No abstract

Visible and near‐infrared (VNIR, 400–2500 nm) diffuse reflectance spectroscopy (DRS) is a rapid, proximal‐sensing method that has proven useful in quantifying constituents of dried and ground soil samples. Very little is known, however, about how DRS performs in a field setting on soils scanned in situ. The overall goal of this research was to evaluate the feasibility of VNIR‐DRS for in situ quantification of clay content of soil from a variety of parent materials. Seventy‐two soil cores were obtained from six fields in Erath and Comanche counties, Texas. Each soil core was scanned with a visible near‐infrared spectrometer, with a spectral range of 350 to 2500 nm, at four different combinations of moisture content and pretreatment: field‐moist in situ, air‐dried in situ, field‐moist smeared in situ, and air‐dried ground. The VNIR spectra were used to predict total and fine clay content of the soil using partial least squares (PLS) regression. The PLS model was validated with 30% of the original soil cores that were randomly selected and not used in the calibration model. The validation clay predictions had a root mean squared deviation (RMSD) of 61 and 41 g kg−1 dry soil for the field‐moist and air‐dried in situ cores, respectively. The RMSD of the air‐dry ground samples was between the two in situ RMSDs and comparable to values in the literature. Smearing the samples increased the field‐moist in situ RMSD to 74 g kg−1 Whole‐field holdout validation results showed that soils from all parent materials need to be represented in the calibration samples for maximum predictability. In summary, DRS is an acceptable technique for rapidly measuring soil clay content in situ for various water contents and parent materials.

Stable carbon isotope analysis of organic carbon in alluvial deposits and soils of three streams in central Texas reveals significant shifts in the ratio of C3 to C4 plant biomass production during the past 15,000 yr. These temporal changes in vegetation appear to be in response to changes in climate. During the late Pleistocene, C4 plants comprised only about 45 to 50% of the vegetative biomass in this area, suggesting that conditions were cooler and wetter than at any time during the past 15,000 yr. The time between 11,000 and 8000 yr B.P. is interpreted as transitional between late Pleistocene conditions and warmer and drier Holocene conditions based on a slight increase in the abundance of C4 plant biomass. During the middle Holocene, between approximately 6000 and 5000 yr B.P., mixed C3/C4 plant communities were replaced almost completely by C4-dominated communities, indicating prairie expansion and warmer and drier climatic conditions. By 4000 yr B.P., the abundance of C4 plant biomass decreased to levels similar to the early Holocene transitional period, suggesting a return to cooler and wetter climatic conditions. No significant shift in the ratio of C3 to C4 productivity has occurred during the last 4000 yr, except for a slight increase in the abundance of C4 plant biomass around 2000 yr B.P. The results of this investigation correlate well with other regional late Quaternary climatic interpretations for central and north Texas, the Southern Plains region, and with other portions of the Great Plains.

Compelling archaeological evidence of an occupation older than Clovis (~12.8 to 13.1 thousand years ago) in North America is present at only a few sites, and the stone tool assemblages from these sites are small and varied. The Debra L. Friedkin site, Texas, contains an assemblage of 15,528 artifacts that define the Buttermilk Creek Complex, which stratigraphically underlies a Clovis assemblage and dates between ~13.2 and 15.5 thousand years ago. The Buttermilk Creek Complex confirms the emerging view that people occupied the Americas before Clovis and provides a large artifact assemblage to explore Clovis origins.

Pedotransfer functions (PTFs) have gained recognition in recent years as an approach to translate simple soil characteristics found in soil surveys into more complicated model input parameters. However, existing pedotransfer functions have not yet incorporated critical soil structural information. This study showed that soil hydraulic properties could be estimated from morphological features determined in situ (including texture, initial moisture state, pedality, macroporosity, and root density) through a morphology quantification system. Comparison between the class and continuous PTFs developed in this study indicated that the use of quantified morphological properties yielded predictive power similar to that of physical properties in estimating hydraulic conductivity at zero potential; water flow rates in macro‐, meso‐, and micropores; and a soil structure and texture parameter αmacro The results confirmed that soil structure was crucial in characterizing hydraulic behavior in macropore flow region; whereas texture had major impact on those hydraulic properties controlled by micropores. Depending on the flow domain to be included, estimation of hydraulic properties required the use of different combinations of morphometric indices or physical properties. The PTFs established may be used as starting points for estimating model input parameters.