Characterization of Soil Water Content Variability and Soil Texture Using GPR Groundwave Techniques

Accurate characterization of near-surface soil water content is vital for guiding agricultural management decisions and for reducing the potential negative environmental impacts of agriculture. Characterizing the near-surface soil water content can be difficult, as this parameter is often both spatially and temporally variable, and obtaining sufficient measurements to describe the heterogeneity can be prohibitively expensive. Understanding the spatial correlation of near-surface soil water content can help optimize data acquisition and improve understanding of the processes controlling soil water content at the field scale. In this study, ground penetrating radar (GPR) methods were used to characterize the spatial correlation of water content in a three acre field as a function of sampling depth, season, vegetation, and soil texture. GPR data were acquired with 450 MHz and 900 MHz antennas, and measurements of the GPR groundwave were used to estimate soil water content at four different times. Additional water content estimates were obtained using time domain reflectometry measurements, and soil texture measurements were also acquired. Variograms were calculated for each set of measurements, and comparison of these variograms showed that the horizontal spatial correlation was greater for deeper water content measurements than for shallower measurements. Precipitation and irrigation were both shown to increase the spatial variability of water content, while shallowly-rooted vegetation decreased the variability. Comparison of the variograms of water content and soil texture showed that soil texture generally had greater small-scale spatial correlation than water content, and that the variability of water content in deeper soil layers was more closely correlated to soil texture than were shallower water content measurements. Lastly, cross-variograms of soil texture and water content were calculated, and co-kriging of water content estimates and soil texture measurements showed that geophysically-derived estimates of soil water content could be used to improve spatial estimation of soil texture

Triclosan, Chlorinated Triclosan Derivative, and Dioxin Levels in Minnesota Lakes

The Microsoft Excel files (.xls) are available in their original form. For preservation and long-term access, the multiple-tab structure of the excel files have been converted to comma separated value (.csv) files and included here as a zip. The data is identical in these two versions, except that the archived version will not include any special formatting of the excel files (colored cells, bold, etc.) or graphs generated from the data.The data were collected and generated during the period of 2010-2012 by collecting sediment cores from lakes in Minnesota, dating the years the sediment was deposited as a function of depth, and extracting sections of the cores with solvent to determine the levels of triclosan (TCS), chlorinated triclosan derivatives (CTD), and dioxins in the sediment (PCDD). Dating was performed at the St. Croix Watershed Research Station, triclosan and chlorinated triclosan derivative measurements at the University of Minnesota Department of Civil Engineering, and dioxin analysis by Pace Analytical. The data consists of eight Excel files that include the following tabs 1) accumulation rate and focus corrected accumulation rate of the target contaminants as function of time (FF_Flux), 2) the concentrations of the target contaminants and function of time, 3) the calibration curves of the instruments for triclosan and chlorinated triclosan derivatives, and 4) various statistical analyses (ANOVA). Note that the further back in time, the deeper the sediment that the sample was derived from.Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota ResourcesNational Science FoundationCBET 096716

Quantification of Triclosan, Chlorinated Triclosan Derivatives, and their Dioxin Photoproducts in Lacustrine Sediment Cores

When discharged into surface waters via wastewater effluents, triclosan, the antimicrobial agent in handsoaps, and chlorinated triclosan derivatives (CTDs, formed during disinfection with chlorine) react photochemically to form polychlorinated dibenzo-<i>p</i>-dioxins. To evaluate the historical exposure of waters to these compounds, the levels of triclosan, CTDs, and their derived dioxins were determined in sediment cores collected from wastewater-impacted Minnesota lakes. The accumulation rates and temporal trends of triclosan, CTDs, and dioxins in aquatic sediments were found to be a function of historical wastewater treatment operations and lake system scale. Cores collected from large-scale riverine systems with many wastewater sources recorded increasing concentrations of triclosan, CTDs, and their derived dioxins since the patent of triclosan in 1964. In small-scale lakes with a single wastewater source, the trends were directly attributed to increased triclosan use, local improvements in treatment, and changes in wastewater disinfection since the 1960s. In the lake with no wastewater input, no triclosan or CTDs were detected. Overall, concentrations of triclosan, CTDs, and their dioxins were higher in small-scale systems, reflecting a greater degree of wastewater impact. In cores collected in northern MN, the four dioxins derived from triclosan are present prior to the patent of triclosan, suggesting a secondary source. It is clear, however, that triclosan and CTDs are the dominant source of these congeners after 1965 in systems impacted by wastewater