Plankton populations of Lake Leake and Tooms Lake—Oligotrophic Tasmanian Lakes

The characteristic feature of Lake Leake and Tooms Lake is their great similarity in physical and chemical limnology. This similarity extends to the plankton populations in general terms, both lakes being dominated by Cyclotella stelligera Cleve et Grun. and having few other species. Floristic differences are minimal. Despite this floristic similarity distinct differences exist in plankton periodicity, principally in that of Cyclotella stelligera. The extreme oligotrophy of the lakes, already suspected from their low nutrient levels, is confirmed by the extremely meagre standing crops.     

Lake Name or Name Lake? The etymology of lake nomenclature in the United States

相似文献   

Zooplankton of Lake Peipsi-Pihkva in 1909–1987

164 taxa were identified in the net zooplankton of the pelagial of L. Peipsi-Pihkva in 1909–1987, including 3 species of protozoans, 74 species of rotifers, 58 species of cladocerans, 28 species of copepods and 1 mollusc. One rotifer species, Ploesoma peipsiense Mäemets et Kutikova, has been described as new for science here. The zooplankton of L. Peipsi-Pihkva is remarkably rich in species including rarities in Estonia: Limnosida frontosa, Drepanothrix dentata, Bythotrephes longimanus, B. cederstroemi etc. Due to its large surface area, L. Peipsi-Pihkva provides a large scale of biotopes of a diverse trophic state and humic content, which support species with different ecological requirements. Most of the aquatory of the lake has lately been mesotrophic, favouring the coexistence of indicators of oligo- and mesotrophic state and species preferring a higher trophic state. The occurrece of 10 species of the genus Bosmina including B. berolinensis, B. gibbera, B. lilljeborgi, B. thersites and B. crassicornis, sparse in Estonian lakes, is the most noteworthy feature of the zooplankton of L. Peipsi-Pihkva. The coexistence of B. coregoni and B. berolinensis, B. gibbera, B. lilljeborgi etc. which were earlier regarded as subspecies of B. c. coregoni proves that they are different species producing usually no hybrids. The species composition was subjected to certain changes during the years under consideration. Larvae of Dreissena were first found in zooplankton in 1962. The oligo-mesotrophic indicator Holopedium gibberum occurred in the lake in 1909–1964, but was lacking in later samples.     

The Origin and Evolution of Lake Vähä-Pitkusta, SW Finland – A Multi-Proxy Study of a Meromictic Lake

Lake Vähä-Pitkusta is a 35-m deep meromictic kettle-hole lake in SW Finland. The topmost 15cm of the sediment stratigraphy consists of black gyttja, representing the last ca. 600years. A sediment core from the deepest point was examined with multi-proxy methods to determine the origin and evolution of the basin, the onset of the meromictic conditions and the primary factors that initiated the meromictic processes. The results indicate that Lake Vähä-Pitkusta became isolated from the Baltic basin during the Yoldia Sea stage. After initial unstable sedimentary conditions the development continued steadily until ca. 2500–2300 cal.BP when there is indication of lake level rise and/or increased surface runoff, probably resulting from a cooler and moister climate. The diatom and cladoceran results indicate only a slight rise in the trophic state following the increased erosion. Pollen evidence suggests weak anthropogenic activity in the catchment during the last 1000 years, and this had only little effect on the trophic state, which remained rather low. Thus, it is most unlikely that the trophic state was the primary reason for the origin of meromixis, although it may have contributed to it. We tentatively suggest that the primary reason was the peculiar morphometric dimensions of Lake Vähä-Pitkusta (small, deep, sheltered from winds) which made it very sensitive and that even a very slight increase in soluble electrolytes may push it over the edge into meromixation. It is possible that this did not occur during the cold/moist period around ca. 2300 cal.BP but during the Medieval Climate Anomaly. Studies on sediment geochemistry are needed to verify this assumption.     

Fishery of Lake Ladoga — past, present and future

The post-war fishery of Lake Ladoga can be divided according to its catch level into four periods. In the years 1945–1954 the total annual catch increased, and reached the level of 4000 tonnes. In this period the fish stocks that had increased during the war years were intensively exploited. However, this fishery was not in balance with the stocks during the period 1955–1963. As a consequence, the catch decreased drastically, being sometimes less than 2000 tonnes.Controlling the fishery restored the abundance of whitefish Coregonus lavaretus (L.) and zander Stizostedion lucioperca (L.). This increased the total annual catch to about 5500 tonnes in 1964–1989. However, the fishery control measures have not been sufficient to achieve the conservation of salmon Salmo solar L. m. sebago, brown trout Salmo trutta L. and the migratory lake whitefish stocks.A decrease in the total fish catch has been observed since 1990. This decrease may be related to the deterioration of the environment of Lake Ladoga, caused by anthropogenic factors. The unfavourable state of the ecosystem has led to decline of the whitefish stocks and, especially during the last few years, to drastical decline of zander.Acute problems, to be faced in the near future, are connected with the hatchery maintenance of several river-spawning stocks, e.g. salmon, brown trout and migratory whitefish, because the existing fish hatcheries are insufficient in capacity and technically outdated.     

Spatial–temporal patterns of methane dynamics in Lake Taihu

Many European lakes are monitored according to the EU Water Framework Directive (WFD), with focus on phytoplankton biomass and species composition. However, the low-frequency WFD monitoring may miss short-term phytoplankton changes. This is an important issue because short-term extreme meteorological events (heat waves and heavy rain) are predicted to increase in frequency and intensity with climate change. We used records from Lake Mondsee (Austria) from 2009 to 2015 to test if a reduction from monthly to seasonal sampling affected the average annual phytoplankton biovolume. Furthermore, we combined inverted light microscopy, FlowCAM and flow cytometry to estimate the effect of sampling during extreme events on average phytoplankton biovolume. Relative to monthly sampling, seasonal sampling significantly overestimated phytoplankton biomass. A heat wave in 2015 and two episodes of heavy rain in 2015 and 2016 caused species-specific changes; biovolumes of chlorophytes and the filamentous cyanobacterium Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek increased significantly during the heat wave. Using live material with FlowCAM and flow cytometry, we detected small and fragile cells and colonies that were either ignored or underrepresented by analysing fixed samples with light microscopy. We suggest a modified sampling and analysis strategy to capture short-term changes within the phytoplankton community.     

Seasonality of chlorophyll and nutrients in Lake Erken – effects of weather conditions

The effect of submerged macrophytes on interactions among epilimnetic phosphorus, phytoplankton, and heterotrophic bacterioplankton has been acknowledged, but remains poorly understood. Here, we test the hypotheses that the mean summer phytoplankton biomass (chlorophyll a): phosphorus ratios decrease with increased macrophyte cover in a series of nine lakes. Further, we test that both planktonic respiration and bacterioplankton production increase with respect to phytoplankton biomass along the same gradient of increasing macrophyte cover. Increased macrophyte cover was associated with a lower fraction of particulate phosphorus in epilimnia, with total particulate phosphorus declining from over 80% of total phosphorus in a macrophyte free lake to less than 50% in a macrophyte rich lake. Phytoplankton biomass (chlorophyll a) too was lower in macrophyte dominated lakes, despite relatively high levels of total dissolved phosphorus. Planktonic respiration and bacterioplankton production were higher in macrophyte rich lakes than would be expected from phytoplankton biomass alone, pointing to a subsidy of bacterioplankton metabolism by macrophyte beds at the whole lake scale. The results suggest that the classical view of pelagic interactions, which proposes phosphorus determines phytoplankton abundance, which in turn determines bacterial abundance through the production of organic carbon, becomes less relevant as macrophyte cover increases.     

Shoreline displacement of Lake Ladoga — new data from Kilpolansaari

Dating of sediments sampled from small lakes in the Kilpolansaari region, in the NW part of Lake Ladoga, indicate that the River Neva, which is the present outlet of Lake Ladoga, originated at 3,100 radiocarbon years BP This is in agreement with some earlier estimations but no consensus concerning the age of the River Neva has previously been reached. New diatom data provide information concerning salinity and nutrient conditions in northern Lake Ladoga prior to the formation of the River Neva, when the Litorina Sea occupied the Baltic basin and approached the level of the ancient Lake Ladoga. Some slightly brackish water diatom species may indicate occasional saline water incursions into the Ladoga basin but, on the other hand, slightly brackish water species also occur in the present Lake Ladoga.     

Paleolimnology of the Petén Lake district,Guatemala

The long-term impact of Maya culture on a lowland tropical watershed is assessed, using data from a 9.2 m sediment core taken from deep water (28 m) in Lake Quexil. Human population growth, estimated by the 1980 archaeological survey, is associated with a shift in the composition of the sediment to a dominance by inorganic material, the Maya clay formation, beginning ca. 3500 B.P. Increasing settlement densities are correlated with accelerated influxes of phosphorus, carbonates, and siliceous sediment. However, chemical data do not track short-term population fluctuations closely. Because much of the sediment is delivered as colluvium, and not by running water, there is a lag between terrestrial disturbance and impact on the aquatic system. As an indication of this lag, contemporary high sedimentation rates are a residual of Maya activity that virtually ceased some 300–400 years B.P. Comparison of the deep-water core with a shallow-water (7 m) section, based on palynological correlation, reveals only minor differences in proximate chemical composition. Chemical influxes are much higher at the deep-water site, however, as a consequence of sediment focusing in this hyperconical basin. Chemical analyses of soil samples from 21 test pits in the Quexil basin support the principal conclusion that bulk soil movement was the mode of nutrient transfer to the lake, following forest clearance by the Maya.     

Some physical and chemical characteristics of Lake Atnsjøen

The physical and chemical characteristics of the dimictic, ultraoligotrophic, and subalpine Lake Atnsjøen are described based on data from the period 1985–2001. The temperature stratification of the lake is weakly developed, with the thermocline at about 10 m depth. The surface temperature during summer is usually lower than 14–15?°C. The Secchi disk transparency is normally higher than 8–10 m in summer and autumn, but can be as low as 4.3 m during spring. The pH is about 6.0, and the specific conductivity about 1.0 mS m^{? 1}. The dominating cation and anion are Ca (≈0.8 mg l^?1 or 42 μeq l^?1), and SO₄ (≈1.5 mg l^?1 or 33 μeq l^?1), respectively. The concentration of bicarbonate (HCO₃, μeq l^?1) is sometimes lower, sometimes higher than that of SO₄.     

Biomass and element pools of understory vegetation in the catchments of Čertovo Lake and Plešné Lake in the Bohemian Forest

This paper presents data on species composition, biomass, and element pools (C, N, P, Ca, Mg, Na, K, Al, Fe, Mn) of the understory vegetation of spruce forests in the catchments of lakes ?ertovo jezero (CT) and Ple?né jezero (PL) in the Bohemian Forest (?umava, Czech Republic). Calamagrostis villosa was the most abundant species in the CT catchment, while Vaccinium myrtillus was the most abundant species in the PL catchment. The catchments weighted mean (CWM) of above-ground biomass of the understory vegetation was 288 and 723 g m^?2 in the CT and PL catchments, respectively. The significant difference in the biomass between the catchments was caused by the much higher abundance of V. myrtillus in the PL catchment. The CWM of below-ground biomass of the fine roots was 491 and 483 g m^?2 in the CT and PL catchments, respectively. The respective CWM element pools of biomass in the CT and PL catchments were: C (33 and 51 mol m^?2), N (0.8 and 1.0 mol m^?2), P (24 and 34 mmol m^?2), Ca (53 and 113 mmol m^?2), Mg (24 and 41mmol m^?2), Na (3.7 and 6.5 mmol m^?2), K (83 and 109 mmol m^?2), Al (50 and 42 mmol m^?2), Fe (13.3 and 7.3 mmol m^?2), and Mn (4.2 and 8.8 mmol m^?2).     

The effects and interactions of three invasive fish species introduced to the aquatic ecosystem of a Turkish Lake (Eğirdir Lake)

We studied feeding behavior and prey selection of topmouth gudgeon (Pseudorasbora parva), big-scale sand smelt (Atherina boyeri) and pike-perch (Sander lucioperca) in Lake E?irdir, the second largest freshwater lake in Turkey. Fish specimens were collected between January and August in 2010 and 2011 using gill-nets and purse seines. A total of 941 specimens were analyzed for stomach contents analysis. We expressed the importance of the food items present in their guts with the relative importance index (IRI) and estimated their diet selectivity indices with Pearre’s index. Pseudorasbora parva had a diverse diet comprising mainly Nitokra hibernica (copepod), Chydorus sphaericus, and Bosmina longirostris (cladoceran) (each, at p?<?0.01), but Chironomus sp. (insect) was not a significant component of its diet (p?>?0.05). Big-scale sand smelt often preferred B. longirostris, N. hibernica, and Alona quadrangularis (each at p?<?0.01). Pike-perch positively, but not statistically significant, selected Atherina boyeri (p?>?0.05), Carassius gibelio was not preferred by pike-perch as food item (p?>?0.05). Our results indicate that invasive species altered the food chain in Lake E?irdir. Thus, because these fish species constitute a major threat for native fish species for food and breeding grounds, extensive care should be taken to prevent invasive fish species entering lakes in Turkey.

     

Long-term Patterns of Shifts between Clear and Turbid States in Lake Krankesjön and Lake Tåkern

During the past century, Lake Tåkern and Lake Krankesjön, southern Sweden, have shifted repeatedly between a state of clear water and abundant submerged vegetation, and a state of turbid water and sparse vegetation. Long-term empirical data on such apparently alternative stable state dynamics are valuable as complements to modeling and experiments, although the causal mechanisms behind shifts are often difficult to identify in hindsight. Here, we summarize previous studies and discuss possible mechanisms behind the shifts. The most detailed information comes from monitoring of two recent shifts, one in each lake. In the 1980s, L. Krankesjön shifted to clear water following an expansion of sago pondweed, Potamogeton pectinatus. Water clarity increased when the pondweed was replaced by characeans. Zooplankton biomass in summer declined and the concentration of total phosphorus (TP) was reduced to half the previous level. The fish community changed over several years, including an increasing recruitment of piscivorous perch (Perca fluviatilis). An opposite directed shift to turbid water occurred in Lake Tåkern in 1995, when biomass of phytoplankton increased in spring, at the expense of submerged vegetation. Consistent with the findings in L. Krankesjön, phyto- and zooplankton biomass increased and the average concentration of TP doubled. After the shift to clear water in L. Krankesjön, TP concentration has increased during the latest decade, supporting the idea that accumulation of nutrients may lead to a long-term destabilization of the clear water state. In L. Tåkern, data on TP are inconclusive, but organic nitrogen concentrations oscillated during a 25-year period of clear water. These observations indicate that intrinsic processes cause gradual or periodic changes in system stability, although we cannot exclude the possibility that external forces are also involved. During such phases of destabilization of the clear water state, even small disturbances could possibly trigger a shift, which may explain why causes behind shifts are hard to identify even when they occur during periods of extensive monitoring.     

The management of fisheries in Lake Vörtsjärv

L. Vörtsjärv is a eutrophic lake in Central Estonia. The area of the lake is 270 km², the average depth only 2.8 m. The biological productivity of the lake is rather low. Twelve to fifteen years ago the main fish were ruff and perch (80–90% of catch), while the numbers of valuable fish were small. At the same time the total catch of fish was relatively high — about 300 tons a year. Attempts were made to reduce the numbers of undesirable fish by intense trawl-catch but no marked results were achieved. Subsequently trawl-catch was ended, elvers were regularly introduced into the lake and protection of valuable fish was improved. At the present time the total catch of fish has decreased (184 tons in 1979), but pike-perch and eels are now the main game fish (50–60% of catch) and the value of the catch of fish has risen 2–3 times.     

Chemical analysis of Lake Shira water (1997–2000)

The paper presents the results of chemical analysis of Shira during summer (July-August). The chemical composition of waters in the water body was found to be fairly homogeneous horizontally. However, the concentrations of most ions increased with depth. The near-bottom layers were characterised by higher total mineral content and ash content, higher concentration of sulphates, sulphites, sulphide, phosphorus, ammonium nitrogen, as compared to the layers above. Maximum concentration of oxygen was recorded in 6–8 m stratum, where the photosynthetic processes were most active. The anaerobic layer which lay below the 12 m depth contained high concentrations of sulphide and sulphite. The composition of the lake water could be characterised as sulphate-chloride-bicarbonate sodium-magnesium. The changes in the water quality due to any anthropogenic emissions were not marked.     

Changes of Copepoda populations in Lake Kiret during 1969–1985

Long period analysis of Copepoda populations in Lake Kinneret indicated significant reductions in total biomass and production as well as densities of nauplii and adult stages, particularly females. The reduction of adult Mesocyclops sp. was statistically significant, but that of Thermocyclops sp. was not. Annual averages of eggs/female values and densities of copepodite stages did not show significant changes. Concentrations of adult Thermocyclops sp. became higher relative to the larger genus Mesocyclops sp. It is suggested that densities of large copepods were affected by intensification of predation pressure by particulate feeding fishes. The densities of nauplii were probably reduced by increased predation pressure of filter feeding fish.     

Species composition of phytobenthos in the littoral of Lake Xolotlán (Managua)

The species composition of the phytobenthos in the littoral of Lake Xolotlán (Managua) was determined. Sampling was carried out in November 1987 (end of the rainy season) and in July–August 1988 (rainy season). Sixty-eight taxa were identified;viz. 47 Bacillariophyceae, 13 Cyanophyta and 8 Chlorophyta. The presence of diatom species likeNavicula veneta, Nitzschia amphibia andNitzschia palea indicate eutrophic conditions, high ionic concentration, alkaline conditions and intense organic pollution.     

Joint Russian—Finnish study of radioactive contamination in the NW part of Lake Ladoga

In August 1992 a joint Russian-Finnish expedition was arranged to the NW part of Lake Ladoga to study radioactive contamination in the region. Special attention was paid to the area surrounding the Heinämaa Islands, where the wreck of the former mine carrier ship Kit had been lying about 30 years before it was moved to Novaya Zemlya in 1991. During this period the wreck had been used as a store for radioactive waste containing principally ⁹⁰Sr, ¹³⁷Cs and ^239,24OPu. Lake water, bottom sediment and some biological samples were collected for strontium, plutonium and gammaspectrometric analyses. In all the samples the radioactivity concentrations were very low, indicating radioactive contamination of about the same level as caused by global fallout in the 1960's and the Chernobyl fallout in the area. Only in two water samples taken close to the former site of the wreck slightly elevated ^239,240Pu concentrations were detected. The great water volume of Lake Ladoga and effective water exchange at the wreck site may explain the very low levels of radioactive wastes detected in the aquatic environment.     

Natural diet of fish from Lake Xolotlán (Managua)

Food habits ofMelaniris sardina, Astyanax fasciatus andDorosoma chavesi (n=562) were analyzed in Lake Xolotlán (Managua). Quality and quantity of ingested food were studied by dissecting the alimentary canal and observing its content. Cladocera were the main food forM. Sardina andA. fasciatus. Melaniris sardina could play an important role in maintaining low cladoceran population densities in the lake. Rotifers are the main food forD. chavesi.