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Sediments and Sedimentary Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Chemical components dissolved in water may derive from chemical weathering or impure rainfall or can be picked up from river banks or bottoms. These dissolved materials make up a stream’s dissolved load. The loads are generally much smaller than suspended loads or bed loads (although such may not be the case for rivers that receive large chemical contributions from agriculture, industry, or other anthropogenic sources). Dissolved loads are eventually delivered to lakes or to the oceans where they accumulate until concentrations reach the saturation limit. Except under unusual circumstances, if that limit is passed, water becomes oversaturated, precipitation will occur, and mineral deposits will form. Such deposits generally contain interlocking crystals that grew together as they formed.
Water Drop Algorithm
Published in Nazmul Siddique, Hojjat Adeli, Nature-Inspired Computing, 2017
The specific characteristics of the sediment load are another key factor influencing channel form and process. The load is the total amount of sediment being transported. There are three types of sediment load in the river: dissolved, suspended, and bed load, as shown in Figure 6.3. The dissolved load is made up of the solutes that are generally derived from chemical weathering of bedrock and soils. Fine sands, clay, and silt are typically transported as suspended load. The suspended load is held up in the water column by turbulence. The bed load is made up of sands, gravel, cobbles, and boulders. Bed load is transported by rolling, sliding, and bouncing along the bed of the channel (Allan, 1995). While dissolved and suspended loads are important components of the total sediment load, in most river systems, the bed load is what influences the channel morphology and stability (Kondolf et al., 2002).
River action and control
Published in F.G. Bell, Geological Hazards, 1999
Since shear stress is related to the velocity gradient, as well as the energy gradient and the hydraulic radius (R), then frictional velocity (U*) is given by: ()U*=gRS The hydraulics of sediment transport involves dissolved load, which offers no resistance, and suspended load, which serves to dampen turbulence thus increasing stream efficiency. In order to determine what set of flow conditions cause entrainment of a particle it is important to calculate such factors as the critical flow velocity, the critical boundary shear stress and the critical lifting force. These factors are contained in the relationship provided by the Shields entrainment function (Fs): ()Fs=τ(ρg−ρf)gd where t is the boundary shear stress, ρg is the particle density, ρf is the density of the water, g is the acceleration due to gravity and d is the diameter of the particle. The energy and forces of a stream are derived from its gravitational component as reflected by velocity and discharge. Thus each stream contains potential energy, which is a function of the weight and head of water. This energy is converted to kinetic energy (Ek) during downhill travel. Most kinetic energy is lost to friction but that which remains is available for erosional and transportation processes. This relationship is embodied in the kinetic equation: ()Ek=M2v2 where M is the mass and v is the velocity, so that velocity determines energy and varies according to stream gradient and channel characteristics. When the channel cross-sectional area increases, the stream velocity decreases because water is not compressible.
Basin-scale seawater lead isotopic character and its geological evolution indicated by Fe-Mn deposits in the SCS
Published in Marine Georesources & Geotechnology, 2020
Xiaoxia Tu, Huaiyang Zhou, Chonghui Wang, Qunhui Yang, Benduo Zhu
There are three potential routes for the supply of continental lead and volcanic arc lead to the SCS: aeolian dust, river particulate matter and riverine dissolved load. Modern aeolian dust has been dominated by anthropogenic inputs since the industrial revolution (Widory, Liu, and Dong 2010; Cai et al. 2017; Chien et al. 2017). Therefore, the Pb isotope of modern air aerosols could not be used as the basis for judging the lead source, and the Hong Kong air aerosol significantly deviates from the natural background (Bollhöfer and Rosman 2001). Fortunately, China loess is also of aeolian origin from the Asian continent (Maher 2016), and the Pb isotope composition of natural aeolian dust is recovered. The Pb isotopic composition overlaps with the Fe-Mn deposits (Figure 9). Leaching experiments on Chinese loess have revealed the presence of an easily leachable component adsorbed onto the surface of the grains that have a lower 206Pb/204Pb ratio than that of the silicate dust particles (Jones et al. 2000; Ling et al. 2005). The leachable absorbed Pb of the aeolian dust is more easily dissolved in the seawater and adsorbed by the amorphous FeOOH to enter the Fe-Mn deposits. Therefore, aeolian dust may be a significant Pb source for the SCS.
Sources and downstream variation of surface water chemistry in the dammed Waitaki catchment, South Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2018
Vincent Pettinger, Candace E. Martin, Christina R. Riesselman
Although some previous studies have attributed an excess of dissolved Ca relative to Na to the chemical weathering of trace amounts of calcite (Blum et al., 1998; Jacobson et al., 2003, 2015; Moore et al., 2013), as discussed above, chemical weathering of other Ca-bearing minerals such as Ca-bearing plagioclase, apatite, epidote and fluorite, may also contribute dissolved Ca (Blum et al., 2002; Oliva et al.,2003; Andrews et al., 2016). The Ca/Na ratio has been used to estimate the sources of Ca in the dissolved load of waters across the world (Blum et al.,1998; Gaillardet et al., 1999; Anderson et al.,2000; Jacobson and Blum, 2000; Lyons et al.,2005) including the Waitaki catchment (Moore et al., 2013). Using the Ca/Na molar ratio (c. 0.35) of sandstones in the region (Moore et al., 2013) it is possible to estimate how much of the riverine Ca comes from silicate weathering for waters of the Waitaki catchment in this study. Results of this calculation indicate that, on average, 90% of the dissolved Ca is attributable to weathering of carbonate minerals (range 83%–96%), meaning that 10% (range 4%–17%) of the Ca is coming from weathering of silicates (+/− other Ca-bearing non-silicate minerals such as apatite). Earlier work across the Southern Alps by Jacobson et al., (2003) found that on average carbonate weathering provides 91% of the Ca in the dissolved load.
Gold and associated minerals in the Waikaia placer gold mine, Northern Southland, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2018
Christine McLachlan, Marianne Negrini, Dave Craw
Groundwaters entering the mine and the waters in the settling ponds have broadly similar compositions (Table 1). Water pH is consistently near neutral and the dissolved load is low, with total dissolved solids < 90 mg/L (Table 1). The waters are generally type, which is typical of the Waikaia catchment and surrounding areas (Craw et al. 2017). However, the settling pond waters have higher dissolved sulphate and lower alkalinity than the incoming groundwaters (Table 1).