Slow-Release Fertilizer for Rehabilitating Oligotrophic Streams: a Physical Characterization

摘要

A combination of habitat degradation and overharvesting of anadromous salmonids in many of B.C.'s oligotrophic watersheds has prompted the addi- tion of inorganic nutrients to streams, which increases autotrophic production and aids in the restoration of salmonid production. A new slow-release fertilizer (7-40-0, N-P_2O_5-K_2O, percent by weight) was examined to determine its phos- phate (PO_4~3-) release rates using laboratory and field trough experiments. A series of indoor trough experiments indicated that the fertilizer pellet dissolu- tion rate (0.393 g·days~(-0.401)) was independent of the experimental range of water velocity (0.03-0.30 m· s~(-1)), fertilizer pellet size (2-9 g) and water tempera- ture (8-14.5?). Resulting phosphate additions (0.5-5 μg P· L~(-1)) in outdoor trough experiments increased periphyton biomass and altered the dominance pattern of periphytic diatoms. An optimal phosphate concentration for peri- phyton biomass was achieved with calculated 3.0 μg P· L~(-1) phosphate additions from May to June. In June to July, periphyton biomass increased proportion- ately to fertilizer additions. Saturation of the relative specific growth rate of the diatom community occurred with 1.0 μg P· L~(-1) phosphate additions. Nitrogen analysis was not conducted since inorganic nitrogen is typically available in non- limiting concentrations (i.e., >50 μg· L~(-1) dissolved inorganic nitrogen) in the majority of B.C.'s oligotrophic salmonid streams. These studies indicated that slow-release fertilizer may be effective in stimulating autotrophic production and restoring salmonid production in nutrient deficient sreams.