Impact of Salinity on DOM Release from Soils Following Seawater Inundation
EMSL Project ID
60985
Abstract
A recent large-scale field manipulation experiment exposed large coastal forest plots to extreme flooding by estuarine water and fresh water. Elevated dissolved organic carbon (DOC) concentrations and changes in the optical properties of dissolved organic matter (DOM) in upland soil porewater were observed for months following the estuarine water flood event compared to porewater measurements made in both the plot flooded with freshwater and the control forest plot (i.e., no flood manipulation), suggesting that such events directly impact the resilience of terrestrial carbon stocks sequestered in coastal landscapes in response to changing hydrological conditions. To better understand the geochemical processes leading to the observed mobilization of DOM, this proposal is designed to test the hypothesis that “The release of DOM from upland soils following exposure to saline waters will become elevated in response to a decrease in soil porewater ionic strength resulting from subsequent saturation with freshwater from rain events”. The effects of salinity and ionic strength on the release of DOM from upland soils will be determined in laboratory-based experiments using soil collected from the Control Plot (i.e., the plot not exposed to either freshwater or estuarine-water inundation) at the field manipulation experimental study site described above. Soil samples will be suspended in solutions representing a gradient of salinities from distilled water (DI) water to seawater (0%, 0.1%, 1%, 10%, and 100% Artificial Seawater (ASW), prepared in triplicate) and placed on an end-over-end mixer for 24 h. The suspensions will then be centrifuged, the supernatant filtered (0.45- um filter), and 30 mL of DI will be added to all treatments (simulating subsequent rain events). The suspensions will be mixed for 24 and processed as described, for up to 5 DI cycles. A parallel set of experiments will be conducted using a gradient of NaCl (0 mM, 0.7 mM, 70 mM, 70 mM, and 700 mM, which corresponds to the ionic strength of the ASW gradient indicated above to distinguish the effects of salinity from ionic strength alone; ASW contains polyvalent cations (primarily Ca2+ and Mg2+) that can affect DOM interactions with the surfaces of soil constituents via lead to cation bridging. The pH and conductivity of the filtrates will be measured, and a subsample will be saved for analysis of anions by ion chromatography and metals by inductively coupled plasma optical emission spectroscopy. Additional subsamples will be saved for determination of DOC and CDOM, and DOC molecular mass and polydispersity by high pressure size exclusion chromatography. The remaining filtrate from each set of triplicate treatments will undergo solid phase extraction and be sent to EMSL for characterization by FTICR-MS, GC-MS, and LC-MS (up to 90 samples per experiment for a total of 180). The first experiment will be performed in the summer of 2023 and available to ship to EMSL upon project start.
Project Details
Project type
Exploratory Research
Start Date
2024-01-01
End Date
N/A
Status
Active
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members