Heterogeneity of Transparent Exopolymer Particles in a Coastal Marine Environment (Sagami Bay, Japan): Seasonal Variation and Its Possible Bacterial Causes

Transparent exopolymer particles (TEPs) play important roles in the regulation of carbon and pollutant (microplastics and spilled oils) transport in marine environments; however, the factors controlling TEP dynamics in coastal systems have yet to be fully clarified. A widely used colorimetric method quantifies TEPs as a homogeneous pool, which hampers the examination of internal TEP dynamics. Here, we used the microscopy to elucidate the seasonal dynamics of TEP subgroups and their controlling factors in Sagami Bay, Japan. TEPs were classified into three types: those not associated with other types of particles (Type I), those colonized by multiple types of particles (bacteria, algal cells, and detritus) (Type II), and those densely colonized by only bacterial clusters (Type III). Type II was generally the most dominant TEP component in terms of area, except in February, when Type I contributed substantially to the total TEP area. Type III was less abundant in terms of area but contributed substantially (up to 34%) to the total number of TEPs. The mean diameters were 14.0 ± 2.8 μm, 17.0 ± 5.8 μm, and 7.5 ± 0.9 μm for Type I, Type II, and Type III TEPs, respectively. Type I and Type III TEPs likely represent a transient phase of TEP development toward the formation of Type II, characterized by a high turnover and relatively low abundance in terms of area. The power-law slopes of the distributions of each TEP size, which reflected geometric features of the TEPs at steady state, changed dynamically over the seasons. The abundance of each type of TEP was significantly positively correlated with bacterial abundance, suggesting that bacteria are intimately involved in the regulation of internal TEP dynamics in Sagami Bay. Our results highlight the importance of investigating the internal dynamics of TEPs to improve current understanding of their roles in the regulation of carbon and pollutant transfer in marine environments.

Transparent Exopolymer Particles in Drinking Water Treatment—A Brief Review

Transparent exopolymer particles (TEP) have been described as a class of particulate acidic polysaccharides, which are commonly found in various surface waters. Due to their unique physicochemical characteristics, they have recently been receiving increasing attention on their effects in water treatment. Currently, TEP are commonly known as clear, gel-like polysaccharides. This review first introduced the definition of TEP in water treatment and the relationship between TEP and algal organic matter (AOM). Further, in the review, the authors attempt to offer a holistic view and critical analysis concerning the research on TEPs in source water reservoirs, water plants and membrane treatment processes. It was clearly demonstrated in this review that the formation of TEP in source water reservoirs is largely related to water quality and phytoplankton, and the seasonal water stratification may indirectly affect the formation of TEP. In the waterworks, the relationship between TEP and water treatment process is mutual and there is limited research on this relationship. Finally, the mechanism of TEP-induced membrane fouling and the effect of alleviating TEP-induced membrane fouling is discussed in this review. The TEP removed by ultrafiltration can be recombined after membrane, and the recombination mechanism may be an important way to reduce reverse osmosis membrane contamination.

Seasonal Variations in the Biochemical Compositions of Phytoplankton and Transparent Exopolymer Particles (TEPs) at Jang Bogo Station (Terra Nova Bay, Ross Sea), 2017–2018

The biochemical composition of particulate organic matter (POM) mainly originates from phytoplankton. Transparent exopolymer particles (TEPs) depend on environmental conditions and play a role in the food web and biogeochemical cycle in marine ecosystems. However, little information on their characteristics in the Southern Ocean is available, particularly in winter. To investigate the seasonal characteristics of POM and TEPSs, seawater samples were collected once every two weeks from November 2017 to October 2018 at Jang Bogo Station (JBS) located on the coast of Terra Nova Bay in the Ross Sea. The total chlorophyll-a (Chl-a) concentrations increased from spring (0.08 ± 0.06 μg L−1) to summer (0.97 ± 0.95 μg L−1) with a highest Chl-a value of 2.15 μg L−1. After sea ice formation, Chl-a rapidly decreased in autumn (0.12 ± 0.10 μg L−1) and winter (0.01 ± 0.01 μg L−1). The low phytoplankton Chl-a measured in this study was related to a short ice-free period in summer. Strong seasonal variations were detected in the concentrations of proteins and lipids (one-way ANOVA test, p < 0.05), whereas no significant difference in carbohydrate concentrations was observed among different seasons (one-way ANOVA test, p > 0.05). The phytoplankton community was mostly composed of diatoms (88.8% ± 11.6%) with a large accumulation of lipids. During the summer, the POM primarily consisted of proteins. The composition being high in lipids and proteins and the high caloric content in summer indicated that the phytoplankton would make a good food source. In winter, the concentrations of proteins decreased sharply. In contrast, relatively stable concentrations of carbohydrates and lipids have been utilized for respiration and long-term energy storage in the survival of phytoplankton. The TEPS values were significantly correlated with variations in the biomass and species of the phytoplankton. Our study site was characterized by dominant diatoms and low Chl-a concentrations, which could have resulted in relatively low TEP concentrations compared to other areas. The average contributions of TEP-C to the total POC were relatively high in autumn (26.9% ± 6.1%), followed by those in summer (21.9% ± 7.1%), winter (13.0% ± 4.2%), and spring (9.8% ± 3.1%).

Transparent Exopolymer Particles (TEP), phytoplankton and picocyanobacteria a littoral-to-pelagic depth-gradient in a large subalpine lake

Transparent Exopolymer Particles (TEP) play an important role in the organic carbon cycle of many aquatic systems but the production and distribution of TEP have been studied mainly in the marine environment, neglecting the large oligotrophic lakes. We selected Lake Maggiore, one of the most important freshwater reserve in Northern Italy, to study the horizontal and vertical distribution of TEP and of its possible drivers. Samplings along a transect in the Borromeo basin were performed in May, July and September 2019. Total Organic Carbon (TOC), TEP, chlorophyll-a (Chl) of different algal groups, picocyanobacteria, bacteria and eukaryotes counting, were measured at six stations and five depths. Our study showed that TEP exhibited a clear vertical heterogeneity from surface to the bottom related to the autotrophic microorganisms that are the main source of TEP and are prevalent in the euphotic zone of the lake. On the other hand, TEP was fairly evenly distributed along the horizontal transect from littoral to pelagic zone, although patches were present in spring, when TEP concentrations were low. In contrast to TEP, TOC and to a lesser extent Chl and bacteria showed horizontal heterogeneity, in some months. In Lake Maggiore TEP indeed was an important fraction of Total Organic Carbon (TOC), making up to 54% of TOC (in carbon units: 910 µg C L-1) and it was significantly correlated with Chl. The highest TEP concentration (1.44 mg GX eq L-1) was measured in September 2019, in coincidence with an episode of superficial foam appearance. Considering the biomass as Chl concentrations, the algal group mostly related to TEP was that of brown algae, particularly diatoms; but considering the numbers, the picocyanobacteria and bacteria were more significantly correlated to TEP. The presence of pennate diatoms in May and July, with their TEP-related chlorophyll, did not produce TEP in as high concentration as that observed in September in the presence of centric diatoms and of very high numbers of picocyanobacteria and bacteria.

Transparent Exopolymer Particles in Deep Oceans: Synthesis and Future Challenges

Transparent exopolymer particles (TEP) are a class of abundant gel-like particles that are omnipresent in seawater. While versatile roles of TEP in the regulation of carbon cycles have been studied extensively over the past three decades, investigators have only recently begun to find intriguing features of TEP distribution and processes in deep waters. The emergence of new research reflects the growing attention to ecological and biogeochemical processes in deep oceans, where large quantities of organic carbon are stored and processed. Here, we review recent research concerning the role of TEP in deep oceans. We discuss: (1) critical features in TEP distribution patterns, (2) TEP sources and sinks, and (3) contributions of TEP to the organic carbon inventory. We conclude that gaining a better understanding of TEP-mediated carbon cycling requires the effective application of gel theory and particle coagulation models for deep water settings. To achieve this goal, we need a better recognition and determination of the quantities, turnover, transport, chemical properties, and microbial processing of TEP.

Environmental influences on sinking rates and distributions of transparent exopolymer particles after a typhoon surge at the Western Pacific

A multidisciplinary approach was used to investigate the causes of the distributions and sinking rates of transparent exopolymer particles (TEPs) during the period of September–October (2017) in the Western Pacific Ocean (WPO); the study period was closely dated to a northwest typhoon surge. The present study discussed the impact of biogeophysical features on TEPs and their sinking rates (sTEP) at depths of 0–150 m. During the study, the concentration of TEPs was found to be higher in areas adjacent to the Kuroshio current and in the bottom water layer of the Mindanao upwelling zone due to the widespread distribution of cyanobacteria, i.e., Trichodesmium hildebrandti and T. theibauti. The positive significant regressions of TEP concentrations with Chl-a contents in eddy-driven areas (R2 = 0.73, especially at 100 m (R2 = 0.75)) support this hypothesis. However, low TEP concentrations and TEPs were observed at mixed layer depths (MLDs) in the upwelling zone (Mindanao). Conversely, high TEP concentrations and high sTEP were found at the bottom of the downwelling zone (Halmahera). The geophysical directions of eddies may have caused these conditions. In demonstrating these relations, the average interpretation showed the negative linearity of TEP concentrations with TEPs (R2 = 0.41 ~ 0.65) at such eddies. Additionally, regression curves (R2 = 0.78) indicated that atmospheric pressure played a key role in the changes in TEPs throughout the study area. Diatoms and cyanobacteria also curved the TEPs significantly (R2 = 0.5, P < 0.05) at the surface of the WPO. This study also revealed that TEP concentration contributes less to the average particulate organic carbon in this oligotrophic WPO.