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Karen L. Hunter Dewayne A. Fox Lori M. Brown Kenneth W. Able 《Estuaries and Coasts》2006,29(3):487-498
Modification of brackish marshes by nonindigenousPhragmites australis has occurred across a broad geographical area in eastern North America. Among its effects on marsh processes,Phragmites may be increasingly unfavorable to marsh surface fishes as its invasion progresses within an estuary. We assessed the effect
of thePhragmites invasion on resident marsh surface fishes by examining the population response ofFundulus heteroclitus (mummichog, 5–48 mm TL) andF. luciae (spotfin killifish, 5–41 mm TL) to four distinct invasion stages in three estuaries of the U.S. mid Atlantic region (New
Jersey, Delaware, and Maryland). We documented precipitous declines in mean catch per unit effort ofF. heteroclitus in pit traps from natural marsh (51.6), through initial (33.8), early (12.3), and late invasion stages (2.4) across all sites.
A similar pattern was documented forF. luciae, with mean catch per unit effort in pit traps declining from natural marsh (48.9), through initial (39.1), early (9.3), and
late invasion stages (2.7). Population structure of both species also changed somewhat across invasion stages such that we
collected a narrower size range of individuals of both species from late invasion stages. Patterns suggest that as thePhragmites invasion progresses, there is a decline in habitat function for larval and juvenileF. heteroclitus and an increased risk of extirpation ofF. luciae from brackish marshes along the east coast of the U.S. 相似文献
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Seawater is constantly circulating through oceanic basement as a low-temperature hydrothermal fluid (<150°C). In cases when
ultramafic rocks are exposed to the fluids, for instance during the initial phase of subduction, ferromagnesian minerals are
altered in contact with the water, leading to high pH and formation of secondary magnesium hydroxide, among other – brucite,
that may scavenge borate and phosphate from seawater. The high pH may promote abiotic formation of pentoses, particularly
ribose. Pentoses are stabilized by borate, since cyclic pentoses form a less reactive complex with borate. Analyses have shown
that borate occupies the 2' and 3' positions of ribose, thus leaving the 5' position available for reactions like phosphorylation.
The purine coding elements (adenine, in particular) of RNA may be formed in the same general hydrothermal environments of
the seafloor. 相似文献
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The genesis of Lower Eocene calcite-cemented columns, “pisoid”-covered structures and horizontal interbeds, clustered in dispersed outcrops in the Pobiti Kamani area (Varna, Bulgaria) is related to fossil processes of hydrocarbon migration. Field observations, petrography and stable isotope geochemistry of the cemented structures and associated early-diagenetic veins, revealed that varying seepage rates of a single, warm hydrocarbon-bearing fluid, probably ascending along active faults, controlled the type of structure formed and its geochemical signature. Slow seepage allowed methane to oxidize within the sediment under ambient seafloor conditions (δ18O = − 1 ± 0.5‰ V-PDB), explaining columns' depleted δ13C ratios of − 43‰. Increasing seepage rates caused methane to emanate into the water column (δ13C = − 8‰) and raised precipitation temperatures (δ18O = − 8‰). Calcite-cemented conduits formed and upward migrating fluids also affected interbed cementation. Even higher-energy fluid flow and temperatures likely controlled the formation of “pisoids”, whereby sediment was whirled up and cemented. 相似文献
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