Enviro-Days 1997
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Kindra Loomis and Jay Zieman
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Enviro-Days 1997
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Kindra Loomis and Jay Zieman
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It has long been accepted that elevation is an important factor in determining Spartina alterniflora growth in salt marshes. Elevation controls inundation time by the tides and can significantly affect drainage of salt marsh sediments. Drainage, in turn, can affect such sediment phyiscochemical parameters as redox potential, salinity, sulfide and nutrient levels. The growth of the dominant macrophyte in the low marsh, Spartina alterniflora, responds to these changes accordingly. A ‘natural experiment’ to study the affects of elevation and drainage in salt marsh systems is found on the southern end of Hog Island, on the eastern shore of Virginia. In this marsh, there are slightly elevated areas adjacent to regions of normal marsh slope. These ‘hummocks,’ as we have termed them, are relatively linear features, 1-2 m wide, with an elevation change of about 10-20 cm. The sediments of the hummocks are also sandier than the adjacent old marsh sediments. The result of this natural experiment into the effect of elevation and grain size is areas of highly productive Spartina alterniflora amidst areas of lower productivity. Higher redox potentials and sulfide concentrations suggest that drainage is a likely cause of the high productivity seen on the hummocks. Nutrient concentrations, especially ammonium, are depressed on the hummocks suggesting that the plants are utilizing the porewater ions. In the adjacent short Spartina zones, nutrient concentrations are generally high but this is not reflected in productivity, most likely due to sulfide and redox potential stress. The preliminary results suggest that drainage is reducing stresses on the plants of the hummocks such that, even in the higher marsh, they can be highly productive.