Dissolved coloured compounds and suspended matter in the waters of the middle Waikato River

Abstract

Concentrations of suspended matter and filtrable hydroxylated aromatic compounds (HAC) together with turbidity and light absorbance measurements at 270 and 750 nm are reported for monthly samples, over one year, of water from the tailraces of the nine hydroelectric power stations on the Waikato River, North Island, New Zealand. Between Lakes Aratiatia and Karapiro the suspended matter concentrations increase 3-fold. The concentrations of HAC increase only slightly in all lakes except Lake Maraetai where a 3-fold increase occurs because of Kraft bleach effluent from the New Zealand Forest Products Limited, Kinleith Mill. This effluent also causes a marked increase in the absorbance at 270 nm, a measure of the brown colour attributable to dissolved organic compounds. The HAC in the effluent are linearly related to absorbance at 270 nm. The use of these easily measured parameters for detecting changes in water appearance, i.e., colour and clarity, are discussed. Measurements of light scattering, either turbidity or absorbance, appear to have sufficient sensitivity to detect changes in relative water clarity. The ratio of inorganic to organic suspended matter increases down the river and measurements of these two components could be used to detect changes in water appearance resulting from changes in the suspended matter composition. The absorbance at 270 nm of filtered water is a convenient and sensitive indicator of dissolved colour but a range of unidentified compounds contribute to this absorbance and for control of the brown coloration caused by timber processing effluents, limits on the discharge of HAC may be more useful.

Lithium and rubidium in the Waikato River, New Zealand

“…4). These results for the Waikato River are consistent with those reported previously (Timperley 1979).…”

“…In this section of the river, therefore, the concentrations of conservative elements such as Li and Rb would not change substantially throughout the year. This has been demonstrated for Na and K (Timperley 1979).…”

“…Suspended solids Dry weight concentrations of river water suspended solids in the reservoirs were reported by Timperley (1985) and these data, together with particulate metal concentrations from our study, allowed estimates of alkali metal concentrations in dry suspended solids. The average concentrations (+ s.d.)…”

“…1) other inflows of geothermal fluids exist; those from Ohaaki, the Waiotapu Stream, and Orakei Korako are of substantial magnitude. Several geothermal fields occur in the river catchment below Lake Ohakuri but the fluid escaping from these fields is not sufficient to cause measurable changes to the river water chemistry (Timperley 1979).…”

“…Several authors have studied the concentrations of arsenic in components of the river system (Reay 1973;Timperley 1979;Aggett & Aspell 1980) and a model for some aspects of this element's behaviour in the river has been proposed (Aggett & O'Brien 1985). The Waikato River catchment showing sampling sites for water and macrophytes at the eight reservoir dams (2-10), at the Lake Taupo outlet (1), in the Waipa River (12), and at four sites on the lower Waikato River (11,(13)(14)(15).…”