Littoral-benthic primary production estimates: Sensitivity to simplifications with respect to periphyton productivity and basin morphometry

Periphyton is a critical energy source for consumers in lakes of all sizes, but estimates of average, area-specific littoral zone benthic primary production (LBP) have been hampered by low spatial and temporal resolution of productivity data. We analyzed the sensitivity of estimates of LBP to depth-specific variation in photosynthesis-irradiance (PE) parameters and temporal variation in water clarity using monitoring data from five northern temperate lakes. Maximum photosynthesis rates peaked in the upper epilimnion in all five lakes, and our best daily estimates of LBP ranged from 125 mg C m^-2 d^-1 to 425 mg C m^-2 d^-1. Nonlinear variation in maximum photosynthesis (P_MAX) with depth caused overestimates in LBP by an average of 10% when mean values of P_MAX were applied throughout the euphotic zone. Conversely, applying values of light levels at onset of saturation (E_k) from the upper epilimnion resulted in underestimating LBP by an average of 19% compared with the most data-rich (optimal) calculations. Simplified approximations of bathymetry yielded underestimates or overestimates of LBP, depending on basin shape. Incorporating temporal variation in water clarity and daily solar irradiance did not substantially improve estimates of average summer LBP compared with estimates that incorporated summer average values of K_d, but this result should not be extrapolated to lakes with more variable water clarity. Estimates of average littoral zone benthic primary production can be optimized by incorporating depth-specific variation in maximum periphyton productivity, saturation light intensity, and sediment surface area into calculations.