Thermodynamic Reformulation of Water Quality Indices: A Gibbs Free Energy Approach for Philippine Coastal Waters

Thermodynamic Reformulation of Water Quality Indices: A Gibbs Free Energy Approach for Philippine Coastal Waters | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thermodynamic Reformulation of Water Quality Indices: A Gibbs Free Energy Approach for Philippine Coastal Waters perry neil fernandez, elaine grace fernandez This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6634937/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This research compares the DENR-WQI framework by the Philippine Department of Environment and Natural Resources (DENR) with a new thermodynamic-based Gibbs-WQI method using surface water data collected from Iloilo City, Philippines. The Gibbs-WQI was developed to investigate cases where coastal waters labeled as suitable by the DENR-WQI displayed fecal coliform levels that exceedingly surpassed legal limits. The Gibbs-WQI uses entropy-based calculations to evaluate deviations from ideal reference states which helps detect anomalies dynamically. The analysis of 287 surface water samples included key parameters such as fecal coliform, phosphate, and dissolved oxygen through computational methods implemented in Python. The Gibbs-WQI system tended to place samples initially classified as Class SB or SC by the DENR-WQI into poorer quality categories when fecal coliform concentrations surpassed 5,000 MPN/100 mL. The Chi-square statistical test ( χ = 134.43 and p = 0) demonstrated a highly significant difference between the two indices. The Cohen’s Kappa coefficient value of 0.321 showed that there was only fair agreement between the classification systems. While DENR-WQI meets regulatory standards the study reports that Gibbs-WQI offers improved real-time environmental responsiveness. The study recommends combining both indices to achieve optimal monitoring and management outcomes. Predictive modeling in water quality management requires future research to explore both temporal-spatial analysis and the incorporation of machine learning techniques. water quality monitoring water quality index ecological modeling coastal management Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6634937","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":456903057,"identity":"a04459d6-238b-493d-92e6-2d2c6e5c091c","order_by":0,"name":"perry neil fernandez","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8klEQVRIiWNgGAWjYFCCgw8g9AEGxgdQBgMzfi2HDWBamA2I1MIM18ImQZQWc8bDjI8rd9jl8R1vf1bNu4NBju9GAtvjAjxaLBsOMxuePZNcLHnmQNpt3jMMxpI3EtiNZ+DRYnDg/DHJxjbmxA03Eo7d5m1jADHYpHnwajnM/rOxrT5xw/2HbcVALfXEaGFjbGw7DDScmY0ZqCXBgJAWkF+ADjueOPNMGrPk3DMShjPPPGw3xqfFXOIw48fGturEvuPHH354u8NGnu948rHHeB0mcQCJx9gAihrGNjwagFr4G1C0gCk2vFpGwSgYBaNgxAEA/fhVE//Eeh8AAAAASUVORK5CYII=","orcid":"","institution":"University of the Philippines Visayas","correspondingAuthor":true,"prefix":"","firstName":"perry","middleName":"neil","lastName":"fernandez","suffix":""},{"id":456903058,"identity":"77428246-13c7-4552-ab5e-dd7ebb32397b","order_by":1,"name":"elaine grace fernandez","email":"","orcid":"","institution":"Department of Economy, Planning, and Development","correspondingAuthor":false,"prefix":"","firstName":"elaine","middleName":"grace","lastName":"fernandez","suffix":""}],"badges":[],"createdAt":"2025-05-10 13:08:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6634937/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6634937/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86026680,"identity":"6d6ccc43-0276-4865-9266-4fd4dc9696a3","added_by":"auto","created_at":"2025-07-04 13:16:49","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":415021,"visible":true,"origin":"","legend":"","description":"","filename":"gibbs.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6634937/v1_covered_8abb0372-585b-4b58-8bcc-9c32cc70fc7e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thermodynamic Reformulation of Water Quality Indices: A Gibbs Free Energy Approach for Philippine Coastal Waters","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"water quality monitoring, water quality index, ecological modeling, coastal management","lastPublishedDoi":"10.21203/rs.3.rs-6634937/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6634937/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"This research compares the DENR-WQI framework by the Philippine Department of Environment and Natural Resources (DENR) with a new thermodynamic-based Gibbs-WQI method using surface water data collected from Iloilo City, Philippines. 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