New records of Chara connivens P. Salzmann ex A. Braun 1835 – an extremely rare and protected species in Polish brackish waters

The stonewort Chara connivens was rediscovered in the Vistula Lagoon in 2011, almost 35 years after its last record. In 2012, the species was recorded for the first time in the Szczecin Lagoon. Chara connivens occurred at shallow (0.5–1.2 m) sandy-muddy and muddy bottoms of small embayments. In the Vistula Lagoon, the stonewort was represented by single small specimens, while in the Szczecin Lagoon, it formed dense and extensive patches

Epiphytic bacterial community composition on two common submerged macrophytes in brackish water and freshwater

<p>Abstract</p> <p>Background</p> <p>Plants and their heterotrophic bacterial biofilm communities possibly strongly interact, especially in aquatic systems. We aimed to ascertain whether different macrophytes or their habitats determine bacterial community composition. We compared the composition of epiphytic bacteria on two common aquatic macrophytes, the macroalga <it>Chara aspera </it>Willd. and the angiosperm <it>Myriophyllum spicatum </it>L., in two habitats, freshwater (Lake Constance) and brackish water (Schaproder Bodden), using fluorescence <it>in situ </it>hybridization. The bacterial community composition was analysed based on habitat, plant species, and plant part.</p> <p>Results</p> <p>The bacterial abundance was higher on plants from brackish water [5.3 × 10⁷cells (g dry mass)^-1] than on plants from freshwater [1.3 × 10⁷cells (g dry mass)^-1], with older shoots having a higher abundance. The organic content of freshwater plants was lower than that of brackish water plants (35 vs. 58%), and lower in <it>C. aspera </it>than in <it>M. spicatum </it>(41 vs. 52%). The content of nutrients, chlorophyll, total phenolic compounds, and anthocyanin differed in the plants and habitats. Especially the content of total phenolic compounds and anthocyanin was higher in <it>M. spicatum</it>, and in general higher in the freshwater than in the brackish water habitat. Members of the Cytophaga-Flavobacteria-Bacteroidetes group were abundant in all samples (5–35% of the total cell counts) and were especially dominant in <it>M. spicatum </it>samples. Alphaproteobacteria were the second major group (3–17% of the total cell counts). Betaproteobacteria, gammaproteobacteria, and actinomycetes were present in all samples (5 or 10% of the total cell counts). Planctomycetes were almost absent on <it>M. spicatum </it>in freshwater, but present on <it>C. aspera </it>in freshwater and on both plants in brackish water.</p> <p>Conclusion</p> <p>Bacterial biofilm communities on the surface of aquatic plants might be influenced by the host plant and environmental factors. Distinct plant species, plant part and habitat specific differences in total cell counts and two bacterial groups (CFB, planctomycetes) support the combined impact of substrate (plant) and habitat on epiphytic bacterial community composition. The presence of polyphenols might explain the distinct bacterial community on freshwater <it>M. spicatum </it>compared to that of <it>M. spicatum </it>in brackish water and of <it>C. aspera </it>in both habitats.</p

Uncertainty Assessment of Ice Discharge Using GPR-Derived Ice Thickness from Gourdon Glacier, Antarctic Peninsula

Ice cliffs within a glacier represent a challenge for the continuity equations used in many glacier models by interrupting the validity of input parameters. In the case of Gourdon Glacier on James Ross Island, Antarctica, a ∼300–500 m high, almost vertical cliff, separates the outlet glacier from its main accumulation area on the plateau of the island. In 2017 and 2018 we conducted ice thickness measurements during two airborne ground penetrating radar campaigns in order to evaluate differences to older measurements from the 1990s. The observed differences are mostly smaller than the estimated error bars. In comparison to the in situ data, the published “consensus ice thickness estimate” strongly overestimates the ice thickness at the outlet. We analyse three different interpolation and ice thickness reconstruction methods. One approach additionally includes the mass input from the plateau. Differences between the interpolation methods have a minor impact on the ice discharge estimation if the used flux gates are in areas with a good coverage of in situ measurements. A much stronger influence was observed by uncertainties in the glacier velocities derived from remote sensing, especially in the direction of the velocity vector in proximity to the ice cliff. We conclude that the amount of in situ measurements should be increased for specific glacier types in order to detect biases in modeled ice thickness and ice discharge estimations

Gravel pits support waterbird diversity in an urban landscape

We assessed the benefit of 11 gravel pits for the settlement of waterbird communities in an urbanized area lacking natural wetlands. Gravel pits captured 57% of the regional species pool of aquatic birds. We identified 39 species, among which five were regionally rare. We used the Self Organizing Map algorithm to calculate the probabilities of presence of species, and to bring out habitat conditions that predict assemblage patterns. The age of the pits did not correlate with assemblage composition and species richness. There was a positive influence of macrophyte cover on waterbird species richness. Larger pits did not support more species, but species richness increased with connectivity. As alternative wetland habitats, gravel pits are attractive to waterbirds, when they act as stepping stones that ensure connectivity between larger natural and/or artificial wetlands separated in space

Dynamics of the ice cap on King George Island, Antarctica: field measurements and numerical simulations

ABSTRACT. King George Island is located at the northern tip of the Antarctic Peninsula, which is influenced by maritime climate conditions. The observed mean annual air temperature at sea level is -2.

ODREĐIVANJE BROJNOSTI PREDATORA KORIŠTENJEM EKSPERIMENTALNOG RIBOLOVA: USPOREDBE UNUTAR I IZVAN MORSKIH ZAŠTIĆENIH PODRUČJA U SREDNJEM JADRANU

A fundamental question in ecology is the role of predators in limiting their prey populations. This question can be approached for shallow marine fish communities by comparison of abundance of species inside and outside marine protected areas (MPAs), where fishing restrictions may enforce large abundance differences in large (top) predators. The first step in demonstrating differences in these populations is the development and testing of methods capable of estimating abundance of fast-swimming and alert species which generally are difficult to quantify with traditional net-based sampling or visual census. That the method of experimental fishing with hook and line is capable of sampling predatory fish of a wide range of sizes, from 15 to 125 cm, inside and outside an MPA in the central Adriatic Sea, Kornati National Park, Croatia, was demonstrated in this preliminary study. Evidence of significantly more abundant top predators inside the MPA and a significantly higher mean size of fish overall was found. A total of 11 species of fish were sampled across several benthic habitats, of which six were found only in the MPA. It is concluded that the MPA represents a natural experiment with greater abundance of larger predators than outside, and that experimental fishing can take advantage of these differences to test the hypothesis of top-down regulation of fish communities.Temeljno pitanje u ekologiji je uloga predatora u kontroli populacije plijena. Za zajednice riba u plitkom moru, na ovo pitanje može se odgovoriti uspoređujući brojnost vrsta unutar morskih zaštićenih područja (MPA) i izvan njih, gdje regulacija ribolovnih aktivnosti može značajno utjecati na brojnost velikih (vršnih) predatora. Prvi korak u dokazivanju razlika u navedenim populacijama je razvoj i testiranje metoda uz pomoć kojih je moguće procijeniti brojnost brzih i opreznih vrsta, koje je obično teško kvantificirati korištenjem tradicionalnih metoda poput lova mrežama ili vizualnim cenzusom. U ovom preliminarnom istraživanju je prikazano da se korištenjem metode eksperimentalnog ribolova mogu uzorkovati predatorske vrste riba raznih veličina, od 15 do 125 cm, unutar i izvan morskih zaštićenih područja u srednjem Jadranu (na području Nacionalnog parka Kornati, Hrvatska). Dokazala se značajno veća brojnost vršnih (top) predatora unutar zaštićenog područja kao i značajno veća prosječna veličina riba. Uzorkovano je ukupno 11 različitih vrsta riba na raznim pridnenim staništima, od kojih je 6 zabilježeno isključivo unutar zaštićenog područja. Može se zaključiti da su morska zaštićena područja svojevrsni prirodni eksperiment gdje je brojnost predatorskih vrsta veća nego izvan zaštićenog područja. Osim toga, eksperimentalni ribolov je učinkovita metoda uz pomoć koje se na temelju uočenih razlika može testirati hipoteza o top-down regulaciji zajednica riba

Ecology of charophytes – permanent pioneers and ecosystem engineers

For almost a century, charophytes have been regarded as a group that is confined to low-nutrient-clear water conditions. In light of recent research, this generalisation of the ecological niche dimensions of charophytes has changed and now includes more facets of ecological existence. In this review, the current knowledge with respect to species-specificity as well as temporal aspects – ontogenetic and successional ones – of the ecological requirements of charophytes are presented and discussed. This review identifies new directions for ecological research on charophytes as well as knowledge gaps to be filled, not just for reasons of academic curiosity, but also for applied purposes such as lake restoration, bioremediation and bioindication of water quality and water regime

Response of Submerged Macrophyte Communities to External and Internal Restoration Measures in North Temperate Shallow Lakes

Submerged macrophytes play a key role in north temperate shallow lakes by stabilising clear-water conditions. Eutrophication has resulted in macrophyte loss and shifts to turbid conditions in many lakes. Considerable efforts have been devoted to shallow lake restoration in many countries, but long-term success depends on a stable recovery of submerged macrophytes. However, recovery patterns vary widely and remain to be fully understood. We hypothesize that reduced external nutrient loading leads to an intermediate recovery state with clear spring and turbid summer conditions similar to the pattern described for eutrophication. In contrast, lake internal restoration measures can result in transient clear-water conditions both in spring and summer and reversals to turbid conditions. Furthermore, we hypothesize that these contrasting restoration measures result in different macrophyte species composition, with added implications for seasonal dynamics due to differences in plant traits. To test these hypotheses, we analysed data on water quality and submerged macrophytes from 49 north temperate shallow lakes that were in a turbid state and subjected to restoration measures. To study the dynamics of macrophytes during nutrient load reduction, we adapted the ecosystem model PCLake. Our survey and model simulations revealed the existence of an intermediate recovery state upon reduced external nutrient loading, characterised by spring clear-water phases and turbid summers, whereas internal lake restoration measures often resulted in clear-water conditions in spring and summer with returns to turbid conditions after some years. External and internal lake restoration measures resulted in different macrophyte communities. The intermediate recovery state following reduced nutrient loading is characterised by a few macrophyte species (mainly pondweeds) that can resist wave action allowing survival in shallow areas, germinate early in spring, have energy-rich vegetative propagules facilitating rapid initial growth and that can complete their life cycle by early summer. Later in the growing season these plants are, according to our simulations, outcompeted by periphyton, leading to late-summer phytoplankton blooms. Internal lake restoration measures often coincide with a rapid but transient colonisation by hornworts, waterweeds or charophytes. Stable clear-water conditions and a diverse macrophyte flora only occurred decades after external nutrient load reduction or when measures were combined.Additional co-authors: Wolf M. Mooij, Ruurd Noordhuis, Geoff Phillips, Jacqueline Rücker, Hans-Heinrich Schuster, Martin Søndergaard, Sven Teurlincx, Klaus van de Weyer, Ellen van Donk, Arno Waterstraat and Carl D. Saye

Near-margin ice thickness from a portable radar: implications for subglacial water routing, Leverett Glacier, Greenland

Ice thickness measurements near the margin of the Greenland Ice Sheet (GrIS) are relatively sparse, presenting issues for modelling ice flow dynamics, ice sheet change and subglacial hydrology. We acquired ice thickness data at Leverett Glacier, western Greenland, using a highly portable, low power commercially-available ice-penetrating radar operating at 10-80 MHz. Imaging of the bed to depths of 270 m was possible using this system. Our ice thickness measurements were incorporated into the BedMachine model of bed elevation created using mass conservation methods. The new data significantly modified the modelled ice thickness and routing of subglacial water in both the Leverett and adjacent Russell Glacier. Though changes to the modelled basal topography and subglacial hydrology are consistent with observations, our new data unrealistically reduced the overall size of the Leverett hydrological catchment. Additional ice thickness measurements are therefore required to realistically constrain subglacial topography and subglacial hydrological routing in this area. Our work has significantly enhanced our understanding of basal topography and subglacial hydrology of Leverett Glacier, with implications for glacier dynamics and assessments of water piracy between catchments in the marginal zone of the GrIS