Abundance Of Transparent Exopolymer Particles Research Articles

Effect of temperature on the accumulation of marine biogenic gels in the surface microlayer near the outlet of nuclear power plants and adjacent areas in the Daya Bay, China.

The surface microlayer (SML) in marine systems is often characterized by an enrichment of biogenic, gel-like particles, such as the polysaccharide-containing transparent exopolymer particles (TEP) and the protein-containing Coomassie stainable particles (CSP). This study investigated the distribution of TEP and CSP, in the SML and underlying water, as well as their bio-physical controlling factors in Daya Bay, an area impacted by warm discharge from two Nuclear power plants (Npp’s) and aquaculture during a research cruise in July 2014. The SML had higher proportions of cyanobacteria and of pico-size Chl a contrast to the underlayer water, particularly at the nearest outlet station characterized by higher temperature. Diatoms, dinoflagellates and chlorophyll a were depleted in the SML. Both CSP and TEP abundance and total area were enriched in the SML relative to the underlying water, with enrichment factors (EFs) of 1.5–3.4 for CSP numbers and 1.32–3.2 for TEP numbers. Although TEP and CSP showed highest concentration in the region where high productivity and high nutrient concertation were observed, EFs of gels and of dissolved organic carbon (DOC) and dissolved acidic polysaccharide (> 1 kDa), exhibited higher values near the outlet of the Npp’s than in the adjacent waters. The positive relation between EF’s of gels and temperature and the enrichment of cyanobacteria in the SML may be indicative of future conditions in a warmer ocean, suggesting potential effects on adjusting phytoplankton community, biogenic element cycling and air-sea exchange processes.

Inter-annual variability of transparent exopolymer particles in the Arctic Ocean reveals high sensitivity to ecosystem changes

Transparent exopolymer particles (TEP) are a class of marine gel particles and important links between surface ocean biology and atmospheric processes. Derived from marine microorganisms, these particles can facilitate the biological pumping of carbon dioxide to the deep sea, or act as cloud condensation and ice nucleation particles in the atmosphere. Yet, environmental controls on TEP abundance in the ocean are poorly known. Here, we investigated some of these controls during the first multiyear time-series on TEP abundance for the Fram Strait, the Atlantic gateway to the Central Arctic Ocean. Data collected at the Long-Term Ecological Research observatory HAUSGARTEN during 2009 to 2014 indicate a strong biological control with highest abundance co-occurring with the prymnesiophyte Phaeocystis pouchetii. Higher occurrence of P. pouchetii in the Arctic Ocean has previously been related to northward advection of warmer Atlantic waters, which is expected to increase in the future. Our study highlights the role of plankton key species in driving climate relevant processes; thus, changes in plankton distribution need to be accounted for when estimating the ocean’s biogeochemical response to global change.

Transparent Exopolymer Particles (TEP) in the NE Aegean Sea frontal area: Seasonal dynamics under the influence of Black Sea water

The abundance of Transparent Exopolymer Particles (TEP) was determined on a seasonal basis (autumn, spring and summer) along a north-south transect in the NE Aegean Sea and the vicinity of the Dardanelles Straits. Their distribution patterns were studied in respect to hydrographic conditions and water mass characteristics in the area, as well as particulate organic carbon (POC) concentrations, changes in standing stocks of chlorophyll-α and bacterial production. TEP concentrations ranged from 15.4 to 188µg GX eqL-1. Their spatial distribution patterns within the euphotic zone displayed significant seasonal variability, which appears to closely reflect the temporal variation of the water column structure, resulting from the encounter and interplay of the Black Sea and Levantine Water masses, and the associated biogeochemical processes. Minimum TEP concentrations during autumn could be likely attributed to a minor quantity of TEP and/or its dissolved precursors exuded by phytoplankton and their enhanced degradation due to their long residence time in the water column. During spring, high TEP production was mediated by actively growing phytoplankton, while during summer a positive link to the intense stratification of the water column and the enhanced bacterial growth within the Black Sea Water layer was observed. The results reported in this study highlight the fact that TEP carbon represents a significant fraction of the POC pool. Moreover, TEP production is critical in promoting particle coagulation rates, playing an important role in carbon cycling/transportation out of the euphotic zone.

Experimental evidence of formation of transparent exopolymer particles (TEP) and POC export provoked by dust addition under current and high pCO2 conditions.

The evolution of organic carbon export to the deep ocean, under anthropogenic forcing such as ocean warming and acidification, needs to be investigated in order to evaluate potential positive or negative feedbacks on atmospheric CO2 concentrations, and therefore on climate. As such, modifications of aggregation processes driven by transparent exopolymer particles (TEP) formation have the potential to affect carbon export. The objectives of this study were to experimentally assess the dynamics of organic matter, after the simulation of a Saharan dust deposition event, through the measurement over one week of TEP abundance and size, and to evaluate the effects of ocean acidification on TEP formation and carbon export following a dust deposition event. Three experiments were performed in the laboratory using 300 L tanks filled with filtered seawater collected in the Mediterranean Sea, during two ‘no bloom’ periods (spring at the start of the stratification period and autumn at the end of this stratification period) and during the winter bloom period. For each experiment, one of the two tanks was acidified to reach pH conditions slightly below values projected for 2100 (~ 7.6–7.8). In both tanks, a dust deposition event of 10 g m-2 was simulated at the surface. Our results suggest that Saharan dust deposition triggered the abiotic formation of TEP, leading to the formation of organic-mineral aggregates. The amount of particulate organic carbon (POC) exported was proportional to the flux of lithogenic particles to the sediment traps. Depending on the season, the POC flux following artificial dust deposition ranged between 38 and 90 mg m-2 over six experimental days. Such variability is likely linked to the seasonal differences in the quality and quantity of TEP-precursors initially present in seawater. Finally, these export fluxes were not significantly different at the completion of the three experiments between the two pH conditions.

Distribution of transparent exopolymer particles (TEP) across an organic carbon gradient in the western North Atlantic Ocean

In this study, the abundance of transparent exopolymer particles (TEP) is examined across a surface water gradient of organic carbon from a phytoplankton bloom region in the western North Atlantic to oligotrophic waters in the Sargasso Sea, including a coastal region sampled near Cape Cod. TEP are macrogels that reach up to millimeters in size and abiotically assemble from dissolved acidic polysaccharides secreted by phytoplankton. Due to their great stickiness, TEP self aggregate and also form aggregates with non-TEP particulate organic carbon (POC). Aggregation enhances ballasting, thereby mutually facilitating export and subsequent sedimentation of both TEP and POC, increasing the efficiency of the biological pump. Here, four distinct regions with varying chlorophyll a concentrations, temperature, and salinity were sampled in the upper column, at the surface, and from the sea surface microlayer (SML). While TEP in seawater shows no correlation to chlorophyll a, nutrients, or total organic carbon (TOC) concentration, a strong correlation exists between TEP and TOC in the SML; and concentrations of both variables are inversely proportional to surface productivity as indicated by chlorophyll a concentrations. As open ocean regions show greater enrichments of TEP and TOC in the SML compared to the coastal region, we suggest that the role of the SML in organic carbon cycling is dependent on regional biogeochemistry and productivity. We hypothesize that a lower abundance of particles in oligotrophic regions compared to bloom regions limits TEP export by sinking, thus increasing the residence time of TEP in the upper water column and the SML.

The organic sea-surface microlayer in the upwelling region off the coast of Peru and potential implications for air–sea exchange processes

Abstract. The sea-surface microlayer (SML) is at the uppermost surface of the ocean, linking the hydrosphere with the atmosphere. The presence and enrichment of organic compounds in the SML have been suggested to influence air–sea gas exchange processes as well as the emission of primary organic aerosols. Here, we report on organic matter components collected from an approximately 50 µm thick SML and from the underlying water (ULW), ∼ 20 cm below the SML, in December 2012 during the SOPRAN METEOR 91 cruise to the highly productive, coastal upwelling regime off the coast of Peru. Samples were collected at 37 stations including coastal upwelling sites and off-shore stations with less organic matter and were analyzed for total and dissolved high molecular weight (> 1 kDa) combined carbohydrates (TCCHO, DCCHO), free amino acids (FAA), total and dissolved hydrolyzable amino acids (THAA, DHAA), transparent exopolymer particles (TEP), Coomassie stainable particles (CSPs), total and dissolved organic carbon (TOC, DOC), total and dissolved nitrogen (TN, TDN), as well as bacterial and phytoplankton abundance. Our results showed a close coupling between organic matter concentrations in the water column and in the SML for almost all components except for FAA and DHAA that showed highest enrichment in the SML on average. Accumulation of gel particles (i.e., TEP and CSP) in the SML differed spatially. While CSP abundance in the SML was not related to wind speed, TEP abundance decreased with wind speed, leading to a depletion of TEP in the SML at about 5 m s−1. Our study provides insight to the physical and biological control of organic matter enrichment in the SML, and discusses the potential role of organic matter in the SML for air–sea exchange processes.

Abundance, characteristics, and size spectra of transparent exopolymer particles and Coomassie stainable particles during spring in a large shallow lake, Taihu, China

Abstract Abundance, characteristics, and size spectra of transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) were investigated in Lake Taihu for the first time during spring. Abundance, equivalent spherical volume (ESV), and equivalent surface area (ESA) of particles were quantified by combining microscopic observation with image analysis. Average concentration of TEP in water was approximately seven-fold higher than that of CSP, and the average ESV and ESA of TEP were both greater than those of CSP. TEP abundance ranged from 5.27 × 10 3 to 2.3 × 10 4 particles/mL, with ESV from 1.09 × 10 6 to 7.44 × 10 6 μm 3 /mL and ESA from 3.28 × 10 6 to 2.23 × 10 7 μm 2 /mL. CSP abundance varied from 2.43 × 10 2 to 3.81 × 10 3 particles/mL, with ESV from 1.62 × 10 4 to 7.12 × 10 5 μm 3 /mL and ESA from 4.85 × 10 4 to 2.14 × 10 6 μm 2 /mL. During spring, small particles (equivalent spherical diameter (ESD) Microcystis begins to bloom, and they could be especially important for influencing bloom outbreaks.

Contribution of combined carbohydrates to dissolved and particulate organic carbon after the spring bloom in the northern Bay of Biscay (North-Eastern Atlantic Ocean)

Two cruises were conducted after the diatom spring bloom in the northern Bay of Biscay (2006, 2007), to assess the contribution of combined carbohydrates to organic carbon partitioning. Partitioning of total organic carbon (TOC) into particulate organic carbon (POC) and dissolved organic carbon (DOC) differed between the two years, particularly for depths above 60m, and was related to the vernal development of the system: a post spring-bloom system in 2007, and a more stratified summer system with higher coccolithophore abundance in 2006. In general, contribution of POC to TOC ranged between 4% and 28% and decreased with depth. Concentration of high-molecular-weight (HMW;>1kDa) dissolved combined carbohydrates (dCCHO) ranged from 0.6 to 1.4μmolL−1 and contributed between 4% and 11% to DOC. Concentration of particulate combined carbohydrates (pCCHO) varied between 0.03 and 1.3μmolL−1. A high contribution of pCCHO to POC was observed in 2007, i.e. 22–60% C compared to 3–10% C in 2006, and coincided with a higher abundance of transparent exopolymer particles (TEP). TEP accounted for 0.4–2.0μmolCL−1 in 2007 and 0.5–1.5μmolCL−1 in 2006. Above 60m, differences in contribution of TEP-C to POC were most pronounced yielding 15.4±3.0% in 2007 compared to relatively low 4.8±1.4%, in 2006. TEP-C could explain about 60% in 2007 and about 40% of pCCHO-C in 2006. Hence, TEP were identified as a substantial component of pCCHO and POC, particularly in the wake of the spring bloom. Molecular composition of CCHO, i.e. HMW−dCCHO+pCCHO, revealed little difference between the years but strong variation over depth. Uronic acids (URA) were identified as a major component of CCHO (20–40%). Our study indicates that the distribution and composition of CCHO in surface seawater are determined by biogeochemical processes on a seasonal scale. A better knowledge of CCHO cycling and molecular signature has therefore a high potential for a better tracing of carbon dynamics in shelf sea ecosystems.

Diatom-associated bacteria are required for aggregation of Thalassiosira weissflogii

Aggregation of algae, mainly diatoms, is an important process in marine systems leading to the settling of particulate organic carbon predominantly in the form of marine snow. Exudation products of phytoplankton form transparent exopolymer particles (TEP), which acts as the glue for particle aggregation. Heterotrophic bacteria interacting with phytoplankton may influence TEP formation and phytoplankton aggregation. This bacterial impact has not been explored in detail. We hypothesized that bacteria attaching to Thalassiosira weissflogii might interact in a yet-to-be determined manner, which could impact TEP formation and aggregate abundance. The role of individual T. weissflogii-attaching and free-living new bacterial isolates for TEP production and diatom aggregation was investigated in vitro. T. weissflogii did not aggregate in axenic culture, and striking differences in aggregation dynamics and TEP abundance were observed when diatom cultures were inoculated with either diatom-attaching or free-living bacteria. The data indicated that free-living bacteria might not influence aggregation whereas bacteria attaching to diatom cells may increase aggregate formation. Interestingly, photosynthetically inactivated T. weissflogii cells did not aggregate regardless of the presence of bacteria. Comparison of aggregate formation, TEP production, aggregate sinking velocity and solid hydrated density revealed remarkable differences. Both, photosynthetically active T. weissflogii and specific diatom-attaching bacteria were required for aggregation. It was concluded that interactions between heterotrophic bacteria and diatoms increased aggregate formation and particle sinking and thus may enhance the efficiency of the biological pump.

Removal and Deposition of Transparent Exopolymer Particles in a Seawater UF-RO System

AbstractThe abundance of transparent exopolymer particles (TEPs) in seawater has been reported for many years. Recently, however, TEPs have been implicated as one of the leading causes of biofouling in reverse osmosis (RO) systems. A pilot plant study of a seawater ultrafiltration (UF)–RO system was conducted to monitor seasonal variation of TEPs, removal through pretreatment processes, and deposition in the RO system. Operational performance of the UF and RO systems was also monitored to evaluate the effects of TEPs on plant operations. A spectrophotometric assay measured TEPs in the particulate and colloidal size range at different stages of the plant. TEP monitoring of raw water indicated a significant increase of p-TEPs and c-TEPs from late March until early May, after which TEPs subsided to lower levels. The period was also marked by increased chlorophyll a and total organic carbon, indicating algal blooms in the seawater source. TEPs in the raw water were partially removed by microstraining and UF p...

The fate of Transparent Exopolymer Particles (TEP) in integrated membrane systems: Removal through pre-treatment processes and deposition on reverse osmosis membranes

The abundance of Transparent Exopolymer Particles (TEP) in surface waters has been unnoticed for many years until recently as a potential foulant in reverse osmosis systems. Recent studies indicate that TEP may cause organic and biological fouling and may enhance particulate/colloidal fouling in reverse osmosis membranes. The presence of TEP was measured in the raw water, the pre-treatment processes and reverse osmosis (RO) systems of 6 integrated membrane installations. A spectrophotometric method was used to measure TEP in the particulate size range (>0.40 μm) and was extended to measure TEP in the colloidal size range (0.05–0.40 μm). Ultrafiltration pre-treatment applied in 4 plants, totally removed particulate TEP while microfiltration systems (2 plants) and coagulation/sedimentation/rapid sand filtration systems (3 plants) partially removed this fraction. None of the pre-treatment systems investigated totally removed colloidal TEP. Biopolymer analysis using LC–OCD showed consistency between colloidal TEP and polysaccharide removal by UF pre-treatment and further verified the presence of TEP in the RO feedwater. TEP deposition in the RO system was determined after measuring total TEP concentrations in the RO feed and concentrate. The TEP deposition factors and specific deposition rates indicate that TEP accumulation had occurred in all plants investigated. This observation was verified by an autopsy of RO modules from two RO plants. Further improvement and verification of the (modified) TEP method, in particular the calibration, is necessary so that it can be employed to investigate the role of TEP in the fouling of RO systems.

Transparent exopolymer particles (TEP) as a component of hydrothermal plume particle dynamics

Transparent exopolymer particles (TEP) have recently been recognized as a class of sticky particles that often stimulate macroaggregate formation. Until now, TEP studies were focused on surface waters, particularly in association with diatom blooms. This is the first report of TEP concentrations in an open ocean deep-sea hydrothermal plume environment. The occurrence of TEP in deep water demonstrates its existence in an environment that is devoid of growing phytoplankton, the organisms generally regarded as TEP's primary source. The main objective of this study was to investigate the presence and potential abundance of TEP within hydrothermal plumes over the Juan de Fuca Ridge. Samples for TEP and bacteria were collected from CTD-rosette casts through hydrothermal plumes over the Juan de Fuca Ridge during the summers of 1999 and 2000. Concentrations of TEP and bacteria within the hydrothermal plumes were significantly greater than in background seawater. TEP number and volume concentrations reported here are low compared to reported values for shallow environments, but are substantially higher than published reports of TEP in other deep water environments. Ratios of TEP anomalies to temperature anomalies (a conservative hydrothermal tracer) increased with distance from the apparent plume source, suggesting that TEP are produced within the aging hydrothermal plumes. Potential TEP sources associated with hydrothermal plumes are discussed. TEP in hydrothermal plumes could stimulate in situ aggregate formation, support populations of attached bacteria, and serve as a potential food source to zooplankton.

Ascending marine particles: Significance of transparent exopolymer particles (TEP) in the upper ocean

The high abundance of transparent exopolymer particles (TEP) in marine and freshwater greatly affects particle dynamics. TEP act as glue for colliding particles and form the matrix in aggregates, thereby altering aggregation dynamics. We studied the sinking behavior of freshly produced, particle‐free TEP and of aggregates composed of TEP and latex spheres in a laboratory using water collected from Santa Barbara Channel, California. Particle‐free TEP ascend and accumulate in the surface layer of a settling column at an average velocity of 1.6 x 10−4 cm s−1. The estimated density of TEP ranges from 0.70 to 0.84 g cm−3. TEP also transported latex spheres of 45.6 and 1.82 µm in diameter and a density of 1.05 g cm−3 to the surface layer. We describe a simple model illustrating the role of TEP for the vertical transport of solid particles. The densities and relative proportions of TEP, solid particles, and interstitial water within an aggregate determine its sinking or ascending velocity. High ratios of TEP to solid particles retard the sinking of aggregates, prolonging their residence time in the surface ocean. Our results demonstrate that TEP can provide a vehicle for the upward flux of biological and chemical components in the marine environment, including bacteria, phytoplankton, carbon, and reactive trace elements.

Distribution of transparent exopolymer particles (TEP) in the northeast Atlantic Ocean and their potential significance for aggregation processes

The abundance of transparent exopolymer particles (TEP) was determined in the northeast Atlantic Ocean (40–55°N, ∼20°W) during several cruises from June to November 1996. An accumulation of TEP in the water column was observed at bloom and post-bloom sites along a 20°W transect in June/July (maximum concentration: 124 μg Gum Xanthan equivalents (Xeq.) l −1), but concentrations were uniformly low (mean concentration: 28.5±10.2 μg Xeq. l −1) during autumn at the BIOTRANS site (47°N, 20°W). TEP concentrations in the open northeast Atlantic were considerably lower than previously published values from coastal sites. However, during June/July TEP:Chl a (weight/weight) ratios were comparable to values at coastal seas. It is suggested that phytoplankton production modulates TEP concentration in the open ocean as it does in coastal systems. TEP contributed significantly to the organic carbon pool as derived from the ratio TEP-C:POC, in summer (mean percentage: 17±7.5; w/w), as well as in autumn (mean percentage: 18±11, w/w). The potential influence of TEP on particle coagulation rates in the northeast Atlantic was assessed from estimates of their influence on particle stickiness and on particle volume concentrations. This indicated that TEP may be essential for initiating particle aggregation at low biomass concentrations, typical for open ocean sites.

Abundance and variability of microorganisms and transparent exopolymer particles across the ice-water interface of melting first-year sea ice in the Laptev Sea (Arctic)

The distribution and abundance of transparent exopolymer particles (TEP) was determined in and below pack ice of the Laptev Sea from July to September 1995. Samples were collected from the lowermost 10 cm of ice floes and at 10 cm below the ice–water interface. Abundance of bacteria, protists and TEP was determined, and the sea ice–water boundary layer was characterized using temperature, salinity and molecular viscous shear stress. TEP, with a distinct size distribution signal, were found in highest concentrations inside the sea ice, ranging from not detectable to 16 cm2 l−1 (median: 2.9 cm2 l−1). In the water, concentrations were one order of magnitude lower, ranged from below detection to 2.7 cm2 l−1 (median: 0.2 cm2 l−1) and decreased after the middle of August, whereas abundances of autotrophic flagellates (AF), diatoms, heterotrophic flagellates (HF) and ciliates increased. The abundance of TEP decreased with its size in all samples following a power law relationship. The relation of TEP to the microbial community differed between the sea ice and water, being positively correlated with bacteria and diatoms in the ice and negatively correlated with HF in the sea water. The presence of a pycnocline significantly influenced the abundance of organisms, diatom composition and TEP concentrations. Pennate diatoms dominated by Nitzschia frigida were most abundant inside the ice. Though bacteria have the potential to produce exopolymeric substances (EPS), the results of this study indicate that the majority of TEP at the ice–water interface in first-year Arctic summer pack ice are produced by diatoms.

Dynamics and bacterial colonization of microaggregates in a large mesotrophic lake

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 26:23-35 (2001) - doi:10.3354/ame026023 Dynamics and bacterial colonization of microaggregates in a large mesotrophic lake Till Brachvogel1, Bernhard Schweitzer1, Meinhard Simon2,* 1Limnological Institute, University of Constance, 78457 Konstanz, Germany 2Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, PO Box 2503, 26111 Oldenburg, Germany *Corresponding author. E-mail: m.simon@icbm.de Abstract: We studied the occurrence and dynamics of transparent exopolymer particles (TEP) and 4¹-6¹-diamidino-2-phenylindole (DAPI)-stained microaggregates (MA) and the bacterial colonization of the latter by fluorescence in situ hybridization with rRNA-targeted oligonucleotides in Lake Constance, Germany, from June to December 1996. MA were categorized into the size classes 8 to 20, 20 to 60 and >60 μm. Total abundance of TEP varied between 71 and 2554 ml-1 and that of MA between 310 and 1526 ml-1 with the largest proportion in the size class 8 to 20 μm (140 to 959 ml-1). Numbers of TEP and of MA >60 μm, never exceeding 100 ml-1, decreased with depth and were correlated to the biomass of total phytoplankton, diatoms, chrysophytes and dinoflagellates. Numbers of the smaller-sized MA did not systematically decrease with depth. Four types of DAPI-stained MA were identified: aggregates composed of bacterial and of cyanobacterial colonies, aggregates fluorescing yellow (DAPI yellow particles), and phytoplankton and zooplankton fragments fluorescing faintly blue after DAPI staining. The latter and DAPI yellow particles were most abundant. The majority of MA was densely colonized by bacteria. At least 20% of the DAPI-stainable cells were detected by the Bacteria-specific probe EUB338 and a mean between 44 and 56% of the various types of MA. b-Proteobacteria dominated aggregates composed of remains of diatoms and often also on fragments. On DAPI yellow particles bacteria of this phylogenetic lineage and the Cytophaga/Flavobacteria cluster were equally abundant. γ-Proteobacteria usually constituted only minor proportions except on fragments of Dinobryon spp. and of zooplankton origin on which they constituted up to 62% of the DAPI-stainable cells. a-Proteobacteria were not detected at all. Together, all group-specific probes constituted >95% of the bacteria detected by the EUB338 probe on MA except for bacterial aggregates on which only 59% were detected. The different spatio-temporal dynamics of TEP and MA and the bacterial colonization of the latter suggested that TEP and MA >60 μm were early decomposition products mainly of diatoms and other algae whereas smaller MA were more degraded stages of detrital particulate organic matter. KEY WORDS: Microaggregates · Transparent exopolymer particles · Bacteria · In situ hybridization · Lake Constance Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 26, No. 1. Online publication date: October 26, 2001 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2001 Inter-Research.

Rapid formation and sedimentation of large aggregates is predictable from coagulation rates (half-lives) of transparent exopolymer particles (TEP)

Two hypotheses have been proposed to account for the precipitous formation of large, rapidly settling aggregates at the termination of phytoplankton blooms in nature; aggregation due primarily to cell-cell collisions, and aggregation resulting from the presence of abundant transparent exopolymer particles (TEP), a recently discovered class of particles formed from polysaccharides excreted by phytoplankton. The hypothesis of TEP-driven coagulation in three disparate systems, a freshwater lake, a coastal ocean, and a saltwater mesocosm was evaluated, by comparing TEP abundance to several related factors including phytoplankton concentrations, measured sediment fluxes, and abundances of large aggregates. The timing of large aggregate formation and sedimentation events was related to coagulation rates expressed in terms of particle half-lives, t 1 2 , calculated as the time for TEP or phytoplankton to decrease to half their concentration through shear coagulation. While TEP have been previously investigated only in marine systems, it is reported here that TEP also can be present in high concentrations (860 ml −1) in freshwater lakes (Lake Constance, Germany) and that high fluxes of particulate organic matter at depth coincide with the disappearance of abundant TEP from overlying waters. The half-lives of TEP in the three different systems indicate that large aggregate formation and massive sedimentation events following diatom blooms occur when the TEP half-life decreases to less than a few days. By comparing TEP and phytoplankton half-lives in these systems, it is concluded that the formation of rapidly sinking aggregates following blooms of mucous-producing diatoms is primarily controlled by concentrations of TEP, not phytoplankton.

The role of particulate carbohydrate exudates in the flocculation of diatom blooms

Diatom blooms are frequently terminated by mass aggregation of cells into large, rapidly sinking aggregates. It has been hypothesized that transparent exopolymer particles (TEP), abundant particles formed from the polysaccharides exuded by living cells, may be essential for this mass flocculation processes. We investigated the abundance of TEP and their role in the aggregation of diatoms in laboratory cultures and during a natural diatom bloom off California. TEP and dissolved carbohydrates accumulated appreciably over the growth cycle of Chaetoceros gracilis in the laboratory. The flocculation of C. gracilis in a laboratory flocculator was dominated by TEP, not cells, and large flocs, consisting predominantly of particulate polysaccharides, formed at a rate more than an order of magnitude higher than predicted by coagulation theory for cells alone. The frequency of interparticle attachment was three orders of magnitude higher for TEP than for cells. The pattern of flocculation of a natural diatom bloom was similar to that of laboratory cultures. Prior to bloom flocculation the abundance and total quantity of TEP and the concentration of particulate carbohydrates increased, while dissolved carbohydrate concentrations decreased. During the flocculation stage TEP aggregated into fewer, but much larger particles and concentrations of dissolved carbohydrates decreased further. The percentage of diatom cells which were attached to TEP increased during the flocculation period from 3 to 90% and TEP formed the matrix of all the natural diatom aggregates observed. During the late flocculation stage the quantity of TEP and TEP aggregates did not increase further and concentrations of diatoms decreased, presumably because large flocs sank out. Our findings indicate that TEP should be included in models of particle aggregation in the ocean. The abundance, large size and high sticking coefficient of TEP make them essential to the aggregation of diatom blooms. The extracellular release of polysaccharides by growing cells may be an adaptation for aggregation. The abiotic formation of particulate organic matter (TEP) from dissolved organic matter (DOC) may help to explain the extremely high turnover rates of DOC observed during blooms.