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Travis G. Gerwing Kieran Cox Alyssa M. Allen Gerwing Charmaine N. Carr-Harris Sarah E. Dudas Francis Juanes 《国际泥沙研究》2018,33(2):149-156
The usefulness of the apparent redox potential discontinuity (aRPD) in assessments of marine benthic habitat quality was explored at two intertidal mudflats along the north Pacific coast of Canada. Two transects were established at each intertidal site, with three sediment biogeochemistry cores collected from each transect four times over the summer of 2016. Measurements of the sediment pore water dissolved oxygen (DO) content and redox (Eh) conditions were taken at the surface of the core (measured vertically), as well as at increasing depths (1 cm between readings) into the sediment (measured horizontally through predrilled holes in the biogeochemistry corer). While oxic, anoxic, oxidized, and reduced sediment pore water was observed above and below the aRPD, in general, sediment above the aRPD had higher DO content, and higher Eh values than sediment below the aRPD. Therefore, the aRPD depth can be used as a relative indicator of sediment pore water DO and Eh conditions: sediment with a deeper aRPD depth has more available DO, and the pore water has higher Eh values (more oxidized or less reduced) than sediment with a shallower aRPD depth. As such, the aRPD depth is a useful parameter to include in models that assess the quality of marine benthic habitats. 相似文献
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Stephen R. Parker Simon R. Poulson M. Garrett Smith Charmaine L. Weyer Kenneth M. Bates 《Aquatic Geochemistry》2010,16(1):61-84
Here we report diel (24 h) and seasonal differences in the concentration and stable carbon isotope composition of dissolved
inorganic (DIC) and organic carbon (DOC) in the Clark Fork (CFR) and Big Hole (BHR) Rivers of southwestern Montana, USA. In
the CFR, DIC concentration decreased during the daytime and increased at night while DOC showed an inverse temporal relationship;
increasing in the daytime most likely due to release of organic photosynthates and decreasing overnight due to heterotrophic
consumption. The stable isotope composition of DIC (δ13C-DIC) became enriched during the day and depleted over night and the δ13C-DOC displayed the inverse temporal pattern. Additionally, the night time molar rate of decrease in the concentration of
DOC was up to two orders of magnitude smaller than the rate of increase in the concentration of DIC indicating that oxidation
of DOC was responsible for only a small part of the increase in inorganic carbon. In the BHR, in two successive years (late
summer 2006 & 2007), the DIC displayed little diel concentration change, however, the δ13C-DIC did show a more typical diel pattern characteristic of the influences of photosynthesis and respiration indicating that
the isotopic composition of DIC can change while the concentration stays relatively constant. During 2006, a sharp night time
increase in DOC was measured; opposite to the result observed in the CFR and may be related to the night time increase in
flow and pH also observed in that year. This night time increase in DOC, flow, and pH was not observed 1 year later at approximately
the same time of year. An in-stream mesocosm chamber used during 2006 showed that the night time increase in pH and DOC did
not occur in water that was isolated from upstream or hyporheic contributions. This result suggests that a “pulse” of high
DOC and pH water was advected to the sampling site in the BHR in 2006 and a model is proposed to explain this temporal pattern. 相似文献
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Stephen R. Parker Christopher H. Gammons Simon R. Poulson Michael D. DeGrandpre Charmaine L. Weyer M. Garrett Smith John N. Babcock Yasuhiro Oba 《Chemical Geology》2010,269(1-2):22-32
Rates of diel (24-h) biogeochemical processes in rivers and their effect on daily changes in the concentration of metals and metalloids have been well documented in the literature over the last 20 years. Investigations into the effects of these processes on aquatic systems and the underlying mechanisms that control the processes can significantly improve our understanding of how natural aquatic environments function and will respond to changing environmental conditions and anthropogenic impacts. Daily changes in the rates of biogeochemical processes have, more recently, been shown to influence the stable isotope composition of dissolved oxygen and dissolved inorganic carbon in natural waters. Here we present a comprehensive picture of the persistence and reproducibility of diel cycles of the 18O composition of dissolved molecular oxygen (δ18O-DO) and the 13C composition of dissolved inorganic carbon (δ13C-DIC) across five Montana, USA rivers investigated over a 4-year period. A mesocosm experiment showed the same behavior in δ18O-DO and δ13C-DIC as seen in riverine settings across light and dark periods.A cross plot of δ18O-DO and δ13C-DIC from each stream exhibits a clockwise elliptical pattern which is attributed to the daily changes in the balance of metabolic rates as well as air–water gas exchange. The amplitude of the change in the isotope composition is shown to be directly related to the trophic state of the river and a relationship between net productivity and diel changes in δ18O-DO and δ13C-DIC is presented. This relationship between trophic status with δ18O-DO, δ13C-DIC and production emphasizes the significance of how rates of biogeochemical processes in natural systems can influence the daily changes in the composition of surface waters. 相似文献
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DUNCAN F. M. MCGREGOR CHRISTOPHER P. GREEN 《Boreas: An International Journal of Quaternary Research》1983,12(1):23-33
The recognition of materials and structures which are unrelated to the original floodplain processes of terrace formation is essential to the proper understanding of terrace morphology and stratigraphy. Two groups of processes have been active in modifying the Lower and Middle Pleistocene terraces of the River Thames since their formation: non-fluvial deposition; and structural rearrangement by subsidence associated with solution of the underlying Chalk. Non-fluvial deposits comprise solifluction gravels which are variable in character and may incorporate a range of pre-existing deposits; and brickearths which appear in most cases to be redistributed loess mixed with non-loessic components. The distinction between fluvial and non-fluvial deposits is made using particle size, composition and fabric analysis. Structural rearrangement of terrace sediments has occurred due to subsidence into deep, narrow, steep-sided pipes. Within such pipes, disturbance of primary structures and fabrics is severe. Over a wider area. primary bedding may be inclined towards pipes, and sediments may show evidence of shearing, faulting and brecciation. Interpretative problems arising from post-depositional modification are exemplified. 相似文献
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