Marhte Chemistry 41 (19931 299-310 299 Elsevier Science Publishers B.V., Amsterdam Factors influencing fatty acid and hydrocarbon composition of sedimenting particles in the northeastern Adriatic Sea Mirjana Najdek 'Ruder Bo.ikovid" Institute. Center.for Mar#le Research Rovinj. 52210 Rovinj. Croatia (Received 7 January 1992; revision accepted 18 June 19921 ABSTRACT Najdek, M., 1993 Factors influencing fatty acid and hydrocarbon composition of sedimenting particles in the northe-stern Adriatic Sea. Mar. Chem., 41: 299-310. Fatty acids and hydrocarbons of sedimenting particles were investigateu in the northeastern A,~:-atic Sea from November 1988 to December 1989. Particles were collected at approximately monthly intervals, using sedimec.t traps deployed at 30m depth (2m above bottom). Seasonal changes in sedimentation of particulate matter were very pronounced. Hydrocarbon fluxes and concentrations were found to vary significantly depending on the season. They averaged 2 69 _+ 1.44mgm -" day and 232r4 + 90.93#gg" U in winter, respectively. In late spring-early summer the corresponding vah:es amounted to 0.045 _+ 0.015mgm 2day i and 13.72 _+ 5.56ttgg ~, and they increased towards autumn, when mean values of 0.517 ± 0.228mg m -2 day- ~ and 98.86 ± 48.72pgg J were obtained. In contrast, fatty acid fluxes and concentrations were low during winter I0.26 _+ 0.08"rlgm--" day ~ and 21.95 ± 3.351~gg-t), increased slightly towards the summer (0.48 ± 0.12 mgm -" day ~ and 139.9 ± 44.6ttgg i) and reached maximum rate and conctntration in autumn, when average values were 1.08 ± 1.30mg m-~ day - ~ and 489.1 ± 186.7,ug g - k, respectively. The differences in composition, concentrations and fluxes of the fatty acids and hydrocarbons vmre related to the sources of sedimentine material, reflecting the influence of resuspension of bottom sediments during winter and the appearance of mucus aggregates during summer ,and their subsequent deposition in autumn. INTRODUCTION Various processes influence the biogeochemical cycle of organic matter in the northern Adriatic, one of the most productive regions of the Mediter- ranean Sea (Sournia, 1973). Nutrient input from the Po River greatly increases marine primary production of the open waters (Degobbis and Gilmartin, 1990; Gilmartin et al., 1990). Signifi- cant quantities of sewage, inadequately treated, are dispersed from urban and tourist centers along the coast directly into the sea. As a result of the Adriatic's shallowness (depth less than 50m), organic matter exchange at the water- sediment interface may be of considerable import- ance for the northern Adriatic ecosystem. Period- Correspondence to: A. Najdek, "Ruder Bo~kovi6" Institute, Center for Marine Research, Rovinj, 52210 Rovinj, Croatia. ically, the cycling of organic matter is influenced by hyperproduction of algal-derived mucus (Fonda-Umani et al., 1989), which forms large aggregates in the water column and extended gelatinous layers at the sea surface (Stachowitsch et al., 1990). Such phenomena occurred recently (1988, 1989 and 1991) and also during this inves- tigation. Most processes involving the cycling of organic matter are poorly understood in the northern Adriatic. The relative importance of the various organic matter sources has not yet been quantified. Although lipids represent only a minor proportion 3f the organic matter, they provide information on the origin and pathways of organic matter i~1 the ecosystem. Seasonal changes in fatty acid composition are often related to environmental factors (Kattner et al., 0304-4203/93/$06.00 ~ 1993 Elsevier Science Publishers B.V. All rights reserved