Chemical and Isotopic Tracers Illustrate Pathways of Nitrogen Loss in Cranberry Floodwaters

Abstract

Limited research exists on the sources of nitrogen (N) in cranberry floodwaters, which have been identified as a prominent cause of concern to watershed N loading in the cranberry-producing region of southeastern Massachusetts. In this study, we used naturally occurring chemical and isotopic tracers to infer the sources of N transported by harvest floodwaters. In 2012, the cranberry bed was a net source of total N (TN), exporting 0.8 kg N ha (primarily as organic N) to a nearby lake. Systematic increases in TN concentration were associated with increasing fractions of pre-event soil water and groundwater ("porewater") in discharge. Results showed that N concentrations in porewater generally derive from the natural mixing of soil water and perched groundwater within the cranberry bed but locally display a connection to deep groundwater where the underlying peat is absent. These findings illustrate the environmental significance of stored pools of porewater in cranberry beds and the ability to focus on moments of disproportionate N transfer to most efficiently curtail floodwater N losses (i.e., 58% of N export occurred in only 22% of floodwater discharge).