A Multi‐Scale Analysis of Nitrate Concentration‐Discharge Relationships in a Small Agricultural Watershed

Abstract Applying a nested watershed framework to concentration‐discharge ( cQ ) relationships provides insight into how solute transport dynamics vary across spatial and temporal scales. We examined nitrate‐N cQ relationships at two nested sites within a small agricultural watershed using 3 years of 30‐min data. Composite (all data) and event‐scale responses were evaluated using multiple metrics, including the flushing index (FI), hysteresis index (HI), cQ slope ( b ) and CV C / CV Q . Random forest models were used to identify hydrologic controls on inter‐event variability and spatial consistency in cQ behavior. Composite relationships showed nitrate‐N enrichment, while event‐scale patterns were dominated by dilution, a discrepancy due in part to nitrate‐N enrichment during storm recession. Antecedent moisture primarily governed inter‐event variability in FI and b , while storm magnitude more strongly regulated HI. Rising limb (FI) responses were generally more consistent across sites, while whole‐event ( b ) and hysteresis (HI) behavior exhibited greater divergence, particularly under dry antecedent conditions. Spatial consistency increased when hydrologic connectivity was high, either due to wet antecedent conditions or high‐intensity storms that rapidly activated flow networks. These findings underscore the need for multi‐scale, event‐based monitoring to improve water quality prediction.