Estuarine sediments oxidation processes

Although the major components of seawater are relatively constant, a number of factors can cause the ocean and estuarine waters to be nonconservative. These processes occur in estuaries, anoxic basins and sediments, hydrothermal vents, and evaporation basins and include precipitation, dissolution, evaporation, freezing, and oxidation processes. Some examples will be discussed briefly. 

In an attempt to assess the quantitative contribution of reactive processes to the overall cycling of anthropogenic source contamination, two examples will be considered (i) vinyl chloride oxidation at groundwater-surface water interface (GSI) St. Joseph, Michigan (e.g., Lendvay et al., 1998a,b), and (ii) dioxin dechlorination in estuarine sediment cores collected from the Passaic River, New Jersey... 

Oxidation of ammoninm to nitrogen gas (ANAMOX) is now considered as a significant process in marine, coastal, and estuarine sediments (see Chapter 8). Several studies have now provided evidence using a combination of N-based tracer studies, lipid biomarkers, FISH, and phylogenetic and quantitative PCR analysis (Francis et al., 2007). 

Some studies have reported conservative behavior during estuarine mixing. In the unpolluted Krka Esmary of Yugoslavia, Seyler and Martin (1991) observed a linear increase in total arsenic with increasing salinity, ranging from 0.13 xgL in freshwaters to 1.8 JLgL offshore. Other studies however, have observed nonconservative behavior in estuaries due to processes such as diffusion from sediment pore waters, co-precipitation with iron oxides, or anthropogenic inputs (M. O. Andreae and T. W. Andreae, 1989 Andreae et al., 1983). The flocculation of iron oxides at the freshwater-saline interface as a result of increase in pH and salinity can lead to major decrease in the arsenic flux to the oceans (Cullen and Reimer, 1989). 

PROBABLE FATE photolysis, may be important, but is probably impeded by adsorption, photooxidation by U.V, in aqueous medium (Ty 90-95°C time for the formation of CO, (% of theoretical) 25% 75.3 hr, 50% 160.6 hr, 75% 297.4 hr, photooxidation half-life in air 6.81 hrs-2.i du>s, degrades quickly by photochemically produced hydroxyl radicals, with an estimated half-life of 29 hr oxidation-, chlorine and/or ozone in sufficient quantities may oxidize fluorene hydrolysis, not an important process volatilization probably not an important transport process, volatilization half-lives from a model river and a model pond 15 and 167 respectively sorption adsorption onto particles, biota, and sediments is probably the dominant transport process, half-life in soil ranges from 2-64 days biological processes bioaccumulation is short-term, metabolization and biodegradation are very important fates in estuarine waters 15pg/L, 12% adsorbed on particles after 3 hr... 

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