The effects of tributyltin within aThalassia seagrass ecosystem

Flow-through seagrass core microcosms were used to examine responses of species and processes to a logarithmic gradient of dosing with¹⁴C-labeled tributyltin-chloride (TBT-CI). Experiments involved delivery of TBT-CI to the water column of replicate cores of a treatment (n=16) once per week; one-half of the cores were sacrificed after 3 wk of dosing, the others were dosed for 6 wk. Initial water column concentrations for the three treatments averaged 0.205, 2.23, and 22.21 μg I^?1, expressed as the TBT⁺ cation, but these concentrations dropped rapidly. Retained¹⁴C tracer, an estimate of total organotin species, was distributed to sediments, plants, and other biological tissues, all of whose tracer concentrations increased with time. Measures to indicate responses of both autotrophic and heterotrophic organisms were made; in general, treatment effects were demonstrable statistically only at the highest dose level. Accumulation of chlorophyll and biomass on glass slides was highest when suspended for the entire experiment in the water of the highest treatment; this unexpected result was perhaps an indirect effect related to reduced grazing activity in the microcosms. The highest dose of TBT-CI resulted in virtual population mortality of a few macrobenthic species and decreased loss of plant material in litter bags, both demonstrated within the first 3 wk of dosing. Reduced litter loss was coincident with mortality of an amphipod (Cymadusa compta) capable of shredding plant material, and a causal relation between the two effects is plausible. Thus, if concentrated to similar levels in aThalassia bed, TBT⁺ may have direct species-level effects and process-level effects, potentially causing ecosystem change via disruption of a species-process linkage influential in seagrass detrital food web dynamics.     

Origins of metamorphic lode gold deposits: Implications of stable isotope data from the central Rocky Mountains,Canada

Summary The stable isotope geochemistry of native gold-bearing quartz veins contained within low-grade metasedimentary strata in the central Canadian Rocky Mountains, British Columbia is examined. The data augment previous geological and geochemical studies.Vein pyrite ³⁴S values cluster between + 14.2 and + 16.3 (CDT). Coeval galenas exhibit ³⁴S values between + 11.4 and 13.3. Pyrite-galena geothermometry reveals a mean temperature of mineralization of 300 ± 43°C. Comparison of ³⁴S values for the vein pyrites, with values for pyrite porphyroblasts in country rocks suggests that vein sulfur was probably derived from the host rocks.¹⁸O(SMOW) values of host quartzites and pelites cluster between + 12.0 and + 13.5, and + 9.5 and + 10.5, respectively. Auriferous vein quartz exhibits ¹⁸O values between + 13.0 and + 15.0. Veins were likely deposited from fluids undergoing post-peak metamorphic cooling.Vein inclusion fluids exhibit values between –105 and –124 (SMOW). Combined O-H-isotope data are most compatible with a source fluid involving chemically- and isotopically-evolved meteoric waters.The critical role of H-isotope data in the evaluation of source fluids for such mesothermal gold lodes is stressed. The paucity of H-isotope data pertaining to the study of lode gold deposits in similar low-grade metasedimentary domains suggests that the involvement of meteoric waters may at times be overlooked.

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Der Ursprung metamorphogener Gold-Ganglagerstätten: Bedeutung stabiler Isotopendaten aus den zentralen Rocky Mountains, Kanada

Zusammenfassung Die vorliegende Arbeit befaßt sich mit der Untersuchung der Geochemie stabiler Isotope goldführender Quarzgänge in schwach metamorphen Sedimenten der zentralen Rocky Mountains in Britisch Kolumbien, Kanada. Die Resultate ergänzen früher publizierte geologische und geochemische Daten.Die ³⁴S-Werte von Gang-Pyrit liegen zwischen + 14.2 und + 16.3 (CDT); gleichzeitig gebildeter Bleiglanz hat ³⁴S-Werte von + 11.4 bis + 13.3. Die Isotopengeothermo metrie des Pyrits und Bleiglanzes ergibt eine mittlere Mineralisationstemperatur von 300°C + 43° für diese beiden Minerale. Vergleiche der 8345-Werte des Gang-Pyrits mit denen von Pyrit-Porphyroblasten des Nebengesteins lassen für die Gang-Pyrite eine Herkunft des Schwefels aus dem Nebengestein als wahrscheinlich erscheinen.Die ¹⁸O-Werte von Quarziten und Peliten, die als Nebengesteine auftreten, streuen von + 12.0 bis + 13.5 (SMOW), beziehungweise von +9.5 bis + 10.5 Quarz goldführender Gänge hat ¹⁸O-Werte, die zwischen + 13.0 und + 15.0 (SMOW) liegen. Er wurde als Gangfüllung wahrscheinlich bei sinkenden Temperaturen aus post metamorphen wäßrigen Lösungen abgesetzt.Flüssigkeitseinschlüsse von Gangmineralien zeigen D-Werte von -105 bis -124 (SMOW). Die H-O-Isotope sind deshalb ein Hinweis dafür, daß als mineralisierende Lösungen isotopisch veränderte meteorische Wässer in Betracht zu ziehen sind. Bei der Deutung der Herkunft der mineralisierenden wäßrigen Lösungen von mesothermalen Goldgängen muß die Kenntnis der H-Isotope als kritisch betrachtet werden. Die Seltenheit mit der H-Isotopendaten dieses Lagerstättentyps in der Literatur diskutiert werden, dürfte ein wesentlicher Grund dafür sein, daß die Rolle meteorischer Wässer bei der Genese mesothermaler, in Metasedimenten liegender Goldgänge, vielfach übersehen wurde.

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With 4 Figures     

Long-term change in eelgrass distribution at Bahía San Quintín,Baja California,Mexico, using satellite imagery

Seagrasses are critically important components of many marine coastal and estuarine ecosystems, but are declining worldwide. Spatial change in distribution of eelgrass,Zostera marina L., was assessed at Bahía San Quintín, Baja California, Mexico, using a map to map comparison of data interpreted from a 1987 Satellite Pour l'Observation de la Terre multispectral satellite image and a 2000 Landsat Enhanced Thematic Mapping image. Eelgrass comprised 49% and 43% of the areal extent of the bay in 1987 and 2000, respectively. Spatial extent of eelgrass was 13% less (−321 ha) in 2000 than in 1987 with most losses occurring in subtidal areas. Over the 13-yr study period, there was a 34% loss of submerged eelgrass (−457 ha) and a 13% (+136 ha) gain of intertidal eelgrass. Within the two types of intertidal eelgrass, the patchy cover class (<85% cover) expanded (+250 ha) and continuous cover class (≥85% cover) declined (−114 ha). Most eelgrass losses were likely the result of sediment loading and turbidity caused by a single flooding event in winter of 1992–1993. Recent large-scale agricultural development of adjacent uplands may have exacerbated the effects of the flood. Oyster farming was not associated with any detectable losses in eelgrass spatial extent, despite the increase in number of oyster racks from 57 to 484 over the study period.     

Sustainability of groundwater in Mali,West Africa

The following paper describes the goals and some preliminary work in the Bani sustainability study, an ongoing project in Mali, West Africa. Rural communities in Mali are increasingly relying on hand-pumps, which tap groundwater resources, as a means of obtaining potable water. The long-term sustainable yield of groundwater resources is not known but can be evaluated in sustainability study. In 2005, a groundwater sustainability study was established along the Bani River of Mali. The Bani study collected groundwater levels that were used in a conceptual groundwater flow model—the Bani model—to develop an understanding of current aquifer conditions and to make limited predictions of sustainability under various future scenarios. The Bani model showed the climatic parameters of recharge (derived from precipitation) and evapotranspiration to influence simulated groundwater levels and groundwater volume available, while increased pumping rates, due to population growth, showed little effect. When considered in the context of the actual Bani sustainability study area, the change in groundwater levels resulting from climatic parameters may have negative implications, especially during several consecutive years of decreased precipitation, such as drought, or if downward trends anticipated for precipitation continue.     

Pure-phase transport and dissolution of TCE in sedimentary rock saprolite

The objective of this study was to experimentally determine the influence of pore structure on the transport and dissolution of trichloroethylene (TCE) in clay-rich saprolite. In order to simulate a "spill," pure-phase TCE containing a water-insoluble fluorescent dye was injected into two heterogeneous 24-cm-diameter by 37-cm-long undisturbed columns of water-saturated saprolite. TCE entry occurred at capillary pressures of 2.7 and 4.0 kPa. Ten or 28 d after injection, the column was sliced horizontally into three sections and visually examined. The distribution of fluorescent dye indicated that pure-phase TCE migrated mainly through fractures in the shale saprolite and through fine root holes or other macropores in the limestone saprolite residuum. Analysis of saprolite subsamples indicated that TCE was present throughout much of the saprolite column but usually at concentrations less than the solubility of TCE. This spreading was caused by diffusion, which also contributed to the rapid dissolution of TCE in the fractures and macropores. Modeling was carried out using previously published dissolution and diffusion equations. The calculations confirm that rapid disappearance of immiscible TCE can occur in this type of material because of the small size of fracture or macropore openings and the high porosity of the fine-grained material. This study indicates that industrial solvents can readily enter fractures and macropores in otherwise very fine-grained subsoils and then rapidly dissolve and diffuse into the fine-pore structure, from which they may be very difficult to remove.     

Recent developments with the Anglo-Australian Telescope

This report describes the instruments currently available on the 3.9 m Anglo-Australian Telescope, with particular reference to the recent additions of optical fibres for multi-object spectroscopy, a low resolution spectrograph with a red-sensitive charge-coupled device and software for obtaining infrared images by scanning the telescope in synchronism with the recording of data from the InSb photometer.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

The sediment and hydrographic characteristics of three horseshoe crab nursery beaches in hong kong

1　Introduction　Thelifecycleofhorseshoecrabsislengthywhencom paredtoothermarinearthropodssuchasbluecrabsandshrimpspecies (Sekiguchietal.,1988) .Thetwospecies,TachypleustridentatusandCarcinoscorpiusrotundicauda,knowntooccurinHongKongrequire ,respectively ,betweenthirteentofourteenandtentoelevenyearstomaturebeforedepartingtheirnurserybeachesfordeeperwaters (ChiuandMorton ,1999a ;Sekiguchietal.,1988) .Thelivingenvironmentofthenurserybeacheswheretheeggsarelaidandincu bated ,andfromwhichtheyoun…     

Limits on the trapping of atmospheric CH4 in martian polar ice analogs

Recent detection of methane (CH₄) on Mars has generated interest in possible biological or geological sources, but the factors responsible for the reported variability are not understood. Here we explore one potential sink that might affect the seasonal cycling of CH₄ on Mars - trapping in ices deposited on the surface. Our apparatus consisted of a high-vacuum chamber in which three different Mars ice analogs (water, carbon dioxide, and carbon dioxide clathrate hydrates) were deposited in the presence of CH₄ gas. The ices were monitored for spectroscopic evidence of CH₄ trapping using transmission Fourier-Transform Infrared (FT-IR) spectroscopy, and during subsequent sublimation of the ice films the vapor composition was measured using mass spectrometry (MS). Trapping of CH₄ in water ice was confirmed at deposition temperatures <100 K which is consistent with previous work, thus validating the experimental methods. However, no trapping of CH₄ was observed in the ice analogs studied at warmer temperatures (140 K for H₂O and CO₂ clathrate, 90 K for CO₂ snow) with approximately 10 mTorr CH₄ in the chamber. From experimental detection limits these results provide an upper limit of 0.02 for the atmosphere/ice trapping ratio of CH₄. If it is assumed that the trapping mechanism is linear with CH₄ partial pressure and can be extrapolated to Mars, this upper limit would indicate that less than 1% is expected to be trapped from the largest reported CH₄ plume, and therefore does not represent a significant sink for CH₄.