Table 3.

Average nitrate content (% w/w) and nitrogen stable isotope ratio of efflorescences from S. Pietro a Corte (EFSPC) and Fruscione Palace (EFFP), and salts from the well in the frigidarium (WFD).

Sample	Nitrate (%)	N; σ; 2σ	δ 15N (‰)	N; σ; 2σ
EFSPC	95	6; 3; 6	+ 9.3	6; 0.2; 0.4
EFFP	92	3; 2; 4	+ 8.6	3; 0.2; 0.4
WFD	49	6; 1; 2	+ 2.9	6; 0.3; 0.6