Biomedical subjects

A Louise Heathwaite

Publications and source records attributed to A Louise Heathwaite.

3 recordsLinked to original sources

PubMed2006

Noninvasive quantitative measurement of colloid transport in mesoscale porous media using time lapse fluorescence imaging.

We demonstrate noninvasive quantitative imaging of colloid and solute transport at millimeter to decimeter (meso-) scale. Ultraviolet (UV) excited fluorescent solute and colloid tracers were independently measured simultaneously during co-advection through saturated quartz sand. Pulse-input experiments were conducted at constant flow rates and ionic strengths 10(-3), 10(-2) and 10(-1) M NaCl. Tracers were 1.9 microm carboxylate latex microspheres and disodium fluorescein. Spatial moments analysis was used to quantify relative changes in mass distribution of the colloid and solute tracers over time. The solute advected through the sand at a constant velocity proportional to flow rate and was described well by a conservative transport model (CXTFIT). In unfavorable deposition conditions increasing ionic strength produced significant reduction in colloid center of mass transport velocity over time. Velocity trends correlated with the increasing fraction of colloid mass retained along the flowpath. Attachment efficiencies (defined by colloid filtration theory) calculated from nondestructive retained mass data were 0.013 +/- 0.03, 0.09 +/- 0.02, and 0.22 +/- 0.05 at 10(-3), 10(-2), and 10(-1) M ionic strength, respectively, which compared well with previously published data from breakthrough curves and destructive sampling. Mesoscale imaging of colloid mass dynamics can quantify key deposition and transport parameters based on noninvasive, nondestructive, spatially high-resolution data.

Colloids↗

PubMed2006

Differential E. coli die-off patterns associated with agricultural matrices.

The investigation of fecal bacterial die-off in various agricultural and catchment related matrices remains important because of the growing concern over pathogens in agricultural environments and watercourses. The aim of this research was to investigate the die-off of Escherichia coli within cattle manure (both slurry [liquid mix of excrement and urine produced by housed livestock] and feces), soil, and runoff water and to determine if cell numbers would be influenced by the presence of cattle manure within soil and runoff water. E. coli survived better within feces than in slurry; cells within feces declined from 7.5 to 3.3 log CFU g(-1) in 76 days. Within slurry, cells fell from 8.5 log CFU g(-1) to below levels of detection by day 42. E. coli died off more quickly within manure and slurry than in soil amended with the same fecal material, and declined significantly faster within microcosms when introduced to the soil via sterile water rather than cattle manure. E. coli was found to decline more rapidly within wet (50% moisture w/w), rather than dry (25% moisture w/w), soil. Conversely, in runoff water, die-off of E. coli was increased in the presence of feces. Overall, E. coli die-off was most rapid in water incorporated with cattle manure > unincorporated cattle manure > soil incorporated with cattle manure. The derived die-off characteristics including half-life and decimal reduction times can now provide (i) input for predictive models and (ii) information upon which to consider mitigation strategies associated with both manure and land management.

Agriculture↗

PubMed2006

Suppression of dissolved organic carbon by sulfate induced acidification during simulated droughts.

The relationship between dissolved organic carbon (DOC) and the acidification of soils and freshwaters by sulfate (SO4(2-)) has been a topic of great debate over the last few decades. Most interest has focused on long-term acidification. Few have considered the influence of episodic drought-induced acidification in peatlands on DOC mobility, even through the increased acidity and ionic strength associated with the oxidation of reduced sulfur to SO4(2-) are known to reduce DOC solubility. Reduced DOC concentrations during droughts have often been attributed to: (i) reduced hydrological export; (ii) physicochemical changes in the peat structure; or (iii) changes in the biological production and/or consumption of DOC. Our experimental drought simulations on peat cores showed that SO4(2-) induced acidification reduced DOC concentrations during droughts. However, the relationships between SO4(2-)/pH/ ionic strength and DOC were only apparent when the reductions in observed DOC were expressed as a fraction of the estimated DOC concentration in the absence of SO4(2-), which were derived from soil depth, temperature, and watertable data. This analysis showed that a pH fall from 4.3 to 3.5, due to a SO4(2-) rise from < 2.5 to 35 mg L(-1), caused a 60% reduction in DOC concentrations. In contrast, poor correlations were recorded between S042-/pH/ionic strength and the observed DOC data. As DOC both influences acidity and is influenced by acidity, the relative change in DOC needed to be considered to disentangle the effect of inputs of mineral acids into a system naturally dominated by variable concentrations of organic acids.

Carbon↗