Intertidal Mudflat Sediments Research Articles

The impact of coal production on the sediment record of the Severn Estuary

A link between historical coal production and sediment coal concentrations in saltmarsh sediments is demonstrated for the Severn Estuary, southwest Britain. It is clear that whilst coal production has varied in accordance with industrial demand, the environmental impact has been manifested in a corresponding increase in environmental pollution. Furthermore, the transfer of coal between production site and estuarine sediment has introduced a lag period into the transfer mechanism, argued to be of different periods by different authors, but generally agreed to exist. With coal production at the present time effectively zero, it can be argued that new input has to come from contaminated sediments already present within the Estuary. Current estimates indicate that the intertidal mudflat sediments of the contemporary system currently hold around 10 5–10 6 tonnes of coal, whilst erosion of the three marshes studied here suggest an input of coal from this source ranging from 76 to 134 tonnes a −1. As a consequence, both contemporary mudflats and saltmarshes must both be regarded as potential future coal pollution sources.

Ecological interaction and sediment transport on an intertidal mudflat II. An experimental dynamic model of the sediment-water interface

Abstract A one-dimensional model is presented which combines simplified biological, chemical and physical dynamics across the sediment-water interface of intertidal mudflat sediments. Interactions between ecology, biogeochemistry and sediment dynamics are simulated during iteration through a short-term sequence of light and tides. The model shows that, under ‘normal’ intertidal conditions, a biolayer composed of unicellular algae can develop at the sediment-water interface. Rapid algal growth generates regularly recurring nitrogen limited conditions in the biolayer. In the model, the algal carbohydrate polymers produced and exuded during nitrogen limitation profoundly influence model sediment dynamics by adjusting sediment cohesion. Stable, but dynamic, sediment surfaces result in the model from a combination of carbohydrate exuding algae, bacterial remineralization of exuded carbohydrate and grazing of the algae by bioturbating macroheterotrophs. Model predictions for sites on an intertidal mudflat in the Humber Estuary, UK show good agreement with the field observations for a range of different physical, chemical and biological variables. The results imply that sediment accretion may be more directly coupled to nitrogen supply than to sediment supply. The results are discussed in terms of an algal growth advantage to carbohydrate exudation.

Carbon and nitrogen cycling in intertidal sediments near Doel, Scheldt Estuary

Carbon and nitrogen cycling in intertidal mud flat sediments in the Scheldt Estuary was studied using measurements of carbon dioxide, methane and nitrous oxide emission rates and pore-water profiles of ΣCO2, ammonium and nitrate. A comparison between chamber measured carbon dioxide fluxes and those based on ΣCO2 pore-water gradients using Fick's First law indicates that apparent diffusion coefficients are 2 to 28 times higher than bulk sediment diffusion coefficients based on molecular diffusion. Seasonal changes in gaseous carbon fluxes or ΣCO2 pore water concentrations cannot be used directly, or in a simple way, to determine seasonal rates of mineralization, because of marked seasonal changes in pore-water storage and exchange parameters. The annual amount of carbon delivered to the sediment is 42 mol m-2, of which about 42% becomes buried, the remaining being emitted as methane (7%) or carbon dioxide (50%). Each year about 2.6 mol N m-2 of particulate nitrogen reaches the sediment; 1.1 mol m-2 is buried and 1.6 mol m-2 is mineralized to ammonium. Only 0.42 mol m-2 yr-1 of the ammonium produced escapes from the sediments, the remaining being first nitrified (1.2 mol m-2 yr-1) and then denitrified (1.7 mol m-2 yr-1). Simple calculations indicate that intertidal sediments may account for about 14% and 30% of the total estuarine retention of nitrogen and carbon, respectively. © 1995 Kluwer Academic Publishers.

Succinate decarboxylation by Propionigenium maris sp. nov., a new anaerobic bacterium from an estuarine sediment.

Enrichments on succinate plus yeast extract under anoxic conditions from intertidal mud-flat sediments yielded cultures dominated by oval to round-ended rod-shaped cells. Strain 10succ1, obtained in pure culture, was characterized in detail. The non-motile cells possessed a gram-negative cell wall and did not form spores. Carbohydrates were fermented to formate, acetate, ethanol, and lactate. Succinate was decarboxylated to propionate. Other organic and amino acids were variously fermented to formate, acetate, propionate, and butyrate. Sulfur, sulfate, thiosulfate, and nitrate were not used as electron acceptors. Growth required the presence of yeast extract and at least 5 g/l NaCl, and was possible only in the absence of oxygen. No cytochromes were detected. The DNA base ratio was 40 mol% G + C. Phylogenetically, strain 10succ1 is closely related to Propionigenium modestum, as revealed by 16S rDNA analysis, but is physiologically distinct. Accordingly, strain 10succ1 (DSM 9537) is described as the type strain of a new species of the genus Propionigenium, P. maris sp. nov.

SHORT-TERM CHANGES IN THE VERTICAL DISTRIBUTION OF BENTHIC MICROALGAL BIOMASS IN INTERTIDAL MUDDY SEDIMENTS

Benthic microalgae inhabiting marine sediments, composed primarily of diatoms, are an important carbon source for a variety of meiofaunal and macrofaunal organisms. The purpose of our study was to determine if this benthic microalgal assemblage exhibits short-term (hourly) changes in the vertical distribution of biomass in the upper few mm of intertidal mudflat sediments in North Inlet estuary (South Carolina, U.S.A.). Sediment cores were collected and subsampled at 2 and 3 h intervals over 2 tidal cycles on 4 different dates to quantify changes in chlorophyll a concentrations at 1 mm intervals in the upper 3 or 5 mm of sediment. Benthic microalgal biomass showed significant changes in vertical distribution over time that were attributed to migration by motile benthic diatoms. Migration was limited primarily to the upper 3 mm of sediment with ca. 33% of the total biomass in the upper 1 mm undergoing migration. Comparisons with a microalgal production model, which was based on tide and sun variables, showe...

The coupling of microbial respiration processes within the two-dimensional spatial structure of an intertidal mud flat sediment of the Elbe Estuary

The coupling of microbial respiration processes within the two-dimensional spatial structure of an intertidal mud flat sediment of the Elbe Estuary

A new method to study biogeochemical processes in sediments by a percolation technique

A device for analysis under simulated natural conditions is described. It continuously exchanges the porewater in undisturbed sediment zones under controlled laboratory conditions. Using this percolation technique, defined aerobic and anaerobic conditions in the sediment and the mean velocity of the porewater can be maintained or varied over extended periods of time. The concentrations of chloride and humic substances in the porewater of an intertidal mudflat sediment were determined continuously in the outflow of the analog model and compared with the results of in situ porewater profile analyses for the same chemicals in the same type of sediment. The pore volume affected by the percolation technique was measured with an amended fluorescent tracer together with chloride as a conservative tracer in the sediment. Vertical gradients of the chemicals in the porewater of an intertidal mudflat sediment were determined using both the percolation and the in situ porewater analysis techniques. Both chloride and humic substances decreased with increasing depth of the sediment. The results obtained using this device indicate differences in the distribution within a sediment layer due to such processes as the accumulation of humic substances in the micropores. In the surface layer, up to 11 times the concentrations of humic substances had accumulated compared to in situ porewater measurements. The application of the percolation technique for the investigation of different biogeochemical processes in sediments is discussed.

Microscale dispersion of meiobenthic copepods in response to food-resource patchiness

Microscale (mm 2-cm 2) spatial patterns of harpacticoid copepods were determined in intertidal mud-flat sediments using contiguous coring and were analysed with spatial autocorrelation. Associations with potential major food resources (diatoms) were further examined in laboratory studies. In the field, patches of Microarthridion littorale (Poppe) are positively correlated with high concentrations of diatoms (as measured by Chl a concentration) at low tide. Also, laboratory preference experiments show that this species seeks and locates sediments containing high concentrations of diatoms and/or their chemical exudates. During high water, significant patchiness in M. littorale disappears as some individuals frequent the water column. Scottolana canadensis (Willey) is not associated with sediment chlorophyll pigments. S. canadensis is a burrow dweller which feeds primarily during times of water cover on suspended planktonic material and laboratory preference experiments indicate it does not actively seek sediments containing high concentrations of sediment food resources. Microspatial dispersion of intertidal meiofauna does not appear to be regulated by any single factor and patterns vary with species and feeding mode (benthic or planktonic). Additionally, spatial pattern in epibenthic mud dwelling copepods appears to be disrupted with each tidal cycle due to active or passive resuspension processes. Spatial patterns, therefore, probably develop relatively quickly and are influenced by processes occurring during the proceeding tidal stage.

Biological and granulometric controls on sedimentary organic matter of an intertidal mudflat

A variety of measures of organic matter concentration and quality were made on samples collected from the top few mm of intertidal mudflat sediment over the course of a year, in order to assess the relative importance of biological and sedimentological influences on sedimentary organic matter. Winter and summer were times of relatively fine-grained sediment accumulation, caused by biological deposition or stabilization processes and resulting in higher organic matter concentrations. Stable carbon isotope and Br:C ratios indicated a planktonic source of bulk organic matter. Ratios of organic carbon to specific surface area of the sediments were consistent with an organic monolayer coverage of sediment grains. Correction for changing grain size during the year showed no change in the organic concentration per unit surface area, in spite of organic matter inputs by in situ primary production, buildup of heterotroph biomass and mucus coatings, and biodeposition of organic-rich seston. There were also no indications of changes in bulk organic quality, measured as hydrolyzable carbohydrates and amino acids, in response to these biological processes. It is concluded that biological processes on a seasonal time scale affect the bulk organic matter of these sediments via a modulation of grain size rather than creation or decay of organic matter.

The effect of tidal resuspension on the distribution of intertidal epipelic algae in an estuary

The distribution of microalgal biomass in the sediments and water column of a salt marsh and mudflat ecosystem was studied over a fifteen month period by fluorometric analysis of chlorophyll a . Chlorophyll entered the water column on the early flood tide due to the resuspension of intertidal mudflat sediments and associated epipelic algal flora. By mid-flood tide, chlorophyll values were surpassed by its degradation products. Unusually large numbers of bivalves and other suspension feeders present in the system may have processed the water and released fecal materials, thus raising the concentration of pheopigment in the water column between early and mid-flood tide. By mid-ebb, the pigment levels had declined, possibly due to the setting of algal cells and feces. Resuspension recommenced briefly by late ebb as the system emptied. Calculations revealed that if 10 to 15% of the mudflat sediments were resuspended to a depth of 1 mm it could account for the chlorophyll levels inside the estuary, which were high compared to neighboring systems. Pigment gradients in the water column and sediments indicated net transport of epipelic algae from the mudflat to the salt marsh where most of the bivalves were located. Suspended material concentrations as well as counts of epipelic and phytoplankton frustules suggested that epipelic algae in shallow estuarine systems may be an important food source for the filter feeding community when made available twice daily by tidal resuspension of sediments.