Document Type

Thesis

Abstract

Coarse- and fine-grained sediment discharge to the coast can aid in the stability of barrier islands and back-barrier marshes, respectively, as they adapt to sea-level rise and increased storminess. This study presents geologic and historical records to ascertain the anthropogenic impacts from damming and deforestation on sediment discharge from the Merrimack River to the coast in northern Massachusetts. Radiocarbon and short-lived radioisotope dating, combined with geochemical records of industrial contaminants, indicate very low accretion rates at this site during the past 500 years, ranging from 0.01 to 0.25 g cm-2 yr-1 Peak rates near 0.25 g cm-2 yr-1 coincide with the period following the industrial revolution (ca. 1850-1900) but have since remained relatively high (0.14 g cm-2 yr-1, 1955-2015). These data demonstrate that this environment has undergone minimal sedimentary reworking and that sediment accretion has long been outpaced by rates of historic relative sea-level rise (1.0-2.8 mm/yr). Records of δ13C indicate a shift in sediment source from more marine to more terrestrial coincident with the arrival of Europeans in New England (ca. 1614-1700). While colonial deforestation may have facilitated rapid marsh expansion in this system along small coastal rivers in the 17th and 18th century, these geologic and historical records indicate that increased sediment discharge from larger rivers is delayed by comparison.

Date Awarded

2016

Department

Geology

Advisor 1

Christopher Hein

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