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Abstract

A new slow-release fertilizer has been developed to restore productivity in nutrient deficient streams. The product (7-40-0; N-P₂O₅-K₂O) was studied to determine physical and chemical conditions which might inhibit phosphate release. In laboratory analyses, hardness (> 40 mg Ca²⁻-L⁻¹) and humic material (> 100 colour units) complexed phosphate and inhibited its dissolution from the pellets; pH, alkalinity and iron had less effects on phosphate solubility. A series of indoor trough experiments indicated fertilizer dissolution was independent of velocity (0.15-0.30 m/s), pellet size (2-9 g) and water temperature (8-14.5 °C). Fertilizer treatments (0.5-5 μg P L⁻¹) in outdoor trough experiments increased periphyton abundance and altered the dominant diatom species. A saturation level for periphyton growth and biomass was achieved at ~ 1.0 μg L⁻¹ orthophosphate from May- June; in June-July growth and biomass increased proportionally to fertilizer additions. Relationships developed during these controlled experiments demonstrate streams having < 40 mg L⁻¹ calcium, < 100 colour units and ranges within other variables tested are optimal for slow-release fertilizer additions.