River runoff effect on the suspended sediment property in the upper Chesapeake Bay using MODIS observations and ROMS simulations

Abstract

AbstractOcean color data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the satellite Aqua from 2002 to 2012 and simulations from the Regional Ocean Modeling System (ROMS) are used to study the impact of the Susquehanna River discharge on the total suspended sediment (TSS) concentration in the upper Chesapeake Bay. Since the water in the upper Chesapeake Bay is highly turbid, the shortwave infrared (SWIR)‐based atmospheric correction algorithm is used for deriving the normalized water‐leaving radiance nLw(λ) spectra from MODIS‐Aqua measurements. nLw(λ) spectra are further processed into the diffuse attenuation coefficient at the wavelength of 490 nm Kd(490) and TSS. MODIS‐Aqua‐derived monthly TSS concentration in the upper Chesapeake Bay and in situ Susquehanna River discharge data show similar patterns in seasonal variations. The TSS monthly temporal variation in the upper Chesapeake Bay is also found in phase with the monthly averaged river discharge data. Since the Susquehanna River discharge is mainly dominated by a few high discharge events due to winter‐spring freshets or tropical storms in each year, the impact of these high discharge events on the upper Chesapeake Bay TSS is investigated. Both MODIS‐measured daily TSS images and sediment data derived from ROMS simulations show that the Susquehanna River discharge is the dominant factor for the variations of TSS concentration in the upper Chesapeake Bay. Although the high river discharge event usually lasts for only a few days, its induced high TSS concentration in the upper Chesapeake Bay can sustain for ∼10–20 days. The elongated TSS rebounding stage is attributed to horizontal advection of slowly settling fine sediment from the Susquehanna River.