Acyclic Lipids in Amazon Shelf Waters

• Published in: Estuarine, coastal and shelf science Vol. 50; no. 2; pp. 231 - 243
• Main Authors: Elias, V.O., Cardoso, J.N., Simoneit, B.R.T.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.02.2000; Elsevier
• Subjects: alkanes; Amazon shelf; Animal, plant and microbial ecology; Biological and medical sciences; Brazil coast; Fundamental and applied biological sciences. Psychology; lipids; Microbial ecology; organic matter; particles; Various environments (extraatmospheric space, air, water); South America; Brazil; America; ASW, Atlantic; organic matter; Brazil coast; Amazon shelf; lipids; alkanes; particles; Biodegradation; Microbial activity; Water chemistry; Organic matter; Hydrocarbon; Continental shelf; Environmental factor; Lipids; Sedimentation; Coastal zone; Marine environment; Alkane; Chemical composition
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1006/ecss.1999.0574

Acyclic lipids were analysed for dissolved (<1·2μm) and particulate (>1·2μm) material from surface water of the Amazon continental shelf to correlate the direct inputs with diagenetic processes of the organic matter and to assess the differences in compound distribution patterns of the samples. The dissolved samples contained n -alkanes with an unusual even-to-odd carbon number predominance <C30and CPIs (carbon-preference index) varying from 0·35 to 1·22 (C17–C22range) and 0·52 to 1·33 (C23–C28range). Carbon number maxima (Cmax) occurred at C18and/or C22Pr/Ph ratios varied from 0·28 to 2·62. The n -alkanes in particulate samples ranged from C15to C35(CPI17–22from 0·15 to 0·50 and CPI23–28from 0·52 to 1·12) with Cmaxat C18and C20, while pristane and phytane on the other hand were present in particulate matter only at trace amounts and hence Pr/Ph ratios could not be calculated. Both dissolved and particulate phases showed saturated C14, C16and C18alkanoic acids and an unsaturated C16:1acid as major components. The chemical composition of these acyclic lipids indicates an origin from micro-organisms, probably diatoms. Although minor, a contribution of components derived from plant waxes are more abundant in the particulate phase with profiles indicating a remineralized residue. Plant waxes are effectively biodegraded in the shelf waters during downstream transport in the Amazon River. Furthermore, the Pr/Ph ratios calculated for the dissolved samples indicate that the organic matter in the surface of the highly turbid waters passed through an anaerobic stage. The differences in the acyclic hydrocarbon profiles of the dissolved and particulate phases show that organic inputs are preserved differently in smaller and larger particles.