Colloid mobilization in an undisturbed sediment core under semiarid recharge rates

Abstract

[1] The semiarid US Department of Energy Hanford site has a deep vadose zone with low recharge rates. Contaminants originating from nuclear waste processing are expected to move slowly through the vadose zone. The movement of certain contaminants can be facilitated by colloids. We hypothesized that the low recharge rates and low water contents in semiarid regions, however, tend to inhibit movement of colloidal particles, thereby reducing the risk for colloid-facilitated contaminant transport. The goal of this study was to investigate whether in situ natural colloids can be mobilized and transported in undisturbed, deep vadose zone sediments at the Hanford site under typical, semiarid recharge rates. We sampled an undisturbed sediment core (i.d. 50 cm, 59.5 cm height) from a depth of 17 m below ground at the Hanford 200 Area. The core was set up as a laboratory lysimeter and exposed to an infiltration rate of 18 mm/yr by applying simulated pore water onto the surface. Particle concentrations were quantified in the column outflow, and selected samples were examined microscopically and for elemental composition (transmission electron microscopy and energy dispersive X-ray). Measured water contents and potentials were used to calibrate a numerical model (HYDRUS-1D), which was then applied to simulate colloid mobilization from the sediment core. During 5.3 years of monitoring, natural colloids like silicates, aluminosilicates, and Fe-oxides were observed in the core outflow, indicating the continuous mobilization of in situ colloids. The total amount of particles mobilized during 5.3 years corresponded to 1.1% of the total dispersible colloids inside the core. Comparison of the amounts of colloids released with weathering rates suggests that mineral weathering can be a major source of the mobilized colloids. The fitted colloid release rate coefficient was 6 to 7 orders of magnitude smaller than coefficients reported from previous studies, where disturbed Hanford sediments and higher flow rates were used. Our findings demonstrate that even under low recharge rates and water contents typical for semiarid, deep vadose zone sediments, particles can continuously be mobilized, although the total mass of particles is low.Citation: Liu, Z., M. Flury, J. B. Harsh, J. B. Mathison, and C. Vogs (2013), Colloid mobilization in an undisturbed sediment core under semiarid recharge rates, Water Resour. Res., 49,[4985][4986][4987][4988][4989][4990][4991][4992][4993][4994][4995][4996]

Effect of biochar on leaching of organic carbon, nitrogen, and phosphorus from compost in bioretention systems

“…The surface area of the co-composted biochar was about 20% less than that of the original biochar, likely because of clogging of intraparticle pores (Prost et al, 2013). The sand was calcareous and had a fairly high surface area for sand, which is due to the presence of silt and clay particles (Liu et al, 2013).…”

“…Sand was taken from the Environmental Restoration Disposal Facility (ERDF) at the semi-arid Hanford site (WA). The sand consisted of 92% sand fraction (2 mm to 53 μm), 5% silt (53 to 2 μm), and 1% clay (b2 μm) (Liu et al, 2013) and contained illite, smectite, kaolinite, vermicullite, mica, quartz, feldspars, and pyroxene (Mashal et al, 2004).…”

Colloid transport through soil and other porous media under transient flow conditions—A review

“…The dynamic changes in flow velocity, flow region as well as the configuration of AWIs are the main drivers of colloid transport under transient flow conditions (Liu, Flury, Harsh, et al, 2013; Zhuang et al, 2007). Transient flow induces movement of AWS contact lines and AWIs, extension/shrinkage of water films, and connection/disconnection of pendular rings and immobile water zones.…”

Particle Leaching Rates from a Loamy Soil Are Controlled by the Mineral Fines Content and the Degree of Preferential Flow

“…O ur ability to estimate the mobilization and leaching of colloid soil particles is essential for the environment, as colloids have a strong affinity for adsorption and transport of specific chemicals (McCarthy and Zachara, 1989; Liu et al, 2013; Norgaard et al, 2014). Colloids are defined as soil particles measuring approximately 10 nm to 10 μm in diameter (DeNovio et al, 2004), and due to their large surface area and high sorption capacity, they may act as carriers of, for example, pesticides (de Jonge et al, 2000; Gjettermann et al, 2009; Villholth et al, 2000; Kjær et al, 2011), P (Vendelboe et al, 2011; Ulén et al, 2012), heavy metals (Pontoni et al, 2016), bacteria (Vasiliadou and Chrysikopoulos, 2011; Yang et al, 2012), and viruses (Syngouna and Chrysikopoulos, 2013, 2015).…”