Attributes for NHDPlus Catchments (Version 1.1) for the Conterminous United States: Normalized Atmospheric Deposition for 2002, Total Inorganic Nitrogen

This data set represents the average normalized atmospheric (wet) deposition, in kilograms,
of Total Inorganic Nitrogen for the year 2002 compiled for every catchment of NHDPlus for
the conterminous United States. Estimates of Total Inorganic Nitrogen deposition are based
on National Atmospheric Deposition Program (NADP) measurements (B. Larsen, U.S.
Geological Survey, written commun., 2007). De-trending methods applied to the year 2002
are described in Alexander and others, 2001. NADP site selection met the following criteria:
stations must have records from 1995 to 2002 and have a minimum of 30 observations.

The NHDPlus Version 1.1 is an integrated suite of application-ready geospatial datasets
that incorporates many of the best features of the National Hydrography Dataset (NHD)
and the National Elevation Dataset (NED). The NHDPlus includes a stream network
(based on the 1:100,00-scale NHD), improved networking, naming, and value-added
attributes (VAAs). NHDPlus also includes elevation-derived catchments (drainage areas)
produced using a drainage enforcement technique first widely used in New England, and
thus referred to as "the New England Method." This technique involves "burning in" the
1:100,000-scale NHD and when available building "walls" using the National Watershed
Boundary Dataset (WBD). The resulting modified digital elevation model (HydroDEM) is
used to produce hydrologic derivatives that agree with the NHD and WBD. Over the past
two years, an interdisciplinary team from the U.S. Geological Survey (USGS), and the
U.S. Environmental Protection Agency (USEPA), and contractors, found that this method
produces the best quality NHD catchments using an automated process (USEPA, 2007).
The NHDPlus dataset is organized by 18 Production Units that cover the conterminous
United States.

The NHDPlus version 1.1 data are grouped by the U.S. Geologic Survey's Major River
Basins (MRBs, Crawford and others, 2006). MRB1, covering the New England and
Mid-Atlantic River basins, contains NHDPlus Production Units 1 and 2. MRB2, covering
the South Atlantic-Gulf and Tennessee River basins, contains NHDPlus Production Units
3 and 6. MRB3, covering the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy
River basins, contains NHDPlus Production Units 4, 5, 7 and 9. MRB4, covering the
Missouri River basins, contains NHDPlus Production Units 10-lower and 10-upper. MRB5,
covering the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf River basins, contains
NHDPlus Production Units 8, 11 and 12. MRB6, covering the Rio Grande, Colorado and
Great Basin River basins, contains NHDPlus Production Units 13, 14, 15 and 16. MRB7,
covering the Pacific Northwest River basins, contains NHDPlus Production Unit 17. MRB8,
covering California River basins, contains NHDPlus Production Unit 18.