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The effects of a silvicultural sludge application on small mammal populations and the potential of Giardia contamination in a forest ecosystem Cheng, Chris

Abstract

The effects of a silvicultural sludge application on resident small mammal populations were assessed by monitoring their demographic responses before and after sewage sludge treatment. Potential contamination of the forest ecosystem by Giardia duodenalis, a parasitic protozoan, was also investigated. Populations of the deer mouse (Peromyscus maniculatus), Oregon vole (Microtus oregoni), Townsend chipmunk (Eutamias townsendii), shrews (Sorex spp.), and a few species caught occasionally, were sampled in control and treatment study sites from May 1990 to October 1991. Sludge application occurred in November 1990. There were no detectable differences in the abundances of deer mice, Oregon voles, and chipmunks on treatment areas relative to controls after sludge application. This was also the case for recruitment, survival, mean body weight, weight at sexual maturity, sex ratio, species diversity and spatial distribution. There was, however, a significant increase in the growth rate of juvenile deer mice on treatment sites after sludge application. This was also the only effect on small mammal population dynamics observed from the sludge treatment. The prevalence of Giardia spp. cysts in small mammal fecal samples on study sites did not differ between pre-sludge and post-sludge periods. My laboratory study using wild deer mice concluded that this species was capable of acting as a host to some strains of human Giardia under specific laboratory conditions. Because of the deer mouse's apparent ability to adapt well to this environmental change, as illustrated by the lack of effect on its survival and reproduction attributes, and this species' potential ability to host human Giardia, additional research and consideration are warranted prior to the implementation of large scale silvicultural sludge applications.

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