Sedimentation rate lakes

Schell, W.R. Sedimentation Rates and Mean Residence Times of Pb and Pb in Lake Washington, Puget Sound Estuaries and a Coastal Regfon. 

The oldest of these sedimentation rates, Region I (150 g m 2 yr-1 or 0.063 cm yr-1) represents natural or the pre-cultural sedimentation rates before 1889. Near this location in the lake a volcanic ash layer overlain by 480 cm of sediment has been found, Gould and Budinger [15]. Radiocarbon dating of... 

Between 1890 and 1902, the sedimentation rate identified as Region II of figure 3 averaged 1800 g m"2 yr-1 or 0.83 cm yr-1, i.e., greater than 10 times the pre-cultural rate. Historical records and photographs show that by 1895 most of the land comprising the watershed had been logged and the suburbs of Seattle had reached the lake shore. This rapid land development in the watershed occurred about the turn of the century. 

Since 1916 the sedimentation rate, Region III of Figure 3, has averaged 644 g m-2 yr-1 or 0.3 cm yr 1 or about 5 times the pre-cultural rate. The diversion of the Cedar River (average flow of 20 m3 s 1 into the lake in 1916 provided the water necessary to operate the ship and canal locks and contributes an estimated 4-5 x 107 kg-yr-1 of allochthonous material, Crecelius [7]. This riverine sediment input would contribute to the greater... 

Cadmium in the Greifensee Lake (Stumm and Morgan, 1981). This Swiss lake has a volume V of 1.25 x 108 m3, water input is (2 = 9 x 107 m3 a"1, sedimentation rate is P=4x 107kga 1. Cd has a sediment-water partition coefficient DCd = 65m3kg1. Calculate the Cd residence time in the lake. 

The processes described and their kinetics is of importance in the accumulation of trace metals by calcite in sediments and lakes (Delaney and Boyle, 1987) but also of relevance in the transport and retention of trace metals in calcareous aquifers. Fuller and Davis (1987) investigated the sorption by calcareous aquifer sand they found that after 24 hours the rate of Cd2+ sorption was constant and controlled by the rate of surface precipitation. Clean grains of primary minerals, e.g., quartz and alumino silicates, sorbed less Cd2+ than grains which had surface patches of secondary minerals, e.g., carbonates, iron and manganese oxides. Fig. 6.11 gives data (time sequence) on electron spin resonance spectra of Mn2+ on FeC03(s). 

Table 11.5 shows that sedimentation rates of 0.1 - 2 g nr2 d 1 are typically observed in lakes still higher values are found in very eutrophic lakes. The settling material can be collected in sediment traps it can then be characterized in terms of chemical composition, morphology, and size distribution of the particles. The composition is subject to seasonal variations caused primarily by different biological activities in the various seasons. Representative examples for Lakes Zurich and Constance are given in Fig. 11.10. These two lakes are prealpine lakes, located in regions of predominantly calcareous rocks, both are under the influence of eutrophication. 

Example Pb in Lake Zurich, summer Sedimentation rate of Pb ... 

McKee PM, Snodgrass WJ, Hart DR, et al. 1987. Sedimentation rates and sediment core profiles of uranium-238 and thorium-232 decay chain radionuclides in a lake affected by uranium mining and milling. Can J Fish Aquat Sci 44 390-398. 

Before fall turnover, there is zero oxygen concentration in the sediments and in the water above the sediments of Lake Harriet. At fall turnover, stratification of the lake is broken down and the water overlying the sediments abruptly reaches approximately Co. You are interested in how fast the sediments will respond to the higher oxygen concentration. To determine, this you must answer two questions (1) What is the oxygen profile in the sediments over time (2) What is the flux rate across the sediment-water interface over time ... 

Figure 1.1 Historical records of the sales/production volumes of (a) DDT and (b) PCBs, and the similarity of these time-varying trends to the accumulation rates of these chemicals in the sediments of Lake Ontario (from Eisenreich et al., 1989).

For Cedar and Mountain lakes, detailed sediment cores collected from the deeper regions of each basin showed increasing sedimentation rates up-core. Thus a slightly different approach was used to provide additional temporal detail from the coarsely sectioned cores. These subsequent cores were extruded into five intervals 5-20 cm long so that dates and sediment accumulation rates could be explicitly calculated for the deeper strata. 

For Little Rock Lake, a single core from each of its two basins was analyzed and dated in stratigraphic detail. The remaining cores were analyzed for Hg content in three coarse intervals as described, but none of these profiles was actually dated. Instead the sedimentation rates were inferred from a series of five nearby cores that had been dated by 210Pb for other purposes (16). The mean sedimentation rates from dated cores collected at similar depth in the same basin were used to calculate Hg accumulation for each undated profile. 

Figure 3. Rates of sulfate reduction (all measured with 35S) reported in the literature (references in Table I) show no obvious relationship to either sediment carbon content or carbon sedimentation rates (measured with sediment traps). The lowest reported rate of sulfate reduction occurs in the lake with the lowest carbon sedimentation rate, but there is no evidence of carbon limitation among the other lakes. Error bars indicate the range of reported sulfate reduction rates.

Relative rates of sulfate reduction and methanogenesis in lakes of varying trophic status are claimed to indicate that sulfate reduction rates are limited by the supply of sulfate (4, 5, 13). According to this hypothesis, at high rates of carbon sedimentation, rates of sulfate reduction are limited by rates of sulfate diffusion into sediments, and methanogenesis exceeds sulfate reduction. In less productive lakes, rates of sulfate diffusion should more nearly equal rates of formation of low-molecular-weight substrates, and sulfate reduction should account for a larger proportion of anaerobic carbon oxidation. Field data do not support this hypothesis (Table II). There is no relationship between trophic status, an index of carbon availability, and rates of anaerobic... 

The studies cited do not clarify what factors determine rates of sulfate reduction in lake sediments. The absence of seasonal trends in reduction rates suggests that temperature is not a limiting factor. Rates of sulfate reduction are not proportional to such crude estimates of carbon availability as sediment carbon content or carbon sedimentation rate, although net reduction and storage of reduced sulfur in sediments often does increase with increasing sediment carbon content. Measured rates of sulfate reduction are not proportional to lake sulfate concentrations, and the relative rates of sulfate reduction and methanogenesis in a variety of lakes do not indicate that sulfate diffusion becomes limiting in eutrophic lakes. Direct comparison of diffusion and reduction rates indicates that diffusion of sulfate into sediments cannot supply sulfate at the rates at which it is reduced. Neither hydrolysis of sulfate... 

Total S content cannot indicate whether increased carbon inputs to sediments cause increased diffusion of sulfate into sediments or restrict reoxidation and release of S from sediments, because the net effect is the same. In a survey of 14 lakes, Rudd et al. (80) did not observe a strong correlation between organic matter content per volume and net diffusive flux of sulfate. However, in English lakes the lowest C S ratios occur in the most productive lakes (24) whether this represents enhanced influx or retarded release is not clear. Among 11 Swiss lakes, ratios of C to S sedimentation rates are relatively constant and substantially below C S ratios in seston net S fluxes... 

The distribution of Hg within seepage lakes is a net result of the processes that control Hg transport between the atmosphere, water column, seston, sediments, and groundwater. This discussion focuses on the processes that control the exchange of Hg between the sediments and lake water. We first present data on spatial and temporal concentrations in the water column, sediments, pore water, and groundwater. These data set the context for a subsequent discussion of the chemical and physical processes responsible for the transport of mercury across the sediment-water interface and are necessary for assessing transport rates. 

Net sedimentation is defined as the flux of material incorporated into the permanent sediment record. 210Pb and 137Cs geochronologies indicate a mass sedimentation rate of 103 g/m2 per year for profundal sediments in Little Rock Lake. By using the mean Hg concentration (118 ng/g) in the top 1-cm slice of our bulk sediment profile, we estimated an annual net sedimentation of 12 xg of HgT/m2 per year. This net accumulation rate is similar to the calculated atmospheric input rate of about 10 xg/m2 per year (18, 19). Additionally, gross deposition rates (from sediment traps) exceeded these estimates by about a factor of 3 this rate suggests substantial internal recycling of material deposited at the sediment-water interface in this lake. 

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