Copepods in turbid shallow soda lakes accumulate unexpected high levels of carotenoids

Carotenoids are protective pigments present in many aquatic organisms that reduce the photooxidative stress induced by short-wavelenght solar radiation, yet increase their susceptibility to predators. Arctodiaptomus spinosus, a calanoid copepod typically found in many fishless shallow soda lakes, shows large between-lake differences in pigmentation. Here, we attribute these differences to the environmental state of these ecosystems, namely, 'dark water' lakes with submersed vegetation and turbid 'white' lakes lacking macrophytes. Copepod carotenoid concentration in the turbid 'white' lakes was significantly (about 20-fold) higher than in the 'dark water' ones, although the latter systems were characterized by higher transparency. In addition, males had on a dry weight basis around three times higher carotenoid concentrations than females. Mycosporine-like amino acids (direct UV screening substances) were found in all cases, but in low concentration. The environmental conditions in these ecosystems were largely shaped by the presence/absence of submersed macrophytes Thus, in the turbid lakes, the strong wind-driven mixis allows for copepods to be brought to the surface and being exposed to solar radiation, whereas in 'dark water' ones, macrophytes reduce water turbulence and additionally provide shelter. Our results explain the counter-intuitive notion of strong red pigmentation in copepods from a turbid ecosystem and suggest that factors other than high UV transparency favor carotenoid accumulation in zooplankton.     

Dual bloom of green algae and purple bacteria in an extremely shallow soda pan

Extremophiles - In April 2014, dual bloom of green algae and purple bacteria occurred in a shallow, alkaline soda pan (Kiskunság National Park, Hungary). The water was only 5 cm deep,...     

The keystone role of anostracans and copepods in European soda pans during the spring migration of waterbirds

1. The European soda pans of the Carpathian Basin provide important stopover sites for several waterbird species. We studied the effect of different invertebrate food types and other characteristics on the habitat choice and distribution of birds on 82 pans (in Hungary, Austria and Serbia) during spring migration. 2. Only three environmental variables proved to be significant determinants of the waterbird communities: pan density (spatial effect) along with the density of Arctodiaptomus spp. and anostracans (local effect). Variance partitioning of the data revealed that aquatic invertebrate food supply (Arctodiaptomus and anostracans) had a greater effect than pan density on the 10 investigated bird species, suggesting a dominant role of species sorting in structuring the communities. Pied avocets (Recurvirostra avosetta) and northern shovelers (Anas clypeata) differed from the other species in their strong association with densities of anostracans (avocet) and Arctodiaptomus (shoveler). 3. Anostracans and microcrustaceans, especially the most frequent Branchinecta orientalis, Arctodiaptomus spinosus and Arctodiaptomus bacillifer, can be regarded as keystone elements of this soda pan habitat because of their bottom‐up role in structuring waterbird assemblages during spring migration.     

Periphyton-macroinvertebrate interactions in light and fish manipulated enclosures in a clear and a turbid shallow lake

In a clear and a turbid freshwater lake the biomasses of phytoplankton, periphytic algae and periphytonassociated macrograzers were followed in enclosures with and without fish (Rutilus rutilus) and four light levels (100%, 55%, 7% and < 1% of incoming light), respectively. Fish and light affected the biomass of primary producers and the benthic grazers in both lakes. The biomass of primary producers was generally higher in the turbid than the clear lake, and in both lakes fish positively affected the biomass, while shading reduced it. Total biomass of benthic grazing invertebrates was higher in the clear than in the turbid lake and the lakes were dominated by snails and chironomids + ostracods, respectively. While light had no effect on the biomass of grazers in the clear lake, snail breeding was delayed in the most shaded enclosures and presence of fish reduced the number of snails and the total biomass of grazers. In the turbid lake ostracod abundance was not influenced by light, but was higher in fish-free enclosures. Density of chironomids correlated positively with periphyton biomass in summer, while fish had no effect. Generally, light-mediated regulation of primary producers was stronger in the turbid than in the clear lake, but the regulation did not nambiguously influence the primary consumers. However, regulation by fish of the benthic grazer community was stronger in the clear than in the turbid lake, and in both lakes strong top-down effects on periphyton were seen. The results indicate that if present-day climate in Denmark in the future is found in coastal areas at higher latitudes, the effect of lower light during winter in such areas will be highest in clear lakes, with typically lower fish biomass and higher invertebrate grazer density.     

Diatom bloom in the tidal freshwater zone of a turbid and shallow estuary,Rupert Bay (James Bay,Canada)

Phytoplankton biomass and species composition were studied from June to September 1991 at the mouth of four major rivers and in the freshwater (sal. 0 %), the estuarine (sal. 2–10%) and the coastal (sal. 10–12%) zones of Rupert Bay, located at the southeast tip of James Bay, Canada.A chlorophyll a maximum (5–14 µg 1^–1) was observed in the freshwater zone from July to September. Chlorophyll values were low at the mouth of the rivers and in the estuarine and coastal zones (chl a < 1.00 µg 1^–1). Diatoms were dominant in the freshwater zone (30–80 % abundance), with flagellates dominating in the estuarine and coastal zones (60–95% abundance). Diversity was low (H: 1.5–2.5) in the freshwater zone and decreased seaward (H: 0.5–1.5).The diatom bloom was composed almost exclusively of the autochthonous planktonic diatom Cyclotella meneghiniana Kütz., which contributed 25–85% of the species composition, and of the subdominant benthic species Diploneis smithii, Navicula lanceolata and Surirella robusta. Peak abundance occurred upstream of the turbidity maximum, in the tidal freshwater zone. In this zone the mean photic depth was 1 m and residence time was from 7 to 8 days during the bloom. Residence time is considered to be the dominant factor controlling the phytoplankton bloom, with light not acting as a limiting factor. The high turbidity due to resuspension and shallow depth of the bay controlled the species composition.     

Macrophytes and groundwater drive extremely high organic carbon concentration of soda pans

1. Endorheic soda pans are among the highest dissolved organic carbon (DOC) content aquatic systems on the planet with concentrations up to 1 g/L. Considering the importance of inland waters in the global carbon cycle, understanding the drivers of such outstanding organic carbon pools is eminent. The soda pans of the Carpathian Basin present a wide variability of biotic and abiotic characteristics that provide an adequate system to assess the determinants of extreme high DOC concentrations. Here, we demonstrate through a multi-site comparison, a multi-year seasonal monitoring, and a laboratory experiment that the dissolved organic matter content of the highest DOC concentration soda pans is primarily of groundwater and emergent macrophyte origin.
2. More precisely, the multi-site comparison of 14 soda pans revealed that variation of coloured dissolved organic matter (CDOM) content of the surface water of soda pans is partially explained by the CDOM content (22% of variation) of local groundwater, indicating the significant role of allochthonous terrestrial DOC sources. Further 23% of CDOM variation could be accounted for by Bolboschoenus maritimus species-specific emergent macrophyte cover, while the contribution of Phragmites australis cover was only minor.
3. In line with the results of the multi-site comparison, our decomposition experiment demonstrated that both B. maritimus and P. australis have the potential to release substantial amount of organic matter into soda pans. However, the organic matter release of B. maritimus leads to twice as high DOC and 3.5-times higher CDOM concentrations than P. australis. Considering previous organic matter release studies, we concluded that P. australis is a relatively low organic matter releaser emergent macrophyte, and therefore the species composition of emergent macrophytes has to be carefully considered in autochthonous plant-derived DOM estimations.
4. Finally, the multi-year seasonal monitoring of two distinctive soda pans showed that the high organic matter concentrations depend not only on their intrinsic characteristics but also on interannual variability. More precisely, we demonstrated that the highest CDOM and DOC concentrations that occurred in a coloured (i.e. brown, low total suspended solids) soda pan with extensive (95%) macrophyte cover dominated by B. maritimus were measured in a period characterised by high pH and low water levels, which were presumably the consequence of increased evaporation due to decreased precipitation and above average temperature.
5. Our results indicate that considering climate change trends common for most endorheic regions (i.e. increased temperature and modified precipitation regimes), extremely high organic matter concentrations might become more frequent in the near future in local water bodies, particularly in those highly influenced by groundwater inflow. Furthermore, soda pans with vast specific macrophyte cover and substantial groundwater inflow might become organic carbon processing hotspots.

     

Ecology of four turbid clay pans during a filling-drying cycle in the Paroo,semi-arid Australia

The clay pans studied were small (<2 ha), shallow (<30 cm) and contained very turbid, alkaline water of low conductivity for 40–90 days. Nutrients peaked early but chlorophyll-a values varied through time. Water temperatures ranged from 3.5 to 25.5 °C. Cumulative species richness ranged from 30 to 55, with mean momentary species richness varying from 15.5 to 29.1 among the four pans. Macroinvertebrate assemblages were dominated by adult phyllopods, hemipterans and coleopterans, and zooplankton was dominated by juvenile phyllopods, copepods and cladocerans. No macrophytes were present. Ordination showed two pairs of pans (A+B and C+D) which matched ordination of physicochemical data, with turbidity the factor best explaining the pattern. Macroinvertebrate assemblages varied between the centre and littoral zone of all pans, particularly in C and D in which CPOM was more abundant in the littoral. Grouping of assemblages was directed as much by differences in abundance as variation in species composition. Succession was directional and continuous. Among macroinvertebrates, insects dominated initially and terminally, but phyllopod crustaceans were important much of the time. In the zooplankton, phyllopods dominated initially then entomostracans, with final assemblages mostly consisting of copepods. Succession was quicker and later assemblages more stable in zooplankton. The feeding group of filter feeders/collectors dominated during the life of the pans, except at the beginning and end when predators were important. The major carbon source was algal, despite the high turbidity and abundant detrital matter.     

Planktonic bacterial community composition of an extremely shallow soda pond during a phytoplankton bloom revealed by cultivation and molecular cloning

Böddi-szék is one of the shallow soda ponds located in the Kiskunság National Park, Hungary. In June 2008, immediately prior to drying out, an extensive algal bloom dominated by a green alga (Oocystis submarina Lagerheim) was observed in the extremely saline and alkaline water of the pond. The aim of the present study was to reveal the phylogenetic diversity of the bacterial communities inhabiting the water of Böddi-szék during the blooming event. Using two different selective media, altogether 110 aerobic bacterial strains were cultivated. According to the sequence analysis of the 16S rRNA gene, most of the strains belonged to alkaliphilic or alkalitolerant and moderately halophilic species of the genera Bacillus and Gracilibacillus (Firmicutes), Algoriphagus and Aquiflexum (Bacteroidetes), Alkalimonas and Halomonas (Gammaproteobacteria). Other strains were closely related to alkaliphilic and phototrophic purple non-sulfur bacteria of the genera Erythrobacter and Rhodobaca (Alphaproteobacteria). Analysis of the 16S rRNA gene-based clone library indicated that most of the total of 157 clone sequences affiliated with the anoxic phototrophic bacterial genera of Rhodobaca and Rhodobacter (Alphaproteobacteria), Ectothiorhodospira (Gammaproteobacteria) and Heliorestis (Firmicutes). Phylotypes related to the phylum Bacteroidetes formed the second most abundant group. Clones related to the mainly anaerobic and alkaliphilic bacterial genera of Anoxynatronum (Firmicutes), Spirochaeta (Spirochaetes) and Desulfonatronum (Deltaproteobacteria) were also abundant. Further clone sequences showed less than 95 % similarity values to cultivated species of the phyla Actinobacteria, Cyanobacteria, Deinococcus-Thermus, Fibrobacteres, Gemmatimonadetes and Lentisphaerae.     

Alternation between clear,high-vegetation and turbid,low-vegetation states in a shallow lake: the role of birds

External phosphorus load to a wetland with two shallow lakes in the Botshol Nature Reserve, the Netherlands, was reduced since 1989, resulting in a rapid reduction of phosphorus levels, phytoplankton biomass and turbidity, and after 4 years, explosive growth of Characeae. The clear water state was unstable, however, and the ecosystem subsequently alternated between clear, high-vegetation and turbid, low-vegetation states. The switch from clear to turbid states occurred at a higher phosphorus level than the switch from turbid to clear states and area covered by macrophytes was significantly correlated to Secchi disc depth (r = 0.86, p < 0.001). Beginning in 1997, phosphorus input from droppings of greylag geese and black-headed gulls increased. The hypothesis that grazing prevented the return of Characeae populations was tested during 1996–1997 using large-scale exclosure experiments. The biomass and cover of Characeae were monitored in 17 exclosures for 2 years. The experiments showed no significant increase in Characeae in the absence of grazers compared with the controls. During the course of the experiments, the entire lake switched from turbid water to clear water and high Chara biomass. These ecosystem developments suggest that light limitation was the main factor controlling the collapse and return of Characeae in Botshol.     

Anostracans and microcrustaceans as potential food sources of waterbirds on sodic pans of the Hungarian plain

Hungarian sodic water bodies have a rich macro- and microcrustacean fauna due to the lack of fish populations. The crustacean population is very abundant, for this reason these wetlands provide good feeding resources for waterbirds. The density of macro- and microcrustacean populations together with feeding waterbirds was investigated in March, April, and May of 2002, on two characteristic sodic pans, “Kelemen-szék” and “Zab-szék”. The following dabbling-filtering waterfowls and pelagic forager wader species were counted: northern pintail (Anas acuta), northern shoveler (Anas clypeata), garganey (Anas querquedula), common teal (Anas crecca), avocet (Recurvirostra avosetta), spotted redshank (Tringa erythropus), greenshank (Tringa nebularia), and marsh sandpiper (Tringa stagnatilis). The dominant macrocrustacean species was the [Anostraca – Branchinectidae] natronophile Branchinecta orientalis, and its density was significantly higher in Zab-szék than in Kelemen-szék. The microcrustacean zooplankton community was also different in the pans, [Cladocera] Daphnia magna density was significantly higher in Kelemen-szék than in Zab-szék, but the density of the [Copepoda] natronophile Arctodiaptomus spinosus, was higher in Zab-szék than in Kelemen-szék. The density of the investigated waterbird species was also significantly higher in Zab-szék than in Kelemen-szék during spring. We can conclude that the macrocrustacean B. orientalis is one of the most important potential food resources for migrating pelagic foraging waders in spring on characteristic Hungarian sodic pans. However, the most abundant available food item for waterbirds are copepod microcrustacean zooplankton, which have a biomass that is larger by approximately one order of magnitude than the macrocrustacean zooplankton biomass. Considering the lack of submerged water vegetation, we suggest that planktonic microcrustaceans are an important food resource for dabbling-filtering ducks because they can utilise the small crustacean biomass more effectively than the less abundant and rapidly moving macrocrustacean B. orientalis.     

Navigation by light polarization in clear and turbid waters

Certain terrestrial animals use sky polarization for navigation. Certain aquatic species have also been shown to orient according to a polarization stimulus, but the correlation between underwater polarization and Sun position and hence the ability to use underwater polarization as a compass for navigation is still under debate. To examine this issue, we use theoretical equations for per cent polarization and electric vector (e-vector) orientation that account for the position of the Sun, refraction at the air-water interface and Rayleigh single scattering. The polarization patterns predicted by these theoretical equations are compared with measurements conducted in clear and semi-turbid coastal sea waters at 2 m and 5 m depth over sea floors of 6 m and 28 m depth. We find that the per cent polarization is correlated with the Sun's elevation only in clear waters. We furthermore find that the maximum value of the e-vector orientation angle equals the angle of refraction only in clear waters, in the horizontal viewing direction, over the deeper sea floor. We conclude that navigation by use of underwater polarization is possible under restricted conditions, i.e. in clear waters, primarily near the horizontal viewing direction, and in locations where the sea floor has limited effects on the light's polarization.     

A test of traditional diversity measures and taxonomic distinctness indices on benthic diatoms of soda pans in the Carpathian basin

Saline lakes are threatened all over the world and their conservation has been a key issue. Various diversity indices are available for ecological status assessments, however, with poorly explored relevance and applicability in saline, alkaline pans. Therefore, traditional diversity measures (species richness and Shannon diversity) and taxonomic distinctness indices (Average [AvTD] and Variance of Taxonomic Distinctness [VarTD]) were tested in more than 100 sampling sites of 39 soda pans in Central-Europe to find sufficient indicators of the ecological condition and simultaneously to facilitate their preservation according to the modern conservation practices. Results of the analyses showed that healthy soda pan ecosystems with high level of natural stress and reduced habitat heterogeneity are characterized by low diversity diatom assemblages. In soda pans where the stress can be extremely high from natural reasons, oligopoly of closely related species can develop: the average taxonomic distinctness appeared between genus and family level. The non-DNA-sequence based phylogenetic diversity measures (AvTD and VarTD), were generally sensitive to the trophic state of the lakes, in contrast to traditional diversity metrics, which were unequivocally indicative for the special physical and chemical parameters (e.g. conductivity, pH) of the soda pans. In some cases, when the response of the diversity measures for a given environmental variable (pH, temperature) overlapped, the AvTD was found to be a more precise indicator of the environmental changes (pH) than traditional ones. The decreasing tendency of the AvTD along the intensified natural impact may be explained by the long available time for the species to adapt to these special environments.     

Analysis and modelling of the interactive effects of temperature and light on phytoplankton growth and relevance for the spring bloom

Global climate change alters the relationship between temperatureand light in aquatic ecosystems, which is expected to affectthe success of different phytoplankton species. To examine this,the interactions between temperature, photoperiod and lightexposure (LE) (integral daily light supply) on specific growthrates were analysed for Limnothrix redekei, Planktothrix agardhii(cyanobacteria), Nitzschia acicularis and Stephanodiscus minutulus(diatoms). A model of factor interactions was developed basedon new (P. agardhii and St. minutulus) and previously publishedlaboratory studies. It describes the measured data with highprecision. Temperature and photoperiod affect the parametersof the light-growth response curve differently, but these effectsare the same for all species. The link between functions fortemperature and photoperiod is more species-specific. Usingmeteorological data, the model developed here was used to studythe interplay of these factors during a spring bloom in LakeMüggelsee (Berlin). It was found that while all three factorsinfluenced phytoplankton growth, temperature and photoperiodwere more important than LE. Both the intensities of the factorsand the interactions between them influenced each species toa different degree. The results may help improve our understandingand ability to predict shifts in phytoplankton communities causedby weather patterns and climate change.     

Light control on phytoplankton production in a shallow and turbid estuarine system

Tagus estuary is one of the largest estuaries of Western Europe. With the aim of unravelling the drivers of primary production in this shallow and turbid nutrient replete estuary, we tested the hypothesis that light availability is a major factor controlling phytoplankton production. Environmental parameters, phytoplankton biomass, community composition, and photosynthetic parameters were monitored at two sites in the estuary during a complete annual cycle. Despite the fact that nutrient concentrations were always above growth-limiting values, Chl a concentrations were relatively low throughout the study period. High water column turbidity, due to riverine inputs, promoted a rapid attenuation of light and created a compressed profile with optimal photosynthetic conditions. Therefore, the phytoplankton community, dominated by small cells, such as diatoms and cryptophycean flagellates, displayed highly photosynthetic efficiency and low light-saturated photosynthetic rates as a photo-acclimation response to low light conditions year-round. Primary production rate was unimodal, peaking in the summer months. In such estuarine system, gross primary production could thus be predicted by an existing robust empirical model based on pigment standing crop (Chl a), surface irradiance (E ₀) and optical depth (Z _eup). Compared to other shallow estuaries, the Tagus can be classified as a low- to moderately productive estuary, being the turbidity-induced low light conditions the principal factor limiting phytoplankton growth.     

Seasonal changes in the invertebrate community of small shallow ephemeral pans at Bain's Vlei, South Africa

Changes in invertebrate population numbers and composition were monitored in six small shallow ephemeral pans during four consecutive inundations of spring, summer and autumn 1988/1989. The community was generally characterized by crustaceans and was invaded by insect larvae in summer. Community changes and succession were prominent in spring but less so in summer and autumn. Large pans supported more species than small pans. During longer inundation there was less difference between the initial and the final population composition than during shorter inundation, although the total population density did not increase significantly. This indicated that population composition stabilized as inundation lengthened. Population changes of six representative taxa were not correlated to changes in the physical and chemical characteristics of the water.     

Particle size distribution and chemical parameters of the sediments of a shallow turbid impoundment

As part of an ecosystem study of a small mesotrophic turbid impoundment in the semi-arid part of South Africa, an investigation was made of the particle size distribution, organic content and inorganic chemical composition of the sediment. Nine transects 50 m apart were made during February 1980. Sediments were sampled with an Eckman grab. The following analyses were made: size fractionation by wet sieving, cation exchange capacity, exchangeable Na, K, Ca, Mg and PO₄, total P, and loss on ignition. From the results it was clear that the finer particles, in or near the original river bed, had higher cation exchange capacity, total P, exchangeable phosphorus and organic content. Littoral areas with avian habitat and extensive macrophyte vegetation, contained coarser sediments. Organic detritus apparently migrated to the deeper part of the impoundment. Sediments of lacustrine and fluvial origin were identified by means of the Passega classification.     

Preservation of the light field in turbid lake and river water in laboratory-scale enclosure

The laboratory-scale enclosure (LSE), as a physical model ofthe water column, has been introduced for studies of sestondynamics in shallow, mixed lakes. Preserving the ‘natural’underwater light climate was among the design criteria. However,lateral exchange of light between the LSE cylinder and its waterbath caused deviations from conditions in the water column insitu. Two modifications of the original design are introducedby providing the LSE cylinder with (i) a masking plate and (ii)a reflective coating. The light fields in the original and modifieddesigns are compared for Osciiiatoria limnetica culture andWestern Scheldt Estuary water. These test suspensions had dryweight concentrations of 50 mg 1^–1 and differed widelyin scattering to absorption ratios, i.e. 4 and 12 for the cultureand natural water, respectively. Using the reflective coating,the LSE provided an underwater light field conforming to generaltheory for diffuse attenuation and reflectance. Using the maskingplate may suffice for cultures of cyanobacteria, but the reflectivecoating is needed for studies of phytoplankton growth in relationto the optical conditions in turbid lake and river water.     

Trait‐based diatom functional diversity as an appropriate tool for understanding the effects of environmental changes in soda pans

Saline lakes, among the most seriously endangered ecosystems, are threatened due to climate change and human activities. One valuable feature of these environments is that they constitute areas of high biodiversity. Ecologists are, therefore, under great pressure to improve their understanding of the effects of natural and anthropogenic disturbances on the biodiversity of saline lakes. In this study, a total of 257 samples from 32 soda pans in Central Europe between 2006 and 2015 were examined. The effects of environmental variables and of geographical and limnoecological factors on functional diversity were analyzed. Furthermore, the explanatory power of the trait‐based approach was assessed, and the applicability of the indices for biomonitoring purposes was determined. It was found that low habitat heterogeneity and harsh environments lead to the selection of a small number of suitable traits, and consequently, to a naturally low level of functional diversity. Anthropogenic activities enhance diversity at functional level due to the shift toward freshwater characteristics. On the regional scale, the effects of the region and status (natural, degraded, reconstructed) on diatom functional diversity were significant and more pronounced than that of the environmental and other limnoecological factors. The degree of variance found in functional diversity ascribed to environmental variables is five times greater in the case of the application of a trait‐based approach, than when a taxonomic one is employed in the literature. Each of the tested functional diversity indices was sensitive to the most important environmental variables. Furthermore, these were type‐specific and proved to be more complex indicators than taxonomic metrics. It is possible to suggest four functional diversity indices (FGR, FRic, FDis, and FDiv) which emphasize their independence from substrate and seasonal variations for ecological status assessment and conservation planning.     

Response of waterbirds to alternating clear and turbid water phases in two shallow Mediterranean lakes

Albufera de Adra (Southern Spain) constitutes an internationally-recognised marsh for waterbirds; important populations of some endangered species such as White-headed Duck and Red-crested Pochard overwinter and breed in its two shallow permanent lakes (Lake Honda and Lake Nueva). In a recently published article, we revealed the factors responsible for the irregular alternation between phytoplankton-dominated turbid phases and macrophyte-dominated clear water phases in Lake Honda and Lake Nueva. In this note, we try to clarify the impact of such an alternation of equilibrium states on the waterbird dynamics. Marked increments in abundance, and brood recruitment of dabbling and diving waterbirds were recorded during the clear water phases in contrast with the turbid water phases, as the increase of macrophytes associated with increased water transparency attract waterbirds for available food. Implications for ecosystem management, restoration and conservation are identified.