Responses of the Roanoke Bayhead Delta to variations in sea level rise and sediment supply during the Holocene and Anthropocene

The response of bayhead deltas to changes in the rate of sea-level rise and sediment supply is difficult to predict, but important to understand because these changes can lead to submergence and erosion of deltaic sediments and loss of important habitat. Here, we show that the Roanoke Bayhead Delta in North Carolina, USA experienced two episodes of retreat during the past 6000 years based on core descriptions and radiocarbon and 210Pb geochronologies. The first event occurred around 3700 BC as sedimentation could not keep up with the rate of sea-level rise and a prominent flooding surface separating delta plain, below, from interdistributary bay, above, formed. Afterwards, sedimentation rates were keeping up with the low rates of sea-level rise until the mid-1600s AD, when the first European settlers began to clear forest and farm the drainage basin. During that time, the delta rapidly accreted and the interdistributary bay filled with legacy sediment from increased agricultural runoff. Regression was also facilitated by the low rates of sea-level rise at that time (−0.01 to 0.047 cm/yr). The second episode of bayhead-delta retreat initiated during the 19th century and continues today. Improved agricultural practices and dam construction decreased the amount of sediment delivered to the bayhead delta. Additionally, the rate of sea-level rise increased to 0.21 cm/yr at that time. Under these conditions, the delta entered an erosional phase and during 1954–2012 the rate of delta loss was 2469 m2/yr and that loss is easily recognized by cypress trees stranded in adjacent Albemarle Sound. This study emphasizes that human-induced modifications to the sediment budget and changes in the rate of sea-level rise strongly influence bayhead-delta evolution.