Biogeochemical reactivity

To maintain a focus on the use of tracers in DOM fractions, this chapter will present only brief descriptions of studies of bulk DOM properties, and will focus primarily on the use of trace moieties from the fulvic acid fraction in freshwater aquatic environments. In addition to being a major DOM fraction, fulvic acid is biogeochemically reactive in natural waters (see Maranger and Pullin, Chapter 8 Chin, Chapter 7 Moran and Covert, Chapter 10). Furthermore, current fractionation methods allow for relatively straightforward isolation of small quantities of fulvic acid from small volume filtered water samples (100-200 mL) in a reproducible manner, as well as for isolation of larger preparative quantities of material. We present examples to illustrate the use of particular trace moieties but do not present a comprehensive review of each trace moiety. 

The speciation of trace metals in soils is related to their biogeochemical reactivity and to several physico-chemical conditions of the soil. The determinations of various fractions of these elements are broadly... 

Once the particle-reactive species have been scavenged, subsequent packaging and/or aggregation can result in the flux of particles and particle-reactive species from the water column. Thorium provides a unique way to study the environmental pathways and the biogeochemical processes that affect particle-reactive species. The four useful thorium isotopes are Th = A x yx), °Th... 

Although there are three Rji isotopes in the U- and Th-decay series, only is sufficiently long lived tm= 3.8 days) to be a useful estuarine tracer. Radioactive decay of Ra continuously produces Rn, which because of its short half-life is generally in secular equilibrium in seawater. Being chemically non-reactive except for very weak Van der Waals bonding makes this isotope a unique marine tracer in that it is not directly involved in biogeochemical cycles. 

From an elemental perspective, most of the mass of POM and DOM is carbon. Thus, DOC and POC concentrations are generally representative of the entire DOM and POM pools. Because DOC and POC concentrations are more easily measured than those of the other elements (nitrogen, phosphorus, oxygen, and hydrogen), far more data has been collected on their concentrations and reactivity as compared to that of DON, PON, DOP, or POP. DOM and POM concentrations are not measured for technical reasons and because the total mass of organic matter provides little insight into the biogeochemical processes responsible for its formation and destruction. 

Table 23.2 indicates that DOM is the largest pool of organic matter in the ocean. From a biogeochemical perspective, marine DOM represents the largest pool of reactive carbon... 

G.K (1999) Biogeochemical dynamics in zero-valent iron columns Implications for permeable reactive barriers. Environ. Sd. Tedm. 33 21709-2177 Gu, X.Y. Hsu, P.H. (1987) Hydrolytic formation of submicron iron(III) oxides from diluted ferric nitrate solutions. Soil Sd. Soc. Am. J. 51 469-474... 

Graedel, T. E and W. C. Keene, Tropospheric Budget of Reactive Chlorine, Global Biogeochem. Cycl., 9, 47-77 (1995). 

Gu B, Phelps TJ, Liang L, Dickey MJ, Roh Y, Kinsall BL, Palumbo AV, Jacobs GK. Biogeochemical dynamics in zero-valent iron columns implications for permeable reactive barriers. Environ Sci Technol 1999 33 2170 2177. 

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.)...

Baskaran, M. (1999) Particle-reactive radionuclides as tracers of biogeochemical processes in estuarine and coastal waters of the Gulf of Mexico. In Biogeochemistry of Gulf of Mexico Estuaries (Bianchi, T.S., Pennock, J.R., andTwilley, R.R., eds.), pp. 381-404, John Wiley, New York. 

Holland, E., Dentener, p., Braswell, B., and Sulzman, J. (1999). Contemporary and pre-industrial global reactive nitrogen budgets. Global Biogeochem. Cycles 43, 7—43. 

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