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

Sterols, n-alkanols, organic carbon OC., CrN ratios and carbon isotope data d13C. were investigated in sediments of the urban Capibaribe River estuary, NE Brazil, in order to assess allochthonous and autochthonous sources of organic matter OM.. Sedimentary OC values are high, but CrN ratios and d13C data generally fall within the range of values reported in other riverine systems, and suggest mixed inputs from aquatic and terrestrial matter. Mean values for total 4-desmethyl sterols and high molecular weight HMW. n-alkanols are 11.0 mgrg and 2.8 mgrg, respectively. Sterols are found at highest levels in areas of enhanced urban outfalls. They can be related to major planktonic species growing in riverine waters. Stanolrstenol ratios suggest a high degree of alteration of the autochthonous OM as a result of elevated temperatures and microbiological proliferation. Even though 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 sewage contaminated hydrosystems, but not as high as expected given the importance of sewage outfalls and low riverine water discharge. However, high coprostanol.r coprostanolqcholestanol. ratio values indicate that fecal contamination is significant.