Is There Light after Depth? Spatial Variation in Periphyton Chlorophyll and Productivity in Oligotrophic Lakes

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Synthetic paradigms of phytoplankton distribution and dynamics are a cornerstone of limnology. However, no analogous conceptual models exist for benthic algae in lakes, even though periphyton is critical basal resource in lake food webs. We compared the depth distribution of periphyton and phytoplankton productivity and chlorophyll in 13 North American lakes and Lake Tanganyika, East Africa. Periphyton chlorophyll increased with depth in the epilimnion, with some lakes displaying declines in the metalimnion. Area-specific periphyton productivity increased to a depth of 30% of surface light intensity, and thereafter, decreased with depth. Unlike for phytoplankton, photosnythesis-irradiance curves for periphyton demonstrated no photoinhibition at ambient light intensities. There was a strong linear decrease in the intensity at onset of photosaturation (Ik) with depth for periphyton. Phosphorus content of the biofilm layer of the sediments increased with depth, which is consistent with either resource or disturbance-limitation of periphyton productivity at high light intensities. The relationships between periphyton and light were remarkably consistent among all 14 lakes, and within-lake spatio-temporal variation of periphyton was not statistically higher than that of phytoplankton.


Presented a the Society of Freshwater Science Annual Meeting, Louisville, KY.