No abstract

The absorption of phosphate by eelgrass (Zostera marina L.) was studied using 32P in a partitioned container where leaves were separated from roots and rhizomes. Absorption, which was greatest in the light, occurred through both leaves and roots, and the absorbed phosphorus was transported rapidly to all parts of the plant. It therefore appears that eelgrass can use phosphate from sediments and from water. Phosphate removed from solution by the roots and rhizomes was returned in part to the surrounding water through the leaves, suggesting that in nature seagrass may act either as a sink or as a source for dissolved phosphorus in estuarine waters.

No abstract

ABSTRACI'Rates of uptake and excretion of phosphorus by both roots and leaves of eelgrass (Zostefu mwina 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 pg-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. INTFLODUCTION The cycle of phosphorus in shallow water differs from the relatively simple one in the open sea (e.g. see Harvey 1957) by the interaction with bottom sediments. Studies of estuaries by Rochford ( 1951)) Pomeroy ( 1960)) and Pomeroy et al. ( 1965Pomeroy et al. ( , 1969 indicate a dynamic interaction of the phosphorus in the water column with that in the surface sediments. This interaction is restricted to at most the upper few centimeters of sediment; below this phosphorus is accumulated. Thus particulate phosphorus, in many environments largely from organic detritus, is buried and lost from short-term circulation. Recent studies have revealed a further complication to this cycle in shallow waters : In areas containing rooted aquatic plants phosphorus from the deeper sediments can be returned to the water via uptake by roots, incorporation into the leaves, and release into the water.For a time it was thought that phosphorus was returned to the water column principally through detritus as portions of the plant die and slough off (Pomeroy et al..I Financial support was provided to the University of Alaska from the Water Quality Office of the Environmental Protection Agency

The magnitude of the inputs and exports of nitrogen was estimated for the tundra ecosystem at Barrow, Alaska. Based on new data and on previous investigations, annual input of nitrogen from all sources was 92.4 mg N/m2 per year, with the most important sources being nitrogen fixation (75%) and ammonia in summer rain (18%). The low input of nitrogen by rain and snow results from both low annual precipitation and extremely low concentrations of nitrogen compounds in precipitation. Despite the meager nitrogen supply, the estimated retention is over 80% of the input, reflecting insignificant leaching due to the impermeable permafrost substrate, low precipitation, and restricted lateral movement of water over and through the nonfrozen soils. Denitrification also is low, at least partially due to nutrient deficiency.Interpretations of these data in respect to the sensitivity of the environment to perturbations, suggest that resource development or other activities which would have minor or negligible effects in temperate latitudes, could alter substantially the nitrogen balance of this arctic ecosystem.