Effects of Sewage Dumping on Macrobenthic Invertebrates in the Jordan Gulf of Aqaba,Red Sea

There are two sewage outfalls along the Jordanian coastline in the Gulf of Aqaba. During 1982 and 1983 a total of 328 core samples (0.01 m² to a depth of 15 cm) were collected from the two outfalls, two control stations which resemble the outfalls in depth and sediment texture, and from two stations 100 m on both sides of each outfall. Faunal analysis revealed that the total number of individuals, number of species, species richness, and faunal similarities of macrobenthic invertebrates were lower at the sewage outfall near the phosphate loading port than the control station during both collections. At the 100 m stations, the numbers of individuals were generally higher than the sewage and control stations. The number of species, however, was highest at the control station and lowest at the sewage outfall. At the other sewage outfall, where the sewage effluent is discharged sporadically, no measurable effects on macrobenthic invertebrates were found.     

达标污水离岸排海末端处置技术研究综述

达标污水离岸排海处置具有低成本、高处理率等优点,是国内外沿海港口和临港工业园区进行污水处置的重要选择。介绍了国内外达标污水离岸排海末端处置技术的发展情况,分析了排污口位置选划、扩散器射流参数及水力结构优化等研究技术上存在的问题。认为排污口位置选划应在水动力、污染物扩散、泥沙冲淤及工程经济因素分析的基础上,还需要重点考虑污水排放对区域生态要素长期的影响;排海末端扩散器射流参数及水力结构优化也尤为关键,不仅直接影响稀释扩散效果,而且涉及到主管、上升管、喷口等多个可控因子,可以采用建立物理模型、数值模型及量纲分析等方法,合理优化扩散器的结构参数和扩散器的型式,对提高达标污水离岸处置的效果具有重要意义。     

Effects of Environmental Toxicants on Metabolic Activity of Natural Microbial Communities

Two methods of measuring microbial activity were used to study the effects of toxicants on natural microbial communities. The methods were compared for suitability for toxicity testing, sensitivity, and adaptability to field applications. This study included measurements of the incorporation of ¹⁴C-labeled acetate into microbial lipids and microbial glucosidase activity. Activities were measured per unit biomass, determined as lipid phosphate. The effects of various organic and inorganic toxicants on various natural microbial communities were studied. Both methods were useful in detecting toxicity, and their comparative sensitivities varied with the system studied. In one system, the methods showed approximately the same sensitivities in testing the effects of metals, but the acetate incorporation method was more sensitive in detecting the toxicity of organic compounds. The incorporation method was used to study the effects of a point source of pollution on the microbiota of a receiving stream. Toxic doses were found to be two orders of magnitude higher in sediments than in water taken from the same site, indicating chelation or adsorption of the toxicant by the sediment. The microbiota taken from below a point source outfall was 2 to 100 times more resistant to the toxicants tested than was that taken from above the outfall. Downstream filtrates in most cases had an inhibitory effect on the natural microbiota taken from above the pollution source. The microbial methods were compared with commonly used bioassay methods, using higher organisms, and were found to be similar in ability to detect comparative toxicities of compounds, but were less sensitive than methods which use standard media because of the influences of environmental factors.     

Benthic transfer and speciation of mercury in wetland sediments downstream from a sewage outfall

In order to evaluate the role of hypoxic conditions of overlying water in the benthic flux and speciation of Hg, we analyzed sediment cores from hypoxic or oxic sites downstream from a sewage outfall in the Damyang Riverine Wetland, Korea. Each core was analyzed for total Hg (THg), monomethylmercury (MMHg), and elemental Hg (Hg⁰) from sediment, and for THg and MMHg from pore water. Hypoxic conditions of the overlying water near the sewage outfall were associated with a peak production of Hg⁰, but the lowest production of MMHg, in the upper 2 cm sediments. The benthic fluxes of THg and MMHg were estimated at 130-2109 ng m⁻² day⁻¹ and −12 to 260 ng m⁻² day⁻¹, respectively. The order of MMHg flux from sediment to overlying water at each site did not follow the order of MMHg concentration in sediment, but was highest in hypoxic water conditions. The results suggest that maintaining oxic conditions in wetland water is important for decreasing the transfer of MMHg from sediment into overlying water.     

Trace metal concentrations in the tropical sponge Spheciospongia vagabunda at a sewage outfall: synchrotron X-ray imaging reveals the micron-scale distribution of accumulated metals

Major and trace elements were measured in sponges, seawater and sediment in Darwin Harbour (Australia) to test the hypothesis that metals are elevated in sponges closer to a sewage outfall compared with unimpacted sites. Seawater and sediment at the sewage discharge site contained high, but localised, concentrations of phosphorus (P), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As) and lead (Pb) compared with background sites. Metal concentrations in the sponge Spheciospongia vagabunda were highly elevated compared with other sponges and, although site specific, high metal concentrations were unrelated to the presence of sewage effluent. X-ray fluorescence microprobe imaging was used to investigate the metal distribution pattern in S. vagabunda. High Fe, Ni and Zn concentrations were either localised in circular patches (100–200 μm size) near water canals or in the pinacoderm, or scattered in spots (approximately 10 μm) throughout the tissue. This supports a microflora-mediated metal bioaccumulation hypothesis. In contrast, Co and Mn were highly dispersed and probably associated with aluminium- and iron-oxide rich sediment inclusions. Although the lack of association between sewage effluent and metal accumulation precludes the use of S. vagabunda as a biomonitor, the apparent differential mechanisms of metal accumulation warrants further investigation.     

Increased death of new leaves of coastal banksia (Banksia integrifolia L.f) around ocean sewage outfall sites

Abstract Salt‐spray damage to coastal vegetation is a worldwide phenomenon. Worsening of such damage by surfactants present in sewage disposed of at sea has been observed in Europe and on trees planted around metropolitan beaches in Australia. Whether adverse impacts of sewage occur on the more widespread native vegetation around non‐metropolitan outfalls in Australia is unknown. The present study investigated the survivorship of existing leaves, and of new shoots and leaves, on Banksia integrifolia around three outfall and three non‐outfall sites in spring/summer of 1997‐1998. Survivorship of existing leaves was almost identical at outfall and non‐outfall sites. When plants initiated new shoots over the spring/summer, plants at outfall sites initiated more than plants at non‐outfall sites; but the proportion of these new shoots lost subsequently differed little between outfall and non‐outfall sites. Survivorship of newly initiated leaves on the new shoots differed between outfall and non‐outfall sites, with 65% of the new leaves on average being lost at outfall sites, and 47% being lost at non‐outfall sites by the end of summer. The probability of observing a difference of this magnitude ranged between P= 0.057 and 0.11 (February‐April 1998). This is the first report of a possible adverse impact on an Australian native plant from sewage discharged to the ocean.     

Detecting human bacterial contamination in Antarctic soils

The presence of non-indigenous microbial contaminants resulting from human faecal contamination of old and currently occupied base and field camp sites in South Victoria Land, Antarctica, was assessed by PCR amplification of extracted soil DNA using species-specific PCR primers. Positive controls (samples recovered from the environs of Scott Base, including the sewage outfall) gave strong signals with Escherichia coli primers whereas Clostridium clostridiiforme primers yielded a signal only with the sewage outfall sample. A comparison was made of PCR amplification results from samples from the abandoned Canada Glacier camp site, the Lake Fryxell summer camp site, the Cape Bird Adelie penguin colony and pristine sites from relatively inaccessible regions of the Taylor Valley. Results indicated a possible residual level of E. coli contamination in the abandoned Canada Glacier camp site, but no significant contamination of the currently occupied Lake Fryxell camp site. These data may provide indirect evidence for improved awareness and standards of waste handling and disposal over the past two decades of Dry Valley field research. Accepted: 25 March 2000     

Microbiota of the Kinderlinskaya cave (South Urals,Russia)

The mesophilic and psychrotolerant microbiota of the air, soil, water, and bottom sediments of the Kinderlinskaya cave (South Urals, Russia) and the factors affecting the structure of microbial communities were investigated. The pattern of microbial distribution in soils was shown to depend on both the configuration of the cave and the level of recreational load. The lowest numbers of bacteria and micromycetes were found in the poorly visited, difficult-to-access sites. Coliform bacteria were revealed in all soil and sediment samples and in some water samples. Micromycetes belonged to 19 genera, with Geomyces pannorum as the dominant species. Air movement was shown to be the main factor affecting the density of the aerial microbiota.     

Rates of Microbial Transformation of Polycyclic Aromatic Hydrocarbons in Water and Sediments in the Vicinity of a Coal-Coking Wastewater Discharge

To facilitate predictions of the transport and fate of contaminants at future coal conversion facilities, rates of microbial transformation of polycyclic aromatic hydrocarbons were measured in stream water and sediment samples collected in the vicinity of a coal-coking treated wastewater discharge from November 1977 through August 1979. Six radiolabeled polycyclic aromatic hydrocarbons were incubated with sediment and water samples; ¹⁴CO₂, cell-bound ¹⁴C, and polar transformation products were isolated and quantified. Whereas ¹⁴CO₂ and bound ¹⁴C were major transformation products in sediment assays, soluble polar ¹⁴C dominated transformation in water samples. Mean rate constants (measured at 20°C) in sediments collected downstream from the effluent outfall were 7.8 × 10⁻² h⁻¹ (naphthalene), 1.6 × 10⁻² h⁻¹ (anthracene), and 3.3 × 10⁻³ h⁻¹ [benz(a)anthracene], which corresponded to turnover times of 13, 62, and 300 h, respectively. No unequivocal evidence for transformation of benzo(a)pyrene or dibenz(a,h)anthracene was obtained. Only naphthalene and anthracene transformations were observed in water samples; rate constants were consistently 5- and 20-fold lower, respectively, than in the corresponding sediment samples. The measured rate constants for anthracene transformation in July 1978 sediment samples were not related to total heterotroph numbers. In late July 1978, the effluent was diverted from the primary study area; however, no differences were observed either in transformation rate constants or in the downstream/upstream sediment rate constant ratio. These results are consistent with the hypothesis that continuous inputs of polycyclic aromatic hydrocarbons result in an increased ability within a microbial community to utilize certain polycyclic aromatic hydrocarbons. However, because transformation rates remained elevated for more than 1 year after removal of the polycyclic aromatic hydrocarbon source, microbial communities may shift only slowly in response to changes in polycyclic aromatic hydrocarbon concentrations.     

Sediment Enzyme Activities and Microbial Community Diversity in an Oligotrophic Drinking Water Reservoir,Eastern China

Drinking water reservoir plays a vital role in the security of urban water supply, yet little is known about microbial community diversity harbored in the sediment of this oligotrophic freshwater environmental ecosystem. In the present study, integrating community level physiological profiles (CLPPs), nested polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and clone sequence technologies, we examined the sediment urease and protease activities, bacterial community functional diversity, genetic diversity of bacterial and fungal communities in sediments from six sampling sites of Zhou cun drinking water reservoir, eastern China. The results showed that sediment urease activity was markedly distinct along the sites, ranged from 2.48 to 11.81 mg NH₃-N/(g·24h). The highest average well color development (AWCD) was found in site C, indicating the highest metabolic activity of heterotrophic bacterial community. Principal component analysis (PCA) revealed tremendous differences in the functional (metabolic) diversity patterns of the sediment bacterial communities from different sites. Meanwhile, DGGE fingerprints also indicated spatial changes of genetic diversity of sediment bacterial and fungal communities. The sequence BLAST analysis of all the sediment samples found that Comamonas sp. was the dominant bacterial species harbored in site A. Alternaria alternate, Allomyces macrogynus and Rhizophydium sp. were most commonly detected fungal species in sediments of the Zhou cun drinking water reservoir. The results from this work provide new insights about the heterogeneity of sediment microbial community metabolic activity and genetic diversity in the oligotrophic drinking water reservoir.     

Ecological risk assessment of toxic elements,microbial loads,parasites and antinutritional factors in Telfairia occidentalis grown on sewage contaminated soil

The aim of this study was to evaluate the ecological health risk assessment of toxic elements, microbial load, and anti-nutrient constituent build-up in vegetables, Talfairia occidentalis, grown on sewage contaminated soil. Samples of soil and vegetables were taken from farms near the dumpsites (sites A). As a control, samples were taken from an area with no dump sites (sites B). Atomic Absorption Spectrophotometry was used to determine the potentially toxic elements. The basic titrimetric method was used to estimate Phytate and Oxalate in the vegetables in order to assess anti-nutrient constituents. The content of cyanogenic glycosides, tannins, and alkaloids in vegetable samples was determine using a standard method. Total heterotrophic bacteria, E. coli, total coliform, faecal coliform, Staphylococcus aureus, Salmonella, and intestinal parasites were all determined using APHA standard methods. For all samples analyzed, the concentrations of metals – Cr, Zn, Pb, Cu, and Ni in site A were higher than those in site B. The soil and vegetable samples differed from the controls by a significant amount (P <0.05). Vegetable samples from site A were mainly infected with faecal coliform TO (9.7 × 10⁵cfu/g) and other bacteria at levels higher than the recommended levels. In contrast to samples from site B, which were not infected with human intestinal helminth parasites, Ascaris lumbricoides ova and Entamoeba histolytica cryst were present in vegetables in site A samples. The majority of the values obtained for the sewage dumpsite were significantly higher than the values recorded by the World Health Organization (WHO). However, sewage wastes, anthropogenic sources, and atmospheric depositions cause higher concentrations of heavy metals, anti-nutrients, and microbial load around dumpsites, which bioaccumulate in vegetables through uptake from the soil and eventual entry into the food chain. The overall evaluation found that consumption of vegetables grown on sewage soil poses a risk of heavy metals, microbial loads, and anti-nutrients adversely affecting human health.     

Effects of fish farming on microbial enzyme activities and densities: comparison between three Mediterranean sites

AIM: The effects of fish farming on microbial enzyme activities and heterotrophic bacterial density were investigated in three Mediterranean sites before and after the start of mariculture. METHODS AND RESULTS: Microbial activities were measured on water and sediment samples by using fluorogenic substrates specific for leucine aminopeptidase, beta-glucosidase and alkaline phosphatase (AP); bacterial counts were determined by Marine agar plates. SIGNIFICANCE AND IMPACT OF THE STUDY: Comparison of activity and abundance values obtained before and after the experiment showed that fish farming mainly affected the levels of microbial activities; they were significantly enhanced both in water and sediments, reaching an increase of 183.66 times for AP in Castellammare Gulf. After mariculture, no significant variations were recorded in heterotrophic bacterial density in the waters, while significant changes were observed in the sediments. Effects induced appeared to be extended not only to stations in which cages were located, but also to control sites far from the direct influence of fish farming.     

Temporal Variations in Heterotrophic Mesophilic Bacteria from a Marine Shallow Hydrothermal Vent off the Island of Vulcano (Eolian Islands, Italy)

Abstract The fluctuations of the total microbial abundance, the culturable heterotrophic bacterial population, and the composition of heterotrophic bacteria were investigated in relation to environmental parameters in a shallow, marine hydrothermal vent off the Island of Vulcano (Eolian Islands, Italy). Standing stock dynamics were studied by measuring the total population of picoplankton by direct count and the population of viable heterotrophic bacteria in water and sediment samples collected monthly. The environmental factors most strongly linked to the total microbial abundance and heterotrophic bacterial populations were pH and H₂S content in water and C/N ratio in sediment samples. The pattern of variation of microbial populations associated with water was different from those associated with sediment. Assessment of the qualitative composition of aerobic heterotrophic bacterial communities was based on 30 morphological and biochemical characteristics for each strain. Numerical analysis was used for an initial survey of the similarity among the isolates. The data were successively used to determine the structure and the metabolic potential of water and sediment bacteria. Metabolic properties varied between water- and sediment-isolated bacteria. Bacteria from water were structurally more diverse, and active in the use of carbohydrates, than those from sediment. Moreover, most of the sediment bacteria were able to grow at a high temperature (60 and 70°C). The fluctuations of bacterial characteristics in relation to environmental parameters present an evident temporal variation in water, but not in the sediment habitat. Received: 13 January 1997; Accepted: 7 August 1997     

Heterotrophic Activity Throughout a Vertical Profile of Seawater and Sediment in Halifax Harbor, Canada

The relative heterotrophic activity of marine microorganisms was determined at two sites by the heterotrophic uptake technique throughout the water column, the sediment-water interface, and the surface layer of sediment. In the water column, uptake was greatest at the surface and steadily decreased with depth. The percentage of the substrate that was respired also decreased with depth from 69 to 56%. The activity of the sediment-water interface was several orders of magnitude greater than that of the overlying water and twice that of the sediment immediately below. Hand-collected water samples carefully taken as close as 1 cm from the sediment-water interface had the same characteristically low activity as the bottom few meters of water. Microautoradiography with ³H-labeled glucose, glutamic acid, or thymidine revealed a general decrease in the percentage of active cells with depth from 35 to <1%. The number of active cells in the interface and sediment averaged <10% of the total population. The data indicate that the sediment-water interface is the most active region in this system due to an increased number of active cells rather than an increased percentage of active cells or increased per-cell activity.     

A stressed stream ecosystem: macroinvertebrate community integrity and microbial trophic response

A year-long study of a second-order stream in Southwestern Virginia was carried out from 1979–80. One of the objectives of the study was to evaluate the effects of sewage and electroplating plant effluent stress on the trophic response of aquatic invertebrate assemblages and microbial communities in the stream. Quantitative benthic samples were collected periodically at three reference stations and four stressed stations below the outfalls. Invertebrates were counted, identified taxonomically, and classified into functional groups based on their feeding strategies. Ash-free dry weights were obtained for each functional group by date and station, and the number and density of different taxa were calculated as well. Reference stations had diverse invertebrate assemblages; scrapers were well represented and all functional groups were present in reasonably equivalent proportions. Stressed stations were dominated by collector gatherers and filterers to the virtual exclusion of scrapers. The trophic status of the microbial community was determined by suspending artificial substrates in the stream for 1-week periods. The community that colonized the substrates was assayed for ATP and chlorophyll a, and an autotrophy index (AI) was calculated using these values. The autotrophic component of the microbial community was greatest at the reference stations, and the community became primarily heterotrophic below the outfalls. The AI correlated well with the proportion of scrapers. Aquatic invertebrate assemblages and microbial communities responded to stress by changing their trophic structure to fit best the available energy sources. Where heterotrophic microbes dominated, gathering and filtering invertebrates utilized the abundant organic matter. In areas where a mainly autotrophic microbial community existed, scrapers, gatherers, and filterers were all present in balanced proportions.     

Near-Bottom Pelagic Bacteria at a Deep-Water Sewage Sludge Disposal Site

The epibenthic bacterial community at deep-ocean sewage sludge disposal site DWD-106, located approximately 106 miles (ca. 196 km) off the coast of New Jersey, was assessed for changes associated with the introduction of large amounts of sewage sludge. Mixed cultures and bacterial isolates obtained from water overlying sediment core samples collected at the deep-water (2,500 m) municipal sewage disposal site were tested for the ability to grow under in situ conditions of temperature and pressure. The responses of cultures collected at a DWD-106 station heavily impacted by sewage sludge were compared with those of samples collected from a station at the same depth which was not contaminated by sewage sludge. Significant differences were observed in the ability of mixed bacterial cultures and isolates from the two sites to grow under deep-sea pressure and temperature conditions. The levels of sludge contamination were established by enumerating Clostridium perfringens, a sewage indicator bacterium, in sediment samples from the two sites. The results of hybridization experiments in which DNAs extracted directly from the water overlying sediment core samples were used indicate that the reference site epibenthic community, the disposal site epibenthic community, and the community in a surface sludge plume share many members. Decreased culturability of reference site mixed cultures in the presence of sewage sludge was observed. Thus, the culturable portions of both the autochthonous and allochthonous bacterial communities at the disposal site may be inhibited in situ, the former by sewage sludge and the latter by high pressure and low temperature.     

Extracellular Hydrolytic Enzyme Activities of the Heterotrophic Microbial Communities of the Rouge River: An Approach to Evaluate Ecosystem Response to Urbanization

The potential effects of urbanization on the bioavailability of dissolved organic carbon (DOC) were tested by determining the extracellular enzyme activities of the heterotrophic microbial communities of the Rouge River. The activities of 19 enzymes were monitored across two water samples (river water and groundwater) at different spatial and temporal scales. High phosphatase, esterase, and aminopeptidase activities was observed in site 9 (site most exposed to anthropogenic sources) showed higher concentrations of DOC compared to sites 1 and 8 (sites exposed to less anthropogenic sources), where moderate activities of diverse range of enzymes were observed. High relative contributions of phosphatase, esterase, and aminopeptidase activities to the overall enzyme activity as observed in site 9 stressed the increased importance of peptides as C source for heterotrophic communities and high in-stream carbon processing, which account for high nonspecific extracellular enzyme activities. In contrast, high contribution of glycosyl hydrolases occurred consistently across all sites, which highlights the significance of microbial detrital and plant biomass as carbon sources. Majority of the enzymes showed evidence of activity at various extents during spring and summer. However, higher activities of leucine aminopeptidase, valine aminopeptidase, β-glucosidase, and α-mannosidase were observed in the summer; and alkaline phosphatase and α-glucosidase in the spring. The results presented here suggest a shift in organic carbon bioavailability across all sites of contrasting urbanization, despite similarities in DOC concentrations. Hence, API ZYM technique can be used as an effective indicator of river water and groundwater system health across an urban gradient.     

Microbial Activity at the Sediment-Water Interface in Halifax Harbor, Canada

The sediment-water interface in Halifax Harbor supports a microbial population of 6.95 × 10⁹ cells per g (dry weight). As determined by the standard technique of suspending subsamples in filtered seawater, the uptake of added glutamic acid by this population is 113.5 ng g (dry weight)⁻¹ h⁻¹. An alternate technique was developed to measure the heterotrophic activity of the interface over longer periods of time, using undisturbed cores with the sediment-water interface intact. Under these conditions, the microbes in the water column and the interface increased exponentially in number, with mean doubling times of 9.6 and 4.5 days, respectively. The uptake of glutamic acid by the microbial population of the interface was determined to be 12.7 ng g (dry weight)⁻¹ h⁻¹, almost an order of magnitude less than the uptake determined by the previous method. This indicates that substrate diffusion and competition for substrate by the microbes in the water column are important factors when considering the heterotrophic activity of the sediment microbial population. After 48 h of incubation, uptake and respiration ceased, probably due to the exhaustion of labeled substrate. Additional substrate added after 48 h of incubation was taken up at a rate similar to that measured after the first addition. It appears that the microbial population of the interface is able to respond quickly and repeatedly to relatively large nutrient additions. After 10 days of incubation, the number of “viable” cells as determined by autoradiography was much smaller than the increase in numbers as determined by direct counts. Apparently a large part of the viable population is unaffected by nutrient addition.     

Differences in Hyporheic-Zone Microbial Community Structure along a Heavy-Metal Contamination Gradient

The hyporheic zone of a river is nonphotic, has steep chemical and redox gradients, and has a heterotrophic food web based on the consumption of organic carbon entrained from downwelling surface water or from upwelling groundwater. The microbial communities in the hyporheic zone are an important component of these heterotrophic food webs and perform essential functions in lotic ecosystems. Using a suite of methods (denaturing gradient gel electrophoresis, 16S rRNA phylogeny, phospholipid fatty acid analysis, direct microscopic enumeration, and quantitative PCR), we compared the microbial communities inhabiting the hyporheic zone of six different river sites that encompass a wide range of sediment metal loads resulting from large base-metal mining activity in the region. There was no correlation between sediment metal content and the total hyporheic microbial biomass present within each site. However, microbial community structure showed a significant linear relationship with the sediment metal loads. The abundances of four phylogenetic groups (groups I, II, III, and IV) most closely related to α-, β-, and γ-proteobacteria and the cyanobacteria, respectively, were determined. The sediment metal content gradient was positively correlated with group III abundance and negatively correlated with group II abundance. No correlation was apparent with regard to group I or IV abundance. This is the first documentation of a relationship between fluvially deposited heavy-metal contamination and hyporheic microbial community structure. The information presented here may be useful in predicting long-term effects of heavy-metal contamination in streams and provides a basis for further studies of metal effects on hyporheic microbial communities.     

The adaptation of nitrate-reducing bacterial communities in estuarine sediments in response to overlying nitrate load

Examination of the nitrate and ammonium concentrations at 10 stations in the estuary of the River Colne, Essex, UK, revealed the presence of a pollution gradient within the estuary. The greatest concentrations of nitrate, both in the water and within the sediment, were measured near the outfall of a sewage works from which well-nitrified effluent was discharged. Measurements of the rate of nitrate reduction at each site, incubated at constant temperature and constant initial nitrate concentration, showed adaptation of the sediment bacterial communities, with those sediments having greater nitrate concentrations exhibiting faster rates of nitrate reduction. In addition, the proportion of nitrate reduced to gaseous products (denitrified), rather than to nitrate or ammonium, also increased with the nitrate concentration. These changes were interpreted as being the result of adaptation of the in situ sedimentary bacterial nitrate-reducing communities in response to the ambient concentrations of nitrate at each station.