Document Type

Thesis

Abstract

Dissolved organic carbon (DOC) and particulate organic carbon (POC) play a critical role in nutrient cycling, contaminant transport and the global carbon cycle, but total organic carbon (TOC) fluxes are not well constrained across different land uses and environments. Recent work has shown that runoff from agricultural watersheds can have high DOC contents due to leaching of crop residues and soil organic matter by rain and irrigation waters. We use automated high resolution sampling of agricultural storm runoff and stream height to quantify DOC and POC fluxes and dynamics in an ephemeral channel on the coastal plain of Virginia. Discharge measurements are determined using a rating curve developed using stream stage height and salt dilution measurements. DOC and POC were characterized using high temperature catalytic oxidation and specific UV absorbance at 254 nm (SUVA254). During a two week period in fall 2011 when a hurricane and tropical storm passed over the region, we measured a DOC flux of 22 kg ha-1 and a POC flux of 11.3 kg hal. SUVA»s4 values indicated that the aromatic portion of DOC ranged from a minimum 18.6% at the beginning of the first event to a maximum of 44.0% during the second event; this represents an increase in soil derived DOC. Hysteresis plots and SUVA254 indicated that plant derived aliphatic DOC was depleted while soil sourced aromatic DOC was readily available. Field conditions, particularly the degree of saturation from previous rain events, were found to influence the fluxes and character of DOC. While ephemeral channels are often overlooked as sources of agricultural runoff, they can facilitate the export of large quantities of organic carbon during flashy, storm generated flows.

Date Awarded

2012

Department

Geology

Advisor 1

James M. Kaste

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