The first decade of oligotrophication in Lake Constance

Phytoplankton biomass and species composition were measured with a relatively high temporal resolution (once or twice a week during the growing season) from 1979 to 1989 in Lake Constance/Überlingersee. Over this period soluble reactive phosphorus (SRP) concentrations during winter mixing were reduced by ca. 50% from 104 to 47 g 1^–1, which caused a prolongation and amplification of the epilimnetic P depletion during the growth period. Seasonal dynamics of phytoplankton reacted to the decrease of SRP in the following ways: (1) Algal biomass decreased at least proportionally to the winter SRP concentrations in summer, but not in spring and autumn when biomass fluctuated irregularly. (2) The peak of biomass concentration changed from summer to spring. (3) The earlier onset of epilimnetic P depletion during the season in recent years promoted a stronger growth of some pennate diatoms in spring. It caused an amplification of the silicon depletion in summer, which may cause still greater reduction of diatoms and total algal biomass in summer. (4) Reduction of algal biomass during the clear-water phase proper became shorter and less pronounced. (5) The temporal variability of algal biomass decreased in summer and autumn but not in spring. (6) Average cell sizes remained unchanged in summer and autumn but increased in spring during the beginning of oligotrophication. These results are largely in agreement with other studies on lake restoration and expectations derived from the PEG (Plankton Ecology Group) model (Sommer et al. 1986). They show that a 50% reduction of SRP concentrations during homothermy may have pronounced effects on seasonal dynamics of algal biomass in a large and deep lake. The algal response to the external change of SRP concentrations can be described by the Le Chatelier principle, implying that the internal structure of the system (e.g. species composition) changes in order to minimize the effect of the external pressure (e.g. reduction of total biomass). Suggestions are made as to how this system behaviour may emerge from local interactions.     

Fecundity of whitefish (Coregonus lavaretus) during the eu-and oligotrophication of Lake Constance

About 20 ovaries of the whitefish 'Blaufelchen' ( Coregonus lavaretus L.) of Lake Constance (Bodensee) were collected annually from 1964-1991. Absolute and relative fecundity peaked in the early 1980s, lagging about 2 years behind the maximum of total-P in the water (during the circulation period). Out of the biological time-series of Lake Constance, whitefish fecundity is the only one known to follow the phosphorus curve, and this may be the first time-series documented case of parallel trend reversal in the trophic state of a lake and fish biology. It is concluded that fish fecundity serves, at best, as an unspecific monitor of the overall well-being of the fish.     

Seasonal and interannual variability in the taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake,Oregon

Taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake, Oregon, were examined during time periods between 1984 and 2000. The objectives of the study were (1) to investigate spatial and temporal patterns in species composition, chlorophyll concentration, and primary productivity relative to seasonal patterns of water circulation; (2) to explore relationships between water column chemistry and the taxonomic composition of the phytoplankton; and (3) to determine effects of primary and secondary consumers on the phytoplankton assemblage. An analysis of 690 samples obtained on 50 sampling dates from 14 depths in the water column found a total of 163 phytoplankton taxa, 134 of which were identified to genus and 101 were identified to the species or variety level of classification. Dominant species by density or biovolume included Nitzschia gracilis, Stephanodiscus hantzschii, Ankistrodesmus spiralis, Mougeotia parvula, Dinobryon sertularia, Tribonema affine, Aphanocapsa delicatissima, Synechocystis sp., Gymnodinium inversum, and Peridinium inconspicuum. When the lake was thermally stratified in late summer, some of these species exhibited a stratified vertical distribution in the water column. A cluster analysis of these data also revealed a vertical stratification of the flora from the middle of the summer through the early fall. Multivariate test statistics indicated that there was a significant relationship between the species composition of the phytoplankton and a corresponding set of chemical variables measured for samples from the water column. In this case, concentrations of total phosphorus, ammonia, total Kjeldahl nitrogen, and alkalinity were associated with interannual changes in the flora; whereas pH and concentrations of dissolved oxygen, orthophosphate, nitrate, and silicon were more closely related to spatial variation and thermal stratification. The maximum chlorophyll concentration when the lake was thermally stratified in August and September was usually between depths of 100 m and 120 m. In comparison, the depth of maximum primary production ranged from 60 m to 80 m at this time of year. Regression analysis detected a weak negative relationship between chlorophyll concentration and Secchi disk depth, a measure of lake transparency. However, interannual changes in chlorophyll concentration and the species composition of the phytoplankton could not be explained by the removal of the septic field near Rim Village or by patterns of upwelling from the deep lake. An alternative trophic hypothesis proposes that the productivity of Crater Lake is controlled primarily by long-term patterns of climatic change that regulate the supply of allochthonous nutrients.     

The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana,Croatia)

The shallow Lake Vrana was studied over a 1-year period, special attention being paid to the phytoplankton. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. The regular annual development observed was in species contribution to total biomass rather than in seasonal changes in species composition. The assemblage was dominated by Cosmarium tenue Arch. and Synedra sp. In winter and in spring the phytoplankton assemblage was dominated by Cosmarium tenue and high contribution of Synedra sp. was observed during the summer and autumn. Results suggest that concentrations of inorganic nitrogen and phosphorus were critical in regulating phytoplankton biomass and species dominance.     

Sublittoral and profundal Oligochaeta fauna of the Lake Constance (Bodensee-Obersee)

Fourteen tubificid species and one lumbriculid make up the oligochaete population of the northern half of Lake Constance, a meso- to mesoeutrophic lake. Tubifex tubifex makes up 72% of the total abundance, the clean water species Stylodrilus heringianus only 0.1%. No correlation exists between total worm abundance and organic carbon content of the sediment, only 4% of the organic carbon being used by the worms. A highly significant correlation between particulate organic matter loading and its organic carbon content from 10 tributaries and total oligochaete abundance is demonstrated. The ecological index I_PA is defined and used to assess the biologically relevant trophic status of the lake bed. This integrates information on the percent representation of three groups of worm species classified on atrophic basis and total abundance of the worms. Despite control of the increase in phosphorus loadings progressive eutrophication of sediments was observed after an 8 year interval.     

氯化物型盐碱池塘浮游植物种类和多样性的研究

1997年 4月 5日至 1 998年 9月 1日对山东高青县赵店乡渔场盐碱池塘浮游植物的种类组成和生物量进行了研究 ,池塘盐度变动于 1 .3 6— 2 0 g/L,总碱度变动于 2 .4— 7.2 mmol/L,p H值 8— 9。采集了 3 87个浮游植物定量水样。结果表明 ,高青盐碱池塘浮游植物主要是广盐性淡水种类 ,一些是典型的盐水种。浮游植物的平均生物量为 49.90± 3 1 .92 mg/L,硅藻和裸藻占优势 ,金藻占有相当比重。无鱼对照池的浮游植物生物量较养鱼池塘低得多。     

Absence of intrinsic post‐zygotic incompatibilities in artificial crosses between sympatric coregonid species from upper Lake Constance

A full factorial crossing experiment with five females and five males of each of two coregonid species from upper Lake Constance was used to test for intrinsic post‐zygotic incompatibilities during early ontogeny. Up until shortly before hatching, there was no difference in embryo mortality between homo and heterologous crosses. A maternal effect on mortality was found in both species, but paternal effects and female–male interactions were absent. Thus, genetic incompatibility during early ontogeny does not appear to prevent introgressive hybridization, suggesting that genetic divergence between these species is maintained primarily by pre‐zygotic barriers. The recent genetic homogenizations of coregonid species flocks in European alpine lakes may have been caused by a flattening of adaptive landscapes through eutrophication, but intensive stocking with larvae obtained in hatcheries from artificially fertilized eggs is also likely to be a contributing factor. To safeguard diversity among sympatric coregonids, it is important to re‐establish ecological conditions conducive to species divergence and to revise traditional management strategies.     

威宁草海的浮游植物

从2004年1月至2005年1月,对贵州威宁草海的浮游植物进行采集和鉴定,共鉴定出浮游植物390种(含变型和变种),分属7门10纲23目41科96属。其中绿藻门种类最多,达205种,占总种数的52.56%;其次是蓝藻门的种类,有85种,占21.79%;硅藻门的种类有55种,占14.10%;其他藻类有45种,占11.15%。全年均能采集到的有60种,多数为小型的、富营养湖泊种常见的水华藻类,如铜绿微囊藻(Microcystis aeruginosa)、铜绿微囊藻小型变种(M. aeruginosa var. minor)。鉴定出的藻类植物种有105种为污染指示种,其中全年出现的多污性(ps)指示种有6种,β-多污性(β-ps)指示种有44种,α-中污性(α-ms) 指示种有78种,β-中污性(β-ms) 指示种有64种,寡污性(os) 指示种有17种,分别占总污染指示种总数的5.71%,41.90%、74.29%、60.95%、16.19%(有的种类具有多种污染级别的指示,在统计过程中均分别计算),草海的污染指示种以α-中污染和β-污染指示种为主。根据草海浮游植物种类组成的历史演变来看,硅藻门的种类减少较多,其他一些适宜生活于清洁水体种的藻类,如小黄丝藻(Heterotrichales minus)从1989年以后就未曾发现。所有结果都显示出草海已受到严重污染,属于富营养型的湖泊。     

珠江口近海浮游植物生态特征研究

1998～1999年对珠江口近海浮游植物进行了5个航次现场调查,共鉴定出浮游植物239种．其中。硅藻最多,占72．4％,甲藻次之,占23．8％,其他门类合占3．8％．种类组成以暖水种和广温种为主;优势种季节更替明显,四季的主要优势种依次为伏氏海毛藻(Thalassiothrix frauenfeldli)、柔弱菱形藻(Nitzschia delicatlssima)、伏氏海毛藻、细弱海链藻(Thalassiosira subtilis)．细胞密度全年变幅0．2×10^4～2767．1×10^4cell·m^-3,四季平均98．7×10^4cell·m^-3,夏、冬季明显高于春、秋季．平面分布呈近岸明显高于外海趋势。密集区终年出现在西北海域上川岛附近．Shannon—Wiener指数、Pielou均匀度和多样性阈值四季均值变幅分别为2．63～3．17、0．53～0．71和1．74～2．23,群落多样性水平较高,结构较稳定．     

Elemental composition of two coexisting Daphnia species during the seasonal course of population development in Lake Constance

Summary In 1986 and 1987 the seasonal course of population density, life history traits and biomass composition (CHN-elemental and ash) of two coexisting Daphnia species from L. Constance (Überlinger See) were studied. The two daphnids are morphologically similar, but demonstrate different seasonal variation of behaviour (i.e. diurnal vertical migration). With the exception of nitrogen content, the mean biomass composition of adults and that of eggs were significantly different: the dry biomass of eggs (adults) contained on average 55.6 (46.1) % C, 7.9 (6.5) % H, 9.7 (9.7) % N, and 10.0 (23.8) % ash. These values were similar to those of other daphnids; it may be concluded that the average daphnid composition is not species specific, but is determined mainly by the position in the life cycle and by the nutritional state of the animal. A distinct seasonal variation in the elemental composition of the biomass of adult daphnids was observed. It related significantly to the concentration of food, as indicated by the epilimnetic chlorophyll-a concentrations and by Secchi depth. From the amplitude of seasonal variation of elemental composition and from the shape of relationships between the elemental composition of daphnids and their food, it can be concluded that in summer the non-migrating D. galeata lives under stronger food limitation than the migrating H. hyalina. In spring, there were no differences in the biomass composition of either species. In summer, the adult fcmales of D. galeata contained significantly less carbon, and hydrogen than those of D. hyalina. In most parameters of biomass (i.e. biomass composition of adults) and of life history (i.e. clutch size, mean adult weight), D. galeata displayed higher coefficients of variation. A tendency in D. galeata to have peaks of population development carlier in the season and in D. hyalina to have them towards autumn was observed. These contrasting responses of the populations development, the seasonal variability of the biomass composition seem to support the view of Geller (1986) who called D. galeata and D. hyalina exploitative and conservative strategists respectively.This research was supported by the Deutsche Forschungsge-meinschaft within the Sonderforschungsbereich Cycling of Matter in Lake Constance (SFB 248), and by scholarship to R.B. from the Deutscher Akademischer Austauschdienst (DAAD)     

Distribution of perch (Perca fluviatilis L.) during their first year of life in Lake Constance

The distribution and behaviour of larval and juvenile perch (Perca fluviatilis L.) were studied for two years in large, deep Lake Constance. After hatching larvae were transported by water currents to the open water. The majority of larvae remained in the pelagic zone for about one month. In both years, their return to the littoral zone coincided with the decline of pelagic zooplankton abundance. After returning to the littoral zone, juveniles stayed among submerged macrophytes within 5 m depth and lived apart from larger perch which lived at depths of 6–20 m. By late summer, juveniles changed their distribution pattern: during the day they stayed intensively close to piers and ports, but increased their swimming activity at dusk, cruising among shallow and deep waters and feeding on zooplankton, and rested on the bottom at night. This behaviour appears to be related to the decrease of inshore food resources and to the presence of predators in deeper water. 0⁺ perch left the littoral zone and moved into deep waters when autumnal mixing began in late October. They overwintered near the bottom at depths of more than 30 m. During most of the year, juvenile and adult perch were separated from each other. But as soon as they occupied the same habitat, the occurrence of cannibalism increased.     

Location-dependent infection of fish parasites in Lake Constance

Perch Perca fluviatilis and roach Rutilus rutilus were caught at various locations around Lake Constance (Bodensee). Infection of perch and roach with the eyeflukes Diplostomum spathaceum and Tylodelphis clavata was greatest in the western location (Bottighofen). The varied occurrence of parasite species at different locations indicated that maximum interchange between fish populations was slight. Whitefish Coregonus lavaretus migrating up the River Rhine were less infected with both the tapeworm Proteocephalus exiguus and the copepod Ergasilus sieboldi than whitefish from the middle of the lake. Some of the parasites had already left their hosts. Newly established infections were not found in migrating whitefish.     

Methane production in littoral sediment of Lake Constance

Maximum rates of CH₄ production in the littoral sediment were observed in 2–5 cm depth. The CH₄ production rates increased during the year from about 5 mmol m⁻²d⁻¹ in December to a maximum of about 95 mmol m⁻²d⁻¹ in September. CH₄ production rates showed a temperature optimum at 30°C and an apparent activation energy of 76 kJ mol⁻¹. A large part of the seasonality of CH₄ production could be ascribed to the change of the sediment temperature. Most of the produced CH₄ was lost by ebullition. Gas bubbles contained about 60–70% CH₄ with an average δ¹³C of −56.2% and δD of −354%, and 2% CO₂ with an average δ¹³C of −14.1% indicating that CH₄ was produced from methyl carbon, i.e. mainly using acetate as methanogenic substrate. This result was confirmed by inhibition of methanogenesis with chloroform which resulted in an accumulation rate of acetate equivalent to 81% of the rate of CH₄ production. Most probable numbers of methanogenic bacteria were in the order of 10⁴ bacteria g⁻¹d.w. sediment for acetate-, methanol- or formate-utilizing, and of 10⁵ for H₂-utilizing methanogens. The turnover times of acetate were in the order of 2.3–4.8 h which, with in situ acetate concentrations of about 25–50 μM, resulted in rates of acetate turnover which were comparable to the rates of CH₄ production. The respiratory index (RI) showed that [2−¹⁴C]acetate was mainly used by methanogenesis rather than by respiratory processes, although the zone of CH₄ production in the sediment overlapped with the zone of sulfate reduction.     

Sulfate-reducing bacteria in littoral sediment of Lake Constance

Abstract The viable population of sulfate-reducing bacteria (SRB) in littoral sediments of Lake Constance was investigated using enrichment and enumeration techniques. Enrichment studies established that most types of SRB grew best in media with low salt concentrations (max. 0.4 g Cl⁻/1), consistent with the low salinity of the freshwater habitat. Enumerations were based on an adequate medium with the following electron donors: H₂, lactate, acetate, propionate, butyrate, caprylate, succinate, benzoate, or S₂O₃²⁻ for thiosulfate-disproportionating bacteria. Cultures were incubated for 6 weeks to obtain maximum counts. A maximum cell density of 6.3 × 10⁶ cells per ml sediment was estimated, which is the highest number of SRB ever reported for anoxic sediments. A comparison with measured sulfate reduction rates showed that the enumeration techniques were about 10–100-fold more efficient than those previously used. The population of SRB had a characteristic structure consisting of 87.7% H₂-utilizing SRB (physiologically resembling the classical Desulfovibrio species); 12.0% propionate utilizers (tentatively identified as Desulfobulbus species); 0.3% long chain fatty acid-oxidizing Desulfovibrio sapovorans species. Acetate-utilizing SRB ( Desulfotomaculum acetoxidans ) constituted ≤ 0.05% of the total estimated population. Moreover, the latter species was only present as inactive spores. Benzoate-degrading SRB were not detected.     

Structure of plankton communities in Ilchir, an alpine lake in eastern Siberia

 Lake Ilchir is an alpine lake located 1963 m above sea level in the mountain ranges of eastern Sayan, eastern Siberia. Observations are presented from October 1998 to September 1999 in order to provide the phytoplankton and zooplankton community structures. Sixty-six taxa of phytoplankton and 66 taxa of zooplankton were recorded. Of much interest was the finding of rare species, such as the dinoflagellate Gymnodinium coeruleum, the diatoms Pliocaenicus costatus and Cyclotella tripartita, and the calanoids Acanthodiaptomus tibetanus and Arcthodiaptomus (S.) paulseni. Received: August 24, 2001 / Accepted: April 13, 2002     

The destruction of an endemic species flock: quantitative data on the decline of the haplochromine cichlids of Lake Victoria

Synopsis The Lake Victoria fish fauna included an endemic cichlid flock of more than 300 species. To boost fisheries, Nile perch (Lates sp.) was introduced into the lake in the 1950s. In the early 1980s an explosive increase of this predator was observed. Simultaneously, catches of haplochromines decreased. This paper describes the species composition of haplochromines in a research area in the Mwanza Gulf of Lake Victoria prior to the Nile perch upsurge. The decline of the haplochromines as a group and the decline of the number of species in various habitats in the Mwanza Gulf was monitored between 1979 and 1990. Of the 123+ species originally caught at a series of sampling stations ca. 80 had disappeared from the catches after 1986. In deepwater regions and in sub-littoral regions haplochromine catches decreased to virtually zero after the Nile perch boom. Haplochromines were still caught in the littoral regions where Nile perch densities were lower. However, a considerable decrease of species occurred in these regions too. It is expected that a remnant of the original haplochromine fauna will survive in the littoral region of the lake. Extrapolation of the data of the Mwanza Gulf to the entire lake would imply that approximately 200 of the 300+ endemic haplochromine species have already disappeared, or are threatened with extinction. Although fishing had an impact on the haplochromine stocks, the main cause of their decline was predation by Nile perch. The speed of decline differed between species and appeared to depend on their abundance and size, and on the degree of habitat overlap with Nile perch. Since the Nile perch upsurge, the food web of Lake Victoria has changed considerably and the total yield of the fishery has increased three to four times. Dramatic declines of native species have also been observed in other lakes as a result of the introduction of alien predators. However, such data concern less speciose communities and, in most cases, the actual process of extinction has not been monitored.     

Ecological effects of reduced nutrient loading (oligotrophication) on lakes: an introduction

1. The variable ecological response of lakes to reduced nutrient loading (oligotrophication) at sites in Europe and North America was discussed at a workshop held in Silkeborg (Denmark) in January 2003. Studies of lake oligotrophication were presented based on both long‐term monitoring and data generated by palaeolimnological methods. 2. This introduction to the special issue provides short summaries of a series of the papers presented and their limnological context. Results show that the majority of lakes had approached a new equilibrium of phosphorus (P) and nitrogen (N) concentrations 10–15 years (P) and 0–5 years (N) after a major reduction in loading, irrespective of hydraulic retention time. Phytoplankton biomass decreased and a shift towards meso‐oligotrophic species dominance occurred. The fish responded surprisingly fast to the loading reduction in most lakes. As a result, the percentage of piscivores increased and total fish biomass declined markedly, which may explain an increase in the body size of cladocerans and an increase in the zooplankton to phytoplankton biomass ratio seen in many of the lakes. 3. Monitoring has in general been initiated after the effects of eutrophication became apparent. In this context palaeolimnological techniques become very useful because they allow limnologists to extend time scales of coverage and to define restoration targets and baseline conditions. Moreover, lake sediments pre‐dating anthropogenic disturbance can be used to examine ecological response to, for instance, climate variability, allowing problems associated with multiple stressors to be addressed. 4. It is concluded that there is a great need for a synthetic, holistic approach to studying lake oligotrophication, combining multiple techniques of palaeolimnological sediment analysis with detailed but temporally limited long‐term monitoring of chemical and biological variables. This is important, not least to assess future responses to nutrient loading reductions, as global warming will interact with a range of external stressors and ultimately affect lake management strategies to deal with the resultant feedbacks.     

Coupling of strontium and calcium cycles in Lake Constance

The contents of Sr and Ca were measured weekly in Lake Constance in 1986. Epilimnetic concentrations of Ca changed between 1.30 × 10^-3 mol l^-1 (during homothermy) and 0.9 × 10 -3 mol l^-1 (during thermal stratification). The seasonal fluctuations of Ca were correlated with those of Sr (between 4.61 and 5.36 mol l^-1). The epilimnion was permanently oversaturated with respect to calcite but not with respect to SrCO₃. Analysis of the settling process by use of sedimentation traps revealed two short episodes of very high authigenic settling fluxes of CaCO₃, triggered by phytoplankton diatoms. Seasonal changes of the Ca contents (between 4.1 and 30.7 percent of the dry weight) and of the Sr concentrations (from 12 to 75 × 10^-3 percent) in the settling material were closely correlated. This suggests a coprecipitation mechanism with a nearly constant stoichiometry of (atoms Sr/atoms Ca) × 1000 of 0.84. Coprecipitation of Sr or Ca with organic matter was insignificant. In the hypolimnion some Sr and Ca were released from the settling material. These results strongly suggest that the cycle of Sr in Lake Constance is driven predominantly by coprecipitation with calcite. The principal chemical mechanisms leading to coprecipitation are discussed.