High-frequency NO<sub>3</sub><sup>−</sup> isotope (δ<sup>15</sup>N, δ<sup>18</sup>O) patterns in groundwater recharge reveal that short-term land use and climatic changes influence nitrate contamination trends

Abstract

Abstract. Poultry manure is the primary source of nitrate (NO3−) exceedances in the transboundary Abbotsford-Sumas aquifer (Canada-USA) based on synoptic surveys two decades apart, but serious questions remained about seasonal and spatial aspects of agricultural nitrate fluxes to the aquifer to help better focus remediation efforts. We conducted over 700 monthly δ15N and δ18O of nitrate assays, focusing on newly recharged groundwater (

A Ti(III) reduction method for one‐step conversion of seawater and freshwater nitrate into N2O for stable isotopic analysis of 15N/14N, 18O/16O and 17O/16O

“…Stable isotopes are proven tools in this regard, as the δ 15 N, δ 18 O and δ 17 O isotopic composition of NO 3 − provides essential information about nitrogen (N) sources and biogeochemical sinks, allowing one to distinguish between organic waste, fertilizers, and atmospheric N sources . Furthermore, isotopic time series and geospatial depictions of nitrate in ground and surface water reveal important changes in agricultural land use, inform optimization of fertilization practices not achievable based on NO 3 − concentrations alone, and allow for detection of natural bioremediation processes such as bacterial denitrification . NO 3 − stable isotopes have also been instrumental in studies of the natural N cycle in a variety of systems including the global ocean and large‐scale variations in NO 3 − δ 15 N and δ 18 O values have been used to understand the ocean N balance between losses from denitrification and gains from N 2 fixation .…”

Quantification of Groundwater Nitrate Loading after Raspberry Field Renovation Using High‐Resolution Passive Diffusion Sampling

“…4A). Similar renovation activities occur across the ASA, and the interannual variations in NO 3 loading resulting from renovation, likely contribute to the interannual variation of shallow groundwater NO 3 concentration observed in the ASA (Graham et al, 2015; Zebarth et al, 2015; Suchy et al, 2018).…”

“…Land‐use on the Canadian portion of the ASA is primarily high‐density poultry with intensively managed perennial small fruit crops of red raspberries ( Rubus idaeus L.) and highbush blueberries ( Vaccinium corymbosum L.; Zebarth et al, 1998, 2015). Many groundwater monitoring wells in the ASA exhibit intra‐annual (i.e., seasonal) and interannual (i.e., over several years or decades) variation in groundwater NO 3 concentration (Zebarth et al, 2015; Graham et al, 2015; Suchy et al, 2018). Some of this variation can be explained by the seasonal nature of precipitation and crop management practices (e.g., fertilizer N applications and irrigation).…”

“…However, not all temporal variation in groundwater NO 3 concentrations can be explained by these factors. It has been hypothesized that the practices associated with raspberry field renovation and replanting may be responsible for some of this unexplained spatial and temporal variation in groundwater NO 3 concentrations (Zebarth et al, 2015; Gallagher and Gergel, 2017; Suchy et al, 2018).…”