Modeling Daily Production of Aquatic Macrophytes from Irradiance Measurements: A Comparative Analysis

The importance of submerged aquatlc macrophytes to coastal ecosystems has generated a need for knowledge of minlmum l ~ g h t levels that wlll support the ma~n tenance and restoration of healthy populations Our goals were (1) to evaluate the s e n s ~ t ~ v ~ t y to natural, non-sinusoidal fluctuatlons in irradiance I of analytical integration techniques for calculating daily carbon gain (2) to evaluate the H,,, (the daily period of I-saturated photosynthesis) model of daily production re la t~ve to models based on Instantaneous photosynthesis vs Irradiance ( P v s I ) and (3) to provlde some guidance for the temporal dens~ ty of Irradiance data r equ~red for accurate estimation of dally carbon gain Monthly measures of the P v s I response of an eelgrass Zostera manna L population were used to p ~ e d l c t rates of dally carbon galn from continuous in sjtu recordings of I Dally ~n teg ra t ed I was not a reliable predictor of daily product~on Numencal (iterative) integration of H,,, was much more r e l~ab le but r e q u ~ r e d repeated measures of I within a day as did numencal in tegra t~on of P vs I Analytical (non-iterative) models based only on observations of l,, (noon) could not p red~c t daily production accurately Analyt~cal models of P v s I and H,,, agreed with each other, however, indicating that the analyt~cal models may be useful where the daily pattern of I is sinusoidal Given the h ~ g h degree of temporal vanability in coastal 11ght environments continuous monltonng of hght ava~ lab~ l i t y may be required for calculation of daily production and rehable management of aquatlc macrophyte populations