Along the Delmarva Peninsula, USA, salt marshes are rapidly migrating into freshwater uplands, such as forests and agricultural land, resulting in widespread vegetation mortality and shifts in groundwater levels and salinity dynamics. The extent and persistence of saltwater intrusion (SWI) in coastal wetlands are shaped by the interplay between vertical and lateral salinization, as well as freshwater events. To disentangle these simultaneous processes, we instrumented transects at six field sites along the Peninsula, each equipped with shallow wells, soil moisture sensors, and redox probes, capturing space-for-time changes. Through three years of high-resolution data collection, our findings reveal that vertical salinization is episodic, driven by storm surges that primarily affect shallow soils, with recovery time dictated by soil type and the magnitude of salinization. In contrast, lateral salinization progresses gradually, controlled by shallow hydraulic gradients and exacerbated by droughts, which lower upland groundwater heads on intermediate timescales, or by sea-level rise over longer periods. Freshwater events act as both buffers and drivers of change, flushing salinity following salinization events, but also lowering redox potentials in shallow soils, which may cause anoxia and subsequent vegetation stress. These dynamic interactions underscore the complexity of the coastal critical zone, where hydrology, geomorphology, biogeochemistry, and ecology interact to create feedbacks that may accelerate or slow coastal change. Our study highlights that some coastal wetland transitions may occur more rapidly than previously thought when considering only sea-level rise or storm surges alone. By capturing multi-scale hydrological drivers, we provide new insights into SWI processes and marsh migration, offering a more comprehensive understanding of coastal wetland transition in response to climate change.