@article{moorberg_vepraskas_niewhoener_2017, title={Phosphorus Dynamics Near Bald Cypress Roots in a Restored Wetland}, volume={81}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2017.07.0228}, abstractNote={Phosphorus (P) dissolution occurs commonly in wetland soils restored from agricultural land. Associated with P release are high concentrations of dissolved organic carbon (DOC) and Fe²⁺. This field study evaluated the effect of a fluctuating water table on the root dynamics of bald cypress (Taxodium distichum L. Rich.) to determine whether root death created soil reduction microsites, potentially contributing to P dissolution. The study site is a restored Carolina bay wetland with organic soils. Root growth and death were monitored on 16 6-yr-old bald cypress using minirhizotrons. Root dynamics, water table levels, and soil porewater chemistry and redox potential in the root zone were monitored for 2 yr. Soil solution samples were analyzed for Fe²⁺, pH, DOC, and P. High rates of root growth occurred during dry conditions, whereas root death occurred during sustained periods of saturation, particularly within 20 cm of the surface. Cyclic changes in concentrations of Fe²⁺, DOC, and dissolved total P (DTP) were related to water table position but not to changes in root numbers. After sustained periods of saturated conditions, redox potential decreased to 0 mV, Fe²⁺ increased to 1.75 mg Fe²⁺ L–¹, and DOC increased to 350 mg L–¹, resulting in peak DTP concentrations of 750 μg L–¹, compared with 100 μg L–¹ during dry periods. This study showed that in these high-C soils (∼20% organic C) rooting dynamics had minimal impact on changes in P concentrations and that P dissolution was largely controlled by Fe reduction processes occurring within the C-rich soil matrix.}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Moorberg, Colby J. and Vepraskas, Michael J. and Niewhoener, Christopher P.}, year={2017}, pages={1652–1660} }
 @article{moorberg_vepraskas_niewoehner_2015, title={Phosphorus Dissolution in the Rhizosphere of Bald Cypress Trees in Restored Wetland Soils}, volume={79}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2014.07.0304}, abstractNote={Phosphorus release to ground or surface waters has been observed in wetlands restored from farmland. This study examined whether rhizospheres of bald cypress (Taxodium distichum L.) are a source of increased P dissolution compared with the soil matrix. The study was conducted in root-box rhizotrons filled with mineral and organic soil materials (Aeric Alaquods and Terric Haplosaprists, respectively) from a Carolina bay wetland restored from row crop agriculture. Rhizotrons were planted with bald cypress saplings or left unplanted to simulate rhizosphere and matrix conditions, respectively. Ponding was imposed for 128 d. Soil pore water was sampled in three layers (0–22, 22–41, and 41–59 cm) in each rhizotron twice monthly for dissolved total and reactive P, dissolved organic C (DOC), Fe²⁺, and redox potential (Eh). Manual root counts monitored growth and death monthly. Root death was most prevalent at 41 to 59 cm, while vigorous root growth was observed near the surface. The rhizosphere treatments exhibited increased Fe²⁺ dissolution and increased concentrations of DOC relative to matrix conditions; however, no corresponding P increase occurred. Near the surface, rhizosphere P concentrations declined below matrix concentrations after 60 d of ponding. Our results show that the rhizosphere of bald cypress did not cause higher P concentrations than matrix values for mineral and organic soils with 3.5 and 19.5% C, respectively. In addition, root growth near the surface resulted in more oxidizing conditions and/or plant uptake of P, which decreased P concentrations below matrix values.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Moorberg, Colby J. and Vepraskas, Michael J. and Niewoehner, Christopher P.}, year={2015}, pages={343–355} }
 @article{moorberg_vepraskas_niewoehner_2013, title={Dynamics of P dissolution processes in the matrix and rhizospheres of bald cypress growing in saturated soil}, volume={202}, ISSN={["1872-6259"]}, DOI={10.1016/j.geoderma.2013.03.017}, abstractNote={Phosphorus release to ground or surface waters is commonly observed in wetlands that were restored on previously drained and farmed land, but the precise location of where the P is dissolved within the soil is unknown. This study compared the concentration of dissolved P in both the rhizospheres and soil matrix under saturated conditions. Experiments were conducted in rhizotrons (glass-walled boxes) which were filled with Ap horizon material from an Aeric Alaquod in a restored wetland. Phosphorus release was monitored from the rhizospheres of bald cypress roots (Taxodium distichum, L.), and an unplanted control representing the soil matrix. The rhizotrons were saturated for 120 days, and soil water was collected twice monthly at three depths. Numbers of live and dead roots were determined monthly. Following saturation, vigorous root growth was observed near the surface (0 to 22 cm depth) throughout the 120 days saturation period, while up to 30% of the roots in the lower layer (41 to 59 cm depth) died after 20 days of saturation. Rhizosphere processes did not increase P concentrations in the soil solution compared to the matrix controls. In the top layer of the planted treatment dissolved total P concentrations were 3.5 times lower than matrix concentrations (peak DTP of 700–900 μg P L− 1””) due to oxygen loss by root aerenchyma. Significantly larger amounts of dissolved organic C and Fe2 + were found in the rhizospheres than the matrix. Dissolved total P concentrations in the rhizosphere were equal to DTP concentrations in the matrix during the first 54 days of saturation, but lower than those of the matrix thereafter, most likely due to plant uptake. These findings indicate that under saturated conditions plant rhizospheres do not cause more P to be released to the soil water over that of the matrix, and may contain lower amounts of P than the soil matrix due to plant uptake. These results pertain to soils having an organic C concentration of at least 26 g kg− 1 or higher.}, journal={GEODERMA}, author={Moorberg, Colby J. and Vepraskas, Michael J. and Niewoehner, Christopher P.}, year={2013}, month={Jul}, pages={153–160} }
 @article{abit_amoozegar_vepraskas_niewoehner_2012, title={Soil and hydrologic effects on fate and horizontal transport in the capillary fringe of surface-applied nitrate}, volume={189}, ISSN={["1872-6259"]}, DOI={10.1016/j.geoderma.2012.05.029}, abstractNote={Substantial horizontal solute transport has been demonstrated to occur in the capillary fringe (CF) above a flowing ground water, yet the importance of the CF for solute movement has generally been ignored. This study was conducted to evaluate the fate and horizontal transport of surface-applied nitrate (NO3−) in the CF under simulated hydrologic conditions that varied flow rates. Two soils of different organic carbon content were packed in separate 240-cm long, 60-cm high and 25-cm thick flow cells. A simulated water table (WT) was established at 20 cm above the bottom of each flow cell and different pore-water velocities across the flow cell were simulated while a solution containing NO3− and bromide (Br−) was continuously applied over a small area on the surface of the soil in the flow cell. Soil solution samples were collected from two depths below the WT and two depths within the CF above the WT at four locations along the flow cell. Subsurface horizontal transport of surface-applied NO3− tended to occur exclusively in the CF as the pore-water velocity was increased. In the flow cell with soil having a small amount of organic carbon (0.3 g kg− 1), normalized concentration of NO3− and Br− remained very comparable at all monitoring locations above and below the WT. Nitrate loss via denitrification in this case was not observed as conditions were oxidizing. In flow cells with soils having an organic carbon content of 35 g kg− 1, some Br− was detected below the WT while NO3− was essentially absent. Conditions below the WT favored NO3− loss via denitrification as reflected by very low redox potentials (< 250 mV). These results suggest that collection of samples from the CF should be considered when monitoring subsurface fate and transport of surface-applied NO3− in locations with laterally moving shallow ground water.}, journal={GEODERMA}, author={Abit, Sergio M., Jr. and Amoozegar, Aziz and Vepraskas, Michael J. and Niewoehner, Christopher P.}, year={2012}, month={Nov}, pages={343–350} }
 @article{abit_amoozegar_vepraskas_niewoehner_2008, title={Solute transport in the capillary fringe and shallow groundwater: Field evaluation}, volume={7}, DOI={10.2136/vzj.2007.0102}, number={3}, journal={Vadose Zone Journal}, author={Abit, S. M. and Amoozegar, Aziz and Vepraskas, Michael and Niewoehner, C. P.}, year={2008}, pages={890–898} }
 @article{amoozegar_niewoehner_lindbo_2008, title={Water flow from trenches through different soils}, volume={13}, DOI={10.1061/(ASCE)1084-0699(2008)13:8(655)}, abstractNote={It is often assumed that soils are homogeneous when designing septic systems or modeling wastewater flow from their trenches. The main objective of this study was to assess water infiltration and movement from the trenches similar to the ones commonly used for on-site wastewater dispersal by septic systems. Four separate experiments, each using a small drainfield with four parallel trenches, were conducted at three sites with different soils. In two experiments the trenches were in the coarse-textured soil above a clayey Bt horizon. In the other two experiments the trenches were in the Bt horizon. For each experiment, 50 L of a solution containing potassium bromide and brilliant blue FCF (as a tracer dye) were applied once a day to each trench for 14 or 15 days. A sampling pit was dug perpendicular to the trenches after the tracer solution application, and the distribution of the tracer dye and Br− around the trenches on the two walls of the pit were assessed. Tracer solution infiltration from the trenche...}, number={8}, journal={Journal of Hydrologic Engineering}, author={Amoozegar, Aziz and Niewoehner, C. and Lindbo, D.}, year={2008}, pages={655–664} }
 @article{caldwell_adams_niewoehner_vepraskas_gregory_2005, title={Sampling device to extract intact cores in saturated organic soils}, volume={69}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2005.0150}, abstractNote={Physical property data on organic soils are lacking due to difficulty in collecting undisturbed samples from these frequently saturated and weakly consolidated soils. A sampling device was constructed to extract undisturbed cores from saturated organic soils in a forested setting. The sampler consists of a 100-cm-long, 7.6-cm-diam. schedule 40 PVC pipe that was fitted with female threaded adapters on either end. A cutting head was constructed to cut through the fibric root mat and other woody debris in the profile by gluing a 7.6-cm-diam. hole-saw to a male threaded adaptor that was attached to the PVC pipe. The sampler was rotated by hand into the organic soil with gentle downward pressure. When the desired depth was reached, the remaining air space in the PVC pipe was filled with water and a threaded cap was used to seal the top of the sampler. A 1.3-cm-diam. galvanized pipe was inserted next to the sampler to add water to the bottom of the core, relieving the suction created as the core was pulled from the soil. The sampler and vent pipe were pulled from the soil either by hand or with a tripod-winch arrangement. Before the cutting head was raised above the water table, it was removed and replaced with another threaded PVC cap. The 100-cm-long pipe containing the soil core was then cut into 7.6-cm-long sections using a wheel-type PVC pipe cutter. Saturated hydraulic conductivity and soil water characteristics were then measured in the laboratory using the resulting 7.6-cm-long samples encased in the PVC cylinders.}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Caldwell, PV and Adams, AA and Niewoehner, CP and Vepraskas, MJ and Gregory, JD}, year={2005}, pages={2071–2075} }