TABLE 1.

List of landscape variables (independent criteria) used in CART analyses

Variable namea	Variable description (unit)b
SHREVE	Stream order. Lower orders (numbers) represent smaller tributaries, while higher orders (numbers) represent larger watercourses. Shreve's method adds the order of each converging branch together regardless of size.
DBARN_xK	Barn density in catchment area 2, 5, 10, and 20 km upstream (obs. km−2)
DDEVHI_xK	High-density development in catchment area 2, 5, 10, and 20 km upstream (obs. km−2)
DDEVLO_xK	Low-density development in catchment area 2, 5, 10, and 20 km upstream (obs. km−2)
DFORE_xK	Forest density in catchment area 2, 5, 10, and 20 km upstream (obs. km−2)
DPAST_xK	Pasture density in catchment area 2, 5, 10, and 20 km upstream (obs. km−2)
CROPP-xK	Cropland coverage in catchment area 2, 5, 10, and 20 km upstream (km2 km−2)
DEVELP-xK	Developed land coverage in catchment area 2, 5, 10, and 20 km upstream (km2 km−2)
FORAGEP-xK	Forage land coverage in catchment area 2, 5, 10, and 20 km upstream (km2 km−2)
PASTP-xK	Pasture land coverage in catchment area 2, 5, 10, and 20 km upstream (km2 km−2)
SHRUBP-xK	Shrub land coverage in catchment area 2, 5, 10, and 20 km upstream (km2 km−2)
VEGP-xK	Forest coverage in catchment area 2, 5, 10, and 20 km upstream (km2 km−2)
WATWETP-xK	Water plus wetland coverage in catchment area 2, 5, 10, and 20 km upstream (km2 km−2)
BASIN_(landuse)	Cropland, developed land, forage land, pasture land, and forest coverage in entire catchment area (km2 km−2)
NUD_(landuse)	Upstream distances (km) from sample location to nearest land use observations listed above and further land use observations, including poultry barns (POULTRY BARN), pasture with livestock access to sampled tributary (PASTURE ACCESS), horse barns (HORSE BARN), hog barns (HOG BARN), dairy operations (DAIRY OP), and cattle barns (CATTLE BARN)

^ax, maximum upstream distance from the sample site at which the sample site catchment area was defined.

^bobs., number of observations.