Ecological Engineering 53 (2013) 89–99 Contents lists available at SciVerse ScienceDirect Ecological Engineering j ourna l ho me page: www.elsevier.com/locate/ecoleng A mesocosm study on biogeochemical role of rice paddy soils in controlling water chemistry and nitrate attenuation during infiltration Byoung-Young Choi a,b , Seong-Taek Yun a,∗ , Kangjoo Kim c , Kyoung-Ho Kim a , Jeong-Ho Lee a , Jin-Seok Han d a Department of Earth and Environmental Sciences and the KU-KIST Green School, Korea University, Seoul 136-701, South Korea b CO2 Sequestration Research Department, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, South Korea c School of Civil and Environmental Engineering, Kunsan National University, Jeonbuk 573-701, South Korea d National Institute of Environmental Research (NIER), Incheon, South Korea a r t i c l e i n f o Article history: Received 2 March 2012 Received in revised form 25 November 2012 Accepted 3 December 2012 Available online 23 December 2012 Keywords: Mesocosm Redox geochemistry Removal of agricultural nitrate Rice paddy soil a b s t r a c t Rice paddies typically lie near surface water and play an important role in controlling surface water qual- ity. To evaluate the role of rice paddy soils in determining the fate of nitrate, three different mesocosms were used in this study. Two mesocosms (M1 and M2) were covered with a rice paddy soil and the other mesocosm (M3) with a dry field soil. Rice was harvested in two mesocosms (M2 and M3) during the growing season. An amended groundwater containing high concentrations of NaNO 3 and KBr was repeatedly applied to the mesocosms to infiltrate under saturated conditions. Under these experimental conditions, we monitored time-series variations of pH, Eh, DO, DOC, alkalinity and the concentrations of nitrate, bromide (as a conservative tracer) and dissolved Fe and Mn in the inflow water (flooding water just below the water/soil interface) and outflow water (drained water after infiltration through meso- cosm materials) for about two months to examine the fate of nitrate. The Eh and DO data in all mesocosms showed that strong reducing conditions were rapidly and efficiently established in infiltrating waters. In the mesocosms (M1 and M2) with a rice paddy soil, dramatic decreases of nitrate concentrations were observed both in the inflow and outflow waters. Nitrate removal from the inflow waters occurs due to immobilization, while nitrate is removed during infiltration through mesocosm materials by denitrifica- tion coupled with organic carbon oxidation, as is indicated by the increases in alkalinity and dissolved Fe and Mn. Interestingly, there was no significant difference in the nitrate removal capacity between M1 (no cultivation) and M2 (rice cropping). In contrast to M1 and M2, there was no large decrease of nitrate concentrations in the inflow waters of M3 (rice cropping with a dry field soil). In addition, nitrate concen- trations in the outflow waters of M3 rose steeply again after 30 days, in concert with increasing Eh and decreasing alkalinity. These observations in M3 are attributed to both the low organic carbon content and the generation of large pores by root growth, resulting in the rapid loss of denitrification capacity. This study implies that rice paddy fields play an important role in controlling (attenuate) agricultural nitrate in groundwater discharging to streams; thus, the extent of rice paddies should be carefully considered when evaluating the nitrate loads to streams via groundwater flow. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Over the last few decades, the deterioration of natural water quality by agricultural activities has been of great concern in many countries. The excessive application of nitrogen-bearing chemical fertilizers and manure on agricultural fields has increased the con- centrations of nitrate in surface water and groundwater (Spalding ∗ Corresponding author. Tel.: +82 2 32903176; fax: +82 2 3290 3189. E-mail address: styun@korea.ac.kr (S.-T. Yun). and Exner, 1993; Zebarth et al., 1999; Di and Cameron, 2002; Agyin- Birikorang et al., 2012). The presence of nitrate in groundwater is considered to be an indicator of water resource sustainability. High concentrations of nitrate in groundwater can cause adverse effects on human health (e.g., ‘blue baby’ disease and potentially gastric cancer) and may contribute to the eutrophication of nearby sur- face water (Jacobs and Gilliam, 1985; Fleming and Adams, 1997; Chapelle, 2001; Buzek et al., 2009). However, nitrate also can be naturally reduced by denitrification in reducing environments (Appelo and Postma, 1993; Xu et al., 1997; Mosier et al., 1998; Cey et al., 1999; Kim et al., 2009; Vilain et al., 2012). 0925-8574/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2012.12.017