Causes for vegetation dieback in a Louisiana salt marsh: A bioassay approach

The Effects of Flooding on Four Common Louisiana Marsh Plants

“…Mendelssohn and McKee (1988) related the decrease in aboveground biomass to decreased soil redox potential as well as to increased interstitial sulfide and ammonium concentrations, whereas soil acidity was not a significant factor controlling growth. Spartina alterniflora aboveground biomass increased when its elevation in the marsh was raised by 20-30 cm, which drastically reduced the frequency of flooding (Wilsey et al, 1992;Webb et al, 1995). Spartina patens in our study showed a rapid decline in biomass with increased flooding, reaching the lowest values in treatments that were flooded more than 50% of the time.…”

“…In our study, competition was absent and soil porosity constant among the different flooding treatments. Webb et al (1995) showed that the aboveground biomass of Spartina patens increased fourfold when marsh sods were raised 20 cm above the ambient marsh surface, which increased the soil redox at 2 cm depth from ,2100 mV to ,+125 mV. We found Spartina patens aboveground biomass at 0% and 20% flooding to be four times higher than the aboveground biomass of .50% flooded treatments.…”

“…Previous studies evaluated the effects of a 100% flooding treatment vs a saturated soil condition (Mendelssohn et al, 1981;Mendelssohn and McKee, 1983;Koch and Mendelssohn, 1989;Pezeshki and DeLaune, 1993;Lessman et al, 1997), or the effect of changing marsh sod elevation under field conditions resulting in altered flooding stress Webb et al, 1995;Grace and Ford, 1996;Gough and Grace, 1998). In general, these studies show a decrease in primary production with permanent flooding as well as with increased flooding depth.…”

Cordgrass Biomass in Salt Marshes

“…increase S. alterniflora biomass accumulation growing on sandy sediment by enhancing nutrient deposition (Holdredge et al, 2010) and grazing by small grazers may carry out a top-down control on Spartina biomass dynamic (Sala et al, 2008;Tyrrell et al, 2008). Above-ground biomass of cordgrasses may collapse very fast as a result of die-back processes related with long flooding periods and sediment anoxia, drought events or nutrient exhaustion (Webb et al, 1995;Castillo et al, 2000;McKee et al, 2004;Ogburn & Alber, 2006;). For example, S. densiflora invading populations in European salt marshes behave as perennial at middle and high marshes but they are biannual at low marshes.…”

Influence of invasive Spartina growth stages on associated macrofaunal communities

“…Dieback of invasive hybrid Spartina, S. anglica and S. townsendii was noted as early as the mid-1920s in Britain (Gray et al 1991 and references therein). Dieback zones have also been observed in mature S. alterniflora meadows in North Carolina (Linthurst and Seneca 1980), Louisiana (Webb et al 1995;McKee et al 2004), New York (Hartig et al 2002), and recently in Georgia, New England, and Virginia (GCRC 2004). Recent studies provide evidence that the interplay between physicochemical stressors and trophic interactions have an important role in dieback of coastal salt marshes (Silliman and Bertness 2002;Silliman et al 2005).…”