Dissolved and particulate organic carbon fluxes from an agricultural watershed during consecutive tropical storms

Abstract

Low‐frequency high‐magnitude hydrologic events mobilize a disproportionate amount of dissolved organic carbon (DOC) from watersheds, but few studies measure the role of extreme storms in exporting organic carbon from croplands. We use high‐resolution measurements of storm runoff to quantify DOC and particulate organic carbon (POC) fluxes from an agricultural field during consecutive tropical storms that delivered 41 cm of rainfall to the Virginia Coastal Plain. Over a 2 week period, we measured exports of 22 kg DOC ha−1 and 11.3 kg POC ha−1. Ultraviolet absorbance measurements indicate that the aromatic DOC fraction systematically increased as plant‐derived aliphatic carbon was depleted during the initial event. Croplands can have event‐scale carbon losses that equal or exceed published estimates of annual export for perennial streams draining forested and mixed land use watersheds. We quantify aromatic DOC fractions approaching 50%, indicating that agricultural stormflow can produce a significant load of relatively photoreactive carbon.