Is there light after depth? Distribution of periphyton chlorophyll and productivity in lake littoral zones

摘要

Periphyton and phytoplankton contribute to the base of lake food webs, and both groups of microalgaeare influenced by resources and physical forcing. Spatial variation in light availability interacts with the physicaldynamics of the water column to create predictable depth gradients in resources and disturbance that maydifferentially affect periphyton vs phytoplankton. We characterized the depth distribution of chlorophyll andproductivity of periphyton on sediments (epipelon) and phytoplankton in the euphotic zones of 13 oligomesotrophiclakes that span a large size gradient (0.017–32,600 km2). Epipelic chlorophyll usually increased withdepth in the epilimnion. Light was the primary driver of the consistent within-lake patterns in periphyton productivityacross this lake-size gradient. In 5 lakes, epipelic periphyton exhibited a unimodal distribution of productivitywith depth in the photic zone, but no evidence of photoinhibition was found for periphyton. Rather, patternsin sediment N and P and observed changes in biofilm structure were consistent with determination of epipelicbiomass by disturbance at depths ≤1 m in the smaller lakes and by light limitation at depths >1 m. Further quantificationof the effects of disturbance on epipelon is needed. Nonetheless, our data demonstrate that the perceivedhigh spatial variability in periphyton biomass and productivity is not an impediment to development of robustmodels of whole-lake primary production that include both phytoplankton and periphyton.