The Co-Evolution Aspects of the Biogeochemical Role of Phytoplankton in Aquatic Ecosystems: A Review.

In freshwater and marine ecosystems, the phytoplankton community is based on microalgae and cyanobacteria, which include phylogenetically very diverse groups of oxygenic photoautotrophs. In the process of evolution, they developed a wide range of bio(geo)chemical adaptations that allow them to effectively use solar radiation, CO2, and nutrients, as well as major and trace elements, to form O2 and organic compounds with a high chemical bond energy. The inclusion of chemical elements in the key processes of energy and plastic metabolism in the cell is determined by redox conditions and the abundance and metabolic availability of elements in the paleoenvironment. Geochemical evolution, which proceeded simultaneously with the evolution of biosystems, contributed to an increase in the number of metals and trace elements acting as cofactors of enzymes involved in metabolism and maintaining homeostasis in the first photoautotrophs. The diversity of metal-containing enzymes and the adaptive ability to replace one element with another without losing the functional properties of enzymes ensured the high ecological plasticity of species and allowed microalgae and cyanobacteria to successfully colonize a wide variety of habitats. In this review, we consider the main aspects of the modern concepts of the biogeochemical evolution of aquatic ecosystems and the role of some metals in the main bioenergetic processes in photosynthetic prokaryotes and eukaryotes. We present generalized data on the efficiency of the assimilation of key nutrients by phytoplankton and their importance in the cycle of carbon, silicon, nitrogen, phosphorus, sulfur, and iron. This article presents modern views on the evolutionary prerequisites for the formation of elemental signatures in different systematic groups of microalgae, as well as the possibility of using the stoichiometric ratio in the study of biological and geochemical processes in aquatic ecosystems.

Production of Fluorescent Dissolved Organic Matter by Microalgae Strains from the Ob and Yenisei Gulfs (Siberia).

Dissolved organic matter (DOM) is an important component of aquatic environments; it plays a key role in the biogeochemical cycles of many chemical elements. Using excitation-emission matrix fluorescence spectroscopy, we examined the fluorescent fraction of DOM (FDOM) produced at the stationary phase of growth of five strains of microalgae sampled and isolated from the Ob and Yenisei gulfs. Based on the morphological and molecular descriptions, the strains were identified as diatoms (Asterionella formosa, Fragilaria cf. crotonensis, and Stephanodiscus hantzschii), green microalgae (Desmodesmus armatus), and yellow-green microalgae (Tribonema cf. minus). Three fluorescent components were validated in parallel factor analysis (PARAFAC): one of them was characterized by protein-like fluorescence (similar to peak T), two others, by humic-like fluorescence (peaks A and C). The portion of fluorescence intensity of humic compounds (peak A) to the total fluorescence intensity was the lowest (27 ± 5%) and showed little variation between species. Protein-like fluorescence was most intense (45 ± 16%), but along with humic-like fluorescence with emission maximum at 470 nm (28 ± 14%), varied considerably for different algae strains. The direct optical investigation of FDOM produced during the cultivation of the studied algae strains confirms the possibility of autochthonous production of humic-like FDOM in the Arctic shelf regions.

Towards Automated Classification of Zooplankton Using Combination of Laser Spectral Techniques and Advanced Chemometrics.

Zooplankton identification has been the subject of many studies. They are mainly based on the analysis of photographs (computer vision). However, spectroscopic techniques can be a good alternative due to the valuable additional information that they provide. We tested the performance of several chemometric techniques (principal component analysis (PCA), non-negative matrix factorisation (NMF), and common dimensions and specific weights analysis (CCSWA of ComDim)) for the unsupervised classification of zooplankton species based on their spectra. The spectra were obtained using laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy. It was convenient to assess the discriminative power in terms of silhouette metrics (Sil). The LIBS data were substantially more useful for the task than the Raman spectra, although the best results were achieved for the combined LIBS + Raman dataset (best Sil = 0.67). Although NMF (Sil = 0.63) and ComDim (Sil = 0.39) gave interesting information in the loadings, PCA was generally enough for the discrimination based on the score graphs. The distinguishing between Calanoida and Euphausiacea crustaceans and Limacina helicina sea snails has proved possible, probably because of their different mineral compositions. Conversely, arrow worms (Parasagitta elegans) usually fell into the same class with Calanoida despite the differences in their Raman spectra.

A novel approach for discovering correlations between elemental and molecular composition using laser-based spectroscopic techniques.

Modern analytical techniques, including laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy, yield multidimensional data, which are most efficiently used in conjunction with chemometric techniques, including multi-block algorithms. In this study, we use several algorithms for the processing of laser-induced breakdown and Raman spectra of zooplankton organisms, which are found to accumulate lithium for an unknown reason. Correlations between elemental and molecular composition of zooplankton have been found. We studied 29 samples: crustaceans, arrow worms, and sea snails. The obtained spectra were examined by principal component analysis (PCA), non-negative matrix factorization (NMF), consensus PCA (CPCA), and analysis of common components and specific weights (CCSWA, or ComDim). LIBS spectra are more sensitive towards taxonometric differences than Raman spectra. All the algorithms gave similar results, although still differing in details. Data fusion revealed a number of relationships, including the correlation of Li with potassium (R = 0.83, n = 14), with Raman bands of carotenoids (R = 0.89, n = 11) and tryptophan (R = 0.94, n = 9). The correlations were most pronounced in light-coloured parts of the inhomogeneous biological material. Ratios of fatty acids are associated with Li concentration if above 200 mg kg-1. Valine is also related to the Li accumulation. Thus, it is shown that the combination of LIBS and Raman spectroscopy, followed by appropriate mathematical treatment, is a convenient tool for comprehensive studies of environmental objects.

Multi-Element Composition of Diatom Chaetoceros spp. from Natural Phytoplankton Assemblages of the Russian Arctic Seas.

Data on the elemental composition of the diatom Chaetoceros spp. from natural phytoplankton communities of Arctic marine ecosystems are presented for the first time. Samples were collected during the 69th cruise (22 August-26 September 2017) of the R/V Akademik Mstislav Keldysh in the Kara, Laptev, and East Siberian Seas. The multi-element composition of the diatom microalgae was studied by ICP-AES and ICP-MS methods. The contents of major (Na, Mg, Al, Si, P, S, K and Ca), trace (Li, Be, B, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, Sn, Sb, Cs, Ba, Hg, Tl, Pb, Bi, Th and U) and rare earth (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) elements varied greatly, which was probably associated with the peculiarities of the functional state and mineral nutrition of phytoplankton in the autumn period. Biogenic silicon was the dominant component of the chemical composition of Chaetoceros spp., averaging 19.10 ± 0.58% of dry weight (DW). Other significant macronutrients were alkaline (Na and K) and alkaline earth (Ca and Mg) metals as well as biogenic (S and P) and essential (Al and Fe) elements. Their total contents varied from 1.26 to 2.72% DW, averaging 2.07 ± 0.43% DW. The Al:Si ratio for natural assemblages of Chaetoceros spp. of the shelf seas of the Arctic Ocean was 5.8 × 10-3. The total concentrations of trace and rare earth elements on average were 654.42 ± 120.07 and 4.14 ± 1.37 µg g-1 DW, respectively. We summarize the scarce data on the average chemical composition of marine and oceanic phytoplankton and discuss the limitations and approaches of such studies. We conclude on the lack of data and the need for further targeted studies on this issue.

Dataset on the abundance, enrichment and partitioning of chemical elements between the filtered, particulate and sedimentary phases in the Cai River estuary (South China Sea).

This data article refers to the paper entitled "Multi-element signatures in solid and solution phases in a tropical mixing zone: A case study in the Cai River estuary, Vietnam" (Koukina et al., 2021), which considers the fate of major, trace, and rare-earth elements transported through the estuarine geochemical filter of the typical tropical estuary. The present work contributes to the local geochemical baselines as a background for long-term monitoring of potential hazardous elements. Therefore, the dataset covers the abundance, enrichment, and partitioning parameters of 53 chemical elements in the water, suspended particulate matter, and bottom sediment samples collected in the Cai River estuary and the adjacent part of the Nha Trang Bay (South China Sea) between July and August 2013. The total filtered, particulate, and sedimentary elements were determined by atomic emission and inductively coupled plasma mass spectrometry (ICP-AES; ICP-MS). The environmental indices (the enrichment factor and geoaccumulation index) and partition coefficients were calculated from the total element contents. The data provided is essential for the comprehensive environmental assessment of the anthropogenic impact on the coastal ecosystem as well as for the evaluation and modelling of element fractionation and mobility at the estuarine gradients.

Multi-element signatures in solid and solution phases in a tropical mixing zone: A case study in the Cai River estuary, Vietnam.

This study provides baseline concentrations of major, trace, and rare earth elements (REEs) in the solid and solution phases of the tropical Cai River estuary under influence of multiple stresses. The application of the selected multivariate analysis tools (principal component analysis and redundancy analysis) to the enrichment factor and partitioning coefficients (KSPM/Water and KSPM/Sed) calculated from the bulk element contents highlighted the strongest relationships (considered as multi-element signatures) according to the efficiency of the transfer across the estuarine gradients (considered as a selective geochemical filter). Thus, most of the major and trace elements, and REEs studied mainly settle within the mixing zone due to the association with terrigenous aluminosilicate clay minerals, whereas Co, Ni, Cu, As, and Mo are transferred seaward because of their association with the most labile fraction of the fluvial particulate load (such as clays, organic colloids, and carbonates). The major and trace elements, and REEs investigated in this study are mainly introduced in the Cai River and its estuary via basement rock weathering under enhanced monsoonal precipitation, whereas Bi showed the most severe enrichment in the non-weathering distribution pattern. The fractionation of the fluvial element load within the estuarine geochemical filter is mainly controlled by the differential settling of fluvial mineral element-bearing phases along with estuarine colloid dynamics - a topic that must warrants further investigation.

Dataset on the content of major, trace, and rare-earth elements in the bottom sediments and bivalve mollusks of the Kara Sea (Arctic Ocean).

The ability of bivalve mollusks to accumulate chemical elements from the environment makes them an important object for environmental monitoring and assessments of anthropogenic impact on marine ecosystems. The paper presents the data on the content of 65 chemical elements in soft tissues and shells of five species of bivalve mollusks (Astarte crenata, Ciliatocardium ciliatum, Portlandia arctica, Chlamys islandica, Hiatella arctica), as well as in the upper layer (0-5 cm) of bottom sediments of the Kara Sea, the Arctic Ocean. The content of major-, trace and rare-earth elements was determined by atomic emission and inductively coupled plasma mass spectrometry (ICP-AES; ICP-MS). The age, size, and weight of mollusks were measured. There were differences in the content of chemical elements accumulated in soft tissues and shells of mollusks, as well as the significant interspecific difference in the chemical composition of the studied mollusks. The soft tissues of mollusks were accumulated with toxic metals (Hg, Ag, and Cd) in comparison with the content of these elements in bottom sediments. In Chlamys islandica and Hiatella arctica, the shell was accumulated in Cd in contrast to other species. The data obtained may be used for a comprehensive assessment of the state of ecosystems in the seas of the Siberian sector of the Arctic Ocean under changing environment and for studying the fundamental base of the accumulation of chemical elements by marine organisms.

Experimental data on bacterial abundance and morphological changes in copepod carcasses during their decomposition (in vitro).

The biogeochemical role of zooplankton in the ocean is determined not only by life-long accumulation of chemical elements from the environment, but also by post-mortal transformation of carcasses chemical composition. The contribution of zooplankton carcasses to vertical flux of major and trace elements depends on sedimentation and remineralization rates of detrital particles. Carcasses decomposition rate during sinking from the upper to the deeper water layers determines the rapid recycling of chemical elements and depends on ambient temperature and microbial activity. This data set summarizes 21-day experiment in microcosms that simulates temperature conditions in the Arctic environment. The data show slow decomposition of copepod carcasses compared with initial material on days 14-21 of the experiment. In addition to visual evidence, we provide data on changes in bacterial abundance and biomass during the whole experimental period.

Relationship between enrichment, toxicity, and chemical bioavailability of heavy metals in sediments of the Cai River estuary.

This study focuses on heavy metals (HMs) (Cr, Co, Ni, Cu, Zn, and Pb) along with Al, Fe, Mn, organic carbon (TOC), and carbonates (TIC) detected in surface sediments from the River Cai-Nha Trang Bay estuarine system (South China Sea). The enrichment factors (EFAl and EFFe), Geoaccumulation Index (Igeo), Adverse Effect Index (AEI), and toxic units (TUs) were used to assess the HM enrichment and toxicity in the sediments. The selective single-step extraction procedure was applied to determine the chemical forms of HMs in order to assess their potential bioavailability. The EF and Igeo calculations suggest that sedimentary Fe, Mn, Cr, Co, Ni, and Cu are derived mainly from natural sources (EFAl and EFFe < 1.5 and Igeo < 0 at all sampling sites), while the moderate Pb enrichment (EFAl and EFFe ≥ 2 and Igeo ≥ 1 at all sampling sites) may indicate a moderate contamination. Cr, Cu, and Zn suggest low potential toxicity, while both Ni and Pb show above threshold AEI levels (AEI ≥ 1) and contribute up to 30-40% to the sum of toxic units (∑TUs) at all sampling sites. According to their comparative ability to mobilize metals from the sediments, the single extractants applied were arranged in descending order: acetic acid > ammonium oxalate >> sodium pyrophosphate. All single-step extractants mobilized substantive amounts of Pb (7-30% of total content, on average) from sediments, indicating considerable potential bioavailability. Among HMs studied, the percentage of acid-soluble Pb (23-35%) significantly exceeded the respective ranges in the sediments of other coastal regions. Pearson's correlation and PCA analyses revealed that among HMs studied, Cr, Ni, and Co enrichment is positively associated with the salinity gradient due to the accumulation of the most fine-grained Fe-rich aluminosilicate host minerals in the bay zone, while sediments in the transitional zone are mainly enriched in Cu, Zn, and Pb due to the local accumulation of metal-rich detrital heavy minerals. The percentages of bioavailable forms of most of the HMs are negatively associated with the salinity gradient due to the preferential accumulation with fluvial Fe/Mn oxyhydroxides in the frontal and transitional zones. Generally, distribution of the enrichment indices of most of the HMs is not associated or even negatively associated with the percentage of the bioavailable forms. The intensity of monsoonal precipitation is shown to be an essential factor in the natural enrichment of estuarine sediments with bioavailable metals. Determining the local geochemical background of HMs and Pb, in particular, is a major goal for future study.

Major, trace, and rare-earth elements in the zooplankton of the Laptev Sea in relation to community composition.

We investigated the concentrations of major, trace, and rare-earth elements in zooplankton in relation to species community composition from the eastern part of the Lena Delta to the continental slope of the Laptev Sea in September 2015. The elemental composition of zooplankton inhabiting different areas demonstrated similarities. Cross-shelf changes were found for only 4 (Li, Zn, As, and U) of the 56 elements analyzed. Zinc was the only element concentration of which successively reduced across coastal-open ocean gradient. Considering own and literary data, we can assume that the cross-shelf decrease of zinc accumulation in zooplankton is a universal pattern, manifested in different climatic and biogeochemical environmental conditions and with different species compositions of the zooplankton community. Cross-shelf changes were also established for Li, As, and U. However, the concentrations of these elements increased along the gradient. We assume that increased As concentration in zooplankton across the shelf-continental slope gradient of the Laptev Sea is associated with a change in the feeding behavior of the species of the zooplankton community. However, a sharp increase in the concentrations of Li and U in zooplankton was associated with the appearance of Calanus copepods in the community. The average total concentration of rare-earth elements and yttrium in zooplankton of the Laptev Sea was 752.8 ng g-1 of dry weight. We found record high levels of rare-earth elements for zooplankton of the inner shelf, near the eastern part of the Lena Delta. From the inner shelf to the continental slope of the Laptev Sea, La, Ce, and Nd were the dominant rare-earth elements. The elemental composition of zooplankton in the Arctic Seas is characterized by a much lower content of major and trace elements in comparison with the zooplankton and total plankton of the ocean.