Transparent exopolymer particles (TEP) are ubiquitous in marine and freshwater environments. For the past two decades, the distribution and ecological roles of these polysaccharide microgels in ...aquatic systems were extensively investigated. More recent studies have implicated TEP as an active agent in biofilm formation and membrane fouling. Since biofouling is one of the main hurdles for efficient operation of membrane-based technologies, there is a heightened interest in understanding the role of TEP in engineered water systems. In this review, we describe relevant TEP terminologies while critically discussing TEP biological origin, biochemical and physical characteristics, and occurrence and distributions in aquatic systems. Moreover, we examine the contribution of TEP to biofouling of various membrane technologies used in the desalination and water/wastewater treatment industry. Emphasis is given to the link between TEP physicochemical and biological properties and the underlying biofouling mechanisms. We highlight that thorough understanding of TEP dynamics in feedwater sources, pretreatment challenges, and biofouling mechanisms will lead to better management of fouling/biofouling in membrane technologies.
Observations that the majority of silica dissolution occurs within the upper 200 m of the ocean, and that sedimentation rates of diatom frustules generally do not decrease significantly with depth, ...suggested reduced dissolution rates of diatoms embedded within sinking aggregates. To investigate this hypothesis, silica dissolution rates of aggregated diatom cells were compared to those of dispersed cells during conditions mimicking sedimentation below the euphotic zone. Changes in the concentrations of biogenic silica, silicic acid, cell numbers, chlorophyll
a and transparent exopolymer particles (TEP) were monitored within aggregates and in the surrounding seawater (SSW) during two 42-day experiments. Whereas the concentration of dispersed diatoms decreased over the course of the experiment, the amount of aggregated cells remained roughly constant after an initial increase. Initially only 6% of cells were aggregated and at the end of the experiment more than 60% of cells were enclosed within aggregates. These data imply lower dissolution rates for aggregated cells. However, fluxes of silica between the different pools could not be constrained reliably enough to unequivocally prove reduced dissolution for aggregated cells.
The marine diatom Thalassiosira pseudonana was grown in continuous culture systems to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO2 ...(pCO2) on its growth and physiological characteristics. The cells were able to grow at all combinations of low and high irradiance (50 and 300 μmol photons · m−2 · s−1, respectively, of visible light), low and high pCO2 (400 and 1,000 μatm, respectively), nutrient limitation (nitrate‐limited and nutrient‐replete conditions), and temperatures of 10–32°C. Under nutrient‐replete conditions, there was no adverse effect of high pCO2 on growth rates at temperatures of 10–25°C. The response of the cells to high pCO2 was similar at low and high irradiance. At supraoptimal temperatures of 30°C or higher, high pCO2 depressed growth rates at both low and high irradiance. Under nitrate‐limited conditions, cells were grown at 38 ± 2.4% of their nutrient‐saturated rates at the same temperature, irradiance, and pCO2. Dark respiration rates consistently removed a higher percentage of production under nitrate‐limited versus nutrient‐replete conditions. The percentages of production lost to dark respiration were positively correlated with temperature under nitrate‐limited conditions, but there was no analogous correlation under nutrient‐replete conditions. The results suggest that warmer temperatures and associated more intense thermal stratification of ocean surface waters could lower net photosynthetic rates if the stratification leads to a reduction in the relative growth rates of marine phytoplankton, and at truly supraoptimal temperatures there would likely be a synergistic interaction between the stresses from temperature and high pCO2 (lower pH).
The explosion of the Deepwater Horizon platform in the Gulf of Mexico in 2010 caused an oil spill that was unique in that it originated at great depth and persisted for an extended period of time, ...resulting in release of a very large quantity of oil and gas into the environment. What happened to all of this oil and gas? This paper briefly discusses the various physical, chemical, and biological processes that affected the fate and distribution of the spilled petrocarbon: some of the spilled oil was directly removed by mitigating measures, some was rapidly biodegraded, and some was deposited on the seafloor. Part of what remained entered food webs or contaminated shorelines. Consolidation of different estimates of the diverse distribution pathways provides a "guesstimate" budget that assesses the fate of the spilled petrocarbon after it partitioned between the deep plume and the sea surface.
Research funded under the Gulf of Mexico Research Initiative provided new insights into the biogeochemical processes influencing the fate of petroleum chemicals entering the Gulf of Mexico from the ...Deepwater Horizon (DWH) accident. This overview of that work is based on detailed recent reviews of aspects of the biogeochemistry as well as on activities supported by the US Natural Resource Damage Assessment. The main topics presented here are distribution of hydrocarbons in the water column; the role of photo-oxidation of petroleum compounds at the air-sea interface; the role of particulates in the fate of the DWH hydrocarbons, especially marine oil snow (MOS) and marine oil snow sedimentation and flocculent accumulation (MOSSFA); oil deposition and accumulation in sediments; and fate of oil on beaches and in marshes. A brief discussion of bioaccumulation is also included. Microbial degradation is addressed in a separate paper in this special issue of Oceanography. Important future research recommendations include: conduct a more robust assessment of the mass balance of various chemical groupings and even individual chemicals during specific time intervals; seek a better understanding of the roles of photo-oxidation products, MOS, and MOSSFA and their relationships to microbial degradation; and determine the fates of the insoluble highly degraded and viscous oil residues in the environment.
Future shifts in phytoplankton composition and productivity are anticipated given that continuing changes are expected in environmental conditions such as temperature, the partial pressure of CO₂ ...(pCO₂) and light climate, all of which regulate phytoplankton communities and their physiology through bottom-up control. Culture experiments revealed that future (elevated) pCO₂ had no effect on Thalassiosira weissflogii in the absence of environmental stressors, whereas growth rates drastically decreased under future pCO₂ when cells were grown under light and temperature stress. Reduction in growth rates and a smaller decline in cellular photosynthesis under high pCO₂ were associated with 2- to 3-fold increases in the production of transparent exopolymer particles (TEP) and in the cell quotas of organic carbon, as well as a similar decrease in the C:chl a ratios. Results suggest that under light- and temperature-stressed growth, elevated pCO₂ led to increased energy requirements, which were fulfilled by increased light harvesting capabilities that permitted photosynthesis of acclimatized cells to remain relatively high. This was combined with the inability of these cells to acclimatize their growth rate to sub-optimal temperatures. Consequently, growth rate was low and decoupled from photosynthesis, and this decoupling led to large cell sizes and high excretion rates in future pCO₂ treatments compared to ambient treatments when growth temperature and light were sub-optimal. Under optimal growth conditions, the increased energy demands required to re-equilibrate the disturbed acid-base balance in future pCO₂ treatments were likely mediated by a variety of physiological acclimatization mechanisms, individually too small to show a statistically detectable response in terms of growth rate, photosynthesis, pigment concentration, or excretion.
The sedimentation of oil via marine snow was observed during and after the Deepwater Horizon oil spill in 2010. We conducted laboratory experiments to characterize the chemical composition of oil ...associated with marine oil snow (MOS), identify mechanisms responsible for the incorporation of oil compounds into MOS, and describe the impact of the dispersant Corexit on oil incorporation into MOS. Phytoplankton was incubated in roller tanks in the presence or absence of Macondo crude oil and Corexit and the partitioning of n-alkanes and PAHs between MOS > 1 mm, the dissolved phase and particles <1 mm was analyzed.
Oil incorporation into MOS depended largely on the physiochemical properties of the respective oil compounds. Insoluble compounds, namely n-alkanes and high molecular weight (HMW) PAHs, were integrated into MOS within entire oil droplets that were scavenged by phytoplankton. The water-soluble fraction of the oil, namely low molecular weight PAHs, was sorbed by cells in MOS. Droplet incorporation took place immediately, while sorption only occurred after an experimental period longer than 1 day. The dispersant Corexit significantly increased the amount of oil trapped in MOS, and caused MOS to be enriched in HMW oil compounds, of which many act as toxins. Alteration of the chemical composition of oil in MOS after an experimental period of 4 days suggests biodegradation of oil compounds, especially in the presence of Corexit.
These results allow further insights into processes affecting MOS formation and sedimentation and assist future research and spill response planning.
Display omitted
•Incorporation of oil compounds into MOS depends on their physiochemical properties.•Trapping of oil drops by phytoplankton introduces insoluble oil compounds into MOS.•Sorption by phytoplankton introduces water-soluble oil compounds into MOS.•Dispersants increase the oil content of MOS.•Dispersants cause the enrichment of MOS in high molecular weight oil compounds.
Transparent exopolymer particles (TEP) are biologically derived, polysaccharide‐rich, gel‐like particles that play important roles in ocean carbon cycling. The original spectrophotometric method for ...TEP quantification published in 1995 by Passow and Alldredge describes staining TEP with the dye Alcian Blue (AB), and calibration of the AB staining solution using a commercially available polysaccharide xanthan gum (XG) powder as the reference material. In the original method, a XG solution is prepared to create gel‐like particles that resemble TEP. The solution is filtered to collect the XG gels onto a filter, and the filters are stained with AB solution. However, recently, it has been found that the XG powder commercially available today has higher solubility and forms negligible amounts of gel particles in solution, which precludes its use as described in the original method. Here, we present an updated calibration method to generate reproducible XG calibration curves using the currently available XG powder, whereby a XG dilution series is stained with AB solution prior to filtration resulting in AB‐stained XG gels that are retained on a filter. Subsequent extraction and spectrophotometric analysis are performed as described in the original method. The updated calibration method described here yielded calibration curves consistent with those reported in the original method. The updated method should only be used in the preparation of a calibration curve when the new soluble XG is available, whereas samples for TEP quantification should be processed as described in the original method.
Transparent exopolymer particles (TEP) form from polysaccharides released by many phytoplankton species, but this process by which dissolved organic matter becomes particulate is poorly understood. ...Here, the abiotic formation of TEP from precursors <0.2 μm and the minimum molecular weight (MW) of TEP-precursors were studied. In most samples TEP formed from material <0.2 μm (polycarbonate membrane filters, Poretics) when exposed to laminar shear in Couette flocculators. This result was unexpected as no TEP formed from material <0.45 μm (polycap capsules, Whatman) due to surface coagulation onto bubbles (Zhou et al. 1998; Limnol Oceanogr 43:1860–1871). Some TEP-precursors were able to pass through dialysis bags with a nominal pore size of 8 kDa (natural cellulose, Spektrum), although their MW is presumably 2 orders of magnitude larger, suggesting that TEP-precursors can be fibrillar. It is suggested that freshly released precursors are fibrillar and that these fibrillar precursors form larger colloids and eventually TEP within hours to days after their release.
PDF
