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GCE III - Key Finding in 2019

    Biomass patterns differ in fresh as compared to salt marshes

    Li et al. (2018) synthesized 15 years of monitoring data collected at GCE site 7, a tidal freshwater marsh dominated by wild rice, Zizaniopsis miliacea. In contrast to stands of Spartina alterniflora in salt marshes downstream, which experience regular disturbance of several types (Li and Pennings 2016), the plots in the tidal freshwater marsh were almost free of disturbance. In an analysis of annual productivity, Li et al. (2018) found that overall productivity was similar to or greater than that of brackish and salt marshes downstream in the estuary. Above-ground live biomass peaked in July-October, above-ground dead biomass peaked in December, and below-ground macro-organic matter (live plus dead) peaked in October, likely indicating translocation of photosynthate from above- to below-ground biomass at the end of the growing season. End of year biomass varied ~1.7 fold among years, and was negatively related to temperature in both the creekbank and mid-marsh zones and positively related to river discharge in the creekbank zone. These responses were muted compared to similar responses of Spartina alterniflora in tidal salt marshes downstream (Wieski and Pennings 2014), indicating that fluctuations in climate may affect salt marshes more than tidal fresh marshes. Nevertheless, the results indicate that rising temperatures may threaten the productivity of southeastern U.S. tidal fresh marshes in coming decades.


    Fig. 1 Relationships between (A) biomass at the creekbank and maximum temperature (n = 15, R2 = 0.29, p = 0.02, y = -274.1x +10242.4), (B) biomass at the creekbank and mean temperature (n = 15, R2 = 0.24, p = 0.04, y = -335x + 10442.5), (C) biomass at the creekbank and river discharge (n = 15, R2 = 0.23, p = 0.04, y = 0.9x + 1639.5), (D) biomass at the midmarsh and maximum temperature (n = 15, R2 = 0.27, p = 0.03, y = -132.3x + 4943.8), and (E) biomass at the midmarsh and mean temperature (n = 15, R2 = 0.43, p = 0.005, y = -212.5x + 6338.0). From Li et al. 2018.


This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.