Abstract
Despite comprising a small portion of the earth’s surface, lakes are vitally important for global ecosystem cycling. However, lake systems worldwide are extremely fragile, and many are shrinking due to changing climate and anthropogenic activities. Here, we show that Poyang Lake, the largest freshwater lake in China, has experienced a dramatic and prolonged recession, which began in late September of 2003. We further demonstrate that abnormally low levels appear during October, 28 days ahead of the normal initiation of the dry season, which greatly imperiled the lake’s wetland areas and function as an ecosystem for wintering waterbirds. An increase in the river-lake water level gradient induced by the Three Gorges Dam (TGD) altered the lake balance by inducing greater discharge into the Changjiang River, which is probably responsible for the current lake shrinkage. Occasional episodes of arid climate, as well as local sand mining, will aggravate the lake recession crisis. Although impacts of TGD on the Poyang Lake recession can be overruled by episodic extreme droughts, we argue that the average contributions of precipitation variation, human activities in the Poyang Lake catchment and TGD regulation to the Poyang Lake recession can be quantified as 39.1%, 4.6% and 56.3%, respectively.
Highlights
Despite comprising a small portion of the earth’s surface, lakes are vitally important for global ecosystem cycling
Impacts of Three Gorges Dam (TGD) on the Poyang Lake recession can be overruled by episodic extreme droughts, we argue that the average contributions of precipitation variation, human activities in the Poyang Lake catchment and TGD regulation to the Poyang Lake recession can be quantified as 39.1%, 4.6% and 56.3%, respectively
In the case of the extreme drought in 2004 (Auxiliary material, Fig. S6), the October water discharge from all five tributaries to the Poyang Lake dropped by 23.9 × 108 m3 compared to the pre-TGD stage, which results in 1.87 m of lake level decrease, or explains 83.5% of the post-TGD annual lake level drop (Auxiliary material, Table S4). These results suggest that extreme climate conditions can dominate the influence of the TGD on Poyang Lake recession, which is similar to the effects of climate on the Changjiang River in 200625
Summary
Despite comprising a small portion of the earth’s surface, lakes are vitally important for global ecosystem cycling. The lake receives water from five main tributaries, the Ganjiang, Fuhe, Xinjiang, Xiushui and Raohe Rivers, and discharges to the Changjiang River at Hukou (Fig. 1, Auxiliary material, Table S1), which results in a considerable annual fluctuation of water level and creates approximately a 3000 km[2] ephemeral wetland system[11]. These extensive wetlands provide a home for millions of migrant birds during the lake’s low water stages in late autumn and winter, including 95% of the world’s endangered white cranes (the Siberian crane, Grus leuceogeranus)[12,13]. There has been no studies that attempting to distinguish and quantify the contribution of each possible factor on the recent lake recession
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