Chironomidae in shallow water bodies of a protected lowland freshwater floodplain ecosystem.

Lowland floodplains are complex ecosystems comprised of standing and flowing waters interacting with terrestrial habitats, and the main force creating, shaping and influencing, both habitats and biotic communities, is a hydrological regime and water supply from the parent river. In areas not much altered by anthropogenic influence, the Danube creates such floodplain areas, and temporary shallow water bodies within represent biodiversity important habitats. In the Kopacki Rit Nature Park floodplain in Croatia, diversity based on Chironomidae (Diptera) in both benthic and epiphytic communities was studied in eight ponds (temporary shallow water body) and at two channel locations (permanent shallow water body). At each location samples of sediment and macrophytes were taken at three sites. The benthic chironomid community was comprised of 29 taxa, most abundant being representatives of the Chironomus genus and Tanypus kraatzi in ponds, and Polypedilum nubeculosum and Cladotanytarsus sp. in channel samples. Cricotopus gr. sylvestris, Paratanytarsus sp. and Endochironomus tendens were dominant epiphytic chironomids (18 taxa). Non-metric multidimensional scaling and analysis of similarity analyses showed there was a clear grouping of sampling locations based on their position in the park and the distance from each other, more evident in the case of benthic chironomid communities. Furthermore, when the water bodies were compared based on the community structure from different locations and substrates, there was also a statistically significant separation. Community composition indicates high productivity and organic matter production of studied water bodies, but moreover, the differences in substrate preferences evident in 16 common out of 31 recorded chironomid taxa, indicate the importance of habitat complexity preservation in a floodplain.

Algal migration and nutrient enrichment contribute to patterns in phytoplankton versus epiphyton communities.

Algal dominance between phytoplankton and epiphyton plays an essential role in predicting shallow lake shifts between clear-water and turbid-water states. However, compared to resources competition, studies on algal life-form shifts between phytoplankton and epiphyton have traditionally received less interest, as few studies have focused on algal communities in both habitats concurrently. We conducted a 4 × 3 factorial design microcosm experiment to explore the mutual feedback relationship between phytoplankton and epiphyton. The initial algal life-form (epiphytic algae and phytoplanktonic algae alone or together) and nutrients enrichment (ambient, enrichment with N and P alone or together) were manipulated. After 28 days of incubation, the results suggested that the nutrient effects on the phytoplankton and epiphyton communities differed among the three different initial algal life-forms. A significant competitive advantage of phytoplankton was found even in treatments containing only epiphytic algae as the initial algal community. The contribution of nutrient enrichment to phytoplankton abundance (13%) was similar to that of epiphyton abundance (11%). In the mutual influence between two algal communities, epiphyton was likely to be a beneficiary as the phytoplankton community contributed 15% of the variance in epiphyton abundance. In addition, significant algal life-form shifts between phytoplankton and epiphyton only occurred in treatments containing one algal life-form, but not in treatments containing both algal life-forms at the beginning of the experiment. Our results emphasized the competitive advantage of phytoplankton in utilizing nutrient resources in the water column of shallow lakes. Moreover, we demonstrated that algal life-form shift was an adaptive behavior closely correlated with environmental variation. These results will provide broader insights to explore algal succession between phytoplankton and epiphyton in shallow lakes. To better understand the mutual influence mechanism between two algal life-forms under different nutrient conditions, research on multiple short time-scales based on algal migration is needed in the future.

Drivers of variability in mercury and methylmercury bioaccumulation and biomagnification in temperate freshwater lakes.

The four largest freshwater lakes in southwestern France are of both ecological and economic importance. However, some of them are subjected to mercury (Hg) contamination, resulting in the ban of human consumption of piscivorous fish. Moreover, beyond predatory fish, little information exist regarding Hg levels in other species of these ecosystems. In this context, we used a food web analytical approach to investigate Hg bioaccumulation and biomagnification in relation to the trophic structure of these four lakes. More specifically, various organisms (macrophytes, epiphyton, invertebrates and fish) were collected at the four lakes and analysed for carbon and nitrogen stable isotopes as well as for total Hg (THg) and methylmercury (MeHg). A spatial variability of bioaccumulation in organisms was observed, particularly in carnivorous fish, with higher Hg levels being found in the two more northern lakes (median±SE: 3491 ± 474 and 1113 ± 209 ng THg.g-1 dw in lakes HC and L, respectively) than in the southern pair (600 ± 117 and 911 ± 117 ng THg.g-1 dw in lakes CS and PB, respectively). Methylmercury biomagnification was observed through the food webs of all four lakes, with different trophic magnification slopes (HC = 0.16; L = 0.33; CS = 0.27; PB = 0.27), even though the length of the food chains was similar between the lakes. Our results suggest that rather than the food web structure, anthropogenic inputs (sulfate in northern lakes and phosphorus inputs in southern ones) may have a strong impact, more or less directly, on Hg methylation in freshwater environments, and lead to concentrations exceeding environmental recommendations despite low Hg backgrounds in sediment and water.

Multifunctional Periphytic Biofilms: Polyethylene Degradation and Cd2+ and Pb2+ Bioremediation under High Methane Scenario.

Priority pollutants such as polyethylene (PE) microplastic, lead (Pb2+), and cadmium (Cd2+) have attracted the interest of environmentalists due to their ubiquitous nature and toxicity to all forms of life. In this study, periphytic biofilms (epiphyton and epixylon) were used to bioremediate heavy metals (HMs) and to biodegrade PE under high (120,000 ppm) methane (CH4) doses. Both periphytic biofilms were actively involved in methane oxidation, HMs accumulation and PE degradation. Epiphyton and epixylon both completely removed Pb2+ and Cd2+ at concentrations of 2 mg L-1 and 50 mg L-1, respectively, but only partially removed these HMs at a relatively higher concentration (100 mg L-1). Treatment containing 12% 13CH4 proved to be most effective for biodegradation of PE. A synergistic effect of HMs and PE drastically changed microbial biota and methanotrophic communities. High-throughput 16S rRNA gene sequencing revealed that Cyanobacteria was the most abundant class, followed by Gammaproteobacteria and Alphaproteobacteria in all high-methane-dose treatments. DNA stable-isotope probing was used to label 13C in a methanotrophic community. A biomarker for methane-oxidizing bacteria, pmoA gene sequence of a 13C-labeled fraction, revealed that Methylobacter was most abundant in all high-methane-dose treatments compared to near atmospheric methane (NAM) treatment, followed by Methylococcus. Methylomonas, Methylocystis, Methylosinus, and Methylocella were also found to be increased by high doses of methane compared to NAM treatment. Overall, Cd+2 had a more determinantal effect on methanotrophic activity than Pb2+. Epiphyton proved to be more effective than epixylon in HMs removal and PE biodegradation. The findings proved that both epiphyton and epixylon can be used to bioremediate HMs and biodegrade PE as an efficient ecofriendly technique under high methane concentrations.

Mesocosm experiment reveals a strong positive effect of snail presence on macrophyte growth, resulting from control of epiphyton and nuisance filamentous algae: Implications for shallow lake management.

Increased nutrient loading has adverse effects on the growth of submerged macrophytes in eutrophic shallow lakes. Where growth of phytoplankton, epiphyton and filamentous algae is excessive, all may contribute to shading that limits macrophyte growth. However, when abundant, herbivorous snails may dampen this effect by reducing the biomass of epiphyton, and perhaps also of nuisance filamentous algae, both which have the potential to become more abundant in a future warmer world. We studied the effects of herbivorous snails (Radix swinhoei) on the biomass of phytoplankton, epiphyton and filamentous algae as well as the growth of the submerged macrophyte, Vallisneria denseserrulata, under contrasting nutrient loadings (low, nitrogen (N) 113 µg L-1·d-1 and phosphorus (P) 10 µg L-1·d-1; high, N 339 µg L-1·d-1 and P 30 µg L-1·d-1) in a 30 day outdoor mesocosm experiment, conducted on the shore of subtropical Lake Taihu, China. We found significant interactive effects of nutrient loading and snail presence on biomasses of epiphyton and filamentous algae and on the biomass and relative growth rate of submerged macrophytes. When snails were absent, the biomass of epiphyton and the biomass and coverage of filamentous algae all increased markedly, while the biomass, density and relative growth rate of V. denseserrulata decreased significantly with increased nutrient loading. When snails were present, biomasses of epiphyton, phytoplankton and filamentous algae were significantly reduced and growth of V. denseserrulata significantly increased under both high and low nutrient loading scenarios, and the effect was most pronounced in the nutrient-rich treatment. The present study suggests that in shallow aquatic ecosystems, herbivorous snails reduce the negative impact of nutrient loading on submerged macrophyte growth, by controlling both epiphyton and nuisance filamentous algae. How best to protect snails from fish predation in order to realize this potential under natural conditions is a matter that warrants further studies.

A freshwater analog for the production of Epiphyton-like microfossils.

Calcified microbial microfossils-often interpreted as cyanobacteria-were important components of Precambrian and Paleozoic limestones, but their paucity in modern marine environments complicates our ability to make conclusive interpretations about their taxonomic affinity and geologic significance. Freshwater spring-associated limestones (e.g., travertine and tufa) serve as terrestrial analogs to investigate mineralization in and around aquatic biofilms on observable timescales. We document the diagenesis of calcite fabrics associated with the freshwater algae Oocardium stratum, an epiphytic colonial green algae (desmid) known for producing stalks of extracellular polymeric substances (EPS) and passively producing a bifurcating tubular calcite monocrystal. Bifurcating EPS stalks produced by Oocardium colonies can become calcified and preserved in ancient carbonate deposits. Calcified micritic EPS stalks have a filamentous morphology, show evidence of branching, and maintain uniformity in diameter thickness throughout the mm-scale colony, much like the enigmatic calcimicrobe Epiphyton. We provide a mechanism by which calcification associated with a colonial semispherical micro-organism produces microfossils that deceptively resemble filamentous forms. These findings have implications for the use of morphological traits when assigning taxonomic affinities to extinct microfossil groups and highlight the utility of calcifying freshwater modern environments to investigate microbial taphonomy.

Mercury in the Diatoms of Various Ecological Formations.

Mercury is a neurotoxin, its main source in the human organism being fish and seafood. The first level in the marine food web is formed of planktonic and benthic photosynthetic microorganisms, which form a biofilm on the surface of the hard bottom (epilithon) or plants (epiphyton). They are carriers of nutritional as well as toxic substances and pass these on to subsequent levels of the trophic web. Their biomass is often dominated by diatoms. This was the basis for the presented study into Hg accumulation in epilithic, epiphytic and planktonic diatoms, which was carried out in 2012-2013 in the coastal zone of the Puck Lagoon and the Gulf of Gdansk (southern Baltic). In this coastal area, both micro- and macroorganisms develop particularly intensively. The collected results indicate an increase in Hg concentration in the biofilm during the warm season which, with the lengthening of the vegetative period due to global warming in recent years, is of great significance. As a consequence, the annual mercury load entering the trophic web is larger in comparison with a year in which there is a long, cold winter. An important parameter influencing the accumulation of Hg was the function of those organisms from the biofilm-forming communities. In this case, the highest concentrations of Hg were measured in organisms forming high-profile guilds.

Influence of littoral periphyton on whole-lake metabolism relates to littoral vegetation in humic lakes.

The role of littoral habitats in lake metabolism has been underrated, especially in humic lakes, based on an assumption of low benthic primary production (PP) due to low light penetration into water. This assumption has been challenged by recent recognition of littoral epiphyton dominance of whole-lake PP in a small highly humic lake and of epiphyton as an important basal food source for humic lake biota. However, as these studies have mostly concerned single lakes, there is a need to test their wider generality. We studied the whole-lake PP and community respiration (CR) in eight small humic lakes in southern Finland during July 2015 using 14 C incorporation to measure pelagic PP and the changes in dissolved inorganic carbon in light and dark in situ incubations to measure CR and littoral PP by epiphyton. Changes in O2 concentration in both pelagic and littoral surface water were measured periodically from each lake and, additionally, continuously with a data logger from one lake during the study period. The results revealed that the littoral dominated whole-lake net primary production (NPP) in five of the eight lakes, which was supported by observed O2 supersaturation in the littoral surface water in most of the lakes. Calculated pelagic:littoral ratios by area correlated negatively with both littoral NPP and littoral contribution to whole-lake NPP. Moreover, there was a significant positive relationship between littoral proportion of whole-lake NPP and the fraction of lake surface area covered by littoral aquatic vegetation. This demonstrates that increased aquatic littoral vegetation cover increases the overall importance of the littoral to whole-lake PP in highly humic lakes. Littoral NPP also correlated strongly with littoral O2 saturation, and the continuously measured O2 revealed substantial temporal variation in O2 saturation, particularly in the littoral zone. Whole-lake gross primary production:community respiration (GPP:CR) ratios revealed that accounting for littoral metabolism produced a marked shift towards lake metabolic balance, although all the eight lakes remained net heterotrophic. This study emphasizes that littoral metabolism needs to be accounted for when estimating whole-lake C fluxes in all lakes, even in highly colored humic waters.

Contribution of benthic microalgae to the temporal variation in phytoplankton assemblages in a macrotidal system.

Suspended marine benthic microalgae in the water column reflect the close relationship between the benthic and pelagic components of coastal ecosystems. In this study, a 12-year phytoplankton time-series was used to investigate the contribution of benthic microalgae to the pelagic system at a site along the French-Atlantic coast. Furthermore, all taxa identified were allocated into different growth forms in order to study their seasonal patterns. The highest contribution of benthic microalgae was observed during the winter period, reaching up to 60% of the carbon biomass in the water column. The haptobenthic growth form showed the highest contribution in terms of biomass, dominant in the fall-winter period when the turbidity and the river flow were high. The epipelic growth form did not follow any seasonal pattern. The epiphytic diatom Licmophora was most commonly found during summer. As benthic microalgae were found in the water column throughout the year, the temporal variation detected in the structure of pelagic assemblages in a macrotidal ecosystem was partly derived from the differentiated contribution of several benthic growth forms.

Species complexes within epiphytic diatoms and their relevance for the bioindication of trophic status.

The popularity of aquatic bioassessments has increased in Europe and worldwide, with a considerable number of methods being based on benthic diatoms. Recent evidence from molecular data and mating experiments has shown that some traditional diatom morphospecies represent species complexes, containing several to many cryptic species. This case study is based on epiphytic diatom and environmental data from shallow fishponds, investigating whether the recognition and use of fine taxonomic resolution (cryptic species) can improve assessment of community response to environmental drivers and increase sharpness of classification, compared to coarse taxonomic resolution (genus level and species level with unresolved species complexes). Secondly, trophy bioindication based on a species matrix divided into two compartments (species complexes and remaining species) was evaluated against the expectation that species complexes would be poor trophy indicators, due to their expected wide ecological amplitude. Finally, the response of species complexes and their members (cryptic species) to a trophic gradient (phosphorus) were compared. Multivariate analyses showed similar efficiency of all three taxonomic resolutions in depicting community patterns and their environmental correlates, suggesting that even genus level resolution is sufficient for routine bioassessment of shallow fishponds with a wide trophic range. However, after controlling for coarse taxonomic matrices, fine taxonomic resolution (with resolved cryptic species) still showed sufficient variance related to the environmental variable (habitat groups), and increased the sharpness of classification, number of indicator species for habitat categories, and gave better separation of habitat categories in the ordination space. Regression analysis of trophic bioindication and phosphorus concentration showed a weak relationship for species complexes but a close relationship for the remaining taxa. GLM models also showed that no species complex responded to phosphorus concentration. It follows that the studied species complexes have wide tolerances to, and no apparent optima for, phosphorus concentrations. In contrast, various responses (linear, unimodal, or no response) of cryptic species within species complexes were found to total phosphorus concentration. In some cases, fine taxonomic resolution to species level including cryptic species has the potential to improve data interpretation and extrapolation, supporting recent views of species surrogacy.

Algae mediate submerged macrophyte response to nutrient and dissolved inorganic carbon loading: a mesocosm study on different species.

Nutrient and dissolved inorganic carbon are two important factors that influence the development and species composition of submerged macrophyte communities in shallow lake ecosystems. Yet little is known about their potential interactive effects on the submerged macrophytes and competition outcome of macrophyte-phytoplankton. We performed a mesocosm experiment to investigate the growth and photosynthetic performance of three submerged macrophytes in relation to phytoplankton/epiphyton with nutrient and bicarbonate enrichment. During the experimental period (42 d), increase in nutrient loading in water column resulted in a substantial burst of phytoplankton and epiphyton growth and increased light attenuation. When combined with nutrient loading, bicarbonate enrichment also resulted in a heavily phytoplankton- and epiphyton-dominated state, although bicarbonate enrichment per se does not cause the phytoplankton and epiphyton growth. However, increase in nutrient loading in water column had significant negative impact on individual performances (growth and photosynthesis) of the three submerged macrophytes and bicarbonate enrichment increased the effect of eutrophication on two dissected-leaf macrophytes (M. spicatum and E. nuttallii). Furthermore, our results also suggest that species-specific photosynthetic performances occurred when submerged macrophytes in an environment with high abundance of phytoplankton/epiphyton. This study highlighted that increase in nutrient loading and bicarbonate in water column is likely to interactively impact both abiotic and biotic properties of a freshwater ecosystem. The interactions of these two factors could select macrophyte species that are able to resist the shading from phytoplankton/epiphyton, making these species more dominant in natural freshwater ecosystems.

Distribution of periphytic algae in wetlands (Palm swamps, Cerrado), Brazil / Distribuicao de algas perifiticas em areas umidas (Veredas, Cerrado), Brasil

The distribution of periphytic algae communities depends on various factors such as type of substrate, level of disturbance, nutrient availability and light. According to the prediction that impacts of anthropogenic activity provide changes in environmental characteristics, making impacted Palm swamps related to environmental changes such as deforestation and higher loads of nutrients via allochthonous, the hypothesis tested was: impacted Palm swamps have higher richness, density, biomass and biovolume of epiphytic algae. We evaluated the distribution and structure of epiphytic algae communities in 23 Palm swamps of Goiás State under different environmental impacts. The community structure attributes here analyzed were composition, richness, density, biomass and biovolume. This study revealed the importance of the environment on the distribution and structuration of algal communities, relating the higher values of richness, biomass and biovolume with impacted environments. Acidic waters and high concentration of silica were important factors in this study. Altogether 200 taxa were identified, and the zygnemaphycea was the group most representative in richness and biovolume, whereas the diatoms, in density of studied epiphyton. Impacted Palm swamps in agricultural area presented two indicator species, Gomphonema lagenula Kützing and Oedogonium sp, both related to mesotrophic to eutrophic conditions for total nitrogen concentrations of these environments.

A distribuição de comunidades de algas perifíticas depende de vários fatores, como tipo de substrato, nível de distúrbio, disponibilidade de nutrientes e luz. De acordo com a predição de que impactos de ação antrópica proporcionam alterações nas características ambientais – tornando Veredas impactadas relacionadas a alterações ambientais, como desmatamentos e maiores cargas de nutrientes via alóctone –, a hipótese testada foi: Veredas impactadas apresentam maiores riqueza, densidade, biomassa e biovolume de algas epifíticas. Avaliaram-se a distribuição e a estruturação de comunidades de algas epifíticas em 23 Veredas do Estado de Goiás sob diferentes impactos ambientais. Os atributos da estrutura de comunidade avaliados foram composição, riqueza, densidade, biomassa e biovolume. Este estudo revelou a importância das características ambientais na distribuição e na estruturação das comunidades de algas, relacionando os maiores valores de riqueza, biomassa e biovolume dos organismos aos ambientes impactados. Águas ácidas e altas concentrações de sílica foram fatores importantes no estudo. Ao todo, foram identificados 200 táxons, sendo as zignemafíceas o grupo mais representativo em riqueza e biovolume, enquanto as diatomáceas, as mais representativas em densidade do epifíton estudado. Veredas impactadas em área de agropecuária apresentaram duas espécies indicadoras, Gomphonema lagenula e Oedogonium sp., ambas relacionadas com condições mesotróficas a eutróficas, para concentrações de nitrogênio total desses ambientes.

MICROFISSURATA GEN. NOV. (BACILLARIOPHYTA), A NEW DIATOM GENUS FROM DYSTROPHIC AND INTERMITTENTLY WET TERRESTRIAL HABITATS(1).

A new freshwater benthic diatom genus, Microfissurata gen. nov., was identified from light and scanning electron micrographs. The most characteristic morphological feature (referred to also by the name of the new genus) is the structure of the striae/alveoli, which are simple, mostly uninterrupted, transapical slits. The combination of characteristics of the new genus is unique. It includes two new species: Microfissurata paludosa Cantonati et Lange-Bert. sp. nov. and M. australis Van de Vijver et Lange-Bert. sp. nov., distributed in Europe and on an austral island, respectively. The new genus occurs in freshwater dystrophic lakes, pools, seepage springs, mires, and in intermittently wet terrestrial habitats. It is not abundant but widespread wherever these habitat types are well developed, in Nordic-alpine and sub-Antarctic areas. Overall, the new genus appears to be mostly epiphytic (bryophilous) and capable of tolerating a wide range of moisture conditions (xerotolerant). The finding of the type species (M. paludosa) in a well-investigated area like central Europe highlights the diatom species richness of dystrophic habitats and their importance for diatom biodiversity conservation.