The transport of bacteria in the sediments of a temperate marsh

The number of bacteria in sediments, interstitial water and overlying tidal water of an oligohaline marsh system are about 10⁹, 10⁶ and 10⁶ cells cm^?3, respectively. Average cell size in the overlying water (about 0·06 μm³), is much smaller than that in sediments and interstitial water (about 0·18 μm³). Most bacterial cells in sediments are bound to sediment particles and less than 1% of the cells were displaced by percolating water through sediment columns. Concentration of bacteria in flooding tidal waters is generally higher than that in ebbing waters. Movement of bacterial biomass does not appear to be a significant mechanism of particulate organic transport in marsh sediments and marsh sediments do not appear to be a source of suspended bacteria for estuaries.     

Transport and distribution of bacteria and diatoms in the aqueous surface microlayer of a salt marsh

The effects of tide and wind upon the distribution and transport of bacteria and diatoms in the aqueous surface microlayers of a Massachusetts and San Francisco Bay salt marsh were examined. The compression of the surface films by both tide and wind resulted in significant enrichments of bacterioneuston. At the San Francisco Bay site, significant numbers of diatoms were transported within the microlayer over a tidal cycle.     

Bacterial sulphate reduction in sediments of a european salt marsh: Acid-volatile and tin-reducible products

The products of ³⁵S-sulphate reduction by sedimentary bacteria were measured at two sites in a salt marsh on the east coast of England. Non-acid-volatile products were measured, after acid-volatile sulphide was removed, by their reduction to sulphide by digestion with tin. The proportion of the sulphate reduced to tin-reducible products varied between 25% in a salt marsh pan and 61% in creek sediment, over a 0–25 cm depth profile. There were also variations with depth at each site in the proportions of sulphate reduced to tin-reducible products. Further examination revealed differences in the proportions of sulphate which were reduced to free sulphide, acid-volatile sulphide, sulphur or pyrite at the two sites. The data suggest that previous work which did not measure non-acid-volatile products underestimated sulphate reduction rates by three-fold in the creek site, but by only one third in the pan.     

Comparison of four numerical models for simulating seepage from salt marsh sediments

A boundary integral equation method (BIEM) model and three differently formulated finite element method (FEM) models were implemented to explore the spatial and temporal patterns in marsh pore water seepage that each generated. The BIEM model is based on the Laplace equation coupled to a dynamic free-surface condition that assumes that, as the water-table changes, the aquifer instantaneously loses or gains an amount of water equal to the change in head times the specific yield. The FEM models all implement a simplified Richards equation that allows gradual desaturation or resaturation and thus flow in both the saturated and unsaturated zones of the aquifer. Two of the FEM models are based on the governing equation for the USGS model SUTRA and thus take into account fluid and aquifer compressibility. One of these was modified to take into account the effect of tidal loading on the total stress, which is assumed to be constant in the derivation of the original version of SUTRA. The third FEM model assumes that neither the fluid or aquifer matrix is compressible so that changes in storage are due solely to changes in saturation. The unmodified SUTRA model generated instantaneous boundary fluxes that were up to two orders of magnitude greater, and spatially more uniform, than those of the other models. The FEM model without compressibility generated spatial and temporal patterns of the boundary fluxes very similar to those produced by the BIEM model. The SUTRA model with the tidal stress modification gave fluxes similar in magnitude to the BIEM and no compressibility models but with distinctly different distributions in space and time. These results indicate that accurate simulation of seepage from marsh soils is highly sensitive to aquifer compressibility and to proper formulation of the effect of tidal loading on the total stress in the aquifer. They also suggest that accurate simulation may require total stress correction not only for tidal loading but for changes in the water table as well. Finally, to aid the development of methods for the measurement of compressibility, we present a schematic, pore-scale model to illustrate the factors that may govern the compressibility of marsh soils.     

Nitrogen losses from a Louisiana Gulf Coast salt marsh

Losses of ¹⁵N labelled nitrogen in a Spartina alterniflora salt marsh was measured over three growing seasons. Labelled $\text{NH}{}_4{}^{\mathrm{+}}\text{N}$ equivalent to 100 μg ¹⁵N g^?1 of dry soil was added in four instalments over an eight week period. Recovery of the added nitrogen ranged from 93% 5 months after addition of the $\text{NH}{}_4{}^{\mathrm{+}}\text{N}$ to 52% at the end of the third growing season which represented a nitrogen loss equivalent to 3·4 gNm^?2. The availability of the labelled $\text{NH}{}_4{}^{\mathrm{+}}\text{N}$ incorporated into the organic fraction was estimated by calculation of the rate of mineralization. The time required for mineralization of 1% of the tagged organic N increases progressively with succeeding cuttings of the S. alterniflora and ranged from 152 to 299 days. Only 2% of the nitrogen applied as ¹⁵N labelled plant material to the marsh surface in the fall could be accounted for in S. alterniflora the following season.     

Arsenic incorporation in a salt marsh ecosystem

Replicate portions of a Delaware salt marsh were enclosed in cylindrical microcosms and exposed to elevated levels of inorganic arsenic (arsenate). All biotic and abiotic components in dosed cylinders rapidly incorporated arsenic. Spartina blades showed the greatest arsenic enrichment, with dosed plants incorporating arsenic concentrations an order of magnitude higher than controls. Spartina detritus and sediments also exhibited greatly elevated arsenic concentrations. Virtually all of the arsenic was incorporated into plant tissue or strongly sorbed to cell surfaces. Thus, elevated arsenic concentrations in estuarine waters will be reflected in living and non-living components of a salt marsh ecosystem, implying that increased arsenic will be available to organisms within the marsh ecosystem.     

Copepod colonization of natural and artificial substrates in a salt marsh pool

Pre-weighed packets of Spartina alterniflora and of plastic (polypropylene) twine were placed in a salt marsh pool and recovered on 40 dates spanning 14 months. New packets were placed out regularly to provide a contrast with ageing material. Twelve species of copepods were extracted, counted, and identified. Dry weight and Kjeldahl-nitrogen were determined for Spartina packets.Eight species of copepods, Amphiascus pallidus, Onychocamptus mohammed, Cletocamptus deitersei, Halicyclops sp., Harpacticus chelifer, Mesochra lilljeborgii, Metis jousseaumei and Nitocra sp. were found in higher densities on old grass or plastic packets than on new. The quantity of material was important in that the relative attractiveness of old grass was much lower early in the second year when 7–15% dw and 0·7% nitrogen remained than early in the first year when over 60% dw and 2·0% nitrogen remained. Old plastic polypropylene was equally or more attractive than old grass to 7 of 8 species, therefore, nitrogen decline in old grass was not the factor making it less attractive. Once aged, the quantity of substrate was more important than its quality. Apparently, this is due to colonization by microflora or settlement of detritus but these were not studied. The four clear exceptions to these trends were Darcythompsonia fairliensis and Eurytemora affinis which showed highest densities 72% and 50% of the time in new grass, Apocyclops spartinus with 70% in grass and equal numbers between old and new packets and Acartia tonsa a bay calanoid with 82% of highest densities in the water column and only two occurrences out of 40 dates in the packets.     

潮间带盐沼植物黏附悬浮颗粒物的差异性研究

为了研究潮间带盐沼植物黏附悬浮颗粒物的差异性,在长江口选择了三种盐沼植物群落对它们黏附的颗粒物质量进行测定,结果表明:(1)植物群落距潮沟或光滩越近,生长位置的滩面高程越低,则黏附颗粒物越多,而在盐沼前缘单位滩地面积上植物黏附颗粒物的质量以1%~3%/m(单位水平距离)的速率从水体悬浮颗粒物含量相对较高的盐沼外缘光滩或潮沟向盐沼内部减小;(2)植物黏附的颗粒物量在垂向上从上到下急剧增大,通常在靠近滩面5~10 cm的部分植物的黏附量占植物黏附总量的三分之一以上;(3)相邻群落单位滩地面积的互花米草[(220.6±172.7)g/m2]的总黏附量明显多于芦苇[(64.9±38.1)g/m2]和海三棱藨草[(45.2±31.7)g/m2],而按单位生物量来说单位滩地面积上三种盐沼植物黏附的颗粒物以海三棱藨草最多[(150.5±134.8)g/kg],芦苇最少[(28.8±22.8)g/kg],互花米草介于两者之间[(57.5±32.9)g/kg];(4)海三棱藨草的黏附量在季节上差异性明显,秋初(9月)是春末(5月)的6倍,在冬季该植物消失,其黏附颗粒物的功能也消失。造成盐沼植物黏附悬浮颗粒物差异的根本原因是生物量、悬浮颗粒物含量和淹没条件(淹没的深度、时间、频率)的不同。     

Aquatic macroinvertebrate communities of natural and ditched potholes in a San Francisco Bay salt marsh

Differences in macroinvertebrate community structure and composition were examined from April 1980 to March 1981 in three potholes that had been ditched for mosquito control and three natural (i.e. unditched) potholes, which are located in a San Francisco Bay, California, U.S.A. salt marsh. Measurements of incipient tidal flooding into potholes (i.e. pothole inundation threshold) indicated that these sites comprise a gradient of tidal influences. Exponential decreases in the frequency and duration of tidal inundation corresponded to linear increases in inundation threshold. Since ditched study sites had low thresholds they tended to be more uniformly and regularly influenced by tides, were less saline, had less variable temperature regimens, and supported less filamentous algae than natural potholes. Habitat conditions were generally more similar among ditched than unditched potholes, but environmental conditions were most severe at natural sites near the upper limit of the inundation threshold gradient, where some potholes desiccate during the dry season each year.Differences in macroinvertebrate communities corresponded to differences in habitat conditions. Species richness and diversity (Simpson's Index) were generally highest near the middle of the inundation threshold gradient, which is a pattern predicted by the Intermediate Disturbance Hypothesis. Analysis of faunal composition using discriminant functions indicated more similarity among potholes located at the lowest positions of the inundation gradient than among potholes with intermediate thresholds. Since ditching lowers the inundation thresholds of potholes, it reduces species richness and diversity, while increasing faunal similarity. As a result, extensive ditching to control salt marsh mosquitoes can reduce the overall complexity of lentic macroinvertebrate communities.     

Nitrogen and phosphorus concentrations within North Inlet,South Carolina—Speculation as to sources and sinks

The daily concentrations of $\text{NH}{}_4{}^{\mathrm{+}}$, $\text{NO}{}_3{}^{\mathrm{?}}$, and $\text{NO}{}_3{}^{\mathrm{?}}\text{+ NO}{}_2{}^{\mathrm{?}}$ within the North Inlet system are all negatively associated with tidal stage during the late summer, this association breaking down during the winter. The high concentrations of these constituents during low tide coupled with the lack of streamflow during the late summer suggests that there is an internal source for these species. Ammonium and orthophosphate most likely have their source in sediment diffusion from tidal creek sediments and/or seepage from the vegetated marsh surface during tidal exposure. It is hypothesized that high nitrate plus nitrite values at low tide are caused by nitrification within the tidal water or tidal creek sediments. During the summer there is evidence for a source of dissolved organic nitrogen and dissolved organic phosphorus within the North Inlet system, probably via diffusion from creek sediments. In general the main source of dissolved organic nitrogen is via stream-flow from the adjacent watershed. Particulate nitrogen and phosphorus concentrations are a function of: (1) wind and rain events which cause resuspension of particulate material from the tidal creek banks, (2) rain events which scour the marsh surface during tidal exposure, and (3) high tidal velocities which scour the creek bottoms.     

The process of sedimentation on the surface of a salt marsh

An unditched salt marsh-creek drainage basin (Holland Glade Marsh, Lewes, Delaware) has a sedimentation rate of 0·5 cm year^?1. During normal, storm-free conditions, the creek carries negligible amounts of sand and coarse silt. Of the material in the waters flooding the marsh surface, over 80% disappears from the floodwaters within 12 m of the creek. About one-half of the lost material is theoretically too fine to settle, even if flow were not turbulent; however, sediment found on Spartina stems can account for the loss.The quantity of suspended sediment that does reach the back marsh during these normal tides is inadequate to maintain the marsh surface against local sea level rise. This suspended sediment is also much finer than the deposited sediments. Additionally, remote sections of low marsh, sections flooded by only the highest spring tides, have 15–30 cm of highly inorganic marsh muds.This evidence indicates that normal tidal flooding does not produce sedimentation in Holland Glade. Study of the effects of two severe storms, of a frequency of once per year, suggests that such storms can deposit sufficient sediment to maintain the marsh.The actual deposition of fine-grained sediments (fine silt and clay) appears to result primarily from biological trapping rather than from settling. In addition, this study proposes that the total sedimentation on mature marshes results from a balance between tidal and storm sedimentation. Storms will control sediment supply and movement on micro- and meso-tidal marshes, and will have less influence on macro-tidal marshes.     

Particulate matter at the estuarine salt marsh surface microlayer: Particle-size distributions and comparison to bulk suspension

Particle-size distributions have been measured for paired samples from the surface microlayer and bulk suspension in a South San Francisco Bay salt marsh. Comparison of size distributions reveals no consistent differences in surface microlayer and bulk particle populations; however, particle numbers were, at times, considerably enriched at the marsh microlayer. An empirical power curve was found to fit the particle-size distributions. The fitted exponents of particle size distributions indicate a slightly greater fraction of particle volume and a substantially greater fraction of particle surface area reside in small (colloidal) particle-size ranges.     

The ebb and flood of Silica: Quantifying dissolved and biogenic silica fluxes from a temperate salt marsh

Salt marshes are widely studied due to the broad range of ecosystem services they provide including serving as crucial wildlife habitat and as hotspots for biogeochemical cycling. Nutrients such as nitrogen (N), phosphorus (P), and carbon (C) are well studied in these systems. However, salt marshes may also be important environments for the cycling of another key nutrient, silica (Si). Found at the land–sea interface, these systems are silica replete with large stocks in plant biomass, sediments, and porewater, and therefore, have the potential to play a substantial role in the transformation and export of silica to coastal waters. In an effort to better understand this role, we measured the fluxes of dissolved (DSi) and biogenic (BSi) silica into and out of two tidal creeks in a temperate, North American (Rowley, Massachusetts, USA) salt marsh. One of the creeks has been fertilized from May to September for six years allowing us to examine the impacts of nutrient addition on silica dynamics within the marsh. High-resolution sampling in July 2010 showed no significant differences in Si concentrations between the fertilized and reference creeks with dissolved silica ranging from 0.5 to 108 μM and biogenic from 2.0 to 56 μM. Net fluxes indicated that the marsh is a point source of dissolved silica to the estuary in the summer with a net flux of approximately 169 mol h⁻¹, demonstrating that this system exports DSi on the same magnitude as some nearby, mid-sized rivers. If these findings hold true for all salt marshes, then these already valuable regions are contributing yet another ecosystem service that has been previously overlooked; by exporting DSi to coastal receiving waters, salt marshes are actively providing this important nutrient for coastal primary productivity.     

Behaviour of iron,manganese, phosphate and humic acid during mixing in a Delaware salt marsh creek

The mixing behaviour of iron, manganese, phosphate and humic acid in a Delaware salt marsh creek was studied using field data, laboratory mixing experiments, and geochemical mass balance equations. Property-salinity diagrams for field data indicated that the removal of iron is 56–70% in the 0–10‰ salinity range. A proposed mechanism of removal is the flocculation of colloidal iron, perhaps with humic acid. Phosphate, however, undergoes 195% addition in the same low salinity region, which may be due to release of phosphate from resuspended sediments. Dissolved manganese is conserved, as is humic acid throughout the salt marsh mixing zone. Within the uncertainty of the data the maximum possible removal of humic acid is 23%.Laboratory mixing experiments that simulated salt marsh mixing along the same salinity gradient as observed in the field (5–25‰) showed only small-scale additions and removals compared to the field results. Such small-scale changes occurred largely at salinities >10‰ in the laboratory experiments, whereas most removals and additions occurred at salinities <10‰ in the field. Mixing studies also showed little difference between prefiltered and unfiltered mixes. The studies suggest that simple mixing of salt marsh waters, with or without suspended material, does not strongly influence the observed behaviour of dissolved constituents in salt marshes, and that other processes (e.g. sediment or intertidal exchange) must dominate their behaviour.     

俄罗斯库页岛潮间带沉积物可培养细菌的系统发育多样性

采用2216E、R2A、M1培养基,首次从俄罗斯库页岛潮间带沉积物样品中分离到82株可培养海洋细菌,经查重并菌后选取其中45株具有代表性的菌株进行了16S r RNA基因序列分析和多样性研究。结果发现,它们共分布于变形细菌门(Proteobacteria)、放线菌门(Actinobacteria)、拟杆菌门(Bacteroidetes)和厚壁菌门(Firmicutes)4个类群(分别占45株代表菌株的42.2%、20.0%、20.0%和17.8%),代表着6个纲、27个属、44个种;同时发现其中有8个潜在新种和1个潜在新属。本研究结果表明,俄罗斯库页岛潮间带沉积物可培养细菌的系统发育多样性非常高,大部分菌株与分离自日本和韩国近海的细菌物种在系统发育关系上高度同源,但也存在不少潜在的新物种。