Toxicity testing with artificial streams: Effects of differences in current velocity

Abstract

When designing toxicity tests with lotic organisms, the role of current velocity is a key consideration when evaluating the test organism's response. We conducted a series of short‐term toxicity experiments with the mayfly Baetis tricaudatus Dodds to determine the effect of current velocity on mayfly response to the reference toxicant sodium chloride. The tests were run at three substratum‐level velocities: low (0 cm/s), medium (6 cm/s, typical of estimated intrasubstratum velocities in the field), and high (12 cm/s). The end points measured for the mayflies were immobilization and number of molts. The animals showed signs of stress, and the EC50 was lower in the 0 cm/s treatment, probably due to insufficient delivery of oxygen to the gills. This did not, however, lead to much change in sensitivity (measured as lowest‐observed‐effect concentration; LOEC) to the reference toxicant. Furthermore, neither EC50 nor LOEC differed between 6 and 12 cm/s. This suggests a threshold between 0 and 6 cm/s above which the effect of current velocity was no longer measurable. These results provide initial support for the recommendation that short‐term toxicity tests using lotic organisms should ensure that the animals are exposed to at least some flow. Long‐term tests, and those with different toxicants, may require further fine‐tuning of current velocity.

Emergent body size of mayfly survivors

“…Soluble agricultural insecticides such as imidacloprid can impair the development and growth of larval mayflies, potentially reducing their reproductive success. Previous studies have shown that mayflies emerge earlier and at a smaller body size in response to sublethal stresses such as temperature (Atkinson, 1995), predation (Scrimgeour et al, 1994;Peckarsky et al, 2001) or toxic substances (Lowell, Culp & Wrona, 1995). These are examples of trade-offs that mayflies experience between reaching a suitable reproductive stage and achieving the optimal body size.…”

A comparison of chronic cadmium effects on Hyalella azteca in effluent‐dominated stream mesocosms to similar laboratory exposures in effluent and reconstituted hard water

“…Also, organisms exposed in the stream mesocosms grew to be larger and had many more young per female than the organisms exposed in the laboratory effluent test (Figs. [1][2][3][4]. This difference in growth and reproduction between the two effluent tests indicates that the general health of the H. azteca caged in the stream mesocosms was greater than that of their laboratory counterparts.…”

“…Naturally occurring processes such as intensity and spatial distribution of light, wind, flow, and variation in dissolved oxygen and temperature cannot be reproduced easily and accurately under laboratory conditions [3]. Factors such as these are known to affect the bioavailability of some classes of contaminants and/or cause a change in the overall physiological condition of an organism, potentially making it more susceptible to anthropogenic stressors [4,5]. Other factors such as organic matter and suspended solids, not normally present in reconstituted laboratory exposures, can influence metal bioavailability and predictions of field responses by laboratory toxicity tests [6,7].…”

A Weight-of-Evidence Approach for Northern River Risk Assessment: Integrating the Effects of Multiple Stressors

“…Small artificial streams were set up beside the Thompson River adjacent to the Weyerhaeuser pulp mill in Kamloops to investigate the mechanisms of PME effects on periphyton and benthic invertebrates under near-ambient conditions. The facility included a water distribution system, treatment reservoirs for mixing varying amounts of Weyerhaeuser PME with a continuous supply of upstream river water, and the circular artificial streams themselves [20][21][22]. Although the experiments conducted at this facility focused on physiological and population-level responses, addressing community-level questions regarding periphyton-grazer interactions was also possible.…”