Enrichment lake sediment

The oldest profile (CBAC 215) was preserved beneath Paleocene lake sediments. The least weathered saprock in this profile (59 m beneath the unconformity) has a REE pattern very similar to North American shale composite (NASC). The light REE show marked relative depletion in the upper part of the profile and enrichment near the weathering front. Cerium shows marked enrichment at depth (Fig. 2). 

Sulfur typically is enriched in lake sediments (300-64,000 xg/g) relative to crustal materials (30-2700 ig/g 39, 40) and surface soils (50-2000 xg/g ... 

As shown in Chapter 2, Section 2.10.3, the system of lead ion/calcium-montmoril-lonite lead enrichments may form when, based on thermodynamic conditions, their formation is not expected. The process was considered as surface precipitation or coprecipitation, depending on the chemical composition of the lead enrichments. Since lead enrichments are fairly bulky (a few hundred nanometers to micrometers), their migration rate is practically zero. Therefore, if they form under natural conditions, they should be observed on the surface of natural clay. In fact, lead enrichments were found on clay mineral surfaces from lake sediments (Figure 3.6 Nagy et al. 2003a). 

Brannvall M. L., Kurkkio H., Bindler R., Emteryd O., and Renberg I. (2001) The role of pollution versus natural geological sources for lead enrichment in recent lake sediments and surface forest soils. Environ. Geol. 40, 1057-1065. 

Commonly enriched in ultramaflc rocks and their associated ore deposits. Much naturally occurring Cr is relatively insoluble chromite. Soluble Cr may occur naturally in evaporative lake sediments or other evaporative environments, as a trace element within other soluble salts. Anthropogenic Cr can occur in soils, sediments, and waters affected by industrial wastes and byproducts (i.e., leather tanning, electroplating., cement use). 

Black shales, phosphatic sediments. Sometimes enriched in soluble evaporative salts formed in evaporative lake sediments, and in agricultural soils developed from Se-rich rocks. Smelter particulates and smelter-affected soils. Some rock and sediment types, as well as their derived soils, are naturally depleted in Se, for example some dust-derived sediments (loess), some granites or gneissic metamorphic rocks. 

Soils and waters affected by emissions from smelters, power plants. Soils and waters affected by mining wastes and by-products. Some playa lake sediments. Soils and dusts derived from naturally As-enriched rocks and sediments. Waters that have leached As from As-rich rocks, soils, and sediments. Pesticides, other industrial chemicals. By-products or wastes from chemical manufacturing or other industrial processes. 

In remote softwater lakes, sediment profiles may be used to evaluate enrichment trends due to anthropogenic activities. Trace metal profiles in sediments of 10 lakes in Ontario (Algonquin Provincial Park) indicate a 2-fold enrichment of Ni, Cu, Zn, and Cd and a 25-fold increase of Pb during the past 100 years (Wong et al. 1984). 

Several other approaches concerning retrospective studies of trace metal enrichment in lake sediments, ombrotrophic peatlands, and tree-rings have been proposed during the past years. The use of lake sediments for long-term retrospective trace metal monitoring has been questioned because of the... 

Fig. 2 shows the different pathways in which chemical elements contained in rocks are released to the different environmental compartments. Five main processes are responsible for their dispersion into the different ecosystems (1) Weathering, either directly by rain water on rock outcrops, by soil percolation water or by root exsu-dates, which interact with rock fragments, contained in the soil cover (2) Down hill mechanical transport of weathered rock particles, such as creep and erosion and subsequent sedimentation as till material or alluvial river and lake sediments (3) Transport in dissolved or low size colloidal form by surface and groundwater (4) Terrestrial and aquatic plants growing in undisturbed natural situations will take up whatever chemical elements they need and which are available in the surface and shallow groundwater. Trace elements taken up from the soil will accumulate in the leaves and will possibly enrich the soil by litterfall (5) Diffuse atmospheric input by aerosols and rain rock particles from volcanic eruptions, desertic areas (Chester et al., 1996), seaspray and their reaction with rain water. A considerable part of this can be anthropogenic. 

Figure 13. Overview of contamination processes induced by an ore deposit in a river catchment of a mountainous area. The different places potentially affected by the dispersed chemical elements are indicated with numbers (1) natural outcrop, (2) open pit, (3) mine dump, (4) local vegetation, (5) local surface water, (6) river draining the area of the ore deposit, (7) uncontaminated control area, (8) major river water, possibly carrying trace elements from the ore deposit, (9) river sediment and water plants (e.g. mosses), possibly enriched in trace elements, (10) lake sediments, possibly enriched in trace elements.

In Lake Okeechobee, Elorida, Reddy and Eisher (1991) estimated that under normal wind events, the resuspension flux of soluble phosphorus can account for approximately 6-18 times the diffusive flux. In comparison, resuspension of loosely bound, organically rich sediments into the water column was found not to be a major factor for delaying the recovery of shallow Danish lakes (Jeppesen et al., 2003). However, the resuspension of nutrient-enriched benthic sediments (accumulated during eutrophication process) along with the diffusive flux can result in the release of nutrients supporting phytoplankton productivity and delay the overall recovery process. 

Wolfe, A. P. J. W. Hartling, 1997. Early Holocene trace metal enrichment in organic lake sediments, Baffin Island, Arctic Canada. Arctic and Alpine Res. 29 24-31. 

Reductive dechlorination of toxaphene homologs has also be observed in Lake Ontario sediments (Howdeshell Hites, 1996). Amounts of hexa- and heptachlorobornanes were shown to increase with increasing years of burial of the sediments. Miskimmin et al. (1995) and Stem et al, (1996) identified a hexachlorobornane, B-923 (Hx-sed), and a heptachlorobornane (B7-1001) as stable endproducts in lake sediments treated with toxaphene. The appearance of B6-923 and B7-1001 in sediments from Yukon lakes appeared to be consistent with past use patterns of toxaphene for biting fly control, while low amounts were consistent with solely atmospheric sources (Stern et al., 1998). Enantiomer ratio (ER) values for these congeners in one of the lakes treated with toxaphene showed evidence for enantio-enrichment of B7-1001 butnotB6-923 (Vetter et al, 1999). This suggests that not all dechlorination is microbially mediated. 

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