Data on stable isotopic composition of 818 O and 815 N in nitrate in groundwater, and 815 N in solid matter in the Vara?din area, NW Croatia

The Varazdin aquifer is the only source of drinking water for inhabitants of the Varazdin County. In the last decades, groundwater contamination with nitrate has become an in-creasing problem. Therefore, there is a need to define the origin of nitrate as the first step in groundwater remedia-tion. The data in this article consist of 818 O and 815 N values in nitrate in groundwater, and 815 N in solid matter. Ground-water was sampled in the period from April 2018 to Decem-ber 2019 at 10 different sites by pumping the wells, and di-rectly in the gravel pit in Sijanec. Representative solid sam-ples of plants, soil, manure, and synthetic fertilizers were col-lected from arable land in two field campaigns (July and Oc-tober 2019). The presented dataset can be used as a base-line for identification of nitrate sources in groundwater and possible nitrate attenuation processes. The data is related to the research article "Tracking the nitrogen cycle in a vulnera-ble alluvial system using a multi proxy approach: case study Varazdin alluvial aquifer, Croatia." [1] .(c) 2022 The Author(s). Published by Elsevier Inc.This is an open access article under the CC BY license( http://creativecommons.org/licenses/by/4.0/ )