Water quality monitoring has traditionally been done by measuring  
benthic algal biomass that has grown on fertilized or unfertilized  
patches of habitat produced by nutrient-diffusing substrata (NDS).  
This method requires the destruction of the accumulated periphyton  
communities and thus does not allow for convenient monitoring through  
time. Optical fluorometric methods of estimating benthic algal biomass  
and photosynthetic activity have been used in marine environments, but  
generally not across nutrient treatments or over long durations. This  
study evaluated the use of a pulse amplitude modulated (PAM)  
fluorometer for measuring biomass and photosynthetic activity in  
conjunction with NDS over several weeks. Our results suggest that this  
is a useful method for measuring algal biomass responses to nutrients  
and evaluating the effect of nutrients on photosynthetic efficiency.