Water balance of municipal wastewater irrigation in a coastal forested watershed

Abstract

In the southeastern U.S., coastal communities face challenges for water resources and wastewater treatment capacity. In North Carolina, fifty-one municipalities irrigate forests with municipal wastewater to absorb nutrients, reduce direct effluent discharge to surface waters, and recharge groundwater. Most facilities have land-applied wastewater for decades, but there are no quantitative studies on the hydrologic impacts of this practice. This study developed a simulated water balance for the largest forest land-application system in North Carolina which treats wastewater daily by irrigating 30 square kilometers of a mixed hardwood-loblolly pine forest. A distributed hydrological model (MIKE SHE) was adapted to simulate 20 years of watershed evapotranspiration (ET) and water table depth (WTD) under irrigated and non-irrigated conditions. We found that irrigation impact to annual and monthly WTD was negligible in years with average and above average rainfall. For wet years, drainage increased with irrigation, while ET and WTD remained similar to non-irrigated conditions. In dry years, ET was 31mm to 39 mm higher in irrigated forest than non-irrigated forest though the change in groundwater storage This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as