During the austral summer of 1990 an intense, diatom-dominated, ice-edge phytoplankton bloom in the southwestern Ross Sea resulted in depletion of silicic acid, nitrate and phosphate to concentrations much lower than is typical for Antarctic surface waters. Silicic acid was depleted to <6 FM within the core of the meltwater field, where biogenic particulate silica concentrations exceeded 20 pm01 1-' Three Si uptake kinetic experiments were conducted on natural phytoplankton assemblages from the nutrient-depleted zone; 30Si-labeled Si(OH), was used to measure the uptake rate at concentrations ranging from 1 to 20 PM above ambient. Dependence of the spec~fic uptake rate ( V ) on silicic acid concentration conformed well to a Michaelis-Menten saturation model; maximum uptake rates (V,,,,,) ranged from 0.0022 to 0.0028 h-' which corresponds to maximum growth rates of 0.08 to 0.10 doublings d-l. Half-saturation constants (km) ranged from 1.1 to 4.6 PM, a range similar to values found in other areas of the ocean and considerably lower than those previously reported for several Antarctic d~atom species in culture studies. Results indicate detectable, but weak, substrate limitation of s~llcic acid uptake rate by the naturally occurring diatom assemblage in the western Ross Sea. Significant Si limitation in other subsystems of the Southern Ocean would be possible only if their resident diatom assemblages had much lower affinity for silicic acid than we observed.
Potato (Solanum tuberosum) production in Canada and the United States totals approximately 30 × 106 Mg yr-1. Approximately half of this is unsuitable for human consumption. This potato by-product comprises cull potatoes and potato processing waste (PPW). Liquid waste from processing plants can be applied to agricultural land. With strict environmental monitoring and control, crops such as corn (Zea mays L.), vegetables and grass can be used to divert large volumes of liquid waste. Solid waste and culls have traditionally been put in landfills or disposed of on agricultural land as a fertilizer. However these can be diverted from landfill sites or agricultural land and used as a high-quality animal feed, principally in beef feedlots. Research has shown that PPW can replace corn and barley (Hordeum vulgare L.) grain without negative effects on growth of beef cattle or meat quality. Indeed, efficiency of animal growth per unit diet intake is improved. These effects have been observed with diets containing up to 80% PPW. Results to date suggest that PPW is a valuable livestock feed ingredient and has no deleterious effects on beef quality. In areas where PPW is available, feeding to beef cattle represents a viable alternative to other disposal options. Key words: Potato, processing waste, by-product, cattle, land disposal
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