however, random resampling showed that the data were insufficient to separate didymo-infested and high-risk sites from medium-risk sites. The relationships we discovered suggest that success of D. geminata in New Zealand could be mediated by indigenous nitrogen-fixing cyanobacteria. [ABSTRACT FROM AUTHOR]

The strategy of decreasing size with increasing temperature operates at regional and phenotypic scale and presents a puzzle to researchers. In this work, we studied two aspects of the temperature-performance relationship along a temperature gradient, (i) comparing the population growth rates of three cryptic Brachionus species differing in adult size, and (ii) assessing the phenotypic plasticity of adult size, in one clone per species. The working hypotheses were that (i) the bigger the species the lower its optimal temperature for population growth, and (ii) the higher the temperature the smaller the individual within each focal species. The results showed that (i) the optimal temperature for population growth is related to species size in a manner foreseen by Bergmanns' rule for two of the three species (the third, biggest species, performed evenly well at all temperatures examined, what could be explained by its generally eurioic character), and that (ii) the strategy of body size adjustment to environmental temperature differs between species and may depend on the level of temperature specialization. This work demonstrated the usefulness of inter- and intraspecific comparisons for studying the role of growth strategies in adaptation to temperature. [ABSTRACT FROM AUTHOR]

We studied if biomass, cell dimensions and microcystin concentration of the cyanobacterium Anabaena sp. (strain BIR 257; recently also referred to as Dolichospermum) change in the presence of turbidity caused by clay and a eukaryotic green algal species. Anabaena sp. was incubated in experimental lab bioassays, with added clay and the chlorophyte Brachiomonas submarina. A control was established containing a single species of Anabaena sp. Biomass of Anabaena, given as carbon concentration increased in response to clay addition, suggesting that Anabaena was stimulated by lower light conditions whereas B. submarina was not. Cell lengths increased most likely as a response to lower light conditions. Dissolved toxin concentration decreased in treatments containing clay. Increased clay turbidity may favour the cyanobacterium Anabaena sp. over its eukaryotic competitors in the future Baltic Sea, especially in low-salinity estuaries. [ABSTRACT FROM AUTHOR]

The effects of invasive macrophytes, water level fluctuations and predation on freshwater unionids Pyganodon grandis and Utterbackia imbecillis were studied in three small impoundments in Northeastern Texas in 2003–2005. Mussel density was sampled with quadrats. Mortality, associated with the water level fluctuations and predation, was estimated by collecting dead shells on the shore at about two month intervals. In two ponds, horizontal distribution of unionids was limited by dense beds of invasive and noxious macrophytes (mainly Eurasian watermilfoil Myriophyllum spicatum and American lotus Nelumbo lutea): mussel densities were significantly lower in these macrophyte beds ( P < 0.001). In the third pond with the lowest density of macrophytes (stonewort Chara sp.), unionids were distributed more evenly, and the average unionid biomass was the highest among all ponds studied. Vertical distribution of unionids in all ponds was likely limited by low oxygen at depth >2 m. The total amount of shells found on the shore per year varied from 0.1% to 28% of the total population in the pond and was negatively correlated with water level ( r = −0.72 to −0.81, P < 0.005). Mammalian predators consumed up to 19% of the total unionid population and predation was facilitated by water level fluctuations. [ABSTRACT FROM AUTHOR]

Submerged aquatic plants can act as measurable indicators of ecological conditions occurring within a lake, and they need only be monitored once a year or even less. Historically in New Zealand there has been a reliance on water quality sampling for monitoring the health of lakes and these methods can be complex and costly involving multiple site visits and chemical analysis of water samples. As a result, lake monitoring has been irregular, or not done at all. LakeSPI or ‘Lake Submerged Plant Indicators’ is a new management tool that uses aquatic plants to monitor and assess ecological condition in a wide range of lake types. The method generates three indices: a Native Condition Index (extent and diversity of native plants) and an Invasive Condition Index (extent and impact of alien weeds), which are generated from scores allocated to carefully selected vegetation features; and an integrated LakeSPI Index which is largely derived from components of the other two indices and provides an overall indication of lake ecological condition. The LakeSPI method can be used to assess the status of lakes and monitor trends occurring within them, and it is expected that the use of LakeSPI will facilitate regular monitoring and reporting on a much wider range of lakes than has been possible using traditional water quality methods. By utilizing submerged aquatic plants the method focuses on lake littoral margins where there is greatest public interaction and interest. [ABSTRACT FROM AUTHOR]

A novel aquatic bioassay with Lemna minor (duckweed), a representative of higher plants, was applied to pore waters (interstitial waters) from river sediments. The results have been used for the ecotoxicological assessment of sediments in several German rivers. The aim of the present study is to demonstrate the usefulness of a macrophyte bioassay, as a supplement to the standardised algae bioassays, with regard to the ecotoxicological assessment of aquatic systems. Results relating to the development of a sediment contact test (using the whole sediment) with Lemna minor are also presented. [ABSTRACT FROM AUTHOR]

The spatial distribution of bacterial abundance and production were measured every 4 h in a recently flooded oligo-mesotrophic reservoir (the Sep Reservoir, Puy-De-Dôme, France), in relation to concentrations of dissolved carbohydrates and combined amino acids. The concentration of dissolved organic matter (DOM) components in the recently flooded Sep Reservoir were higher than those measured in other lakes of similar trophic status. Short-term variations in the bacterial production in this new reservoir appeared cyclical and endogenous to bacterial communities. These results highlight the need for the evaluation of diel changes in bacterial production, if estimation of the daily production rate of bacteria is to be done accurately for a reliable model of carbon flow through bacterioplankton and ultimately through aquatic microbial food webs. Bacterial growth, measured over time and space, did not appear exclusively governed by DOM components from phytoplankton primary production. [ABSTRACT FROM AUTHOR]

The degree to which biodegradation of dissolved organic matter (DOM) depends on microbial community structure and source remains unknown. In this study, we concentrated the microbial biomass from two streams in northern Michigan and a dystrophic ‘bog’ lake in northern Wisconsin with varying initial DOM concentration (6.7-78.8 mg C l-1) and DOM chemical characteristics (e.g. DOM average molecular weights from 808-1887 Da). Each of the three microbial inocula was added to each of the three DOM sources atin situpopulation levels for a total of nine treatments. Changes in DOM concentration and bacterial productivity, along with chemical characteristics, were examined over 308 h. The [3H]-leucine incorporation method was used to measure microbial production. In two of three sampling sites, bacterial communities were most productive when metabolizing DOM in their native waters. A variable peak in productivity was seen between 16-48 h after inoculation, followed by a drop in productivity in most treatments, with periods of DOM production most likely due to microbial turnover. These data suggest that microbial communities are better able to degrade the DOM of their native habitats, suggesting that biodegradation of DOM is influenced by source-specific microbial species and DOM chemical characteristics. [ABSTRACT FROM AUTHOR]

Electrospray ionization mass spectra of phycocyanins of eight samples from natural blooms of Microcystis aeruginosa f. aeruginosa collected at different eutrophic pond and lakes indicated that the ? subunits of phycocyanins in the same species have different molecular masses, whereas the ? subunits have almost constant molecular masses. A negative linear relationship between the molecular mass of ? subunit of phycocyanin and the concentration of chlorophyll of natural and colonial cyanobacterial samples was found. An interannual similarity of the ? subunit molecular masses of phycocyanins was observed from samples collected at the same sampling site at Lake Kasumigaura during 1994and 1995. A locational variability of the ? subunit molecular massesof phycocyanins was also observed among samples collected at three eutrophic pond and lakes. [ABSTRACT FROM AUTHOR]