Table 3. Measures of disturbance used to define the disturbance gradient.

Measure of disturbance	Data type	Index description
Agriculture disturbances	Buffer	Number of proximity-weighted* observed agriculture disturbances within the buffer, including pasture/hay, row crops, irrigation, confined animal feeding operations and so on
Residential and urban disturbances	Buffer	Number of proximity-weighted observed residential and urban disturbances within the buffer, including roads, parking lots, golf courses, housing, trash, landfill, dumping and so on
Hydrologic disturbances	Buffer	Number of proximity-weighted observed hydrologic disturbances within the buffer, including ditching, dikes and dams, water level control structures, excavation, fill, riprap and so on
Industrial disturbances	Buffer	Number of proximity-weighted observed industrial disturbances within the buffer, including oil drilling, gas wells, mines (surface or underground) and military operations
Habitat modifications	Buffer	Number of proximity-weighted observed habitat modifications within the buffer, including clear cuts, tree plantations, mowing, highly grazed grasses, soil compaction, recent burning and so on
Buffer summary	Buffer	The summary of threshold scores from the buffer indices (agriculture, residential/urban, hydrologic, industrial, habitat)
High impact hydrologic disturbances	Hydrology	Number of observed high impact hydrologic disturbances within the AA, including damming features, impervious surfaces, pumps, pipes, culverts and so on
Moderate impact hydrologic disturbances	Hydrology	Number of observed moderate impact hydrologic disturbances within the AA, including shallow channels, animal trampling, vehicle ruts and so on
Soil heavy metal index	Soil Metal Content	Sum of the number of heavy metal concentrations (Ag, Cd, Co, Cr, Cu, Ni, Pb, Sb, Sn, V, W, Zn) measured in the uppermost horizon above published thresholds
Relative cover of alien plant species	Vegetation	Calculated percentage of relative cover of alien plant species† in the AA, measured within five 100 m2 plots

Modified from US Environmental Protection Agency's, 2011 National Wetland Condition Assessment Technical Report¹⁶.

^*Buffer observations were recorded by proximity to the AA, with observed stressors closest to the AA receiving higher stressor scores than those farthest from the AA.

^†Alien plant species are defined as those that are either introduced to the conterminous United States or are adventive to the location of occurrence.