Title: Modeling Monthly Nitrate Concentration in a Karst Spring with and without Discrete Conduit Flow

Abstract

Understanding the coupled continuum pipe-flow framework for modeling contaminant transport in karst systems is critical for protecting water resources therein. This study simulated point and non-point source nitrate concentration in a karst spring and investigated the results generated from the flow and transport model with and without discrete conduit flow. CFPv2 and CMT3D models were integrated to address the changes in nitrate concentration at a monthly scale in a karst spring, and the results were compared with that from an equivalent porous media (EPM) model with high-hydraulic conductivity (K) zones set in the main karstified area to represent conduits. The results show that the CFPv2+CMT3D model is able to describe well the recession of nitrate concentration in spring discharge, and the relatively larger deviation (slower nitrate recession) from the observed trend for the EPM model is probably a result of the limitation of utilizing high hydraulic conductivity cells to represent conduit. Moreover, simulated hydraulic heads in poorly karstified areas from the two models both show slight differences from the observations (the head RMSE values of calibration/validation for CFPv2 and MODFLOW models are 0.16 m/0.25 m and 0.26 m/0.17 m, respectively), indicating the inclusion of conduits may not affect the simulationmore » considerably, and the lower the proportion of karstic area, the slight effects brought from the inclusion of conduits in the model. For highly karstified areas, the CFPv2+CMT3D model could provide more accurate results (head RMSE of calibration/validation for CFPv2 and MODFLOW are 0.22 m/0.06 and 0.52 m/0.47 m, respectively), showing the coupled continuum pipe-flow framework may be more appropriate for applying to highly and maturely karstified areas where the variations in the behavior of flow and contaminant transport are more affected by turbulent flow regime.« less

Authors:

Gao, Yuan ^[1]; Xu, Zexuan ^[2]; Li, Shen ^[1]; Yu, Wenjie ^[1]

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+ Show Author Affiliations

1. Xinjiang University, Urumqi (China)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Publication Date:

Wed May 18 00:00:00 EDT 2022

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); Doctor Scientific Research Startup Foundation of Xinjiang University; Natural Science Foundation of Xinjiang Uygur Autonomous Region; Florida Department of Transportation

OSTI Identifier:

1894314

Grant/Contract Number:  

AC02-05CH11231; 620321004; 2022D01C40

Resource Type:

Accepted Manuscript

Journal Name:

Water (Basel)

Additional Journal Information:

Journal Name: Water (Basel); Journal Volume: 14; Journal Issue: 10; Journal ID: ISSN 2073-4441

Publisher:

MDPI

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; karst aquifer; conduit flow process; nitrate; spring