Climate and oceanic driver effects on primary production of Spartina alterniflora saltmarshes of the coast of Georgia

Background/Question/Methods

Global climate changes are altering functioning of the earth’s ecosystems. Tidal saltmarshes  are threatened by sea level rise and changes in weather  patterns and river discharge. In order to predict the consequences of climate change on coastal communities, we need to understand how climate drivers mediate ecosystem production. In case of the tidal marshes this understanding is currently ambiguous and geographically limited to the central and northern part of the Atlantic coast.

In 2000-2011 we conducted annual surveys of Spartina alterniflora biomass in tidal marshes of the coast of Georgia. Plant length was measured at permanent plots established near the creekbank and in the midmarsh zone at 9 sites located over a salinity gradient of the Altamaha river estuary. Data on plant length was converted into biomass using site specific regressions. Spartina alterniflora biomass, air temperature, precipitation, sea level and Altamaha river discharge were analyzed using multilevel modeling.

Results/Conclusions

Spartina ANPP strongly varied between years: in the creekbank zone biomass was up to 8 times greater in El Nino years as in La Nina years, in the midmarsh zone the difference was up to 4.8 fold.  Biomass fluctuations resulted from changes in plant density as well as plant size.  River discharge had stronger effects on creekbank than mid-marsh production and  local precipitation conversely had stronger effects on mid-marsh than creekbank production. The effects of river discharge were correlated with average salinity at the site, with sites having higher average salinities (closer to the river mouth) being more strongly affected. No effect of sea level on ANPP had been detected. The decrease in salinity in high discharge years was most likely the proximate driver of the increased production. Our results differ from analyses from tidal marshes of the central and northern part of the Atlantic coast which can be due to differences in climate or hydrology and/or reflect differences in statistical and sampling methodology.