Phototrophic biofilm activity and dynamics of diurnal Cd cycling in a freshwater stream

Optimization of H2O2 Production in Biological Systems for Design of Bio-Fenton Reactors

The treatment of antibiotic wastewater, which is known for its micro-toxicity, inhibition, and poor biochemistry, poses significant challenges, including complex processes, high energy demands, and secondary pollution. Bio-Fenton, a novel Fenton technology, enables the in situ production of H2O2 at near-neutral pH, having low energy requirements and sustainable properties, and reduces the hazards of H2O2 transportation and storage. We preliminary self-designed a heterogeneous Bio-Fenton reactor. An aerobic SBBR system with pure algae, pure bacteria, and bacteria-algae symbiosis was first constructed to investigate the optimal process conditions through the effects of carbon source concentration, light duration, bamboo charcoal filling rate, and dissolved oxygen (DO) content on the H2O2 production and COD removal. Second, the reactor was constructed by adding iron-carrying catalysts to remove ROX and SDZ wastewater. The results demonstrated that the optimal operating parameters of aerobic SBBR were an influent carbon source concentration of 500 mg/L, a water temperature of 20 ± 2 °C, pH = 7.5, a dissolved oxygen content of 5 mg/L, a light-dark ratio of 12 h:12 h, a light intensity of 2500 Lux, an HRT of 10 h, and a bamboo charcoal filling rate of 33%. Given these conditions, the bacterial-algal system was comprehensively found to be the most suitable biosystem for this experiment. Ultimately, the dynamically coupled Bio-Fenton process succeeded in the preliminary removal of 41.32% and 42.22% of the ROX and SDZ from wastewater, respectively.

Diversity characterization of bacteria and fungi in water, sediments and biofilms from Songhua River in Northeast China

Water, sediments, and biofilms are the typical microbial carriers in natural water environments. However, comparative analysis of the distribution of bacterial and fungal communities in different carriers within the same habitat is relatively lacking. Therefore, this study employed 16 S and ITS rRNA gene sequencing to identify bacterial and fungal community structures in water, sediments, and biofilm. The results show that (1) the OTUs numbers revealed that the bacterial abundance, at the levels of species, genus, and family, followed the order of sediments > water > biofilms, while the fungal abundance order was water > sediments > biofilms. In addition, bacteria were mainly present in sediments, while fungi were mainly present in water. (2) The α diversity index (Shannon, ACE, Simpson, and Chao1) order, for bacteria was: sediments > water > biofilms, indicating that the diversity and homogeneity of bacteria in sediments were relatively higher; for fungi was: water > sediments > biofilms, indicating that the diversity and abundance of fungi in water were high. (3) The core phylum of bacterial in the water, sediments, and biofilms was Cyanobacteria (31.3-46.1%) and Actinobacteria (27.6-36.1%); Proteobacteria (35.0-41.8%), Cyanobacteria (14.7-36.6%); and Proteobacteria (63.3-69.2%), respectively. (4) The mainly colonized fungal phyla in biofilms in the water, sediments, and biofilms were Basidiomycota (29.3-38.7%) and Ascomycota (16.2-27.7%); Zygomycota (13.1-17.5%), Basidiomycota (5.6-17.6%); and Zygomycota (23.8-44.2%). (5) There were significant species differences in bacterial and fungal communities in water, sediments, and biofilm by NMDS analysis. Findings are useful for guiding significance for the Biogeochemical cycle of elements, the environmental fate of pollutants, and the study of water ecosystems.

On-Chip Antifouling Gel-Integrated Microelectrode Arrays for In Situ High-Resolution Quantification of the Nickel Fraction Available for Bio-Uptake in Natural Waters

We aimed to monitor in situ nickel (Ni(II)) concentrations in aquatic systems in the nanomolar range. To achieve this, we investigated whether an analytical protocol for the direct quantification of cobalt (Co(II)) using adsorptive cathodic sweep voltammetry (Ad-CSV) on antifouling gel-integrated microelectrode arrays (GIME) we recently developed is also suitable for direct Ni(II) quantification. The proposed protocol consists of the reduction of the complex formed between Ni(II) (or Ni(II) and Co(II)) and nioxime adsorbed on the surface of the GIME-sensing element. The GIME enables to (i) avoid fouling, (ii) control the metal complex mass transport and, when interrogated by Ad-CSV, (iii) selectively determine the dynamic (kinetically labile Ni-nioxime) fraction that is potentially bioavailable. The nioxime concentration and pH were optimized. A temperature correction factor was determined. The limit of detection established for 90 s of accumulation time was 0.43 ± 0.06 in freshwater and 0.34 ± 0.02 nM in seawater. The sensor was integrated in a submersible probe in which the nioxime-containing buffer and the sample were mixed automatically. In situ field measurements at high resolution were successfully achieved in Lake Geneva during a diurnal cycle. The determination of the kinetically labile Ni-nioxime fraction allows one to estimate the potential ecotoxicological impact of Ni(II) in Lake Geneva. Additional Ni fractions were measured by ICP-MS and coupled to the in situ Ad-CSV data to determine the temporal Ni(II) speciation.

New insights into trace metal speciation and interaction with phytoplankton in estuarine coastal waters

In coastal productive zones, phytoplankton activity may influence trace metal speciation and partitioning at short temporal scale. We coupled hourly in situ voltammetry quantification of the lead (Pb), cadmium (Cd), and copper (Cu) potentially bioavailable fractions, using an innovative submersible sensing probe (the TracMetal), to surface water sampling for the quantification of the targeted trace metals in the dissolved <0.2 μm and <0.02 μm fractions, suspended particles, and phytoplankton nets in the Gironde Estuary mouth. The in situ TracMetal monitoring reflected real-time dynamic Cd and Cu regeneration related to algal cells under post-bloom conditions as well as Pb remobilization due to photoreduction of colloids. The potentially bioavailable fraction consisted in 30, 30-50 and <10 % of the total dissolved fraction for Pb, Cd, and Cu, respectively, representing crucial ecotoxicological information. Metal bioconcentration factors using the dynamic fraction concentrations showed levels up to 10⁷ for Cu in phytoplankton.

Advanced multichannel submersible probe for autonomous high-resolution in situ monitoring of the cycling of the potentially bioavailable fraction of a range of trace metals

We report here on the development and application of a submersible, compact, low power consumption, integrated multichannel trace metal sensing probe (TracMetal). This probe is unique in that it allows high-resolution, simultaneous in-situ measurements of the potentially bioavailable (so-called dynamic) fraction of Hg(II), As(III), Cd(II), Pb(II), Cu(II), Zn(II). The TracMetal incorporates nanostructured Au-plated and Hg-plated gel-integrated microelectrode arrays. In addition to be selective to the fraction of metal potentially bioavailable, they offer protection against fouling and ill-controlled convective interferences. Sensitivities in the low pM for Hg(II) and sub-nM for the other target trace metals is achieved with precision ≤ 12%. The TracMetal is capable of autonomous operation during deployment, with routines for repetitive measurements (1-2 h^-1), data storage and management, data computer visualization, and wireless data transfer. The system was successfully applied in the Arcachon Bay, to study the temporal variation of the dynamic fraction of the trace metals targeted. The in situ autonomous TracMetal measurements were combined with in situ measurements of the master bio-physicochemical parameters and sample collection for complementary measurements of the dissolved metal concentrations, organic matter concentrations and proxy for biological activities. The integration of all data revealed that various biotic and abiotic processes control the temporal variation of the dynamic fractions of the target metals (Me_dyn). The difference in the percentage of the dynamic forms of the metals studied and the short-term processes influencing their variation highlight the TracMetal potentiality as metal bioavailability-assessment sentinel to achieve comprehensive environmental monitoring of dynamic aquatic systems.

PHYSICAL AND CHEMICAL CONNECTIVITY OF STREAMS AND RIPARIAN WETLANDS TO DOWNSTREAM WATERS: A SYNTHESIS

Streams, riparian areas, floodplains, alluvial aquifers and downstream waters (e.g., large rivers, lakes, oceans) are interconnected by longitudinal, lateral, and vertical fluxes of water, other materials and energy. Collectively, these interconnected waters are called fluvial hydrosystems. Physical and chemical connectivity within fluvial hydrosystems is created by the transport of nonliving materials (e.g., water, sediment, nutrients, contaminants) which either do or do not chemically change (chemical and physical connections, respectively). A substantial body of evidence unequivocally demonstrates physical and chemical connectivity between streams and riparian wetlands and downstream waters. Streams and riparian wetlands are structurally connected to downstream waters through the network of continuous channels and floodplain form that make these systems physically contiguous, and the very existence of these structures provides strong geomorphologic evidence for connectivity. Functional connections between streams and riparian wetlands and their downstream waters vary geographically and over time, based on proximity, relative size, environmental setting, material disparity, and intervening units. Because of the complexity and dynamic nature of connections among fluvial hydrosystem units, a complete accounting of the physical and chemical connections and their consequences to downstream waters should aggregate over multiple years to decades.

Mercury bioavailability, transformations, and effects on freshwater biofilms

Mercury (Hg) compounds represent an important risk to aquatic ecosystems because of their persistence, bioaccumulation, and biomagnification potential. In the present review, we critically examine state-of-the-art studies on the interactions of Hg compounds with freshwater biofilms, with an emphasis on Hg accumulation, transformations, and effects. Freshwater biofilms contain both primary producers (e.g., algae) and decomposers (e.g., bacteria and fungi), which contribute to both aquatic food webs and the microbial loop. Hence they play a central role in shallow water and streams, and also contribute to Hg trophic transfer through their consumption. Both inorganic and methylated mercury compounds accumulate in biofilms, which could transform them mainly by methylation, demethylation, and reduction. Accumulated Hg compounds could induce diverse metabolic and physiological perturbations in the microorganisms embedded in the biofilm matrix and affect their community composition. The bioavailability of Hg compounds, their transformations, and their effects depend on their concentrations and speciation, ambient water characteristics, biofilm matrix composition, and microorganism-specific characteristics. The basic processes governing the interactions of Hg compounds with biofilm constituents are understudied. The development of novel conceptual and methodological approaches allowing an understanding of the chemo- and biodynamic aspects is necessary to improve the knowledge on Hg cycling in shallow water as well as to enable improved use of freshwater biofilms as potential indicators of water quality and to support better informed risk assessment. Environ Toxicol Chem 2017;36:3194-3205. © 2017 SETAC.

Impact of chronic lead exposure on metal distribution and biological effects to periphyton

Chronic Pb exposure microcosm studies were carried out on two different periphyton communities over the course of 3 weeks to link Pb distribution to biological effects in periphyton. We show that three-week exposures of periphyton to 20.6 ± 0.4 μM PbT (330 nM Pb(2+)) did not have observable biological effects on photosynthesis, respiration, extracellular enzymatic activities, or biomass accrual. Metal distribution studies showed that the majority of Pb was associated with the operationally defined sorbed and non-EDTA-exchangeable fractions, and relatively little with extracellular polymeric substances (EPS). No significant effects of Pb on Fe and Mn distributions were observed, whereas higher Cu accumulation occurred from increased free Cu(2+) in the exposure medium. High Fe:C and Mn:C ratios indicated the presence of inorganic Fe and Mn material associated with the non-EDTA-exchangeable fraction, which likely sequesters Pb and explains the absence of measurable biological effects. Although no toxic effects of Pb were observed on the periphytic organisms themselves, periphyton can be a significant source of Pb to grazing organisms in aquatic ecosystems.

The degradation of linear alkylbenzene sulfonate (LAS) in the presence of light and natural biofilms: the important role of photosynthesis

Photosynthesis of algae usually changes the chemical conditions of microenvironment in natural waters. However, few studies have been carried out to examine the effects of diurnal variation and photosynthesis on behavior of organic pollutants in aquatic environments. In this study, linear alkylbenzene sulfonate (LAS) was selected as a representative of non-persistent organic pollutants to investigate the degradation of this type of pollutants in the presence of light and natural biofilms by laboratory batch experiments, with special emphasis on the effect of photosynthesis of the biofilms. The maximum decrease of LAS was observed in the coexistence of both illumination and fully active biofilms, and about 75% of the LAS were removed after a 36-h degradation experiment. The removal of LAS was found to be dominated by photosynthesis of the biofilms, with lesser roles attributed to biodegradation and adsorption by the biofilms, and the role of direct photolysis was negligible. The production of some reactive oxygen species might account for the role of photosynthesis in decomposing the LAS. The study confirms the important roles of algae biofilms and their photosynthesis in determining the fate of organic pollutants in aquatic environments.

Long-term water-quality changes in East Fork Poplar Creek, Tennessee: background, trends, and potential biological consequences

We review long-term changes that have occurred in factors affecting water quality in East Fork Poplar Creek (EFPC; in East Tennessee) over a nearly 25-year monitoring period. Historically, the stream has received wastewaters and pollutants from a major United States Department of Energy (DOE) facility on the headwaters of the stream. Early in the monitoring program, EFPC was perturbed chemically, especially within its headwaters; evidence of this perturbation extended downstream for many kilometers. The magnitude of this perturbation, and the concentrations of many biologically significant water-quality factors, has lessened substantially through time. The changes in water-quality factors resulted from a large number of operational changes and remedial actions implemented at the DOE facility. Chief among these were consolidation and elimination of many effluents, elimination of an unlined settling/flow equalization basin, reduction in amount of blow-down from cooling tower operations, dechlorination of effluents, and implementation of flow augmentation. Although many water-quality characteristics in upper EFPC have become more similar to those of reference streams, conditions remain far from pristine. Nutrient enrichment may be one of the more challenging problems remaining before further biological improvements occur.

Assessing contaminated sediments in the context of multiple stressors

Sediments have a major role in ecosystem functioning but can also act as physical or chemical stressors. Anthropogenic activities may change the chemical constituency of sediments and the rate, frequency, and extent of sediment transport, deposition, and resuspension. The importance of sediments as stressors will depend on site ecosystem attributes and the magnitude and preponderance of co-occurring stressors. Contaminants are usually of greater ecological consequence in human-modified, depositional environments, where other anthropogenic stressors often co-occur. Risk assessments and restoration strategies should better consider the role of chemical contamination in the context of multiple stressors. There have been numerous advances in the temporal and spatial characterization of stressor exposures and quantification of biological responses. Contaminated sediments causing biological impairment tend to be patchy, whereas more pervasive anthropogenic stressors, such as alterations to habitat and flow, physical disturbance, and nutrient addition, may drive large-scale ecosystem responses. A systematic assessment of relevant ecosystem attributes and reference conditions can assist in understanding the importance of sediments in the context of other stressors. Experimental manipulations then allow for the controlled study of dominant stressors and the establishment of causal links. This approach will result in more effective management of watersheds and waterways.