Raster dataset showing the probability of elevated concentrations of nitrate in ground water in Colorado, hydrogeomorphic regions and fertilizer use estimates included

[摘要] This dataset is one of eight datasets produced by this study.Four of the datasets predict the probability of detectingatrazine and(or) desethyl-atrazine (a breakdown product of atrazine)in ground water in Colorado; the other four predict the probabilityof detecting elevated concentrations of nitrate in ground water inColorado. The four datasets that predict the probability ofatrazine and(or) desethyl-atrazine (atrazine/DEA) are differentiatedby whether or not they incorporated atrazine use and whetheror not they incorporated hydrogeomorphic regions. The four datasetsthat predict the probability of elevated concentrations of nitrateare differentiated by whether or not they incorporated fertilizeruse and whether or not they incorporated hydrogeomorphicregions. Each of the eight datasets has its own unique strengthsand weaknesses. The user is cautioned to read Rupert (2003, Probabilityof detecting atrazine/desethyl-atrazine and elevated concentrationsof nitrate in ground water in Colorado: U.S. Geological SurveyWater-Resources Investigations Report 02-4269, 35 p.,http://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 detectingelevated concentrations of nitrate in ground water in Colorado withhydrogeomorphic regions and fertilizer use included. The followingtext was extracted from Rupert (2003).Draft Federal regulations may require that each State develop aState Pesticide Management Plan for the herbicides atrazine,alachlor, metolachlor, and simazine. Maps were developed that theState of Colorado could use to predict the probability of detectingatrazine/DEA in ground water in Colorado. These maps can beincorporated into the State Pesticide Management Plan and can helpprovide a sound hydrogeologic basis for atrazine management inColorado. Maps showing the probability of detecting elevated nitriteplus nitrate as nitrogen (nitrate) concentrations in ground water inColorado also were developed because nitrate is a contaminant ofconcern in many areas of Colorado.Maps showing the probability of detecting atrazine/DEA at or greaterthan concentrations of 0.1 microgram per liter and nitrateconcentrations in ground water greater than 5 milligrams per literwere developed as follows: (1) Ground-water quality data were overlaidwith anthropogenic and hydrogeologic data by using a geographicinformation system (GIS) to produce a dataset in which each well hadcorresponding data on atrazine use, fertilizer use, geology,hydrogeomorphic regions, land cover, precipitation, soils, and wellconstruction. These data then were downloaded to a statisticalsoftware package for analysis by logistic regression. (2) Relationswere observed between ground-water quality and the percentage ofland-cover categories within circular regions (buffers) around wells.Several buffer sizes were evaluated; the buffer size that providedthe strongest relation was selected for use in the logistic regressionmodels. (3) Relations between concentrations of atrazine/DEA andnitrate in ground water and atrazine use, fertilizer use, geology,hydrogeomorphic regions, land cover, precipitation, soils, andwell-construction data were evaluated, and several preliminarymultivariate models with various combinations of independent variableswere constructed. (4) The multivariate models that best predictedthe presence of atrazine/DEA and elevated concentrations of nitratein ground water were selected. (5) The accuracy of the multivariatemodels was confirmed by validating the models with an independentset of ground-water quality data. (6) The multivariate models wereentered into a geographic information system and the probabilityGRIDS were constructed.

[发布机构] U.S. Geological Survey

[学科分类] 地球科学(综合)