Surface Microlayer Water Research Articles

Environmental concentrations of anionic surfactants in lake surface microlayers enhance the toxicity of Microcystis blooms: Insight from photosynthesis, interspecies competition, and MC production

Anionic surfactants represented by linear alkylbenzene sulfonate (LAS) exhibit vertical heterogeneity of concentrations in aquatic environments owing to their amphiphilic structure. Field investigations showed that the concentration of anionic surfactants (mainly LAS) in the water surface microlayer (SML) of Lake Taihu reached 580 μg/L, higher than that in the lower layer. Floating Microcystis blooms overlap in space with the high concentration of anionic surfactants in SML. However, few studies have focused on the effects of anionic surfactants (e.g., LAS) on the interspecies competition between toxic and nontoxic Microcystis. In this study, coculture and monoculture experiments were conducted with both toxic and nontoxic Microcystis species to explore how the environmental concentration of LAS regulates the dominance of toxic Microcystis and toxicity from the perspective of photosynthesis, species dominance, and MC production. The results showed that LAS concentrations above 0.267 or 0.431 mg/L (depending on light conditions) selectively promoted the photosynthetic competitive advantage of toxic Microcystis, leading to its higher population proportion in the community. Additionally, LAS concentrations above 0.5 mg/L induced the synthesis and release of microcystins (MCs). The results of chlorophyll fluorescence analysis, electron microscopy and transcriptome sequencing suggested that compared with nontoxic Microcystis, toxic Microcystis can better resist LAS stress by dissipating excess light, maintaining an intact membrane structure and maintaining cellular homeostasis. Transcriptome sequencing revealed that the photosynthetic damage of nontoxic Microcystis might be attributed to the impacts of LAS on the absorption and assimilation of nitrogen, which finally resulted in the degradation of phycobilisomes. This study can provide novel insight for establishing standards and safety management of wastewater discharge.

Higher Apparent Gas Transfer Velocities for CO2 Compared to CH4 in Small Lakes.

Large greenhouse gas emissions occur via the release of carbon dioxide (CO2) and methane (CH4) from the surface layer of lakes. Such emissions are modeled from the air-water gas concentration gradient and the gas transfer velocity (k). The links between k and the physical properties of the gas and water have led to the development of methods to convert k between gases through Schmidt number normalization. However, recent observations have found that such normalization of apparent k estimates from field measurements can yield different results for CH4 and CO2. We estimated k for CO2 and CH4 from measurements of concentration gradients and fluxes in four contrasting lakes and found consistently higher (on an average 1.7 times) normalized apparent k values for CO2 than CH4. From these results, we infer that several gas-specific factors, including chemical and biological processes within the water surface microlayer, can influence apparent k estimates. We highlight the importance of accurately measuring relevant air-water gas concentration gradients and considering gas-specific processes when estimating k.

Microbial communities in the water surface microlayer and associations with microbes in aerosols, beach sand, and bulk water.

The water surface microlayer (SML) serves as a boundary through which microbes can be exchanged. To evaluate exchanges of microbes, this study compared microbial communities within different reservoirs, with an emphasis on the water SML and aerosols. Additionally, the microbial communities during a sewage spill and perigean tides were evaluated and the results were compared to times without these events. Results show that during perigean tides and during the sewage spill, levels of culturable bacteria were highest and showed an increase via sequencing in potential pathogenic bacteria (Corynebacterium and Vibrio, which increased from 3.5%-1800% depending on sample type). In the aerosol samples, Corynebacterium (average of 2.0%), Vibrio (1.6%), and Staphylococcus (10%), were the most abundant genera. Aerosolization factors, which were used to examine the transfer of the microbes, were high for these three genera. Measurements of general marine bacteria (GMB) by culture showed a weak but significant correlation between culturable GMB in aerosol samples versus in water and in the SML. More research is needed to evaluate the exchange of pathogens between the SML and air, given the increase in potentially pathogenic microbes within the SML during rare events and evidence that suggests that microbes maintain viability during transfers across reservoirs.

A Persistent Submesoscale Frontal Slick: A Novel Marker of the Mesoscale Flow Field in a Large Lake (Lake Geneva)

AbstractSubmesoscale fronts often become visible when the accumulation of biosurfactants in the water surface microlayer causes smooth surfaces, called frontal slicks, to develop. Based on in situ and remotely‐sensed data, a frontal slick was documented for the first time in a lake (Lake Geneva). A quasi‐stationary ∼10‐km long slick formed on the warm side of a surface temperature front with strong horizontal velocity strain. The slick width increased from ∼50 to ∼200 m in ∼1.5 hr due to “feeding” by wind‐driven, rapidly‐moving smaller slicks. Numerical modeling results, confirmed by satellite data, indicated that the boundary between mesoscale gyres isolated warm surface water from cold water associated with wind‐induced coastal upwelling. Measurements and modeling suggest that frontogenetic sharpening of the submesoscale temperature gradient created an active front with strong convergent flow. Such dynamics must be considered in buoyant material transport and the vertical exchange of surface water with deeper layers in lakes.

Enrichment of poly- and perfluoroalkyl substances (PFAS) in the surface microlayer and foam in synthetic and natural waters

Bench-scale experiments were performed to interrogate poly- and perfluoroalkyl substance (PFAS) enrichment in the water surface microlayer (SML). In initial experiments using electrolyte-only solutions, the perfluorooctane sulfonate (PFOS) and perfluorooctane carboxylate (PFOA) enrichment in the SML were reasonably (with a factor of 2) described by the Gibbs adsorption equation coupled with a Freundlich-based interfacial adsorption model. Enrichment in the SML among perfluorinated sulfonates and perfluorinated carboxylates of varying chain lengths was proportional to their surface activity. The PFOS enrichment factor (EF), defined as the PFAS concentration in the SML divided by the concentration in the bulk water, was 18 in a 200 mg/l NaCl solution. The presence of elevated organic carbon levels in synthetic surface waters inhibited PFAS accumulation in the SML, with resulting EF values of approximately 1 for all PFAS. However, in the presence of elevated organic levels coupled with foam, PFAS enrichment in the foam was observed, with a foam EF of 25 measured for PFOS in synthetic surface waters. PFAS EF values measured in several natural surface waters without foam showed little variation among the waters tested, with PFOS EF values ranging between 6 and 10. Together, these results suggest that PFAS accumulation in the SML is largely controlled by PFAS sorption at the air-water interface for the conditions examined in this study, and the presence of foam with natural organics enhances PFAS uptake at the water surface.

Wildfires as a Source of PAHs in Surface Waters of Background Areas (Lake Baikal, Russia)

Polycyclic aromatic hydrocarbons (PAHs) were detected in different types of PAH-containing samples collected in Lake Baikal during wildfires in the adjacent areas. The set of studied samples included the following: (i) water from the upper layer (5 m); (ii) water from the surface microlayer; (iii) water from the lake tributaries; (iv) water from deep layers (400 m); and (v) aerosol from the near-water layer. Ten PAHs were detected in the water samples: naphthalene, 1-methylnaphthalene, 2-methylnaphthalene acenaphthylene, acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, and chrysene. The total PAH concentrations (ƩPAHs) were detected in a wide range from 9.3 to 160 ng/L, characterizing by seasonal, intersessional, and spatial variability. In September 2016, the ƩPAH concentration in the southern basin of the lake reached 610 ng/L in the upper water layer due to an increase in fluorene, phenanthrene, fluoranthene, and pyrene in the composition of the PAHs. In June 2019, ƩPAHs in the water from the northern basin of the lake reached 290 ng/L, with the naphthalene and phenanthrene concentrations up to 170 ng/L and 92 ng/L, respectively. The calculation of back trajectories of the atmospheric transport near Lake Baikal, satellite images, and ƩPAH concentrations in the surface water microlayer of 150 to 960 ng/L confirm the impact of wildfires on Lake Baikal, with which the seasonal increase in the ƩPAH concentrations was associated in 2016 and 2019. The toxicity of PAHs detected in the water of the lake in extreme situations was characterized by the total value of the toxic equivalent for PAHs ranging from 0.17 to 0.22 ng/L, and a possible ecological risk of the impact on biota was assessed as moderate.

Characterization of photoautotrophic microbial communities in the coastal water of Lake Baikal

In this study, we determined the concentration of chlorophyll a in biofilms formed on rocky substrates, in the surface water microlayer, water column, and near-bottom water layer of the coastal zone of Lake Baikal. High throughput sequencing of 16S rRNA and rbcL gene libraries revealed high genetic and taxonomic diversity of photoautotrophic microbial communities in the studied ecotopes of the lake. The UPGMA analysis indicated that the composition of photoautotrophic communities largely depends on both the geographical location and ecotope. Using electron microscopy, we described the structure and composition of biofilms.

Occurrence and Environmental Distribution of 5 UV Filters During the Summer Season in Different Water Bodies

Organic UV filters are used worldwide in various personal care products as well as textiles, paints, plastic, food, and adhesives. They are main ingredients in sunscreen lotions that are used heavily by beachgoers in the summer season. There is thus an increasing concern regarding the fate of organic UV filters in the environment and their impact on living organisms. Many of the UV filters in use are hydrophobic and are expected to accumulate in the sediment phase in aquatic systems, but this has yet to be validated in situ. We targeted the UV filters benzophenone 3 (BP3), butyl methoxydibenzoylmethane (BMDBM), diethylhexyl butamido triazone (DBT), bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT), and methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT) in a freshwater lake and in a coastal bay in order to understand their distribution during summer 2016. Further, we examined their environmental partitioning by collecting samples from the surface water, the sediment phase, and water surface microlayer (SML). We show for the first time the presence of DBT, BEMT, and MBBT in environmental matrices (water, SML, and sediment). Notably, these UV filters were detected at low amounts in surface waters with maximum concentrations of 9.9 ng/L for DBT, 18.4 ng/L for BEMT, and below detection limits for MBBT and somewhat higher concentrations in the SML, with maximum concentrations of 43.3 ng/L for DBT, 5625.4 ng/L for BEMT, and 45.6 ng/L for MBBT. These filters were detected at even greater concentrations in the sediments, with maximum concentrations of 652.6 ng/g for DBT, 115.0 ng/g for BEMT, and 75.2 ng/g for MBBT (dry weight sediment). We also performed controlled laboratory experiments to determine their partitioning behavior, and we verified the actual solubility of many of the filters. This will help in determining the environmental fate and finally lead to a better risk assessment of these compounds. Together, these results corroborate the hypothesis that hydrophobic UV filters accumulate in the sediment phase and highlight the importance of discerning whether these UV filters impact the benthic community and their potential for bioaccumulation.

Air-Water Interface in an Estuarine Lake: Chlorophyll and Nutrient Enrichment

The surface water microlayer (SML) is a thin layer found at the interface of the hydrosphere and the atmosphere. It is capable of accumulating chemical substances and microorganisms at a rate as high as 100-fold greater than that observed in the subsurface water. The rate of accumulation of biogens and chlorophyll a in SML of an estuary, where marine and fresh waters mix, varies considerably and it depends on the degree mixing of these waters, which is manifested in the varying values of the enrichment factor (EF, calculated as the ratio of nutrients concentration in SML versus subsurface water). The influence of the Baltic Sea marine water and the freshwater Łeba River inflows on the estuarine Lake Łebsko (Poland) was examined. Nine sampling sites were located in the estuary. Water samples were collected from two layers: the surface microlayer (thickness 242 µm ± 40) and the subsurface water (15 cm depth). The capacity of the SML to enrich the water in nutrients and chlorophyll differed among various parts of the estuary, as well as between seawater and river waters. Statistically significant higher EF were found in the marine waters than in river waters for the nitrogen and phosphorus compounds as well as chlorophyll. There were also differences in EF between marine and lake waters. The highest EF were also recorded for organic forms of nitrogen and phosphorus in marine water. Most probably, marine flux into the estuarine Lake Łebsko, resulted in the increased EF for these investigated components.

Microbiological studies of Lake Baikal in a Limnological institute: past and present

The article deals with the history of studies of microbial communities in Lake Baikal performed by the researchers of Limnological Institute SB RAS. We provide the information about the studies of freshwater organisms in the world and the formation of aquatic microbiology in Russia. Initial data on bacteria from the lake were obtained in the 1920s of the past century. The studies were carried out at Baikal Biological Station and Baikal Limnological Station of the USSR Academy of Sciences. The frst studies and large discoveries at Lake Baikal were made by microbiologists who came at different times from research institutes of Moscow and Leningrad. When Baikal Limnological Station was reorganized into Limnological Institute of the USSR Academy of Sciences, the studies of microorganisms in Lake Baikal became systematic and complex, and they were mostly performed by the researchers from the Laboratory of Aquatic Microbiology. The long-term regular observations have provided signifcant results on the species composition, abundance, seasonal and interannual dynamics, horizontal and spatial distribution of bacteria in the water column and bottom sediments of Lake Baikal, as well as their functional role. In the past decades, the introduction of molecular-biological, electronic-microscopic and analytical methods allowed determination of the genetic, taxonomic and morphological diversity of bacteria and viruses. Since 2009, main research area of Laboratory of Aquatic Microbiology is the study of bioflm microbiocenoses, including the determination of the taxonomic composition, structural organization, formation features, as well as biotechnological potential of bacterial and viral communities of the surface microlayer of water and bioflms formed on biogenic and abiogenic substrates. The 90-year period of microbiological research of a unique ecosystem of Lake Baikal appeared to besuccessful and rich in discoveries.

Natural formation and transformation of silver nanoparticles in the aquatic environment

Silver nanoparticles (AgNPs) are well known for their excellent antibacterial ability and superior physiochemical properties, and are widely used in a growing number of applications, including home disinfectants, medical devices and water purificants. During the production, use and disposal of AgNP-containing products, AgNPs may be released into the environment. AgNPs are highly dynamic in aqueous systems. They could undergo different chemical and morphology transformation, which greatly affects their final fate, transport, distribution and potential bioeffects. The study on the fate and transformation of AgNPs in natural systems is the basis and prerequisite for the accurate assessment of environmental and biological safety of AgNPs. Herein, we reviewed the recent progress of the natural formation and transformation of AgNPs in the aquatic environment, including the chemical and biosynthesis of AgNPs, the aggregation, enrichment in water surface microlayer, oxidation and dissolution, sulfidation and chlorination of AgNPs in the aquatic environment. The prospects and possible directions in the field are also discussed.

The mechanism of self-organization in a surface water microlayer utilizing thermocapillary convection

The formation of helical macrostructures in a surface-water layer has been experimentally studied. The thermocapillary Marangoni convection bringing about self-organizing helical and dissipative structures in a thin subsurface layer of cooling water with a free surface was demonstrated in an experiment for the first time. The most likely candidates that allow the motion in the corresponding basic experiments were found. These candidates are thermocapillary cells that result from Marangoni convection. The described mathematical tools for modeling the dynamics of thermocapillary Marangoni diffusion are the nonlinear equations of heat diffusion and the equations of self-organization (nonlinear differential equations of a parabolic type). The results of a computational experiment confirmed the mechanisms of self-organization in a surface-water layer.

Significant Enrichment of Engineered Nanoparticles in Water Surface Microlayer

Water surface microlayer (SML), as the interface between water and the atmosphere, shows distinct physicochemical properties that differ from those of underlying water. Herein, for the first time, we demonstrate the SML enrichment of nanoparticles (NPs) by using silver nanoparticles (AgNPs) as a model via indoor experiments. The occurrence of SML enrichment of AgNPs was confirmed by the increased concentration of NPs in the SML relative to that in the bulk phase, and the in situ recording of the enhanced Raman spectroscopy intensity of a probe adsorbed on AgNPs in the SML. The significant enrichment of NPs is strongly influenced by environmentally relevant factors such as the solution pH, ionic strength, and natural organic matter. Additionally, the SML enrichment factor was estimated to be 14.6–26.5 for AgNPs in natural waters. Our findings indicate that NPs are inclined to accumulate in the SML, which could cause environmental effects that are differential to the bulk phase.

Macroelements in the surface microlayer of water of urban ponds

Abstract Analyses were conducted concerning the accumulation of four metals representing the group of macroelements, i.e. sodium, potassium, calcium and magnesium in two ponds located in the city of Słupsk. Water samples for chemical analyses were collected from the surface microlayer using a Garrett net. At the same time subsurface water samples were collected. Concentrations of metals were determined using a mass spectrometer. Generally, amounts of sodium, potassium, calcium and magnesium were similar in surface microlayer and subsurface water. Only in the case of potassium and calcium was low enrichment observed in the surface microlayer in one pond, while the greatest extent for magnesium enrichment was observed in the spring period.

Total dissolved inorganic carbon and physicochemical characteristics of surface microlayer and upper mixed layer water from Lagos Lagoon, Nigeria

<p>The carbonate and physicochemical characteristics of the surface microlayer and upper mixed layer of a tropical coastal lagoon were investigated. Data on the physicochemical parameters generally indicated a moderately polluted ecosystem. The influence of the ocean environment over the Lagoon system was evident by elevated salinity levels. The mean total dissolved inorganic carbon (DIC) for the surface microlayer (SML) and subsurface water (SSW) samples were 2626.6 and 2550.9 µmol/kg SW respectively. The dominant inorganic form of DIC in the lagoon water samples was HCO<sub>3</sub><sup>-</sup> with a calculated average abundance >95.4% in the SML and >94% in the SSW. The bicarbonate species derived abundance varied between 1.6% (SML) and 8.4% (SSW), while the aqueous carbon dioxide were generally low in percentages ranging from 0.4 in SSW to 1.5 in SML water samples. In general, the occurrence of the carbonate species was in the order HCO<sub>3</sub><sup>-</sup> > CO<sub>3</sub><sup>2-</sup> > CO<sub>2</sub>. Results showed that total alkalinity (A<sub>T</sub>) was relatively greater than the DIC. Long term monitoring studies in the coastal lagoon systems is needed to understand the coastal water chemistry and pollution status.</p>

Seasonal Fluctuations In Co, Ni, Cu, Zn, Cd, Pb Concentrations In Surface Microlayers And Subsurface Water Of Two City Ponds

We owe the knowledge concerning the surface water microlayer to the wide research into marine environment and relatively scarce research done into inland city ponds ecosystems. The surface microlayer is a very thin, several hundred micrometers thick layer at the contact of water and atmosphere. This important form of air-water exchange ecotone, which constitutes the surface microlayer of water, is a specific environment as to its chemical and physical characteristics and is different from subsurface waters. It can absorb chemical substances like heavy metals, phytoneuston and bacteria in larger quantities in comparison to lower parts of the water. This characteristic feature results, among others, from the processes of transport at the contact of hydrosphere-atmosphere and also transport within the very area of surface water microlayer. The paper describes transport processes of six heavy metals: Co, Ni, Cu, Zn, Cd, Pb from subsurface water to surface water microlayer and vice versa, analyzed in a one year cycle. The transport of chemical substances under consideration was described on a basis of experiments made during the period of one year at five city pounds in Slupsk (Polish Pomerania). During the research, samples of the surface water microlayer were collected by means of application of the Garrett mesh technique. At the same time, samples of subsurface water were collected and tested as to the content of the same parameters as the surface microlayer. Samples were sampled in month intervals. The concentration of aforementioned heavy metals was measured by mass spectrometry method and used Perkin Elmer Elan DRC aparature.

Nonylphenol and 4-tert-octylphenol in the Gulf of Gdansk coastal zone

Abstract The concentrations of nonylphenol and 4-tert-octylphenol were measured in surface waters in the Gulf of Gdansk coastal zone (summer 2010). The mean concentration in the samples of subsurface water were 34.49 ng dm−3 (nonylphenol) and 3.04 ng dm−3 (4-tert-octylphenol). The highest nonylphenol concentrations were detected in the samples of subsurface water collected from the Sea Boulevard (Gdynia) while the highest concentrations of 4-tert-octylphenol were found in the yacht harbor Marina Gdynia, and in the Kacza and Gizdebka rivers. A significant enrichment (13–45 times) of 4-tert-octylphenol was observed in the surface microlayer of water. These levels exceeded the predicted no effect concentration by 2–9 times.

Modeling the environmental fate of perfluorooctanoic acid and perfluorooctanoate: An investigation of the role of individual species partitioning

A multimedia multi-species environmental fate model was developed for the conjugate pair perfluorooctanoic acid (PFOA):perfluorooctanoate (PFO). The model allows assessment of the relative contribution of each individual species, in equilibrium with each other, to the overall environmental movement of the pair. The Lake Ontario (Canada/USA) watershed system was selected for this investigation and is simulated in a single-region, seven-compartment model, including a water surface microlayer, and aqueous aerosol generation and redeposition. Results indicate that in the equilibrated presence of both PFOA and PFO, the environmental fate of the pair can be accomplished by consideration of the physical properties of the neutral acid, which govern the intermedia distribution of the pair, coupled with processes of media advection, such as air or water flow. The role of the anion, while the most populous species in the aqueous phase, appears merely to be as a source of the neutral acid for subsequent partitioning. Thus, when only the bulk aqueous phase anion concentrations are of interest a multimedia fate model is not required because these concentrations are largely predictable from the magnitude of emissions to and the advection of the phase. With neutral species partitioning, all local field measurement concentrations of the conjugate pair, PFO(A), are explained by the model to within approximately an order of magnitude, with the exception of lake sediment solids. Model results indicate that bulk aqueous phase PFO acts as a net source for PFOA to the atmosphere, where it may be subject to long-range transport (LRT). Initial calculations suggest an atmospheric LRT potential for PFO(A) of thousands of kilometers, rendering it comparable to hexachlorobenzene.

Characterization of Streptomyces spp. Isolated from the Sea Surface Microlayer in the Trondheim Fjord, Norway

The water surface microlayer is still poorly explored, although it has been shown to contain a high density of metabolically active bacteria, often called bacterioneuston. Actinomycetes from the surface microlayer in the Trondheim fjord, Norway, have been isolated and characterized. A total of 217 isolates from two separate samples morphologically resembling the genus Streptomyces have been further investigated in this study. Antimicrobial assays showed that about 80% of the isolates exhibited antagonistic activity against non-filamentous fungus, Gram-negative, and Gram-positive bacteria. Based on the macroscopic analyses and inhibition patterns from the antimicrobial assays, the sub-grouping of isolates was performed. Partial 16S rDNAs from the candidates from each subgroup were sequenced and phylogenetic analysis performed. 7 isolates with identical 16S rDNA sequences were further studied for the presence of PKS type I genes. Sequencing and phylogenetic analysis of the PKS gene fragments revealed that horizontal gene transfer between closely related species might have taken place. Identification of unique PKS genes in these isolates implies that de-replication can not be performed based solely on the 16S rDNA sequences. The results obtained in this study suggest that streptomycetes from the neuston population may be an interesting source for discovery of new antimicrobial agents.

Photodegradation of Pentachlorophenol by Sunlight in Aquatic Surface Microlayers

Photodegradation of pentachlorophenol (PCP) in aquatic surface microlayer (SM) was examined under natural sunlight. SM samples were collected using a glass plate, along with corresponding subsurface waters. PCP was added to samples of the SM and subsurface water. When all samples were exposed to the same natural sunlight conditions, the first order photodegradation rates of PCP in the SM water samples were different from those of PCP in corresponding subsurface water samples. The difference was correlated with the enrichment of dissolved organic carbon (DOC) in SM compared to the corresponding subsurface waters. Enhanced photodegradation in SM may be due to increased abundance of photoreactants related to the UV-absorbing properties of dissolved organic materials in the SM as the result of photo-induced reactions. Effects of environmental factors, pH and salinity, on photodegradation process of PCP in SM were also evaluated.