Investigating Rainstorm Disturbance on Suspended Substance in Coastal Coral Reef Water Based on MODIS Imagery and Field Measurements

Abstract

From July 11-12, 2009, the tropical storm Soudeler swept the study area with a Level 8 wind and disturbed the suspended substance in this coastal area, which may have caused some fatal impact on the health condition of coral reef in Xuwen coral reef coast located in Leizhou Peninsula of South China. In order to evaluate the impact of extreme weather on coral reef, this study applied and validated a TSS model to map the TSS variation based on red and infrared spectral bands of MODIS data through one before-storm and two after-storm images after applying the atmospheric correction of in-water linear regression analysis. By mapping and comparing the changes of TSS values before- and after- tropical storm, this study found substantial increases of TSS concentrations as a mean value of 47.8 mg/L (~3.6 times of mean TSS value before rainstorm) in the area during the passage of tropical storm compared to those under no-storm condition. Besides, the TSS returned back to even lower values five days after the passage of tropical storm as a mean value of 3.6mg/L (~one quarter of mean TSS value (13.4 mg/L) before rainstorm). The conclusion was made that the TSS concentration in estuary and coastal areas under local rainstorm tends to return to a normal level faster (approximately 2.5 days) than under a hurricane [1] or tropical storm as discovered in this study (approximately 5 days). Compared to the less frequent and non-synoptic in-situ field sampling approach, the synoptic and frequent sampling facilitated by frequent remote sensing imagery of MODIS provides an improved assessment of TSS concentration and two-dimensional distribution patterns and is recommended to be used as a valuable tool for frequently monitoring coral reef water quality in coastal water bodies of China and other areas in the world if applicable.