Mass accumulation rate

The time-space resolution that may be achieved with filter sampling techniques is dependent on the collection rate, limit of detection, and ambient concentrations. In aircraft applications, filters are typically operated at high flows (100-500 L/min) to maximize the mass accumulation rate. At these flow rates, sampling times on the order of 20 to 30 min are generally sufficient for measurement of substances in the urban troposphere. For sampling in the upper troposphere or in areas remote from pollutant sources, collection times of several hours may be necessary to obtain measurable quantities of material. 

It would be an oversimplification to suggest that a pair of cores could be considered duplicates or that information from a single core could be extrapolated to basin-wide processes. However, carefully chosen core sites can provide a basis for reasonable estimates and hypothesis formation. Both basins of LRL have similar morphometric and edaphic conditions (Figure 1), suggesting similar depositional regimes and histories. Core locations were chosen near sites where extensive pore-water measurements had been made (4, 17, 59) and where sediment cores had been dated by 210Pb. Mean mass accumulation rates calculated over the top 4-5 cm were comparable between basins 105 and 126 g/m2 per year for the treatment and reference basin, respectively (65, 66). 

Rate oj mass accumulation =Rate of massin-Rate of mass out (6.32)... 

FIGURE 14.8 Spatial distribution of long-term average (100 years) linear sedimentation rates (LSRIOO) and sediment mass accumulation rates (MAR). Gray crosses indicate the location of sampling stations. 

The basinwide mean values for organic carbon, total nitrogen, and total phosphorus (expressed in g/(m year)) are 14.8 13.7, 1.60 1.58, and 0.20 0.18, respectively. Because the element concentrations (e.g., TOC, Fig. 14.10 top left) are much less variable than the bulk sediment accumulation rates (Fig. 14.8), the spatial distribution pattern of element accumulation rates mainly reflects the total mass accumulation rates. 

Fig. 12.20 Results of a steady-state simulation with a coupled model for ocean circulation, water chemistry and sediment diagenesis. Major control parameters and forcings comprise a large-scale geostrophic flow field, primary productivity controlled by nutrient advection, export production and sediment accumulation, as well as CO input by weathering and CO -exchange with the atmosphere, a) Export production (mol m yr ), b) CaCO export production (both mol m yr ), c) wt% CaCOj, d) CaCO mass accumulation rate (g cm kyr ) (from Archer et al. 1998).

In the paleo-oceanographic context, constant flux tracers are valuable tools because they enable the reconstruction of particulate fluxes. One of the advantages of this approach is that it allows us to establish mass accumulation rates independently from single-point age models (e g., O). These models frequently are biased and sensitive to sediment redistribution effects. For example, this holds true for paleoceanographic studies in the Quaternary, where many interpretations of the sediment record rely on potentially erroneous sediment accumulation rates derived from 5 0 stratigraphy. 

Mass accumulation rate (MAR) in the ECS varied from >2 to 0.05 g/(cm -yr). The maximum MAR appeared in the mouth of the Changjiang River, and the value generally decreased southward along the inner shelf and eastward offshore. Based on this valuable published data, Fang et al. (2007) calculated the phosphorus burial flux in the ECS. To facilitate the calculation, the calculated area is divided into five boxes estuary (box I), inner shelf (box II), middle shelf (boxes III and IV), and outer shelf (box V) (Fig. 4.43), according to the value of MAR in each box observed by Huh and Su (1999) and to the phosphorus content in surface sediments found by Fang et al. (2007). 

Table 4.14. The area, mass accumulation rate, P total concentration, P accumulation rate, and P burial flux for each box of the ECS (Fang et al., 2007) (With permission from Elsevier s Copyright Clearance Center)...

There is, however, an additional dimension to the problem of accumulation rates. The interpretation of two specific types of component is very sensitive to mass accumulation rate. First, elements that are transported to the lake in a soluble form, and only partially captured by the lake, have concentrations which can be highly sensitive to the sediment accumulation rate. Second, any component for which the supply rate is completely independent of catchment particle supply rates, is sensitive to variable dilution. For many atmospherically supplied trace elements both of these situations apply. The model described below can be used to evaluate these effects. 

If an element that is independent of the dominant panicle supply (i.e., in solution from catchment, or from the atmosphere) is captured efficiently by the lake system, then variation in the particle mass accumulation rate will cause an inverse variation in its sediment... 

Mass accumulation rate (MAR) The accumulation rate of either total sediment or of any sediment component that is calculated from the linear sedimentation rate and the sediment dry bulk density. 

The estimated sedimentation and mass accumulation rates for three time periods (1955-1965, 1965-1971, 1971-1981) at station 3C are reasonably consistent with the historical trends in solids emissions from the outfall system (cf. Table 2, Fig. 6). The sedimentation rates for station 522 during the same time periods are similar to those for station 3C. However, mass accumulation rates are systematically higher at station 522 than at station 3C, and there is a marked increase in both sedimentation rate and mass accumulation rate in the 1981-1992 period based on molecular stratigraphy (station 522 only). The latter observation is significant because emissions of wastewater effluent solids from the LACSD outfall system during the post-1981 period continued to decline (see Fig. 5 in Eganhouse and Pontolillo, 2000). Thus, the increase in sedimentation for the period 1981-1992 near station 522 (and presumably 3C) cannot be ascribed to an overriding influence of the outfall system. 

Mass rate in - Mass rate out = Mass accumulation rate... 

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