SALTEx - Seawater Addition Long Term Experiment Dr. Christopher B. Craft Indiana University at Bloomington

Indiana University - School of Public and Environmental Affairs Room 408. MSB II. 702 N. Walnut Grove Ave. Bloomington Indiana 47405 USA

ccraft@indiana.edu https://orcid.org/0000-0002-6225-786X Georgia Coastal Ecosystems LTER Project

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

gcelter@uga.edu https://gce-lter.marsci.uga.edu/ Dr. Christopher B. Craft Indiana University at Bloomington

Indiana University - School of Public and Environmental Affairs Room 408. MSB II. 702 N. Walnut Grove Ave. Bloomington Indiana 47405 USA

ccraft@indiana.edu https://orcid.org/0000-0002-6225-786X Principal investigator 2011-04-01 Dr. Merryl Alber University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

malber@uga.edu https://marsci.uga.edu/directory/people/merryl-alber https://orcid.org/0000-0002-9467-4449 Co-investigator 2011-04-01 Dr. Steven C. Pennings University of Houston

Department of Biology and Biochemistry University of Houston Houston Texas 77204-5513 USA

scpennin@central.uh.edu https://uh.edu/nsm/biology-biochemistry/people/profiles/steven-pennings/ https://orcid.org/0000-0003-4757-7125 Co-investigator 2011-04-01 Elizabeth Ashby Nix University of Georgia Marine Institute

University of Georgia Marine Institute Sapelo Island Georgia 31327 USA

anix@uga.edu Research technician 2012-04-01 2013-06-14 Dontrece Smith University of Georgia Marine Institute

University of Georgia Marine Institute Sapelo Island Georgia 31327 USA

dtsmith@uga.edu Research technician 2014-04-01 Justin P. Manley University of Georgia

University of Georgia Marine Institute Sapelo Island Georgia 31327 USA

manley@uga.edu Research technician 2011-04-01 2012-04-01 Sasha Greenspan University of Georgia Marine Institute

University of Georgia Marine Institute Sapelo Island Georgia 31327 USA

sgreensp@uga.edu Research technician 2013-08-01 2014-04-30 Dr. Ellen Herbert Ducks Unlimited

Ducks Unlimited Memphis Tennessee USA

eherbert@ducks.org Graduate research assistant 2011-04-01 Fan Li University of Houston

Department of Biology and Biochemistry 369 Science and Research Bldg 2 University of Houston Houston Texas 77204-5001 USA

lifan.uh@gmail.com Graduate research assistant 2012-09-01 Owen Langman Indiana University

School of Public and Environmental Affairs Indiana University Bloomington Indiana 47405 USA

olangman@indiana.edu Graduate research assistant 2012-12-01 2013-12-31 2026

Most experimental studies of saltwater intrusion on low-salinity tidal marshes have been over small spatial and short temporal scales. SALTEX (Seawater Addition Long Term Experiment) is a long-term field experiment that we recently initiated in a Zizaniopsis marsh in the Altamaha River. Due to the unprecedented spatial and temporal scale of this experiment, we anticipate that it will generate new insights into how low-salinity tidal marshes respond to saltwater intrusion. We are increasing porewater salinity in 3 m x 3 m replicated (n=6) plots from the ambient salinity of <0.5 to a target range of 5–8 in two treatments: constant (press), with salinities elevated continuously to simulate sea level rise, and episodic (pulse), with salinities elevated temporarily to simulate drought.

Area 3: Responses to Salinity and Inundation (more information) Question 1: What are the long-term patterns of environmental forcing to the coastal zone? (more information) Question 3: What are the underlying mechanisms by which the freshwater-saltwater gradient drives ecosystem change along the longitudinal axis of an estuary? (more information)

marsh above ground biomass below ground biomass chemistry chloride DIC dissolved inorganic carbon dissolved organic carbon DOC fauna hydrogen sulfide porewater salinity sulfate vegetation LTER NSF GCE Zizaniopsis experiment inundation plants press pulse saltwater intrusion Overall geographic extent of the research project -81.582311 -81.237936 31.401403 31.296034 2011-04-01

National Science Foundation grant numbers OCE-9982133 and OCE-0620959

estuary marsh complex Altamaha River - Altamaha River transect used for GCE quarterly hydrographic monitoring surveys. Nominal profiling stations are defined every 2km from -4km to 40km (relative to station 0km at the line of demarcation), based on an estimated Thalweg line running up the main river channel. -81.582311 -81.237936 31.401403 31.296034 SALTEx_Well1 - Groundwater monitoring well for the GCE SALTEx research project -81.466637 -81.466637 31.339439 31.339439

The pulse treatment will be designed using an analysis of the frequency and duration of high salinity at the SALTEX site that will be generated using the SqueezeBox modeling application (Sheldon & Alber 2002, 2005). The study includes unmanipulated control plots and "inundation control" plots that are pressed or pulsed with equivalent amounts of freshwater. Water is delivered from a head tank connected to a surface irrigation system. Porewater salinity is measured in samples collected several times per week from wells in each plot, and treatment water delivery adjustments are made as necessary to keep salinity within the target range. Once the treatments are established, we will measure changes in porewater chemistry (Cl-, SO4 2-, H2S, DIC and DOC (monthly)), soil biogeochemistry (decomposition and sulfate reduction (quarterly)), vegetation (photosynthesis and respiration (quarterly)), above- and belowground biomass and species composition (annually), leaf N and herbivory (quarterly), fauna (insects and invertebrates (biannually)) and soil properties and processes (chromium reducible S, organic C, N, P and organic matter quality (annually), sedimentation and surface elevation/subsidence using SETs sediment elevation tables (biannually)). We plan to run this experiment throughout GCE-III and into GCE-IV.

We hypothesize that episodic (pulse) additions of saltwater will have short-term effects on porewater (increase in Cl- and SO4), plant physiology (increased respiration/decreased photosynthesis due to salt stress), and plant interactions with fauna (increased susceptibility to herbivory), but that community composition and soils will be largely unaffected. Once the pulse is withdrawn, we expect the system will recover to baseline conditions over a period of months to one year. In contrast, we hypothesize that the press treatment will begin by showing the pulse effects, but that these will be followed by a cascade of medium- and longer-term responses as the various components of the system move through the different levels of the hierarchical response framework (see figure). These will include increased organic matter decomposition and decreased N retention and C sequestration in soils, a decrease in biomass of freshwater plant species over the medium-term and a shift towards brackish or salt marsh vegetation over the longterm, and a concurrent increase in favorable habitat for benthic fauna that generally inhabit brackish areas (Thomas & Blum 2010). We also hypothesize that, over the very long term, soil subsidence will create a negative feedback loop that leads to greater inundation and salinization of the area. A handful of previous studies have evaluated the response of tidal freshwater vegetation to increasing salinity using small-scale experiments (i.e. Neubauer 2011; Andrew Baldwin unpubl.) and uncontrolled studies (i.e. tide gate removal, Pearlstine et al. 1993). Other studies show the effects of salty storm surge on low-salinity marshes (Chabreck & Palmisano 1973; Guntenspergen et al. 1995; Michener et al. 1997; Doyle et al. 2007). We will review these studies along with our experimental results in a synthesis paper that will compare the directions and magnitudes of responses of tidal freshwater marshes to pulses and presses in salinity over different time scales.

Li, F., Angelini, C., Byers, J., Craft, C.B. and Pennings, S.C. 2022. Responses of a tidal freshwater marsh plant community to chronic and pulsed saline intrusion. Journal of Ecology. 110:1508-1524. (DOI: 10.1111/1365-2745.13885) https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.13885 Li, F. and Pennings, S.C. 2019. Response and Recovery of Low-Salinity Marsh Plant Communities to Presses and Pulses of Elevated Salinity. Estuaries and Coasts. 42:708-718. (DOI: 10.1007/s12237-018-00490-1) Herbert, E., Schubauer-Berigan, J.P. and Craft, C.B. 2018. Differential effects of chronic and acute simulated seawater intrusion on tidal freshwater marsh carbon cycling. Biogeochemistry. 138:137–154. (DOI: 10.1007/s10533-018-0436-z) https://doi.org/10.1007/s10533-018-0436-z Li, F. and Pennings, S.C. 2018. Responses of tidal freshwater and brackish marsh macrophytes to pulses of saline water simulating sea level rise and reduced discharge. Wetlands. 38:885-891. (DOI: 10.1007/s13157-018-1037-2) Widney, S., Smith, D., Schubauer-Berigan, J.P., Herbert, E., Desha, J. and Craft, C.B. 2017. Poster: Changes in sediment porewater chemistry in response to simulated seawater intrusion in tidal freshwater marshes, Altamaha River, GA. Society of Wetland Scientists Annual Meeting, June 5-8, San Juan, Puerto Rico. Smith, D., Herbert, E., Li, F., Widney, S., Desha, J., Schubauer-Berigan, J.P., Pennings, S.C., Angelini, C., Medeiros, P.M., Byers, J., Alber, M. and Craft, C.B. 2016. Poster: Seawater Addition Long Term Experiment (SALTEx). Georgia Department of Natural Resources Coastal Resources Division 2016 Climate Conference, November 2-3, 2016, Jekyll Island, GA. Craft, C.B., Herbert, E., Li, F., Smith, D., Schubauer-Berigan, J.P., Widney, S., Angelini, C., Pennings, S.C., Medeiros, P.M., Byers, J. and Alber, M. 2016. Climate change and the fate of coastal wetlands. Wetland Science and Practice. 33(3):70-73. https://www.researchgate.net/publication/311263349_Climate_Change_and_the_Fate_of_Coastal_Wetlands_Wetland_Science_and_Practice_33370-77 Herbert, E., Boon, P., Burgin, A.J., Neubauer, S.C., Franklin, R.B., Ardon, M., Hopfensperger, K.N., Lamers, L. and Gell, P. 2015. A global perspective on wetland salinization: Ecological consequences of a growing threat to freshwater wetlands. Ecosphere. 6(10)(206):1-43. (DOI: 10.1890/ES14-00534.1) https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/ES14-00534.1 NUT-GCES-1608 - Porewater chemistry measurements from the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx) https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=586 GND-GCED-1802 - Continuous groundwater well temperature, salinity and water level measurements at the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx) site from May 2014 to February 2018 https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=656 ALG-GCED-1610 - Green algae, cyanobacteria and diatom concentrations from the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx) Project https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=609 GEL-GCED-1610 - Soil surface temperature measurements from the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx) Project https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=608 NUT-GCES-1609 - Baseline soil chemistry data measurements from the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx) https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=601 INS-GCED-1612 - Grasshopper counts and feeding damage at the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx) in 2016 https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=710 PLT-GCET-1510 - Pot experiment on fresh and brackish marsh plants responses to salinity pulses in summer 2013 https://gce-lter.marsci.uga.edu/public/app/dataset_details.asp?id=573 Figure. Conceptual model showing the hypothesized effects of increases in sea level or decreases in river inflow on the fresh/brackish marsh over different time scales. Predicted changes are indicated as positive (+), negative (-), or variable (triangle). http://gce-lter.marsci.uga.edu/public/resources/projects/saltex_figure.png Map image: SALTEx map and plot layout https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=814 Document: SALTEx - Bentho Torch Sampling Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=777 Document: SALTEx - Soil Surface Temperature Measurement Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=776 Document: SALTEx - BBE BenthoTorch Operational Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=775 Document: SALTEx - Total Phosphorus https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=771 Document: SALTEx - Labile Phosphorus Extraction https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=770 Document: SALTEx - CHN Anaysis https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=769 Document: SALTEx - Ammonia Analysis https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=768 Document: SALTEx - Nitrogen Fractionation in Soils https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=767 Document: SALTEx - Bulk Density Analysis https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=766 Document: SALTEx Total Phosphorus and Total Dissolved Phosphorus Wet Chemistry Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=762 Document: SALTEx Reactive Phosphorus Wet Chemistry Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=761 Document: SALTEx Total Nitrogen and Total Dissolved Nitrogen Wet Chemistry Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=760 Document: SALTEx Ammonium (NH4) Wet Chemistry Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=759 Document: SALTEx Quarterly Porewater Sampling Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=758 Document: SALTEx Sulfide Analysis Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=757 Document: SALTEx Ion Chromatograph Analysis protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=756 Document: SALTEx DOC Protocol https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=755 Photograph: SALTEx Site Photo https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=677 Photograph: SALTEx Plants https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=675 Photograph: SALTEx Plants https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=676 Photograph: SALTEx Porewater Sampling Valves https://gce-lter.marsci.uga.edu/public/app/resource_details.asp?id=674