Groundwater controls ecological zonation of salt marsh macrophytes
Ecological zonation of salt marsh macrophytes is strongly influenced by hydrologic factors, but these factors are poorly understood. We examined groundwater flow patterns through surficial sediments in two salt marshes in the southeastern United States to quantify hydrologic differences between dist...
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Published in | Ecology (Durham) Vol. 96; no. 3; pp. 840 - 849 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
Ecological Society of America
01.03.2015
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Subjects | |
Online Access | Get more information |
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Summary: | Ecological zonation of salt marsh macrophytes is strongly influenced by hydrologic factors, but these factors are poorly understood. We examined groundwater flow patterns through surficial sediments in two salt marshes in the southeastern United States to quantify hydrologic differences between distinct ecological zones. Both sites included tallâ or mediumâform Spartina alterniflora near the creek bank; shortâform Spartina alterniflora in the midâmarsh; salt flats and Salicornia virginica in the high marsh; and Juncus roemarianus in brackishâtoâfresh areas adjacent to uplands. Both sites had relatively small, sandy uplands and similar stratigraphy consisting of marsh muds overlying a deeper sand layer. We found significant hydrologic differences between the four ecological zones. In the zones colonized by S. alterniflora, the vertical flow direction oscillated with semiâdiurnal tides. Net flow (14âday average) through the tall S. alterniflora zones was downward, whereas the short S. alterniflora zones included significant periods of net upward groundwater flow. An examination of tidal efficiency at these sites suggested that the net flow patterns rather than tidal damping controlled the width of the tall S. alterniflora zone. In contrast to the S. alterniflora zones, hypersaline zones populated by S. virginica were characterized by sustained periods (days) of continuous upward flow of saline water during neap tides. The fresher zone populated by J. roemarianus showed physical flow patterns that were similar to the hypersaline zones, but the upwelling porewaters were fresh rather than saline. These flow patterns were influenced by the hydrogeologic framework of the marshes, particularly differences in hydraulic head between the upland water table and the tidal creeks. We observed increases in hydraulic head of |
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Bibliography: | http://dx.doi.org/10.1890/13-2183.1 |
ISSN: | 0012-9658 1939-9170 |
DOI: | 10.1890/13-2183.1 |