Transport and retention of a conservative tracer in an isolated creek–marsh system

A study of tracer transport and retention in a small tidal creek and marsh system located in the southeastern US was conducted using a three-dimensional hydrodynamic model and data from a dye tracer release. The model simulated tidally driven flow, including inundation and drying out of the marshes and the dispersal of the dye tracer. Flow measurements in the tidal creek showed that the simulations appeared to generally duplicate the tidally driven flow into and out of the tidal creeks and marshes. The dye tracer experiment was conducted to test the hydrodynamic model's ability to simulate dispersal of a point release of pollutants into the creek during an incoming tide. The simulations reproduced much of the experimental measurements, but bathymetric errors and lack of resolution of the smallest arms of the tidal creeks affected the ability to faithfully reproduce the initial peak in measured dye tracer concentrations at a sampling location far from the boundary. The lack of the smallest tidal creeks led to some trapping of water and dye in the marshes. Two independent estimates of flushing time yielded values between 1.6 and 2.4 days. An uncertainty analysis indicates that model simulations are sensitive to variations in parameters such as water depth and marsh grass density. On the other hand, omission of the smallest tidal creeks in simulations may be partially offset by decreasing marsh grass density. Further improvements must rely on more accurate and detailed bathymetric data that resolves the smaller arms of the tidal creeks and includes quantitative information about the density and distribution of marsh grass.     

Terminal Proterozoic mid-shelf benthic microbial mats in the Centralian Superbasin and their environmental significance.

A combined sedimentological and biogeochemical study has been conducted on several Terminal Proterozoic mid-shelf microbial mat facies from the Centralian Super-basin. Isotopic and organic geochemical analysis of the bitumen and kerogen indicated that two sources of organic matter from 'planktonic' and 'benthic microbial-mat' populations contributed to the sediment. The 'planktonic' source provided a suite of n-alkanes with C20, whereas, the 'benthic' source contributed an overlay of n-alkanes >C20 with a strong even preference, together with mid-chain methyl alkanes. Kerogen and biomarkers derived from the microbial mat were found to be depleted in 13C relative to planktonic material. Pyrite in the microbial mats was also found to be depleted in 34S compared to surrounding facies. The combination of these observations suggested that the mats may have been at least partly composed of sulfide oxidising bacteria. These organisms have specific environmental tolerances that set limits on palaeo-environment. Their requirement for oxygen indicates that the water column above the mid-shelf could not have been anoxic. Accordingly, from the results and age determinations reported here, it would appear that mid-shelf environments of the Centralian Superbasin of Australia were seeing significant levels of oxygen through the Ediacarian.     

Molecular and isotopic analysis of anaerobic methane-oxidizing communities in marine sediments

Convergent lines of molecular, carbon-isotopic, and phylogenetic evidence have previously indicated (Hinrichs, K.-U., Hayes, J.M., Sylva, S.P., Brewer, P.G., DeLong, E.F., 1999. Methane-consuming archaebacteria in marine sediments. Nature 398, 802–805.) that archaea are involved in the anaerobic oxidation of methane in sediments from the Eel River Basin, offshore northern California. Now, further studies of those same sediments and of sediments from a methane seep in the Santa Barbara Basin have confirmed and extended those results. Mass spectrometric and chromatographic analyses of an authentic standard of sn-2-hydroxyarchaeol (hydroxylated at C-3 in the sn-2 phytanyl moiety) have confirmed our previous, tentative identification of this compound but shown that the previously examined product was the mono-TMS, rather than di-TMS, derivative. Further analyses of ¹³C-depleted lipids, appreciably more abundant in samples from the Santa Barbara Basin, have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in ¹³C. These are additional glycerol ethers and fatty acids. The alkyl substituents in the ethers (mostly monoethers, with some diethers) are non-isoprenoidal. The carbon-number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar, suggesting strongly that they are produced by the same organisms. Their structures, n-alkyl and methyl-branched n-alkyl, require a bacterial rather than archaeal source. The non-isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic, sulfate- and nitrate-reducing organisms which lie near the base of the rRNA-based phylogenetic tree. Based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate, it appears likely that the non-archaeal, ¹³C-depleted lipids are products of one or more previously unknown sulfate-reducing bacteria which grow syntrophically with the methane-utilizing archaea. Their products account for 50% of the fatty acids in the sample from the Santa Barbara Basin. At all methane-seep sites examined, the preservation of aquatic products is apparently enhanced because the methane-oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column.     

Precipitation of iron,manganese, zinc,and copper on clean,ceramic surfaces in a stream draining a polymetallic sulfide deposit

Acid-cleaned ceramic plates placed upstream and downstream from a Cu-Zn-Pb sulfide deposit (Magruder mine) developed a precipitate of Fe-Mn oxides in a 36-day period. Copper and Zn concentrations on the coated surface, normalized to surface area and ratios with Fe and/or Mn, are distinctly anomalous for a distance of 2 km downstream from the mine.The major source of metals in the coatings is interpreted to be groundwater percolating into the stream bed. Anomalous concentrations of Cu and Zn in groundwater from the Magruder mine area, due to oxidation of sulfide minerals, probably accounts for the anomaly identified on the ceramic plates.     

Low abundance of the dinoflagellates,Pfiesteria piscicida, P. shumwayae, andCryptoperidiniopsis spp., in South Carolina tidal creeks and open estuaries

The toxicPfiesteria complex are a group of dinoflagellates that have received considerable attention in recent years as causative factors in fish kill or lesion events in North Carolina estuaries and in the Pocomoke River of Chesapeake Bay. In response to the potentialPfiesteria threat, the South Carolina Task Group on Harmful Algae was formed in late 1997 and implemented programs to monitor harmful algal blooms and respond to fish kills or lesion events with particular emphasis on the Bushy Park (Cooper River, Charleston) region, a site of annually recurrent menhaden lesion events.Pfiesteria piscicida, Pfiesteria shumwayae, andCryptoperidiniopsis spp. were documented in South Carolina estuaries. Routine monitoring and fish kill or lesion event sampling consistently indicated low abundances compared to estimates from similar programs in North Carolina and Maryland that sampled areas with a history ofPfiesteria toxic activity. The finding thatPfiesteria-like organism (PLO) abundances were always low in samples collected during menhaden lesion events in Bushy Park suggested other causes for lesion progression, althoughPfiesteria spp. could not be ruled out as a factor in lesion initiation. Based on the previously demonstrated positive relationship between PLO abundance, chlorophylla, and inorganic nutrient concentrations (in laboratory experiments and North Carolina field observations), we hypothesized that the relatively low abundance ofPfiesteria spp. and other PLO (e.g.,Cryptoperidiniopsis) in South Carolina estuaries is related to the relatively low supply of phytoplankton prey, as supported by interstate comparisons in chlorophylla concentrations. Nitrate concentrations were generally much lower in South Carolina estuaries. Estuarine eutrophication may be an important consideration in explaining interstate differences in susceptibility toPfiesteria-related toxic events.     

Consistent fractionation of 13C in nature and in the laboratory: growth-rate effects in some haptophyte algae

The carbon isotopic fractionation accompanying formation of biomass by alkenone-producing algae in natural marine environments varies systematically with the concentration of dissolved phosphate. Specifically, if the fractionation is expressed by epsilon p approximately delta e - delta p, where delta e and delta p are the delta 13C values for dissolved CO2 and for algal biomass (determined by isotopic analysis of C37 alkadienones), respectively, and if Ce is the concentration of dissolved CO2, micromole kg-1, then b = 38 + 160*[PO4], where [PO4] is the concentration of dissolved phosphate, microM, and b = (25 - epsilon p)Ce. The correlation found between b and [PO4] is due to effects linking nutrient levels to growth rates and cellular carbon budgets for alkenone-containing algae, most likely by trace-metal limitations on algal growth. The relationship reported here is characteristic of 39 samples (r2 = 0.95) from the Santa Monica Basin (six different times during the annual cycle), the equatorial Pacific (boreal spring and fall cruises as well as during an iron-enrichment experiment), and the Peru upwelling zone. Points representative of samples from the Sargasso Sea ([PO4] < or = 0.1 microM) fall above the b = f[PO4] line. Analysis of correlations expected between mu (growth rate), epsilon p, and Ce shows that, for our entire data set, most variations in epsilon p result from variations in mu rather than Ce. Accordingly, before concentrations of dissolved CO2 can be estimated from isotopic fractionations, some means of accounting for variations in growth rate must be found, perhaps by drawing on relationships between [PO4] and Cd/Ca ratios in shells of planktonic foraminifera.     

What is a wave-dominated coast?

During the past decade or so, various coasts have been designated as wave-dominated or tide-dominated. Typically there is an association made between coastal morphology and the dominant process that operates on the coast in question. Most authors consider long, smooth, barrier coasts with few inlets and poorly developed ebb deltas as “wave-dominated”. These coasts are associated with microtidal ranges. Conversely, mesotidal coasts tend to develop short, drumstick-shaped barriers with well-developed ebb deltas. They are considered as tide-dominated barriers. Such generalizations may be restricted to coasts with moderate wave energy although this is commonly not stated.

Exceptions to these stated generalizations are so numerous that wave energy and tidal prism must also be included in characterizing coasts. The relative effects of waves and tides are of extreme importance. It is possible to have wave-dominated coasts with virtually any tidal range and it is likewise possible to have tide-dominated coasts even with very small ranges. The overprint of tidal prism will also produce tide-dominated morphology on coasts with microtidal ranges.     

The rotational periods of Uranus and Neptune

Observations of tilts of spectral lines in the spectrum of Uranus and Neptune yield the following rotational periods: “Uranus,” 24 ± 3 hr; “Neptune,” 22 ± 4 hr. Neptune is confirmed to rotate in a direct sense. The position angle of the pole of Uranus, projected onto the plane of the sky, is found to be 283 ± 4°. The value for Neptune is 32 ± 11°. These results agree with the direction of the pole of Uranus inferred from the common plane of its four brightest satellites and with the direction of the pole of Neptune as inferred from the precession of Triton's orbit. The rotational period of Uranus is found to be consistent with modern values of its optical and dynamical oblateness and the theory of solid-body rotation with hydrostatic equilibrium. This is barely the case for the period derived for Neptune and we suspect that future observations made under better seeing conditions may lead to a shorter rotation period between 15 and 18 hr. Because of a substantial difference between our results and those of earlier spectroscopic and photometric investigations we include an assessment of several previously published photometric studies and a new reduction of the original Lowell and Slipher spectroscopic plates of Uranus [Lowell Obs. Bull. 2, 17–18, 19–20 (1912)]. The early visual photometry of Campbell (Uranus) and Hall (Neptune) is found to be more satisfactorily accounted for by periods of 21.6 and 23.1 hr, respectively, than by the periods originally suggested by the observers. Our reduction of the Lowell and Slipher Uranus plates yields a period near 33 hr uncorrected for seeing. This value is consistent with the results based on the 4-m echelle date.