Impacts of simulated storm surge and sea level rise on soil biogeochemistry in marsh-forest transition zones
Date
2024
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Publisher
University of Delaware
Abstract
Coastal ecosystems are threatened by sea level rise and storm surge events, which cause marsh migration upland. These disturbances result in the creation of ghost forests as the forest vegetation begins to die and new marsh vegetation migrates upland. How sea level rise and storm surges affect soil C and N in these soils remains understudied. In a laboratory mesocosm experiment, we studied the effects of simulated storm surge and sea level rise on the soil biogeochemistry of both Delaware and Maryland forest soils collected at the interface of a ghost forest and migrating marsh. The incubations, lasting a total of 81 days per soil, included five control (CTRL), five storm surge (SS), and five sea level rise (SLR) mesocosms. CTRL mesocosms received a small, constant volume of synthetic rain from the top of the mesocosm. SS consisted of multiple five-day fast flood events of brackish tidal creek water over the top of the soil, which quickly drained through the mesocosm for five days before flooding again. SLR was represented by slow continuous flooding with brackish tidal creek water from the bottom of the mesocosm starting at day 25 until the end of the incubation. Porewater and export water chemistry, as well as before and after solid phase analyses, were conducted. Salinity and Fe2+ concentrations reflected the hydrologic processes imparted to the soil in the SS and SLR rise treatments with concentration increases and decreases that mimicked the pattern of flooding. SS and SLR events also mobilized dissolved organic carbon (DOC) and total nitrogen (TN) from the soil. Using linear regression analysis, we show that the sea water is controlling TN release in the porewater in all treatments and flushing the TN through the bottom of the mesocosms in SS treatments, while DOC released in the porewater is controlled by the reductive dissolution of Fe oxides and desorption of weakly held DOC and is not moving within the system. The treatments also impact the global warming potential (GWP) but impact each soil differently. Maryland CTRL had the highest GWP driven by N2O, while Delaware SLR had the highest GWP driven by CH4; these results indicate how soil characteristics impact gas emissions and how salinity may be inhibiting microbial processes. This experiment demonstrates the important controls SS and SLR have on the movement of C and N in ecosystems and the potential for GHG emissions.
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Keywords
Coastal ecosystems, Organic carbon, Ecosystems, Water chemistry