A greenhouse experiment was conducted involving complete/intact 100 cm cores of a fragipan soil. The cores were maintained in moist conditions throughout the experiment as annual ryegrass (Lolium multiflorum) or festu...A greenhouse experiment was conducted involving complete/intact 100 cm cores of a fragipan soil. The cores were maintained in moist conditions throughout the experiment as annual ryegrass (Lolium multiflorum) or festulolium (Lolium spp and Fescue spp hybrid) were grown with and without additional surface applied amendments, including NaF, NaNO3, NaCl, and KCl. The results suggest a significant effect of annual ryegrass and festulolium on fragipan horizon degradation after 24 months. Annual ryegrass and festulolium were found to effectively change the structure of the fragipan horizon when planted on the soil surface and roots grew through the upper soil profile and penetrated into the fragipan. The fragipan structural change (degradation) appeared to increase with each planting sequence, particularly with soybean crop rotations. Sodium nitrate added to the soil surface with the growth of annual ryegrass resulted in a significant synergistic effect for degrading the fragipan horizon. The other amendments were not as effective in causing additional fragipan degradation.展开更多
A greenhouse experiment was conducted involving intact fragipan soil cores of 50 cm thickness after removing the topsoil horizons. The cores were maintained in moist condition throughout the experiment and received se...A greenhouse experiment was conducted involving intact fragipan soil cores of 50 cm thickness after removing the topsoil horizons. The cores were maintained in moist condition throughout the experiment and received several treatments with various amendments for different periods ranging from 9 to 17 months. The amendments included annual ryegrass or Festulolium residues, powder limestone and various humate compounds alone or in combination with the grass residues. The results suggested a significant effect of ryegrass and Festulolium in reducing penetration resistance into the top 10 cm of the fragipan within 9 - 17 months, particularly when used in combination with certain humate materials such as Leonardite. Apparently, this is the result of the release of certain soluble organic compounds from the plant residues or the humate amendments that increase the solubility of Si and Al associated with the fragipan brittleness, thus decreasing the density of the compacted fragipan material.展开更多
Limited information exists on natural nanocolloid sorption behavior of As, Se, Cu and Pb in the environment. They are expected to have variable competitive sorption characteristics depending on size and composition an...Limited information exists on natural nanocolloid sorption behavior of As, Se, Cu and Pb in the environment. They are expected to have variable competitive sorption characteristics depending on size and composition and may transport elevated contaminant loads into surface and ground waters. A comprehensive characterization of their interactions with contaminants could provide a better understanding of the risks they pose to the environment. This study evaluated the sorption behavior of soil and biosolid nano- and macro-colloids with different mineralogical compositions for As, Se, Cu, and Pb contaminants. Single- and multi-contaminant Freundlich isotherms were us- ed to evaluate sorption affinity for the contaminants among the different colloid sizes and compositions. Sorption trends based on size indicated greater affinity for As and Cu by the smectitic and kaolinitic nanocolloids, greater affinity for Pb by the kaolinitic nanocolloids, and greater affinity for As, Se and Pb by bio-nanocolloids over corresponding macrocolloid fractions. Both, single- and multi-contaminant isotherms indicated sorption preferences for cation over anion contaminants, but with somewhat contrasting sequences depending on size and composition. Multi-contaminant isotherms generally predicted greater sorption affinities likely due to bridging effects, particularly for anionic contaminants. Surface properties such as zeta potentials, cation exchange capacity (CEC), surface area (SA), organic carbon (OC), and OC:SA significantly but variably affected sorption characteristics among the differing colloid sizes and compositions. Colloid zeta potential and pH shifts in the presence of different contaminant loads suggested prevalence of inner sphere bonding mechanisms for sorption of cation contaminants by mineral colloids and outer sphere sorption for cation and anion contaminants by bio-colloids.展开更多
Due to their enhanced stability and contaminant transport potential, environmental nanoparticles derived from soil and biosolid materials may pose a considerable risk to groundwater quality. Very little information ex...Due to their enhanced stability and contaminant transport potential, environmental nanoparticles derived from soil and biosolid materials may pose a considerable risk to groundwater quality. Very little information exists on the stability and transportability of environmental or natural nanocolloids in the presence of As, Se, Pb and Cu contaminants, all of which are considered to represent substantial threats to human and animal populations through groundwater contamination. This study involved stability settling experiments of nanocolloids (NCs) (<100 nm) and macrocolloids (MCs) (100 - 2000 nm) fractionated from Bt horizons of three Kentucky soils and one biosolid waste material in water suspensions of 0, 2, and 10 mg·L-1 of As, Se, Pb and Cu. The results indicated greater stability in the mineral than the biosolid colloid fractions, and enhanced stability of NCs over corresponding MCs in the presence or absence of contaminants at low contaminant loads. At high contaminant loads nearly all colloids were unstable except for the bio-nanocolloids which still sustained considerable stability. At low contaminant loads, the MC fraction stability sequence was smectitic > mixed > kaolinitic > biosolid. Among the nano-fractions, the smectitic and kaolinitic colloids demonstrated lower stability than the MCs, but higher than those of the mixed and biosolid fractions. Physicochemical characterizations indicated that extensive organic carbon surface coatings and higher Al/Fe:Si ratios may have induced higher stability in the NC fractions, but their overall stability may also have been hindered in some cases by nano-aggregation phenomena.展开更多
文摘A greenhouse experiment was conducted involving complete/intact 100 cm cores of a fragipan soil. The cores were maintained in moist conditions throughout the experiment as annual ryegrass (Lolium multiflorum) or festulolium (Lolium spp and Fescue spp hybrid) were grown with and without additional surface applied amendments, including NaF, NaNO3, NaCl, and KCl. The results suggest a significant effect of annual ryegrass and festulolium on fragipan horizon degradation after 24 months. Annual ryegrass and festulolium were found to effectively change the structure of the fragipan horizon when planted on the soil surface and roots grew through the upper soil profile and penetrated into the fragipan. The fragipan structural change (degradation) appeared to increase with each planting sequence, particularly with soybean crop rotations. Sodium nitrate added to the soil surface with the growth of annual ryegrass resulted in a significant synergistic effect for degrading the fragipan horizon. The other amendments were not as effective in causing additional fragipan degradation.
文摘A greenhouse experiment was conducted involving intact fragipan soil cores of 50 cm thickness after removing the topsoil horizons. The cores were maintained in moist condition throughout the experiment and received several treatments with various amendments for different periods ranging from 9 to 17 months. The amendments included annual ryegrass or Festulolium residues, powder limestone and various humate compounds alone or in combination with the grass residues. The results suggested a significant effect of ryegrass and Festulolium in reducing penetration resistance into the top 10 cm of the fragipan within 9 - 17 months, particularly when used in combination with certain humate materials such as Leonardite. Apparently, this is the result of the release of certain soluble organic compounds from the plant residues or the humate amendments that increase the solubility of Si and Al associated with the fragipan brittleness, thus decreasing the density of the compacted fragipan material.
文摘Limited information exists on natural nanocolloid sorption behavior of As, Se, Cu and Pb in the environment. They are expected to have variable competitive sorption characteristics depending on size and composition and may transport elevated contaminant loads into surface and ground waters. A comprehensive characterization of their interactions with contaminants could provide a better understanding of the risks they pose to the environment. This study evaluated the sorption behavior of soil and biosolid nano- and macro-colloids with different mineralogical compositions for As, Se, Cu, and Pb contaminants. Single- and multi-contaminant Freundlich isotherms were us- ed to evaluate sorption affinity for the contaminants among the different colloid sizes and compositions. Sorption trends based on size indicated greater affinity for As and Cu by the smectitic and kaolinitic nanocolloids, greater affinity for Pb by the kaolinitic nanocolloids, and greater affinity for As, Se and Pb by bio-nanocolloids over corresponding macrocolloid fractions. Both, single- and multi-contaminant isotherms indicated sorption preferences for cation over anion contaminants, but with somewhat contrasting sequences depending on size and composition. Multi-contaminant isotherms generally predicted greater sorption affinities likely due to bridging effects, particularly for anionic contaminants. Surface properties such as zeta potentials, cation exchange capacity (CEC), surface area (SA), organic carbon (OC), and OC:SA significantly but variably affected sorption characteristics among the differing colloid sizes and compositions. Colloid zeta potential and pH shifts in the presence of different contaminant loads suggested prevalence of inner sphere bonding mechanisms for sorption of cation contaminants by mineral colloids and outer sphere sorption for cation and anion contaminants by bio-colloids.
文摘Due to their enhanced stability and contaminant transport potential, environmental nanoparticles derived from soil and biosolid materials may pose a considerable risk to groundwater quality. Very little information exists on the stability and transportability of environmental or natural nanocolloids in the presence of As, Se, Pb and Cu contaminants, all of which are considered to represent substantial threats to human and animal populations through groundwater contamination. This study involved stability settling experiments of nanocolloids (NCs) (<100 nm) and macrocolloids (MCs) (100 - 2000 nm) fractionated from Bt horizons of three Kentucky soils and one biosolid waste material in water suspensions of 0, 2, and 10 mg·L-1 of As, Se, Pb and Cu. The results indicated greater stability in the mineral than the biosolid colloid fractions, and enhanced stability of NCs over corresponding MCs in the presence or absence of contaminants at low contaminant loads. At high contaminant loads nearly all colloids were unstable except for the bio-nanocolloids which still sustained considerable stability. At low contaminant loads, the MC fraction stability sequence was smectitic > mixed > kaolinitic > biosolid. Among the nano-fractions, the smectitic and kaolinitic colloids demonstrated lower stability than the MCs, but higher than those of the mixed and biosolid fractions. Physicochemical characterizations indicated that extensive organic carbon surface coatings and higher Al/Fe:Si ratios may have induced higher stability in the NC fractions, but their overall stability may also have been hindered in some cases by nano-aggregation phenomena.
