Measurement of light absorption by aquatic particles retained on filters: determination of the optical pathlength amplification by the 'transmittance-reflectance' method

The optical pathlength amplification (ß factor), inducedby multiple scattering in glass-fibre filters used for lightabsorption measurements of aquatic particles, has been measuredby the transmittance-reflectance (T-R) method for algal specieswith cell diameter in the range from 1 to 5 µm. Theßfactors obtained showed a much lower dispersion than that observedin similar measurements carried out by the standard transmittancemethod, suggesting that this could be due, at least in part,to the incomplete account of the scattering losses taken bythe latter method. An experimental test has verified that theß factor expression derived from measurements carriedout by the T-R method on an algal culture is also applicableto detrital particles.     

A sensitivity analysis of the 'Transmittance-Reflectance' method for measuring light absorption by aquatic particles

A thorough sensitivity analysis of the ‘Transmittance–Reflectance’(T-R) method for measuringin vivo light absorption by aquaticparticles retained on glass-fiber filters has been carried out.Particular attention has been devoted to the error contributionby the variability of the optical properties of the GF/F filtersused. The overall error of the measurement of the filter-retainedparticle optical density, OD_s, has been evaluated as ~0.002(1), with 0.0015 error contribution by the filter variability.The corresponding error of the optical density of the particlesuspension, OD_sus, has been obtained by differentiation of theequation expressing the experimental correlation (OD_susversusOD_s); the error increases with the optical density value, from= 0.0015 (for OD_sus = 0.05) to = 0.027 at the upper limit ofthe optical density range tested (OD_sus = 0.59). The validityrange of the experimental (OD_sus versus OD_s) correlation hasbeen shown to extend to OD_s = 0.75. The importance of the accuratecorrection for light backscattering performed by the T-R methodhas been investigated by comparison with results given by thestandard ‘Transmittance’ (T) method; it has beenshown that the coarse correction for light scattering includedin the T method may cause serious errors in the measured opticaldensity spectra of mineral detritus. This evidence confirmsthe need to resort to the T-R method for the measurement ofparticle samples of detritus-rich coastal waters. The papersummarizes the latest developments of the T-R method and includesan Appendix with asynopsis of the routine now used by the authors.     

Proposal for the simultaneous measurement of light absorption and backscattering by aquatic particulates

The paper presents a new experimental method that measures lightabsorption and backscattering by aquatic particles, combiningthe innovative features of the ‘modified filter–transfer–freeze’(FTF) and ‘transmittance–reflectance’ (T-R)techniques, namely no path-length amplification and accuratecorrectionfor scattering loss, respectively. This method (in short: theFTF/T-R method) measures both the transmittance and the reflectanceof particles deposited on a glass slide, using a double-beamspectrophotometer equipped with an integrating-sphere attachment.The data are interpreted by an algorithm that yields both theabsorption and the backscattering coefficients of the particlesample. The paper includes a summary of results of validationtests, that have been performed using samples ranging from purephytoplankton (low light scattering) to pure detrital particles(high light scattering), as well as a detailed analysis of theexperimental error. The FTF/T-R measurement is somewhat morelaborious than the standard transmittance measurement of particlesretained on glass fibre filters. However, it has the importantasset of permitting the simultaneous determination of lightabsorption and backscattering and it yields more accurate absorptiondata in situations where the magnitude of path amplificationby glass fibre filters is uncertain and light scattering bythe particles is high.     

A method for the experimental determination of light absorption by aquatic heterotrophic bacteria

A method has been set up for the experimental determinationof the volume coefficient for light absorption in vivo by aquaticheterotrophic bacteria. The application described here is theabsorption measurement of the bacterial fraction that passesthrough the commonly used GF/F ifiter and remains unaccountedfor. The experimental samples were prepared by successive waterfiltra tions through GF/F and 0.22 µm Millipore membranes.Light-transmission and light-reflection measurements of thefilter-retained samples were performed using a dual-beam spectrophotometerequipped with an integrating sphere attachment. Sample absorptionwas derived from the data by a procedure that corrects for thecontamination of the results due to the high degree of lightscattering by the bacteria. The bacterial absorption was discriminatedfrom fine detritus absorption by bleaching the bacterial respiratorypigments using a K₂S₂O₈ solution. The absorption amplificationcaused by multiple scattering in the filter was corrected forby an expression that was obtained experimentally. A test ofthe method, including error analysis, was performed on samplescollected in both marine and inland waters. The relative contributionsto light absorption by heterotrophic bacteria and various typesof particulate matter were also measured for a typical situation.Combining the measured volume absorption coefficients with backscatteringcoefficients computed by Mie theory yields a set of input datato multicomponent optical models that is needed to assess thecontribution of these heterotrophic bacteria to the radiativetransfer process.     

Seasonal cholera caused by Vibrio cholerae serogroups O1 and O139 in the coastal aquatic environment of Bangladesh

Since Vibrio cholerae O139 first appeared in 1992, both O1 El Tor and O139 have been recognized as the epidemic serogroups, although their geographic distribution, endemicity, and reservoir are not fully understood. To address this lack of information, a study of the epidemiology and ecology of V. cholerae O1 and O139 was carried out in two coastal areas, Bakerganj and Mathbaria, Bangladesh, where cholera occurs seasonally. The results of a biweekly clinical study (January 2004 to May 2005), employing culture methods, and of an ecological study (monthly in Bakerganj and biweekly in Mathbaria from March 2004 to May 2005), employing direct and enrichment culture, colony blot hybridization, and direct fluorescent-antibody methods, showed that cholera is endemic in both Bakerganj and Mathbaria and that V. cholerae O1, O139, and non-O1/non-O139 are autochthonous to the aquatic environment. Although V. cholerae O1 and O139 were isolated from both areas, most noteworthy was the isolation of V. cholerae O139 in March, July, and September 2004 in Mathbaria, where seasonal cholera was clinically linked only to V. cholerae O1. In Mathbaria, V. cholerae O139 emerged as the sole cause of a significant outbreak of cholera in March 2005. V. cholerae O1 reemerged clinically in April 2005 and established dominance over V. cholerae O139, continuing to cause cholera in Mathbaria. In conclusion, the epidemic potential and coastal aquatic reservoir for V. cholerae O139 have been demonstrated. Based on the results of this study, the coastal ecosystem of the Bay of Bengal is concluded to be a significant reservoir for the epidemic serogroups of V. cholerae.     

Population dynamics of aquatic bacteria in relation to environment change as measured by factor analysis

In order to determine the relationship changes in river water bacteria populations and environmental changes, a multivariate statistical analysis, factor analysis was performed on two datasets: one the bacterial test responses, the other certain physicochemical parameters of the water. When sampling bacteria from natural environments, the process is highly selective and the question of the representative nature of the population arises. If a relationship between the environment and the predominant bacterial population can be established, there is an increased level of confidence in the ecological significance of the observed population.Bacterial isolates from river water were examined for positive and negative responses to 223 physiological and nutritional tests. The dichotomous database was factor analyzed. Each factor was interpreted according to its major biological attributes. A parallel dataset on 19 physical and chemical parameters was also analysed for factors. The two datasets were correlated and a relationship was demonstrated between the physiological attributes of the bacterial population and the environmental parameters was also analyzed for factors. The two datasets were correlated and a relationship was bacteria was related to ion concentration and specific conductance. Subtile changes in nutrient and oxygen levels were shown to relate to shifts from nitrate reduction to nutrification. The analytical method demonstrates the possibility of expanding the measurement of the parameters controlling bacterial populations by multivariate statistics without loss of the essential variance.     

Consumption of aquatic subsidies by soil invertebrates in coastal ecosystems

Routes of aquatic allochthonous inputs (aquatic subsidies) to detrital food webs are studied, as is the effect of aquatic subsidies on the functional and taxonomic structure of soil invertebrate communities in coastal ecosystems. The study took place in the coastal zone of an oxbow lake of the Pra River in the Oka Reserve. The results indicate a strong dependence of soil animals in the coastal habitats on aquatic subsidies. Isotopic analysis shows that aquatic resources enter soil food webs not only via predators feeding on flying insects or aquatic prey, but also via saprophages decomposing organic debris of aquatic origin. The contribution of aquatic subsidies to the energy balance of soil invertebrates decreases rapidly with increasing distance from the lake. The fraction of aquatic carbon in tissues of collembolans and saprophages is negligible already a few meters from the water edge. The dependence of predatory invertebrates on aquatic resources can be traced at somewhat greater distance (tens of meters).     

Diversity of Salmonella strains isolated from the aquatic environment as determined by serotyping and amplification of the ribosomal DNA spacer regions

Salmonella species are pathogenic bacteria often detected in sewage, freshwater, marine coastal water, and groundwater. Salmonella spp. can survive for long periods in natural waters, and the persistence of specific and epidemic strains is of great concern in public health. However, the diversity of species found in the natural environment remains unknown. The aim of this study was to investigate the diversity of Salmonella strains isolated from different natural aquatic systems within a Mediterranean coastal watershed (river, wastewater, and marine coastal areas). A total of 574 strains isolated from these natural environments were identified by both conventional serotyping and the ribosomal spacer-heteroduplex polymorphism (RS-HP) method (M. A. Jensen and N. Straus, PCR Methods Appl. 3:186-194, 1993). More than 40 different serotypes were found, and some serotypes probably mobilized from widespread animal-rearing activities were detected only during storm events. These serotypes may be good indicators of specific contamination sources. Furthermore, the RS-HP method based on the PCR amplification of the intergenic spacer region between the 16S and 23S rRNA genes can produce amplicon profiles allowing the discrimination of species at both serotype and intraserotype levels. This method represents a powerful tool that could be used for rapid typing of Salmonella isolates.     

Beta-propeller phytases in the aquatic environment

Phytate, which is one of the dominant organic phosphorus compounds in nature, is very stable in soils. Although a substantial amount of phytate is carried from terrestrial to aquatic systems, it is a minor component of organic phosphorus in coastal sediments. The ephemeral nature of phytate implies the rapid hydrolysis of phytate under aquatic conditions. Among the four classes of known phytases that have been identified in terrestrial organisms, only β-propeller phytase-like sequences have been identified in the aquatic environment. A novel β-propeller phytase gene (phyS), cloned from Shewanella oneidensis MR-1, was found to encode a protein with two beta-propeller phytase domains. The characterization of recombinant full-length PhyS and its domains demonstrated that Domain II was the catalytic domain responsible for phytate hydrolysis. The full-length PhyS displayed a K_m of 83 μM with a kcat of 175.9 min⁻¹ and the Domain II displayed a K_m of 474 μM with a kcat of 10.6 min⁻¹. These results confirm that the phyS gene encodes a functional β-propeller phytase, which is expressed in S. oneidensis under phosphorus deficienct condition. The presence of multiple sequences with a high similarity to phyS in aquatic environmental samples and the widespread occurrence of the Shewanella species in nature suggest that the β-propeller phytase family is the major class of phytases in the aquatic environment, and that it may play an important role in the recycling of phosphorus.     

Calculating light scattering when determining true absorption magnitudes of virus particles

Results of the study by V. I. Permogorov et al. (Molecular Biology, 1977, 11, 134--138) on the absence of a deficit of hypochromism in intraphage DNA are discussed. It is deduced that the conclusion of V. I. Permogorov and coworkers is erroneous since it is based on: 1) incorrect interpretation of the results of determination of lightscattering contribution to the absorption of intact phages; 2) not taking into account the lightscattering contribution in the case of disrupted phages; 3) underestimation of the value of hyperchromism of melting of phage DNAs.     

Survival ofLegionella pneumophila in the aquatic environment

Survival ofLegionella pneumophila SG 1 in seawater and river water was assessed using plate counts on buffered charcoal yeast extract agar amended with α-ketoglutarate (BCYEα) and [³H]thymidine-labeling. The [³H]thymidine-labeling method for assessing survival ofL. pneumophila in aquatic environments was compared with viable counts, direct fluorescent microscopy (DFA), and acridine orange direct counts (AODC). Protozoa were isolated from the samples employed in the study and identified by characteristic trophozite and cyst morphology. Selective filtration employing 2.0 μm Nucleopore filters was used to determine the effect of grazing on survival ofL. pneumophila in seawater and river water.Legionella viability as measured by plate counts (CFU/ml), declined to a greater extent than cell lysis, assessed by thymidine, DFA, and AODC counts, suggesting thatL. pneumophila survives in aquatic habitats to a greater extent than revealed through culturable counts.     

How to avoid pharmaceuticals in the aquatic environment

Pharmaceuticals and other micropollutants in wastewater pose a new challenge to wastewater professionals as well as to the pharmaceutical industry. Although there is a great deal of uncertainty concerning the possible detrimental effects on the aquatic ecosystems, the precautionary principle--or possibly new scientific evidence--may give rise to more stringent demands on wastewater treatment in the future. In conventional wastewater treatment plants, a combination of biological treatment with high sludge residence times and ozonation of the effluent seems to be the most promising technology. Ozonation, however, is an energy-intensive technology. Moreover, in conventional end-of-pipe systems a large part of the pollutants will always be lost to the environment due to leaking, primarily during rain. In the long term, source separation offers the more sustainable solution to the entire wastewater problem, including organic micropollutants. Urine source separation is an elegant solution to the problems of nutrients and pharmaceuticals alike and losses of untreated pollutants to the environment can be minimized. Although few technologies for the separate treatment of urine have been developed to date, the 100-500 times higher concentrations of micropollutants promise more efficient conditions for all removal technologies known from conventional wastewater treatment.     

Veterinary antibiotics in the aquatic and terrestrial environment

The fate of antibiotics in the environment, and especially antibiotics used in animal husbandry, is subject to recent studies and the issue of this review. The assumed quantity of antibiotics excreted by animal husbandry adds up to thousands of tonnes per year. Administered medicines, their metabolites or degradation products reach the terrestrial and aquatic environment by the application of manure or slurry to areas used agriculturally, or by pasture-reared animals excreting directly on the land, followed by surface run-off, driftage or leaching in deeper layers of the earth. The scientific interest in antimicrobially active compounds in manure and soil, but also in surface and ground water, has increased during the last decade. On the one side, scientific interest has focused on the behaviour of antibiotics and their fate in the environment, on the other hand, their impact on environmental and other bacteria has become an issue of research. Analytical methods have now been developed appropriately and studies using these new techniques provide accurate data on concentrations of antimicrobial compounds and their residues in different organic matters. Some antibiotics seem to persist a long time in the environment, especially in soil, while others degrade very fast. Not only the fate of these pharmaceuticals but their origin as well is an object of scientific interest. Besides human input via wastewater and other effluents, livestock production has been recognised as a source of contamination. One main concern with regard to the excessive use of antibiotics in livestock production is the potential promotion of resistance and the resulting disadvantages in the therapeutic use of antimicrobials. Since the beginning of antibiotic therapy, more and more resistant bacterial strains have been isolated from environmental sources showing one or multiple resistance. There have been several attempts to use antibiotic resistance patterns in different bacteria as indicators for various sources of faecal pollution. This review gives an overview of the available data on the present use of veterinary antibiotics in agriculture, on the occurrence of antibiotic compounds and resistant bacteria in soil and water and demonstrates the need for further studies.     

Role of plasmids in mercury transformation by bacteria isolated from the aquatic environment

Eight mercury-resistant bacterial strains isolated from the Chesapeake Bay and one strain isolated from the Cayman Trench were examined for ability to volatilize mercury. Mercury volatilization was found to be variable in the strains tested. In addition, plasmids were detected in all strains. After curing, two of the bacterial strains lost mercury resistance, indicating that volatilization is plasmid mediated in these strains. Only two cultures demonstrated ability to methylate mercuric chloride under either aerobic or anaerobic conditions. Methylation of mercury, compared with volatilization, appears to be mediated by a separate genetic system in these bacteria. It is concluded that mercury volatilization in the estuarine environment can be mediated by genes carried on plasmids.     

Bioavailability of organic chemicals in the aquatic environment.

1. Bioavailability in the aquatic environment can be defined as the external availability of a chemical to an organism. The availability of sediment-sorbed chemicals to organisms is a particularly important aspect of this phenomena. 2. Various experiments described in the literature, such as toxicity and accumulation experiments, have investigated the influence of suspended sediment in the aqueous phase on bioavailability. 3. The bioavailability of a chemical appears to be influenced by the chemical, the sediment, and the organism being examined. Thus, describing "the bioavailability" of a chemical in the aquatic environment is not a simple process.     

Olfactory assessment of predation risk in the aquatic environment

The aquatic environment is well suited for the transmission of chemical information. Aquatic animals have evolved highly sensitive receptors for detecting these cues. Here, I review behavioural evidence for the use of chemical cues by aquatic animals for the assessment of predation risk. Chemical cues are released during detection, attack, capture and ingestion of prey. The nature of the cue released depends on the stage of the predation sequence in which cues are released. Predator odours, disturbance pheromones, injury-released chemical cues and dietary cues all convey chemical information to prey Prey use these cues to minimize their probability of being taken on to the next stage of the sequence. The evolution of specialized epidermal alarm substance cells in fishes in the superorder Ostariophysi represent an amplification of this general phenomenon. These cells carry a significant metabolic cost. The cost is offset by the fitness benefit of the chemical attraction of predators. Attempts of piracy by secondary predators interrupt predation events allowing prey an opportunity for escape. In conclusion, chemical cues are widely used by aquatic prey for risk assessment and this has resulted in the evolution of specialized structures among some taxa.