Hidden legacies: Investigating buried pre-colonial stream corridors in the Mid-Atlantic Coastal Plain, Maryland, USA

Within the Mid-Atlantic United States, widespread landscape disturbance during European colonization resulted in erosion and subsequent storage of legacy sediments within river valleys and floodplains, altering their form, function, and flora. Previous studies of precolonial river corridors have influenced river restoration designs and targets throughout the region, but the generalizability of these studies into other physiographic settings, such as the Coastal Plain, is unknown. Therefore, our study investigated the physical form and riparian vegetation of pre-colonial stream corridors located within the Coastal Plain of Anne Arundel County, Maryland, documenting changes from pre- to colonial and postcolonial time periods. Our study provides evidence of buried, precolonial riparian ecosystems with dates ranging between 750 years to 8000 years Before Present. These valley bottom ecosystems were likely a dynamic patch mosaic, largely dominated by dense Alnus (alder) scrub swamps with variable Poaceae (grass) and Cyperaceae (sedge) dominated meadows and both multi-threaded and single-threaded channel forms. These precolonial floodplains are buried by vast amounts of legacy sediment to the extent that pre-colonial sediments are largely not exposed in the modern valley bottom. Notably, the Coastal Plain precolonial corridors investigated in this study contrast to studies in the Piedmont physiographic region with precolonial sediments exposed in streambanks and with precolonial ecosystems described as herbaceous stream-wetlands. Our findings provide critical historical context as to the magnitude of alteration for modern stream channels and suggest an alternative precolonial ecosystem which can be used to inform restoration designs, management targets, and reestablishment of channel functional processes in areas of the Mid-Atlantic Coastal Plain.