Lake circulation and sediment transport in Lake Myvatn

Lake circulation and sediment transport in Lake Myvatn have been calculated using AQUASEA, a numerical model developed by Vatnaskil Consulting Engineers. The goal of the modelling was to calculate changes in sediment transport within the lake due to changes in lake bathymetry caused by diatomite mining. The model uses the Galerkin finite element method and consists of a hydrodynamic flow model and a transport-dispersion model. The flow model is based on the shallow water equations and the wave equation. The transport model is based on the conservation of mass for suspended sediment. The model was calibrated against measurements performed during the summer of 1992. These included measurements of water elevation, current velocity, wave height, and concentration of suspended sediment. After calibration, the model was run for different mining scenarios to determine their impact on the sediment transport in the lake.     

Lake Torrens brine

The chloride content of the groundwater increases towards Lake Torrens. Major enrichment occurs on the playa and is caused by evaporation from the capillary zone. The chloride is sea derived via cyclic aeolian transport.     

Lake flies and the deep-water demersal fish community of Lake Malawi

Larvae and pupae of Chaoborus edulis may be the most important food resource of some deep-water demersal fish species in southern Lake Malawi. C. edulis feed on crustacean zooplankton, which in turn feed on phytoplankton. Hence, demersal fish production is supported directly by planktonic primary production, rather than through a detrital food chain.     

Biogeochemical silica mass balances in Lake Michigan and Lake Superior

Silica budgets for Lake Michigan and Lake Superior differ in several respects. Mass balance calculations for both lakes agree with previous studies in that permanent burial of biogenic silica in sediments may be only about 5% of the biogenic silica produced by diatoms. Because dissolution rates are large, good estimates of permanent burial of diatoms can not be obtained indirectly from the internal cycle of silica (silica uptake by diatoms and subsequent dissolution) but must be obtained from the sediment stratigraphy. The annual net production of biogenic silica in Lake Michigan requires 71% of the winter maximum silica reservoir which must be maintained primarily by internal cycling in this large lake whereas the comparable silica demand in Lake Superior is only 8.3%. The greater silica demand in Lake Michigan is the result of phosphorus enrichment which has increased diatom production. It is hypothesized that steady-state silica dynamics in Lake Michigan were disrupted by increased diatom production between 1955 and 1970 and that a new steady state based on silica-limited diatom production developed after 1970. Mass balance calculations for Lake Michigan show in contrast with previous work that the hypothesized water column silica depletion of 3.0 g · m^–3 could have occurred even though 90% or more of the biogenic silica production is recycled.     

Hydrochemistry of Lake Glubokoe

Results of hydrochemical observations in the summer of 1983 are presented and compared to the data of previous years. Some trends in the changing conditions of the lake over the last fifty years are characterized. Data on the chemical composition of bottom deposits are also reported.     

Benthos of Lake Glubokoe

This paper presents the results of studies on the benthos of Lake Glubokoe in 1980 as compared to data for 1949 and 1950. The abundance of chironomids increased at medium depths, that of oligochaetes became higher along the entire depth and that of Chaoborus remained the same. The community of Sergentia was replaced by that of Chironomus.     

Is Lake Prespa Jeopardizing the Ecosystem of Ancient Lake Ohrid?

Lake Prespa and Lake Ohrid, located in south-eastern Europe, are two lakes of extraordinary ecological value. Although the upstream Lake Prespa has no surface outflow, its waters reach the 160 m lower Lake Ohrid through underground hydraulic connections. Substantial conservation efforts concentrate on oligotrophic downstream Lake Ohrid, which is famous for its large number of endemic and relict species. In this paper, we present a system analytical approach to assess the role of the mesotrophic upstream Lake Prespa in the ongoing eutrophication of Lake Ohrid. Almost the entire outflow from Lake Prespa is found to flow into Lake Ohrid through karst channels. However, 65% of the transported phosphorus is retained within the aquifer. Thanks to this natural filter, Lake Prespa does not pose an immediate threat to Lake Ohrid. However, a potential future four-fold increase of the current phosphorus load from Lake Prespa would lead to a 20% increase (+0.9 mg P m⁻³) in the current phosphorus content of Lake Ohrid, which could jeopardize its fragile ecosystem. While being a potential future danger to Lake Ohrid, Lake Prespa itself is substantially endangered by water losses to irrigation, which have been shown to amplify its eutrophication.     

The Morphometry of Lake Palmas,a Deep Natural Lake in Brazil

Lake Palmas (A = 10.3km²) is located in the Lower Doce River Valley (LDRV), on the southeastern coast of Brazil. The Lake District of the LDRV includes 90 lakes, whose basic geomorphology is associated with the alluvial valleys of the Barreiras Formation (Cenozoic, Neogene) and with the Holocene coastal plain. This study aimed to investigate the relationship of morphometry and thermal pattern of a LDRV deep lake, Lake Palmas. A bathymetric survey carried out in 2011 and the analysis of hydrographic and wind data with a geographic information system allowed the calculation of several metrics of lake morphometry. The vertical profiling of physical and chemical variables in the water column during the wet/warm and dry/mild cold seasons of 2011 to 2013 has furnished a better understanding of the influence of the lake morphometry on its structure and function. The overdeepened basin has a subrectangular elongated shape and is aligned in a NW-SE direction in an alluvial valley with a maximum depth (Z_max) of 50.7m, a volume of 2.2×10⁸ m³ (0.22km³) and a mean depth (Z_mv) of 21.4m. These metrics suggest Lake Palmas as the deepest natural lake in Brazil. Water column profiling has indicated strong physical and chemical stratification during the wet/warm season, with a hypoxic/anoxic layer occupying one-half of the lake volume. The warm monomictic pattern of Lake Palmas, which is in an accordance to deep tropical lakes, is determined by water column mixing during the dry and mild cold season, especially under the influence of a high effective fetch associated with the incidence of cold fronts. Lake Palmas has a very long theoretical retention time, with a mean of 19.4 years. The changes observed in the hydrological flows of the tributary rivers may disturb the ecological resilience of Lake Palmas.     

Macrozoobenthos of Lake Verevi

An overview on studies of macrozoobenthos in the small, hard-water, stratified and hypertrophic Lake Verevi (South-Eastern Estonia) is given. The list of macroinvertebrates comprises at least 105 taxa. In the open water habitats, the biomass and abundance of macrozoobenthos (except the phantom midge Chaoborus flavicans) was rather constant beginning from the epilimnion up to the upper hypolimnion (depth 2–4 m), but very low in the lower hypolimnion (depth 6 m), which was inhabited mainly by Chaoborus. Comparison with long-term reference data from other Estonian lakes, belonging to similar limnological types, indicated that the total biomass and abundance (without Chaoborus) in the profundal of Verevi were very low.     

Microbiological examination of Lake Erie and Lake Ontario sediments

Diver collected cores from three sites in Lake Erie, west of Cleveland, Eastern basin and near Buffalo, and one from Lake Ontario near the mouth of the Niagara River, were sectioned to 20 cm and examined for sulfur cycle and nitrogen cycle bacteria, heterotrophic bacteria, insoluble organic and inorganic phosphate solubilizing bacteria and manganese oxidizing bacteria. Eh, pH, nitrogen, organic carbon and percentage moisture determinations were also made. Data from this study support and confirm other microbiological data collected from Lower Great Lakes sediment and also support the hypothesis that microbial flora of similar type sediments are numerically similar irrespective of the sediments source within the Lower Great Lakes.     

Lake Whitefish and Lake Herring Population Structure and Niche in Ten South-Central Ontario Lakes

Synopsis This study compares simple fish communities of ten oligotrophic lakes in south-central Ontario. Species densities and population size structure vary significantly among these lake communities depending on fish species present beyond the littoral zone. Lake whitefish are fewer and larger in the presence of lake herring than in their absence. Diet analysis indicates that lake whitefish shift from feeding on both plankton and benthic prey when lake herring are absent to a primarily benthic feeding niche in the presence of lake herring. When benthic round whitefish are present, lake whitefish size and density decline and they move lower in the lake compared to round whitefish. Burbot are also fewer and larger in lakes with lake herring than in lakes without herring. Burbot, in turn, appear to influence the population structure of benthic coregonine species. Lower densities of benthic lake whitefish and round whitefish are found in lakes containing large benthic burbot than in lakes with either small burbot or where burbot are absent. Predation on the pelagic larvae of burbot and lake whitefish by planktivorous lake herring alters the size and age structure of these populations. As life history theory predicts, those species with poor larval survival appear to adopt a bet-hedging life history strategy of long-lived individuals as a reproductive reserve.     

Nutrient relationships in shallow water in an African Lake,Lake Naivasha

Summary In the littoral zone of a shallow, tropical lake (Lake Naivasha, Kenya), average nutrient composition of emergent macrophytes along a permanent transect (0–2m depth) on a dry weight basis was: P 0.23%; N 0.96%; and S 0.11%. In the hydrosoil the average composition was much lower, sediments were: P 0.03%; N 0.24%; and S 0.05%. The water depth varied, with lake edge being exposed during the annual drawdown for a part of the year and subsequently being inundated. Water quality varied considerably during the year (temperature 19–28°C; pH 7.0–8.0; conductivity 282–975 Scm^-1).Of the three nutrients in the water of the littoral zone, N had the highest mean concentration (4.25 mg·1^-1) while P was intermediate (1.90) and sulphur had the least (0.99). The distribution of nutrients followed a decreasing gradient from shore to open water. High levels of nutrients were recorded in September following the inundation of drawdown soil and plant material.The large stock of nutrients generated in the littoral zone helps to replenish nutrients in the open lake where low concentrations are typical.     

湖泊生态系统服务功能评估初探--以湖北保安湖为例

随着生物资源价值估算方法的日益成熟 ,生态系统的服务评估成为生态系统研究的热点 .鉴于国内对于湖泊生态系统的服务评价的研究较少 ,本文运用生态系统学与生态经济学方法研究了湖北保安湖生态系统的部分生态服务 .计算得到 1992年保安湖水生态系统有机质生产价值为 15 14 .93万元 ,固定CO2 的价值为 4 772 .99万元 ,释放O2 的价值为 36 2 6 .5 3万元 ,主要初级生产者储存N、P的价值为 4 4 .4 8万元 ,而年吸收量的价值为 15 0 7.99万元 ,调蓄和供水的价值为 10 92 8.93万元 ,消除排入湖水SO2 价值为5 1.5 0万元 ,合计 2 .2 4× 10 8元 .据不完全估计 ,可以认为 ,生态系统具有巨大的生态经济效益。     

Archaea in Yellowstone Lake

The Yellowstone geothermal complex has yielded foundational discoveries that have significantly enhanced our understanding of the Archaea. This study continues on this theme, examining Yellowstone Lake and its lake floor hydrothermal vents. Significant Archaea novelty and diversity were found associated with two near-surface photic zone environments and two vents that varied in their depth, temperature and geochemical profile. Phylogenetic diversity was assessed using 454-FLX sequencing (∼51 000 pyrosequencing reads; V1 and V2 regions) and Sanger sequencing of 200 near-full-length polymerase chain reaction (PCR) clones. Automated classifiers (Ribosomal Database Project (RDP) and Greengenes) were problematic for the 454-FLX reads (wrong domain or phylum), although BLAST analysis of the 454-FLX reads against the phylogenetically placed full-length Sanger sequenced PCR clones proved reliable. Most of the archaeal diversity was associated with vents, and as expected there were differences between the vents and the near-surface photic zone samples. Thaumarchaeota dominated all samples: vent-associated organisms corresponded to the largely uncharacterized Marine Group I, and in surface waters, ∼69–84% of the 454-FLX reads matched archaeal clones representing organisms that are Nitrosopumilus maritimus-like (96–97% identity). Importance of the lake nitrogen cycling was also suggested by >5% of the alkaline vent phylotypes being closely related to the nitrifier Candidatus Nitrosocaldus yellowstonii. The Euryarchaeota were primarily related to the uncharacterized environmental clones that make up the Deep Sea Euryarchaeal Group or Deep Sea Hydrothermal Vent Group-6. The phylogenetic parallels of Yellowstone Lake archaea to marine microorganisms provide opportunities to examine interesting evolutionary tracks between freshwater and marine lineages.     

Conochilus in Lake Washington

The rotifer Conochilus unicornis appeared in Lake Washington sporadically and usually in small numbers during a total of 28 years of observation since 1933. Conochilus hippocrepis was present even less frequently until the 3 year period 1977–1979, when it became extraordinarily abundant. The abundances of food organisms and known predators have been examined.The only consistent correlation found was between the seasonal maximum of Leptodora and the decrease of C. hippocrepis from its peak abundance each year. Leptodora was generally less abundant during 1977–1979 than during most of the preceding years and the years following the C. hippocrepis episode. No such correlations were found with Epischura, Cyclops or edible algae.In July 1985, there was a small resurgence of C. hippocrepis preceded by a small population of C. unicornis. Leptodora was less abundant than in the immediately preceding years. Observations were made on stomach contents of both animals and colony size of C. hippocrepis. Recommendations are made for programs of new field studies and laboratory experiments to establish the actual requirements for successful populations of Conochilus.     

Algae of periphyton of Lake Teletskoye

The generalized data are given on the composition and structure of phytoperiphyton of Lake Teletskoye on different substrates (rocks, macrophytes and their residues). It is noted that in spite of the differences in the taxonomic structure and level of development the algocenoses of periphyton of various substrates have similar ecological range. This gives a possibility of using the algocenoses of periphyton on different substrates for assessing the quality of the lake water.     

Phytophilous zoocoenoses of Lake Teletskoye

The composition, structure, and spatial distribution of zoobenthos and zooperiphyton at plantfilled regions of the littoral of Lake Teletskoye have been analyzed. The dependence of the taxonomic composition, number, and biomass of zoobenthos on vegetation type has been discovered. A multilevel character of the distribution of invertebrates in macrophyte overgrowths has been shown. An analysis of the trophic structure of the communities of macroinvertebrates revealed the predominance of algodetritophagous animals in zooperiphyton. The role of plant overgrowth as a “life concentrator” in an oligotrophic lake has been revealed.