Influence of the Three Gorges Dam on total suspended matters in the Yangtze Estuary and its adjacent coastal waters: Observations from MODIS

Abstract Several studies showed the linkage of the Three Gorges Dam to the downstream coastal ecosystem in the East China Sea, yet its potential influence on the total suspended matters (TSM) in the Yangtze Estuary and its adjacent coastal waters has not been reported, possibly due to technical difficulties in obtaining statistically meaningful results. Here, a new remote sensing algorithm was established to estimate TSM from MODIS observations over the Yangtze Estuary and its adjacent coastal waters. The algorithm was based on a piecewise regression between TSM and surface reflectance at 645 and 869 nm, leading to RMS uncertainties of only 20–30% for TSM between 2 mg L− 1 and 1762 mg L− 1. The algorithm was applied to MODIS data to derive TSM distribution maps from 2000 to 2010 at 250 m resolution, which revealed significant spatial and temporal (seasonal and inter-annual) variability. Mean TSM in the Yangtze Estuary increased from 44.4 ± 34.1 mg L− 1 in May to 96.0 ± 58.0 mg L− 1 in October, while much higher TSM was found in the nearby Hangzhou Bay (between 100.3 ± 51.6 mg L− 1 in August and 290.2 ± 120.0 mg L− 1 in February). Two regions showed significantly out-of-phase seasonality: region A1 in the Yangtze Estuary driven by sediment discharge from the Yangtze River and region A2 in offshore waters and part of Hangzhou Bay driven by winds. The annual mean TSM in region A1 showed significantly decreasing trend in the 11-year period (− 2.8 mg L− 1/yr), which appeared to be caused by the construction of the TGD. The study also has established a TSM environmental data record (EDR) to assess future TSM in the ecologically and economically important Yangtze Estuary and Hangzhou Bay.

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