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The Response of Biota in Experimental Stream Channels to a 24-hour Exposure to the Herbicide, Velpar L.

出版	Université d'Ottawa / University of Ottawa, 1994
URL	http://books.google.com.hk/books?id=0jaUoAEACAAJ&hl=&source=gbs_api

註釋Ten experimental stream channels, fed from a Laurentian steam were used to examine the short-term impact of a pulse of Velpar L on stream periphyton and invertebrates. Velpar L was added to five alternating channels for 24 hours with the other five channels serving as controls. The mean concentration of hexazinone in the treatment channels varied over time from 145 $\mu$g L$\sp{-1}$ to 432 $\mu$g L$\sp{-1}$. Periphyton chlorophyll a-specific productivity was significantly reduced during the Velpar L treatment. Within 24 hours after the termination of the Velpar L treatment, productivity returned to control levels. Mean periphyton biomass, measured as the quantity of chlorophyll a per unit area, was not affected by the Velpar L treatment. In addition, the concentration of hexazinone that reduced periphyton chlorphyll a-specific productivity by 50% after a four hour exposure was determined. This value was only 3.6 $\mu$g L$\sp{-1}$ of hexazinone. Thus, low concentrations of Velpar L affect stream periphyton but the impact appears to be temporary. Velpar L did not cause an increase in the drift of insects or other macroinvertebrates. Mean density of benthic macroinvertebrates increased slightly with time in the Velpar L-treated channels and nearly doubled in the control channels. The mean length of individual macroinvertebrates decreased slightly over time in the control channels but not in the treated channels. However, the changes in mean density, biomass and length were not statistically significant. The variance of the invertebrate lengths increased over time in both the control and Velpar L-treated channels, which suggests that the size distribution of the invertebrate community varied with time. (Abstract shortened by UMI.).