Estuaries processes affecting

Figure 5.6 Biogeochemical processes affecting their flux rates across the air-water interface of the four biogases (N2O, O2, CO2, NH3) analyzed in a full transient, one-dimensional reactive transport CONTRASTE model (Coupled, networked, transport-reaction algorithm for strong tidal estuaries) for the Scheldt estuary (The Netherlands) (Modified from Vanderborght et al., 2002.)...

Coagulation processes in estuaries are affected by other factors such as clay composition, particle size, and concentration of dissolved organic matter, to mention a few. For example, early work has shown that metal hydroxides can flocculate from dis-solved/colloidal organic matter during the mixing of river-derived iron and seawater in the mixing zone of estuaries (Sholkovitz, 1976, 1978 Boyle et al, 1977 Mayer, 1982) (more details are provided on metal colloidal interactions in chapter 14). Surface sediments in... 

Although mechanisms of DOM removal by physical/chemical processes in the mixing zone of estuaries are not well understood, they are believed to be important processes affecting the composition of riverine/estuarine DOM. Some of the earliest work on DOM removal processes noted that iron is important in the initial steps of flocculating humic substances across an estuarine salinity gradient and that much of this humic material was composed of humic acids (Swanson and Palacas, 1965 Eckert and Sholkovitz, 1976 ... 

Fogel, M.L., Velinsky, D.J., Cifuentes, L.A., Pennock, J.R., and Sharp, J.H. (1988) Biogeochemical processes affecting the stable carbon isotopic composition of particulate carbon in the Delaware Estuary. Carnegie Inst. Wash. Annu. Rep. Director, 107-113. 

Santschi, P.H., Lenhart, J.J., and Honeyman, B.D. (1997) Heterogeneous processes affecting trace contaminant distribution in estuaries the role of natural organic matter. Mar. Chem. 58, 99-125. 

Aquatic chemistry is concerned with the chemical reactions and processes affecting the distribution and circulation of chemical species in natural waters. The objectives include the development of a theoretical basis for the chemical behavior of ocean waters, estuaries, rivers, lakes, groundwaters, and soil water systems, as well as the description of processes involved in water technology. Aquatic chemistry draws primarily on the fundamentals of chemistry, but it is also influenced by other sciences, especially geology and biology. 

Salomons, W., Eysink, W., In "Biogeochemical and Hydrodynamic Processes Affecting Heavy Metals in Rivers, Lakes and Estuaries". Delft Hydraulics Laboratory Publication No. 253 Delft 1981, The Netherlands. 

Figure 1 Processes affecting the transport and biogeochemistry of metal pollutants in estuaries and shelf seas. FBI = fresh water-brackish water interface. Metal compartments are designated. Md, dissolved Mp, suspended particulate Mg, sediment M, interstitial water Mp, biogenic particulate.

In summary, the lanthanides undergo an array of reactions in estuaries which affect both their absolute and relative lanthanide abundances. Hence, estuaries are excellent natural laboratories to test and study the influence of aquatic geochemical processes on lanthanide fractionation. To what extent does fractionation in estuaries control the composition of seawater Is the release of dissolved lanthanides from estuarine shelf sediments a quantitatively important process with respect to the ocean budget and composition Answers to these and other related questions will require more detailed study and modeling. 

The results of two surveys are reported on Fig. 6, S.S.A. appears to be lower in the river part, especially for the Gironde estuary. It usually increases as soon as the tidal influence is observed with a clear maximum located around the salt intrusion. Many processes can affect particulate matter in this part of estuaries. The increase could be due to the destruction of some floes formed upstream as observed by Eisma (personal communication) or to a chemical evolution of the superficial composition of particles as discussed below. 

Typical DB values for Long Island Sound estuary (USA) and Chesapeake Bay have been estimated to range from 0.5 to 110 cm2 y-1 (Aller and Cochran, 1976 Aller et al., 1980) and 6 to >172 cm2 y 1 (Dellapenna et al., 1998), respectively. Since mixing is clearly not a one-dimensional process, estimated biodiffusivity values may seriously underestimate mass transport when mixing is affected by horizontal advection (Wheatcroft et al., 1991). 

Seventeen genera of facultative anaerobic bacteria (e.g., Pseudomonas and Bacillus) can perform denitrification under anaerobic or low-oxygen conditions, where they use NO3- as an electron acceptor during anaerobic respiration (Jaffe, 2000). In fact, in many estuaries, denitrification is limited by the availability of NC>3 (Koike and Sprensen, 1988 Cornwell et al., 1999). Sources of NC>3 and NC>2 for denitrification are from diffusive inputs from the overlying water column and nitrification in the sediments (Jenkins and Kemp, 1984). The activity of other bacterial processes under anoxic conditions has been shown to affect the activity of denitrifying bacteria. For example, SO42- reduction occurs in anoxic sediments whereby SC>42 is reduced to sulfide (Morse et al., 1992)—more... 

The partitioning of trace metals between the dissolved and particulate fractions in estuaries can be affected by variability in river flow, tidal and wind energy, storms, coagulation, and flocculation in the estuarine turbidity maximum (ETM), resuspension events (of sediments and porewaters), and inputs from wetland and mudflat processes. 

The lateral and vertical distributions of these carrier-phase metals in estuaries are largely controlled by particle dynamics, as opposed to other metals (e.g., Cu, Zn, and Co) which will be more affected by biotic uptake processes. 

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