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361.
Fatimah Sulu-Gambari Mathilde Hagens Thilo Behrends Dorina Seitaj Filip J. R. Meysman Jack Middelburg Caroline P. Slomp 《Estuaries and Coasts》2018,41(4):921-939
Recycling of phosphorus (P) from sediments contributes to the development of bottom-water hypoxia in many coastal systems. Here, we present results of a year-long assessment of P dynamics in sediments of a seasonally hypoxic coastal marine basin (Lake Grevelingen, the Netherlands) in 2012. Sequential phosphorus extractions (SEDEX) and X-ray absorption spectroscopy (XAS) indicate that P was adsorbed to Fe-(III)-(oxyhydr)oxides when cable bacteria were active in the surface sediments in spring. With the onset of summer hypoxia, sulphide-induced dissolution of the Fe-(III)-(oxyhydr)oxides led to P release to the pore water and overlying water. The similarity in authigenic Ca-P concentrations in the sediment and suspended matter suggest that Ca-P is not formed in situ. The P burial efficiency was ≤ 32%. Hypoxia-driven sedimentary P recycling had a major impact on the water-column chemistry in the basin in 2012. Water-column monitoring data indicate up to ninefold higher surface water concentrations of phosphate in the basin in the late 1970s and a stronger hypoxia-driven seasonal P release from the sediment. The amplified release of P from the sediment in the past is attributed to the presence of a larger pool of Fe-bound P in the basin prior to the first onset of hypoxia. Given that P is not limiting, primary production in the basin has not been affected by the decadal changes in P availability and recycling over the past 40 years. The changes in P dynamics on decadal time scales were not recorded in sediment profiles of total P or organic C/total P. 相似文献
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365.
Jack B. Hartung 《Meteoritics & planetary science》1976,11(3):187-194
As reported in medieval chronicles, on the evening of June 18, 1178, the upper horn of a new moon split, and from the division a flaming torch sprang up. We interpret this observation in terms of a large impact event which formed the 20-km-diameter crater, Giordano Bruno. 相似文献
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367.
Current conceptual runoff models hypothesize that stormflow generation on the Canadian Shield is a combination of subsurface stormflow and saturation overland flow. This concept was tested during spring runoff in a small (3.3 ha) headwater basin using: (1) isotopic and chemical hydrograph separation and (2) field mapping and direct tracing of saturated areas. Isotopic and chemical hydrograph separation indicated three runoff components: (1) pre-melt subsurface flow; (2) subsurface flow of new (event) water; and (3) direct precipitation on to saturated areas (DPS). During early thaw-freeze cycles, their relative contributions to total flow remained constant (65 per cent, 30 per cent, and 5 per cent respectively). It is hypothesized that lateral flow along the bedrock/mineral soil interface, possibly through macropores, supplied large volumes of subsurface flow (of both old and new water) rapidly to the stream channel. Much higher contributions of DPS were observed during an intensive rain-on-snow event (15 per cent of total flow). Mapping and direct tracing of saturated areas using lithium bromide, suggested that saturated area size was positively correlated to stream discharge but its response lagged behind that of discharge. These observations suggest that the runoff mechanisms, and hence the sources of stream flow, will vary depending on storm characteristics. 相似文献
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Jack L. Kindinger 《Geo-Marine Letters》1989,9(2):59-66
The northern Gulf of Mexico continental shelf is characterized by superimposing deltas. One such delta, informally named Lagniappe,
extends east of the Mississippi Delta from mid-shelf to the continental slope. This late Wisconsinan delta is adjacent to,
but not associated with the Mississippi Delta complex: the fluvial source was probably the ancient Pearl and/or Mobile Rivers.
The fluvially dominated Lagniappe Delta is characterized by complex sigmoid-oblique seismic-reflection patterns, indicating
delta switching of high-energy sand-prone facies to low-energy facies. The areal distribution and sediment thickness of the
delta were partially controlled by two diapirs. 相似文献
370.
Novel prebiotic model systems: interactions of nucleosides and nucleotides with aqueous micellar sodium dodecanoate 总被引:1,自引:0,他引:1
Joseph Nagyvary Jack A. Harvey Faruk Nome Dan Armstrong Janos H. Fendler 《Precambrian Research》1976,3(6):509-516
The partition coefficients, K-values, of adenosine, guanosine, cytidine, uridine, 51-adenylic acid (AMP), 51-guanylic acid (GMP), 51-cytidylic acid (CMP), and 51-uridylic acid (UMP) between water and aqueous sodium dodecanoate has been determined by gel filtration on Sephadex G-25. Below the critical micelle concentration of the surfactant, K-values for all nucleotides and nucleosides are similar. Differential uptake of the four nucleotides and nucleosides is observed, however, by micellar sodium dodecanoate. K-values for adenosine, AMP; guanosine, GMP; cytidine, CMP; and uridine, UMP are 6.16·103, 9.52·103; 12.0·103, 14.6·103; 19.6·103, 19.6·103, 34.2·103 and 40.3·103. Similar K-values for corresponding pairs of nucleotides and nucleosides imply that the predominant interaction is between the pyrimidine or purine rings of the substrates and the charged Stern layer of the surfactant. Prebiotic significance of these results is discussed. 相似文献