• Microcosms;
  • Nutrients;
  • Diquat;
  • Periphyton;
  • Stress


The interaction between community nutrient status and toxicity was studied in laboratory microcosms containing natural periphyton communities The three experimental nutrient treatments (low, medium, high) increased by orders of mag nitude from 0 05 mg N per liter + 0 01 mg P per liter Communities were developed with nutrient treatments for 25 d and were then exposed to 3 5 mg/L diquat, a photosynthetic inhibitor, and studied for an additional 23 d The effects of toxicant addi tion were assessed by measuring changes in biomass (protein, chlorophyll), enzyme activity (alkaline phosphatase electron trans port), nutrient release, diurnal changes in microcosm oxygen (gross productivity), and toxicant fate The rate of diquat loss was lowest in the low nutrient treatment Gross photosynthesis was nearly eliminated by diquat in the low nutrient treatment and showed limited recovery Productivities in the medium and high nutrient treatments were equivalent and showed evidence of both effect (approximately 50% reduction) and recovery Protein biomass was reduced in low nutrient microcosms treated with diquat, but no effect on chlorophyll biomass was observed Diquat inhibited respiratory electron transport activity, and mi crocosms with low nutrient availability had limited ability to recover from the diquat stress These studies suggest that commu nity nutrient status affects both the magnitude of effect and the rate of recovery of processes following stress