Effects of pH on aquatic biodegradation processes

Environmental context Fulvic acids account for a large proportion of dissolved organic matter in aquatic environments and affect the transportation and bioavailability of organic and inorganic pollutants. The structural and spectroscopic characteristics of fulvic acids mainly depend on the sources, seasons and anthropogenic activity. We present an advanced approach using fluorescence spectroscopy as a rapid and cost-effective method to investigate the composition, properties and origins of fulvic acids. Abstract Fulvic acids (FAs) isolated seasonally from the sediments of East Lake and Liangzi Lake in central China were comparatively investigated. The structural features of the FAs were characterised using chemical and spectroscopic methods, including elemental analysis, UV-Vis spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). The O/C, (O + N)/C and C/N ratios of FA extracted from Liangzi Lake (FAL) were higher than those of FA extracted from East Lake (FAE), indicating higher oxygen-containing functionality and polarity and less nutrient in FAL compared with FAE. The two FAs had similar UV-Vis spectra with different absorbance intensities. The FT-IR spectra showed that the two FAs had similar functional groups. The total fluorescence intensity and aromaticity of samples from Liangzi Lake were higher than those of East Lake except for those taken in the summer. The two FAs were largely terrestrially derived organic materials. Five fluorescent components, including four humic-like and two fulvic-like components, were identified by PARAFAC modelling of the EEM spectral data. The fluorescence was dominated by two components. The findings suggest that EEM fluorescence spectroscopy together with PARAFAC is a rapid and cost-effective method for understanding the characteristics and origins of FAs in natural water systems.

In colloids isolated from Chesapeake Bay and its subestuaries the concentrations of Al, Fe, and a number of trace elements were determined to vary with the clay mineral fraction that was most abundant in freshwater samples collected during the winter. The elements As, Ba, Sb, and Zn, however, increased with increasing organic content, indicating a covariance with the organic component. Organic analyses for amino acids (proteins), carbohydrates, and lipids indicate that these biopolymers comprised 4 to 22%, 20 to 60%, and less than 1%, respectively, of the colloidal organic carbon in these samples. The results are significant because amino acids and carbohydrates contain oxygen, nitrogen, and sulfur functional groups capable of reacting with trace metals and organic pollutants. The sorption properties of several neutral hydrophobic organic compounds, including PAHs and herbicides, and several aromatic amines were investigated using the estuarine colloidal material. The effects of several environmental variables on these sorption properties were determined. The results indicate that colloids have the capacity to sorb and transport relatively insoluble pollutants that otherwise might remain immobile in the environment. Colloidal organic matter in natural water systems (lakes, rivers, estuaries and the oceans, as well as groundwater) may serve as substrates for the sorption or binding of organic contaminants. Although most of the data has been developed using neutral hydrophobic organic compounds, data also exist for selected polar compound groups such as aromatic amines. The chemical behavior of these compound groups in interaction with DOM appears to have some similarity to their chemical interaction with sediments and soils. Partitioning constants are linear, except for polar compounds, and appear to be closely correlated to fundamental compound properties such as solubilities and octanol-water partition coefficients. Even though a variety of methods were used to collect the colloids for study and to determine partition coefficients, no single method appears to be superior. Ultrafiltration techniques appear to be optimal for collecting the colloids, since this method subjects the materials to less extreme chemical conditions than the preparation of humic extracts, whereas equilibrium techniques such as dialysis and head space analysis appear to yield the best results for partitioning constants. However, each of these techniques has limitations with respect to the classes of compounds that can be studied successfully.

There are two principal sources of organic matter in aquatic environments, living (biomass) and nonliving (detritus) (Odum and Cruz, 1963; Wetzel, 1983). It has long been noted that nonliving organic matter plays an important role in the structure and function of aquatic ecosystems (Krogh and Lange, 1932; Birge and Juday, 1934; Ohler 1934; Odum, 1963; Saunders, 1977). The detritus food chains were established along parallel lines with the classical phytoplankton-zooplankton grazing food chains. Wetzel et al. (1972) have developed a detailed scheme and model for the detritus food chain and have emphasized its fundamental differences from the classical grazing food chain. The nonpredatory loss of organic matter was found to be essential for understanding the whole aquatic ecosystem. Detrital organic matter tends to accumulate in aquatic environments until a quasi equilibrium is attained. This equilibrium is regulated by many environmental processes, such as decomposition, utilization, aggregation, and sedimentation.

In contrast to many other metal/metalloid contaminants, mercury (Hg) displays a complex environmental speciation behaviour. Widespread, detectable environmental Hg species include divalent mercury (Hg2+), elemental mercury (Hgo) and monomethylmercury (CH3Hg+). Less frequently encountered compounds include dimethylmercury ((CH3)2Hg; more common in marine environments), monovalent mercury (Hg22+; a species that disproportionates via the following reaction: Hg22+ ⟺ Hg2+ + Hgo) and, more recently, detectable quantities of ethylmercury compounds (e.g., C2H5Hg+, C2H5HgC2H5, etc.) have been reported in environmental media. Environmental mercury is frequently observed to be associated with natural organic matter in aquatic environments. The present study assesses the potential binding of Hg2+, Hgo, CH3Hg+ and (CH3)2Hg with natural organic matter by hydrophobic and ionic mechanisms. The findings suggest: (1) although potential hydrophobic binding with natural organic matter will likely occur in the following sequence (CH3)2Hg > Hgo > CH3HgX (where X = OH− or Cl−), none of these species appear to be strongly hydrophobic and hence, hydrophobic processes cannot explain observed organic matter-mercury associations in low-solids-content aquatic systems; (2) hydrophobic binding mechanisms of the various mercury species are insufficient to explain observed environmental bioconcentration factors; (3) ionic mercury binding with carboxyl-type sites on natural organic carbon is not sufficiently energetic to explain observed Hg-organic matter associations in the environment; and (4) environmental mercury binding with organic matter probably occurs through ionic reactions with naturally occurring sulfhydryl binding sites.

Freshwater ecosystems have been recognized as important components of the global carbon cycle, and the flux of organic matter (OM) from freshwater to marine environments can significantly affect estuarine and coastal productivity. The focus of this study was the assessment of carbon dynamics in two aquatic environments, namely the Florida Everglades and small prairie streams in Kansas, with the aim of characterizing the biogeochemistry of OM. In the Everglades, particulate OM (POM) is mostly found as a layer of flocculent material (“floc”). While floc is believed to be the main energy source driving trophic dynamics in this oligotrophic wetland, not much is known about its biogeochemistry. The objective of this study was to determine the origin/sources of OM in floc using biomarkers and pigment-based chemotaxonomy to assess specific biomass contributions to this material, on a spatial (freshwater marshes vs. mangrove fringe) and seasonal (wet vs. dry) scales. It was found that floc OM is derived from the local vegetation (mainly algal components and macrophyte litter) and its composition is controlled by seasonal drivers of hydrology and local biomass productivity. Photo-reactivity experiments showed that light exposure on floc resulted in photo-dissolution of POC with the generation of significant amounts of both dissolved OM (DOM) and nutrients (N & P), potentially influencing nutrient dynamics in this ecosystem. The bio-reactivity experiments determined as the amount and rate of CO2 evolution during incubation were found to vary on seasonal and spatial scales and were highly influenced by phosphorus limitation. Not much is known on OM dynamics in small headwater streams. The objective of this study was to determine carbon dynamics in sediments from intermittent prairie streams, characterized by different vegetation cover for their watershed (C4 grasses) vs. riparian zone (C3 plants). In this study sedimentary OM was characterized using a biomarker and compound specific carbon stable isotope approach. It was found that the biomarker composition of these sediments is dominated by higher plant inputs from the riparian zone, although inputs from adjacent prairie grasses were also apparent. Conflicting to some extent with the River Continuum Concept, sediments of the upper reaches contained more degraded OM, while the lower reaches were enriched in fresh material deriving from higher plants and plankton sources as a result of hydrological regimes and particle sorting.

Lactate and pH were measured in frontal and temporal cortex, cingulate gyrus, and caudate nucleus in brains from sudden infant death syndrome (SIDS) cases, control infants, and control adults. Both the lactate levels and the pH values were significantly correlated (p less than 0.001) between the four brain areas, whereas lactate and pH values were significantly correlated within each brain area (p less than 0.001) with a value of pH 7.2 for zero lactate. The lactate concentration in heart blood was significantly correlated with brain lactate (p less than 0.001). Adult sudden death cases (heart attacks) had low lactate and high pH values, whereas agonal state cases had high lactate and low pH values. Control infants who had died because of accidents also had low lactate and high pH values, but infants who might have been exposed to hypoxia before death had high lactate and low pH values. SIDS cases fell into two groups: the first, consisting of all victims over 30 weeks of age and about one-half to two-thirds of those aged less than 30 weeks, had low lactate and high pH values; the second group, consisting of about one-third to one-half of those less than 30 weeks old, had high lactate and low pH values. The changes in lactate levels and pH values indicate that the majority of SIDS cases had died suddenly, but that a sizeable minority had been exposed to hypoxia prior to death.

Wetlands are important global carbon sinks, an increasingly important ecosystem service. Invasive plants can disrupt wetland carbon budgets, although efforts to suppress invasive plants may also have unintended effects. Invasive Phragmites australis subsp. australis (European common reed) produces extensive monocultures that displace resident plant communities. In Long Point (Ontario, Canada), a glyphosate-based herbicide was used to control over 900 ha of P. australis. We determined how this ongoing management, and different environmental conditions, influence net primary productivity and decomposition rates. We compared above- and below-ground biomass, belowground:aboveground biomass ratios, standing dead stems, and litter in un-treated P. australis stands, in herbicide-treated areas, and in reference vegetation. We also conducted a reciprocal transplant experiment to measure the decomposition rates of plant litter. One-year post-treatment, control efforts dramatically reduced aboveground biomass (122 g/m2 ± 133 SD) compared to un-treated P. australis (1254 g/m2 ± 449 SD) and reference habitat (821 g/m2 ± 335 SD). An interaction between the plant community of the site and water depth predicted litter decomposition rates, with litter loss ranging from 5.75 to 74.65% across all species, and submerged litter decomposing faster. These results emphasize that secondary treatment, such as rolling, burning, or cutting, encourages the decomposition of dead P. australis stems, opening up space for the recovery of native plants. While herbicide-treated sites had low biomass immediately following treatment, aquatic vegetation began rapidly colonizing treated areas, suggesting that plant community recovery may restore the wetland carbon uptake in subsequent years.

The effects of pH (6.2, 7.2, 8.2, 9.2, and 10.2) under rising temperature (30 °C vs 20 °C) on Agarophyton vermiculophyllum growth and bio-physiology were investigated. Results showed that A. vermiculophyllum exhibited lower growth rates under elevated temperature in all pH values. Chlorophyll a, carotenoid, and phycocyanin levels were significantly enhanced by temperature elevation (p < 0.05). Enhanced H2O2 production either at lower or higher pH values correlated with lipid peroxidation (LPO) levels under elevated temperature, which suggested oxidative stress development. Oxidative damage was more severe at elevated pH values, which is confirmed by higher reactive oxygen species (ROS) levels. Compared with ambient pH 8.2 value, lower pH values under elevated temperature lead to increase activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST), indicating that these enzymes played an important role to combat stress. However, decreased glutathione reductase (GR) and glutathione peroxidase (GPx) activities indicate least contribution for ROS scavenging at lower pH values. On contrary, SOD and CAT declined at elevated pH values compared with ambient pH, suggesting least contribution for ROS removal. Moreover, enhanced GR and GPx activities at elevated pH and temperature are not enough to scavenge ROS production. These data are consistent with higher H2O2 and LPO levels, and lower GST activities. Collectively, our results indicated that either pH fluctuations or elevated temperature displayed a disadvantageous influence on growth and bio-physiology of A. vermiculophyllum. Therefore, rising temperature alleviates adverse effects of seawater acidification, but it aggravates the negative effects of seawater alkalization on growth and bio-physiology of A. vermiculophyllum.

Litter decomposition and organic matter turnover in northern forest soils

Fish waste management is one of the main problems in fishing industry which can be possible to eliminate through making compost. Though nutrient content is high in fish waste and most of the nutrients are removed from final product during composting process due to low decomposition rate. The present study was carried out to increase decomposition rate by adding different additives to fish waste compost at International Food Stuff Company Farm at Kamburupitiya in October 2014. Pit method was used for making compost and two additives, i.e., sulfuric acid and citric acid were used with two concentrations (0.5 ppm and 1.0 ppm). Five treatments i.e., fish waste compost treated with 1.0 ppm sulfuric acid (T1), fish waste compost treated with 0.5 ppm sulfuric acid (T2), fish waste compost treated with water (control) (T3), fish waste compost treated with 0.5 ppm citric acid (T4) and fish waste compost treated with 1.0 ppm citric acid (T5) were used as treatments and pits were arranged in complete randomised block design (RCBD) with tri-replicates. Temperature, pH, EC, nitrogen, phosphorous, potassium and particle size distribution of end product was taken as variables. Data were analysed using ANOVA. Fish waste compost treated with water showed maximum temperature within three days time while acid treated fish waste composts (T1,T2,T4 and T5) took five days time to reach their maximum temperature.1.0 ppm sulfuric acid treated fish waste compost showed significantly lower (P<0.05) pH value than all other treatments while pH ranges from 5.4 to 6.5 in all the treatments. Significantly higher (P<0.05) EC value (961 μs/cm) was in acid treated fish waste compost and lowest value (583 μs/cm) was in control treatment. Significantly higher (P<0.05) nitrogen content (0.5016 g/kg) was recorded in T1 followed by fish waste compost treated with others (T1,T2,T4 and T5) respectively. Fish waste compost treated with 1ppm sulfuric acid showed significantly higher phosphorous concentration (46.4 ppm) while T3 showed significantly lower phosphorous (35.62 ppm). With regard to phosphorous, there was no significant difference among all other acid treated fish waste compost was detected. Compared to all acid treated fish waste compost potassium concentration was higher in control treatment (36.40 ppm). There was no significant difference in particle size distribution of all the treatments was detected. Acid treatment showed positive effect on nitrogen and phosphorous availability while negative effect on potassium availability of fish waste compost. This trend increased with the increment of the concentration of acid. Among the different fish waste compost mixtures, 1.0 ppm sulfuric treated fish waste compost showed higher N and P content and low K content with better pH and EC values compared to all other treatments. Therefore, 1.0 ppm sulfuric acid could be used as additive for treating fish waste compost.

In this paper, the capture of radiocadmium (Cd(II)) by adsorption onto the titanate nanotube/iron oxide (TNT/IOM) magnetic composite as a function of contact time, pH, ionic strength, foreign cation and anion ions, humic acid (HA) and fulvic acid (FA) was studied using batch technique. The results indicated that the adsorption of Cd(II) onto the TNT/IOM magnetic composite was dependent on ionic strength at pH 9.0. Outer-sphere surface complexation were the main mechanism of Cd(II) adsorption onto the TNT/IOM magnetic composite at low pH values, whereas the adsorption was mainly dominated via inner-sphere surface complexation at high pH values. The adsorption of Cd(II) onto the TNT/IOM magnetic composite was dependent on foreign cation and anion ions at low pH values, but was independent of foreign cation and anion ions at high pH values. A positive effect of HA/FA on Cd(II) adsorption onto the TNT/IOM magnetic composite was found at low pH values, while a negative effect was observed at high pH values. From the results of Cd(II) removal by the TNT/IOM magnetic composite, the optimum reaction conditions can be obtained for the maximum removal of Cd(II) from water. It is clear that the best pH values of the system to remove Cd(II) from solution by using the TNT/IOM magnetic composite are 7.0–8.0. Considering the low cost and effective disposal of Cd(II)-contaminated wastewaters, the best condition for Cd(II) capture by the TNT/IOM magnetic composite is at room temperature and solid content of 0.5 g L−1. These results are quite important for estimating and optimizing the removal of Cd(II) and related metal ions by the TNT-based magnetic composite.

The extremely acidic environment of the mammalian stomach, with a pH range usually between 1 and 3, represents a stressful challenge for enteric pathogenic bacteria such as Escherichia coli before they enter into the intestine. The hdeA gene of E. coli was found to be acid inducible and was revealed by genetic studies to be important for the acid survival of the strain. This study was performed in an attempt to characterize the mechanism of the activity of the HdeA protein. Our data provided in this report strongly suggest that HdeA employs a novel strategy to modulate its chaperone activity: it possesses an ordered conformation that is unable to bind denatured substrate proteins under normal physiological conditions (i.e. at neutral pH) and transforms into a globally disordered conformation that is able to bind substrate proteins under stress conditions (i.e. at a pH below 3). Furthermore, our data indicate that HdeA exposes hydrophobic surfaces that appear to be involved in the binding of denatured substrate proteins at extremely low pH values. In light of our observations, models are proposed to explain the action of HdeA in both a physiological and a molecular context.

Short-term facilitation of microbial litter decomposition by ultraviolet radiation

Heat sterilization of peritoneal dialysis solutions influences ingestive behavior in non-uremic rats

Sorption behavior of Eu(Ⅲ) on Tamusu clay under strong ionic strength: Batch experiments and BSE/EDS analysis