Geoscience Reference
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has been developed to assist with the model implementation. The AVDLBRM
interface was written in ArcView Avenue scripts by modifying the ArcView
Nonpoint Source Modeling interface by He et al. ( 2001 ) and He ( 2003 ). It consists
of six modules: (1) Soil Processor, (2) DLBRM Utility, (3) Parameter Generator,
(4) Output Visualizer, (5) Statistical Analyzer, and (6) Land Use Simulator.
Databases required for the DLBRM include meteorological data, soil, digital
elevation model (DEM), land use/cover, and hydrology and hydrography
(Tables 6.1 and 6.2 ). The databases identified in Table 6.1 are used by the interface
and those in Tables 6.1 and 6.2 are used to derive the DLBRM input variables and
visualize the simulation results (He and Croley 2007a ,c;Heetal. 2008 ; He and
DeMarchi 2010 ).
6.5 Estimating Nonpoint Sources Loading Potential
Nutrients (N and P 2 O 5 ) loading potential from livestock manure and fertilizer
applications was estimated at the 5-digit zip code and county scales respectively.
The livestock manure loading potential within a county was estimated by using the
five-digit zip code from the Census of Agriculture for the periods of 1987, 1992,
1997, and 2002 ( http://www.nass.usda.gov/Census_of_Agriculture/index.asp ). The
census data were tabulated farm counts of animal units by five-digit zip code in three
classes: 0-49, 50-199 and 200 ( i.e. number of farms with animal units up to 49,
between 50 and 199, or 200 or more per zip code) for 1987 and 1992. But those
classes were not available for the 1997 and 2002 census data. To be consistent in
determining the number of animals per farm, the weighted mean number of animals
per farm was computed for each type of animal according to the percentage of three
classes of animals for the 1987 and 1992 census data The mean values of 25, 100, and
200 were used for each of the three classes of the animal units in the computation.
The weighted mean number of animals per farm in the study area were computed as:
57 cattle and calves, 84 hogs and swine, 18 lamb and sheep, 2,650 chicken, and
6 horses for the census years of 1987, 1992, 1997, and 2002. These were the only data
available to estimate number of animals per zip code area and discrepancies between
the actual animal number and these estimates should be well noted when using those
results for water resources planning (He and Shi 1998 ; USDA Agricultural Statistic
Service 2004 ).
The computed numbers of livestock per zip code were matched with the
five-digit zip code boundary file ( http://www.census.gov/geo/www/cob/z52000.
html#shp ) and multiplied by animal manure production coefficients to estimate
animal manure loading potential (tons/year) by zip code. The coefficients from
the Livestock Waste Facilities Handbook MWPS-18 (Midwest Plan Service 1985 )
were used in this study. For example, a 1,000 lb. dairy cow produces 13 metric tons
of manure in a year (20-25 % solids content and 75-80 % moisture content) with
150 lbs. of nitrogen and 60 lbs. of phosphate; a 150 lb. pig produces 1.6 metric tons
of manure in a year with 25 lbs. of nitrogen and 18 lbs. of phosphate. As animal
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