ORGANIC RICH FRESHWATER SEDIMENTS (SAPROPEL) AS POTENTIAL SOIL AMENDMENT FOR RECULTIVATION OF AREAS CONTAMINATED WITH HEAVY METALS

Sapropel is organic rich freshwater lake sediment with broad range of applications. Firstly it was named as "gyttja" in 1862 when Swedish scientist Hampus von Post called so a light-colored coprogenic deposit consisting of a mixture of plankton particles, mollusk shells, chitin remains from the exoskeletons of insects, pollen and spores of higher plants and mineral particles, formed in eutrophic water bodies. Term "sapropel" means "decayed sludge" - it was proposed by Lautenberg in 1901 and by G. Potogne in 1904. Sapropel relates to renewable natural resources and is typically found only in freshwater basins; however, usually this term is used in saline aquifer stratigraphy studies. Sapropel's chemical composition and peculiarities of different minefields are significantly different and defined by its formation conditions and by lakes' flora and fauna. Sapropel as it contains organic matter is able to bind metal ions and change their speciation forms in soils forming stable complexes. The ability to form complexes with metal ions depends on the type of soil, type of metal, as well as quantity of sapropel as soil amendment. The main sapropel reserves are found in the lake-bottom sediments - reserves in Latvia are estimated as 800-900 million m(3) or 170-190 million tons (with moisture content of 60%). In 1957-1967 more than 250 lakes in Latvia have been studied in detail on sapropel reserves and properties, later from 1990-2000 more than 1300 lakes were studied additionally. There are 56 strongly and more than thousand potentially contaminated sites with heavy metals in Latvia. The aim of this paper is to give overview status description on theoretical possibilities to use sapropel as the agent for remediation of contaminated with heavy metals soil.