Temporal variability of particulate organic carbon in the lower Changjiang (Yangtze River) in the post‐Three Gorges Dam period: Links to anthropogenic and climate impacts

Abstract

Suspended particles from the lower Changjiang were collected monthly from 2003 to 2011, which corresponds to the three construction periods of the Three Gorges Dam. Organic carbon (%OC), organic carbon to total nitrogen molar ratio, stable carbon isotope, and terrestrial biomarkers were examined. Rating curve studies were applied for the temporal trend analysis. The composition of particulate lignin phenols exhibited clear annual and periodic variations but only minor seasonal changes. Lignin phenol ratios (vanillyl/syringyl and cinnamyl/vanillyl) indicated that the terrigenous organic matter (OM) was primarily composed of woody and nonwoody tissue derived from angiosperm plants. The low-lignin phenol yields (Λ8) in combination with higher acid to aldehyde ratios reflected a substantial contribution from soil OM to the particle samples or modifications during river transport. The temporal shift of the lignin phenol vegetation index with the sediment load during the flood seasons revealed particulate organic matter (POM) erosion from soils and the impact of hydrodynamic processes. The dam operations affected the seasonal variability of terrigenous OM fluxes, although the covariation of lignin and sediment loads with discharged water implies that unseasonal extreme conditions and climate change most likely had larger influences, because decreases in the sediment load and lignin flux alter the structure and composition of particulate OM (POM) on interannual time scales, indicating that they may be driven by climate variability. The modification of the composition and structure of POM will have significant impacts on regional carbon cycles and marine ecosystems.

Sources, Transport, and Transformation of Dissolved Organic Matter in a Large River System: Illustrated by the Changjiang River, China

“…Variation in the hydrological conditions did not alter the total dissolved lignin concentrations, which is consistent with a previous study of minor seasonal lignin variation in the Changjiang River (Wu et al, ). The significant lower S/V in 2012 seemed to indicate a higher contribution of gymnosperm tissues at high discharge (Table and Figure c).…”

“…Hence, the ratio of DHBA to vanillyl phenols (DHBA/V) characterizes the degradation state of terrigenous organic matter (Farella et al, ; Pautler et al, ). The ratio of vanillin acid to vanillin ((Ad/Al)v) increases as side‐chain oxidation increases (Hedges & Mann, ; Wu et al, ; Yu et al, ).…”

Spatiotemporal Variation of the Quality, Origin, and Age of Particulate Organic Matter Transported by the Yangtze River (Changjiang)

“…River systems are becoming increasingly affected by human activities such as dam construction, deforestation and agriculture, water diversion, and sand mining (Bianchi & Allison, ; Yang et al, ). Large‐scale alterations to the hydrological plumbing of rivers have changed the fluxes and ratios of carbon and nutrients, as well as the proportions of dissolved versus particulate materials, reaching coastal waters (Bao et al, ; Wu et al, ). Large river systems developed on passive margins have significant capacity to store eroded sediments.…”

“…Sediment decline associated with dam emplacement carries important biogeochemical implications. There have been numerous studies of the biogeochemical characteristics of OM and human impacts on the river with bulk proxies and lignin phenols, which have successfully elucidated the effect of dam construction on the composition and structure of particulate OM (POM; e.g., Bao et al, ; Dai et al, ; Wu et al, , ; Yang et al, , , ; Yu et al, ; Zhang et al, ). However, there is currently very limited available information on the age of OM, particularly in the lower reach downstream of TGD only (Li et al, ; Wang et al, ).…”

On the Origin of Aged Sedimentary Organic Matter Along a River‐Shelf‐Deep Ocean Transect

“…SPM from the Yangtze River was collected in July 2012 at Xuliujing (XLJ; 120.93°E, 31.78°N), ~100 km upstream from the Yangtze River mounth (Figure ). Detailed information about sample site and collection methods was described in Wu et al (). The seven ECS surface sediment (0–2 cm) samples were collected using a box corer along the P‐Line from the prodelta to the upper slope on the R/V Dongfanghong II in July–August 2013 (Figure ).…”