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The Poyang Lake catchment, an important sub-catchment of Changjiang, experienced ‘Little Ice Age’ (LIA) and accelerating intensity of human activities during the last 1000 years. As such, the area and time period serve as a perfect case to study the variations in water and sediment discharge under combined natural and anthropogenic impact. Simulation results of the model HydroTrend indicate that the annual average cumulative water discharge of the five rivers entering Poyang Lake over the last 1000 years is 103.65 ± 1.80 km3, and climate change is the dominating factor determining water discharge variations over time. Influenced by the LIA (AD 1451–1850), the total water discharge of the five rivers was reduced by 10%. Sediment load discharging into Poyang Lake by the five rivers was only 9.21 ± 0.43 Mt yr−1 between AD 1000 and 1700, when the anthropogenic impact on the landscape was still low. However, with the human activities accelerating during the past 300 years, the sediment load entering Poyang Lake underwent a drastic change. Because of intensified soil loss, the total sediment load entering Poyang Lake during AD 1800–1950 increased by 58.7%, compared with AD 1000–1700. After AD 1950, the sediment load variation is mainly reflected by the combined impact of dam emplacement and soil erosion. As sediment interception by dams continuously increased over time, the total sediment load entering Poyang Lake during AD 1990–2000 is only 60.9% of that of the highest riverine sediment flux during AD 1951–1980, which is almost equal to that of the lowest level during AD 1000–1700. The sediment load of many rivers in the world exhibited similar variation trends as that of Poyang Lake under combined impact of climate change and human activities. Better understanding the mechanisms of these variation trends is helpful to analyzing the formation and evolution of an estuary-shelf sedimentary system over the Holocene. [ABSTRACT FROM AUTHOR]

Abstract: To study the fluvial interaction between Changjiang River and Poyang Lake, we analyze the observed changes of riverine flux of the mid-upstream of Changjiang River catchment, the five river systems of Poyang Lake and Poyang Lake basin. Inter-annual and seasonal variations of the water discharge and sediment exchange processes between Changjiang River and Poyang Lake are systematically explored to determine the influence of climate change as well as human impact (especially the Three Gorges Dam (TGD)). Results indicate that climate variation for the Changjiang catchment and Poyang Lake watershed is the main factor determining the changes of water exchanges between Changjiang River and Poyang Lake. However, human activities (including the emplacement of the TGD) accelerated this rate of change. Relative to previous years (1956–1989), the water discharge outflow from Poyang Lake during the dry season towards the Changjiang catchment increased by 8.98km3 y−1 during 2003–2010. Evidently, the water discharge flowing into Poyang Lake during late April–late May decreased. As a consequence, water storage of Poyang Lake significantly reduced during late April–late May, resulting in frequent spring droughts after 2003. The freshwater flux of Changjiang River towards Poyang Lake is less during the flood season as well, significantly lowering the magnitude and frequency of the backflow of the Changjiang River during 2003–2010. Human activities, especially the emplacement and operation of the TGD and sand mining at Poyang Lake impose a major impact on the variation of sediment exchange between Changjiang main river and Poyang Lake. On average, sediments from Changjiang River deposited in Poyang Lake before 2000. After 2000, Changjiang River no longer supplied sediment to Poyang Lake. As a consequence, the sediment load of Changjiang River entering the sea increasingly exists of sediments from Lake Poyang during 2003–2010. As a result, Poyang Lake converted from a depositional to an erosional system, with a gross sediment loss of 120.19Mty−1 during 2001–2010, including sand mining. [Copyright &y& Elsevier]