Direct connectivity between upstream and downstream promotes rapid response of lower coastal‐plain rivers to land‐use change

Abstract

[1] Low-relief fluvial systems that originate in the lower coastal plain and discharge into estuaries are common along passive margins. These watersheds are thought to be disconnected from their termini by floodplains, which buffer the sediment-routing system by sequestration. Here, we present a detailed study of the Newport River, a typical lower coastal-plain system, which reveals high connectivity between watershed and delta. Connectivity is measured as the time lag between initiation of a silviculture operation, which increased landscape erosion, and when the sediment appeared at the bay-head delta. The time lag, measured from aerial photographs and sedimentation rates calculated from 210 Cs-activities in cores from the watershed and delta, is <3 years. Most lower coastal-plain rivers are steeper and have less floodplain accommodation available for storage than their larger counterparts that originate landward of the fall line, which promotes higher connectivity between upstream and downstream.

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

“…Bayhead deltas are very sensitive to changes in sedimentation and accommodation, thus, human alterations within watersheds greatly affect bayhead delta evolution (Nichols et al, 1986). Increased erosion in the watershed associated with deforestation, or land-use change, increases sediment supply (Ver et al, 1999;Hupp et al, 2009a;Mattheus et al, 2009), while construction of impoundments effectively restrict sediment delivery to the river mouth (Meade, 1982;Jaffe et al, 2007). Previous studies report bayhead deltas retreat rapidly (backstep) in response to a small increase in the rate of sea-level rise (Rodriguez et al, 2010), but the rate of retreat can also decrease as sediment supply increases or when transgression is confined by an abrupt increase of valley gradient at tributary junctions (Simms and Rodriguez, 2014).…”

The utility of estuarine settling basins for constructing multi-decadal, high-resolution records of sedimentation

“…Unlike the estuarine saltmarsh shoreline, which acts as a natural buffer to over-land sediment flow, developed land has a higher potential to increase suspended sediment load to the system through direct runoff from the land. Mattheus et al (2009) showed rapid accretion along the Newport River Bayhead delta front as the result of runoff from a large silviculture operation directly adjacent to the watershed. That increase in sedimentation rate occurred between 1964 and 1967, just as suddenly as what we measured at CLB (Mattheus et al, 2009).…”

“…Mattheus et al (2009) showed rapid accretion along the Newport River Bayhead delta front as the result of runoff from a large silviculture operation directly adjacent to the watershed. That increase in sedimentation rate occurred between 1964 and 1967, just as suddenly as what we measured at CLB (Mattheus et al, 2009). Another land-use change in the area has been farming.…”

“…Over decadal to millennial timeframes, variations in anthropogenic influences (e.g. dams, land-use and cover modifications, shoreline armoring), sea level, and climate can also affect changes in sediment flux to the estuary (Patton and Horne, 1992;Small and Cohen, 2004;Poff et al, 2006;Mattheus et al, 2009;Walling 2012).…”

Rapid wetland expansion during European settlement and its implication for marsh survival under modern sediment delivery rates: REPLY

“…Deforestation occurred especially early in our study area: the town of Rowley passed laws restricting tree cutting in 1660 (Gage, 1840) and nearly 98% of Ipswich's forest was cut by 1831 (Tarule, 2004). Deforestation in the watersheds of small coastal rivers leads to large changes in estuarine sedimentation rates with little lag time (Mattheus et al, 2009).…”