Seasonal groundwater nitrate dynamics in a riparian buffer zone

Nitrate residue measurements, groundwater NO3- and chloride (Cl-) concentration patterns and delta(15)N-NO3- data were used to evaluate groundwater nitrate dynamics in a vegetated riparian buffer strip. Within the riparian zone, shallow groundwater surveys (< 2 m) showed a temporal and spatial variation of nitrate concentrations. Nitrate concentrations on the input side of the riparian zone peaked in autumn after harvest (up to 22 mg NO3- -N.L-1) and continued to be high during winter and spring. In all seasons, nitrate concentrations could be reduced to below 5 mg NO3- -N.L-1 over a short distance (< 12 m). As NO3- concentrations in the groundwater of the riparian zone decreased during its flow through the riparian zone, a progressive enrichment in delta(15)N-NO3- was observed. Consequently, denitrification could be identified as a significant process for NO3- retention.