New Zealand Journal of Marine and Freshwater Research abstracts

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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

PDF file of entire paper: medium quality (915K); (scanned from paper original: notes about this process)

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