Photosynthetic Characteristics of Lotic Periphyton

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Abstract
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, PBmax, varied from 1.16 to 5.49 mgC∙(mg Chl a)−1∙h−1; and the inhibition parameter, Ib, ranged from 1500 to 6900 μEinst.∙m−2∙s−1. These values are similar to those reported for other periphyton and phytoplankton. PBmaxstrongly 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, Im, 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.