Transport behavior of groundwater protozoa and protozoan-sized microspheres in sandy aquifer sediments

Abstract

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 (0.5to 1.0-mm grain size) aquifer sediments. The minute (average in situ cell size, 2 to 3 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-m flagellates appeared to be near the optimal size for transport, judging from flowthrough column experiments involving a polydispersed (0.7 to 6.2 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 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-m carboxylated microspheres may be useful as analogs in investigating several abiotic aspects of flagellate transport behavior in groundwater.

Predicting colloid transport through saturated porous media: A critical review

“…Extended tailing may occur during the elution phase of unfavorable experiments (Figure 2, left and middle top row). Tailing is defined by the slow release of colloids from the column (illustrated in Figure 2) and is indicative of significant reentrainment, as observed for microbes in the laboratory [Fontes et al, 1991;Hornberger et al, 1992;Lindqvist et al, 1994;McCaulou et al, 1994;Johnson et al, 1995b;McCaulou et al, 1995;Hendry et al, 1997Hendry et al, , 1999Harter et al, 2000;, field [Scholl and Harvey, 1992;Harvey et al, 1995;DeBorde et al, 1999;Ryan et al, 1999;Schijven et al, 1999], and nonbiological colloids [Li et al, 2004;Tufenkji et al, 2004;Tong et al, 2005;Johnson et al, 2007b]. The reentrainment behavior under unfavorable conditions is sensitive to solution chemistry and fluid flow as shown for reentrainment with perturbations, including variation in ionic strength [Ryan et al, 1999;Tufenkji andElimelech, 2004a, 2005a;Shen et al, 2007;Mattison et al, 2011;Jiang et al, 2012a;Shen et al, 2012], variation in pH [Ryan et al, 1999;Tufenkji andElimelech, 2004a, 2005a], and variation in fluid velocity [Shang et al, 2008;Pazmino et al, 2014a].…”

“…As such, slight differences in colloid size and/or surface properties may generate effective heterogeneity in ''stickiness'' among the colloid population. Demonstrating this effect may yield a mechanistic explanation for the apparent heterogeneity in retention rate coefficients among apparently uniform populations, which is thought to drive the observed nonlog linear profiles of retained colloids observed under unfavorable conditions [Albinger et al, 1994;Harvey et al, 1995;Hendry et al, 1997;Baygents et al, 1998;Simoni et al, 1998;Bolster et al, 1999;Schijven et al, 1999;Bolster et al, 2000;Li et al, 2004;Tufenkji and Elimelech, 2004a;Tufenkji et al, 2004;Tufenkji and Elimelech, 2005a,b;Tong and Johnson, 2007;Liang et al, 2013;D. Wang et al, 2014].…”

“…Colloid transport from septic systems, agricultural runoff, and other sources through near-shore soils may lead to elevated concentrations of pathogenic colloids in beach sands [e.g., Lipp et al, 2001] and transport across the groundwater/ surface water interface may be the cause of frequent beach closures [e.g., Russell et al, 2012]. A wide array of research into pathogen transport has been undertaken including virus transport [Ryan et al, 1999;Schijven et al, 1999;Jin and Flury, 2002] and column-scale bacteria transport [e.g., Albinger et al, 1994;Baygents et al, 1998;Simoni et al, 1998;Torkzaban et al, 2008], bacteria transport in the field [Bales et al, 1989;Powelson et al, 1993;Harvey et al, 1995;DeBorde et al, 1999;Ryan et al, 1999;Schijven et al, 1999;Zhang et al, 2001a;Ryan et al, 2002;Blanford et al, 2005;van der Wielen et al, 2008;Scheibe et al, 2011], and phage persistence in soils [e.g., Yates et al, 1985] among many others; numerous reviews of pathogen transport in groundwater are available [Bitton and Harvey, 1992;Harvey, 1997;Taylor et al, 2004;Sen, 2011].…”

Pore‐scale processes that control dispersion of colloids in saturated porous media

“…There are several classes of colloids, biotic and abiotic. Among biotic colloids, significant attention has been given to viruses [Burge and Enkiri, 1978;Pieper et al, 1997;Bales et al, 1997;Woessner et al, 2001], bacteria [Edniond, 1976;Harvey et al, 1989] and protozoa [Sinclair and Ghiorse, 1987;Harvey et al, 1995;Harter et al, 2000]. The motivation comes from a growing concern about potential health problems from contaminated drinking water aquifers [Hejkal et al, 1982] and bioremediation strategies that introduce exogenous bacteria strains [Straube et al, 2003].…”

Quantifying diffusive mass transfer in fractured shale bedrock

“…A vast accumulation of literature in the fields of soil science, geosciences, and petroleum engineering has provided overwhelming evidence that solute transport in undisturbed subsurface media is often influenced by preferential flow coupled with matrix diffusion [Shuford et al, 1977;Shaffer et al, 1979;Frohne and Mercer, 1984;Abelin et al, 1987Abelin et al, , 1991Seyfried and Rao, 1987;Jardine et al, 1988Jardine et al, , 1990Jardine et al, , 1993a with grossly different sizes. At the field scale, techniques 4 and 5 are most practical for quantifying advective preferential flow and time-dependent diffusion into the soil and bedrock matrix [Abelin et al, 1987;Harvey et al, 1989Harvey et al, , 1993Harvey et al, , 1995Raven et al, 1988;Zuber, 1990, 1993;McKay et al, 1993aMcKay et al, , b, 1995Sanford and Solomon, 1998;Jaynes and Horton, 1998]. The use of multiple tracers with different diffusion coefficients is particularly useful because the influence of matrix diffusion on the overall system dispersion can be quantified.…”