The profile distributions of NO3-N for both 4
microbial processes to occur that will promote the
and 10 mg/L NO3-N exhibited high initial con-
metabolism of added organic material.
centrations of NO3-N, essentially equivalent to that
Like all dynamic simulation models that de-
in the applied wastewater, in the upper profile (Fig.
scribe a series of complex, interrelated processes,
5). During the cycle, NO3-N levels decreased as
WASTEN estimates the impacts that might result
denitrification proceeded.
from changing input variables. The results from
A high, uniform initial ammoniacal-N con-
model simulations provide insight into the trends
centration of 5.0 mg/L NHx-N in the soil profile
and direction of potential outcomes resulting from
was also tested to demonstrate the release of NH4-
changing conditions. The model output is a legiti-
N from the 150-cm profile. For this simulation the
mate means to express magnitude and direction,
nitrification coefficient was set to zero, thereby
but it does not necessarily represent the exact val-
forcing all NH4-N to leach. After an initial release
ues that will be measured in the field. This con-
the NH4-N had relatively insignificant effects on
cept can be appreciated by considering the diffi-
N concentrations in the leachate (Fig. 6a). Due to
culty in accurately measuring existing properties
cation exchange processes between the soil and
and concentrations in field samples. Nevertheless
NH4-N cations, movement of NH4-N is slow in
the validity and utility of using models to estimate
the impact of different design and operation op-
the soil profile (Fig. 6b). Even starting with a high,
tions is well accepted.
uniform distribution and setting model parameters
to allow leaching as the only loss pathway, as was
done in the simulation, N contributions to the
leachate were diffused over an extended time and
LITERATURE CITED
therefore made relatively minor contributions to
Benes, V., V. Pekny, J. Skorepa and J. Vrba (1989)
leachate N levels.
Impact of diffuse nitrate pollution sources on
groundwater quality--some examples from
Soil-water potential
Czechoslovakia. Environmental Health Perspectives,
Soil-water potential, expressed in tension val-
83: 524.
ues, are shown in Figure 7. At lower soil depths
Burford, J.R. and J.M. Bremner (1975) Relation-
the soil remains essentially saturated. In the up-
ships between the denitrification capacities of soils
per soil profile, above approximately 75 cm, the
soil cycles between saturated and unsaturated con-
and total, water soluble, and readily decompos-
ditions. It is the cycling conditions in the vadose
able soil organic matter. Soil Biology and Biochemis-
zone that allow both aerobic and anaerobic pro-
try, 7: 389394.
cesses to readily occur.
In Nitrogen in Agricultural Soils, (F.J. Stevenson,
Ed.). Agronomy 22, p. 289326.
Gamble, T.N., M.R. Betlach and J.M. Tiedje (1977)
RECOMMENDATIONS
Numerically dominant denitrifying bacteria from
Wastewater treatment in soil by land applica-
world soils. Applied Environmental Microbiology, 33:
tion is a proven and effective technology. In addi-
926939.
tion to cost benefits, soil has a natural ability to
Gilliam, J.W. and R.P. Gambrell (1978) Tempera-
recover from a wide variety of stresses it may en-
ture and pH as limiting factors in loss of nitrate
counter. Denitrification, the major microbial pro-
from saturated Atlantic Coastal Plain soils. Journal
cess for reducing NO3-N, is well documented and
of Environmental Quality, 7: 526532.
occurs in virtually all soils under appropriate con-
Green, R.E. and J.C. Corey (1971) Calculation of
ditions.
hydraulic conductivity: A further evaluation of
Because denitrification is driven by microbial
some predictive methods. Soil Science Society of
processes, it is carbon dependent. Eliminating all
America Proceedings, 35: 38.
carbon from the applied wastewater could inhibit
Iskandar, I.K. (1978) The effect of waste water re-
denitrification. Hence, excessive removal of all or-
use in cold regions on land treatment systems. Jour-
ganics from the wastewater could be detrimental
nal of Environmental Quality, 7(3): 361368.
for nitrogen treatment. The alternating wetdry,
Klemedtsson, L., B.H. Swenson, T. Lindberg and
aerobicanaerobic conditions that will occur in the
T. Rosswall (1978) The use of acetylene inhibition
vadose zone should provide for a wide range of
of nitrous oxide reductase in quantifying denitri-
9
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