δ¹⁵N-NO₃^- values of waters for each study location.

Coastal groundwater (CGW) sample data is shown as circles and marine surface water sample (ms) data is shown as squares. Study locations Waiehu (WB), Honomanū (HM), Honolua (HB), Kahului (KW), Māʻalaea (MB), and Kūʻau (KB) Bays appear in order of increasing marine surface DIN concentration as shown in Fig 2. The mean δ¹⁵N value of each category is shown as a cross. The dotted line represents the mean δ¹⁵N (‰) value of dissolved nitrate (2.3 ± 1.8 ‰) in water sampled from 15 drinking water wells near study locations during 2013 and 2014 [53]. The dashed line represents the δ¹⁵N value of nitrate in treated wastewater effluent (21.3 ‰) sampled at the Kahului WRF.