A comparison of physicochemical variables across plant zones in a mangal/salt marsh community in Louisiana

Three vegetation zones were delineated in a mangal/salt marsh community at Bay Champagne, Louisiana - a zone dominated by Avicennia germinans adjacent to the bay, an inland zone dominated by Spartina alterniflora , and a transition zone between the two containing both species. Analysis of variance revealed highly significant zone differences for most individual variables. The Avicennia zone was characterized by the highest relative elevation and soil bulk density. Higher concentrations of ions associated with sea water, such as potassium, calcium, and magnesium, occurred in the Avicennia zone, which also caused interstitial water salinity to be higher in that zone. The transition and Spartina zones were more biochemically reduced than the Avicennia zone. Iron and manganese were lower in the more reduced zones. The transition and Spartina zones only differed in interstitial water potassium and sulfide and relative elevation. The Spartina zone had a lower elevation and usually higher sulfide concentrations than the transition zone. The relatively high sulfide and lower elevation of the Spartina zone may limit the establishment of Avicennia propagules there.