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Oxygen consumption, ammonia excretion and changes in 0:N ratios by the dragonfly Somatochlora cingulata were measured in four nymphal growth stages, relative to aluminum concentrations and low pH. A differential reduction in respiration and ammonia excretion rates resulted in an increase in 0:N ratios for all nymphal stages. The earlier stages, however, were the most sensitive. The ratios obtained were indicative of a decreased dependence on protein reserves and increased utilization of carbohydrates or lipid reserves. Also observed was an increase in the haemolymph pH and glutamate levels with a concomitant accumulation of tissue ammonia.

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When subjected to a series of elevated Al and H + concentrations spanning environmentally relevant levels, the dragonfly Libellula julia respired at a rate lower than the controls. This trend was consistent at all levels but only attained significance (p < 0.05) at pH 4.0 with Al levels of 3.0 and 30 mg 1-. Low pH alone does not depress respiratory rates as greatly as Al and low pH combined. The authors speculate on some apparent inconsistencies found in the literature.

COLER, R. A. and GUNNER, H. B. 1969. The rhizosphere of an aq~latic plant (Lrtmza niinor). Can. J .Microbial. 15: 964-966. Dominant epiphytes colonizing the surface of Lenztza minor were identified and enumerated. The distribution of these organisms compared to populations on inert surfaces at depths 0, 4-, 1 , 2 , 4 and 8 in. revealed greater than a 100-fold increase in population density. This enhanced carrying capacity of the plant diminished with depth.

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Pomacea lineata, an extremely ubiquitous snail and pest to rice farmers throughout Asia, holds promise as a valuable resource for monitoring water quality in northeast Brazil. In this paper, we present data demonstrating the rate of weight gain in P. lineata neonates as a consistent measure of the stress imposed by sublethal concentrations of the herbicides Paraquat and Round-up. Our secondary agenda is to demonstrate the feasibility of incorporating bioassay into the standard municipal and state procedure of monitoring water quality. Growth data to assess chronic toxicity were generated in experiments of four and four, eight, twelve and sixteen days for Paraquat and Round-up, respectively. We estimated a 96 h no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for Paraquat of 0.12 and 0.25 mg/L. The 96 h Round-up data yielded NOEC and LOEC values, respectively, of 0.25 and 0.5 mg/L. All concentrations of Round-up tested for the 192 h exposure yielded significantly lower growth than the control. Consequently, no NOEC could be derived. The LOEC was < 0.12 mg/L. Furthermore, there was no mortality during the test. At the lowest concentrations of Paraquat tested (0.005 mg/L) there was a significant increase in growth compared with the controls, suggesting a hormetic effect.Keywords: biomonitoring, herbicide pollution, weight gain, toxicity. Palavras-chave: biomonitoramento, poluição por herbicida, toxicidade, ganho de peso. RESUMO