Table 2.

Results of Wilcoxon and Kruskal–Wallis rank sums tests comparing historical (1846–1916) and 2015 specimens at the four study sites. The number of specimens for each element at each site for each time period is indicated on Fig. 2.

		Wilcoxon 2-sample rank sums test			Kruskal–Wallis 1-way rank sums test
Study site	Element	S	Z	P	χ2	df	P
Block Island	Cu	20	−0.32	0.74	0.18	1	0.67
	Pb	10	−2.45	0.01*	6.55	1	0.01*
	Zn	17	−0.96	0.34	1.14	1	0.29
Cove Lands	Cu	17	−0.61	0.54	0.54	1	0.46
	Pb	10	−2.33	0.02*	6.00	1	0.01*
	Zn	14	−1.35	0.18	2.16	1	0.14
Mashapaug Pond	Cu	42	0.40	0.69	0.23	1	0.63
	Pb	23	−2.48	0.01*	6.56	1	0.01*
	Zn	49	1.52	0.13	2.56	1	0.11
Seekonk River	Cu	19	−0.12	0.90	0.06	1	0.81
	Pb	30	2.33	0.02*	6.00	1	0.01*
	Zn	26	1.35	0.18	2.16	1	0.14

Note: df = degrees of freedom; S = score sum; Z = test statistic.

^*Significant differences (P < 0.05).