Accretion balance

FIGURE 16.13 Processes that affect the accretion balance in response to relative sea-level rise of coastal wetlands. 

Accretion balance refers to the net change in sea level relative to marsh surface elevation at a particular site over time. For a coastal wetland to remain at the same elevation over time, accretion must be equal to subsidence plus eustatic sea-level rise. 

Submergence refers to negative accretion balance, that is, a marsh surface being flooded to greater and greater depths with time. 

The rates of organic matter accumulation and decomposition in fresh, brackish, and saline marsh soils of the Mississippi River deltaic plain (Table 18.1) have been used to estimate the amount of soil organic matter production required to maintain a positive accretion balance (Nyman et al, 1990). 

Inputs + Sources = Outputs + Sinks + Accumulations where each of these terms may be a quantity or a rate. Inputs and Outputs are accomplished by crossing the boundary of the reference volume. In case of mass transfer this occurs by bulk flow and diffusion. Sources and Sinks are accretions and depletions of a species without crossing the boundaries. In a mass and energy balance, sinks are the rate of reaction, rdVr, or a rate of enthalpy change, AHrpdC. Accumulation is the time derivative of the content of the species within the reference volume, for example, (<9C/3t)dVr or... 

Numerous ways have been proposed to explain a net loss of molecular oxygen. Oxidation of volcanic gases, ferrous iron, sulfur, sulfide, and manganese, and the accretion of hydrogen from the solar wind are among these. Such processes are sometimes referred to as oxygen sinks. Estimates by Holland (1962) indicate that the net gam and net loss over geologic time are essentially in balance. 

To solve Eq. (3.4) or Eq. (3.6) we need to know the value of cs, or in other words the temperature Tm near the mid-plane. This is determined by balancing the heating rates due to the viscous evolution of the disk and its irradiation by the central star with the cooling rate due to the thermal emission from the disk. The vertically integrated heating rate due to viscosity (i.e. accretional heating) is ... 

Ingestion Absorption Urinary excretion Endogenous fecal excretion Bone Accretion Bone resorption Total fecal excretion Total calcium balance... 

Kurtz A. C., Derry L. A., and Chadwick O. A. (2001) Accretion of Asian dust to Hawaiian soils isotopic, elemental, and mineral mass balances. Geochim. Cosmochim. Acta 65, 1971-1983. 

Earth-forming planetesimals, which later evolved as a result of the late accretion of asteroids and comets. Thus, the mass of asteroids and comets incident on Earth since the time of its accretion required to balance the low D/H ratio of the deep mantle is estimated to be 4 x 10 to 2 x 10 kg (Dauphas et al. 2000). It is worth while to note that fractionation of D/H within the Earth might explain the isotopic heterogeneity of Earth, but we wish to emphasize that the few elements for which there exists an isotopic heterogeneity are those that are not efficiently recycled, those that are prone to record the heterogeneous accretion of the Earth. 

Tryptophan is one of 20 to 22 amino acids that are required for the synthesis of protein within tissues. Tryptophan is assumed to consist of 1.5% of the total amino acids in tissue protein. Assuming that the adult male at nitrogen equilibrium synthesizes approximately 225 to 250 g of protein daily (approximately 3 g/kg/d), then approximately 3.5 g of tryptophan is utilized daily for protein synthesis. This is of special interest because there is no net accretion of body protein at nitrogen balance. Thus, a large flux of amino acids, including tryptophan, participates in this pathway daily. Actually, the tryptophan... 

In this article a simplified mass balance has been used to describe the net transport of sand over an accreting mud bottom. The combination of these two sedimentary processes controls the transition from sand to mud on the floor of the Sound. The distribution of sand may be described with three parameters an advection velocity of sand grains, an eddy-diffusion coefficient for mobile sand, and a rate of accumulation of marine mud. (Only the ratios of these quantities are needed if the distribution is in a steady state.) The motion of sand is thereby represented with both a deterministic part and a statistical part. The net, one-way advection of sand is the result of the superposition of an estuarine circulation on the tidal stream, and unpredictable variations in the rate of sand transport are represented as an eddy-diffusion process. Sand is immobilized when it is incorporated into the permanent deposit of marine mud. 

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