PNNL

Abstract

Flooding of wetlands mediates the exchange of soils, sediments, and solutes across coastal terrestrial-aquatic interfaces, potentially altering their fate. Specifically, inundation can impact biogeochemical processes that influence aquatic respiration and greenhouse gas cycling, with implications for coastal carbon and nutrient budgets. To better understand initial responses of coastal waters flooding wetlands, we conducted short-term laboratory experiments where seawater was amended with sediments and soils collected across regional gradients of inundation exposure (i.e., frequently to rarely inundated) for 14 sites across the Mid-Atlantic, USA. We measured changes in dissolved oxygen and greenhouse gas concentrations in order to calculate gas consumption or production rates occurring during seawater exposure to terrestrial materials. We also measured soil and water physical and chemical properties to explore potential drivers. Our observed higher oxygen consumption rates when incubating seawater with samples from frequently inundated locations and higher carbon dioxide production with samples from rarely inundated transect locations. Incubations with soil from rarely inundated sites produced the highest global warming potential, primarily driven by carbon dioxide and secondarily by nitrous oxide. We also found environmental drivers of gas rates varied notably between transect locations. Our findings indicate that seawater responses to soil and sediment inputs across coastal terrestrial-aquatic interfaces exhibit some consistent patterns and high intra- and inter-site variability, suggesting potential biogeochemical feedback loops as inundation regimes shift inland.