CHARACTERIZATION OF LIGHT EXTINCTION AND ATTENUATION IN CHESAPEAKE BAY, AUGUST, 1977

When solar radiation penetrates the sea, it is both scattered and absorbed at rates which depend upon the concentration of dissolved organic substances and suspended particulate matter present in the water column. Both scattering and absorption act in unison to produce a rate of attenuation. It is well known that as a transformation from clear oceanic waters to more turbid coastal waters occurs, short wavelengths of light are attenuated more quickly while yellow light penetrates the deepest. This phenomenon is termed “Yellow Shift.” Light penetration measurements at selected wavelengths (430, 470, 514.5, 540, and 600 nm ± 10 nm) taken in August, 1977 in the upper 200 km of Chesapeake Bay from the mouth of the Susquehanna River, suggest that there may be an estuarine “Orange Shift.” It was found for 50% of all light penetration measurements that orange light (600 nm) exhibited the smallest average attenuation coefficient (i.e., orange light penetrated the deepest). Beam transmission volume attenuation coefficients (α) calculated for stations from the mouth of the Susquehanna River to just offshore (6.3 km) from the mouth of Chesapeake Bay indicate that Chesapeake Bay can be divided into three turbidity zones: Estuarine Turbidity Maximum (α values of 3.50 to 4.77 ln/m); Estuarine Turbidity Normal (2.79 to 2.91); Estuarine Turbidity Minimum (2.73 to 2.76). The Turbidity Maximum of northern Chesapeake Bay is examined by comparing the relationship of contours of attenuation coefficient, turbidity, suspended sediment, salinity and chlorophyll a.