『Abstract
　This study focuses on denitrification in a sandy aquifer using geochemical analyses of both sediment and groundwater, combined with groundwater age dating (³H/³He). The study sites are located underneath cultivated fields and an adjacent forested area at Oostrum, The Netherlands. Shallow groundwater in the region has high nitrate concentrations (up to 8 mM) due to intense fertilizer application. Nitrate removal from the groundwater below cultivated fields correlates with sulfate production, and the release of dissolved Fe²⁺ and pyrite-associated trace metals (e.g. As, Ni, Co and Zn). These results, and the presence of pyrite in the sediment matrix within the nitrate removal zone, indicate that denitrification coupled to pyrite oxidation is a major process in the aquifer. significant nitrate loss coupled to sulfate production is further confirmed by comparing historical estimates of regional sulfate and nitrate loadings to age-dated groundwater sulfate and nitrate concentrations, for the period 1950-2000. However, the observed increases in sulfate concentration are about 50％ lower than would be expected from complete oxidation of pyrite to sulfate, possibly due to the accumulation of intermediate oxidation state sulfur compounds, such as elemental sulfur. Pollutant concentrations (NO3, Cl, As, Co and Ni) measured in the groundwater beneath the agricultural areas in 1006 and 2006 show systematic decreases most likely due to declining fertilizer use.』

1. Introduction
2. Materials and methods
　2.1. Sampling location
　2.2. Sample collection and chemical analyses
3. Results
　3.1. Groundwater and sediment geochemistry
　3.2. Groundwater ages
4. Discussion
　4.1. Groundwater ages
　4.2. Denitrification coupled to pyrite oxidation
　4.3. Temporal changes
　4.4. Net reaction stoichiometry
　4.5. Denitrification rates
5. Conclusions
Acknowledgments
Appendix A. Supplementary data
References