KINETICS AND TEMPERATURE-DEPENDENCE OF POTENTIAL DENITRIFICATION IN RIPARIAN SOILS

We studied factors influencing potential denitrification activity (PDA ) in anaerobic soil samples amended with NO3- from a riparian meadow w ith 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, Hig h correlations were seen between PDA and mineralizable and water solub le C. At the meadow site, high apparent K-m values (29-51 mu M N) were found in the upper 150 cm of the soil profile due to a lateral flow o f nitrate-rich water, Below this depth, K-m 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 K-m (89 mu M 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 mu M N). The capacity to reduce nitrate (V-max) was in the order riparian meadow congruent to high loaded reedswamp > low loaded reedswamp, The activation energy for PDA ranged from 47 to 89 kJ mol(-1), and Q(10) f or the 5 to 15 degrees C interval ranged from 2 to 3.8, Our data sugge st that long-term use of riparian areas to attenuate high loads of NO3 - can increase the maximum NO3- removal capacity of these areas, but a t the same time increase the concentration of NO3- in water leaving th is area compared with water leaving low loaded sites.