Historical Pollution Records and Perturbatory Processes in Lakes

2 Perturbatory Processes in Lake Sediments. The extent to which conditions for preservation of records are met depends upon the characteristics of the specific individual systems and contaminants under study. In reviewing the perturbation of historical pollution records in aquatic sediments. Farmer has suggested that in the case 

Upon dissolution of oxides and (hydr)oxides of manganese and iron under reducing conditions at depth, divalent cations of these elements can diffuse upwards through the pore waters to be oxidized and precipitated in near-surface oxic layers, leading to the characteristic near-surface enrichment of manganese and iron in the sediments of many well oxygenated lakes (see Section 3.2.4.3). Phosphorus and 

For lakes which have undergone significant acidification, it has been suggested that heavy metals could be released from surface sections by pH-dependent dissolution, resulting in sub-surface maxima in sedimentary heavy metal concentrations. In two Canadian acid lakes, however, Carignan and Tessier found that downward diffusive fluxes of dissolved zinc from overlying waters into anoxic pore waters were responsible for the pronounced sub-surface sediment maxima in solid phase zinc, presumably as the insoluble sulfide. 

The Solvay Process, which was introduced for the manufacture of the industrially important chemical, soda ash , i.e. sodium carbonate (Na2C03), along the west shore of Onondaga Lake in 1884, was cheaper and less polluting than the existing Leblanc Process. Essentially, it made use of two cheap and plentiful naturally occurring substances in the area 

NaCl from the deep brine springs and CaC03 from limestone outcroppings in a simple reaction, which yielded two useful products. 

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