T. Grischek et al., FACTORS AFFECTING DENITRIFICATION DURING INFILTRATION OF RIVER WATER INTO A SAND AND GRAVEL AQUIFER IN SAXONY, GERMANY, Water research, 32(2), 1998, pp. 450-460
River infiltration into a sand and gravel aquifer was investigated to
assess the importance of dentrification in maintaining low-NO3- ground
water supplies. Samples from the River Elbe and groundwater sampling p
oints along a section of the aquifer were analysed for dissolved organ
ic carbon, major ions and the N-15/N-14 isotopic ratio of dissolved NO
3-. Input of NO3- to the aquifer is influenced by seasonal, temperatur
e-dependent denitrification in the river bed sediments. Along an upper
flowpath in the aquifer from the River Elbe to a sampling point at a
distance of 55 m, the median NO3- concentration decreased by 4.8 mg li
tre(-1) and the delta(15)N composition increased by + 9.0%, consistent
with denitrification. Similar isotopic enrichment was demonstrated in
a laboratory column experiment with a reduction in NO3- of 10.5 mg li
tre(-1) for an increase in delta(15)N of + 9.8%, yielding an isotopic
enrichment factor of -14.6%. A mass balance for denitrification shows
that oxidizable organic carbon required for denitrification is derived
from both the infiltrating river water and solid organic matter fixed
in the river bed sediments and aquifer material. (C) 1998 Elsevier Sc
ience Ltd. All rights reserved.