THE APPLICATION OF STEROL BIOMARKERS TO THE STUDY OF THE SOURCES OF PARTICULATE ORGANIC-MATTER IN THE SOLO-RIVER SYSTEM AND SERAYU RIVER, JAVA, INDONESIA

Sterols were analyzed in suspended particles collected in January 1991 in the Solo River system and in the Serayu River, Java, Indonesia. Fr ee sterols were extracted from particles larger than 0.7 mu m and anal yzed, after derivatization into their trimethylsilyl esters, by GC and GC/MS. Concentrations of total sterols ranged from 438 to 7992 ng/l, or from 2.4 to 183.8 ng/mg of total suspended matter, which varied fro m 3.3 to 400 and 471 mg/l, respectively in the Serayu River and at the downstream station in the Solo River. POC concentrations also varied in a wide range, from 0.91 to 4.72 and 6.13% of TSM, respectively at t he above stations, and were associated with sterol/POC values ranging from 0.15 to 1.75 mu g/mg. Eleven structures of C-27, C-28 and C-29 st enols and associated stanols were identified. 28 Delta(5,22) was only found at downstream stations in the Solo River and in the Serayu River . This unique distribution, different from that of other C-27, C-28 an d C-29 sterols, suggests a predominantly autochthonous origin for thes e compounds associated with an increased planktonic biosynthesis near the estuary. Concentrations of 28 Delta(5), 29 Delta(5,22) and 29 Delt a(5) showed similar spatial distributions and increased downstream, re flecting the significant accumulation of organic matter originating fr om the vegetation of the various drainage basins. Values of the autoch thonous versus terrigenous sterol index, defined as 27 Delta(5)/29 Del ta(5,22) + 29 Delta(5) were in the 1.4-1.9 range at upstream stations, whereas at downstream stations lower values were found, 0.4-0.6, whic h also corresponded to higher concentrations of TSM and lower POC valu es. Insofar as the stanol/stenol values can be used to estimate the ba cterial activity of oxic waters, simultaneous variations of C-27 and C -29 stenol/stanol pairs suggest rather different bacterial degradation capacities of autochthonous versus allochthonous organic matter. The wide differencies between the values of the stenol/stanol pairs observ ed in one of the main tributaries and in downstream stations of the So lo River is evidence that allochthonous organic matter is much more re sistant than autochthonous matter. The low index value observed in the Serayu River indicates the highly refractory nature of both autochtho nous and allochthonous organic material.