Stoichiometric Determination of Nitrate Fate in Agricultural Ecosystems during Rainfall Events

Ecologists have found a close relationship between the concentrations of nitrate (NO(3) (-)) and dissolved organic carbon (DOC) in ecosystems. However, it is difficult to determine the NO(3) (-) fate exactly because of the low coefficient in the constructed relationship. In the present paper, a negative power-function equation (r (2) = 0.87) was developed by using 411 NO(3) (-) data points and DOC:NO(3) (-) ratios from several agricultural ecosystems during different rainfall events. Our analysis of the stoichiometric method reveals several observations. First, the NO(3) (-) concentration demonstrated the largest changes when the DOC:NO(3) (-) ratio increased from 1 to 10. Second, the biodegradability of DOC was an important factor in controlling the NO(3) (-) concentration of agricultural ecosystems. Third, sediment was important not only as a denitrification site, but also as a major source of DOC for the overlying water. Fourth, a high DOC concentration was able to maintain a low NO(3) (-) concentration in the groundwater. In conclusion, this new stoichiometric method can be used for the accurate estimation and analysis of NO(3) (-) concentrations in ecosystems.