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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Freshwater inundation effects on emergent vegetation of a hypersaline salt marsh
Auteurs :	H. D. Alexander, Auteur ; K. H. Dunton, Auteur
Type de document :	Article
Dans :	Estuaries (25(6B) DEC 2002)
Article en page(s) :	1426-1435
Résumé :	The coastal marshlands of the Nueces estuary, Texas depend upon periodic freshwater inundation to support current community structure arid promote further establishment and expansion of emergent halophytes. Decades of watershed modifications have dramatically decreased freshwater discharge into the upper estuary resulting in hypersaline and dry conditions. In an attempt to partially restore inflow, the U.S. Bureau of Reclamation excavated two overflow channels re-connecting the Nueces River to the marshlands. Freshwater-mediated (precipitation and inflow) changes in tidal creek and porewater salinity and emergent marsh vegetation were examined over a 5-yr period at three stations in the upper Nueces Marsh with the aid of a Geographical Information System (GIS). Two stations were potentially subjected to freshwater inflow through the channels, while one station experienced only precipitation. Decreased tidal creek and porewater salinity were significantly correlated with increased freshwater at all stations (R(2) = 0.37 to 0.56), although porewater salinities remained hypersaline. GIS analyses indicated the most considerable vegetation change following freshwater inundation was increased cover of the annual succulent Salicornia bigelovii. Fall inundation allowed seed germination and rapid expansion of this species into previously bare areas during the subsequent winter and following spring. The station affected by both inflow and precipitation exhibited greater S. bigelovii cover than the station affected solely by precipitation in both spring 1999 (58.7% compared to 27.9%) and 2000 (48.6% compared to 1.9%). Percent cover of the perennial Batis maritima temporarily increased after periods of consistent rainfall. The response was short term, and cover quickly returned to pre-inundation conditions within 3 mo. Prolonged inundation led to long-term (>2 yr) decreases in percent cover of B. maritima. Our results suggest that the timing and quantity of freshwater inundation strongly dictate halophyte response to precipitation and inflow. Brief periods of freshwater inundation that occur at specific times of year alleviate stress and promote seed germination and growth, but extended soil saturation can act as a disturbance that has a negative impact on species adapted to hypersaline conditions.

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