Predicting responses of chlorophyll and primary production to changes in phosphorus, grazing, and dissolved carbon (reply to comment by Nurnberg)

Carpenter et al. (1998) showed that the dynamics of primary producers in experimental lakes are predictable from phosphorus (P) input rate, grazer body size, and concentration of colored dissolved organic carbon (DOC). The negative effect of colored DOC on areal chlorophyll could be explained by light limitation alone. Nurnberg (1999) objected to our (1) use of areal chlorophyll rather than surface water concentration, (2) use of P input rate instead of surface water P concentration, and (3) extrapolation of results from experimental lakes to a larger population of lakes. In this rejoinder, we show that (1) areal measures of primary pro-ducers are more appropriate for ecosystem analysis and more relevant to analysis of algal blooms, (2) prediction of chlorophyll from P input rates links lakes to the surrounding landscape and provides models that are useful for management focused on control of P input, and (3) these experimental lakes conform to published relationships between P input rate and chlorophyll and that Nurnberg’s characterization of the lakes as outliers is incorrect.