| Worldwide, invasive species are increasingly more apparent within wetland ecosystems. One example is the growing presence of Phragmites australis , the common reed, in marshes of the mid-Atlantic and Eastern U.S. Due to its rapid formation of primarily monospecific stands, Phragmites has been labeled as 'weedy' and 'undesirable', a type of biological pollution that reduces the ecological function and value of its newly invaded habitat. Although most claims negating the species lack any scientific support, wide-scale eradication efforts have been enacted since the 1980's.;This body of work focuses on the functional role of Phragmites in the sedimentary environment, furthering our understanding of its contribution to marsh stability in Chesapeake Bay. Daily and monthly patterns of deposition over 2-yr indicate Phragmites has, at minimum, twice the accretionary potential as Spartina spp. at an eroding island (Phragmites = 388 g/m2/month, Spartina spp. = 31 g/m2/month) and subsiding creek bank (Phragmites = 648 g/m2/month, Spartina spp. = 297 g/m2/month) marsh. Greater deposition in Phragmites is correlated with greater structural complexity on the sediment surface, a result of the accumulation of slowly decaying litter. Phragmites can retain >2000 gdw/m2 of litter in the marsh interior versus ∼200 gdw/m2 in Spartina spp.;In an assessment of elevation change over time (2.5 yr), those areas where vegetation was in advanced stages of marsh deterioration, Phragmites populations appeared to be no more effective than Spartina spp. in reducing bank edge loss or subsidence. However, integrated rates (40-yr post-invasion) of vertical accretion mid-marsh in Phragmites effectively shows accretionary gains, 1.39 cm/yr, clearly above that of Spartina spp., 0.79 cm/yr, in a creek bank environment.;Interestingly, autogenic changes associated with the invasion of Phragmites can result in dramatic increases in aboveground biomass (i.e. doubles the litter concentration) at the landscape level which ultimately enhances the rate of sediment trapping and organic input. Rapid accretion was demonstrated 7 years post-invasion in a 20-yr Phragmites stand, 0.95 cm/yr, while 5-yr Phragmites and surrounding oligohaline marsh species averaged 0.56 cm/yr. Therefore, Phragmites habitat modification was shown here to illicit positive ecosystem consequences when considering Chesapeake Bay marsh sustainability. |
