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Appl. Environ. Microbiol., Jan 1995, 209-217, Vol 61, No. 1
RW Harvey, NE Kinner, A Bunn, D MacDonald and D Metge
Transport behaviors of unidentified flagellated protozoa (flagellates) and
flagellate-sized carboxylated microspheres in sandy, organically
contaminated aquifer sediments were investigated in a small-scale (1 to 4-m
travel distance) natural-gradient tracer test on Cape Cod and in
flow-through columns packed with sieved (0.5-to 1.0-mm grain size) aquifer
sediments. The minute (average in situ cell size, 2 to 3 (mu)m)
flagellates, which are relatively abundant in the Cape Cod aquifer, were
isolated from core samples, grown in a grass extract medium, labeled with
hydroethidine (a vital eukaryotic stain), and coinjected into aquifer
sediments along with bromide, a conservative tracer. The 2-(mu)m
flagellates appeared to be near the optimal size for transport, judging
from flowthrough column experiments involving a polydispersed (0.7 to 6.2
(mu)m in diameter) suspension of carboxylated microspheres. However,
immobilization within the aquifer sediments accounted for a log unit
reduction over the first meter of travel compared with a log unit reduction
over the first 10 m of travel for indigenous, free-living groundwater
bacteria in earlier tests. High rates of flagellate immobilization in the
presence of aquifer sediments also was observed in the laboratory. However,
immobilization rates for the laboratory-grown flagellates (initially 4 to 5
(mu)m) injected into the aquifer were not constant and decreased noticeably
with increasing time and distance of travel. The decrease in propensity for
grain surfaces was accompanied by a decrease in cell size, as the
flagellates presumably readapted to aquifer conditions. Retardation and
apparent dispersion were generally at least twofold greater than those
observed earlier for indigenous groundwater bacteria but were much closer
to those observed for highly surface active carboxylated latex
microspheres. Field and laboratory results suggest that 2-(mu)m
carboxylated microspheres may be useful as analogs in investigating several
abiotic aspects of flagellate transport behavior in groundwater.
Copyright © 1995, American Society for Microbiology
Transport Behavior of Groundwater Protozoa and Protozoan-Sized Microspheres in Sandy Aquifer Sediments
U.S. Geological Survey, Boulder, Colorado, and Department of Civil Engineering, University of New Hampshire, Durham, New Hampshire
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