Phytoplankton and periphyton responses to in situ experimental nutrient enrichment in a shallow subtropical lake

Abstract

Experiments were performed in situ in shallow, subtropical Lake Okeechobee (Florida, USA) to quantify and compare the responses of phytoplankton (in 201 clear polycarbonate carboys) and periphyton (on nutrient-diffusing clay substrates) to additions of nitrogen and/or phosphorus. Dur- ing early and late summer, 1994, both assemblages were nitrogen limited or co-limited by nitrogen and phosphorus, indicating the potential for competition between benthic and planktonic communities. During late summer, there was evidence that high phytoplankton biomass reduced light penetration through the water column and may have suppressed periphyton growth. The similar phytoplankton and periphyton taxonomic structures, both dominated by Lyngbya sp. and pennate diatoms, suggested that in shallow regions of this lake, resuspended meroplankton might account for a large portion of phytoplankton biomass. This phenomenon has been observed in other shallow, wind-driven Florida lakes.