Aquatic Surface Microlayer Research Articles

The changes in iron ions concentration and organic matter composition during the surface microlayer membrane formation process in freshwater

The surface microlayer membrane (SMM) is a complex and unique water body ecosystem. The SMM has a significant effect on water quality and the water ecological system. However, despite the long-lasting interest in the SMM formation process and its environmental effect mechanism in freshwater, studies on it are still scarce. This paper studied the changes in iron ions concentration and organic matter composition during the SMM formation process. Our results revealed that the iron ions enriched in the SMM, at a concentration of up to 8.02 μg/mL, exist in the form of Fe3+. The main organic matter is polysaccharides and proteins in the SMM. Additionally, the microbial community structure revealed that the changes in iron ion morphology in water and the SMM was a significant association with the presence of Aeromonas and Zoogloea. The rapid enrichment process of iron ions and organic matter in the aquatic surface microlayer is involved in the rapid formation of early SMM. Obviously, these findings provide new insights and a basis for the SMM of freshwater.

Bacterioneuston Abundance and Physicochemical Properties of the Surface Microlayer of Lake Baikal

Abstract—The aquatic surface microlayer at the interface between the atmosphere and the hydrosphere occupies 70% of the Earth’s surface, covering all water bodies. The surface microlayer is about 50 μm thick. The special microbial community formed here is referred to as neuston. The total bacterial abundance in the surface microlayer (SML) and underlying waters (UW) of Lake Baikal was studied by epifluorescence microscopy. The physicochemical features of the surface microlayer of Lake Baikal have been established for the first time. SML was sampled throughout all of Lake Baikal in May–June of 2013–2016 and in August of 2013, 2015, and 2016. SML samples were taken from a boat with Garret’s metal mesh screen (26.5 cm in diameter) mostly in calm weather. The average values of total bacterial abundance in SML varied from year to year within the range of (0.93–1.49) × 106 cells/mL in May–June and (1.73–2.24) × 106 cells/mL in August; in the UW (at a depth of about 15–20 cm), these values were 0.79–0.89 × 106 cells/mL in May–June and 1.15–1.4 × 106 cells/mL in August. There was a significant difference and direct relationship between the total abundances of neuston and plankton bacteria of Lake Baikal in the summer period. The differences in chemical composition between the surface microlayer and the subsurface water layer were revealed in all the seasons under study. The surface microlayer was enriched in $${\text{PO}}_{4}^{{3 - }}$$, total organic carbon, and suspended particulate matter compared to the underlying water layers. There was a direct relationship between bacterial numbers in the surface microlayer and the concentration of suspended particulate matter.

Bacterioneuston in Lake Baikal: Abundance, Spatial and Temporal Distribution.

An aquatic surface microlayer covers more than 70% of the world’s surface. Our knowledge about the biology of the surface microlayer of Lake Baikal, the most ancient lake on Earth with a surface area of 31,500 km2, is still scarce. The total bacterial abundance, the number of cultured heterotrophic temporal bacteria, and the spatial distribution of bacteria in the surface microlayer and underlying waters of Lake Baikal were studied. For the first time, the chemical composition of the surface microlayer of Lake Baikal was determined. There were significant differences and a direct relationship between the total bacterial abundance in the surface microlayer and underlying waters of Lake Baikal, as well as between the number of cultured heterotrophic bacteria in studied water layers in the period of summer stratification. In the surface microlayer, the share of cultured heterotrophic bacteria was higher than in the underlying waters. The surface microlayer was characterized by enrichment with PO43−, total organic carbon and suspended particulate matter compared to underlying waters. A direct relationship was found between the number of bacteria in the surface microlayer and environmental factors, including temperature, total organic carbon and suspended particulate matter concentration.

Численность бактерионейстона и физико-химические особенности поверхностного микрослоя озера Байкал

The aquatic surface microlayer is located at the atmosphere–hydrosphere boundary and occupies 70% of Earth's surface, covering all water bodies. The depth of the surface microlayer is about 50 μm. A special microbial community called neuston is formed there. The total bacterial abundance in the surface microlayer (SML) and underlying waters (UW) of LakeBaikalwas studied using epifluorescence microscopy. Physicochemical features of the surface microlayer of LakeBaikalwere revealed for the first time. The SML was sampled throughout LakeBaikalin May–June of 2013 to 2016 and in August of 2013, 2015 and 2016. SML samples were taken from a boat, mainly during calm weather, using Garrett’s metal mesh screen (a diameter of 26.5 cm). The average values of total bacterial abundance in the SML varied through years within a range of (0.93–1.49)×10 6 cells/mL in May–June and (1.73–2.24)×10 6 cells/mL in August; in the UW, at a depth about 15–20 cm, there were (0.79 – 0.89)×10 6 cells/mL in May– June and (1.15–1.4)×10 6 cells/mL in August. Significant differences and a direct relationship between the total bacterial abundance in the surface microlayer and underlying waters ofLakeBaikal in the summer period have been shown. Differences between the chemical composition of the surface microlayer and the subsurface water layer in all studied seasons were revealed. The surface microlayer was enriched with PO43-, total organic carbon and suspended particulate matter as compared with the underlying waters. A direct relationship was found between the numbers of bacteria in the surface microlayer and the suspended particulate matter concentration.

Macrophyte disturbance alters aquatic surface microlayer structure, metabolism, and fate

Macrophytes drive the functioning of many salt marsh ecosystem components. We questioned how temporary clearing of the macrophyte community, during restoration, would impact processes at the scale of the aquatic surface microlayer. Development, deposition, and breakup of the tidal creek surface microlayer were followed over tidal cycles seasonally in a cleared "former" Phragmites marsh and an adjacent restored Spartina marsh. Metabolic and physical processes of the mobile surface microlayers and underlying water were compared, along with distribution of organic and inorganic components onto simulated plant stems. In July and October, chlorophyll-a quantities were less on simulated stems in the cleared site than in the restored site. The aquatic microlayer in the cleared site creek exhibited lower photosynthesis and respiration rates, fewer diatoms and green algae, and less chlorophyll-a. There was a lower concentration (250 times) and reduced diversity of fatty acids in the surface microlayer of the cleared site, reflecting a smaller and less diverse microbial community and reduced food resources. Fiddler crab activity was an order of magnitude higher where macrophytes had been cleared. Their consumption of edaphic algae on the mud surface may account for the reduced algae and other organics in the creek surface microlayer, thus representing a redirection of this food resource from creek consumers. Overall, there were less total particulates in the creek surface microlayer at the cleared site, and they dropped out of the surface microlayer sooner in the tidal cycle, resulting in a lower sediment load available for deposit onto marsh surfaces.

Influence of the surface microlayer on atmospheric deposition of aerosols and polycyclic aromatic hydrocarbons

Atmospheric dry deposition is an important process for the introduction of aerosols and pollutants to aquatic environments. The objective of this paper is to assess, for the first time, the influence that the aquatic surface microlayer plays as a modifying factor of the magnitude of dry aerosol deposition fluxes. The occurrence of a low surface tension (ST) or a hydrophobic surface microlayer has been generated by spiking milli-Q water or pre-filtered seawater with a surfactant or octanol, respectively. The results show that fine mode (<2.7 μm) aerosol phase PAHs deposit with fluxes 2–3 fold higher when there is a low ST aquatic surface due to enhanced sequestration of colliding particles at the surface. Conversely, for PAHs bound to coarse mode aerosols (>2.7 μm), even though there is an enhanced deposition due to the surface microlayer for some sampling periods, the effect is not observed consistently. This is due to the importance of gravitational settling for large aerosols, rendering a lower influence of the aquatic surface on dry deposition fluxes. ST (mN m −1) is identified as one of the key factor driving the magnitude of PAH dry deposition fluxes (ng m −2 d −1) by its influence on PAH concentrations in deposited aerosols and deposition velocities ( v d, cm s −1). Indeed, v d values are a function of ST as obtained by least square fitting and given by Ln( v d)=−1.77 Ln(ST)+5.74 ( r 2=0.95) under low wind speed (average 4 m s −1) conditions.

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.

Role of aquatic surface microlayer in the dynamics of nutrients and organic compounds in lakes, with implications for their ecotones

Role of aquatic surface microlayer in the dynamics of nutrients and organic compounds in lakes, with implications for their ecotones

Aquatic surface microlayer contamination in chesapeake bay

The aquatic surface microlayer (SMIC), ∼50 μm thick, serves as a concentration point for metal and organic contaminants that have low water solubility or are associated with floatable particles. Also, the eggs and larvae of many fish and shellfish species float on, or come in contact with, the water surface throughout their early development. The objectives of this study were (1) to determine the present degree of aquatic surface microlayer pollution at selected sites in Chesapeake Bay, and (2) to provide a preliminary evaluation of sources contributing to any observed contamination. Twelve stations located in urban bays, major rivers, and the north central bay were sampled three times, each at ∼5-day intervals during May 1986. Samples of 1.4–4.1 each were collected from the upper 30–60-μm water surface (surface microlayer, SMIC) using a Teflon-coated rotating drum microlayer sampler. One sample of subsurface water was collected in the central bay. At all stations, concentrations of metals, alkanes, and aromatic hydrocarbons in the SMIC were high compared with one bulk-water sample and with typical concentrations in water of Chesapeake Bay and elsewhere. SMIC contamination varied greatly among the three sampling times, but high mean contaminant levels (total polycyclic aromatic hydrocarbons, 1.9–6.2 μg 1 −1; Pb, 4.9–24 μg 1 −1; Cu, 4–16 μg 1 −1; and Zn, 34–59 μg 1 −1) were found at the upper Potomac and northern bay sites. Three separate areas were identified on the basis of relative concentrations of different aromatic hydrocarbons in SMIC samples - the northern bay, the Potomac River, and the cleaner southern and eastern portions of the sampling area. Suspected sources of surface contamination include gasoline and diesel fuel combustion, coal combustion, and petroleum product releases. Concentrations of metals and hydrocarbons, at approximately half the stations sampled, are sufficient to pose a threat to the reproductive stages of some fish and shellfish. Sampling and analysis of the surface microlayer provides a sensitive tool for source identification and monitoring of potentially harmful aquatic pollution.

Toxicity and metal speciation relationships for Daphnia magna exposed to brass powder.

Studies were conducted to assess the fate and potential toxicity of brass powder deposited on water surfaces. Laboratory microcosms containing lake water were used to quantify the effects of surface dose, pH, alkalinity, microbiota, and sediment binding on the availability and subsequent toxicity of Cu and Zn from brass powder. Eight days after deposition on the water surface, high concentrations of Cu and Zn remained in the aquatic surface microlayer (upper 33 μm). The concentrations of total Cu and Zn in the subsurface bulkwater were reduced by the presence of bottom sediment but were little affected by biota. Toxicity of brass powder toDaphnia magna increased with increasing surface deposition (dose) and decreased with increasing water pH and alkalinity. Little or no toxicity occurred at brass powder surface doses of 50 and 1,000 mg/m2 for low- and high-alkalinity environments, respectively. Geochemical modeling suggested that toxicity resulted from concentrations of both Cu2+ and Zn2+ ions in solution.

A Hydrophobic Large-Volume Sampler for Collecting Aquatic Surface Microlayers: Characterization and comparison with the Glass Plate Method

The atmosphere–water interface represents a vital biological habitat and a collection point for natural and anthropogenic materials originating in the atmosphere and the water column. A Teflon-coated aluminum rotating drum sampler was constructed and tested. This sampler rapidly collects large-volume samples of the aquatic surface microlayer uppermost 34 μm). The collection characteristics of the sampler are similar to those of the more time-consuming glass plate technique. Samples from estuarine, coastal, and offshore areas are generally highly enriched in selected organic compounds, metals, and microorganisms as compared with the subsurface bulk seawater. The sampler provides an efficient means of collecting hydrophobic pollutants from the water surface.