New Zealand Journal of Marine and Freshwater Research abstracts

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Low flow water chemistry in forested and pasture catchments, Mawheraiti River, Westland

M. P. MOSLEY*

L. K. ROWE

Forest Research Institute New Zealand Forest Service P.O. Box 31 Oil Christchurch, New Zealand

Abstract Water samples taken at 19 locations in the Mawheraiti River catchment at weekly intervals during 1979-80 were analysed for sodium, magnesium, potassium, calcium, phosphate, nitrate, and ammonium ion concentrations and for electrical conductivity. Seasonal discharge effects were apparent, and lithology and land management practice also influenced solute concentrations. Solute concentrations were generally very low; nitrate and soluble phosphate were rarely greater than 0.05 mg.L"¹ and ammonium was rarely greater than 0.01 mg.L"¹. The 4 major cations (Na, Mg, K, and Ca) usually summed to less than 6 mg.L~\ much of which was supplied by precipitation. Forest management (clearfelling and slash-burning) caused significant increases in solute concentrations, but concentrations declined rapidly during succeeding months and approached pretreatment levels after 2-3 years. The higher concentrations associated with forest management in small experimental catchments were rapidly diluted downstream; together with the low natural solute concentrations this suggests that harmful downstream effects of management practices are unlikely under low flow conditions.

Keywords Mawheraiti River; forests; pasture; harvesting; burning; stream flow; water analysis (chemical); calcium; magnesium; sodium; potassium; nitrate; phosphate; ammonium.

New Zealand Journal of Marine and Freshwater Research, 1981, Vol. 15 : 307-320 Received 21 January 1981

PDF file of entire paper: medium quality (1037K); (scanned from paper original: notes about this process)

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