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Laboratory exposures of the urchin Lytechinus pictus to sediment dosed with varying concentrations of hydrogen sulfide (H2S), but without elevated organic material, were conducted. Changes in mortality, behavior, growth and gonad production were measured during 49 days' flow through exposures. Hydrogen sulfide concentrations of 165·8 μ
liter−1 in pore water caused significant changes in all parameters measured. Concentrations as low as 32·9 μ
liter−1 caused significant decreases in wet weight and male gonad production. A concentration of 91·8 μ
liter−1 caused the mortality rate to increase 100-fold over control exposures (0·63 μ
liter−1). Sublethal effects on growth and gonad production could have been caused by either direct biochemical inhibition by H2S or secondarily through behavioral modifications. Hydrogen sulfide concentrations above 165·8 μ
liter−1 are common near sewage outfalls and could contribute to changes in species composition and sediment toxicity that occur there. 相似文献
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George S. Greenstein 《Astrophysics and Space Science》1968,2(2):155-165
We discuss the implications of the Brans-Dicke scalar-tensor theory for cosmology with particular emphasis on the primordial element abundances that would obtain. Two general classes of models are found. Models of one class expand through the nuclear burning stage slightly more rapidly than the general relativistic case: models of the other class may expand at any rate whatsoever. The first class of models yeilds primordial abundances of D, He3 and He4 in agreement with their general relativistic values if the present mass density is low. High-density cosmologies, however, would produce too much He4. The second class of models yields element abundances which are far too high unless the expansion rate was quite large: in this case no He4 at all is produced. Finally, we determine the rate of change of the constant of gravitationG at the present epoch. For all but a very small class of models is negative at the present epoch. Models with positive values of at the present epoch produce no primordial He4 whatsoever, and have ages significantly lower than the corresponding general relativistic ages. 相似文献
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This article follows one object, a rare car, through its life cycle and in so doing engages the literatures in cultural geography on mobilities, materiality, and enthusiasm to show how all three are linked in the restoration of this one automobile, a Czechoslovakian-built Tatra T87 from 1941. Through archival and autoethnographic research, we trace the history of the Tatra company and then follow the production, sale, and subsequent ownerships of this one particular car through two wars and across two continents. We detail its restoration, tracing a geography of automobile enthusiasm that brought this rusted hulk back to life, one facilitated internationally by the Internet but that nevertheless demands extraordinary mobilities of cars, people, and parts. In following this one thing, we join other scholars in complicating the commodity- or global-value chains so often described as linear, to uncover instead complex entanglements of reuse, repurposing, and restoration. Because the car in question is our own, we mobilize our experiences with the car to reveal how the geographies of enthusiasms (automotive and otherwise) involve sustained and profound emotional engagements—emotional engagements often left out of academic accounts where, we suggest, they might be desirable as well. 相似文献
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During the summer of 1997, sediment core samples were taken at 25 stations in Santa Monica Bay. Toxicity testing was performed on 4-cm sections of the entire length of each core using purple sea urchin fertilization and amphipod survival tests. The sea urchin test identified sections as being toxic at six stations, all located near current or former Hyperion Treatment Plant (HTP) wastewater outfall locations. The amphipod test identified sections from 17 stations as having toxic sediments. The stations having toxic sediments were scattered throughout the bay and toxicity was identified at numerous core depths. Spatial and temporal patterns indicated that toxicity was most strongly associated with the historical disposal of municipal wastewater sludge. Many of the sections toxic to the amphipods did not have chemical levels expected to cause toxicity and were in locations where a source of toxicity was not apparent. 相似文献
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Marinas are areas of special water quality concern because of the potential for pollutant accumulation within their protected waters. Perhaps the largest contaminant source to marinas is antifouling paints that leach copper to prevent the growth of encrusting organisms on vessel bottoms. Very little monitoring of marinas is typically conducted despite the potential environmental risk, particularly in the San Diego region of California, USA where as many as 17,000 recreational vessels are berthed. The objective of this study was twofold: (1) determine the extent and magnitude of dissolved copper concentrations in marinas throughout the San Diego region, and (2) determine if elevated copper concentrations in marinas of the San Diego region are resulting in adverse biological impacts. A probabilistic study design was used to sample water column copper concentrations and toxicity (using Mytilus galloprovincialis) at 30 stations. Results indicated that exceedence of state water quality objectives was widespread (86% of marina area), but that toxicity was much less prevalent (21% of marina area). Toxicity identification evaluations (TIEs) conducted at the most toxic sites indicated that toxicity was largely due to trace metals, most likely copper. Toxicity was reduced using TIE treatments that chelated trace metals such as cation exchange column, ethylenediaminetetraacetic acid (EDTA), and sodium thiosulfate (STS). Moreover, increasing dissolved copper concentrations correlated with increasing toxicity and these copper concentrations were high enough to account for virtually all of the observed toxicity. 相似文献
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The occurrence and concentration of the fuel additive methyl-tert-butyl ether (MTBE) were measured in dry weather runoff, municipal wastewater and industrial effluents, and coastal receiving waters in southern California. Combined, refineries and sewage treatment plants release approximately 214 kg day(-1) of MTBE into the marine environment, with Santa Monica Bay receiving most (98%) of this discharge. Dry weather urban runoff was analysed for samples collected from 25 streams and rivers, and accounted for less than 0.5% of the mass of MTBE discharged to coastal waters. Receiving water samples were collected from 23 stations in Santa Monica Bay, Los Angeles Harbour and Mission Bay or San Diego Bay. MTBE was detected at low concentrations near effluent discharges, however there was no evidence of baywide MTBE contamination related to these outfalls. Marinas and areas used intensively for recreational boating had the highest average MTBE concentration (8.8 microg l(-1)). Surface water contamination was most widespread in San Diego Bay and Mission Bay, areas with no refinery or sewage treatment plant inputs. 相似文献
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We compared nekton use of prominent habitat types within a lagoonal system of the northeastern Gulf of Mexico (GoM). These
habitat types were defined by combinations of structure (cover type) and location (distance from shore) as: Spartina edge (≤1 m from shore), Spartina (3 m from shore); Juncus edge (≤1 m from shore); seagrass located 3, 5, and 20 m from shore; and shallow non-vegetated bottom at various distances
from shore. Although seagrass and Spartina edge sites differed little in environmental characteristics, the density and biomass of most abundant taxa, including pink
shrimp (Farfantepenaeus duorarum), were higher in seagrass. Most species within seagrass and Spartina did not differ in abundance or biomass with distance from shore. Our study revealed a shift in peak habitat use in the northeastern
GoM to seagrass beds from the pattern observed to the west where nekton is concentrated within shoreline emergent vegetation. 相似文献