PHOSPHORUS CYCLING IN AN EELGRASS ( ZOSTERA MARINA L.) ECOSYSTEM 1

Rates of uptake and excretion of phosphorus by both roots and leaves of eelgrass ( Zostera marina L.) were dependent on the orthophosphate concentration of the medium. In a typical shallow tidal pool dominated by eelgrass, the interstitial reactive phosphorus concentrations of the sediments were as high as 75 µ g‐atom/liter, while in the water they were ca. 2. The plants absorbed 166 mg P/m 2 ‐day from the sediments, assimilated 104 in the production of fresh eelgrass, and excreted 62 into the water. An amount equivalent to about 41% of the reactive phosphorus excreted, or 3 metric tons P/day, was exported from the lagoon into the Bering Sea. These results add a new pathway to the phosphorus cycle for estuaries containing vascular plants.