The Huanghe (Yellow River) and Changjiang (Yangtze River) deltas: a review on their characteristics, evolution and sediment discharge during the Holocene

Abstract

Today, Asian rivers play an important role in delivering sediment from the land to the oceans. However, past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one-third to one-half of the present level. Chinese rivers have been strongly influenced by human activities, and their sediment discharge has changed over the last 6000 years. For the study of the long-term human impact on rivers and catchment basins, Chinese rivers provide excellent examples because continuous historical records are available. Here, the characteristics, evolution and sediment discharge during the Holocene of the deltas of two large Chinese rivers, Huanghe (Yellow River) and Changjiang (Yangtze River) are summarized. The Huanghe and Changjiang deltas are different with respect to coastal environments, water and sediment discharge, the pattern of development of the delta lobe, thickness of Holocene sediments, and basal topography of the incised valleys formed during the last glacial period. The Huanghe Delta is characterized by a high concentration of sediment, huge sediment discharge, thin Holocene deltaic sediments, a lateral delta lobe shift, and a steep longitudinal profile in its lower reaches. The Changjiang Delta is characterized by a large water discharge, a large interseasonal water-level change, a tide-dominated coastal environment, continuous seaward progradation with isolated river-mouth sand bodies, thick Holocene sediments, and a deep-incised valley formed during the last glacial period. Based on the sediment volume of prograding deltaic sediments over the last 6000 years, the sediment discharge of Huanghe 1000 years ago is estimated to have been 1×10 8 tons/year, 1/10 of the present level. An abrupt increase occurred at ca. 1000 years ago as a consequence of human activities on the Loess Plateau, especially involving cultivation and deforestation. Moreover, the estimated sediment load of Huanghe at Sanmenxia station prior to 1000 years was 2.7–4.0×10 8 tons/year, or about 20% (15–25%) of the present level. Our recent study estimated that the sediment discharge of Changjiang before 2000 years BP was ca. 2.4×10 8 tons/year. Total sediment discharge of both rivers before 2000 years BP is estimated to have been 3.4×10 8 tons/year, or only about 20% of the present level. Moreover, the total sediment load to the lower reaches is estimated to have been 5–6×10 8 tons/year, or one-fourth the present level.