Optical characteristics of water in stratified lakes can be used to study the pigment composition of various groups of photosynthetic organisms, its depth distribution and changes in different seasons. In the Arctic zone it is especially important to explore the evolution of natural water bodies under the influence of climate change and urbanization processes. Several water bodies on the coast of the Kandalaksha Bay of the White Sea are known as being at different stage of isolation from the Sea. In some of them the colored water layers in their chemocline zone resulted from the massive development of anoxygenic phototrophic bacteria were observed. The most numerous inhabitants of the chemocline zone are green sulfur bacteria. Besides green sulfur bacteria and purple sulfur bacteria, there were found cyanobacteria above and inside the chemocline zone. To access the pigment concentration, we measured fluorescence spectra of acetone extractions prepared from water sampled from various depths within chemocline of the lake Trekhtzvetnoe in March 2021. To increase the sensitivity of fluorescence measurements to certain pigments we acquired synchronous spectra of luminescence spectrometer performing scanning with a constant wavelength offset of 30 nm. This paper presents for the first time depth distribution of photosynthetic pigments BChl d (from green sulfur bacteria) accompanied with phycobilins (from cyanobacteria) derived from synchronous fluorescence spectra of acetone extractions prepared from water from various depths. This type of spectral measurements allowed us to receive depth distribution of cyanobacteria within the bacterial plate of green sulfur bacteria with very high depth resolution.
An important characteristic of a natural reservoir is the depth distribution of the pigment composition of various groups of photosynthetic organisms and its changes in different seasons, both qualitative and quantitative. In the Arctic zone it is especially important to explore the evolution of natural water bodies under the influence of climate change and the urbanization processes in the region. This paper presents for the first time the study of bacteriochlorophyll (BChl) depth profiles derived from optical measurements accompanied by metagenomic profiling of bacterial communities in two stratified lakes, Trekhtzvetnoe and Elovoe at the Kandalaksha coast of the White Sea. Natural water with microorganisms along with hydrological measurements was sampled from various depths during expedition in March 2021. The metagenomic studies showed that biodiversity indices in both lakes did not appear to significantly diminish with depth. According to the analysis of similarity, differences between samples grouped by the lake of origin were not statistically significant. There were significant differences when samples were grouped by layer of the water column. This suggests that stratification of bacterial communities occurred according to environmental conditions in each part of the water column (oxygenated surface layer; chemocline, and anoxic bottom layers), and was not influenced by the geographical location of the lake. Differences between bacterial communities had strong correlation to changes in redox potential and light penetration, and were weakly correlated with depth and temperature; correlation with salinity and pH was not statistically significant.
Environmental monitoring of natural water bodies is important in the Arctic zone for studying their evolution under the influence of climate change and the urbanization processes in the region. In connection with the specific life conditions for anoxygenic phototrophic microorganisms their presence can indicate hydrogen sulfide contamination of the water reservoir and serve as a marker of hydrogen sulfide. This makes the problem of optical diagnostics of phototrophic bacteria very urgent and important. There is a number of spectral methods for determination of chlorophyll-containing microorganisms. The spectral properties of photosynthetic bacterial pigments, bacteriochlorophylls (BChls), are still poorly understood, however. For the first time we applied fluorescence spectra of BChl extracts to receive depth distribution of BChl d in the lake. Fluorescence emission spectra were measured using a Solar CM2203 luminescence spectrometer under excitation at wavelength of 425 nm, corresponding to the BChl d absorption peak. In September 2020 the maximal concentration of BChl d was found at the depth of 2.275 m (16700 mg/m3) in Lake Trekhtzvetnoye. The thickness of the bacterial plate did not exceed 5 cm, and the pigment distribution was found vertically asymmetric. We emphasize that fluorescence quantification of BChl d is more sensitive compared to spectrophotometric one, and it makes possible estimation of ultralow BChl concentrations without water sample pre-concentration.
Aquatic humic substances, or chromophoric fraction of dissolved organic matter (СDOM) in natural water have characteristic optical properties. Considerable effort has been devoted to investigate CDOM optical properties and to improve understanding of biogeochemical carbon cycles in the northern regions. However, due to rare observations up to date there is a limited amount of data available on CDOM research in the sub-Arctic zones. This work summarizes the spectral-optical properties of CDOM from several locations along two coasts of the White Sea. The absorption and fluorescence emission spectra with different excitation wavelength were measured for water sampled in August- September 2020 in the expeditions to several locations of the Karelian and Tersky Coasts, differing in geomorphology, hydrology and anthropogenic influence. The fluorescence was found excitation-dependent; we observed the “blue shift” of emission maximum along with rising the excitation wavelength for all studied CDOM samples (surface and deep coastal water). The absorption spectra are similar in shape for all studied CDOM samples, however, absorbance values reflect concentration of humic substances in some samples. In the Lobanikha Bay we did not find the significant difference in deep and surface CDOM, but in the relict lagoon in Eastern Porya Bay the CDOM was concentrated towards bottom. Those findings are important for understanding the mechanisms of the formation of optical properties of natural water with CDOM of various origins.
The paper presents the results of a spectroscopic study of the "colored" water detected in the splash baths in the supralittoral zone of the Alaid Volcano (the Kuril Islands) from 2015 to 2019. The splash baths with magenta, red and red-yellow water located in different parts of the island in various summer seasons. The analysis of fluorescenсе and absorption data of the water samples revealed the presence of a large amount of bacteriochlorophyll a in the water, which is the main photosynthetic pigment of purple sulfur bacteria. The assumption of the presence of cells of microorganisms was confirmed by observations under a microscope. To determine the morphotype of microorganisms the acetonemethanol extracts from the samples were prepared and studied using spectral methods. The characteristic absorption lines of carotenoids and the monomeric form of bacteriochlorophyll identified cells as Thiocystis and Thiorhodococcus morphotypes of purple sulfur bacteria. The regular observation of water samples with microorganisms in the supralittoral zone of the Alaid Volcano leads to the conclusion that the development of the purple phototrophic bacteria is not an accidental event, but a typical phenomenon in this area. The fact that each summer season colored water were found in different places indicates a cyclical changes in living conditions of microorganisms from favorable to unfavorable habitats.
The work presents the results of spectroscopic study of the natural water with microorganisms from the splash baths in the Atlasov Island (the Alaid Volcano). The Alaid Volcano is the highest, northernmost and one of the most active volcanoes of the Kuril Islands, the unique object for interdisciplinary research. In 2015 within the supralittoral zone of the island the several splash pools filled with colored marine water were discovered for the first time. The paper presents the results of spectral measurements and microbiological studies performed on natural water samples taken in 2015-2017 from the supralittoral zone of the Alaid Volcano, the Kuril Islands, as well as the photosynthetic microorganisms cultivated from those samples in laboratory. The absorption spectra of the native samples and the cultures of photosynthetic bacteria cultivated from original water demonstrated pronounced maxima at 380, 590, 806, 854 nm wavelengths and the shoulders peaked at 510, 590 and 890 nm. The observed absorption maxima revealed the presence of bacteriochlorophyll а, the main photosynthetic pigment of purple sulfur bacteria, and additionally the cells of purple sulfur bacteria Thiocystis and Thiorhodococcus morphotypes were detected in water under microscope. Observation of water colored by photosynthetic microbes in different parts of the Atlasov Island within several summer seasons in 2015-2017 allowed us to conclude that the development of the purple phototrophic bacteria in the splash baths above the littoral zone is not an accidental event, but the stable phenomenon. On the other Kuril Islands similar splash baths have not been encountered yet.
We analyze the results received from two expeditions performed in August-September 2013, August-September 2014 and February 2015 in the Kandalaksha Bay of the White Sea. Depth profiles of hydrological characteristics and optical properties of water were recorded for five marine lakes being on different stages of isolation from the White Sea. Those relic lakes demonstrate a tendency to meromixis and are characterized by apparent stratification of the water bodies from the brackish top layer to the bottom salt water. Maximal concentrations of anoxygenic phototrophs (green sulfur bacteria) were found at depths close to the redox interface in all the studied lakes. To discriminate differently pigmented groups of microorganisms the fluorescence emission spectra of bacteriochlorophylls from the living cells were used. We puzzle out the data on light spectrum propagation through the water body in each lake using optical properties of water (attenuation spectra) in the UV, visible and NIR ranges, as well as direct measurements of the total irradiances at various depths. The changes in optical characteristics of water in the stratified reservoirs due to cromophoric dissolved organic matter (CDOM) and microbial pigments affect the light intensity and its spectral distribution at each water layer thus influencing the living conditions for differently pigmented phototrophic microorganisms and determining the composition of microbial community.
Detection of phototropic organisms in their natural habitat using optical instruments operating under water is urgently needed for many tasks of ecological monitoring. While fluorescence methods are widely applied nowadays to detect and characterize phytoplankton communities, the techniques for detection and recognition of anoxygenic phototrophs are considered challenging. Differentiation of the forms of anoxygenic green sulfur bacteria in natural water using spectral techniques remains problematic. Green sulfur bacteria could be found in two forms, green-colored (containing BChl d in pigment compound) and brown-colored (containing BChl e), have the special ecological niche in such reservoirs. Separate determination of these microorganisms by spectral methods is complicated because of similarity of spectral characteristics of their pigments. We describe the novel technique of quantification of two forms of green sulfur bacteria directly in water using bacteriochlorophyll fluorescence without pigment extraction. This technique is noninvasive and could be applied in remote mode in the water bodies with restricted water circulation to determine simultaneously concentrations of two forms of green sulfur bacteria in their natural habitat.
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