Isabela Crater-Lake: a Mexican insular saline lake

Opinion This is a series of contributions, expressing explicit opinions with regard to contemporary topics in limnology. These Opinions are mostly based on new books with a large impact, but can also refer to other currently debated topics. Documented reactions to these contributions should be sent to the editor-in-chief; they will be considered for publication in subsequent issues.     

Limnological study of a Pantanal saline lake.

Limnological studies involving physical, chemical and biological aspects, with emphasis on the zooplankton community, were carried out in a saline lake of the Pantanal floodplain, in the subregion of Nhecolandia (Mato Grosso do Sul, Brazil), during the dry and wet seasons of the local hydrological cycle. The results show that the lake is not directly affected by the flood-pulse through superficial coalescence, probably receiving groundwater instead. Most of the measured variables showed extremely high values, particularly dissolved salts, pH, conductivity, nutrients and chlorophyll a. These values were highest during the dry period due to the system's low water volume. The zooplankton community was basically represented by Metacyclops mendocinus, which displayed high population densities throughout the periods studied. The low diversity recorded is congruent with other studies on continental saline water-bodies.     

Microbial decomposition of reed (Phragmites communis) leaves in a saline lake

Microbial colonization and its relation to the decomposition of reed (Phragmites communis) leaf litter were studied in the littoral area of a saline lake from autumn to summer using litter bag method. There was considerable fungal population on the leaves at the beginning of submergence. These fungi were probably terrestrial in origin. The fungal population rapidly disappeared few days after submergence, when bacteria, including cellulolytic and xylanolytic types, proliferated. Associated with this rapid colonization of bacteria, decomposition rates of cellulose and xylan increased. The rates declined from day 39 to day 100 with decreasing water temperature, though cellulolytic and xylanolytic bacteria maintained a sizeable population until day 150. A community of cellulolytic and xylanolytic fungi increased steeply after day 150. It coincided with a second increase in decomposition rate. These results suggest that the principal decomposers of reed leaf litter were bacteria in the initial phase and fungi in the later phase of the experiment.     

Seasonal Development and Morphological Variability of Cyclotella ocellata (Bacillariophyceae) in the Eutrophic Lake Dagow (Germany)

The development of Cyclotella ocellata Pantocsek was studied systematically in the eutrophic, dimictic hardwater Lake Dagow from March to October, 1994. Cyclotella ocellata was the most important centric diatom in the lake with a maximum cell density of 6 × 10⁶ cells 1⁻¹. The seasonal development, characterized by a spring and a summer maximum, is considered in relation to environmental factors and the succession of the phytoplankton community. The amount of Cyclotella ocellata biomass as a proportion of the total phytoplankton biomass varied from 0.5 to 35%. In addition, seasonal changes in cell size and feature associated with sexual reproduction of Cyclotella ocellata were documented. Light and electron microscopic investigations demonstrate an extremely wide range of morphological variability of this natural population.     

Morphological variability, taxonomy, and distribution of Cyclotella bodanica Eulenstein (Bacillariophyta) in Russia

The morphology of six populations of a rare freshwater species of diatoms, Cyclotella bodanica Eulenstein, from lakes of different geographic location is studied using SEM techniques. It is shown that some features (number of striae and marginal fultoportulae in 10 μm, number of thin costae in alveoli and their branching, relief of the central area and peripheral zone, and arrangement of rimoportulae) vary to a greater extent than is indicated in the literature. The results have made it possible to improve the diagnosis of this species and refer C. intermedia to its synonymy. Similarities and differences between C. bodanica and morphologically similar species of the complex C. comta/C. radiosa are also considered. The distribution of C. bodanica in water bodies of Russia is specified.     

Seasonal change in a saline temporary lake (Fuente de Piedra,southern Spain)

Fuente de Piedra saline lake is located in an endorheic basin in the south of Spain. This lake is very shallow (0.5 m max. depth during 1987–88) and relatively large (± 1350 ha). It is a temporary playa lake, showing irregular cycles, with frequent seasonal drought and a high degree of unpredictability. The lake was sampled monthly during a relatively rainy year (1987–88, 10.5 months permanence). The result of combined analyses for environmental variables (salinity, temperature and soluble inorganic forms of nitrogen and phosphorus), variables related to biological activity (chlorophyll a, sediment organic matter and redox potential) and the direct analysis of the planktonic community, shows the existence of two periods of dominance by autotrophs. The first occurs during winter, exhibits a progressively higher surface to volume ratio for phytoplankton and is followed in the spring by high zooplankton densities (Moina salina, Fabrea salina) and very low phytoplankton densities, suggesting the existence of a period with a detritus-based food web. The summer period coincides with a community better adapted to high salinities that is dominated by Dunaliella salina, D. viridis, diatoms and the ciliate Fabrea salina, and associated with high ammonium concentrations. A new period of organic matter accumulation could be facilitated, in the last moments before the lake dries, by a progressive decrease in zooplankton abundance.     

Reconstruction of historical productivity using visible-near-infrared (VNIR) reflectance properties from boreal and saline lake sediments

Chlorophylls preserved in lake sediments have been used as a proxy to infer past trophic status. Recently, it has been demonstrated that visible-near-infrared (VNIR) reflectance spectroscopy can provide a rapid and non-destructive estimation of fossil chlorophylls from alpine lake sediments. The present study explores, (a) the applicability of VNIR reflectance spectroscopy to reconstructing historical productivity from boreal and saline lakes, and (b) the ability of an inference model combining all lake types to reconstruct historical chlorophyll concentrations from lake sediments. Results revealed that regardless of the lake type, a common sediment spectral feature of a reflectance trough centered near 675 nm, was observed. Additionally, the amplitude of reflectance in the VNIR region differs within and among lakes depending on their trophic states. The inferred concentration of total chlorophylls and derivatives from sediment spectral properties reflected a recent nutrient enrichment in most of the study lakes. Predicted chlorophyll concentration, when plotted against high-pressure liquid chromatography (HPLC) measured concentration combining all lake types, was found to be statically significant (r ² = 0.80, P < 0.01). Collectively, results from this study indicate that regardless of the lake type, a common chlorophyll absorption feature near 675 nm can be detected, which is associated with contrasting limnological settings and, therefore, can be used as a viable tool to reconstruct paleoproductivity. A similar approach can be implemented for rapid and non-destructive detection of historical lake water quality in a wide range of lake sediments.     

Sulfate distribution in a multi-basin, saline lake

Devils Lake in northeastern North Dakota (USA) is a terminal lake of glacial origin with a substantial sulfate content. Since 1940, the lake water level has risen over 13.5m and salinity has decreased. Devils Lake consists of a series of interconnected basins with sulfate concentration increasing in an eastward direction from 450mg/l in West Bay to 3000mg/l in East Devils Lake. Using sulfate as a tracer and linking measurements of specific conductance with observed time series of water surface elevations, wind, and water velocity, this paper illustrates the magnitude and dynamics of mass transport and exchange processes between the multiple basins of Devils Lake. Measurements show small horizontal salinity gradients within the lake basins, but large salinity gradients in some of the exchange zones connecting basins. Vertical salinity gradients were observed in small basins and near exchange zones with strong horizontal salinity differentials. These instances of vertical stratification were associated with buoyancy driven exchange flows and wind sheltering. Exchange flow velocities between selected basins were correlated with wind direction and speed. Interbasin exchange flows were found to reverse direction frequently in response to the prevailing wind direction. Flow direction frequencies in one specific exchange zone were 31% west to east, 48% east to west, and 21% bidirectional (stratified). At the lake level observed in 2000, time averaged, measured interbasin exchange flow rates were 30--40m³/s compared to tributary inflow rates to the lake of 3--9m³/s.     

Cyclotella orientalis sp. nov. (Bacillariophyceae) from South Korea

Cyclotella ortentalis sp. nov, is described from an epilithic sample taken in Lake Imha, located in Kyungsangbuk-do. South Korea. The species is characterized by a conspicuous and short costa regularly extending from each marginal fultoportula to the valve margin. It can be included in the Cyclotella stelligeroid group. The new species can be separated from the most similar species C. stelligera Cleve et Grunov var. stelligera by the more distant position of marginal fultoportulae from the valve margin, the external long tubes of fultoportulae and having short costae. It differs from C. stelligera var. robusta Must, and var. hyalina Hust., in having much denser marginal striae; from C. glomerata H. Bachm., C. pseudostelligera Hust., C. stelligeroides Must, and C. woltereckii Hust., in its much larger valve, coarser marginal striae and short costae with fultoportulae.     

Nutrient limitation in a tropical saline lake: a microcosm experiment

There is increasing evidence that nitrogen limitation is of widespread occurrence in tropical lakes. Nonetheless, data on the deep tropical Lake Alchichica (Mexico) show that dissolved inorganic nitrogen (DIN) to soluble reactive phosphorus (SRP) ratio fluctuates widely. To elucidate further the role of nitrogen and phosphorus limitation on the phytoplankton growth in tropical saline lakes, we present the results of a series of nutrient enrichment experiments with natural assemblages of Lake Alchichica phytoplankton conducted monthly for a year. Our assays indicate that phosphorus and nitrogen alternate in limiting Lake Alchichica phytoplankton biomass. Phosphorous limited phytoplankton growth most (41.7%) of the time, followed by nitrogen (33.3% of the time), and both nutrients for the rest of the time (25.0%). This alternation in nitrogen and phosphorus responsible for phytoplankton growth limitation in Lake Alchichica is attributed to the combination of natural conditions (e.g., young volcanic terrain rich in phosphorus) that would favor nitrogen limitation and anthropogenic impacts (e.g., agricultural nitrogen fertilization) which would cause phosphorus limitation. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Caecidotea williamsi (Crustacea: Isopoda: Asellidae), a new species from a saline crater-lake in the eastern Mexican Plateau

A new species of Caecidotea, an aquatic isopod crustacean is described from Alchichica crater-lake in the state of Puebla, Oriental Basin, central Mexico. This is the first report of an epigean asellid isopod, with cryptic behavior inhabiting inland saline waters in America. Comparisons made with other co-occurring asellid species in the region show that the species Caecidotea pasquinii differs from the new species in lacking eyes, having different features on the male endopod of pleopod 2, a shorter pereiopod 6, and having elongated uropods. The epigean species Caecidotea communis differs from the new species in having pleopod 4 of the A type pattern of Lewis & Bowman (1981) and 5–8 retinacula on pleopod 1 sympod.     

Benthos of a seasonally-astatic, saline, soda lake in Mexico

The benthic macroinvertebrate community (BMC) of Lake Tecuitlapa Sur, central Mexico, was monitored to determine the structure of the community (i.e. species composition, richness, abundance and biomass), throughout an annual cycle. Tecuitlapa Sur is shallow, seasonally-astatic, warm, mesosaline, and soda-alkaline. The physical, chemical and biological variables were determined monthly for a yearly cycle. Tecuitlapa Sur displayed a seasonal patterns of dilution (June–August) and concentration (September–November) phases. Salinity and pH were the most important parameters explaining environmental variance. The BMC consisted of two species: Culicoides occidentalis sonorensis (Diptera: Ceratopogonidae) and Tanypus Apelopia sp. (Diptera: Chironomidae). C. occidentalis was the most important species both numerically and in biomass (95%). Annual density (mean ± sd) of C. occidentalis (1141082 ± 2765879 ind. m^–2, n = 120) was notably higher than other reported for other saline water bodies. However, the mean annual density of T. Apelopia (6782 ± 8310 ind. m^–2, n = 120) was similar to other saline lakes. Seasonal abundance and biomass dynamics of the BMC showed an increasing trend until October (T. Apelopia) and November (C. occidentalis), when massive emergence occurred, just before the lake dried out. Contrary to most temporal waters, Tecuitlapa Sur did not show taxonomic or trophic succession. C. occidentalis, a transient detritivore, dominated over T. Apelopia, a resident predator during the wet period.     

Size structure of plankton in a temporary, saline inland lake

The study of the size structure of a planktonic community ina relatively extensive (1350 ha), very shallow (0.46 m maximumdepth), temporary inland saline lake during a relatively rainyyear (1987–88) showed an average biomass-size spectrumwith four clear modes at nano-, micro-, meso- and macroplanktonsize ranges. The size-abundance distribution was dominated bymedium-sized phytoplankton cells (Gymnodinium cf. excavatum,Tetraselmis apiculata, Dunaliella spp. and several diatom species),large ciliates (Fabrea salina) and a few zooplankton speciesadapted to changing temporary environments within a wide sizerange (Cletocamptus retrogressus, Moina salina, Branchinellaspinosa). This polymodal size distribution is compared withresults obtained in other systems, including small physicallycontrolled lakes, large lakes, oceans and marine benthos. Considerationof the size structure within homogeneous groups of organismsshows slopes less negative than the average for the whole sizerange analysed, a feature which is common in small and physicallycontrolled ecosystems. A seasonal study of the size structurerevealed uneven distributions throughout the year, resultingin discontinuities in the size spectra as well as in differencesof total size range. There were noticeable differences amongthe size spectra at each particular time, showing phases ofprimary producer predominance and phases with a marked predominanceof consumers. The time-integrated size spectrum did not exhibitany distinct discontinuity. The influence of extreme shallownessand resuspension on the shape and dynamics of the size spectrumis examined and discussed compared to deeper aquatic systems.     

Nutrient cycling and productivity in a desert saline lake: observations from a dry,low-productivity year

Seasonal variability of nutrients and productivity were examined in Pyramid Lake, a hyposaline, N-deficient, terminal desert lake, during a dry period. River inflow and N-fixation during 1990 were minimal allowing internal nutrient cycling to be more closely studied. Nutrient cycling was strongly affected by seasonal thermal stratification that was typical for a warm monomictic lake. Concentrations of nitrate, phosphate, and silicate in surface waters were highest during winter mixing and decreased rapidly in the spring due to a diatom bloom. Maximum average chlorophyll concentration in surface waters was 2.7 ± 1.2 µg 1^–1 and occurred in April while surface nutrients were being depleted. In contrast to chlorophyll, maximum particulate carbon in surface waters occurred in July–August when areal productivity was highest (367–398 mg C m^–2 day^–1). Concurrent with spring nutrient depletion in surface waters was increasing N-deficiency in the plankton. After the spring bloom dissipated in May, particulate matter (POM) became increasingly N-deficient reaching maximum elemental C : N of > 18 during summer-fall. Profiles of the C : N ratio of POM were nearly constant with depth for individual sampling dates suggesting that the residence time of POM in the water column was short (< 1 month). While surface waters were nutrient depleted during summer stratification, nutrient concentrations of bottom waters progressively increased, presumably through the oxidation of POM sinking to the bottom (103 m). Converting the rate of oxygen depletion in bottom waters to carbon equivalents of POM suggests that 42 % of mean annual phytoplankton production in overlying waters during 1990 was mineralized in bottom waters.     

The Gammaridae and Corixidae of an inland saline lake from 1975 to 1978

When observations began the population of Watch Lane Flash consisted of Gammarus duebeni and Sigara lateralis. Gammarus tigrinus was then introduced; probably during a transfer of water from a nearby canal. G. tigrinus rapidly increased in numbers and at the same time G. duebeni and S. lateralis decreased to zero. There followed a partial recolonisation by corixids but the species present were Sigara concinna and Sigara dorsalis. Throughout the study period corixid populations were stable in two immediately adjacent water bodies, one of which also contained G. duebeni. Thus the changes described were associated with the presence of G. tigrinus. The reasons for the success of G. tigrinus and its effects on other gammarids and corixids are discussed.