Estimates of bacterial productivity in marine sediments and water from a temperate saltmarsh lagoon

Tritiated thymidine incorporation (TTI) into DNA was used to estimate bacterial productivity in sediment and water samples from two sites in Langebaan Lagoon, South Africa. Routine analysis of isotope dilution showed seasonal variations of approximately threefold in the thymidine precursor pool sizes for bacterial assemblages from each site. Dual label incorporation of [³H]-thymidine and ¹⁴C-leucine into DNA and protein, respectively, showed that pelagic but not sediment assemblages were in a balanced state of growth during TTI. This is the first report of dual label measurements of bacterial production in sediments. Sediments supported bacterial productivities that exceeded those in the water column by factors from five- to 950-fold, whereas bacterial abundance supported by sediments exceeded that in the water column by more than 3 orders of magnitude. Estimates of bacterial productivities in sediments were coincident with levels of organic content in sediments, but not with bacterial abundance. Measurements of TTI activity for 5 different benthic microhabitats at one lagoon site showed highest activity associated with seagrass beds (2.11 ± 0.84 nmol thymidine hours^–1 g-1 dry weight), whereas activities decreased with depth (0.46 ± 0.21 nmol thymidine hours^–1 g^–I dry weight) below sediment surface.Offprint requests to: B. J. Tibbles.     

Nutrient (N,P, Si) fluxes between marine sediments and water column in coastal and open Adriatic

Nutrient benthic fluxes, as well as sediment phosphorus concentration at the open sea and coastal water stations of the Central and South Adriatic were studied during 1997–98. The fluxes were in the ranges: 0.16–2.67 mmol m^–2 d^–1 (silicate); –0.031–0.164 mmol m^–2 d^–1 (phosphate); –0.51–2.03 mmol m^–2 d^–1 (ammonia); and –1.32–1.62 mmol m^–2 d^–1 (nitrate + nitrite). Silicate flux showed a gradient from the coastal area to the open sea. Ammonia was the main nitrogen species in the flux at the estuary and bay stations, while the sum of nitrate and nitrite was predominant at the open sea stations. Relationships between phosphate and ammonia fluxes (r = 0.699, p<0.01) as well as phosphate and silicate (r = 0.529, p<0.01) were established.     

The effect of water depth on bacterial numbers,thymidine incorporation rates and C:N ratios in northeast Atlantic surficial sediments

The effect of water depth on bacterial biomass and their ability to synthesise DNA, by measuring their rate of [³H]-thymidine incorporation, was investigated in the northeast Atlantic at three sites of varying water depth (1100–3580 m) and sediment characteristics. Thymidine incorporation rates (y) in surficial sediments varied between 0.028 and 1.44 pmol h^–1 g^–1 and showed an exponential relationship with depth (x) according to the equation y= 2.05e^–0.0011x (r=0.9830 for n=7, P<0.001). However, this relationship failed when a layer of phytodetritus was found overlying the surface sediment and [³H]-thymidine incorporation rates increased by 80–339%. In contrast, bacterial numbers varied between 1.09 and 11.96 × 10⁸ cells g^–1 (dry weight) and showed no significant relationships with water depth or sediment POC/TN content. Significant exponential relationships were also found between water depth (x) and the POC (y ₁) and total nitrogen (TN, y ₂) content of surficial sediments according to the following equations: where y ₁ = 719e^–0.0003x (r=0.8700 for n=9, P<0.01) and y ₂ = 76e^–0.0002x(r=0.7582 for n=9 P<0.02). These relationships were irrespective of the presence or absence of an overlying layer of phytodetritus. This suggests that the POC and TN content of these surficial deep sea sediments is directly related to the flux of material through the water column, which significantly impacts bacterial production.     

Bacterial biomass and productivity in sediments,stromatolites, and water of hamelin pool,shark bay,Western Australia

Heterotrophic bacterial biomass and growth rates were examined in stromatolites formed from four different types of benthic cyanobacterial mats. Bacteria in algal mats were counted using direct microscopy and biomass was estimated from the numbers of bacteria. Heterotrophic bacterial growth rates were estimated from the rate of incorporation of tritiated thy‐midine into DNA. Pustular mat, which occurs in the upper in‐tertidal zone, contained relatively few bacteria in the surface layers (0–5 mm), having about 0.2 x 10⁶ cells mm^‐3, or 20 mgC m^‐2 per millimetre depth. Other mats in the lower intertidal and subtidal zones had from 1 x 10⁶ cells mm^‐3 to 8 x 10⁶ cells mm^‐3. Heterotrophic bacterial productivities were 2.1 to 5.0 mgC m^‐2 h^‐1. Turnover times were an average of 1 day in the sandy sediment and 5 days in the colloform mat. Although these results are minimum estimates, they indicate that heterotrophic bacteria contribute substantially to the carbon cycle in stromatolites, by utilizing about 20 to 30% of primary production.     

An inventory of 13C abundances in coastal wetlands of Louisiana,USA: vegetation and sediments

Summary Organic carbon-rich sediments from the surface of fresh, intermediate, brackish and salt marshes of coastal Louisiana were sampled and analyzed for their ¹³C content. The average ¹³C from all sites within each wetland type was-27.8,-22.1,-16.9, and-16.2, for fresh, intermediate, brackish and salt marshes, respectively. Means from the fresh, intermediate and brackish marshes were significantly different at the 0.01 level. A mixing model using measurements of standing crop and ¹³C of plant carbon was applied to estimate the contribution of each species to the sedimentary carbon at four of the marsh sites. Sedimentary ¹³C values generally reflected that of the dominant species present at each site. Brackish and salt marsh samples, however, showed a negative shift of ¹³C with respect to whole plant carbon. We interpret these depeleted ¹³C values to be the result of more extensive organic matter decomposition and selective preservation of ¹³C-depleted refractory components in sediments from saline sites. The results of this study suggest that ¹³C composition of sedimentary carbon may offer a valuable tool for distinguishing subtle changes in paleohydrology of wetlands resulting from relative sea level changes.     

Dissolved and particulate trace metal geochemistry in the scheldt estuary,S. W. Netherlands (water column and sediments)

The geochemistry of dissolved and particulate trace metals has been studied in the water column and the sediments of the Scheldt estuary between 1987 and 1990. A strong seasonal influence on the behaviour of dissolved Cd, Cu and Zn is observed, related to the redox conditions in the upper estuary and phytoplankton activity in the lower estuary (which are both seasonally dependent variables). The dissolved trace metal concentrations in the fresh water end-member are remarkably low during spring and summer, due to metal sulphide precipitation in the anoxic Scheldt river. However, the dissolved concentrations increase rapidly with increasing salinity, due to oxidation of metal sulphides that are present in the suspended matter, accompanied by (e.g. chloro-)complexation of the released metals. Readsorption of Cd and Zn occurs in the lower estuary during the spring phytoplankton bloom. During winter, when the Scheldt river is not completely anoxic, much higher dissolved trace metal concentrations are observed in the fresh water end-member since metal sulphide precipitation in the water column is precluded. Rapid trace metal removal is observed in the low salinity, high turbidity zone, due to adsorption onto suspended matter and freshly precipitated iron and manganese oxyhydroxides. Upon further mixing, desorption is apparent, due to a similar oxidation-complexation mechanism as observed during spring and summer. Pore water infusion may also contribute to the enrichment of dissolved Cd, Cu and Zn in the mid-estuarine region. The trace metal contents of the suspended matter and the sediments show a continuous decrease with increasing salinity. This behaviour is to a very large extent due to physical mixing of contaminated fluvial particulates and relatively unpolluted marine particulates. Desorption of Cd, Cu and Zn can be identified but is of minor importance compared to the conservative mixing process. The distribution of dissolved Cd, Cu and Zn in the pore waters of the mid-estuarine region reflects the impact of early diagenetic processes. Trace metal peaks are observed near the sediment-water interface, and at greater depth in the manganese and iron reduction zones. These peaks are attributed to oxidation of reduced trace metal compounds (e.g. sulphides) and reduction of the (iron and manganese) oxide carrier phases, respectively. At greater depth, the dissolved trace metal concentrations are much lower due to metal sulphide precipitation in the sulphate reduction zone. Analysis of a large sediment dataset indicates severe trace metal pollution of the Scheldt estuary at the end of the fifties. A major reduction of the pollution by As, Cr, Hg, Pb, and Zn has occurred in the seventies, and of Cd and Cu in the eighties. The Ni pollution has increased over the time period considered. In spite of this improvement, the present-day pollution status of the Scheldt estuary is still reason for concern.     

MMHg production and export from intertidal sediments to the water column of a tidal lagoon (Arcachon Bay,France)

Hg cycling in biologically productive coastal areas is of special importance given the potential for bioaccumulation of monomethylmercury (MMHg) into aquatic organisms. Field experiments were performed during three different seasons in Arcachon Bay, a mesotidal lagoon (SW France), to assess the variability of the water column concentrations, sediment–water exchanges and potential formation and degradation of MMHg. The objectives were to evaluate the contribution of intertidal mudflats to MMHg production and the various pathways of Hg species export. Dissolved and bulk concentrations of Hg species in the water column downstream of tidal flats were measured throughout several tidal cycles. The Hg benthic fluxes at the sediment–water interface were determined by means of benthic chambers for three different stations. Hg methylation and demethylation potentials were determined in surficial sediments and the water column using isotopic tracers. The tidal surveys demonstrated that benthic remobilization of Hg occurs primarily in association with sediment erosion and advection during ebb tide. However, elevated dissolved Hg concentrations observed at low tide were found to be caused by a combination of pore-waters seeping, benthic fluxes and methylation in the water column. Benthic fluxes were more intense during late winter conditions (median MMHg and inorganic Hg (IHg) fluxes: 64 and 179 pmol m^?2 h^?1, respectively) and subsequently decreased in spring (median 0.7 and ?5 pmol m^?2 h^?1, respectively) and fall (median ?0.4 and ?1.3 pmol m^?2 h^?1, respectively). The trends in methylation and demethylation potentials were at the opposite of the fluxes, two times lower during winter than for spring or fall conditions. In this tidal environment, MMHg production in surface sediments and its subsequent release is estimated to be the major source of MMHg to the water column during winter and spring time. However, during the more productive summer period, the Hg methylation extent in the water column may be very significant and equivalent to the sediment contribution.     

Occurrence of the parasite genus Hematodinium (Alveolata: Syndinea) in the water column

Crustaceans worldwide are infected with alveolate parasites of the genus Hematodinium, causing substantial losses to langoustine and crab fisheries. The distinct seasonality in Hematodinium occurrence in their decapod hosts, as well as unsuccessful attempts at transmission, suggest the existence of life stages outside their benthic crustacean hosts. We used a nested polymerase chain reaction method to detect Hematodinium rDNA in the environment and in potential alternative hosts. Environmental samples from the Clyde Sea, Scotland, were screened during the April release of dinospores and during June and August, when infection prevalence is rare in benthic crustaceans. Hematodinium rDNA was amplified in 15% (14/94) of isolated langoustine larvae, and in 12% (13/111) of crab larvae. In addition, Hematodinium rDNA was present in mixed plankton samples devoid of decapod larvae, but including the 2 μm-10 mm fraction of particulate organic matter in the water column, containing phytoplankton and other zooplankton. These results indicate that Hematodinium occurs in the water column and is harboured by planktonic organisms, including larval stages of the crustacean hosts, when infections are at their lowest in adult hosts.     

Microbial sulfate reduction in sediments of the coastal zone and littoral of the Kandalaksha bay of the White sea

Microbiological and biogeochemical investigations of the coastal zone and the littoral of the Kandalaksha Bay of the White Sea were carried out. The material for investigations was obtained in the series of expeditions of the Institute of Microbiology, Russian Academy of Sciences, in August 1999, 2000, 2001, and in March 2003. The studies were conducted on the littoral and in the water area of the Kandalaksha Preserve, the Moscow University Belomorsk Biological Station, and the Zoological Institute Biological Station, Russian Academy of Sciences, Sediment sampling on the littoral was carried out in the typical microlandscapes differing in the sediment properties and macrobenthos distribution. The maximal sulfate reduction rate (SRR) was shown for the shallow part of the Chemorechenskaya Bay (up to 2550 micrograms S/(dm3 day)) and in the Bab'ye More Bay (up to 3191 micrograms S/(dm3 day)). During the winter season, at a temperature of -0.5-0.5 degrees C, the SRR in the sediments of the Kartesh Bay was 7.9-13 micrograms S/(dm3 day). In the widest limits, the SRR values varied in the sediment cores sampled on the littoral. The minimal values (11 mu]g S/(dm3 day)) were obtained in the core samples on the silt-sandy littoral. The littoral finely dispersed sediments rich in organic matter were characterized by high SRR values (524-1413 micrograms S/(dm3 day)). The maximal SRR values were shown for the sediments present within the stretch of decomposing macrophytes, in local pits at the lower littoral waterline, and in the mouth of a freshwater stream (51-159 mg S/(dm3 day)). A sharp difference in the level of H2S production in the type microlandscapes was shown. The average hydrogen sulfide production in finely dispersed sediments constituted 125 mg S/(m2 day); in stormy discharge deposits, 1950 mg S/(m2 day); in depressions under stones and in silted pits, 4300 mg S/(m2 day). A calculation made with regard to the area of microlandscapes with increased productivity shows that the daily H2S production per 1 km2 of the littoral (August) is 60.8 to 202 kg S/(km2 day), while the organic carbon consumption for sulfate reduction per 1 km2 of the littoral is 46 to 152 kg C(org)/(km2 day).     

A disintegration method for direct counting of bacteria in clay-dominated sediments: dissolving silicates and subsequent fluorescent staining of bacteria

The masking of bacteria by abundant microparticles of the clay and silt fraction and cell losses due to sonication hampered direct enumeration of bacteria in sediments dominated by fine sediments. These problems can be circumvented by dissolving silicate fine particles using hydrofluoric acid and subsequent staining of bacteria by DTAF. The developed disintegration method partly replaces mechanical separation of bacteria from sediment particles by chemical disintegration of the silicates. Recovery efficiency ranged from 90% to 111% for different clays and clay-dominated sediments. Especially for the analysis of fine sediments and clays, this method circumvents both strong dilution of the sediment sample and harsh sonication. The method can also therefore be used in sediments where particle abundance is several orders of magnitude higher than bacterial abundance and simple dilution would not suffice in reliably counting bacteria.     

Distribution and ecology of campylobacters in coastal plain streams (Georgia, United States of America)

Campylobacter is the leading cause of bacterium-associated diarrhea in the United States and most developed countries. While this disease is considered a food-borne disease, many clinical cases cannot be linked to a food source. In rural and agrarian areas environmental transmission may be an important factor contributing to case loads. Here we investigated the waterborne prevalence of campylobacters in a mixed-use rural watershed in the coastal plain of southern Georgia (United States). Six sites representing various degrees of agricultural and human influence were surveyed biweekly to monthly for 1 year for the presence of culturable thermophilic campylobacters and other measures of water quality. Campylobacters were frequently present in agriculture- and sewage-impacted stretches of streams. The mean campylobacter counts and overall prevalence were highest downstream from a wastewater treatment plant that handled both human and poultry slaughterhouse waste (相似文献   

Local distributions of sandhoppers and landhoppers (Crustacea: Amphipoda: Talitridae) in the coastal zone of western Tasmania

Twelve species of talitrid amphipods were recorded from pitfall transects across the supralittoral and maritime zones at three localities on the west coast of Tasmania; three were sandhoppers, the rest were landhoppers. There was a sharp demarcation between the highest range of the sandhoppers and the lowest range of the landhoppers. Organic content and sodium content of the substrate in the range of the sandhoppers were very low, but rose sharply as the sand was colonised by plants, and landhoppers replaced sandhoppers. Coastal group landhopper species were restricted to a zone about 40–70 m above the high tide mark. Cooler, wetter weather increased the activity of sandhoppers, but only affected landhopper activity slightly. These differences support the idea that landhoppers did not evolve directly from sandhopper ancestors.     

Patterns of incorporation of tritiated thymidine by the dorsal polytene foot-pad nuclei of Sarcophaga bullata (Sarcophagidae: Diptera)

The incorporation of tritiated thymidine into the DNA of the dorsal foot-pad nuclei of Sarcophaga bullata, during pharate adult development, was studied by scintillation counting and autoradiography. Incorporation was maximal on day 4 and showed a progressive temporal decline on days 5 to 8. Autoradiographs of chromosomal arms A¹, A² and D¹, from late stages of the prolonged S period, showed discontinuous incorporation. On days 7 and 8 loci which incorporated the radio-labeled precursor were almost exclusively associated with DNA granules. DNA granules were associated with 8 specific loci in chromosomal arm A¹, 10 in A², and 8 in D¹. The relationship between patterns of incorporation of tritiated thymidine and DNA granules is discussed.Deceased June 15, 1975     

Impacts of laurel wilt disease on redbay (Persea borbonia (L.) Spreng.) population structure and forest communities in the coastal plain of Georgia, USA

Laurel wilt disease (LWD), a fungal disease vectored by the non-native redbay ambrosia beetle (Xyleborus glabratus Eichhoff), has caused mortality of redbay (Persea borbonia (L.) Spreng.) in the coastal plain of Georgia since 2003. Despite its rapid spread, little research has evaluated its impacts on redbay population structure and forest communities. Diseased populations of redbay in five sites (2–4 years post infestation) were compared to healthy populations in three uninfested sites in five counties in Georgia. The results showed high redbay mortality, shifts in size structure, and changes in community composition. An average of 90 % of redbay trees ≥3 cm diameter at breast height (DBH) were dead in infested sites, compared to 0–35 % in control sites. Mortality was seen in individuals of the smallest stem diameter category (<1.00 cm diameter at ground height). DBH of live redbay trees in control sites was twice that of those in infested sites. Photosynthetically active radiation was 4.8 times greater at infested sites than control sites due to loss of redbay canopy. Community structure measurements showed redbay trees had the greatest mean importance value (IV) at control sites compared to the 8th mean IV at infested sites for live stems. Two species co-dominant to redbay, sweetbay (Magnolia virginiana L.) and loblolly bay (Gordonia lasianthus (L.) J. Ellis), were of higher importance at infested than control sites, suggesting they are increasing in dominance following the mortality of redbay. This study shows LWD has impacted redbay populations and altered associated forest communities in Georgia.     

Decline in zoobenthos densities in the profundal sediments of Lake Mendota (Wisconsin,USA)

High densities of zoobenthos inhabited Lake Mendota's profundal zone in the early 1900s through the mid-1940s. Chaoborus punctipennis was the most abundant organism during the winter, along with moderate densities of Chironomus spp., Pisidium sp., oligochaetes, and Procladius sp. By the early 1950s, Chaoborus punctipennis densities had declined to 10% of former levels, while Chironomus increased significantly. However, by the mid-1960s, Chaoborus, Chironomus, and Pisidium densities had decreased to very low population levels. By 1987–89, Pisidium was no longer found. Zoobenthos that had not decreased from earlier surveys were oligochaetes and Procladius, although further sampling of oligochaetes is needed to confirm current densities. These organisms are the most tolerant of severe anoxia.Four possible reasons for this decline were evaluated: (a) decline in food availability, (b) increase in fish predation, (c) use of toxic insecticides in the drainage basin, and (d) changes in the profundal sediment environment. Based on literature information and long-term data for Lake Mendota, a change in the profundal sediment environment is the most likely explanation for the decline in the less-tolerant zoobenthos species. Although the duration and extent of anoxia in the hypolimnion have not changed since the early 1900s, hypolimnetic ammonia and hydrogen sulfide concentrations apparently have increased as Mendota became more eutrophic after the mid-1940s. However, further study is needed to determine if these higher concentrations or other factors were responsible for the dramatic decline in lake Mendota's profundal zoobenthos.     

Transport of carbon dioxide and ammonium in bioturbated (Nereis diversicolor) coastal, marine sediments

Two identical experiments with sieved and homogenized sandy and muddy sediment were conducted to determine transport enhancement of porewater solutes (TCO₂ and NH₄ ⁺) by the presence of the polychaeteNereis diversicolor (1000–1500 m^–2). Flux measurements showed thatN. diversicolor enhanced the release of CO₂ and NH₄ ⁺ 1.5–5 times. Accordingly, porewater concentrations of these compounds were reduced considerably in the bioturbated zone of both types of sediments. Two different diagenetic models, effective (eddy) diffusion and nonlocal exchange, were used to describe solute profiles in the bioturbated sediments. In permeable sandy sediments advective porewater movements may occur more readily than in more cohesive muddy sediments. The effective diffusion model (with D_e=1.6–2.0 cm² d^–1) provided an excellent fit to the measured concentrations of both solutes below the bioturbated zone in permeable sandy sediment, whereas this model overestimated the concentration in the bioturbated zone. However, in the less permeable muddy sediment the effective diffusion model overestimated the NH₄ ⁺ profile considerably at all depths. The nonlocal exchange model (with=0.17–0.29 d^–1), on the other hand, provided an excellent fit in the less permeable muddy sediment, suggesting that solute profiles here were controlled by molecular diffusion, even in the presence of burrow irrigation. For the permeable sediment, the nonlocal exchange model (with=0.14 d^–1) underestimated the measured NH₄ ⁺ profile. Accordingly, linear slopes from plots of porewater TCO₂ as a function of porewater NH₄ ⁺ revealed that eddy diffusion (or advective porewater movements) was important in the bioturbated zone of this sediment type. However, combined with the generally more realistic shape of profiles derived by the nonlocal exchange, these evidences suggest that both eddy and molecular diffusion must operate in the bioturbated zone of permeable sediments.