{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,6]],"date-time":"2026-03-06T19:05:29Z","timestamp":1772823929036,"version":"3.50.1"},"reference-count":53,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2016,1,13]],"date-time":"2016-01-13T00:00:00Z","timestamp":1452643200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/2.zoppoz.workers.dev:443\/https\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000139","name":"United States Environmental Protection Agency","doi-asserted-by":"publisher","award":["EPA 319(h)"],"award-info":[{"award-number":["EPA 319(h)"]}],"id":[{"id":"10.13039\/100000139","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000066","name":"National Institute of Environmental Health Sciences","doi-asserted-by":"publisher","award":["grant 5R01ES015634"],"award-info":[{"award-number":["grant 5R01ES015634"]}],"id":[{"id":"10.13039\/100000066","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Texas A&amp;M support","award":["a\/c 02130003"],"award-info":[{"award-number":["a\/c 02130003"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>Nitrate-N (NO3 -- N) is one of the most pervasive contaminants in groundwater. Nitrate in groundwater exhibits long-term behavior due to complex interactions at multiple scales among various geophysical factors, such as sources of nitrate-N, characteristics of the vadose zone and aquifer attributes. To minimize contamination of nitrate-N in groundwater, it is important to estimate hot spots (&gt;10 mg\/L of                                        NO3 -- N), trends and persistence of nitrate-N in groundwater. To analyze the trends and persistence of nitrate-N in groundwater at multiple spatio-temporal scales, we developed and used an entropy-based method along with the Hurst exponent in two different hydrogeologic settings: the Trinity and Ogallala Aquifers in Texas at fine (2 km \u00d7 2 km), intermediate (10 km \u00d7 10 km) and coarse (100 km \u00d7 100 km) scales. Results show that nitrate-N exhibits long-term persistence at the intermediate and coarse scales. In the Trinity Aquifer, overall mean nitrate-N has declined with a slight increase in normalized marginal entropy (NME) over each decade from 1940 to 2008; however, the number of hot spots has increased over time. In the Ogallala Aquifer, overall mean nitrate-N has increased with slight moderation in                                        NME since 1940; however, the number of hot spots has significantly decreased for the same period at all scales.<\/jats:p>","DOI":"10.3390\/e18010025","type":"journal-article","created":{"date-parts":[[2016,1,13]],"date-time":"2016-01-13T22:19:54Z","timestamp":1452723594000},"page":"25","update-policy":"https:\/\/2.zoppoz.workers.dev:443\/https\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Hot Spots and Persistence of Nitrate in Aquifers Across Scales"],"prefix":"10.3390","volume":"18","author":[{"given":"Dipankar","family":"Dwivedi","sequence":"first","affiliation":[{"name":"Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Binayak","family":"Mohanty","sequence":"additional","affiliation":[{"name":"Biological and Agricultural Engineering Department, Texas A&amp;M University, College Station, TX 77843, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2016,1,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1985","DOI":"10.1126\/science.1067123","article-title":"Flow and storage in groundwater systems","volume":"296","author":"Alley","year":"2002","journal-title":"Science"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"37","DOI":"10.1016\/S0022-1694(99)00206-1","article-title":"Regional trends in nitrate content of Texas groundwater","volume":"228","author":"Hudak","year":"2000","journal-title":"J. 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