Coastal sedimentation across North America doubled in the 20th century despite river dams

A B Rodriguez,C B Miller,B A Mckee,M C Bost,A N Atencio

doi:10.1038/s41467-020-16994-z

Abstract

The proliferation of dams since 1950 promoted sediment deposition in reservoirs, which is thought to be starving the coast of sediment and decreasing the resilience of communities to storms and sea-level rise. Diminished river loads measured upstream from the coast, however, should not be assumed to propagate seaward. Here, we show that century-long records of sediment mass accumulation rates (g cm−2 yr−1) and sediment accumulation rates (cm yr−1) more than doubled after 1950 in coastal depocenters around North America. Sediment sources downstream of dams compensate for the river-sediment lost to impoundments. Sediment is accumulating in coastal depocenters at a rate that matches or exceeds relative sea-level rise, apart from rapidly subsiding Texas and Louisiana where water depths are increasing and intertidal areas are disappearing. Assuming no feedbacks, accelerating global sea-level rise will eventually surpass current sediment accumulation rates, underscoring the need for including coastal-sediment management in habitat-restoration projects.

Highlights

The proliferation of dams since 1950 promoted sediment deposition in reservoirs, which is thought to be starving the coast of sediment and decreasing the resilience of communities to storms and sea-level rise
Large areas of intertidal oyster reef and saltmarsh have already been lost in North America[4,5]
To assess coastal sedimentation around North America, we developed records of mass accumulation rates (MAR; g cm−2 yr−1) and sediment accumulation rates (SAR; cm yr−1) from 25 coastal sites using published and new sediment-core geochronologies (Fig. 1; see “Methods” section and Supplementary Note 1 and Supplementary Data 1)

Summary

Introduction

The proliferation of dams since 1950 promoted sediment deposition in reservoirs, which is thought to be starving the coast of sediment and decreasing the resilience of communities to storms and sea-level rise. 1234567890():,; Sediment supply to nearshore areas can play a major role in determining the future of coastal communities and ecosystems threatened by accelerating sea-level rise (SLR) and increasing storminess Intertidal habitats such as oyster reef, salt marsh, and mangrove provide coastal communities some protection from storms, are essential for the maintenance of healthy estuaries, and require allogenic sediment to sustain areal extent with SLR1. Gauges positioned furthest downstream are still far from the coast, located typically ~15–100 km landward of bayhead deltas It is assumed, that the reduction in river load observed at downstream gauges is propagated further downstream, corresponds with a reduction in suspended sediment delivery to coastal areas, and will hasten the degradation of intertidal habitats with accelerated relative SLR12,17. If sediment sources positioned downstream of dams offset sediment lost to reservoirs[18], that will be recorded as constant or increasing sedimentation rates

Objectives

Methods

Results