Anthropogenic pressures induced hydromorphodynamic changes of riverine islands in the Upper Jingjiang reach along the Changjiang (Yangtze) River

Abstract

Riverine islands are widespread fluvial landforms with exceptional economic and environmental values. However, anthropogenic pressures have further induced drastic changes worldwide in fluvial islands, which endanger fluvial organism habitation and enable potential ecological degradation. Here, the hydromorphodynamics on these prominent riverine landforms of the seriously regulated Upper Jinjiang reach (UJR) of the Changjiang (Yangtze) River were detected based on the Google Earth Engine (GEE) platform between 1988 and 2019. The results indicated that total vegetated islands area in the UJR experienced expansion, while bars area exhibited a dramatic decrease by 15% between 1988 and 2019. Given the total areas and their subaquatic bars' volume variations, the island's evolution could be divided into “deposition–erosion–stabilization” stages. During the deposition phase from 1988 to 1999, the bars volumes showed a gradually increasing trend, and then it shifted to erosion between 1999 and 2010. After 2010, the islands maintained stability with a total volume of approximately 177 × 106 m3. The multi-year sediment and water discharge variations contributed to the evolution of riverine islands. In particular, resulting from the Three Gorges Dam (TGD) project in 2003, the fluvial sediment load and duration of overbank discharges (25000 m3/s) decreased significantly, which were the dominant factors inducing islands with their subaquatic bars shrinkage. Recent multiple island protection projects were responsible for defending islands with their subaquatic bars against erosion and maintaining their stability. This work reveals the islands' evolution in the UJR response to the TGD effect and local artificial engineering, which is vital for managing riverine islands in global rivers affected by nature and human activities.