Transport And Burial Of Particulate Terrigenous Organic Matter In Changjiang (Yangtze River) And East China Sea Shelf

In order to understand the spatial-temporal distribution and transport of terrigenous organic matter in Changjiang and East China Sea, plant, soil, sediment and SPM (Suspended Particulate Matter) samples in Changjiang drainage, SPM samples in Xuliujing, Changjiang estuary and East China Sea shelf, core sediment samples in Changjiang estuary were measured for elements, stable isotopes, and lignin phenols. Stable carbon isotopes of individual lignin phenols of some samples in Changjiang drainage were also determined.The signature of lignin phenols of the vascular plant tissues revealed significant differences in C/V ratios among monocotyledon (1.42), dicotyledon (0.43) and phreatophytes (2.84). Elevated lignin concentration was found in soils from middle/down drainage. The (Ad/Al)v ratio of the soil samples suggested that the lignin composition in soils from up reaches was more degraded. Soils from northern and southern tributaries could be discriminated by OC%, δ¹³C and 18 values over the whole drainage. Moreover, the δ¹³C value of individual lignin phenols of plants and soils were quite different. From up to down reaches of Changjiang, lignin concentrations of SPM samples collected in 2003 decreased, while those of sediment samples increased. The (Ad/Al)v ratios showed that SPM samples were relative fresh and sediment samples were greatly degraded. SPM samples collected in middle/down reaches in 2006 were more degraded and depleted in lignin contents. Seasonal variation was found in lignin concentrations of SPM samples collected at Xuliujing monthly from June, 2003 to August, 2006. In flood season, Lig8 values were elevated but ∑8 and ∧8 values decreased. In dry season, E8 and A8 values increased, while Lig8 values decreased. Three-end-member model was established to evaluate the contribution of different sources to the organic matter of SPM and sediment samples. Results showed the contribution from soil to sediment was the largest (40%～90%), the contribution of plant detritus increased from nearly zero in upper stream to about 30% ～ 60% in lower stream. Phytoplankton contributed to sediment lest. In SPM samples collected in 2003, the fraction of soils was almost 50%. The contribution of plant detritus decreased from up to down stream. In SPM samples of 2006, the contribution of soils was elevated for about 10%, and the fraction of phytoplankton significantly increased. The contribution of different end-member to SPM at Xuliujing changed with seasonal variation. In flood season, the contribution of soils was elevated, up to 50% ～ 60%, while that of plant detritus was very little or nearly zero. In dry season, plant detritus contributed more, up to 60%. The contribution of phytoplankton was about 30% to 40% in the whole year. During September, 2004 to May, 2005, the contribution of phytoplankton increased dramatically. Grain size was the main factor controlling the organic compositions in particulate matter. The building of dams, climate and seasonal variation adjusted the water discharge of Changjiang, and changed the compositions of clay, silt and sand in particulate matter, which could influence the transport and burial of terrigenous organic matter. It was estimated that about 160 × 10² ton to 300 × 10² ton of particulate lignin were delivered to the sea every year from 2003 to 2006. The transport fluxes were relative with the water discharge and sediment load of Changjiang. In Changjiang estuary, the concentration of lignin in SPM was highest around the mouth, and decreased with the distance offshore. In Agust, 2005 and June, 2006, lignin concentration of SPM was also relative high in the northern area of estuary, while decreased in October, 2006, which maybe attributed to seasonal variation of water discharge of Changjiang. Higher Lig6 value was observed in surface water than in bottom water, but the ∑8 and ∧8 values were higher in bottom water, which reflected the recalcitrance of lignin. The concentration of TSM (total suspended matter) made great impact on particulate lignin concentration (Lig6). However, Lig6 values were well related to salinity. So, it could be used in tracing the movement of terrigenous organic matter in estuary. Around the mouth of the estuary, the fraction of terrigenous organic matter was most, and decreased outside. The fraction of terrigenous organic matter in TMZ in August, 2005 was more than 100%, which maybe due to the influence of resuspension. The movement of terrigenous organic matter in June, 2006 was similar with in August, 2005. The contribution of terrigenous organic matter was 30% near the mouth and decreased to 8% at the east-southern region (124°E, 28°N). The cover region of terrigenous organic matter dwindled to the southern area of the mouth and the contribution reduced to 8% at 123.5°E. Water discharge of Changjiang and the trap of TMZ were primary factor influenced the transport of terrigenous organic matter in estuary. At E4 station in Changjiang estuary, the lignin parameters of core sediment could reflect the variation of sediment load and water discharge of Changjiang, as well as human activities in Changjiang drainage in recent 50 years. Water discharge was the dominant factor in controlling the transfer and deposition of terrigenous organic matter. Sediment load of Changjiang was altered by human activities, and so the signals in sediment were distorted.Lignin concentration in SPM in surface of East China Sea was influenced not only by Changjiang dilution water, but tide inshore and Taiwan warm current and Kuroshio offshore. In northern area of Changjiang estuary, it also could be disturbed by Yellow Sea Cold Water. In general, with the distance from continent, Lig6 values reduced. 220 Km was estimated the most distance of transport of terrigenous organic matter by Changjiang dilution water.