Effects of a sewage treatment plant outlet pipe extension on the distribution of contaminants in the sediments of the Bay of Vidy, Lake Geneva, Switzerland

In 2001, the municipality of Lausanne extended the outlet pipe of the sewage treatment plant into the Bay of Vidy (Lake Geneva, Switzerland) as a measure to reduce bacterial water pollution and sediment contamination close to the lake beaches. The aim of the present study was to assess the impact of this measure. Lake bottom sediments were collected and analyzed for grain size, organic matter, organic carbon, nitrogen, phosphorus, heavy metals and hydrophobic organic compounds to evaluate their concentration and spatial distribution. Our results demonstrate that, compared to results obtained before the outlet pipe prolongation, the surface area of highly contaminated sediments was reduced by one third after the pipe extension. However, contaminant concentrations are still high and the accumulation of pollutants may represent a significant source of toxicity for benthic organisms. One concludes that contaminant reduction at the source will be necessary for a further improvement.     

Late glacial and early Holocene palaeoenvironmental changes in Geneva Bay (Lake Geneva, Switzerland)

Detailed interdisciplinary investigations demonstrate that Geneva Bay (Lake Geneva) sediments clearly record important palaeoenvironmental and palaeoclimatic changes occurred during the Late glacial and early Holocene. Sediments are in fact differentiated by changes in texture, mineralogical and geochemical composition. Distal turbidite and glacial rhythmite deposition associated with wind-transported sediment supply dominate during the Oldest Dryas. These were replaced during the Allerød by detrital settling of sediment from turbid water and by endogenic calcite precipitation. The Younger Dryas climate reversal (for the first time in Lake Geneva well documented by a pollen record) was characterized by an increase in detrital supply owing to increased run-off from the bay slopes surrounding and within the catchment area, caused by thinning of vegetation cover. A brief pause in endogenic precipitation related to decreased productivity also occurs at this time. Endogenic carbonate sedimentation abruptly resumed at the start of the Preboreal biozone in response to the rapid global climatic warming. In the middle Preboreal, renewed detrital sedimentation is interpreted as the sedimentological response to increased erosion in high-altitude regions of the catchment area, caused by a minor early Holocene cooling phase (Preboreal oscillation), and interrupts the trend towards increasing endogenic calcite precipitation. Favourable limnic conditions are reached during the late Preboreal, when diatom–calcite rhythmites begin to form. Stable isotope analysis (δ¹⁸O, δ¹³C) in bulk carbonate highlight the transition from clastic-dominated to endogenic-dominated sedimentation. Endogenic calcite deposition continues during the Boreal biozone, occasionally interrupted by local high-energy sedimentary processes (wave-induced erosion and reworking of littoral deposits) enhanced by progressive lake-level lowering. During the Older Atlantic biozone, sedimentation was mainly dominated by low-energy deposition, creating enhanced conditions for the development of benthic fauna. We will discuss the factors that make Geneva Bay an important site for recording the Late glacial–Holocene climate and environmental changes. The comparison with other Swiss Plateau lacustrine systems allowed us to emphasize the role played by the particular geographical and morphological setting of the site investigated and links with climate-sensitive regions in the catchment area.     

Distribution of indicator bacteria and Vibrio parahaemolyticus in sewage-polluted intertidal sediments

The impact of a sewage point source on the bacterial densities in an intertidal mud flat in Boston Harbor, Mass., was investigated. The area, Savin Hill Cove, acts as a receiving basin for a combined storm and sewage outlet (CSO). Preliminary examination of sediments and overlying water at high tide demonstrated that fecal coliforms were present in sediments at abundances 2 to 4 orders of magnitude higher than in the overlying water column. The following bacterial counts were determined from sediments along a sampling transect extending 460 m from the CSO: total bacteria by epifluorescent microscopy, heterotrophic bacteria by plate counts on nutrient-rich and nutrient-poor media, fecal coliforms and enterococci by membrane filtration, and Vibrio parahaemolyticus by a most-probable-number technique with a resuscitation step. Median sediment grain size, average tidal exposure, carbon/nitrogen ratio, and total organic carbon were also measured. All bacterial indices, except for V. parahaemolyticus, declined significantly with distance from the outfall. Multiple regression analysis indicated that tidal exposure (low tides) may affect densities of total bacteria. Fecal coliforms and enterococci were still present in appreciable numbers in sediments as far as 460 m away from the CSO. In contrast, V. parahaemolyticus densities did not correlate with the other bacterial counts nor with any of the environmental parameters examined. These results indicate that intertidal sediments which adjoin point sources of pollution are severely contaminated and should be considered as potentially hazardous reservoirs of sewage-borne diseases.     

Persistence and differential survival of fecal indicator bacteria in subtropical waters and sediments

Fecal coliforms and enterococci are indicator organisms used worldwide to monitor water quality. These bacteria are used in microbial source tracking (MST) studies, which attempt to assess the contribution of various host species to fecal pollution in water. Ideally, all strains of a given indicator organism (IO) would experience equal persistence (maintenance of culturable populations) in water; however, some strains may have comparatively extended persistence outside the host, while others may persist very poorly in environmental waters. Assessment of the relative contribution of host species to fecal pollution would be confounded by differential persistence of strains. Here, freshwater and saltwater mesocosms, including sediments, were inoculated with dog feces, sewage, or contaminated soil and were incubated under conditions that included natural stressors such as microbial predators, radiation, and temperature fluctuations. Persistence of IOs was measured by decay rates (change in culturable counts over time). Decay rates were influenced by IO, inoculum, water type, sediment versus water column location, and Escherichia coli strain. Fecal coliform decay rates were significantly lower than those of enterococci in freshwater but were not significantly different in saltwater. IO persistence according to mesocosm treatment followed the trend: contaminated soil > wastewater > dog feces. E. coli ribotyping demonstrated that certain strains were more persistent than others in freshwater mesocosms, and the distribution of ribotypes sampled from mesocosm waters was dissimilar from the distribution in fecal material. These results have implications for the accuracy of MST methods, modeling of microbial populations in water, and efficacy of regulatory standards for protection of water quality.     

Distribution of indicator bacteria and Vibrio parahaemolyticus in sewage-polluted intertidal sediments.

The impact of a sewage point source on the bacterial densities in an intertidal mud flat in Boston Harbor, Mass., was investigated. The area, Savin Hill Cove, acts as a receiving basin for a combined storm and sewage outlet (CSO). Preliminary examination of sediments and overlying water at high tide demonstrated that fecal coliforms were present in sediments at abundances 2 to 4 orders of magnitude higher than in the overlying water column. The following bacterial counts were determined from sediments along a sampling transect extending 460 m from the CSO: total bacteria by epifluorescent microscopy, heterotrophic bacteria by plate counts on nutrient-rich and nutrient-poor media, fecal coliforms and enterococci by membrane filtration, and Vibrio parahaemolyticus by a most-probable-number technique with a resuscitation step. Median sediment grain size, average tidal exposure, carbon/nitrogen ratio, and total organic carbon were also measured. All bacterial indices, except for V. parahaemolyticus, declined significantly with distance from the outfall. Multiple regression analysis indicated that tidal exposure (low tides) may affect densities of total bacteria. Fecal coliforms and enterococci were still present in appreciable numbers in sediments as far as 460 m away from the CSO. In contrast, V. parahaemolyticus densities did not correlate with the other bacterial counts nor with any of the environmental parameters examined. These results indicate that intertidal sediments which adjoin point sources of pollution are severely contaminated and should be considered as potentially hazardous reservoirs of sewage-borne diseases.     

Distribution of iron- and manganese-oxidizing bacteria in the bottom sediments of Lake Baikal

The specific features of the distribution, abundance, and taxonomic diversity of bacteria oxidizing iron and manganese in the bottom sediments sampled from different areas of Lake Baikal are studied. These bacteria are widespread in Baikal bottom sediments. Cultivated iron- and manganese-oxidizing microorganisms are ascribed to six genera: Metallogenium, Leptothrix, Siderocapsa, Naumaniella, Bacillus, and Pseudomonas. The surface layers of the ground and the border between oxidized and reduced sediments serve as ecological niches for iron- and manganese-oxidizing microorganisms. Redox conditions of the environment and the availability of dissolved forms of iron and manganese, as well as of organic matter, which are controlled by the conditions of sedimentation in the lake, are the main factors affecting the abundance and distribution of iron bacteria.     

Pilot- and bench-scale testing of faecal indicator bacteria survival in marine beach sand near point sources

Aim:  Factors affecting faecal indicator bacteria (FIB) and pathogen survival/persistence in sand remain largely unstudied. This work elucidates how biological and physical factors affect die-off in beach sand following sewage spills.
Methods and Results:  Solar disinfection with mechanical mixing was pilot-tested as a disinfection procedure after a large sewage spill in Los Angeles. Effects of solar exposure, mechanical mixing, predation and/or competition, season, and moisture were tested at bench scale. First-order decay constants for Escherichia coli ranged between −0·23 and −1·02 per day, and for enterococci between −0·5 and −1·0 per day. Desiccation was a dominant factor for E. coli but not enterococci inactivation. Effects of season were investigated through a comparison of experimental results from winter, spring, and fall.
Conclusions:  Moisture was the dominant factor controlling E. coli inactivation kinetics. Initial microbial community and sand temperature were also important factors. Mechanical mixing, common in beach grooming, did not consistently reduce bacterial levels.
Significance and Impact of the Study:  Inactivation rates are mainly dependent on moisture and high sand temperature. Chlorination was an effective disinfection treatment in sand microcosms inoculated with raw influent.     

An improved procedure for shipboard enumeration of faecal indicator bacteria in marine sediments from sewage sludge disposal areas

An improved membrane filtration procedure for use on board ship to enumerate Escherichia coli and Group D faecal streptococci in marine sediments is described. Ultrasonication extraction combined with resuscitation of sublethally-injured cells yielded significantly higher counts of E. coli than sediments shaken by hand. Counts of E. coli were also higher on mFC agar (without rosalic acid) after a period of resuscitation on tryptone-soy agar supplemented with 0.1% yeast extract than on a 4% Teepol-lactose medium. Ultrasonication of sediments made no significant difference to counts of Group D faecal streptococci on KF-streptococcus agar. These improved isolation procedures allowed better discrimination of the area affected by sewage sludge at a disposal site off the northeast coast of England.     

Activity of methanotrophic bacteria in Green Bay sediments

Abstract Sediment pore water samples obtained from a 19 m station in Green Bay in Lake Michigan were examined for levels of ambient dissolved methane and copper, and for the potential for in situ methane oxidation by methanotrophs found within surface sediments. The in situ methane concentration in the upper oxic sediment layer ranged from 20–150 μmol · 1⁻¹ at this station. The activity of methanotrophs and the kinetics of methane oxidation in these sediments were demonstrated by the uptake of radiolabeled methane. K_s values varied between 4.1–9.6 nmol · cm³ of sediment slurry. High V_max values (12.7–35.2 nmol · cm⁻³ · h⁻¹) suggest a large population of methanotrophs in the sediments. An average methane flux to the oxic sediments of 0.24 mol · m⁻² · year⁻¹ was calculated from the pore water methane gradients. Pore water concentrations of copper in the upper sediment layer ranged from 10–120 nmol · 1⁻¹. Based upon the copper concentration, other measured parameters, and equilibrium conditions defined by WATEQF4, an estimate for dissolved free Cu²⁺ concentration of 5–38 nmol · 1⁻¹ pore water was obtained. Several factors control the rate of methane oxidation, including oxygen, methane, and the bioavailability of free Cu²⁺.     

Nutrient release rates from the sediments of Saginaw Bay,Lake Huron

Direct measurements of net production rates and pore water profiles of solutes in the fine-grained sediments of Saginaw Bay, imply corresponding steady-state fluxes to the overlying water of 1.1–1.3 (I), 450–1010 (NH₄ ⁺), 1250–2650 (Si(OH)₄), 3000–3400 (Ca²⁺), 440–1330 (Mg²⁺), 1.5–728 (Fe²⁺), and 179–281 (Mn²⁺) moles/m²/day and 11.0–11.8 (alkalinity) meq/m²/day at 17.5 °C. Silica production rates in sediments apparently follow first order kinetics with a rate coefficient of 0.09/day and a steady-state silica concentration of 1.2 mM at 23.5°C. The remaining solutes follow kinetics approximately independent of solute concentration over the range of concentrations observed. Measured solute production rates are consistent with observed solute profiles only if lateral diffusion gradients are maintained in the sediments by the burrowing and irrigation activity of benthic organisms such asChironomous, the dominant burrower in Saginaw Bay. Assuming that solute fluxes from Saginaw Bay are representative of all of the post-glacial sediments of Lake Huron, the iodine flux from sediments is comparable to the total fluvial input of iodine. The extrapolated silica fluxes from Lake Huron sediments balance the estimated biogenic silica flux to the sediments.     

Survival of faecal indicator bacteria in bovine manure incorporated into soil

AIMS: Survival of Escherichia coli and enterococci was evaluated in bovine manure incorporated into two Wisconsin soils. METHODS AND RESULTS: Silty clay loam (SCL) and loamy sand (LS) were mixed with fresh bovine manure, exposed daily to 10 h at 22 degrees C/14 h at 9 degrees C, and watered weekly for 12 weeks. Escherichia coli numbers increased 1-2 log cfu g(-1), then decreased < 1 and about 2 log cfu g(-1) in SCL and LS, respectively. Enterococci numbers rose less and then declined faster than those of E. coli. Watering intervals of 3, 7 and 14 days were evaluated in weeks 13-19, but did not affect the slow decline in numbers of E. coli or enterococci. CONCLUSION: Escherichia coli and enterococci may survive at least 19 weeks at 9-21 degrees C in bovine manure/soil, with E. coli surviving better. SIGNIFICANCE AND IMPACT OF THE STUDY: Quantification of E. coli or enterococci in late spring/early summer soil may be useful in indicating recent application of bovine manure.     

Metal contamination in sediments and biota of the Bay of Quinte,Lake Ontario,Canada

The Bay of Quinte receives drainage from several large river systems, including the Moira River which carried sediment from mines into the Bay from the 1880s to the 1960s. We are investigating possible metal contamination of submerged weed beds and marsh biota which may contribute to the low diversity and biomass of macrophyte beds and Typha marshes in the Bay. In 1987, sediment, macrophytes and snails were sampled in wetlands close to the Moira River and at Hay Bay (part of the Bay of Quinte presumably unaffected by mine effluents) located 20 km from the Moira. Some element concentrations in sediment and biota were determined by neutron activation analysis (NAA) including Al, As, Br, Ca, Co, Cl, Cr, Cs, Fe, Hf, K, La, Na, Mg, Sb, Sc, Rb, Ta, Th, Ti, U, V and Zn. Other elements were analysed by acid dissolution and atomic absorption spectrophotometry (AAS) including Ag, As, Cu, Hg, Ni, Pb, and Zn. Levels of As in sediments and plants were higher close to the Moira River, whereas Cu and Ni showed the opposite pattern in sediments. The usefulness of species as bioassays differed: Stagnicola elodes Say accumulated significantly higher levels of Cu (35 vs 18 ppm) and V (l. l vs 0.5 ppm) than Planorbella trivolvis Say collected from the same sites. The macrophyte, Myriophyllum spicatum L. acted as an accumulator of Pb (up to 9.6 ppm), whereas Pb in Vallisneria americana Michx. at the same sites was undetectable.     

Detection of anaerobic ammonium-oxidizing bacteria in Ago Bay sediments

We identified 16S rRNA gene sequences in sediment samples from Ago Bay in Japan, forming a new branch of the anammox group or closely related to anaerobic ammonium oxidizing (anammox) bacterial sequences. Anammox activity in the sediment samples was detected by (15)N tracer assays. These results, along with the results of fluorescence in situ hybridization (FISH) analysis, suggest the presence of anammox bacteria in the marine sediments.     

Distribution of zinc-tolerant bacteria in stream sediments

The distribution of zinc-tolerant bacteria in sediments from three stream sites containing high (3125 g g^–1), medium (291 g g^–1), and low (109 g g^–1) concentrations of Zn was determined. Zinc tolerance was estimated by the ability of bacteria to grow on media amended with Zn concentrations ranging from 4 to 512 mg 1^–1. The presence of Zn-tolerant bacteria was correlated with the degree of heavy metal contamination; this correlation was more closely associated with readily extractable heavy metal concentrations than with the more rigorously extracted heavy metals. Low concentrations of Zn in media (4 to 16 mg 1^–1) were stimulatory to growth of bacteria from contaminated sites while concentrations as low as 4 mg 1^–1 were inhibitory to bacteria from the control site.     

Sediment penetration depths of epi- and infaunal ostracods from Lake Geneva (Switzerland)

Many (palaeo-)environmental parameters can be deduced from ecological and chemical analyses of ostracods. However, the specific ecology of each taxon has a great impact on its reaction to changing environmental conditions. As a consequence, each taxon records these changes differently. The mean penetration depth (MPD) and relative individual abundances have been documented along sediment depth profiles for the dominant sub-littoral to profundal species of ostracods in western Lake Geneva, Switzerland, and this data can be used to estimate their preferential habitat in terms of sediment depths. Isocypris beauchampi, Limnocytherina sanctipatricii, Cypria ophtalmica forma lacustris at 13-m water depths, Limnocythere inopinata, and a winter generation of Herpetocypris reptans have the shallowest habitat preferences at the study sites (MPDs of 0.45, 0.48, 0.49, 0.60, and 0.81 cm, respectively). These results suggest that these populations may be regarded as being preferentially epifaunal forms. Populations of Cytherissa lacustris (MPDs of 0.61, 0.73, and 0.82 cm at 13-, 33-, and 70-m water depths, respectively), Cypria ophtalmica forma lacustris at 70 m (MPD = 0.96 cm), Fabaeformiscandona caudata (MPD = 0.99 cm), and a summer generation of Herpetocypris reptans (MPD = 1.03 cm) were identified as being infaunal. Candona neglecta is the species that was found the deepest in the sediment of Lake Geneva, with MPDs of 0.65, 1.22, and 1.30 cm at 13-, 33-, and 70-m water depths, respectively. Information on the sediment texture and oxygen concentrations inferred from the analyses of sediment pore water suggest that the oxygen content of the sediment pore water is not the only dominant parameter controlling the differences in ostracod sediment penetration depths observed among the different sites, but that they might also be influenced by the sediment ‘softness,’ which itself depends on grain size, water content, and the abundance of organic matter in sediment.     

Survival of faecal indicator bacteria in tropical estuarine waters (Bangpakong River,Thailand)

AIMS: To investigate the survival of cultivable bacteria in the tropical Bangpakong estuary (Eastern Thailand) under different salinities and light conditions. METHODS AND RESULTS: Dark and light microcosm experiments using membrane diffusion chambers were carried out under three different experimental conditions, namely (i) low salinity, (ii) progressive mixing with brackish water and (iii) fast mixing with high salinity water spiked with raw urban sewage. Faecal coliforms declined faster than faecal enterococci, as shown by survival T90 values ranging from 82.2 +/- 4.2 to 14.5 +/- 0.8 h and 97.5 +/- 0.4-20.6 +/- 1.2 h, respectively. The survival of freshwater heterotrophic bacteria was higher but variable (121.2 +/- 5.0-30.1 +/- 14.3 h), whereas that of heterotrophic marine bacteria was rather stable (81.5 +/- 4.2-44.6 +/- 2.5 h). CONCLUSIONS: Overall survival was higher in low salinities. Light had a further deleterious effect, since it accelerated the decay of faecal indicators, particularly in high salinities. Faecal enterococci had a higher resistance to environmental conditions compared with faecal coliforms. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is relevant to the understanding of the behaviour of different faecal indicator bacteria and the optimization of sewage treatment plants aimed at the reduction and/or elimination of faecal load discharged into estuarine waters submitted to salinity variations.     

Long-term population dynamics of phototrophic sulfur bacteria in the chemocline of Lake Cadagno, Switzerland

Population analyses in water samples obtained from the chemocline of crenogenic, meromictic Lake Cadagno, Switzerland, in October for the years 1994 to 2003 were studied using in situ hybridization with specific probes. During this 10-year period, large shifts in abundance between purple and green sulfur bacteria and among different populations were obtained. Purple sulfur bacteria were the numerically most prominent phototrophic sulfur bacteria in samples obtained from 1994 to 2001, when they represented between 70 and 95% of the phototrophic sulfur bacteria. All populations of purple sulfur bacteria showed large fluctuations in time with populations belonging to the genus Lamprocystis being numerically much more important than those of the genera Chromatium and Thiocystis. Green sulfur bacteria were initially represented by Chlorobium phaeobacteroides but were replaced by Chlorobium clathratiforme by the end of the study. C. clathratiforme was the only green sulfur bacterium detected during the last 2 years of the analysis, when a shift in dominance from purple sulfur bacteria to green sulfur bacteria was observed in the chemocline. At this time, numbers of purple sulfur bacteria had decreased and those of green sulfur bacteria increased by about 1 order of magnitude and C. clathratiforme represented about 95% of the phototrophic sulfur bacteria. This major change in community structure in the chemocline was accompanied by changes in profiles of turbidity and photosynthetically available radiation, as well as for sulfide concentrations and light intensity. Overall, these findings suggest that a disruption of the chemocline in 2000 may have altered environmental niches and populations in subsequent years.     

Dynamics of nutrients and faecal bacteria in a macrotidal estuary,the Bay of Somme (France)

A stratified methodology for water sampling on tidal flats was adopted in 1988 and 1989 in the Bay of Somme. Analyses of nutrients, particulate matter and faecal germs showed the poor mixing of fresh and marine water and the weakness of stratification of the water column. Freshwater is pushed by marine water to the inner reaches of the bay and there are only a few lenses with true estuarine characteristics. In 1990, water was sampled simultaneously on the Somme river, the tidal flats and in the open sea, in order to point out estuarine gradients of several physical and chemical parameters and their evolution during a tidal cycle. The role of continental inputs was confirmed for faecal pollution, nitrate (20–25 mg l⁻¹), nitrite and silicate. The importance of ammonium excreted by the estuarine benthic populations was highlighted. High concentrations of continental chlorophyll (450 mg m⁻³) were also measured and contribute, with nitrates and ammonium, to eutrophication in the Bay of Somme. Pollution of the southern part of the bay by marine waters was regularly observed during the flow, raising doubts about the purifying capacity of sea-water and the conservation of faecal bacteria. A regular survey of fresh-water inputs and sea-water quality, offshore and within the bay, is considered to enable estimation of their respective influences in eutrophication processes in the Bay of Somme.     

Seasonal Distribution of Phytoplankton in Yellowknife Bay,Great Slave Lake

The factors influencing the seasonal distribution of phytoplankton were determined between July 1975 and December 1977 in Yellowknife Bay, Great Slave Lake. The initiation of the spring bloom occurred during April of each year in response to changing light conditions and despite the 0 °C water temperatures. Although the plankton showed some fluctuations in density (100–400 mg/m³) during the summer, there was no vernal decrease in the size of the populations. The end of the growing season was characterized by a sharp drop in numbers near the end of October. Multiple regression analysis indicated that changes in the standing crop of the plankton during the summer were primarily related to temperature (r = 0.60) and the concentrations of NO₃–N (r=–0.74) and SiO₂ (r=–0.82). Changing light conditions probably had little effect on the population during the growing season. Chlamydomonas lapponica was dominant during April of each year. While the growth of this species caused a reduction in the concentrations of total phosphorus and NO₃–N, the level of SiO₂ remained constant and consequently diatoms (Asterionella formosa, Stephanodiscus astraea, Diatoma tenue var. elongatum and Melosira islandica) waxed rapidly during May. By the first of June, nutrient concentrations were low, thereby permitting the development of Dinobryon bavaricum and Dinobryon cylindricum. The extremely rapid decrease in the densities of common species during the fall was probably due to the rapid decline in temperature and light levels and the formation of ice on the bay.