Mj. Waiser et Rd. Robarts, IMPACTS OF A HERBICIDE AND FERTILIZERS ON THE MICROBIAL COMMUNITY OF A SALINE PRAIRIE LAKE, Canadian journal of fisheries and aquatic sciences, 54(2), 1997, pp. 320-329
Prairie wetlands are scattered among cultivated land where herbicides
and fertilizers are regularly used. Avadex-BW(C) (active ingredient tr
iallate) is one of the most popular pre-emergent herbicides used on th
e Canadian prairies to control wild oats and other broadleaf weeds. Tr
iallate enters aquatic systems through processes of runoff and direct
overspray, while fertilizers (nitrogen and phosphorus) enter through r
unoff and aeolian deposition. Microcosm studies on Redberry Lake, an o
ligotrophic prairie lake, indicated that additions of triallate stimul
ated bacterial production ([H-3]thymidine incorporation), metabolism (
[C-14]glucose uptake), and numbers, but only if nitrogen and phosphoru
s were added. Because the microbial community is nutrient limited, the
re is the possibility that triallate could bioaccumulate in this syste
m. Addition of nitrogen and phosphorus (N + P) stimulated measures of
phytoplankton biomass (Chl a), bacterial metabolism, numbers, and prod
uction. Although triallate had little effect on bacteria, at any conce
ntration tested, substantial declines in phytoplankton biomass occurre
d at triallate concentrations greater than or equal to 1000 mu g.L-1.
Greatest impacts of herbicides and nutrients, however, are expected in
spring as a result of runoff events, aeolian deposition, and direct o
verspray.