Sedimentary 4-desmethyl sterols and n-alkanols in an eutrophic urban estuary, Capibaribe River, Brazil

Sterols, n-alkanols, organic carbon (OC), C/N ratios and carbon isotope dat a (delta(13)C) were investigated in sediments of the urban Capibaribe River estuary, NE Brazil, in order to assess allochthonous and autochthonous sou rces of organic matter (OM). Sedimentary OC values are high, but C/N ratios and delta(13)C data generally fall within the range of values reported in other riverine systems, and suggest mixed inputs from aquatic and terrestri al matter. Mean values for total 4-desmethyl sterols and high molecular wei ght (HMW) n-alkanols are 11.0 mu g/g and 2.8 mu g/g, respectively. Sterols are found at highest levels in areas of enhanced urban outfalls. They can b e related to major planktonic species growing in riverine waters. Stanol/st enol ratios suggest a high degree of alteration of the autochthonous OM as a result of elevated temperatures and microbiological proliferation. Even t hough sterols suggest the importance of autochthonous inputs to the river, HMW n-alkanols indicate major terrigenous accumulation at the mouth and 10 km upriver. Coprostanol and epicoprostanol levels are comparable to other s ewage contaminated hydrosystems, but not as high as expected given the impo rtance of sewage outfalls and low riverine water discharge. However, high ( coprostanol)/(coprostanol + cholestanol) ratio values indicate that fecal c ontamination is significant. (C) 1999 Elsevier Science B.V. All rights rese rved.