SALINITY AND NUTRIENT LIMITATIONS ON GROWTH OF BENTHIC ALGAE FROM TWO ALKALINE SALT LAKES OF THE WESTERN GREAT BASIN (USA)1

Enrichment cultures of littoral benthic algae from Mono Lake, California, and Abert Lake, Oregon, were grown under conditions of varied salinity and nutrient content. Field-collected inocula were composed mainly of diatoms and filamentous blue-green and green algae. The yield of long-term cultures (30 days) showed tolerance over a broad salinity range (50–150 g·L^?1) for Mono Lake-derived algae. Algae from Abert Lake had a lower range of tolerance (25–100 g·L^?1) Organic content and pigment concentrations of algae from both lakes were also reduced above the tolerated salinity level. Within the range of salinity tolerance for Mono Lake algae, initial growth rates and organic content were reduced by increased salinity. The effects of macro- and micronutrient enrichment on algal growth in Mono Lake water were also tested. Only nitrogen enrichment (either as ammonium or nitrate) stimulated algal growth. Although the benthic algae cultured here had wide optima for salinity tolerance, the rates of growth and storage were limited by increased salinity within the optimum range. Although the lakes compared had similar species composition, the range and limits of tolerance of the algae were related to salinity of the lake of origin.     

A study of benthic communities in some shallow saline lakes of western Victoria,Australia

The summer benthos of 24 lakes ranging from 1–204 g l^-1 salinity contained 27 species of macroinvertebrates. The worm Antipodrilus timmsi, the ostracod Mytilocypris splendida, the amphipod Austrochiltonia subtenuis, the chironomids Procladius spp. and Chironomus duplex aand the snail Coxiella striata were common at lower salinities (3—ca. 30 g l^-1) while the crustaceans Australocypris robusta and Haloniscus searlei, the chironomid Tanytarsus barbitarsis and a ceratopogonid larva dominated in salinities ca. 20–100 g l^-1. Small ostracods were common from 40–150 g l^-1. Diversity changed little with salinity. Mean dry biomass ranged from 0–3.94 g m^-2; distribution between lakes was negatively skewed with a peak around 7 g l^-1 salinity. Within many lakes, there was considerable spatial heterogeneity which in some cases seemed to result from different bottom characteristics or to point source enrichment. Many groups contributed to the standing crop at low to moderate salinities, and at high salinities crustaceans were important. The lakes were grouped into two low salinity associations, an association which comprised the Red Rock Lakes and a cluster of highly saline lakes. This reflects the grouping of species into halobiont, halophilic and salt-tolerant freshwater species.     

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.     

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.     

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.     

Limnological effects of anthropogenic desiccation of a large, saline lake, Walker Lake, Nevada

Walker Lake is a monomictic, nitrogen-limited, terminal lake located in western Nevada. It is one of only eight large (Area>100 km², Z _{{ mean}}>15 m) saline lakes of moderate salinity (3–20 g l^–1) worldwide, and one of the few to support an endemic trout fishery (Oncorhynchus clarki henshawi). As a result of anthropogenic desiccation, between 1882 and 1996 the lake's volume has dropped from 11.1 to 2.7 km³ and salinity has increased from 2.6 to 12–13 g l^–1. This study, conducted between 1992 and 1998, examined the effects of desiccation on the limnology of the lake. Increases in salinity over the past two decades caused the extinction of two zooplankton species, Ceriodaphnia quadrangula and Acanthocyclops vernalis. Recent increases in salinity have not negatively affected the lake's dominant phytoplankton species, the filamentous blue-green algae Nodularia spumigena. In 1994 high salinity levels (14–15 g l^–1) caused a decrease in tui chub minnow populations, the main source of food for Lahontan cutthroat trout, and a subsequent decrease in the health of stocked trout. Lake shrinkage has resulted in hypolimnetic anoxia and hypolimnetic accumulation of ammonia (800–2000 g-N l^–1) and sulfide (15 mg l^–1) to levels toxic to trout. Internal loading of ammonia via hypolimnetic entrainment during summer wind mixing (170 Mg-N during a single event), vertical diffusion (225–500 Mg-N year^–1), and fall destratification (540–740 Mg-N year^–1) exceeds external nitrogen loading (<25 Mg-N year^–1). Increasing salinity in combination with factors related to hypolimnetic anoxia have stressed trout populations and caused a decline in trout size and longevity. If desiccation continues unabated, the lake will be too saline (>15–16 g l^–1) to support trout and chub fisheries in 20 years, and in 50–60 years the lake will reach hydrologic equilibrium at a volume of 1.0 km³ and a salinity of 34 g l^–1.     

Winter limnology: a comparison of physical,chemical and biological characteristics in two temperate lakes during ice cover

The winter dynamics of several chemical, physical, and biological variables of a shallow, polymictic lake (Opinicon) are compared to those of a deep, nearby dimictic lake (Upper Rock) during ice cover (January to early April) in 1990 and 1991. Both lakes were weakly inversely thermally stratified. Dissolved oxygen concentration was at saturation (11–15 mg l⁻¹) in the top 3 m layer, but declined to near anoxic levels near the sediments. Dissolved oxygen concentrations in the deep lake were at saturation in most of the water column and approached anoxic levels near the sediments only. Nutrient concentrations in both lakes were fairly high, and similar in both lakes during ice cover. Total phosphorus concentrations generally ranged between 10–20 μg l⁻¹, NH₄-N between 16–100 μg l⁻¹, and DSi between 0.9–1.9 mg l⁻¹; these concentrations fell within summer ranges. NO₃-N concentrations were between 51–135 μg l⁻¹ during ice cover, but occurred at trace concentrations (<0.002 μg l⁻¹) during the summer. The winter phytoplankton community of both lakes was dominated by flagellates (cryptophytes, chrysophytes) and occasionally diatoms. Dinoflagellates, Cyanobacteria and green algae were poorly represented. Cryptophytes often occurred in fairly high proportions (20–80%) throughout the water column, whereas chrysophytes were more abundant just beneath the ice. Zooplankton population densities were extremely low during ice cover (compared to maximum densities measured in spring or summer) in both lakes, and were comprised largely of copepods.     

Aquatic macrophytes in saline lakes of the Canadian prairies

Vascular macrophyte species richness decreases with increasing salinity. Only three species of submerged plants (Potamogeton pectinatus, Ruppia maritima, R. occidentalis) tolerate hypersaline waters (>50 g l^-1, total of ionic constituents). Eight emergent species occur in more saline habitats but only five (Scirpus maritimus var. paludosus, Distichlisstricta, Puccinellia nuttalliana, Scirpus americanus, Triglochin maritima) occur commonly over a range of saline lakes into the hypersaline category. Usually, species tolerant of high salinities are found over the entire saline spectrum and even extend into subsaline waters (<3 g l^-1) and thrive there. A major increase in the number of species occurs below 5 g l^-1. As the water recedes plants such as Salicornia rubra, Suaeda calceoliformes, Hordeum jubatum and Sonchus arvensis invade.Submerged angiosperm distribution is controlled by total ion concentration and substrate texture plays no apparent role. Although angiosperms normally grow in all kinds of substrates, they occupy coarse substrates in Wakaw lake because suitable fine substrates are densely colonized by charophytes. In this lake light limited growth occurs to a depth of 5% of surface light. Light was not limiting in Redberry Lake but angiosperm growth was limited to the upper 8 m (10% or more of surface light). Thermal stratification and depth (pressure) were probably limiting istead. In meromictic Waldsea Lake the depth of the chemocline (6 m, 5% surface light) delimits angiosperm growth.     

西藏达则错盐湖沉积背景与有机沉积结构

以西藏拟溞(Daphniopsis tibetana Sars)为优势浮游动物物种的低盐度盐湖是西藏湖泊的一个重要类型,以达则错为代表,分析了其沉积背景及沉积物组成。结果如下:(1)湖泊敞水区无机沉积以内生化学沉积为主,可代表深水盐湖无机沉积物的自然沉积过程。(2)达则错盐湖浮游植物以蓝藻、硅藻、裸藻、绿藻为主,总生物量11.35 mg/L;浮游动物生物量为4.92 mg/L,其中西藏拟溞占 82.30%;浮游植物残体受盐梯度影响在盐梯度层之上聚集,而浮游动物残体及粪粒(Fecal pellets)因外表有碳酸盐附着可穿过盐梯度层沉积湖底,生物残体与浮游动物代谢产物构成了沉积有机物的物质基础。(3)表层沉积物平均含水量为66.70%,粒径0.004-0.02 mm范围内的颗粒物含量最大,占20.42%,其次为<0.004 mm的粘土,占4.53%。(4)表层沉积物总有机碳(TOC)平均含量为27.99 mg/g(干重),其中颗粒有机碳(POC)约为18.11 mg/g,占TOC的64.70%;在POC中,西藏拟溞粪粒贡献最大,约占POC的60.48%,占TOC的39.06%,占沉积物总量的1.12%,其次为西藏拟溞残体,占POC的38.85%。分析结果表明盐湖因其独特的水化学和生物学特征具有较强的沉积能力,以化学沉积为主的无机沉积及以西藏拟溞粪粒和残肢碎屑为主的有机沉积构成了该类型盐湖颗粒物沉降及沉积的主要过程。     

Distribution and Diversity of Cyanobacteria and Eukaryotic Algae in Qinghai–Tibetan Lakes

Cyanobacteria and eukaryotic algae are important primary producers in a variety of environments, yet their distribution and response to environmental change in saline lakes are poorly understood. In this study, the community structure of cyanobacteria and eukaryotic algae in the water and surface sediments of six lakes and one river on the Qinghai–Tibetan Plateau were investigated with the 23S rRNA gene pyrosequencing approach. Our results showed that salinity was the major factor controlling the algal community composition in these aquatic water bodies and the community structures of water and surface sediment samples grouped according to salinity. In subsaline–mesosaline lakes (salinity: 0.5–50 g L^?1), Cyanobacteria (Cyanobium, Synechococcus) were highly abundant, while in hypersaline lakes (salinity: >50 g L^?1) eukaryotic algae including Chlorophyta (Chlorella, Dunaliella), Bacillariophyta (Fistulifera), Streptophyta (Chara), and Dinophyceae (Kryptoperidinium foliaceum) were the major members of the community. The relative abundance ratio of cyanobacteria to eukaryotic algae was significantly correlated with salinity. The algae detected in Qinghai–Tibetan lakes exhibited a broader salinity range than previously known, which may be a result of a gradual adaptation to the slow evolution of these lakes. In addition, the algal community structure was similar between water and surface sediment of the same lake, suggesting that sediment algal community was derived from water column.     

From Local Adaptation to Ecological Speciation in Copepod Populations from Neighboring Lakes

Continental copepods have been derived from several independent invasive events from the sea, but the subsequent evolutionary processes that account for the current diversity in lacustrine environments are virtually unknown. Salinity is highly variable among lakes and constitutes a source of divergent selection driving potential reproductive isolation. We studied four populations of the calanoid copepod Leptodiaptomus cf. sicilis inhabiting four neighboring lakes with a common history (since the Late Pleistocene) located in the Oriental Basin, Mexico; one lake is shallow and varies in salinity periodically (1.4–10 g L^-1), while three are deep and permanent, with constant salinity (0.5, 1.1 and 6.5 g L^-1, respectively). We hypothesized that (1) these populations belong to a different species than L. sicilis sensu stricto and (2) are experiencing ecologically based divergence due to salinity differences. We assessed morphological and molecular (mtDNA) COI variation, as well as fitness differences and tests of reproductive isolation. Although relationships of the Mexican populations with L. sicilis s.s. could not be elucidated, we identified a clear pattern of divergent selection driven by salinity conditions. The four populations can still be considered a single biological species (sexual recognition and hybridization are still possible in laboratory conditions), but they have diverged into at least three different phenotypes: two locally adapted, specialized in the lakes of constant salinity (saline vs. freshwater), and an intermediate generalist phenotype inhabiting the temporary lake with fluctuating salinity. The specialized phenotypes are poorly suited as migrants, so prezygotic isolation due to immigrant inviability is highly probable. This implication was supported by molecular evidence that showed restricted gene flow, persistence of founder events, and a pattern of allopatric fragmentation. This study showed how ecologically based divergent selection may explain diversification patterns in lacustrine copepods.     

Seasonal succession of the phytoplankton in the upper Mississippi River

Species composition and seasonal succession of the phytoplankton were investigated on the upper Mississippi River at Prairie Island, Minnesota, U.S.A. Both the numbers and volume of individual species were enumerated based on cell counts with an inverted microscope. A succession similar to algal succession in the local lakes occurred. The diatoms were dominant during the spring and fall and blue-green algae were dominant during the summer. The algal concentrations have increased up to 40 fold the concentrations of the 1920's, since the installation of locks and dams. The maximum freshweight standing crop was 4 mg · l^–1 in 1928 (Reinhard 1931), 13 mg · l^–1 in 1975 a wet year, and 47 mg · l^–1 in 1976, a relatively dry year with minimal current discharge. The diatoms varied from 36–99%, the blue-green algae from 0–44% and the cryptómonads from 0–50% of the total standing crop. The green algae were always present but never above 21% of the biomass. The dominant diatoms in recent years were centric -Stephanodiscus andCyclotella spp. (maximum 50,000 ml^–1). The dominant blue-green algae wereAphanizomenon flos-aquae (L.) Ralfsex Born.et Flahault andOscillatoria agardhii Gomont (maximum 800 ml^–1). These algal species are also present in local lakes. Shannon diversity values indicated greatest diversity of algae during the summer months.     

Salt lakes of the northern agricultural region,Western Australia

A survey of 11 sites covering three large (>10 km long, 6 sites) playa lakes and four pans (<1 km², 5 sites) of the Yarra Yarra salt lake system in the Northern Agricultural Region of Western Australia commenced in 2001. These salt lakes are shallow and ephemeral, with inundation being more regular following winter rainfall, but summer inundation also occurred in 2001. Salinity was generally higher in playas (156–368 g l⁻¹) than pans (30–284 g l⁻¹), but salinity responded noticeably to heavy rainfall events, especially in pans. pH values in the playa lakes (6.68–7.82) were less variable than in the pans (6.81–8.08). The range of dissolved oxygen concentrations was greater in pans (3.7–14.4 mg l⁻¹) than in playas (3.9–8.2 mg l⁻¹). Cationic concentrations generally followed the pattern of sea water cation dominance. Benthic microbial communities comprised either cohesive to loosely mucilaginous mats, or thin films of diatoms. Five genera of diatom and two species of filamentous cyanobacteria were recorded. Guest Editor: John M. Melack Saline Waters and their Biota     

EFFECT OF CYSTEINE AND METHIONINE ON SULFATE UPTAKE AND PRIMARY PRODUCTIVITY BY AXENIC ALGAL CULTURES AND LAKE MICROPLANKTON COMMUNITIES1

The presence of up to 500 μg sulfur·l^?1 of an equimolar mixture of cysteine and methionine had virtually no effect on the SO₄^2- uptake rate of Navicula pelliculosa, (Bréb.) Hilse whereas the rate of Ankistrodesmus falcatus (Corda) Ralfs was decreased by the presence of 500 μg S· l^?1 and Anabaena flos-aquae (Lyngbye) Bréb. by 50 μg S·l^?1. Primary productivity in these axenic cultures was affected (decreased) only in A. falcatus. The C:S uptake ratio was lowest in N. pelliculosa and highest in A. falcatus. Considering these species as representative of groups of naturally occurring algae, patterns of SO₄^2- uptake and primary productivity in a eutrophic and a moderately oligotrophic lake reflected the results of the algal culturing experiments: SO₄^2- uptake rates, relative to primary productivity, were higher in the presence of diatoms and bluegreen algae and lower when green algae were present; the addition of the cysteine I methionine mixture to the lake waters decreased the rate of microplankton SO₄^2- uptake in correlation with the makeup of the algal community; primary productivity decreased upon the addition of cysteine I methionine when green algae were relatively abundant. It is concluded that, in most fresh water systems, the effects of organic sulfur pollution on algal SO₄^2- uptake and primary productivity are insignificant as compared to other ecological changes that occur due to that pollution.     

Seasonal water quality of shallow and eutrophic Lake Pamvotis, Greece: implications for restoration

Lake Pamvotis is a moderately sized (22 km²) shallow (z _avg=4 m) lake with a polymictic stratification regime located in northwest Greece. The lake has undergone cultural eutrophication over the past 40 years and is currently eutrophic (annual averages of FRP=0.07 mg P l^-1, TP=0.11 mg P l^-1, NH₄ ⁺=0.25 mg N l^-1, NO₃ ^–=0.56 mg N l^-1). FRP and NH₄ ⁺ levels are correlated to external loading from streams during the winter and spring, and to internal loading during multi-day periods of summer stratification. Algal blooms occurred in summer (July–August green algae, August–September blue-green algae), autumn (October blue-green algae and diatoms), and winter (February diatoms), but not in the spring (March–June). The phytoplankton underwent brief periods of N- and P-limitation, though persistent low transparency (secchi depth of 60–80 cm) also suggests periods of light limitation. Rotifers counts were highest from mid-summer to early autumn whereas copepods were high in the spring and cladocerans were low in the summer. Removal of industrial and sewage point sources a decade ago resulted in a decrease in FRP. A phosphorus mass balance identified further reductions in external loading from the predominately agricultural catchment will decrease FRP levels further. The commercial fishery and lake hatchery also provides opportunities to control algal biomass through biomanipulation measures.     

The diatom flora of the Salton Sea, California

We report on diatom species of the Salton Sea, a highly saline (43 g l^–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.     

Selenium as a growth factor for plankton algae in laboratory experiments and in some Swedish lakes

The growth requirements of inorganic and organic selenium (Se) for the dinoflagellate Peridinium cinctum fa. westii and the diatom Stephanodiscus hantzschii var. pusillus and eight species of green algae are demonstrated. A new mineral culture medium for P. cinctum is presented. Using P. cinctum as a test alga, bioassays were carried out on waters from a calciferous lake and from some acidified, fertilized, lime-enriched or humic lakes for determination of their contents of bioavailable forms of Se (bioactive Se). Some of the results were related to Tot-Se and selenite-Se, measured chemically, to pH and the occurrence of ambient phytoplankton. In calcium-rich Lake Erken (pH ～ 8) blooms and decline of algae coincided with decreases (from >70 to ～20 ng Se · l^?1) and increases (up to >80 ng · l^?1) of bioactive Se, indicating uptake and release of inorganic or organic forms of Se. Acidified lakes (pH < 5) generally demonstrated much lower concentrations of bioactive Se (<20 ng · l^?1) than neutral, fertilized, lime-enriched, slightly acidic or humic lakes (>20 ng · l^?1). The correlation between pH and bioactive Se was positive (r ～ 0.92; n = 7). The ecological importance of Se is suggested for some common species of phytoplankton.     

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)     

The effects of phosphorus and temperature on the competitive success of an invasive cyanobacterium

Rising lake temperatures and changing nutrient inputs are believed to favour the spread of a toxic invasive cyanobacterium, Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju, in temperate lakes. However, most evidence for these hypotheses is observational or based on physiological measurements in monocultures. We lack clear experimental evidence relating temperature and nutrients to the competitive success of C. raciborskii. To address this, we performed a 2 × 2 factorial laboratory experiment to study the dynamics of mixed phytoplankton communities subjected to different levels of temperature and phosphorus over 51 days. We allowed C. raciborskii to compete with ten different species from major taxonomic groups (diatoms, green algae, cryptophytes, and cyanobacteria) typical of temperate lakes, under low and high summer temperatures (25 and 30 °C) at two levels of phosphorus supply (1 and 25 µmol L^?1). Cylindrospermopsis raciborskii dominated the communities and strongly decreased diversity under low-phosphorus conditions, consistent with the hypothesis that it is a good phosphorus competitor. In contrast, it remained extremely rare in high-phosphorus conditions, where fast-growing green algae dominated. Surprisingly, temperature played a negligible role in influencing community composition, suggesting that changes in summer temperature may not be important in determining C. raciborskii’s spread.     

Alkaline soda Lake Velika Rusanda (Serbia): the first insight into diatom diversity of this extreme saline lake

Alkaline soda lakes are unique habitats found in specific geographic regions, usually with dry climate. The Carpathian Basin is one of those regions very important for habitat and biodiversity conservation in Europe, with natural soda lakes found in Austria, Hungary and Serbia. In comparison to other two countries from Central Europe, algal biodiversity studies of saline soda lakes in Serbia are scarce. Lake Velika Rusanda has the highest measured salinity of all saline lakes in the Carpathian Basin and there were no reports of its diatom species richness and diversity till now. We conducted 2-year investigation programme to study biodiversity and seasonal dynamics of diatoms in this lake. A total of 27 diatom taxa were found, almost all of them attached to reed and much less in benthos and plankton. Five new diatom species for Serbia were recorded, Craticula halopannonica, Navicymbula pusilla, Hantzschia weyprechtii, Nitzschia thermaloides and Navicula staffordiae. The last mentioned is new for Europe as well. Lake Velika Rusanda is inhabited mostly by alkaliphilous and halophilic diatoms. Since diatoms are used as bioindicators in soda lakes, our results will improve their further application in ecological status assessment of these fragile habitats in the Carpathian Basin.