Mineral Cycling in Coastal Foredune Plant Communities in Cape Hatteras National Seashore

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Abstract
At two sites on the front (oceanside), top, and back of the foredune, measurements were made of salt spray deposition and the quantity of cations (K, Na, Ca, and Mg) present on the surface and 20, 40, and 60 cm below the surface of the soil. Cationic inputs in salt spray were calculated by partitioning the cation content of bulk precipitation collected on the back of the fore dunes into salt spray and rainfall components. The biomass and cationic content of the dominant grasses and forbs were determined in all three zones from a combination of field measurements and estimates of the standing crop and from samples of each dominant species analyzed for their cationic content. On the average 55%, 34%, and 11% of the salt spray deposited on a foredune falls on the front, top, and back respectively. In all three zones Na (250—1,300 kg/ha°yr) was the most abundant cation input in the salt spray. It is followed by Mg (37—120 kg/ha°yr), Ca (19—120 kg/ha°yr), and Kg (13—77 kg/ha°yr). In rainfall, the annual input of cations was calculated to be 1.3, 26, 2.3 and 3.9 at Bodie Island and 1.0, 21, 3.4, and 3.0 kg/ha°yr at Ocracoke for K, Na, Ca, and Mg respectively. It appears that the total annual input of cations exceeds slightly their calculated annual outputs through leaching for all cations in all zones. Subsurface cation levels were very low: K (2—5 kg/ha), Na (17—88 kg/ha), Ca (5—17 kg/ha), and Mg (2—9 kg/ha). Estimates of the total standing crop of cations in the vegetation of a zone and inputs of cations in salt spray and rainfall indicate that the annual inputs of Na and Mg exceed their standing crops, while the annual input of K, and sometimes Ca, is smaller than its standing crop on the back.

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