Michael G. Rupert
20030609
Raster dataset showing the probability of elevated concentrations of nitrate in ground water in Colorado, hydrogeomorphic regions not included and fertilizer use estimates included.
1.0
Raster digital data
Reston, VA
U.S. Geological Survey
https://water.usgs.gov/lookup/getspatial?nit_nhyd_fert
This dataset is one of eight datasets produced by this study.
Four of the datasets predict the probability of detecting
atrazine and(or) desethyl-atrazine (a breakdown product of atrazine)
in ground water in Colorado; the other four predict the probability
of detecting elevated concentrations of nitrate in ground water in
Colorado. The four datasets that predict the probability of
atrazine and(or) desethyl-atrazine (atrazine/DEA) are differentiated
by whether or not they incorporated atrazine use and whether
or not they incorporated hydrogeomorphic regions. The four datasets
that predict the probability of elevated concentrations of nitrate
are differentiated by whether or not they incorporated fertilizer
use and whether or not they incorporated hydrogeomorphic
regions. Each of the eight datasets has its own unique strengths
and weaknesses. The user is cautioned to read Rupert (2003, Probability
of detecting atrazine/desethyl-atrazine and elevated concentrations
of nitrate in ground water in Colorado: U.S. Geological Survey
Water-Resources Investigations Report 02-4269, 35 p.,
https://water.usgs.gov/pubs/wri/wri02-4269/) to determine if he(she)
is using the most appropriate dataset for his(her) particular needs.
This dataset specifically predicts the probability of detecting
elevated concentrations of nitrate in ground water in Colorado with
hydrogeomorphic regions not included and fertilizer use included.
The following text was extracted from Rupert (2003).
Draft Federal regulations may require that each State develop a
State Pesticide Management Plan for the herbicides atrazine,
alachlor, metolachlor, and simazine. Maps were developed that the
State of Colorado could use to predict the probability of detecting
atrazine/DEA in ground water in Colorado. These maps can be
incorporated into the State Pesticide Management Plan and can help
provide a sound hydrogeologic basis for atrazine management in
Colorado. Maps showing the probability of detecting elevated nitrite
plus nitrate as nitrogen (nitrate) concentrations in ground water in
Colorado also were developed because nitrate is a contaminant of
concern in many areas of Colorado.
Maps showing the probability of detecting atrazine/DEA at or greater
than concentrations of 0.1 microgram per liter and nitrate
concentrations in ground water greater than 5 milligrams per liter
were developed as follows: (1) Ground-water quality data were overlaid
with anthropogenic and hydrogeologic data by using a geographic
information system (GIS) to produce a dataset in which each well had
corresponding data on atrazine use, fertilizer use, geology,
hydrogeomorphic regions, land cover, precipitation, soils, and well
construction. These data then were downloaded to a statistical
software package for analysis by logistic regression. (2) Relations
were observed between ground-water quality and the percentage of
land-cover categories within circular regions (buffers) around wells.
Several buffer sizes were evaluated; the buffer size that provided
the strongest relation was selected for use in the logistic regression
models. (3) Relations between concentrations of atrazine/DEA and
nitrate in ground water and atrazine use, fertilizer use, geology,
hydrogeomorphic regions, land cover, precipitation, soils, and
well-construction data were evaluated, and several preliminary
multivariate models with various combinations of independent variables
were constructed. (4) The multivariate models that best predicted
the presence of atrazine/DEA and elevated concentrations of nitrate
in ground water were selected. (5) The accuracy of the multivariate
models was confirmed by validating the models with an independent
set of ground-water quality data. (6) The multivariate models were
entered into a geographic information system and the probability
GRIDS were constructed.
Draft Federal regulations (U.S. Environmental Protection Agency,
Pesticides and Ground Water State Management Plan Regulation; Proposed
Rule, U.S. Federal Register, v. 61, no. 124, June 26, 1996,
p. 33260-33301) may require that each State develop a State Pesticide
Management Plan (PMP) for the herbicides atrazine, alachlor,
metolachlor, and simazine. The Colorado Agricultural Chemicals
and Groundwater Protection Program--a cooperative effort of the
Colorado Department of Agriculture (CDA), the Colorado Department
of Public Health and Environment (CDPHE), and the Colorado State
University Cooperative Extension (CSUCE)--is developing a PMP for
each of the herbicides and would benefit from a map that could be
used to predict the probability of detecting atrazine and DEA in
ground water. The map could be incorporated into the PMP and
provide a sound hydrogeologic basis for atrazine management in
Colorado. Other organizations and programs that could benefit
from maps that predict the probability of detecting atrazine,
DEA, and elevated concentrations of nitrate in ground water
include the agri-chemical industry, county and city governments,
farmers, planning and zoning commissions, education programs for
applicators, and State programs related to Wellhead Protection,
Drinking Water, Home-A-Syst, and Best Management Plans (BMP's).
To address these needs, the U.S. Geological Survey (USGS), in
cooperation with the CDA, CDPHE, and CSUCE, conducted a study to
develop maps to predict the probability of detecting atrazine
and(or) DEA and elevated concentrations of nitrate in
ground water in Colorado.
The finest scale at which this dataset should be used is 1:250,000,
which is the scale of the soils data used to develop this dataset.
This dataset was created by combining several different layers of GIS
data, including herbicide use, fertilizer use, hydrogeomorphic
regions, land cover, and soils. Herbicide-use data were obtained from
Battaglin and Goolsby (1994), who prepared GIS coverages of herbicide-
use estimates for the 20 most-used herbicides in the conterminous United
States based on data compiled by Gianessi and Puffer (1991). Gianessi
and Puffer's (1991) estimates for each county included the number of
acres treated, pounds of active ingredient used, and pounds used per
square mile. Although crop-acreage data represent the 1987 growing year,
the herbicide-use estimates generally reflect 1989 usage amounts
(Gianessi and Puffer, 1991). When the final probability GRIDS were
created for this study, atrazine use was assigned only to areas in GIS
coverages that delineate irrigated agricultural land cover (pasture/hay
and row crops land-cover classification) because these are the areas
where most, if not all, agricultural atrazine use occurs.
Estimates of nitrogen fertilizer use for 1997 were developed by David
Lorenz (U.S. Geological Survey, written commun., 2001). First, estimates
of the total amount of nitrogen fertilizer product that was sold in
Colorado during 1997 were obtained from the Association of American
Plant Food Control Officials (AAPFCO) at the University of Kentucky. The
statewide total was prorated to each county based upon amounts of
fertilizer expenditures by farmers that were reported in the 1997 Census
of Agriculture. When the final probability GRIDS were created for this
study, nitrogen fertilizer use was assigned only to areas in GIS
coverages that delineate agricultural land cover (pasture/hay and row
crops land-cover classification).
A GIS dataset delineating hydrogeomorphic regions in Colorado was
developed for this study. Hydrogeomorphic regions are similar
in concept to regional aquifers but are distinguished from regional
aquifers in that hydrogeomorphic regions are delineated on the basis of
general geographic locations of geologic materials and not on actual
aquifer locations. A comprehensive coverage of regional aquifers for all
of Colorado was not available, but hydrogeomorphic regions satisfied the
needs of this study. Hydrogeomorphic regions were delineated by
combining information from three sources. The first source was the
geologic map of Colorado (Tweto, 1979), which was digitized by Green
(1992). Unconsolidated alluvial regions were delineated by using
the alluvial, gravel, eolian, and glacial deposits of Quaternary age
that are delineated on the geologic map of Colorado. The second source
was a GIS coverage delineating the boundary of the High Plains aquifer
(Cederstrand and Becker, 1999) that was compiled from a digital coverage
created for publication of paper maps in McGrath and Dugan (1993). The
third source was a GIS coverage digitized from reports that delineate
the boundary of the valley-fill aquifer in the lower Arkansas River
Basin (Hurr and Moore, 1972; Nelson and others, 1989a, 1989b, 1989c).
Land-cover data for Colorado were obtained from National Land Cover Data
(NLCD) developed by the U.S. Geological Survey (2000). NLCD were
produced as part of a cooperative project between the U.S. Environmental
Protection Agency and the USGS to produce a consistent land-cover GIS
data layer for the conterminous United States based on 30-meter-
resolution Landsat thematic mapper (TM) data. The NLCD contains 21
categories of land-cover information. The NLCD files were too large for
the computers available to this study to manipulate in raw form, so the
files were generalized to 60-meter resolution. This generalization may
have improved the consistency of the data by reducing the number of
isolated single-cell occurrences of a particular land-cover
classification, which were probably an artifact of spectral processing
and not true differences in land cover.
Soils data were obtained from the State Soil Geographic (STATSGO)
database (U.S. Department of Agriculture, 1991). The finer scale Soil
Survey Geographic (SSURGO) database (U.S. Department of Agriculture,
1995) was not available for all regions in Colorado. The STATSGO data
were not suitable for use by this study in raw form, so STATSGO data
compiled by Schwarz and Alexander (1995) were used. These later data
included weighted averaging of many of the soil characteristics
contained in the database. The U.S. Department of Agriculture
(1993) provides more information on these soil characteristics.
REFERENCES CITED IN ABOVE TEXT
Battaglin, W.A., and Goolsby, D.A., 1994, Spatial data in GIS format on
agricultural chemical use, land use, and cropping practices in the
United States: U.S. Geological Survey Water-Resources Investigations
Report 94-4176, 87 p., accessed July 3, 2001, from
URL https://water.usgs.gov/lookup/getspatial?herbicide1
Cederstrand, J.R., and Becker, M.F., 1999, Digital map of aquifer
boundary for the High Plains aquifer in parts of Colorado, Kansas,
Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming:
U.S. Geological Survey Open-File Report 99-267, accessed July 3, 2001,
from URL https://water.usgs.gov/lookup/getspatial?ofr99-267_aqbound
Gianessi, L. P., and Puffer, Cynthia, 1991, Herbicide use in the
United States: Washington, D.C., Resources for the Future, December
1990 (revised April 1991), 128 p.
Green, G.N., 1992, The digital geologic map of Colorado in ARC/INFO
format: U.S. Geological Survey Open-File Report 92-507, metadata
accessed January 31, 2001, from URL
https://geo-nsdi.er.usgs.gov/metadata/open-file/92-507/metadata.faq.html
Hurr, R.T., and Moore, J.E., 1972, Hydrogeologic characteristics of the
valley-fill aquifer in the Arkansas River valley, Bent County, Colorado:
U.S. Geological Survey Hydrologic Investigations Atlas HA-0461, scale
1:62,500, 2 sheets.
McGrath, Timothy, and Dugan, J.T., 1993, Water-level changes in the
High Plains aquifer--Predevelopment to 1991: U.S. Geological Survey
Water-Resources Investigations Report 93-4088, 53 p.
Nelson, G.A., Hurr, R.T., and Moore, J.E., 1989a, Hydrogeologic
characteristics of the valley-fill aquifer in the Arkansas River Valley,
Prowers County, Colorado: U.S. Geological Survey Open-File Report
89-254, scale 1:62,500, 3 sheets.
Nelson, G.A., Hurr, R.T., and Moore, J.E., 1989b, Hydrogeologic
characteristics of the valley-fill aquifer in the Arkansas River Valley,
Crowley and Otero Counties, Colorado: U.S. Geological Survey Open-File
Report 89-255, scale 1:62,500, 3 sheets.
Nelson, G.A., Hurr, R.T., and Moore, J.E., 1989c, Hydrogeologic
characteristics of the valley-fill aquifer in the Arkansas River Valley,
Pueblo County, Colorado: U.S. Geological Survey Open-File Report
89-256, scale 1:62,500, 3 sheets.
Rupert, M. G., 2003, Probability of detecting atrazine/desethyl-atrazine
and elevated concentrations of nitrate in ground water in Colorado:
U.S. Geological Survey Water-Resources Investigations Report 02-4269,
35 p., https://water.usgs.gov/pubs/wri/wri02-4269/.
Schwarz, G.E., and Alexander, R.B., 1995, State Soil Geographic
(STATSGO) data base for the conterminous United States: U.S. Geological
Survey Open-File Report 95-449, accessed March 10, 2001, from URL
https://water.usgs.gov/lookup/getspatial?ussoils
Tweto, Ogden, comp., 1979, Geologic map of Colorado: U.S. Geological
Survey, scale 1:500,000, 1 sheet.
U.S. Department of Agriculture, 1991, State Soil Geographic (STATSGO)
data base: U.S. Department of Agriculture, Soil Conservation Service,
Miscellaneous Publication 1492, 88 p.
U.S. Department of Agriculture, 1993, Soil survey manual:
U.S. Department of Agriculture, Handbook 18, 437 p.
U.S. Department of Agriculture, 1995, Soil Survey Geographic
(SSURGO) data base: U.S. Department of Agriculture, Natural Resources
Conservation Service, Miscellaneous Publication 1527, 31 p.
U.S. Geological Survey, 2000, National land cover dataset:
U.S. Geological Survey Fact Sheet 108-00, 3 p., accessed November 14,
2000, from URL
https://mapping.usgs.gov/mac/isb/pubs/factsheets/fs10800.html
2003
Variable, input data used to develop this dataset were developed
during the 1980's and 1990's.
None Planned
-109.813
-101.475
41.574
36.424
USGS Thesaurus
Ground water
Ground-water vulnerability
Ground-water probability
Ground-water susceptibility
Vulnerability
Susceptibility
Probability
Nitrate
Atrazine
Desethyl-atrazine
Ground-water quality
Ground-water contamination
Probability of ground-water contamination
inlandWaters
ISO 19115 Topic Categories
elevation
geoscientificInformation
inlandWaters
USGS Metadata Identifier
USGS:cfd48722-0afa-48a1-8ded-9ad7e700f610
Geographic Names Information System
Colorado
None
This dataset should not be used at a scale any larger than 1:250,000,
which is the scale of the soils data used to construct the probability
GRIDS. Soils data at a larger scale were not available for all
regions of Colorado.
This dataset is one of eight datasets produced by this study. The
user is cautioned to read Rupert (2003) to ensure that they are
using the correct dataset for their particular needs.
The probability GRIDS developed by this study are designed to
portray the potential for contamination of ground water in
Colorado. These GRIDS do not show areas that are actually
(currently) contaminated; rather, these GRIDS show the areas that
have a potential (or likelihood) for being contaminated if a
contaminant was released to the environment. More specifically,
each GRID shows the probability of detection (in terms of a percent)
of a particular chemical compound (the contaminant) in ground
water. Probability is not the same as certainty; a well in a
high probability area is not necessarily contaminated because
contamination also can depend on well depth and other local
factors not taken into account by the models used to produce these
probability GRIDS.
The atrazine/DEA and nitrate probability GRIDS were specifically
developed for use by the State of Colorado in its Pesticide
Management Plan to help provide a sound hydrogeologic basis
for the management of atrazine and nitrogen in Colorado. The
GRIDS are intended to be a first approximation at developing a
consistent rating method for the entire State. Additional
site-specific data are needed before site-specific decisions
are made, such as pesticide-use restrictions.
The most appropriate uses of these GRIDS are to focus prevention
programs in areas of greatest concern, to focus ground-water
sampling programs in areas of greatest potential for contamination,
and to assist educational programs for ground-water quality
protection.
The accuracy of the probability GRIDS would be improved if
(1) larger scale soils data were available in digital form,
(2) more complete and detailed chemical-use data were available,
and (3) a larger number and wider distribution of ground-water
quality data, particularly in rangeland areas, were available.
Data differentiating between sprinkler and flood irrigation
methods would probably improve the accuracy in agricultural
areas. Some site-specific variables, such as improper well
construction and local spills of contaminants, were not
accounted for in the models. Accounting for ground-water flow
direction was beyond the scope of this study. Depth to ground
water was not evaluated by this study because a large-scale
statewide coverage was not available. Depth to ground
water may be an important coverage to develop for future studies.
Michael G. Rupert
U.S. Geological Survey
Hydrologist
Mailing
201 W. 8th Street, Suite 200
Pueblo
Colorado
81003
USA
1-888-275-8747
719-544-7155
mgrupert@usgs.gov
This dataset was produced through a cooperative effort with Rob
Wawrzynski of the Colorado Department of Agriculture, Bradford
Austin of the Colorado Department of Public Health and Environment, and
Regan Waskom and Troy Bauder of the Colorado State University Cooperative
Extension.
Microsoft Windows XP Professional
Operating System Version 5.1.2600
ArcInfo version 8.2
U.S. Geological Survey
20030609
Digital geospacial datasets showing the probability of detecting
atrazine/desethyl-atrazine and elevated concentrations of nitrate
in ground water in Colorado
Raster digital data
U.S. Geological Survey Open-File Report
03-234
Denver, Colorado
U.S. Geological Survey
https://water.usgs.gov/lookup/getspatial?nit_nhyd_fert
GRID cells were randomly selected from this dataset and checked to
ensure the correct probability values were calculated using the logistic
regression equation and the input datasets on herbicide use, fertilizer
use, hydrogeomorphic regions, land cover, and soils.
Not applicable for raster data
The extent of this dataset is the entire State of Colorado
This dataset was developed by combining information from multiple
datasets; the horizontal accuracy is dependent on the combined
accuracy from all of the input datasets, which is impossible to
quantify. Probably the best estimate of the horizontal accuracy is
determined by the STATSGO soils data, developed at 1:250,000 scale.
Battaglin, W.A., and Goolsby, D.A., U.S. Geological
Survey
1994
Spatial data in GIS format on agricultural chemical use, land use,
and cropping practices in the United States
Vector digital data
U.S. Geological Survey Water-Resources Investigations
Report
U.S. Geological Survey Water-Resources Investigations
Report 94-4176
Lakewood, Colorado
U.S. Geological Survey
2,000,000
Online
1987
Based upon 1987 Census of Agriculture
cropping data
USGS WRIR 94-4176
Atrazine use for each county in Colorado
Cederstrand, J.R., and Becker, M.F., U.S. Geological
Survey
1999
Digital map of aquifer boundary for the High Plains aquifer in
parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South
Dakota, Texas, and Wyoming
Version 1.0
Vector digital data
U.S. Geological Survey Open-File Report
U.S. Geological Survey Open-File
Report 99-267
Oklahoma City, Oklahoma
U.S. Geological Survey
1000000
Online
1980
Other_Citation_Details These data were compiled from paper maps developed by McGrath
Online_Linkage https://water.usgs.gov/lookup/getspatial?ofr99-267
USGS OFR 99-267
One of three datasets used to delineate hydrogeomorphic regions
in Colorado.
Green, G.N., U.S. Geological Survey
1992
The digital geologic map of Colorado in ARC/INFO format
Version 1.0
Vector digital data
U.S. Geological Survey Open-File Report
U.S. Geological Survey Open-File
Report 92-507
Denver, Colorado
U.S. Geological Survey
These data were digitized from the original scribe sheets used
to prepare the published Geologic Map of Colorado
(Tweto, Ogden, 1979, Geologic map of Colorado: U.S. Geological
Survey, scale 1:500,000, 1 sheet.
https://geo-nsdi.er.usgs.gov/metadata/open-file/92-507
/metadata.faq.html
500,000
Online
1979
Based on 1979 geologic map
USGS OFR 92-507
One of three datasets used to delineate hydrogeomorphic
regions in Colorado.
David Lorenz, U.S. Geological Survey
2001
Estimates of nitrogen fertilizer use, 1997
Vector digital data
Data not formally published
Data not published
Mounds View, Minnesota
David Lorenz, U.S. Geological Survey
Unpublished data on file at U.S. Geological Survey
office, Mounds View, Minnesota
2,000,000
Online
1997
Based on 1997 estimates
Not formally published
Estimates of fertilizer use in each county of
Colorado during 1997.
Schwarz, G.E., and Alexander, R.B., U.S. Geological
Survey
1995
State Soil Geographic (STATSGO) database for the conterminous
United States.
Version 1.1
Vector digital data
U.S. Geological Survey Open-File Report
U.S. Geological Survey Open-File
Report 95-449
Reston, Virginia
U.S. Geological Survey
Soils data in this coverage were originally obtained from the
State Soil Geographic (STATSGO) database (U.S. Department of
Agriculture, 1991, State Soil Geographic (STATSGO) data base:
U.S. Department of Agriculture, Soil Conservation Service,
Miscellaneous Publication 1492, 88 p.). Schwarz and Alexander
(1995) performed weighted averaging of many of the soil
characteristics contained in the original STATSGO database.
https://water.usgs.gov/lookup/getspatial?ussoils
250,000
Online
1991
STATSGO data published in 1991
USGS OFR 95-449
Soils data for the State of Colorado
U.S. Geological Survey
2000
National land cover dataset
Version 20000909
Raster digital data
online data
online data
Sioux Falls, South Dakota
U.S. Geological Survey
Data should be considered preliminary because they were still
being assessed for accuracy at the time of this publication.
https://edc2.usgs.gov/lccp/nlcd/show_data.asp?code=CO&state=Colorado
30-meter GRID cells
Online
1992
Based on 1992 satellite imagery
NLCD
This dataset supplied land use/land cover data for the State of
Colorado.
U.S. Geological Survey
2001
Boundary of valley-fill aquifer in the lower Arkansas River
Basin
1
Vector digital data
not published
not published
Pueblo, Colorado
Data not published
Data not published. Data were digitized from original mylar sheets
produced by Hurr and Moore (1972, Hydrogeologic characteristics
of the valley-fill aquifer in the Arkansas River valley, Bent
County, Colorado: U.S. Geological Survey Hydrologic Investigations
Atlas HA-0461, scale 1:62,500, 2 sheets), Nelson, G.A., Hurr, R.T.,
and Moore, J.E. (1989a, Hydrogeologic characteristics of the
valley-fill aquifer in the Arkansas River Valley, Prowers County,
Colorado: U.S. Geological Survey Open-File Report 89-254,
scale 1:62,500, 3 sheets), Nelson, G.A., Hurr, R.T., and
Moore, J.E. (1989b, Hydrogeologic characteristics of the valley-fill
aquifer in the Arkansas River Valley, Crowley and Otero Counties,
Colorado: U.S. Geological Survey Open-File Report 89-255,
scale 1:62,500, 3 sheets), and Nelson, G.A., Hurr, R.T., and
Moore, J.E. (1989c, Hydrogeologic characteristics of the valley-fill
aquifer in the Arkansas River Valley, Pueblo County, Colorado:
U.S. Geological Survey Open-File Report 89-256, scale 1:62,500, 3 sheets).
None
62,500
digital
1989
Based on 1989 publications
not published
One of three datasets used to delineate hydrogeomorphic
regions in Colorado.
Projected all input datasets to a common projection and datum
(Colorado Albers, NAD 27)
20010330
The 30-meter NLCD GRIDS were too large for the computers available for
this study to manipulate in raw form, so the files were generalized to
60-meter resolution.
The "RESAMPLE" command with the "nearest neighbor assignment"
option in GRID was used to generalize the NLCD GRIDS to 60 meters.
20011120
One of the independent variables used in the logistic regression
models was the percentage of certain land-cover classifications within
500-meter and 2,000-meter buffers around each well. To transfer these
logistic regression models to the probability GRIDS, GRIDS were
constructed that contained the percentage of certain land-cover
classifications within 500-meter and 2,000-meter buffers around each
individual grid cell. These GRIDS were produced from the 60-meter NLCD
GRID produced by the previous step. These GRIDS were made in three
substeps.
1) First, make individual GRIDS coded as one for "land cover present"
and zero for "land cover not present" for the following land-cover
classifications: low-intensity residential, shrubland, pasture/hay,
row crops, and small grains land-cover classifications. As an example,
low-intensity residential land cover is coded as "21" in the NLCD
GRID, so the following equation was used in GRID to convert the
dataset:
low_res_g = con(nlcd_60m_g eq 21,1,0)
2) Second, add up the number of cells of low-intensity residential
cells in each buffer:
temp_num_g = focalsum(low_res_g,circle,33)
where 33 is the 2,000-meter radius in number of cells. Use 8 if you
are calculating 500-meter radius.
3) Third, calculate the percentage of low-intensity residential cells
by dividing the number of cells in each buffer by the total possible:
low_res_pct_g = (temp_num_g / float(3409)) * 100
where 3409 is the total number of 60-meter cells within a 2,000-meter
buffer. Use 197 if you are calculating 500-meter buffers.
20011203
Convert polygon coverages of atrazine use, fertilizer use,
hydrogeomorphic regions, and the various soils factors to 60-meter
GRIDS. Use the "setwindow" and "setcell" commands in GRID to assure
that all new GRIDS line up with the NLCD data, then use the "polygrid"
command to convert the coverages to GRIDS.
20020520
Construct new atrazine-use and fertilizer-use GRIDS where atrazine
and fertilizer use estimates are only assigned to agricultural lands;
all other land-cover categories are assigned values of zero. To do
this, construct grids that are assigned 1 for agricultural land cover
and zero for all other land-cover types. Multiply those GRIDS by the
original atrazine and fertilizer use GRIDS. The resultant GRIDS have
atrazine and fertilizer use estimates only for GRID cells in
agricultural lands.
20020521
Next, construct the actual probability GRIDS. The GRIDS were
constructed by calculating the probability of detecting
atrazine/desethyl-atrazine or nitrate in ground water using the
equation developed with logistic regression (see Rupert, 2003,
Probability of detecting atrazine/desethyl-atrazine and elevated
concentrations of nitrate in ground water in Colorado:
U.S. Geological Survey Water-Resources Investigations Report
02-4269, 35 p., https://water.usgs.gov/pubs/wri/wri02-4269/). The
following is an example of the logistic regression equation:
Prob = (e**(a + b*chem_use + c*land_cover + d*soils))/(1+e**(a + b*chem_use + c*land_cover + d*soils))
In other words, the probability of detecting the compound in ground
water is equal to "e raised to the regression equation" divided by
"one plus e raised to the regression equation," where "a," "b,"
"c," and "d" are the model coefficients calculated by logistic
regression.
The probability GRIDS were constructed in four steps. The first was
to calculate the regression equation:
"temp1 = (a + b*Chem_use + c*land_cover + d*soils)"
The second step was to calculate the actual probability value for
every 60-meter cell in Colorado, times 100 to convert it to percent:
"temp2 = 100 * (exp (temp1)/(1+exp(temp1))"
The third step was to clip out portions of the State that weren't
included in the model (only alluvial aquifers were mapped, so the
mountainous regions of the State were clipped out).
temp3 = temp2 * clip_grid
The fourth step was to set all the non-mapped grid cells to "null"
final_grid = setnull(temp3 eq 0, temp3)
The regression coefficients used for the eight probability GRIDS
constructed by this project are listed in Rupert (2003)
20020522
Randomly selected at least 20 GRID cells in each of the 8
probability GRIDS and calculated probability value by hand to ensure
that the probability values were correctly calculated.
20020523
First draft of metadata created by mgrupert using
FGDCMETA.AML ver. 1.36 01/16/01 on ArcInfo dataset
g:\metadata\atra_use_g
20030130
Metadata imported.
C:\DOCUME~1\MGRUPE~1.STA\LOCALS~1\Temp\xml3A.tmp
000000
Raster
Grid Cell
8353
13523
1
0.000617
0.000617
Decimal degrees
North American Datum of 1983
Geodetic Reference System 80
6378137.000000
298.257222
nit_nhyd_fert
ObjectID
Internal feature number.
ESRI
Sequential unique whole numbers that are automatically generated.
Value
Count
The values stored in the GRID cells equal the predicted probability of
detecting elevated concentrations of nitrate in ground water in
Colorado, in percent probability.
none
U.S. Geological Survey
Michael Ierardi
mailing
445 National Center
Reston
VA
20192
1-888-275-8747 (1-888-ASK-USGS)
mierardi@usgs.gov
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20201117
U.S. Geological Survey
Ask USGS -- Water Webserver Team
mailing
445 National Center
Reston
VA
20192
1-888-275-8747 (1-888-ASK-USGS)
mierardi@usgs.gov
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