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Anthropogenic Contributions of Heavy Metals and Metalloids to Surface and Underground Water
Published in Abhik Gupta, Heavy Metal and Metalloid Contamination of Surface and Underground Water, 2020
It is well-established that a large part of heavy metals and metalloids released into water from industrial, mining, domestic, and other sources get lodged in the sediments through the process of flocculation, adsorption, and sedimentation. Certain changes in the physical or chemical properties of the ecosystem can disturb the dynamic equilibrium in the sediment–water interface and lead to the release of heavy metals and metalloids into the overlying water. pH is an important environmental factor that can affect this equilibrium. A study on heavy metal release from sediments of the Xiaofu river, China, showed that Cd release from sediment gradually decreased from 27.3 to 10.2 mg kg–1 from pH 0 to14. However, it is a matter of great concern that Cd is released from the stable residual fraction, especially at a pH of 0–4. Nickel release from the exchangeable fraction decreased rapidly as the pH increased from 0 to 5 (~140–80 mg kg–1). However, it again increased somewhat beyond pH 10. In the case of Cu, its release from the Fe–Mn oxide fraction rapidly decreased with an increase in pH from 0 to 6.5. Thus, a change in pH towards more acidic conditions could lead to elevated release of these heavy metals from sediment into water (Zhang et al. 2018).
Specific Fugacity Models and Calculations
Published in J. Mark Parnis, Donald Mackay, Multimedia Environmental Models, 2020
Exchange of chemical at the sediment–water interface can be important for the estimation of (1) the rates of accumulation or release from sediments, (2) the concentration of chemicals in organisms living in, or feeding from, the benthic region, (3) which transfer processes are most important in a given situation, and (4) the likely recovery times in the case of “in-place” sediment contamination. The complexity of the system and the varying properties of chemicals of possible concern lead to a situation in which a specific chemical’s behavior is not necessarily obvious. This situation treated here and the resulting model are largely based on a discussion of sediment–water exchange by Reuber et al. (1987), Eisenreich (1987), Diamond et al. (1990), and in part on a report by Formica et al. (1988) and the work of DiToro (2001). It is depicted in Figure 6.3.
Applications of Chemical Kinetics in Environmental Systems
Published in Kalliat T. Valsaraj, Elizabeth M. Melvin, Principles of Environmental Thermodynamics and Kinetics, 2018
Kalliat T. Valsaraj, Elizabeth M. Melvin
Compounds distribute between the various compartments in the environment. One of the repositories for chemicals is the sediment. Chemical exchange at the sediment-water interface is, therefore, important in delineating the fate of environmentally significant compounds. Sediment contamination arose from the uncontrolled pollutant disposal in lakes, rivers, and oceans. As environmental regulations became stricter, most pollutant discharges to our lakes and waterways became controlled. The contaminants in sediments bioaccumulate in marine species and exposure to humans become likely. Hence the risks posed by contaminated sediments have to be evaluated and sediment remediation strategies determined. The risk-based corrective action (RBCA) is predicated upon knowledge of chemical release rate from sediment and transport through air and water environments (Figure 4.42). The first step in this process requires an understanding of potential release mechanisms.
Evaluating the “Gradual Entrainment Lake Inverter” (GELI) artificial mixing technology for lake and reservoir management
Published in Lake and Reservoir Management, 2018
Colin A. Smith, Jordan S. Read, M. Jake Vander Zanden
We have a few recommendations for improvement of the GELI that could increase mixing capacity and efficiency, decrease maintenance, and further improve upon the current version of this technology. One improvement to mixing capacity and efficiency could be obtained by constraining the surface of the GELI to be parallel with the surface of the lake. This would ensure maximized drag-induced mixing as the GELI rises and falls through the water column. In our application at Crystal Lake, the GELI would ascend at a reasonably slow rate and maintain this optimal orientation with the lake surface but would fall through the water column at a sharp angle thereby losing mixing effectiveness. The optimal orientation could be obtained by fixing the GELI into a vertical track. By doing so the risk of sediment resuspension could be reduced by placing a stopping point above the sediment–water interface. Another area for improved performance is to reduce the size of the compressor or regulate compressor operation with a pressure-based switch. This could eliminate the pressure equilibration phase of the GELI cycle and reduce airflow requirements by approximately 25% and thus increase GELI efficiencies and reduce power costs. Finally, a significant number of personnel hours were spent observing and adjusting the GELI system. Incorporating sensors within the system would facilitate automated system control and a more consistent performance.
Subsurface flow and associated oxygen transfer induced by turbulence in a gravel bed river
Published in Journal of Hydraulic Research, 2021
The interaction between surface and subsurface water may play a major role in determining the fluxes of pollutants, reactants, reaction products, and other materials across a sediment/water interface in permeable sediments that consist of coarse sand and gravel. Mass transport within and into the pore system of a sediment bed under a stream or river has been reviewed and summarized by Boano et al. (2014), Jones and Mulholland (2000), Boudreau and Joergensen (2001), Chien and Wan (1998) and Winter et al. (1999), and also has been investigated at laboratory and field scales, and by numerical simulations (e.g. Cardenas & Wilson, 2006, 2007; Elliott & Brooks, 1997; Marion & Zaramella, 2005; Packman et al., 2004; Tonina & Buffington, 2011).