Colloid Transport
Colloids are fine particles (1 nm to ~ 10 μm) that stay suspended in water. Colloids can facilitate the transport of contaminants in the subsurface soil, thereby increasing the risk of groundwater contamination. Our research examines how a transient in weather conditions affects the physical, geochemical, and biological processes responsible for colloid release in the subsurface soil. This work is particularly useful to determine whether extreme weather conditions, which are projected to become more frequent during climate change, could increase the risk associated with particulate contaminants and pathogens in surface or subsurface environments and ultimately groundwater.
Intermittent flow of rainwater increases the transport of microplastics in the subsurface soil, but the mobility is sensitive to microplastic size.
This study examines the mechanism of microplastics transport in subsurface during intermittent rainfall events. Intermittent rainfall events increased the release of sequestered microspheres from a soil core pre-contaminated with microspheres. The microspheres mobility increased with increases in microsphere size and permeability of the soil.
Mohanty, S.K., Bulicek, M.C.D., Metge, D.W., Harvey, R.W., Boehm, A.B. and Ryan, J.N. (2015) Mobilization of microspheres from a fractured soil during intermittent infiltration events. Vadose Zone Journal. 14(1), https://doi.org/10.2136/vzj2014.05.0058 [ pdf ]
Drying duration between rainfalls affects colloid release from subsurface soil.
During climate change, the occurrence of long drying cycles and high-intensity rainfall is expected to increase in some part of the earth. This study examines how drying duration affects the mobility of colloids in a fractured soil. These results reveal that antecedent drying duration and soil hydraulic properties are two key factors that affect that mobility of colloids in the subsurface.
Mohanty, S.K., Saiers, J.E. and Ryan, J.N. (2015) Colloid mobilization from a fractured soil during dry-wet cycles: Effect of drying duration and flow path permeability. Environmental Science & Technology. 49(15), 9100-9106. https://doi.org/10.1021/acs.est.5b00889 [ pdf ]
Freeze-thaw cycles increase the transport of colloids and associated heavy metals in the subsurface.
This study examines how a frequent freeze-thaw cycle would change the export of colloids and colloid-associated contaminants to water resources. Compared to dry-wet cycles (control), freeze-thaw cycles create new preferential flow paths, generate soil colloids that are enriched with iron oxides and clays, and cause a rapid transport of colloids and colloid-associated heavy metals or radionuclides through the preferential flow paths.
Mohanty, S.K., Saiers, J.E. and Ryan, J.N. (2014) Colloid-facilitated mobilization of metals by freeze-thaw cycles. Environmental Science & Technology. 48(02), 977-984. https://doi.org/10.1021/es403698u [ pdf ]
Pore-water exchange between macropores and matrix can cause colloid mobilization hysteresis.
Using an intact soil core in this study, we provided a direct evidence showing how the exchange of water between preferential flow paths and matrix affects the amount of colloid mobilized in soils. We showed that colloid mobilization during a rainfall event depends on the ionic strength of the previous rainfall (hence termed as colloid mobilization hysteresis). The result revealed that the interaction of infiltrating water (new water) with water in soil matrix (old water) either decreased or increased the ionic strength of pore water, which in turn affected the amount of colloids accumulated during flow pause and mobilized from the pores during next rainfall cycle.
Mohanty, S.K., Saiers, J.E. and Ryan, J.N. (2016) Colloid mobilization in a fractured soil: Effect of pore water exchange between preferential flow paths and soil matrix. Environmental Science & Technology. 50(5), 2310-2317. https://doi.org/10.1021/acs.est.5b04767 [ pdf ]
