Ultraviolet radiation sensitivity of photosynthesis in phytoplankton from an estuarine environment, Limnol

We have studied temporal variation in the sensitivity of phytoplankton photosynthesis to inhibition by ultraviolet radiation (UV; 280–400 nm) using biological weighting functions (BWFs) that quantify the biological effect of different wavelengths of UV. Variations in irradiance-dependent BWFs were evaluated for natural phytoplankton assemblages from the Rhode River, a shallow subestuary of the Chesapeake Bay, Maryland, from October 1994 to July 1996. Phytoplankton assemblages were sensitive to UV throughout the year. Rhode River assemblages are inhibited more strongly in the UV-B (280–320 nm), particularly below 300 nm, but there is a significant influence well into the UV-A (320–400 nm). There was no inhibition of phytoplankton photosynthesis by photosynthetically available radiation (400–700 nm), but there was significant seasonal variation in the saturated rate of photosynthesis (P) and in the light saturation parameter (Es). There was little variation in seasonal average BWFs through theBs year, but there was considerable variation in BWFs during each season. Individual BWFs varied both in absolute values of the weightings (reciprocal [mW m22]) and in the spectral shape or relative effect of UV-B versus UV-A, which may be due to changes in species composition, light, temperature, and nutrient availability. Comparison of the most sensitive assemblage (spring) with the least sensitive assemblage (winter) indicates that these BWFs are close to the upper and lower bounds in sensitivity for irradiance-dependent BWFs from all natural and culture