Daniel R. Hirmas

Large near-surface nitrate pools in soils capped by desert pavement in the Mojave Desert, California

We found exceptionally high nitrate levels (up to 12,750 kg ha−1) at shallow depths (≤1 m) in soils mantled by desert pavement, a common land-surface feature in arid regions. Nearby soils without desert pavement had nitrate contents that were one to two orders of magnitude lower. The soil conditions coincident with desert pavement (i.e., stability, antiquity, and virtually no leaching) favor the retention and accumulation of nitrate delivered by atmospheric deposition or in situ fixation. The nitrate stored in soils under desert pavement is a previously unrecognized pool of nitrogen that has the potential to increase the global nitrogen inventory for near-surface desert soils to five times previous estimates. Its near-surface occurrence makes this labile nitrogen pool particularly susceptible to mobilization by climate change or human disturbance, risking contamination of surface and groundwaters.

Empirical Determination of Physical Controls on Megafaunal Footprint Formation Through Neoichnological Experiments with Elephants

ABSTRACT We performed a series of neoichnological experiments with elephants to investigate the relationship between the various factors involved in controlling megafaunal footprint formation. Our ultimate goal was to provide a means to calculate original sedimentary properties of fossil-footprint–bearing siliciclastic rocks, especially those containing sauropod dinosaur tracks. Previous semiquantitative and model-based research identified multiple variables that influence footprint creation and preservation, but no rigorous, empirically based models have been constructed. We conducted track-making trials with experimental sediments and one adult female African elephant (Loxodonta africana) and one adult female Asian elephant (Elephas maximus) in a zoo setting. Data collected included track dimensions, sediment particle size distribution, sediment bulk density (&rgr;b), volumetric water content of the sediment (&thgr;v), and trackmaker walking velocity (v) and weight. We performed multiple regression analysis with a backward elimination technique to obtain the following relationship: where Vn is track volume normalized by track length, measured in cm2, &thgr;v is in percent, &rgr;b is measured in g/cm3, and v is measured in m/s. We demonstrate the utility of this equation by calculating the original moisture content of sauropod-track–bearing siltstone and sandstone beds in the Upper Jurassic Morrison Formation. Original water content values are extremely useful for paleoenvironmental and paleohydrological interpretations of sediments and paleosols. Furthermore, paleoclimate studies can benefit greatly from original soil moisture values calculated from megafaunal footprints associated with paleosols.

Quantifying Soil Structure and Porosity Using Three-Dimensional Laser Scanning

Advancements in three-dimensional (3D) digital surface scanning have opened up the possibility of capturing soil morphological information from irregular objects in high resolution. One of these advancements has been the development of a multistripe laser triangulation (MLT) technique that sweeps a series of laser stripes across a surface, while a camera offset from the laser source monitors the deformation and intensity of the reflected laser stripes. MLT scanning can be used to describe soil architecture (i.e., soil structure and porosity) from soil surfaces and soil specimens. The technique allows for the geometry of both small (<1 cm) and large (several meters) objects to be digitally captured in fine detail. In this paper, we provide examples of how MLT scanning has been applied to 3D soil specimens including the determination of bulk density from clods, the quantification of ped geometries, and the development of morphometrics from casted biopores. Examples of soil surface application of MLT scanning include the quantification of soil structure and interpedal pores from the field (excavation walls) and quantification of volume changes and crack formation in the laboratory (soil cores). When combined with other digital morphometric tools such as computed tomography, 3D laser scanning has the potential to quantify the architecture of soils across scales ranging from submicrometers to meters.

Effects of Ant (Formica subsericea) Nest Development on Physical and Hydrological Properties in a Coarse-Textured Soil

Abstract Ants may compose a large portion of the total biomass in an ecosystem and can play a significant role in soil turnover and nutrient cycling. Monitoring ant nest architecture and growth in the field can be difficult because of the destructive nature of casting ant nests. To examine nest effects on soil hydrology during different stages of development, 828 Formica subsericea workers were placed in each of two large (1.0 × 1.0 × 0.1 m) formicaria and allowed to excavate for 82 days in a coarse-textured soil collected from the field. Photographs and transparencies were used to record nest structure for five different time steps during development. After the fifth time step on Day 82, the nest was cast with dental plaster and the formicarium media were sampled. The development of the nest was associated with an increase in saturated conductivity of the soil. Backfilled entrances and vertical galleries contributed to decreasing saturated conductivity as worker numbers declined toward the end of the experiment. The presence of nests was associated with an increase in water flux through the soil material, although the effect was not as dramatic as in soils with a naturally lower saturated hydraulic conductivity.

Introduction to the Special Issue on Soil Macrofauna as Ecosystem Engineers

S oil is a critical resource for agricultural production, food security, and the maintenance of almost all life processes. The ability of soils to support all or a part of these ecosystem services depends on soil physical, chemical, and biological attributes— which are affected, directly or indirectly, by the biological activity of soil organisms including microorganisms, macrofauna, and plants. Soil macrofauna, in particular, participate actively in edaphic processes influencing soil structure (aggregate and pore formation), nutrient cycling, and the decomposition of organic matter (fragmentation, burial, and mixing of plant residues). As a result of this activity, aeration, water dynamics (infiltration, percolation, and retention processes), and the conditions for root growth in the soil are improved (Barros et al., 2001; Barros et al., 2004). Soil quality is, thus, highly dependent on the activity of soil macrofauna. Although considerable attention has been given in the literature to the role of both vegetation and microorganisms in modifying the soil environment and the consequence of that modification on the allocation of resources for other organisms, significantly less attention has been paid to the role of soil macrofauna in these processes (Botinelli et al., 2015). Yet, understanding this role is important and timely not only because the interactions of soil macrofauna in the creation, modification, and maintenance of soil physical and chemical attributes that influence the success of other organisms are not well understood, but also because global climate change is likely to have a large effect controlling the distribution of these organisms. A recent study by Makoto et al. (2014), for example, illustrates the little-known potential for millipedes to significantly alter the structure of forest litter layers and mineralization of nitrogen in response to air temperature forcings. Two articles in this Special Issue present data on the relationship between soil macrofauna and edaphic processes. In their review, Lavelle et al. (2016) discussed the important role of soil macrofauna in soil organization and the effect that this organization has on smaller organisms, such as microfauna and mesofauna communities. In support of the idea that soil macrofauna play a key role in soil organization and edaphic processes, Castilho et al. (2016) studied the effect of forest conversion to pasture on soil attributes and earthworm communities in the Amazon region of Brazil. The results presented by the authors indicate that earthworms are highly sensitive and related to land-use changes and soil physical quality in that region. The review by JohnsonMaynard and Strawn (2016) also supports the importance of

A New Stereoscopic (3D) Media Database and Teaching Strategy for Use in Large-Lecture Introductory Geoscience Courses

ABSTRACT Stereoscopic displays provide geoscience instructors with the ability to teach students the fundamental, and inherently three-dimensional, components of landforms and landscapes; yet the prevalence of such displays in higher education is limited. As costs of these systems continue to decrease, more instructors may wish to take advantage of stereoscopic display systems in their classroom. This paper serves as a guide for instructors who wish to install and use their own stereoscopic display systems using a case study conducted at the University of Kansas. The operational aspects covered include: creating stereo images, displaying stereoscopic images, selecting a stereoscopic display, and developing a new teaching strategy that incorporates the stereo system into the classroom environment. Additionally, a new database of stereoscopic media is provided to help promote the implementation of stereoscopic displays and free and open distribution of 3D teaching material.

Combined effects of polyacrylamide and nanomagnetite amendment on soil and water quality, Khorasan Razavi, Iran

Nanotechnology is increasingly being used to remediate polluted soil and water. However, few studies are available assessing the potential of nanoparticles to bind surface particles, decrease erosion, and minimize the loading of water pollutants from agricultural surface discharge. To investigate this potential, we treated in situ field plots with two practical surface application levels of anionic polyacrylamide (PAM only) with and without nanomagnetite (PAM-NM), examined soil physical properties, and evaluated the impact of this amendment on contaminant sorption and soil erosion control. Polyacrylamide and PAM-NM treatments resulted in 32.2 and 151.9 fold reductions in Mn2+, 1.8 and 2.7 fold for PO43--P, and 2.3 and 1.6 fold for NH4+-N, respectively, compared to the control. Thus, we found that the combination of PAM and NM, had an important inhibitory effect on NH4+-N and PO43--P transport from soil-pollutants which can contribute substantially to the eutrophication of surface water bodies. Additionally, since the treatment, especially at a high concentration of NM, was effective at reducing Mn2+concentrations in the runoff water, the combination of PAM and NM may be important for mitigating potential risks associated with Mn2+ toxicity. Average sediment contents in the runoff monitored during the rainfall simulation were reduced by 3.6 and 4.2 fold for the low and high concentration PAM-NM treatments when compared to a control. This treatment was only slightly less effective than the PAM-only applications (4.9 and 5.9 fold, respectively). We report similar findings for turbidity of the runoff (2.6-3.3 fold for PAM only and 1.8-2.3 fold for PAM-NM) which was caused by the effects of both PAM and NM on the binding of surface particles corresponding to an increase in aggregate size and stability. Findings from this field-based study show that PAM-modified NM adsorbents can be used to both inhibit erosion and control contaminant transport.

Soils of the Great Plains

The Great Plains is one of the largest physiographic provinces in North America and an important agricultural region. Stretching from Texas to Montana, the US portion of the Great Plains contains a diversity of soils including Mollisols, Alfisols, Aridisols, Inceptisols, and Entisols that reflect the soil-forming factors dominant in the region—parent material, climate, and time. The regional climate sets up a strong, roughly east–west, decreasing precipitation gradient and a north–south latitudinal temperature gradient. Parent material in the Great Plains reflects both the underlying geology and the type and timing of geomorphic processes that have transported that material across the region. This chapter discusses the general environment of and geomorphic processes acting in the Great Plains and explains the genesis and properties of soils found in this region.