Photosynthetic Characteristics of Lotic Periphyton

Periphyton communities, grown in continuous-flow troughs, were suspended in filtered river water and placed in a photosynthesis–light incubator similar to those used for phytoplankton. A three-parameter equation was fitted to the incubator data. Seasonally the initial slope, α, ranged from 12.1 to 53.6 μg C∙(mg Chl a) −1 ∙h −1 ∙(μEinst.∙m −2 ∙s −1 ) −1 ; the maximum photosynthetic rate, P B max , varied from 1.16 to 5.49 mgC∙(mg Chl a) −1 ∙h −1 ; and the inhibition parameter, I b , ranged from 1500 to 6900 μEinst.∙m −2 ∙s −1 . These values are similar to those reported for other periphyton and phytoplankton. P B max strongly correlated with light history, whereas inhibition was inversely related to water temperature, α did not correlate with either irradiance or temperature but with changes in average cell size. Seasonal variations in the light level optimal for photosynthesis, I m , suggested a period in late winter and early spring for potentially serious inhibition of photosynthesis. These Chl a normalized photosynthetic parameters were unaffected by changes in concentration of the growth-limiting nutrient, phosphorus.