Composition of soil lipids in two Chinampas agroecosystems from Xochimilcoand Tlahuac Municipalities, Mexico

The Chinampas are important historically and represent a special agroecosys tem that has been sustainable for many years. However, their agricultural p otential has currently decreased mainly because of irrigation with waste wa ter from Mexico City, leading to progressive salinity and alkalinity proble ms and the subsequent general alteration on the agroecosystem. Chemical com position of the main groups of lipid molecules in anthropogenic organic soi l from Xochimilco and Tlahuac Municipalities (Mexico) were investigated. Th e analysis performed included physicochemical characteristics of the soil a nd the distribution analysis of free alkanes and fatty acids. The successiv e accumulation stages of organic materials in these anthropogenic organic s oils represent a source of irregular distribution in organic carbon, likewi se the concentration of lipid extracts differed noticeably with depth. Ther e is a vertical variability, where hydromorphic environment has played a ke y role in this variability. The major compounds identified in the soil lipi d extracts by gas chromatography-mass spectrometry include series of linear and satured alkanes, fatty acids, as well as individual components such as sterols and hopanes. Most of the lipid components in these soil seem to ha ve a biogenic origin (higher plants and microorganism biomass).