Modeling the effects of ultraviolet radiation on estuarine phytoplankton production: impact of variations in exposure and sensitivity to inhibition

Spectral ultraviolet (UV) irradiance, water column attenuation and biologic al weighting functions for inhibition of phytoplankton photosynthesis have been measured for the Rhode River, a subestuary of the Chesapeake Bay. Toge ther, these measurements can be used to estimate UV effects on water column production, but each factor shows a significant range of variability even just considering summer time conditions. A sensitivity analysis of UV inhib ition is described which assesses the effect of this variation for differen t combinations of 28 irradiance spectra, 8 biological weighting functions ( BWFs) and 16 water column irradiance profiles. Over all combinations, produ ction averaged about 84% relative to potential production in the absence of UV effects. For a few combinations, relative production was as low as 67%, or as high as 97%, but for most combinations the range was 75-95%. Variati ons in the sensitivity of the phytoplankton assemblage, i.e. the BWF, and o ptical properties, represented by a transparency ratio of biologically effe ctive UV to photosynthetically available radiation (PAR), had large effects on water column production. A simple relationship for UV inhibition of wat er column production is developed based on inhibition at the surface and th e ratio of UV and PAR transparency. (C) 2001 Elsevier Science BY. All right s reserved.