Aquatic Sciences

Changes in habitat acoustics over the year can potentially affect fish hearing and orientation to sound, especially in temperate climates. This is the first study where year-round changes in ambient noise in aquatic habitats were assessed. Seven different European fresh-water habitats were chosen for this study. Sound pressure level (SPL) and spectral composition of the ambient noise varied in both quiet stagnant habitats (lakes, backwaters) and in flowing habitats (streams, rivers). Linear equivalent SPL (L(Leq, 60s)) tended to be lower in stagnant habitats (means: 91.6-111.7 dB) than in flowing habitats (means: 111.2-133.4 dB). The changes in SPL were smallest in the river (means: 4.2-4.4 dB, maxima: 8.5-10.1 dB), whereas significantly higher values were measured in stagnant habitats and the stream (means: 9.9-14.9 dB, maxima: 25.1-30.9 dB). The spectral compositions of the ambient noise determined at different times of the year were highly correlated to each other at the river sites (mean cross-correlation coefficients: 0.85 and 0.94) and were weaker or not correlated at the other study sites (means: 0.24-0.76). The changes in ambient noise spectra were negatively correlated to changes in SPL, indicating that large changes in SPLs were accompanied by large changes in spectral composition and vice versa. Comparison of these ecoacoustical data with a preceding study (Amoser and Ladich in J Exp Biol 208:3533-3542, 2005) indicates that the auditory sensitivity in hearing specialists is affected by changes in ambient noise levels and spectra throughout a year and that this effect tends to be more pronounced in stagnant waters and the stream than at river sites. On the other hand, absolute noise levels result in a higher degree of masking in flowing waters.

A short overview of currently available studies on the ecology of viruses in running waters is provided. Additionally, a survey was conducted on the dynamics of both viruses and bacteria in an isolated floodplain segment of the Danube River and in the main channel near Vienna (Austria) during the hydrologically most dynamic phase (spring - summer). The study evaluates the differences between the main channel and the floodplain segment for suspended particle abundance and quality in relation to bacterial and viral parameters; both free-living forms and those attached to particles are examined. The hydrological disconnection of these two contrasting sampling sites influenced particle abundance and quality as well as the distribution of free-living vs. attached bacteria and viruses. The per-cell activity of bacteria attached to particles was significantly higher than that of the free-living fraction, particularly in the isolated water body. The abundance of bacteria and viruses on particles depended on particle quality (size). In the main channel, bacteria were significantly more abundant on surfaces (per mm(2)) of suspended matter > 5 μm (aggregates with organic constituents) compared to particles < 5 μm (mostly mineral grains). In the isolated water body, both bacteria and viruses were more abundant on the larger particles/aggregates. Data from both locations revealed a positive correlation between abundance of particles > 5μm and attached viruses; free-living viruses were less abundant at high > 5μm particle loads. Only in the isolated floodplain section was viral abundance positively influenced by elevated per-cell productivity of potential host bacteria. The results demonstrate that system variability on a relatively small topographical scale (within a river-floodplain system) has consequences for microbial life, including viruses.

The Holocene record of Lake Lugano (southern basin: surface area 20.3 km2, maximum depth 87 m) comprising organic carbon-rich sediments (sapropels), is divided into eight intervals based on radiocarbon- and varve-dating. The content of organic carbon, inorganic carbon, and biogenic silica, as well as the benthic remains of ostracods and oligochaetes, are converted into accumulation rates and benthic abundances in order to assess past production rates and bottom water oxygen status, respectively. The results suggest three periods of distinct palaeolimnological character: (i) low primary production combined with shifts between aerobic and anaerobic profundal conditions (prior to ca. 3000 BC), (ii) moderate rates of production combined with a relatively high profundal oxygen content (after ca. 1500 BC), and (iii), high production rates (460 g C m–2 a–1) combined with anaerobic profundal conditions (present eutrophic state). Corresponding organic carbon contents in the sediments are: up to 5% (i), 4% (ii), and 8% (iii). Until the beginning of this century, the flux of autochthonous sediments to the lake floor correlated with the fluctuations in the allochthonous sediment accumulation rate, indicating that catchment erosion largely controlled lacustrine production during the Holocene history of Lake Lugano. Pollen data show catchment-vegetational transformations at ca. 3500 BC (change from fir to beech forests), at 1400 BC (onset of cereal vegetation) and at ca. A.D. 450 (strong increase in various cultural plants). The first two changes had a relatively large imprint on lacustrine sedimentation. At ca. 3500 BP, erosion increase in the catchment was triggered by vegetation changes in the mountain zone above ca. 1000 m a. s. l., which may have been induced by climatic and human alteration (drop in the treeline altitude). Maximum catchment erosion occurred at ca. 1400 BC which was clearly dominated by human cultivation during the Bronze Age. More oxygenated profundal conditions in the lake after ca. 3000 BC are possibly related to a better mixing of the lake waters during the winter season by increased wind activity.

Scanning tunneling microscopy (STM) is used to observe, at the atomic scale, Cr(III) adsorbed to hematite (001) surfaces from aqueous solution. The Cr(III) adsorbates are relatively immobile, but estimated activation energies for surface self-diffusion are lower than those for water or hydroxyl substitution in aqueous Cr(III). Possible causes are effects of STM imaging (artifacts), high ligand-substitution rates for adsorbed species, or participation of substrate Fe (III) ligand exchange. STM imaging of suitable aqueous surface complexes is shown to be feasible, and constitutes a new way to study the relationships between microscopic and macroscopic chemical behavior of adsorbed species in aqueous systems.

Measurements of the concentrations of Ru-103 and Ru-106 in the water column and sediments of two productive temperate lakes were made during an eight month period following the Chernobyl accident. Ru-103 accumulation in the sediments began simultaneously with that of Cs-134 and a constant ratio (approx. 2.0 on a decay corrected basis) of Ru-103/Cs-137 was observed in surface waters and sediments throughout the measurement period. The ratio is not statistically different from that reported for atmospheric input and for epilimnetic water. The results suggest that the processes of removal of radioactive ruthenium and caesium from the mixed water column to the sediments are the same.Enhancement of Cs, compared with Ru, in the isolated bottom waters of one of the lakes in the summer months provided evidence for Cs release from the sediments during a period of hypolimnetic anoxia.

Measurements of physical properties have been conducted in Mining Lake 111 (ML111), located in Lusatia, Germany over the time period 1996–2002. In the deepest area of the ML111, a monimolimnion was observed, that persisted for the years 1996–1999. It disappeared in 2000 and again formed in 2001. The definition of the main physical properties, such as the temperature compensation for electrical conductivity, in acidic mining lakes required a lake specific approach. The relation between conductivity, temperature and density was determined for the acidic ML111. The variation in dissolved substances affected these relationships such that conductivity varied with temperature even in different layers of the water column and the limitations for a lake wide correlation was evident. Variation in the conductivity of the epilimnion could be verified, and agreed with the estimates of evaporation from the lake surface during summer stratification. Calculations, following the gradient flux method, indicated vertical transport coefficients between 10–7 and 10–6m2/s throughout the hypolimnion. The heat budget indicated that heat was transferred into the lake bed or the ground during spring.

The family Cyprinidae comprises most of the freshwater fauna of the North Mediterranean region and it is often numerically dominant. Taxonomy based on morphology is problematic, owing to the high intraspecific variation in phenotypic traits, their overlap between species and environmental plasticity of morphometric and meristic characters. A difficult diagnosis, particularly for young developmental stages, can increase resource mismanagement. Here we report on the occurrence of species-specific allozymic patterns, consistent from eggs to adults. These allowed the construction of a biochemical-genetic key for the identification of all stages of 13 freshwater fishes, mainly cyprinids native to the North Mediterranean region (Alburnus alburnus alborella, Barbus plebejus, Chondrostoma genei, Gobio gobio, Leuciscus cephalus, L. lucumonis, L. souffia, Rutilus rubilio, R. erythrophthalmus, Scardinius erythrophthalmus, Tinca tinca, Pseudorasbora parva and Padogobius martensii).

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 (*) were adapted to low light by high ratios of chlorophyll-a to photo-protective -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 -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.

Over a period of 17months, variations in 15N and 18O values in drainage water nitrate from two collector- drain outlets were investigated. Both fields were conventionally farmed. One field was 2.5ha (outlet 1) and the other 15ha (outlet 2) in size; each received similar N amounts per hectare during fertilizer application. In tile drain 1, the 15N-NO3 values (concentration weighted mean (cwm) 10.6) and 18O-NO3 values (cwm 5.1) were higher compared to the second tile drain (cwm 15N: 7.2; cwm 18O: 2.9). Changes in isotope values of drainage water nitrate could be observed in tile drain 1 after fertilizer application. These changes included an increase in 15N-NO3 after fertilization with urea and a decrease in 15N-NO3 values associated with increased 18O-NO3 values when nitrate fertilizer was applied. Low 18O values in drainage water nitrate of both tiles indicate that nitrification took place for most of the sampling period. Denitrification was only observed in water of tile 2 for a period of six months during summer and autumn.

In mid latitudes, such as the Mediterranean region, one consequence of global climate change will be a progressive shift of permanent to temporary water courses, altering the life histories of present species or making them disappear. Presented here is a study on the life history of a mayfly species, Serratella ignita, in two Mediterranean streams, one permanent and one temporary. The research focuses on life history parameters such as life cycle, nymphal growth pattern, feeding type, biomass and secondary production. The life cycle was univoltine, showing a fast seasonal nymphal growth during four months in the permanent stream and five months in the temporary stream, with a long egg stage with diapause. The cumulated day-degrees during nymphal growth were similar between streams. Both populations behaved mainly as gatherer-collectors, but the population from the temporary stream also played an important role as a scraper. Animal matter was also consumed by nymphs from both populations. Gut content analysis showed that both S. ignita populations were opportunist/generalists, where changes in diet were correlated with size. Biomass and secondary production were notably higher in the permanent stream, but they were also high in the temporary stream. These data show that S. ignita had a high fitness in both streams. Our results support the idea that species such as this one may cope with future global climate change by maintaining, or even increasing, their populations at the expense of more stenoecic species.

The properties of aquatic dissolved organic matter (DOM) isolated by solid phase extraction (SPE) C-18 cartridges, ultrafiltration, and XAD chromatography are compared. Samples taken from the Suwannee River, Georgia, USA and McDonalds Branch in the Pine Barrens, New Jersey, USA were chosen to represent waters where DOM originates from predominantly terrestrially-derived (allochthonous) precursors. Pony Lake, Antarctica represented an exclusively algal/microbially-derived (autochthonous) DOM. Fluorescence, UV absorption, 13C NMR spectroscopy, and high-pressure size exclusion chromatography (HPSEC) were employed to discern differences and similarities between the DOM isolated by these three methods. Only subtle differences between isolation methods were observed for the terrestrially derived DOM samples when assayed by light and fluorescence spectroscopy. Conversely, the Pony Lake DOM isolates exhibit greater variability when analyzed by these methods. 13C-NMR analyses showed structural differences between the methods for all samples. HPSEC analysis also revealed differences with the C-18 isolates exhibiting the highest molecular weights. Thus, it appears that each method isolates sufficiently different fractions of DOM that can only be delineated when a consortium of analytical methods are used to assay the samples. Nonetheless real differences between autochthonous and allochthonous derived DOM were observed with the algal-derived samples exhibiting high fluorescence ratios and lower aromaticity relative to the terrestrially derived materials. These results demonstrate that caution must be exercised when interpreting DOM reactivity data that rely upon the use of specific fractions.

Rostherne Mere is a small but relatively deep, turbid and highly eutrophic lake. In recent years, the productivity and dynamics of its phytoplankton have been particularly sensitive to the interaction between light income and thermal stability. Analysis reveals that interannual differences in the size and duration of phytoplankton crops, as well as in the predominating species, are not random but that there is a reproducible coherence with weather-generated external forcing. Severe light-limitation restricts phytoplankton development outside the stratified period, though delayed stratification in spring may promote relatively large diatom crops. In summer,Microcystis will usually dominate provided its recruitment period coincides with high water clarity. OtherwiseCeratium generally dominates. Examples of extremely stable stratification leading toScenedesmus dominance and of persistent episodes of summer mixing favouringOscillatoria dominance are found to agree well with previous matrix models.

Pomatoschistus microps (Teleostei, Gobiidae) intensively uses the mesohaline marsh of Westerschelde estuary as a nursery and foraging ground. The sampling campaign covered the semi-lunar, diel and tidal cycles. The density of P. microps and potential hyperbenthic prey species in the marsh creek, fullness index, evacuation rates and daily ration of common goby were calculated. Mesopodopsis slabberi, Neomysis integer and Corophium volutator were the most dominant prey items in terms of biomass. Numerically, copepods dominated the diet. Migrating fish enter the marsh creek with a relatively empty stomach and leave the marsh with a higher stomach content. Pomatoschistus microps seemed to feed more intensively during the day than the night, however the influence of the diel cycle is inferior in comparison with the tidal influence on the feeding behaviour of the common goby. A significant difference in foraging activity occurred between the spring and neap tide. The common goby migrated in lower abundance into the creek during spring tide but foraged more intensively. At both spring and neap tide, a significant difference was found in the fullness index between day and night. At spring tide, gobies feed more during the day, while they forage more intensively at night at neap tide. All the three cycles (tidal, diel and semi-lunar) influenced the feeding rhythm of the common goby. The tidal influence is superior over the diel variation, while the explanation of the combined effect of diel and semi-lunar cycle needs further studies.

In this study we analyzed patterns of sequence divergence in about 1kb of mitochondrial DNA coding for two genes (16S rRNA and Cytochrome Oxidase I, COI) in 15 populations and 61 individuals of the halophilic fairy shrimp Phallocryptus spinosa (Milne-Edwards, 1840). Populations were sampled in saline and hypersaline water bodies from Spain, France, Italy, Greece, Turkey, Ukraine, Iran, Uzbekistan, Cyprus, Algeria, Morocco and Botswana. Our genetic findings suggest complex phylogeographic relationships and pronounced genetic differentiation among populations. Multiple phylogenetic methods and nested clade analysis revealed the existence of four highly divergent maternal lineages with strong phylogeographic patterns and signatures of either allopatric fragmentation or restricted gene flow with isolation by distance. These results are further supported by the hierarchical analysis of molecular variance (AMOVA) and pairwise F ST values, which indicate that most of detected genetic heterogeneity is apportioned among populations. Genetic relationships among haplotypes fit geographical hypotheses in most cases but one. Indeed, one haplotype is shared among French, Iranian and Uzbekistan populations. We hypothesize that this peculiar occurrence might be due to an avian-mediated long distance passive dispersal event.

The diatom biostratigraphy of the topmost sediment meter of Rotsee, Central Switzerland, is characterized by a major change fromCyclotella comensis-dominated toStephanodiscus hantzschii/S. parvus-dominated assemblages. A comparison between old phytoplankton samples, taken between 1910–1930, and subfossil diatom assemblages is used for dating the upper 35 cm of the core. There is evidence that the change in dominant diatoms occurred in 1919/20, thus before the opening of an artificial inlet in 1922, and is due to increasing eutrophication. Furthermore, the sedimentary carbonate content can be used as a good indicator for past phytoplankton productivity in Rotsee.

Using enzyme electrophoresis, the genetic population structure of the freshwater crayfish Austropotamobius pallipes was analysed. The samples exhibited very low levels of genetic variability and several population samples were fixed for alternative alleles, indicating a population history of repeated bottlenecks and genetic drift in isolated populations. An unexpected phylogeographic structure, grouping samples from different river drainages was found. Three non-exclusive hypothesis explaining this structure are discussed. The conservation consequences for the reintroduction of this endangered crayfish in reimproved water bodies is evaluated.

In the present study, we used mitochondrial cytochrome oxidase subunit I (COI) and nuclear D2 region of 28S rDNA sequence data to examine the taxonomic status of the water mite species Hygrobates nigromaculatus from two types of freshwater habitats: lentic (lakes) and lotic (streams). Previous hypotheses about (sub)species status of populations inhabiting lakes and streams based on differences in morphometric data and life-cycle strategy (parasitic vs. non-parasitic larvae) were strongly supported by molecular data. Levels of COI and D2 28S rDNA differentiation between lake and stream populations were much higher (ca. 18 and 7.5%, respectively) than those typically observed for populations of a single species. Both lake and stream populations showed similar high levels of gene diversity (Hd=0.894 and 0.836, respectively). However, nucleotide within-population polymorphism was more than twice as high in lake populations as that in stream populations (π=1.33 and 0.60%, respectively). We hypothesize that the ancestral lake-dwelling population originated from a stream form with parasitic larvae (here: H. setosus nov. stat.). For the observed populations, H. nigromaculatus individuals could be separated from H. setosus by distinct morphometric characters. The loss of phoretic parasitic larvae greatly decreased dispersal ability of lake-dwelling mites and consequently also the gene flow between lake populations. Thus, relatively more differentiated genetic structure in lake populations probably results from a stronger isolation between particular lake habitats, but this hypothesis needs further extensive studies. Keywords Hygrobates setosus nov. stat-Phoretic parasitic larvae-Sibling species-COI-D2 28S rDNA-DNA barcode

Rh. germanica is a European species that, due to human impacts, has progressively disappeared from its original territories and is now considered rare. In SwitzerlandRh. germanica has disappeared from the Aare, Broye and Kleine Emme rivers and is actually found in a limited reach of the River Rhine and some of its tributaries (Limmat, Sihl, Thur and Töss rivers).Rh. germanica is a univoltine species, hatching probably in summer. The emergence occurs from February to the beginning of April. It takes place on the water surface. Laboratory observations have shown that the subimaginal stage lasts four days.Rh. germanica occurs on different substrate types, ranging from stones and cobbles to pebbles and gravel. The larvae are more abundant in zones of erosion with coarse and porous sediments than in depositional zones with fine sediments and silts. They are most abundant in riffles with water velocities from 20 to 150 cm/sec. The species tolerates moderately organic-polluted waters. The particular strategy concerning growth and emergence ofRh. germanica is also discussed.

Les examens des résultats comparatifs effectués sur la base de l'étude deMassol (1893) et sur nos propres analyses quantitatives de 1948, prouvent que les eaux du Léman, tout au moins en ce qui concerne le Petit-Lac, sont plus riches en germes actuellement qu'autrefois. Cette constatation semble découler du fait que la population riveraine a notoirement augmenté; la pratique inconsidérée du tout-à-l'égout habituel des eaux usées ne fera qu'amplifier une situation qui s'obère d'année en année et qui de sérieuse qu'elle est présentement pourrait devenir désastreuse dans un proche avenir. Vergleicht man das Ergebnis der neuesten Untersuchungen mit den ErhebungenMassols aus dem Jahre 1893, so zeigt sich, daß, zum mindesten im unteren Bezirk (Petit-Lac) des Genfersees, die Bakterienzahl im Laufe des letzten halben Jahrhunderts angestiegen ist. Der Verfasser führt dies auf die andauernd zunehmende Belastung durch Abwässer zurück, entsprechend der immer dichter werdenden Besiedelung der Seeufer. Er sieht in dieser Enticklung eine nicht zu unterschätzende Gefährdung der Wasserversorgung aus dem See.

Ohne Zusammenfassung

Besides the old-settledDaphnia hyalina a ‘galeata’-type ofDaphnia immigrated into Lake Constance (Upper Lake) in the beginning of the fifties. Since this time a great number of phenotypes with a high degree of morphological variations was registrated. Since about 1970 a smallDaphnia type became more and more numerous, especially in the eastern part of the lake. An exact determination is not yet possible. In 1972 an extreme maximum ofDaphnia males was found. The share of males increased from 3 to 4% of the population to 30% in autumn 1972. In the following years the percentage decreased again to the formerly observed 3–4%. The relationship to the phytoplankton biomass is discussed.

: A 39-year series (1957 – 1995) of data on fourteen physical, chemical and biological variables from the Austrian section of the River Danube west of Vienna – Nudorf was analysed statistically to detect long-term trends of the variables in relation to human activities (represented by time), discharge and water temperature. Principal component analysis distinguished four main components explaining 72 % of the total variance: PC1 contains total phosphorus, soluble reactive phosphorus, ammonium and potassium permanganate values, PC2 contains nitrate-N, chloride and oxygen, PC3 contains BOD5 and nitrite-N, and PC4 contains numbers of bacteria. Trends in time were most pronounced for variables in PC1, but also occurred in PC2; variables in PC3 and PC4 had no trends. Seasonal patterns were marked for variables in PC2, slightly less in PC1, and least in PC3 and PC4. Concentrations were minimal in summer and maximal in winter, inversely related to discharge (maximal in summer). Following reductions in point-source nutrient inputs to the Danube, in both Germany and Austria, mean concentrations in the river have fallen by at least half since the 1980s. Chloride and nitrate-N also show trends towards lower concentrations. The Danube is well-oxygenated, with concentrations near air saturation values. A mathematical relationship between concentrations of the variables and river discharge (Q), water temperature (T) and time (t), was established to determine mean trends and predictions against a background of considerable seasonal and stochastic variability; for the single variables Q explained 0 – 20 % and T explained 2 – 58 % of the variation in the concentrations. The relationship was highest for variables in PC2 and lowest for those in PC3 and PC4, where Q and T had little or no influence. Reasons for rising and falling long-term trends with time are discussed in detail. Austria now contributes only minor proportions to the nutrient load of the Danube, which is causing eutrophication of the Black Sea downstream, and water quality of the Austrian section of the river is good. The advantages and problems of statistical process analysis are discussed in relation to environmental monitoring programs and the different specific requirements of compliance monitoring.

Sans rsum

Lake Lucerne, Switzerland, "Kreuztrichter"-basin, was investigated between 1961 and 1992. This time period offered a unique opportunity to study an eutrophication event lasting some ten years and the following recovery period as well as the limnological behavior of a deep pre-alpine lake. Results are presented as isopleths and long-term trends. Five year averages show clear patterns in the dynamics of ammonia or nitrite. Lake Lucerne (Kastanienbaum basin) is a monomictic lake, with only one complete overturn every six years. Other basins of Lake Lucerne such as the southernmost basin (Lake Uri), destratify each year, because of its wind-channel orientation.¶Kreuztrichter Basin was physically stabilized for years by trophic-induced processes. As the lake recovered, the density gradient in the bottom water layer decreased and turnover frequency increases. The oxygen peak in summer was usually overridden by temperature effects. Nitrogen concentration increased steadily during the 30 year period. Data for N, P, Si and O2 suggested the concept of compensation depth could be applied. The results were e.g. settling seston had no effect on nitrogen but caused a decrease in soluble phosphorus. In the most productive years silica use was more intense. The abyssal part of the wind-shielded Weggis-Vitznau basin is the most sensitive spot to the effects of nutrients in the lake. This paper is a summary of a more extensive report of the data (Bührer and Ambühl 1996).

The long-term development of crustacean associations in the Obersee of Lake Constance was studied at one central station from 1962 to 1986. In a simultaneously managed program with four additional stations from the eastern part (Bregenz Bay) to the western Überlinger See mainly the differences in horizontal distribution were focussed. It was one aim of these investigations, to get an idea or an indication of a connexion between the recently observed eutrophication of the Obersee, and its crustacean communities. Due to the immigration of several species (cyclopids) or genotypes (Daphnia), the communities had changed in genetical structures, in reproduction rates and in predation or grazing impact. Dependent on the specific annual cycles, there resulted an extermination (Heterocope, Diaphanosoma), or a long-term decrease in annual means (Mesocyclops, Cyclops abyssorum) of the “old-settled” species. A general tendency was seen in an increase of annual averages until the middle of the seventies, and a following decrease of population density of most of the species. The horizontal differences in the species associations were remarkable. The Bregenz Bay showed an own aspect in its crustacean community with high total numbers and in earlier spring development. Most of the newcomers were concentrated in the eastern part of the lake.

L'étude de quatre paramètres (température, oxygène dissous, phosphore total, et azote nitrique) dans les eaux de la baie d'Auvernier, de 1962 à 1973, permet de suivre l'évolution de l'état trophique de cette partie du lac de Neuchâtel (fig. 1). Chaque année, on y observe une période de stratification (juin à novembre) et une période de circulation (décembre à mai) (fig. 2). Bien que la consommation d'oxygène soit particulièrement importante dans le métalimnion en période stratifiée, les eaux restent suffisamment riches en oxygène dissous de la surface au fond (fig. 3). D'ailleurs, en 12 ans, on n'observe aucune diminution des teneurs en oxygène quelle que soit la profondeur considérée (fig. 4). En revanche, la charge nutritive s'est accrue considérablement en azote nitrique (30%) et en phosphore (230%) (fig. 5–8) et si l'on ne considère que ces deux critères d'eutrophisation, la baie d'Auvernier aurait évolué du stade oligotrophe en 1963 au stade eutrophe en 1972. The evolution of the trophic state of a part of the Lake of Neuchâtel was investigated by means of a study of 4 parameters (temperature, dissolved oxygen, total phosphorus and nitrates) in the waters of the Auvernier Bay (fig. 1). Each year is composed of a stratification period (June to November) and a circulation period (December to May) (fig. 2). Notwithstanding the heavy consumption of oxygen in the metalimnion during the stratification period, the waters are sufficiently abundant in dissolved oxygen (fig. 3). As a matter of fact, over the 12-year period studied, no decrease in the oxygen content was observed at any depth (fig. 4). On the other hand, the quantities of nutrients were enriched in nitrates (30%) and phosphorus (230%) (fig. 5–8). The Auvernier Bay may be thought to have evolved from an oligotrophic state in 1963 to an eutrophic state in 1972 if we consider only these latter two criteria. Die trophische Entwicklung der Bucht von Auvernier (Neuenburgersee) von 1962 bis 1973. Die Untersuchung der 4 Parameter Temperatur, gelöster Sauerstoff, Gesamtphosphor und Nitrat in der Ducht von Auvernier erlaubte es, von 1962 bis 1973 die Entwicklung des trophischen Zustandes in diesem Teil des Neuenburgersees zu verfolgen. In all diesen Jahren wechselte eine Periode stabiler Schichtung (Juni bis November) mit einer Periode allgemeinen Austausches der Wassermassen (Dezember bis Mai) ab (Fig. 2). Obwohl der Sauerstoffverbrauch zur Zeit der stabilen Schichtung besonders hoch ist, bleibt das Wasser bis zum Grund reich genug an gelöstem Sauerstoff (Fig. 3). Während der ganzen 12 Jahre war in keiner Tiefenlage eine Verminderung der Sauerstoffgehalte (Fig. 4) festzustellen. Dagegen sind die Nährstoffgehalte stark angewachsen (Nitrat um 30%, Phosphor um 230%, Fig. 5–8). Wenn man nur diese beiden Eutrophierungskriterien in Betracht zieht, ist die Bucht von Auvernier von 1963 bis 1972 vom oligotrophen in den eutrophen Zustand übergegangen.

From January 1964 through January 1966, Dr. F.P. Ide and colleagues at the University of Toronto Great Lakes Institute (GLI) collected benthic macroinvertebrates from up to 63 stations during each of 16 cruises on Lake Ontario. This intensive survey was conducted at a time of rapidly increasing anthropogenic impact. Total invertebrate abundance decreased with increasing depth; this distribution was bimodal on the northern side of the lake, with peaks at ca. 35 and 80 m. Oligochaeta were more abundant along the southern than on the northern side of the lake, except in Humber Bay. The amphipodDiporeia was rarely collected at most stations near the mouth of the Niagara River. Chironomidae were most abundant in the Kingston Basin but were common throughout the lake at depths less than 50 m. Sphaeriidae were confined to water <100 m deep and were most abundant along the southern shore. When compared with the results of subsequent surveys of the deepwater zone, the GLI data provide evidence of two major shifts in the abundance of benthic animals. Numbers of Oligochaeta decreased by about 40% during 1965 and remained at the lower levels through 1990. The abundance ofDiporeia changed little from 1964 through 1977, but increased sharply between 1977 and 1981. These shifts do not appear to reflect implementation of controls on the discharge of phosphorus, or direct predation by fish. Changes in fish and zooplankton communities and inputs of toxic contaminants seem equally likely to be responsible for the shifts in the deepwater benthic community. We have proposed several predictions which could test the relative importance of biotic interactions or chemical stressors.

Ohne Zusammenfassung

Ohne Zusammenfassung

The general features of phytoplankton seasonal succession, abundance and distribution in Lake Kinneret, as based on observations from 1970 through 1989, are summarised. Throughout this period of observation, the large, thecate dinoflagellatePeridinium gatunense formed an annual, late winter to early spring bloom resulting in very high standing stock levels. The dominance of these dinoflagellates has a profound impact upon the lake ecosystem. In the summer and fall the phytoplankton assemblage consisted mainly of nanoplanktonic green and blue-green algae and diatoms. Picophytoplankton, mainly picocyanobacteria, were present in low numbers during the dinoflagellate bloom but reached maximum abundance (105 cells ml–1) in the epilimnion during the summer and fall. Within a given year, chlorophyll concentrations correlated well with estimates of wet weight biomass, derived from microscope counts. However, interannual averages of chlorophyll did not correlate closely with those for wet weight biomass. Both wet weight biomass and chlorophyll standing stocks fluctuated more than 2 fold from 1970 through 1989 but no extreme, long-term, continuous trend of increase or decrease was observed. Thus, phytoplankton has remained relatively stable although there has been a significant rise in the levels of summer-fall biomass since 1981. The main factor responsible for this may have been increased available phosphorus; the abundance of phytoplankton did not show any clear, long-term relation to that of herbivorous zooplankton.

Biological investigations of that part of the River Limmat lying between Quaibrücke and Wettingen were carried out from 1974 to 1980. An influence of the waste water from the Werdhölzli sewage treatment plant on the plant and animal communities of the river bed was evident. This influence was especially plain to be seen immediately below the point of introduction of the waste water. The incidence of pollution indicators decreased downriver from this point. Biotests, using periphyton from stones taken from the shore of the Zürichsee, yielded harvests which were clearly higher in Limmat water taken from points downstream from the sewage works than in water taken from points upstream.

A population explosion of the zebra mussel Dreissena polymorpha in Lake Zürich in the early seventies was followed by a decline, most noticeably in the littoral zone (Burla and Lubini-Ferlin, 1976). To check for further density changes, zebra mussels were counted every winter from 1978 to 1988, and larval settlement was recorded every summer from 1976 to 1988. During this period, mussel densities ranged from 11 to 1500 ind. m−2; juvenile densities from 11 to 108 ind. cm−2. Counts of newly settled juveniles and counts of established mussels were positively correlated between years. This suggests that the number of larvae in any given year depends on the size of the breeding population of mussels. Juvenile counts from different sites were more similar than mussel counts in any given year, indicating that within-lake dispersal of larvae is high. In both newly settled juveniles and established mussels, density variation occurred in what appeared to be two full cycles of 5 years. Mussel densities were positively correlated with total bird counts of three known predators of D. polymorpha, the Coot (Fulica atra), Tufted duck (Aythya fuligula), and Pochard (A. ferina). Higher mussel densities were observed near Zollikon and Goldbach than at other sampling sites. This may be a consequence of a steeper, stonier slope of the lake bed at these sites. Twenty-eight years after it was first recorded in Lake Zürich, D. polymorpha appears to be firmly established in the lake.

In order to create a common comparative biomass basis for the biological interactions between zooplankton and phytoplankton, zooplankton was quantitavely sampled at close intervals, counted and measured at determined development stages. The volumetric values calculated according to stereometric formulas do not indicate an important variability over the years. Significant volume increases of adult crustaceans were observed only from March till May. Comparisons with past plankton analyses revealed a rapid increase of the herbivorous crustaceans, i.e. by a factor of five; while simultaneously, the favourite food (nannoplankton) only increased from 3.1 g/m2 to 5.5 g/m2 wet weight.

The 8th Symposium of the International Association for Cyanophyte Research IAC was attended by 29 specialists from 11 countries. The 19 oral presentations and discussions centered on the following themes: The basic principles of cyanophyte taxonomy (3 lectures), systematic problems of certain taxonomic groups (5 lectures), morphology (6 lectures) and ecology (5 lectures). The intensive discussions between representatives of the classical (european) taxonomic treatment of cyanophytes (based on morphological and ecological characteristics) and those representing the bacteriological study of ‘cyanobacteria’ were especially valuable. The central theme of the meeting was, however, the mutual microscopic study and discussion of problematic blue-greens from natural habitats, that were mostly collected during the three field trips into different areas of central Switzerland (Grimsel-Gotthard-Nufenen. Klewenalp. Gerzensee).

Oligochaete communities (tubificid and lumbriculid worms) were studied between 1982 and 1985 in 23 areas of the mesoeutrophic Lake Geneva (Switzerland). Species numerically dominant in eutrophic lakes (mostlyPotamothrix hammoniensis), in mesotrophic lakes (mostlyP. vejdovskyi) and in oligotrophic lakes (mostlyStylodrilus heringiamus) constituted 52%, 36% et 12% of the worm communities, respectively (means across the 23 areas). The relative abundance of eutrophic species increased (15 to 94%) according to depth or to external organic inputs. In this case, the mean biomass (wet weight) of oligochaetes per area was higher than 15 g·m−2 (up to 210 g). Mesotrophic species decreased (65 to 1%) along the same gradients of depth or of sedimentation. Oligotrophic species increased (0 to 31%) only in areas where the organic sedimentation was lessened by steep bottom slope and by currents. Thus, the structure of oligochaete communities reflected the patterns of sedimentation and the trophic state of Lake Geneva.

Results obtained by means of an ultrasonic current meter in the plume of the Rhone river are summarized as follows:1. Currents of Rhone river water entering the lake were clearly discernible up to a distance of about 1 km from the river mouth. The interflow was observed at depth of 10 to 30 m. 2. Interflow velocities decreased with increasing distance from the river mouth: from 40cm/s at a distance of 350 m to about 15 cm/s at 1 km. 3. Short-term variations of current velocities and directions documented the highly turbulent nature of the interflow. 4. The entering river water (inflow direction to the NNW) interfered with a persisting northeastward current of the lake water. At a distance of 1–2 km from the mouth the interflow gradually assumed the same direction, possibly due to deflection by Coriolis forces. 5. Current velocities showed considerable variations within a time scale in the order of hours at the same measuring position. The reasons for these fluctuations remain unclear. Possible causes may be lateral oscillations of the entering river water or its deviation by river mouth bars during periods of reduced river discharge. Variations of the discharge alone cannot explain these current fluctuations.

Without Abstract

The vernal pool fairy shrimp (Branchinecta lynchi) (Eng et al. in J Crustac Biol 10:247–277, 1990) is broadly distributed throughout California’s Central Valley with disjunct populations in southern California and southern Oregon. A survey of genetic variation at the mitochondrial cytochrome c oxidase subunit I (COI) gene was conducted from individuals collected throughout the range of the species. Phylogenetic analysis of unique haplotypes could not resolve any significant genetic partitions below the species level. A detailed analysis of samples from two pools indicates that sample sizes underestimate overall variation, but that the general phylogeographic pattern still holds. Evidence was found for a putative long-distance dispersal event between Central Valley sites and the Oregon site. These results indicate that geographically limiting stochastic colonization followed by local diversification may be important in governing current genetic structure for this species. Future and current conservation/restoration efforts should recognize the geographic limitations to population structure for this species and focus on local endemic genetic variation. Keywords Branchinecta lynchi –Mitochondrial DNA–Divergence–Conservation

The northern Arabian Gulf experienced one of the world’s worst man-made environmental disasters during the 1991 Gulf War. The marine ecosystem and fisheries resources in Kuwait’s coastal waters were severely damaged. More than 10 years have since passed. Limited work has been done in quantitative evaluation of changes in the Kuwaiti fishery before and after the Gulf War. In this study, using the Iranian prawn fishery as a reference, we identified a significant reduction of landings in the Kuwaiti prawn fishery after the Gulf War. We developed a model to estimate annual prawn recruitment from pre-season survey data and found that the post-war recruitments were significantly lower than those before the war.¶ A regression of finfish landings against prawn catches in Kuwaiti waters revealed a great increase in finfish landings after the war. This study suggests that there has been large reduction in recruitment in Kuwait’s prawn fishery since the Gulf War, which may have contributed to decreased prawn landings. We hypothesize that the lower prawn recruitment and landings after the war may be a consequence of changes in the ecosystem of the Kuwaiti waters, as a result of the Gulf War. However, because of insufficient data on the ecosystem and fisheries, this hypothesis cannot be tested in this study. We recommend this hypothesis be tested in future studies.

The impact of urban air toxics on the proximate water bodies was investigated as part of the AEOLOS Project (Atmospheric Exchange Over Lakes and Oceans). The hypothesis of this project was that emissions of hazardous air pollutants into the coastal urban atmosphere increased atmospheric depositional fluxes to proximate Great Waters. Areas of major field and modeling campaigns were located in southern Lake Michigan near Chicago, IL and northern Chesapeake Bay near Baltimore. The impact on Lake Michigan of PCB emissions from the urban area of Chicago was evaluated through field experiments to determine atmospheric concentrations, surface water concentrations, wet and dry deposition and bi-directional gas exchange. These values were used to construct a PCB mass budget for the Lake Michigan ecosystem, which includes the urban influence. PCB emissions in the Chicago atmosphere lead to dramatically increased atmospheric concentrations of PCBs off shore and significantly increased wet, dry particle and air-water exchange fluxes in southern Lake Michigan compared to the regional signal. High PCB concentrations occur over the lake only when the wind is from the direction of the urban/industrial complex inclusive of the shoreline from Gary, IN to Evanston, IL toward the lake. Although atmospheric loading of PCBs was much higher in the southern basin of Lake Michigan, water column concentrations have significantly decreased from 1980 to 1994 through the rapid uptake by settling particles, and have continued to decrease at a rate of 0.17yr–1. In contrast to earlier PCB mass budgets that missed significant inputs, outputs and/or process terms, inclusion of the urban-influenced air-water exchange processes and a re-evaluation of new lake data effectively closed the PCB budget for Lake Michigan. Atmospheric exchange processes dominated the whole lake budget. The Chicago area, with high industrial density, emits large quantities of hazardous organic pollutants and has important impacts on the down wind coastal atmosphere and proximate surface waters.

The behaviour of particle-reactive metals in natural environments is linked to adsorption, particle erosion, transport and sedimentation. In the field these processes are best studied and quantified on small, local scales, where the number of variables remains manageable. The Muttsee watershed, situated above 2500 m in the north-eastern Swiss Alps, represents such a 'simple' natural test site, a self-contained bedrock-soil-water-sediment system that allows the analysis of radioactive metals in order to study their interaction with water, bedrock, soil and sediment and to quantify radionuclide and particle transfer. A small lake (Muttsee) forms a natural trap for eroded material and ~ 80% of the radionuclides 210Pb and 137, 134Cs deposited in the catchment area. Radionuclide-dated sediment cores from the lake allow the determination of sedimentation rates, which increased from 0.30 cm year-1 during the period 1963-1986 to 0.55 cm year-1 during 1986-1992. The related increase in erosion rate (10 to 19 cm kyrs-1) may be related to a landslide that occurred during the early 1960s, when sections of plant-stabilized soil were covered by rock debris. The data, which can be evaluated using mass balance calculations, allow assessment of the role of a soil cover in controlling radionuclide residence times in the drainage basin, and also allow estimation of changes in the extent of soil cover during the last 40 years. This changing extent of soil cover makes it impossible to use soil profiles for an assessment of atmospheric radionuclide fluxes. Radionuclide measurements in soils serve as a pedological tool, allowing in cases recognition of soil creep and transient cover.

North Sea houting, Coregonus oxyrinchus, became extinct in the River Rhine in the 1940 s and was reintroduced in the 1990 s. To study the migration history of individuals, the 88Sr:44Ca ratio of scales of 39 houting (10–44 cm TL) caught in Lake IJsselmeer was analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Scales of houting inhabiting freshwater ponds and two Danish rivers containing the last original populations in the North Sea basin were used as controls. Fish that lived exclusively in freshwater had 88Sr:44Ca ratios of around 0.2 from the nucleus to the edge; 29 of the analysed houting from Lake IJsselmeer were of this type. Most of these were small, but some were mature and up to 42 cm in length. Seven houting had 88Sr:44Ca ratios over 0.27 from the nucleus to the scale maximum values, indicating migration to the sea at early life stages. Three houting with low 88Sr:44Ca ratios at the scale nucleus and increased 88Sr:44Ca ratios towards the scale edge probably lived in freshwater for a longer period after hatching and then moved to brackish/marine environments. The scale analysis indicates different migration patterns for houting in Lake IJsselmeer and provides evidence that this species (1) is sometimes able to pass the migratory barriers between the Wadden Sea and Lake IJsselmeer, and (2) does not need to migrate to sea to reach maturity.

Statistics for all important fish for the past 60 years and the management measures taken, together with the scientific results, have been evaluated, in order to recognize the development trend and the success or failure of the measures. Although total yields have increased by 500%, the catches for some species i.e. pike, pike-perch and lake trout, have decreased in the past 15 years in spite of enormous measures. The possible reasons are discussed. Cannibalism and decimation through rapacious fish regulate the yield and cause oscillations. Therefore studies on the biology of fish must rather consider the correlations between the single species. For good management, it is more important to plant alevins than fry.