The Geochemistry Of Particle Organic Carbon In Shuangtaizi Estuary

Due to the rapid developing on economy and social activites, the Shuangtaizi Riverplays a key role on the land-sea interaction surrounding the Bohai Sea. In order toexplore the perservation and degraditon of organic carbon in the Shuangtaizi Estuary,particulate particles, surface and core sediments wre collected and analyzed in Augest,2011. The result and disscusions are demonstrated as followed based on the totalorganic carbon, δ¹³C, C/N, and compound specific composition of PAHs and lipids.The particulate organic carbon was located at1.10mg/L-16.41mg/L （5.66mg/L atave.） in the Shuangtaizi Estuary.,Bothe surface and bottom of particulate organiccarbon showed an increasing and then decreasing tendency from river to sea. Thesurface organic carbon in sediment ranged at0.60%-1.84%（1.09%at ave.）, whichpresented decreasingly from the river to the sea, while that waved at the range of0.71%-1.38%（0.97%at ave.） vertically. It was suggested that the macromolecularorganic carbon, which may be hard degraded, accounted for>40%of the totalorganic carbon, with the highest up to91%, based on different measuring methods ofelement analyzer and potassium dichromate oxidation method.The δ¹³C aboundanceranged from-24.36‰to-22.61‰in surface sediment andfrom-23.53‰to-22.89‰vertically, which indicated mixed sources of terrigenousand sea. The terrigenous organic carbon contributed between37.3%-62.3%in surfacesediments, whereas between41.0%-50.2%vertically. The C/N ratios also suggestedmixed sources of organic matter but lower terrigenous contributions to11.1%as anaverage.The particulate PAHs ranged at6.38μg/L-10.59μg/L, in which the surface PAHstrended to increase first and then decrease from reiver to sea, while that bottom oneskept increasing at the same time. The PAHs tended to decrease from3414.69to1466.11ng/g dry weight （ave. at2444.83ng/g） in surface sediments from river to sea,with episodic high PAHs intrutions from branches. Diagnostic ratios of PAHssuggested that human activities printed significantly on the Shuangtaizi Estuary, suchas petroleum explore, coking operating, coal combustion and other mixed origins.32kinds of fatty acid molecules were detected in the particulate and sedimentsamples, including13species of saturated fatty acids （C9:0-C26:0）,5branched chainfatty acids （i-14:0, i-15:0, i-16:0, i-17:0and i-24:0）,9monounsaturated fatty acids （such as C9:1, C17:1, C23:1, et al）, and4polyunsaturated fatty acids （C18:2, C20:2,C20:3, C24:2）.10neutral lipids were detected, including phytol,4sterols (27△0（5-cholestan-3-ol）,27△⁵（Cholest-22E-En-3-ol）,29△⁵（24-Ethylcholest-5-En-3-ol）,29△⁵,22（24-Ethylcholest-5,22-Dien-3-ol） and5alcohols （12-ROH,14-ROH,16-ROH,18-ROH and20-ROH）.Particulate free fatty acid ranged at1.54-22.46μg/L （9.56μg/L at ave）, while freeneutral lipid changed at0.81μg/L-1.79μg/L （1.27μg/L）. The particulate fatty acids andneutral lipids increased first and then decreased from the river to the sea in the surfacewater, while fatty acids kept decreasing and neutral lipid followed the same as that ofthe surface water in bottom water.Free fatty acids varied at204.56μg/g-973.90μg/g （423.31μg/g at ave）, whichwas about3.5times higher than free neutral lipids （52.91μg/g-159.01μg/g （96.70μg/g at ave）） in surface sediments, wheares free fatty acids （149.82-582.81μg/g（280.36μg/g at ave）） was about2.5times higher than free neutral lipids （34.29μg/g-121.94μg/g （78.32μg/g at ave）） vertically.Bound fatty acids waved at277.12μg/g-590.50μg/g and netuarl lipids at22.63μg/g-116.15μg/g in particulate particles, as well as mineral bound fatty acids at163.99-231.07μg/g and netuarl lipids at4.73μg/g-18.53μg/g, respectively. Boundfatty acids ranged at235.92μg/g-698.09μg/g （427.70μg/g at ave） and netuarl lipids at32.07μg/g-76.62μg/g （57.89μg/g at ave） vertically, as well as mineral bound fattyacids at111.32μg/g-390.20μg/g （214.89μg/g at ave） and netuarl lipids at8.24μg/g-27.36μg/g （14.32μg/g at ave）, corresponding. Bound fatty acids fluctuated similar tothat mineral ones, but bound netuarl lipids fluctuated more wide than mineral ones.Indicated by the compound specific fatty acids, organic carbon originated frommultiple sources in surface sediments, in which bacteria contributed more thatphytoplankton and phytobenthos, and the least by terrestrial plants. Neutral lipidsfrom algae were preserved better than the others, which accounts for>70%in boundand mineral bound pools.The significant correlation between particulate organic carbon and salinitysuggested that dilution process primarily controlled the behavior of orgnic carbon inShuangtaizi Estuary.