NOTE: Empirical estimation of non-chlorophyll light attenuation in Missouri reservoirs using deviation from the maximum observed value in the Secchi-Chlorophyll relationship

A quadratic reference line delineates the maximum observed Secchi transparency across the measured range of algal chlorophyll (0.7-297 g/L) in Missouri reservoirs. Deviations below maximum Secchi transparency were common (median = 45% of maximum, interquartile range between 35 and 57%) and are characteristic of water bodies with mineral turbidity. Subtracting the reciprocal of maximum Secchi from the reciprocal of measured Secchi provides an estimate of non-chlorophyll light attenuation (NCLA, m-1= [1/Secchi] - [1/maximum Secchi]). Analyses of several datasets show most cross-system variation in this empirical estimate of NCLA is accounted for by non-algal seston measured gravimetrically and as clay-sized particles. Residual variation is attributed to characteristics of the algal community and color. This simple approach can be applied directly, or with modification, to estimate NCLA in lakes and reservoirs when measurements of mineral particulates are not available. The degree to which response variables, such as Secchi transparency, are less than the maximum is fundamental to our understanding of lake process and their management.