Document Type

Thesis

Abstract

Erosion from agricultural watersheds has been identified as the major process contributing sediment as well as sediment-bound nitrogen and phosphorous to the Chesapeake Bay. In recent decades, population growth and increased development of agricultural areas has accelerated the flux of sediments and contaminants to the nation’s largest estuary. To combat these water quality issues, a common best management practice (BMP) is a riparian buffer, which in Virginia is typically a 100’ zone. This zone distance was suggested by the Chesapeake Bay Program, however, it is an arbitrary thickness and has not been thoroughly tested. To interpret the effectiveness of this BMP, this study quantified sediment transport through riparian systems buffering tributaries to the lower James and York Rivers from agricultural fields. In order to gauge the amount of sediment transport along hillslope transects, '57Cs is used as a tracer to quantify sediment loss and storage along transect points. To complete this process three samples were taken at each point including the O-Horizon, upper mineral soil, and lower mineral soil; these samples were tested for '°7Cs activity and their values were summed into inventories. Multiple transects were taken from agricultural fields and from control sites that have limited anthropogenic impacts. Generally, '°’Cs in the control sites fell between 1500-2500 Bq/m” indicating limited erosional changes. In contrast, the agricultural sites showed lower '57Cs in the field 1100-2400 Bq/m’, with increased levels in the riparian buffer 1000-4000 Bq/m’, relative to the other inventories. At two of the agricultural sites, elevated levels of '57Cs were found near the entrance and these values decreased as the transect approached the tributary. Usually the elevated activity was about 10 m from the entrance of the buffer.

Date Awarded

2010

Department

Geology

Advisor 1

James Kaste

Advisor 2

Gregory S. Hancock

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