Kinetics and Temperature Dependence of Potential Denitrification in Riparian Soils

Abstract

AbstractWe studied factors influencing potential denitrification activity (PDA) in anaerobic soil samples amended with NO3− from a riparian meadow with agricultural uplands, and a reedswamp receiving nitrate‐containing creek water at two loading rates. Both sites had high levels of PDA (3–28 mg N kg−1 h−1), which decreased exponentially with depth. High correlations were seen between PDA and mineralizable and water soluble C. At the meadow site, high apparent Km values (29–51 µM N) were found in the upper 150 cm of the soil profile due to a lateral flow of nitrate‐rich water. Below this depth, Km values were 10 to 30 times lower due to the influence of nutrient poor groundwater. In the 0‐ to 10‐cm profile of the reedswamp soil, the highest apparent Km (89 µM N) was found on the high load site, while no differences between the high and low load sites were seen below this depth (range 0.6–11 µM N). The capacity to reduce nitrate (Vmax) was in the order riparian meadow ≅ high loaded reedswamp > low loaded reedswamp. The activation energy for PDA ranged from 47 to 89 kJ mol−1, and Q10 for the 5 to 15°C interval ranged from 2 to 3.8. Our data suggest that long‐term use of riparian areas to attenuate high loads of NO3− can increase the maximum NO3− removal capacity of these areas, but at the same time increase the concentration of NO3− in water leaving this area compared with water leaving low loaded sites.