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GCE-LTER Key Findings


Sea level rise alters wetland function

The GCE SALTEX experiment was designed to mimic saltwater intrusion caused by droughts and long-term sea level rise. We set up 30 plots (2.5 m2) in a freshwater marsh in 2013 and dosed them with either a press (plots were inundated with brackish water to maintain their porewater at target salinities of 2 5) or a pulse (plots received a 2-month pulse (September and October) of increased salinity for four growing seasons (2014-2017). The press treatments showed changes in: 1) inorganic constituents (elevated porewater N, P, and S, and an increase in reduced sulfur (i.e. pyrite-FeS2); decreased levels of soil iron-bound P); 2) soil conditions (increased temperature and decreased redox potential) and 3) soil organic matter (shifts in bacterial and fungal biomarkers). There were also changes in 4) greenhouse gas emissions (decreased CH4 and net ecosystem production); 5) primary producers (almost complete loss of above- and belowground plant biomass and an increase in benthic microalgae); and 6) sediment elevation (decreasing by 1 cm/y). The press treatments are now essentially bare soil, but with some signs of encroachment by brackish emergent plants. The pulse treatments have shown intermediate responses (Craft et al. 2016; Li et al. in review; Herbert et al. 2018). In accompanying mesocosm experiments, species richness and plant biomass decreased with increasing pulse duration and salinity (Li & Pennings 2019).

Plant-Herbivore interactions

Selected responses observed in SALTEx experiment. a) Porewater NH4 concentration; b) % Ludwigia cover (note that Ludwigia cover was high in all treatments in 2014 but data were not collected until 2015); c) % Zizaniopsis cover; d) elevation as measured by SETs. The press treatment began in April 2014 and is shaded grey; pulse periods (Sept-Oct each year) are shaded blue. Black lines on each graph denote measurements made in press treatments; blue lines denote measurements made in pulse treatments; green lines denote measurements made in untreated controls (procedural controls not shown). Error bars represent standard errors. From Craft et al. 2016.

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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.