Effect of salinity stress on organic and mineral constituents in the leaves of pigeonpea (Cajanus cajan L. Var. C-11)

Summary Effects of sodium chloride and sodium sulphate on the content of some organic and inorganic constituents in the leaves of pigeonpea (Cajanus cajan L. Var. C-11) were studied. Increased water content under saline conditions made the leaves succulent. The concentration of reducing sugars appeared to be higher while that of total sugars and starch was lower. The plants also failed to accumulate proline at higher salinity levels. Phosphorus and potassium content were lowered while those of calcium, magnesium, sodium, chloride and sulphate were increase under both salinities. This indicates that there is no regulation on the uptake of latter elements under saline conditions.     

Genetic Diversity of Picocyanobacteria in Tibetan Lakes: Assessing the Endemic and Universal Distributions

The phylogenetic diversity of picocyanobacteria in seven alkaline lakes on the Tibetan Plateau was analyzed using the molecular marker 16S-23S rRNA internal transcribed spacer sequence. A total of 1,077 environmental sequences retrieved from the seven lakes were grouped into seven picocyanobacterial clusters, with two clusters newly described here. Each of the lakes was dominated by only one or two clusters, while different lakes could have disparate communities, suggesting low alpha diversity but high beta diversity of picocyanobacteria in these high-altitude freshwater and saline lakes. Several globally distributed clusters were found in these Tibetan lakes, such as subalpine cluster I and the Cyanobium gracile cluster. Although other clusters likely exhibit geographic restriction to the plateau temporally, reflecting endemicity, they can indeed be distributed widely on the plateau. Lakes with similar salinities may have similar genetic populations despite a large geographic distance. Canonical correspondence analysis identified salinity as the only environmental factor that may in part explain the diversity variations among lakes. Mantel tests suggested that the community similarities among lakes are independent of geographic distance. A portion of the picocyanobacterial clusters appear to be restricted to a narrow salinity range, while others are likely adapted to a broad range. A seasonal survey of Lake Namucuo across 3 years did not show season-related variations in diversity, and depth-related population partitioning was observed along a vertical profile of the lake. Our study emphasizes the high dispersive potential of picocyanobacteria and suggests that the regional distribution may result from adaptation to specified environments.     

A comparison of zooplankton communities in saline lakewater with variable anion composition

Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO₄ and CO₃, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl^?1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (λ₁ = 0.97 and λ₂ = 0.62, P<0.05). The rotifer Brachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO₄/CO₃-dominated lake water with elevated potassium (79–128 mg l^?1) and total phosphorus concentrations (1322-2915 μg l^?1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO₄/CO₃ are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.     

Response of Aerobic Anoxygenic Phototrophic Bacterial Diversity to Environment Conditions in Saline Lakes and Daotang River on the Tibetan Plateau,NW China

Variations of the pufM gene [encoding the M subunit of the photosynthetic reaction center in aerobic anoxygenic phototrophic (AAnP) bacteria] diversity in response to environmental changes were investigated in waters of six aqueous regimes (including Daotang River and five saline/hypersaline lakes on the Tibetan Plateau) representing a full salinity gradient from freshwater to NaCl-saturation. AAnP bacterial community structures responded to salinity change: Gamma-like AAnP community was predominant in freshwater Daotang River (0.01% salinity). AAnP community structure shifted from Loktanella-like sequences of the Alphaproteobacteria in saline Qinghai Lake to Roseobacter-like sequences in hypersaline lakes (Gahai, Xiaochaidan and Charhan). In addition to salinity, other environmental variables (e.g. N and P availability, TOC and/or DOC, and HCO^? ₃/CO^2? ₃ ions) were also important in affecting the pufM gene diversity in hypersaline lakes. These data have important implications for our understanding of the response of AAnP bacterial community to environmental variables in high-altitude aquatic ecosystems.     

A recently landlocked brackish-water lagoon of Lake Tanganyika: physical and chemical characteristics,and spatio-temporal distribution of phytoplankton

Monthly measurements of physical and chemical characteristics were made at two localities in the eastern part of a recently landlocked lagoon of Lake Tanganyika. Variables analysed were: temperature, pH, conductivity, sodium, potassium, magnesium, calcium, carbonate, bicarbonate, chloride and sulphate. Large seasonal fluctuations of salinity were recorded (1.68–8.21 g l^–1). The seasonal water input controlled algal seasonality mainly through its effect on salinity and indirectly through its influence on nutrient concentration by dissolution and dilution of the excrements of the numerous cattle and other organic matter. Phytoplankton was mainly composed of Cyanophyta and Euglenophyta. Euglenophyta dominated during the dry periods with high salinity and probably very high nutrient levels, while Cyanophyta preferred moderate salt and nutrient concentrations during the rainy periods. The phytoplanktonic community was composed of a large number of perennial and a reduced quantity of annual organisms.A spatial study of the recently landlocked lagoon revealed an ascending salinity gradient, principally due to a sodium bicarbonate/carbonate enrichment, between locations near the lake and more inland situated stations. These facts point to a lake water supply and a salt concentration by evaporation in the swamps. Proportionally lower magnesium, calcium and potassium values were recorded at high salinities, due to chemical precipitation and biotic factors.A blue-green algal bloom was observed in the eastern water-body (salinity: 4.64 g l^–1); simultaneously an important development of diatoms dominated the western water-body (salinity: 2.18 g l^–1). No significant differences in morphometry, exposure, water temperature or nutrient levels (nitrate, nitrite, ammonia, orthophosphate) were observed. The relatively low salinity and high nutrient concentration in the western water-body probably favoured diatom development during the rainy season. The relatively higher salinity in the eastern water-body during the rainy season was probably responsible for the dominance of blue-green algae through its negative influence on silica concentration and notwithstanding the high inorganic nitrogen concentration.     

Chinese and Mongolian saline lakes: a limnological overview

More than half of China's lakes are saline (viz. have salinities > 3 g L⁻¹). Most salt lakes are in northwestern China (Tibet, Qinghai, Sinkiang, Inner Mongolia). Most Mongolian salt lakes are in the west of that country. Tectonic movements have been of the greatest importance in lake origins, but aeolian activity and deflation have also played a role. Many salt lakes in Qinghai-Tibet lie at altitudes > 4 000 m.a.s.l.; Aiding Hu (Sinkiang) lies at −154 m.a.s.l. Again, many lakes are large in area and deep. Small, shallow lakes are also common. Dimictic thermal patterns prevail in deep lakes, polymictic patterns in shallow ones. The highest salinity recorded is 555 g L⁻¹. The salinity of Qinghai Lake, the largest Chinese salt lake, is 14 g L⁻¹, but mean lake salinity on the northern Tibetan plateau is about an order of magnitude greater. Lop Nor has a salinity of ∼ 5 g L⁻¹. Dominant ions are Na and Cl; Mg, Ca, SO₄ and HCO₃ + CO₃ are important in certain lakes. Most major ions originate by weathering and leaching from rocks. pH values are generally high (often > 9.0). There are no bird or fish species confined to salt lakes, though many are associated with lakes of low or moderate salinity. Artemia occurs widely inland and in coastal salt pans, but is the only major macroinvertebrate of highly saline lakes. In lakes of only low to moderate salinity, invertebrate communities comprise widespread halotolerant freshwater forms and halophiles, some regionally endemic. Submerged and emergent macrophytes occur in lakes of low salinity, but phytoplankton species are more halotolerant. Ctenocladus circinatus, a green alga, is known from a Tibetan salt lake with a salinity of 200 g L⁻¹. There is a dearth of basic limnological information on Chinese and Mongolian salt lakes. More work in particular is needed on a variety of geographically widespread lakes to (a) document seasonal physico-chemical events, and (b) compile comprehensive biological inventories of taxa present. Chinese salt lakes are significant sites for palaeoclimatic research, for conservation purposes, and for the resolution of several important biological questions (especially of an ecological and biogeographical sort). They also have important economic values. Unfortunately, the natural existence of many appears to be threatened by decreased inflows, largely the result of human impact on catchments.     

Effects of salinity levels and seed mass on germination in Australian species of Frankenia L. (Frankeniaceae)

Halophyte species demonstrate differing levels of salt tolerance. Understanding interspecific variation to salinity levels is of value from both the scientific perspective, which includes the identification of traits associated with salinity tolerance, as well as from an applied perspective, which includes identifying plant species for specific salinity restoration and remediation projects. This paper investigates the effects of salinity on germination of 12 Australian species of the plant genus Frankenia L. (Frankeniaceae). We use saline solutions that corresponded to the average soil–water salinity concentrations in the arid zones of inland Australia. These solutions consisted of 10 mM calcium chloride, 30 mM magnesium sulphate, and 450 mM sodium chloride. The aims of our study were: (1) to investigate the germination (germination rates, germination success) of Frankenia seeds to four salinity levels (0%, 10%, 20%, 30%), (2) to test for possible interaction effects between seed mass, germination, and salinity, and (3) to examine the effect of salinity levels on the inhibition of germination and/or seed damage. Species varied in their salt tolerance for germination rates and success. Species with larger seeds had higher germination rates and germination success for high salinity levels. Several species did not germinate well at any salinity level. Finally, no seeds were adversely affected by exposure to high salinity levels pre-germination. There is potential for including some Frankenia species in remediation and revegetation projects in areas affected by salinity, and also as garden plants in saline regions.     

Saline systems of the Great Plains of western Canada: an overview of the limnogeology and paleolimnology

In much of the northern Great Plains, saline and hypersaline lacustrine brines are the only surface waters present. As a group, the lakes of this region are unique: there is no other area in the world that can match the concentration and diversity of saline lake environments exhibited in the prairie region of Canada and northern United States. The immense number of individual salt lakes and saline wetlands in this region of North America is staggering. Estimates vary from about one million to greater than 10 million, with densities in some areas being as high as 120 lakes/km². Despite over a century of scientific investigation of these salt lakes, we have only in the last twenty years advanced far enough to appreciate the wide spectrum of lake types, water chemistries, and limnological processes that are operating in the modern settings. Hydrochemical data are available for about 800 of the lake brines in the region. Composition, textural, and geochemical information on the modern bottom sediments has been collected for just over 150 of these lakes. Characterization of the biological and ecological features of these lakes is based on even fewer investigations, and the stratigraphic records of only twenty basins have been examined. The lake waters show a considerable range in ionic composition and concentration. Early investigators, concentrating on the most saline brines, emphasized a strong predominance of Na⁺ and SO₄ ^-2 in the lakes. It is now realized, however, that not only is there a complete spectrum of salinities from less than 1 ppt TDS to nearly 400 ppt, but also virtually every water chemistry type is represented in lakes of the region. With such a vast array of compositions, it is difficult to generalize. Nonetheless, the paucity of Cl-rich lakes makes the northern Great Plains basins somewhat unusual compared with salt lakes in many other areas of the world (e.g., Australia, western United States). Compilations of the lake water chemistries show distinct spatial trends and regional variations controlled by groundwater input, climate, and geomorphology. Short-term temporal variations in the brine composition, which can have significant effects on the composition of the modern sediments, have also been well documented in several individual basins. From a sedimentological and mineralogical perspective, the wide range of water chemistries exhibited by the lakes leads to an unusually large diversity of modern sediment composition. Over 40 species of endogenic precipitates and authigenic minerals have been identified in the lacustrine sediments. The most common non-detrital components of the modern sediments include: calcium and calcium-magnesium carbonates (magnesian calcite, aragonite, dolomite), and sodium, magnesium, and sodium-magnesium sulfates (mirabilite, thenardite, bloedite, epsomite). Many of the basins whose brines have very high Mg/Ca ratios also have hydromagnesite, magnesite, and nesquehonite. Unlike salt lakes in many other areas of the world, halite, gypsum, and calcite are relatively rare endogenic precipitates in the Great Plains lakes. The detrital fraction of the lacustrine sediments is normally dominated by clay minerals, carbonate minerals, quartz, and feldspars. Sediment accumulation in these salt lakes is controlled and modified by a wide variety of physical, chemical, and biological processes. Although the details of these modern sedimentary processes can be exceedingly complex and difficult to discuss in isolation, in broad terms, the processes operating in the salt lakes of the Great Plains are ultimately controlled by three basic factors or conditions of the basin: (a) basin morphology; (b) basin hydrology; and (c) water salinity and composition. Combinations of these parameters interact to control nearly all aspects of modern sedimentation in these salt lakes and give rise to four 'end member' types of modern saline lacustrine settings in the Great Plains: (a) clastics-dominated playas; (b) salt-dominated playas; (c) deep water, non-stratified lakes; and (d) deep water, "permanently" stratified lakes.     

Chemical and algal relationships in a salinity series of Ethiopian inland waters

Most Ethiopian lakes are parts of closed drainage systems and collectively form an extensive salinity series, here treated comparatively for geographical, chemical and algal characteristics. Chemical data are presented for 28 lakes and numerous inflows, including original analyses for 15 lakes, in which total ionic concentration and electrical conductivity vary over 4 orders of magnitude. The principal determinant of a lake's position in the series is the open or closed nature of its individual drainage. At present there are three major closed systems (Awash R. — Afar drainage, northern rift lakes, southern rift lakes), numerous crater lakes with seepage -in and -out, and two cryptodepressions with marine inputs. Salinity is primarily determined by evaporative concentration, enhanced in lakes associated with past marine influence or recent volcanic activity by readily soluble materials in the catchment, and by some thermal-reflux pathways. However, anomalously dilute closed lakes exist, indicative of other processes of solute loss (e.g. past basin overflow, reverse weathering, seepage-out).There are strong positive correlations between increasing salinity and the concentrations of Na⁺, alkalinity and Cl^-. The last is used, in conjunction with other analyses of atmospheric precipitation, to estimate the marine and denudative contributions and the evaporative concentration factor, and to distinguish trends of ionic species during evaporative concentration. With several exceptions, affected by past penetration of sea water into the Danakil and L. Assal cryptodepressions, the most saline lakes are soda lakes with HCO₃ ^- + CO _inf3 ^sup2- and Na⁺ predominant and Ca²⁺ and Mg²⁺ largely eliminated. Soluble reactive silicate and phosphate tend to increase in concentration along the salinity series, but the unknown dynamics of algal growth are likely to introduce variance. Concentrations in some lakes are extremely high, e.g. > 40 mg SiO₂ l^-1 and > 1 mg PO₄-P l^-1.Phytoplankters recorded from individual lakes are tabulated and where available the community biomass concentration as chlorophyll a is given. Lakes of high salinity-alkalinity are typically very productive in terms of phytoplankton biomass and photosynthetic rates (exceptions: the very deep L. Shala and the very saline L. Abhe), supported in part by relatively high concentrations of phosphorus and inorganic carbon. Many species are of restricted salinity-alkalinity range, being characteristic of waters where levels are low (e.g. desmids, Melosira spp.), intermediate (e.g. Planctonema lauterborni), or high (e.g. Spirulina platensis). Phytoflagellates are most strongly represented in waters with higher concentrations of the bivalent cations Ca²⁺ and Mg²⁺. The common cyanophyte Microcystis aeruginosa can tolerate a wide salinity range, here as elsewhere.     

Spanish salt lakes: Their chemistry and biota

A large number of small saline lakes are distributed throughout Spain. Four main lake districts occur from sea level to 1000 m.a.s.l. Most lakes are temporary because of the arid conditions in the Spanish endorheic areas. Many lakes are situated in Tertiary depressions in NE. and S. Spain. Lake basins were formed in karstic areas by hydrologic and aeolian erosion. Saline lakes in NE. Spain occupy areas isolated between river basins. The major ions encountered in these lakes are usually sodium-chloride and magnesium-sulphate; sodium carbonate or sodium-sulphate rich waters also occur.The biota of Spanish salt lakes is related to that of a larger biogeographical region which includes the Mediterranean countries. The main types of salt lakes in Spain include: (1) temporarily mineralized but not highly saline lakes, salinity is less than 7 g l^-1. Chara canescens, C. aspera, Zanichellia palustris, Daphnia atkinsoni, Mixodiaptomus incrassatus and Arctodiaptomus wierzejskii are the most characteristic organisms. (2) Temporary salt lakes, salinity fluctuates between 7 and 300 g l^-1. Chara galioides, Lamprothamnion papulosum, Daphnia mediterranea, Arctodiaptomus salinus and Cletocamptus retrogressus are the most common species. (3) Permanent salt lakes, Ruppia maritima, Najas marina and Artemia salina are the characteristic organisms.     

Saline groundwater as an aquaculture medium: physiological studies on the red drum, Sciaenops ocellatus

Physiological responses of the euryhaline red drum, Sciaenops ocellatus, to chloride salt addition, low salinity, and high sulfate concentration were measured. Survival was increased by addition of calcium chloride (CaCl₂) or magnesium chloride (MgCl₂) to dilute artificial seawater (0.2 ppt salinity). Although survival and routine metabolic rates were greater in MgCl₂ treatments, growth and feed efficiency were greater in CaCl₂ treatments. Marginal metabolic scope increased when CaCl₂ or MgCl₂ were added to dilute artificial seawater. There was a strong positive linear relationship (p=0.0001, r=0.91) between fish survival and salinity of artificial seawater dilutions over the salinity range 0.1 to 3.0 ppt. Monovalent ion concentrations in red drum plasma varied; whereas, divalent ion concentrations were relatively constant. Survival and growth were not affected by high sulfate concentrations (2000 mg l^-1) in 3.0 ppt artificial seawater supplemented with either sodium sulfate or magnesium sulfate. Routine metabolic rate and marginal metabolic scope of red drum exposed to high sulfate concentrations were slightly, but not significantly, lower than those of red drum in 3 ppt artificial seawater.     

Zooplankton Seasonal Abundance of South AmericanSaline Shallow Lakes

The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2‐year period to determine its temporal and spatial variation. The surface of these shallow lakes (<2.5 m depth) varied between 56.8 and 215.9 ha, and some have from 8.4 to 20.8 g · l^–1. The more saline lakes have “clear” water and the less saline lakes “turbid” water. Fishes, Jenynsia multidentata , were present in only two lakes during the last two months of the studied period. The zooplankton was composed of 17 taxa of Rotifera, 5 taxa of Cladocera and 4 taxa of Copepoda. The low diversity and the faunistic composition are characteristic of saline environments. Although the studied lakes share 38% of the species, the faunistic similarity was higher between the two least saline lakes. The lowest diversity was found in the two most saline lakes. All four shallow lakes were characterized by their very high zooplankton density, especially in the least saline lakes (<80000 ind · l^–1). The abundance is significantly correlated with the water transparency but not with salinity. The zooplankton temporal variation was characterized by the alternation of macro‐ and microzooplankton, probably regulated by competition and intrazooplanktonic predation. In each lake, the spatial abundance distribution of the macro‐ and microzooplankton was homogeneous. It was related to the shallow depht of the lakes and their polymictic condition. The Scheffer model on alternative states in shallow lakes acknowledges that it cannot be applied to saline lakes because Daphnia , the main responsible for the clear water state, is not tolerant to high salinity. Our study shows that the most saline lakes, where the halophylic Daphnia menucoensis is abundant, have also the most clear waters. Another difference that we found with regards to the mentioned model is that, in turbid lakes, it could not have had a top‐down control on macrozooplankton exerted by fishes because in these lakes fishes were practically absent. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Limnological studies of the lakes and streams of the upper qu'appelle river system,Saskatchewan, Canada

Summary Physical aspects including geography, geology, climate, soils, vegetation and lake morphometry of the upper Qu'Appelle River basin have been summarized. The importance of multiple use of this area has been stressed.The lakes were studied during the 1959–1969 period. Only Katepwa Lake showed temperature stratification for any length of time. Ice cover persisted for about five months each year. Buffalo Pound Lake had the lowest mean Secchi disc transparency (0.9 m) while Katepwa Lake had the highest (2.1 m). Light transmissibility tended to be lowest during May and September when wind velocities were highest. The 1 % level of light extinction was usually between 1 and 3 meters depth. The yellow portion of the spectrum penetrated the furthest.Buffalo Pound Lake was the least saline (600–700 mg/l TDS) while Last Mountain Lake was most saline (2000–2400 mg/l TDS). Input from Lake Diefenbaker and heavy spring runoffs effected major decreases in all lakes by May 1969. All lakes except Last Mountain were considerably more saline than during the 1937–1941 period. Variations in anions and cations within and between lakes vary with the total dissolved solids. As salinity increases magnesium, sulphate and chloride increase faster proportionally than other ions. The order of concentration of major cations is Na > Mg > Ca > K while the major anions' order of concentration is SO₄ > CO₃.HCO₃ > Cl.Soluble phosphate levels tend to be lowest in Buffalo Pound Lake. Levels increased sharply in Pasqua Lake below sewage outfalls from Moose jaw and Regina. Subsequently levels decreased in each successive downstream lake. Concentrations increased during the period of study. It was estimated that 594 metric tons of orthophosphate were contributed in domestic sewage in 1966. In addition land drainage contributes considerable amounts of phosphate during spring runoff.Nitrogen-bearing compounds vary in similar patterns as soluble phosphate but with smaller fluctuations. Domestic sewage and land drainage contribute significant amounts but of greater importance may be in situ biological fixation.All lakes were basic with usual pH of 8.4–9.0.From a chemical point of view these lakes are distinctly eutrophic.

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Zusammenfassung An fünf Seen des Ober Qu'Appelle Fluszgebietes, Saskatchewan, sind seit 1959 die jahreszeitlichen Veränderungen des Planktons und auch wichtige chemische und physikalische Milieufaktoren studiert worden. In diesem Teil werden die physiographischen Faktoren diskutiert.Dauernde Temperaturschichtung kommt nur im Katepwa See vor. Die 1% Lichtstärke war meistens zwischen 1 und 3 m Tiefe gelegen.Der Salzgehalt der Ober Qu'Appelle Seen liegt zwischen 600 mg/l (Buffalo Pound See) and 2400 mg/1 (Last Mountain See). Die Kationen ordnen sich in der Reihenfolge Na > Mg > Ca > K, die Anionen: SO₄ > CO₃.HCO₃ > Cl. Der pH bleibt meistens zwischen 8.4 and 9.0.Die Phosphatkonzentration ist sehr hoch. Abwasserverunreinigung, verursacht durch die Städte Regina und Moose jaw, ist bedeutsam für Phosphatgehalt in allen Seen auszer Buffalo Pound See. Die Stickstoffkonzentration ist ebenfalls hoch aber schwankt nicht soviel wie das Phosphat.Vom chemischen Standpunkt ausgesehen sind diese Seen sehr eutrophiert.

     

Temporal Changes between Ecological Regimes in a Range of Primary and Secondary Salinised Wetlands

Many rivers and wetlands in south-western Australia are threatened by salinisation due to rising saline watertables, which have resulted from land clearing and the replacement of deep-rooted perennial species with shallow-rooted annual species. A four to six weekly sampling program of water quality, submerged macrophytes and macroinvertebrates was undertaken at six wetlands, from September 2002 to February 2004, to investigate seasonal variation in a range of primary and secondary saline systems. The wetlands dried and filled at different times in response to local rainfall patterns, and salinities varied accordingly with evapoconcentration and dilution. Two types of clear-water wetlands were recognised; those dominated by submerged aquatic macrophytes (Ruppia, Lepilaena and Lamprothamnium) and those dominated by benthic microbial communities. Two types of turbid wetlands were also recognised; those with high concentrations of phytoplankton and those with high concentrations of suspended sediments. A primary saline lake and two lakes that have only recently been affected by secondary salinisation persisted in a clear, macrophyte-dominated regime throughout most of the study period, except during drying and filling. Two lakes with a long history of secondary salinisation (70 years) moved between regimes over the study period. A clear, benthic microbial community – dominated regime only persisted at the wetland which contained permanent water throughout the study period. The turbid regimes were only present during drying and refilling phases. A richer and more abundant macroinvertebrate fauna was associated with the clear, macrophyte- dominated wetlands. Our results suggest that the development of management guidelines that recognise the presence of different ecological regimes and that consider the interactions between water regime, salinity, and primary and secondary production will be more useful in protecting biodiversity and ecological function in these systems than managing salinity as a single factor.     

High Genetic Diversity and Novelty in Eukaryotic Plankton Assemblages Inhabiting Saline Lakes in the Qaidam Basin

Saline lakes are intriguing ecosystems harboring extremely productive microbial communities in spite of their extreme environmental conditions. We performed a comprehensive analysis of the genetic diversity (18S rRNA gene) of the planktonic microbial eukaryotes (nano- and picoeukaryotes) in six different inland saline lakes located in the Qaidam Basin. The novelty level are high, with about 11.23% of the whole dataset showing <90% identity to any previously reported sequence in GenBank. At least 4 operational taxonomic units (OTUs) in mesosaline lakes, while up to eighteen OTUs in hypersaline lakes show very low CCM and CEM scores, indicating that these sequences are highly distantly related to any existing sequence. Most of the 18S rRNA gene sequence reads obtained in investigated mesosaline lakes is closely related to Holozoa group (48.13%), whereas Stramenopiles (26.65%) and Alveolates (10.84%) are the next most common groups. Hypersaline lakes in the Qaidam Basin are also dominated by Holozoa group, accounting for 26.65% of the total number of sequence reads. Notably, Chlorophyta group are only found in high abundance in Lake Gasikule (28.00%), whereas less represented in other hypersaline lakes such as Gahai (0.50%) and Xiaochaidan (1.15%). Further analysis show that the compositions of planktonic eukaryotic assemblages are also most variable between different sampling sites in the same lake. Out of the parameters, four show significant correlation to this CCA: altitude, calcium, sodium and potassium concentrations. Overall, this study shows important gaps in the current knowledge about planktonic microbial eukaryotes inhabiting Qaidam Basin (hyper) saline water bodies. The identified diversity and novelty patterns among eukaryotic plankton assemblages in saline lake are of great importance for understanding and interpreting their ecology and evolution.     

Genetic Diversity of Eukaryotic Plankton Assemblages in Eastern Tibetan Lakes Differing by their Salinity and Altitude

Eukaryotic plankton assemblages in 11 high-mountain lakes located at altitudes of 2,817 to 5,134 m and over a total area of ca. one million square kilometers on the Eastern Tibet Plateau, spanning a salinity gradient from 0.2 (freshwater) to 187.1 g l⁻¹ (hypersaline), were investigated by cultivation independent methods. Two 18S rRNA gene-based fingerprint approaches, i.e., the terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis (DGGE) with subsequent band sequencing were applied. Samples of the same lake type (e.g., freshwater) generally shared more of the same bands or T-RFs than samples of different types (e.g., freshwater versus saline). However, a certain number of bands or T-RFs among the samples within each lake were distinct, indicating the potential presence of significant genetic diversity within each lake. PCA indicated that the most significant environmental gradient among the investigated lakes was salinity. The observed molecular profiles could be further explained (17–24%) by ion percentage of chloride, carbonate and bicarbonate, and sulfate, which were also covaried with change of altitude and latitude. Sequence analysis of selected major DGGE bands revealed many sequences (largely protist) that are not related to any known cultures but to uncultured eukaryotic picoplankton and unidentified eukaryotes. One fourth of the retrieved sequences showed ≤97% similarity to the closest sequences in the GenBank. Sequences related to well-known heterotrophic nanoflagellates were not retrieved from the DGGE gels. Several groups of eukaryotic plankton, which were found worldwide and detected in low land lakes, were also detected in habitats located above 4,400 m, suggesting a cosmopolitan distribution of these phylotypes. Collectively, our study suggests that there was a high beta-diversity of eukaryotic plankton assemblages in the investigated Tibetan lakes shaped by multiple geographic and environmental factors.     

Cladocera and Anostraca from the Interior Plateau of British Columbia,Canada, as paleolimnological indicators of salinity and lake level

Cladoceran and anostracan species assemblages were identified from the surface sediments of 33 closed–basin lakes from the southern Interior Plateau of B.C. in order to explore their effectiveness as quantitative indicators of lakewater salinity and ionic composition. These lakes were chosen to maximize the range of lakewater salinity concentrations (freshwater through hypersaline) as well as brine composition (sulphate and carbonate dominated systems). The distribution of the anostracans and cladocerans were strongly correlated with lakewater salinity, ionic composition and lake depth. Based on these strong relationships significant predictive models were developed, using weighted-averaging techniques, to infer lakewater salinity based on the species composition of anostracans and cladocerans in surface sediments. Furthermore, models were developed to infer lake depth that are superior to previously used techniques based on the ratio of planktonic/littoral Cladocera. Given that the species composition of anostracans and cladocerans can be used to infer changes in salinity and lake level, and that their remains can be identified from sedimentary profiles, there is considerable potential in using their assemblages as paleolimnological indicators of past climatic conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Life and Times of Five Saskatchewan Saline Meromictic Lakes

Five closed saline lakes near Humboldt, Saskatchewan, were found to be meromictic. Two of these lakes (Waldsea, Deadmoose) were first discovered to be meromictic in the early 1970s and three (Arthur, Marie, Sayer) in 1985. The origin of their meromixis is ectogenic. One of the lakes, Waldsea, had surface salinities far higher in 1960–1961 than those of 1970 or later and as high as that of the monimolimnion occasionally was from 1970 to the present. During the late 1960s to 1980 the lake level of Waldsea rose four metres as a result of higher than normal snowpacks and subsequent high snowmelt runoff. Endogenic processes of freezing out of salts from the upper metre during ice formation and precipitation of sodium sulphate during autumn cooling also promote meromixis. The lakes which are located in depressions in a relatively flat topography are very exposed to periodic high velocity westerly winds. Although Deadmoose and Waldsea lakes are relatively deep, Arthur, Marie and Sayer lakes have maximum depths of only three to five metres. Meromixis has persisted until the present in three lakes but Marie and Arthur lakes became holomictic during the autumn of 1988, a severe drought year. Bacterial plates were prominent in Waldsea, Deadmoose and Sayer lakes. BChl-a and BChl-d were present in 1988 with maxima of 2652 mg · m⁻³ BChl-a and 4290 mg · m⁻³ BChl-d in Sayer Lake. BChl-a virtually disappeared in subsequent years.     

Sulphur and phosphorus requirements of Curvularia pallescens Boed

The effect of different sulphur and phosphorus compounds on the growth and sporulation ofCurvularia pallescens Boed. has been studied. Nine different sulphur sources were tried but among them only magnesium sulphate yielded the best dry weight of the fungus. Zinc sulphate, sodium sulphate, sodium thiosulphate, potassium sulphate and calcium sulphate supported good growth. Poor growth was recorded on sodium bisulphite, ammonium sulphate, sodium sulphide and control. Sporulation was excellent on magnesium sulphate. It was good on zinc sulphate, sodium sulphate and potassium sulphate. On sodium thiosulphate, calcium sulphate, sodium bisulphite and control it was fair. Sodium sulphide and ammonium sulphate had inhibitory effect as sporulation was poor and nil on these two compounds respectively.Six phosphorus compounds were studied. Tripotassium phosphate gave best growth and excellent sporulation. Good growth and excellent sporulation was recorded on monobasic potassium phosphate and magnesium phosphate. Growth and sporulation were good on dibasic potassium phosphate and sodium dihydrogen phosphate. Ammonium phosphate was poorly utilized.     

Functional groups of phytoplankton shaping diversity of shallow lake ecosystems

Phytoplankton of eutrophic shallow lakes are frequently dominated by one species or species of the same functional group, resulting in species-pure algal assemblages. Knowledge of the structure of these assemblages is essential to understand their functioning; therefore, species and functional diversity were investigated in five sub-types of eutrophic shallow lake. Among the sub-types, astatic saline lakes and hypertrophic ponds had type-specific assemblages dominated by S_N and W0, W1 codons. The diversity of the phytoplankton in the sub-types was quite similar, except for the astatic saline lakes, which were characterised by lower values of both functional and species diversity. We found that both functional and species diversity were low when bloom-forming cyanobacteria (H1, S_N functional groups) became dominant. Dominance of other groups (J, Y, L_O and W1) did not coincide with decrease in species diversity. Analysis of the biovolume versus diversity relationships revealed that decrease in diversity might be expected at biovolume >20 mm³ l⁻¹ for shallow lakes.