Phosphorus Cycling in an Eelgrass (Zostera Marina L.) Ecosystem1

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 µg‐atom/liter, while in the water they were ca. 2. The plants absorbed 166 mg P/m2‐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.