Intertidal Estuarine Sediments Research Articles

The diverse bacterial community in intertidal, anaerobic sediments at Sapelo Island, Georgia.

The phylogenetic diversity and composition of the bacterial community in anaerobic sediments from Sapelo Island, GA, USA were examined using 16S rRNA gene libraries. The diversity of this community was comparable to that of soil, and 1,186 clones formed 817 OTUs at 99% sequence similarity. Chao1 estimators for the total richness were also high, at 3,290 OTUs at 99% sequence similarity. The program RDPquery was developed to assign clones to taxonomic groups based upon comparisons to the RDP database. While most clones could be assigned to describe phyla, fewer than 30% of the clones could be assigned to a described order. Similarly, nearly 25% of the clones were only distantly related (<90% sequence similarity) to other environmental clones, illustrating the unique composition of this community. One quarter of the clones were related to one or more undescribed orders within the γ-Proteobacteria. Other abundant groups included the δ-Proteobacteria, Bacteroidetes, and Cyanobacteria. While these phyla were abundant in other estuarine sediments, the specific members at Sapelo Island appeared to be different from those previously described in other locations, suggesting that great diversity exists between as well as within estuarine intertidal sediments. In spite of the large differences in pore water chemistry with season and depth, differences in the bacterial community were modest over the temporal and spatial scales examined and generally restricted to only certain taxa.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-008-9481-9) contains supplementary material, which is available to authorized users.

Dual stable isotope abundances unravel trophic position of estuarine nematodes

The role and quantitative importance of free-living nematodes in marine and estuarine soft sediments remain enigmatic for lack of empirical evidence on the feeding habits and trophic position of most nematode species. Here we use natural abundances of carbon and nitrogen stable isotopes of some abundant nematode species/genera from estuarine intertidal sediments to assess their trophic level and major food sources. In all stations, δ15N of different dominant nematode species/genera spanned a range of 3.6 to 6.3 ppt, indicating that at least two trophic levels were represented. The large nematodes Enoplus brevis, Enoploides longispiculosus and Adoncholaimus fuscus consistently had high δ15N, in line with mouth-morphology based predictions and empirical evidence on their predacious feeding modes. Daptonema sp., Metachromadora remanei, Praeacanthonchus punctatus and ‘Chromadoridae’ (dominated by Ptycholaimellus ponticus) had comparatively lower δ15N, and δ13C suggesting that microphytobenthos (MPB) is their major carbon source, although freshly sedimented particulate organic matter may also contribute to their nutrition in silty sediments. The trophic position of Sphaerolaimus sp., a genus with documented predacious feeding mode, was ambiguous. Ascolaimus elongatus had δ15N signatures indicating a predacious ecology, which is at variance with expectations from existing feeding type classifications. Our study shows that—despite limitations imposed by the biomass requirements for EA-IRMS (elemental analyser—isotope ratio mass spectrometry)—natural isotope abundances of carbon and nitrogen are powerful tools to unravel trophic structure within nematode communities. At the same time, the prominence of different trophic levels results in a large span of δ15N, largely invalidating the use of nitrogen isotope abundances to assess food sources and trophic level of whole nematode communities.

Determining the environmental preferences of four estuarine epipelic diatom taxa: growth across a range of salinity, nitrate and ammonium conditions

Intertidal cohesive estuarine sediments frequently support extensive microphytobenthic biofilms, which are usually dominated by epipelic (motile) diatoms. The distribution of different diatom taxa varies along estuarine gradients, but it is not clear what the causative factors are in determining these patterns. In many estuaries, salinity covaries with other environmental gradients, particularly with nutrient concentrations when the river is the main nutrient source. Autecological information is required to aid interpretation of these field distributions. In this study the maximum specific growth rate (μ) and stationary phase biomass of four common taxa of estuarine epipelic diatoms (Navicula phyllepta, N. perminuta, N. salinarum and Cylindrotheca closterium) were measured in axenic unialgal cultures grown under a range of nitrogen and salinity regimes. All three Navicula species and two different clones of C. closterium showed significant differences in their response to a range of ammonium (10–4000 µM) and nitrate (10–2000 µM) concentrations across a salinity range of 10–35‰. Growth rates of N. phyllepta were significantly lower at ammonium concentrations >400 µM, but the other three taxa showed little evidence of ammonium toxicity, even at concentrations >1 mM. On the basis of the response of each species, the following putative ranking of preferences for inorganic nitrogen concentrations (lowest to highest, with salinity optima in parentheses) was constructed: N. phyllepta (10–20‰) – N. perminuta (10–30 ‰) – N. salinarum (20–35‰)/C. closterium (clone 1, 10–25‰, clone 2, 25–35‰). Such a ranking should be interpreted cautiously, as interclonal differences and adaptation to local environmental conditions can alter the preferences of taxa. These autecological data are partially supported by previously published data on field distribution, and suggest that certain taxa may have value as trophic indicator species.

Atmospheric Nitrous Oxide Fluxes from Mangrove Sediments

Although the marine environment is recognized as a net source of nitrous oxide to the atmosphere, current global budgets appear to underestimate the marine source of this radiatively active gas. Mangrove forests occupy a significant fraction of the tropical land/sea interface and receive high inputs of terrestrial nitrogen. Anthropogenic activities increase nitrogen input to mangrove sediments thereby enhancing microbial nitrogen metabolism. Elevated rates of nitrous oxide flux might therefore be expected. Our experimental determinations of nitrous oxide flux from mangrove sediments yield rates of between 0.12 and 7.8 μmol N 2O m −2 h −1; values which are between 2 and 135 times greater than those reported previously for intertidal estuarine sediments. Nitrous oxide yield from these sediments varies greatly in response to both the magnitude and chemical nature of the sediment nitrogen source. Rates appear to be greater when reduced nitrogen is the dominant substrate and nitrification is the main source of nitrous oxide compared to sediments where nitrate and nitrite predominate and nitrous oxide arises from microbial denitrification.

Fortnightly light and temperature variability in estuarine intertidal sediments and implications for microphytobenthos primary productivity

Photosynthetically active radiation (PAR) and temperature were measured continuously at the surface of estuarine intertidal sediments in the Tagus estuary, Portugal, along two spring-neap tidal cycles. PAR and temperature were strongly conditioned by the periodic tidal inundation, with large and abrupt variations occurring during flooding and ebbing. PAR levels reaching the sediment surface decreased very rapidly to zero or very low values during most of the daytime immersion. Inundation during high tide had the general effect of attenuating the amplitude of daily temperature fluctuation, with the incoming water usually warmer than the sediment during the night or early morning and cooler during the day. The daily progression of tidal emersion resulted in a clear fortnightly variation in total daily PAR reaching the sediment surface, while both daily mean temperature and mean temperature of diurnal low tide periods failed to exhibit a well-defined fortnightly periodicity. The obtained results indicate that the estuarine intertidal environment is dominated, at sub-seasonal time scales, by fortnightly periodicity in irradiance and temperature conditions favourable for benthic photosynthesis.

Ascomycetous yeasts from tropical intertidal dark mud of southeast Brazilian estuaries.

Four different intertidal estuarine sediments had distinct yeast communities. One-hundred-ninety-three yeast isolates were classified in 47 species, with 34 of these in the genus Candida. Candida tropicalis was the only ascomycetous species isolated from all four sites. Other opportunistic pathogens including Candida glabrata, Candida guilliermondii, Candida parapsilosis and Candida krusei were present, especially at the more polluted sites. Pichia species were also frequent isolates with Pichia membranaefaciens, and its anamorph, Candida valida, and other phenotypically similar low assimilation profile species the most frequent. Kluyveromyces aestuarii was prevalent at the only site with well established mangrove vegetation, but not present at the other sites. The sediment yeast communities were distinct from each other, but more similar to each other than to the yeast communities of other ecosystems in the same geographic region.

A preliminary investigation into the spectral characteristics of inter-tidal estuarine sediments

Abstract In the Ribble Estuary, Lancashire, U.K., systematic associations between discharge of radionuclides from the British Nuclear Fuels plc (BNFL) plants at Sellafield and Springfields and sediment size-fractions exist. The ability to map these associations through in situ spectroscopy (0·4-2·5 μm) of sediments at low tide was investigated. Laboratory spectra of inter-tidal sediment samples collected from the Ribble show a strong negative correlation (–0·7 to –0·8) between their radionuclide-associated clay content and reflectance within the 0·4-2·5 μm range. Field spectra of the same samples showed a less distinct relationship as a result of the presence of surface moisture, cyanobacteria, and halite within the intertidal zone. Methods are proposed to account for these problems.

A mathematical model for the vertical distribution of chlorophyllA in estuarine intertidal sediments

Coastal and estuarine intertidal sediments are commonly colonized by dense populations of microphytobenthos. Due to wind and tides, important fractions of microphytobenthic populations may be buried. A mathematical model describing the depth variation of chlorophyll a in intertidal sediments was developed and experimentally tested. The model assumed first-order chlorophylla degradation and a constant mean burial velocity which resulted in a negative exponential variationCZ=COexp{-k/vz} (CZ andCO=chlorophylla concentration at depth zand at the surface;k=specific degradation rate of chlorophyll a to pheopigments;V=mean burial velocity). Chlorophylla concentration depth profiles in different sediment types measured at the Tagus estuary and Ria Formosa (Portugal) were used to validate the model. The model was adjusted to field data. The chlorophyll a degradation rate was measured in a microcosm experiment under total darkness and no tidal action, and sampled during three months. This rate was shown to be independent of time and depth for the upper 0–15 mm depth interval. This result allowed the estimation ofV for each sampling site. Comparison of predicted and observed temporal data further confirmed the validity of the model andk andV values. Despite its simplicity, the proposed model adequately described the depth distribution of chlorophylla in different types of intertidal sediments. The model allowed the quantitative characterization of the buried microphytobenthic biomass (depth-integrated biomass) and the assessment of its importance as potentially productive stock of cells.

The measurement of microbial carbohydrate exopolymers from intertidal sediments

Measurements of microbial extracellular polymeric substances (EPS) of natural field populations are required to understand the processes of biogenic stabilization and the microbial ecology of intertidal sediments. EPS in sediments can be measured by the phenol‐sulfuric acid assay to measure carbohydrate concentration in sediment samples. We conducted comparative studies of storage and extraction methods for carbohydrate fractions on intertidal estuarine sediments. Measurements of both total and colloidal (material remaining in suspension after aqueous extraction and centrifugation) carbohydrate concentrations were highly dependent on storage conditions, sample size, extraction media, and time. Precipitation (in 70% ethanol) of EPS from saline (25‰) extractions of colloidal carbohydrate (colloidal S) from four different sediment microbial assemblages showed that 20% of colloidal carbohydrate present in extracts consisted of EPS. Concentrations of colloidal S were highly correlated with diatom biomass as determined by chlorophyll a concentrations. Extractions that used 100 mM Na2EDTA as the extracting medium (colloidal EDTA) increased the concentrations of colloidal carbohydrate obtained and, in sediments dominated by bacteria and cyanobacteria, increased the percentage of EPS in the material to 38%. Uronic acids comprised 20% of the total amount of carbohydrate measured in both total sediment and colloidal‐S extracts but increased to 65% in colloidal‐EDTA extracts, suggesting that colloidal‐EDTA extractions remove bacterial capsular EPS and EPS more closely associated with sediment particles.

Radioisotopes of thirteen elements in intertidal coastal and estuarine sediments in the Irish Sea

A survey has been carried out of40K,60Co,99Tc,106Ru,125Sb,129I,134Cs,137Cs,154Eu,226Ra,228Ra,237Np,238Pu,239,240Pu,241Pu,241Am,242Cm, and243,244Cm activities in sediments from the Irish Sea. Several of these radionuclides were measured independently at two separate laboratories to enable the intercomparison of the results produced. The comprehensive data set generated allows the present spatial distributions of these radionuclides in coastal sediments to be examined in relation to sediment textural characteristics and by comparison with earlier survey, enables the temporal trends in their activities to be determined. In general all artificial radionuclides showed lower activities in sediments in response to falling discharges from Sellafield and relationships with either grain size, distance from Sellafield or both. Isotope ratios were similar to cumulative weighted activity ratios rather than present day values due to sediment mixing. Pu levels supplied evidence for the lag in response of sediment deposits with increasing distance from Sellafield due to sediment transport.

Long-term chemical and cytochemical assessment of oil contamination in estuarine intertidal sediments

The long-term behaviour of an oil spill contamination in intertidal sediments and mussels of the St. Lawrence Estuary was monitored using a series of chemical indexes in conjunction with the lysosomal membrane fragility index in blue mussels. The analysis of aliphatic hydrocarbons in surficial sediments showed the contamination was persistent over the four-year assessment period covered by the study. The low apparent recovery process was attributed to the release of stranded oil from intertidal sandy sediments and the chronic inputs of oily residues from various anthropogenic land activities. The progressive clean up of mussel tissues was assessed by a decrease of the fossil pristane content and a marked reduction of substituted PAH. Total pyrogenic PAH content measured in sediments showed no particular trend with time for contaminated and control stations. The cytochemical results confirmed the environmental stress experienced by mussels sampled at contaminated stations and were in good agreement with chemical indices. The results of this study indicated that the long-term assessment of an oil spill can be conducted by the simultaneous use of both chemical and cytochemical methods. The lysosomal membrane fragility index seems to be a sensitive field method and the combination of this cytochemical technique with chemical indices could be part of a useful approach for the development of effective sediment quality criteria in marine environment.

Apparent sediment diffusion coefficients for oxygen and oxygen consumption rates measured with microelectrodes and bell jars: applications to oxygen budgets in estuarine intertidal sediments (Oosterschelde, SW Netherlands)

Apparent sediment diffusion coefficients for oxygen and oxygen consumption rates measured with microelectrodes and bell jars: applications to oxygen budgets in estuarine intertidal sediments (Oosterschelde, SW Netherlands)

Oxygenation of intertidal estuarine sediments by benthic microalgal photosynthesis

A mathematical model was used to define the relative importance of microalgal photosynthesis and physical processes in the formation and maintenance of the oxygenated zone on the surface of intertidal estuarine sediments. Manometric measurements of sediment uptake and release showed that gross oxygen production usually exceeded aerobic community respiration. Polarometric microprobes measured vertical oxygen distributions in the sediment. Surface levels of oxygen ranged from 200% saturation in summer to 70% in winter. Profiles and flux measurements allowed calculation of sediment diffusion coefficients. Empirical evaluation of the terms of the model showed that epipelic diatom photosynthesis as a source of oxygen at low tide may exceed atmospheric diffusion by an order of magnitude. On a diurnal and seasonal basis, however, the diatoms may be less important to the oxygenation process than the physical forces of the tide.

Denitrification in San Francisco Bay Intertidal Sediments

The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO(3) + NO(2) concentrations (</=26 muM) were below the apparent K(m) (50 muM) for nitrate. During the rainy season, when ambient NO(3) + NO(2) concentrations were higher (37 to 89 muM), an accurate estimate of the K(m) could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N(2)O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N(2)O in the presence of C(2)H(2) was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N(2)O loss was caused by incomplete blockage of N(2)O reductase by C(2)H(2) at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 mumol of N(2) m h (for undisturbed sediments) to 17 to 280 mumol of N(2) m h (for shaken sediment slurries).

Studies on the meiofauna of Sagar Island

Mean number of total meiofauna individuals in the intertidal estuarine sediments around the island ranged from 1/10 cm2 to 517/10 cm2. Nematodes and copepods were the dominant taxa comprising over 80% of the total fauna. Higher meiofaunal densities occurred over the lower shore. The fauna was concentrated mostly in top 4 cm of sediment, showing little submergence towards higher tidal levels. No diurnal and seasonal vertical migrations of meiofauna were observed. Two small seasonal peaks of meiofaunal abundance were noted. Total population values were highest in summer and lowest during monsoon. Nematodes reached their maximum in winter and copepods in summer. Variations in salinity appeared to be responsible for the seasonal pattern. The present meiofaunal densities are considerably lower than those recorded in other areas. The highly fluctuating hydrographical conditions and the fine sediment with silt-clay fraction, poor drainage, low oxygen content, etc., are considered responsible for the paucity of meiofauna in this area.

Preliminary observations on the effects of flooding and desiccation upon the net photosynthetic rates of high intertidal estuarine sediments1

Measurements of gaseous CO2 exchange from high intertidal estuarine sediments revealed that net photosynthetic rates of moist, unflooded sediments were maximal. Flooding of moist sediments with 1–2 mm of agitated seawater reduced net photosynthetic rates by 48–66%. When moist sediments lost 10–15% of their water content CO2 uptake decreased, and high rates of CO2 evolution were observed later as water losses continued.

Nitrogen fixation in the temperate estuarine intertidal sediments of the River Lune

In situ measurements of acetylene reduction in undisturbed temperate intertidal estuarine sediments show that activity occurs from late spring to early autumn and amounts to an annual rate of 1.4 kg of N fixed per hectare. The low rates are caused by the combination of low temperatures, high salinities, and a shortage of carbon substrates for heterotrophic nitrogen‐fixing bacteria. The main contributing organisms are the sulfate‐reducers and salinity‐tolerant strains of Klebsiella pneumoniae. Other nitrogen‐fixing bacteria (photosynthetic bacteria, salinity‐tolerant strains of Azotobacter chroococcum, and cyanobacteria) are present only in low numbers or are unable to fix nitrogen at the salinities found in the sediments.