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Free Content Phytoplankton Nitrogen Metabolism, Nitrogen Budgets, and Observations on Copper Toxicity: Controlled Ecosystem Pollution Experiment

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Phytoplankton growth and nitrogen metabolism seemed typical of coastal temperate plankton in the 0.25-scale CEPEX enclosures used at Saanich Inlet, B.C., in the summer of 1974. Maximum rates of nitrogen assimilation corresponded to a growth rate of about 1.0 day–1 and half-saturation values for nitrate and ammonium uptake were about 1 μM. Although assimilation rates on a day-to-day basis were regulated primarily by ambient nitrate and ammonium levels, overall phytoplankton levels and settlement rates were related to the rate of nutrient loading. Remineralization of nitrogen to ammonium was rapid and important. Although only nitrate (along with phosphate and silicate nutrients) were added to the enclosures, rates of ammonium assimilation by the phytoplankton were similar to those for nitrate.

Several acute effects of copper on phytoplankton were observed, including inhibition of nitrate uptake, photosynthetic carbon assimilation, synthesis of nitrate reductase, and cell disruption and loss of accumulated ammonium in Noctiluca sp. Evidence suggests that the addition of copper to the enclosures resulted in acute inhibition of phytoplankton growth and a replacement of the initial phytoplankton by a copper-tolerant assemblage. Bioassay experiments indicated that even after the shift to copper-tolerant forms, (1) the copper in the enclosures remained in a chemical form still toxic to phytoplankton from control enclosures, and (2) the degree of copper-tolerance of the phytoplankton was related to ambient copper concentrations.

Document Type: Research Article

Publication date: January 1, 1977

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