New Zealand Journal of Marine and Freshwater Research abstracts
Characterisation of lowland streams
using a single-station diurnal curve analysis model
with continuous monitoring data for dissolved oxygen
and temperature
ROBERT J. WILCOCK
JOHN W. NAGELS
GRAHAM B. MCBRIDE
KEVIN J. COLLIER
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 11 115
Hamilton, New Zealand
BRENT T. WILSON
BEAT A. HUSER
Environment Waikato
P. O. Box 4010
Hamilton East, New Zealand
Abstract Twenty-three lowland streams throughout the Waikato
region, New Zealand, in catchments having a wide range of land uses and
intensities, were monitored continuously over 3-4-day periods for changes in
dissolved oxygen (DO) and temperature. A single-station diurnal curve model,
DOFLO (Dissolved Oxygen at Low Flow), was used to produce reach-averaged values
for: K2(20), the reaeration coefficient at 20deg.C; Pmax., the
maximum daily rate of photosynthetic production of oxygen; R20, the
daily respiration rate at 20deg.C; and Q10, the ratio of respiration
rates 10deg.C apart. In addition, 24-h average values for the ratio P/R
were calculated and maximum and minimum values of DO and temperature tabulated
for each site. Values of K2(20) (0.05-40 d-1, median 6.0
d-1) were in broad agreement with values calculated using a modified
form of the O'Connor-Dobbins equation. Values of gross primary production in
daylight (0.5-29.2 g m-2 d-1) calculated from
Pmax. (1.75-86.5 g m-3 d-1) were similar to data
reported for other streams in agriculturally developed catchments in New
Zealand and North America. Respiration rates (3.50-55.0 g m-3
d-1) were generally larger than values reported in the literature,
and P/R ratios were mostly well below 1.0, indicative of
heterotrophic respiration associated with decaying vegetation and other organic
inputs and consistent with diurnal DO excursions of 40 to >=120% saturation
being commonly observed. Maximum daily temperatures up to 25.7deg.C (median
20.5deg.C) were weakly negatively correlated with DO minima. Five groupings of
streams were identified from DOFLO parameter values, with K2(20) being
most critical in regulating average DO deficits.
Keywords dissolved oxygen; temperature; lowland stream;
agriculture; diurnal curve analysis
New Zealand Journal of Marine and Freshwater Research, 1998, Vol. 32:
67-79
0028-8330/98/3201-0067 $7.00/0 (c) The Royal Society of New Zealand
1998
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