Temporal patterns of total ammonia (T-NH3) in the upper layers of an ammoni
a-polluted, saline, hypereutrophic urban lake, Onondaga Lake, New York, and
its status with respect to ammonia toxicity criteria are documented and ev
aluated for the spring to fall interval over 10 years (1989 to 1998). Impli
cations of revisions (n = 5) in the criteria (1985 to 1999) and the omissio
n of ionic strength effects in the most recent revisions for this saline sy
stem are considered. The implications of diurnal variations in pH for appli
cation of both chronic and acute criteria are illustrated based on 14 days
of hourly pH data. Concentrations of T-NH3 in the upper layers of this lake
were extremely high because of discharges received from a 3.5 m(3)/s (80 m
gd) wastewater treatment plant; the average concentration during the April
to June interval for the 10 years was 2.3 mg/L. Substantial interannual and
seasonal variations were observed in the T-NH3 pool of the lake. April con
centrations were largely regulated by the dilution provided by antecedent (
i.e., December to March) tributary flow.
Revisions of the chronic criteria have been progressively less stringent fo
r low ionic strength conditions. However, under the saline conditions of th
is lake, the most recent (1998 and 1999) revisions can be more stringent th
an the earlier criteria. The 1984 chronic criterion (published in 1985) was
exceeded by a wide margin annually (average factor of 2.2 for April to Jun
e) and for durations greater than 75 days. Widely different diurnal pattern
s in pH and the occurrence of an exceedance of the 1998 acute criterion dur
ing a pH maximum are documented. These diurnal variations are an important
factor in the design of programs to assess status and in application of cri
teria for productive systems.