Table 1.

Description of sample sites used to develop the MMIs based on the calibration dataset (2008–2009 NRSA) and evaluate the MMIs using the validation dataset (2013–2014 NRSA). Samples collected from these sites had at least 400 diatom valves.

		Calibration dataset					Validation dataset
MMI	Sites per ecoregion
Region		Total	LD	ID	MD	Revisits	Total	LD	ID	MD	Revisits
National	All sites	2121	341	1167	613	165	1861	274	1017	570	154
East	All Eastern sites	1075	154	594	327	96	942	114	515	313	98
	Northern Appalachians (NAP)	242	44	133	65	31	298	34	183	81	31
	Southern Appalachians (SAP)	354	40	177	137	33	288	22	154	112	36
	Coastal Plain (CPL)	297	39	183	75	20	220	36	112	72	25
	Upper Midwest (UMW)	182	31	101	50	12	136	22	66	48	6
Plains	All Plains sites	596	108	328	160	36	501	97	277	127	30
	Temperate Plains (TPL)	237	22	169	46	18	243	19	163	61	20
	Northern Plains (NPL)	179	50	84	45	10	147	56	67	24	7
	Southern Plains (SPL)	180	36	75	69	8	111	22	47	42	3
West	All Western sites	450	79	245	126	33	418	63	225	130	26
	Western Mountains (WMT)	231	41	129	61	12	275	44	154	77	13
	Xeric Region (XER)	219	38	116	65	21	143	19	71	53	13

LD, least-disturbed sites; ID, intermediate disturbance; MD, most-disturbed sites.