Phosphorus loadings to lakes and some of their responses. Part 1. A new calculation of phosphorus loading and its application to 13 New York lake 1

Changes are proposed in ways of expressing phosphorus loadings to lakes. A composite species of phosphorus (the sum of soluble reactive, soluble unreactive, and that potentially desorbable from particulate matter) is substituted for the total P used by most investigators. Loadings are expressed as the amount added annually to a volume equivalent to that of the epilimnion, for stratified lakes, and to lake volume for those that are unstratified, rather than to surface area or to total volume regardless of mixing depth. These alterations in calculating loading result in values that more closely approximate the supply of phosphorus available for uptake by the phytoplankton community. Procedures followed in estimating the phosphorus contributed to lakes from various sources are critically discussed, with particular emphasis on that from human populations and runoff from rural lands. Phosphorus loss coefficients are given for the latter. Loadings to 13 New York lakes are calculated. The principal effects of using the composite form of phosphorus and loading to the mixed zone rather than total P and areal loading are to de‐emphasize the effects of agriculture and to emphasize phosphorus input to shallow lakes.