P. A. McDaniel

Incorporating livelihoods in biodiversity conservation: a case study of cacao agroforestry systems in Talamanca, Costa Rica

Over the past two decades, various organizations have promoted cacao agroforestry systems as a tool for biodiversity conservation in the Bribri-Cabécar indigenous territories of Talamanca, Costa Rica. Despite these efforts, cacao production is declining and is being replaced by less diverse systems that have lower biodiversity value. Understanding the factors that influence household land use is essential in order to promote cacao agroforestry systems as a viable livelihood strategy. We incorporate elements of livelihoods analyses and socioeconomic data to examine cacao agroforestry systems as a livelihood strategy compared with other crops in Talamanca. Several factors help to explain the abandonment of cacao agroforestry systems and their conversion to other land uses. These factors include shocks and trends beyond the control of households such as crop disease and population growth and concentration, as well as structures and processes such as the shift from a subsistence to a cash-based economy, relative prices of cacao and other cash crops, and the availability of market and government support for agriculture. We argue that a livelihoods approach provides a useful framework to examine the decline of cacao agroforestry systems and generates insights on how to stem the rate of their conversion to less diverse land uses.

Genesis and relationship of macromorphology and micromorphology to contemporary hydrological conditions of a welded Argixeroll from the Palouse in Idaho

Abstract Soils formed in distal loess of the Palouse region have welded profiles that make assessment of their genesis and pedostratigraphic relationships difficult. These soils typically have a mollic-cambic horizon sequence that is underlain by a well-expressed albic E horizon and a strongly developed argillic horizon. In this study, we utilized hydrological monitoring combined with micromorphological analysis and new stratigraphic data to help establish the genesis of a representative Argixeroll of the region and the relationship of its morphology to ancient and contemporary hydrological conditions. Monitoring results indicate that the Argixeroll is seasonally episaturated for approximately 5–6 months per year. Ferrimanganiferous nodules, segregations, hypocoatings, and depletion mottles are observed in thin section throughout the pedon, but dominate within, just above, and below the present-day E horizon. Measured soil Eh is sufficiently low for Fe and Mn reduction to occur for 1–3 months during the period of episaturation, suggesting that at least some of these redoximorphic features are likely to be contemporary. Other compound redoximorphic features are clearly relict, however, as they are coated by illuvial clay which is unaffected by Fe Mn redistribution processes. Thick illuvial clay coatings on interpedal fissures of the argillic horizon postdate pockets of Holocene tephra within deeply bioturbated aggregates, while other channel argillans in the same part of the pedon are clearly older. This indicates that at least two distinct phases of clay accumulation have occurred, the most recent being contemporaneous with loess aggradation during the Holocene. Our results suggest that these welded profiles consist of a mollic-cambic horizon sequence that has formed primarily in Holocene loess and an albic-argillic sequence that has formed in Wisconsinan loess. The modern-day E horizon was initiated as the clay-eluvial surface horizon of the regionally recognized Washtucna paleosol that continued forming into the late-Wisconsinan cold phase and, upon burial by Holocene loess, it has been transformed into an albic horizon and even enlarged as a result of redoximorphic processes associated with seasonal saturation.

Expression of andic and spodic properties in tephra-influenced soils of northern Idaho, USA

Abstract Tephra from Mount Mazama (Crater Lake) has strongly influenced genesis and morphology of forest soils in the Selkirk Mountains of northern Idaho. Characteristics associated with Andisols and their intergrades are common in soils throughout the area. In addition, tephra-influenced soils of the higher elevations exhibit properties of Spodosols as well. This study was initiated to examine development and relative expression of these properties along an elevational transect with its associated bioclimatic gradient. This paper presents data from three soils that encompass the range in expression of andic and spodic properties found along this gradient. Cooler, moister soils of the higher elevations have formed under subalpine fir forest and are strongly influenced by volcanic ash as indicated by color. NaF-pH, glass content, and quantities of oxalate-extractable Fe, Al, and Si. Additionally, podzolization processes have created E-Bhs horizon sequences in these soils within the last 6800 years. The clay fraction of the very strongly acid E horizon is dominated by a well-crystallized smectite mineral. Formation of an E horizon has effectively erased andic characteristics such as accumulation of short-range order minerals (SROMs), high NaF-pH, and high P retention. Soils of the middle elevations have formed under western hemlock forest and also have significant ash influence. These soils have properties transitional to those of the higher-elevation Spodosols and do not exhibit the overprint of podzolization processes. Eluvial horizons are absent although there has been significant accumulation of metal-organic complexes and inorganic SROMs in the upper horizons of these Andisols. Soils of the lower elevations have developed under relatively warmer and drier conditions associated with the lower end of the western hemlock forest zone and have comparatively less volcanic ash influence. The ash has been extensively mixed with coarse-textured glacial drift, and, as a result, these lower elevation soils lack the morphological or chemical properties associated with Spodosol development but do exhibit weak andic characteristics.

Andic soils of the inland Pacific Northwest, USA : Properties and ecological significance

Holocene tephra from the cataclysmic eruption of Mount Mazama in southwestern Oregon is an important component of many soils east of Cascade Mountains in the Pacific Northwest region. This article examines ecologically important properties of these tephra-influenced soils. Characterization data from 886 soil horizons (384 pedons) of the region meeting criteria for andic soil properties or subgroup classification as andic or vitrandic intergrades in Soil Taxonomy were used to compare morphological, chemical, and physical properties. Mazama tephra typically comprises a significant portion of a surface mantle with textures ranging from silt loam in areas distal to the tephra source to very gravelly loamy coarse sand in proximal locations. Tephra has been mixed to varying degrees with other parent materials across the region. On average, volcanic glass only comprises 31.1% of the 0.05 to 2-mm fraction and has a bimodal distribution, suggesting that some tephra was deposited with significant quantities of dust or, that since deposition, considerable reworking and mixing of glass has occurred. Oxalate-extractable Al ranges from 0.04 to 5.4% and provides the best indicator of colloidal surface activity as indicated by P retention. Cation exchange capacity (CEC) determined at field pH (ECEC) averages 7.8 cmolc kg−1 and is less than one-third the CEC determined at pH 8.2, indicating considerable variable charge and relatively low capacity of these soils to store and supply nutrient cations. Mineralogical data suggest that a reduced pool of secondary Al may be limiting allophane formation in soil horizons with less tephra influence. Volumetric water-holding capacity of ash-influenced horizons is as much as twice that of underlying horizons and underscores the importance of tephra in seasonally dry, forested ecosystems of the Inland Northwest region.

Soil Morphologic Properties and Cattle Stocking Rate Affect Dynamic Soil Properties

Abstract Soil properties that influence the capacity for infiltration and moisture retention are important determinants of rangeland productivity. Monitoring effects of grazing on dynamic soil properties can assist managers with stocking rate decisions, particularly if monitoring takes into account environmental variability associated with inherent soil morphological properties. On a Pacific Northwest Bunchgrass Prairie in northeast Oregon, we applied three cattle stocking rates (0.52, 1.04, and 1.56 animal unit months · ha−1) and an ungrazed control in a randomized complete block design for two 42-d grazing seasons and measured the change in four dynamic soil properties: soil penetration resistance, soil aggregate stability, bare ground, and herbaceous litter cover. To address apparent environmental heterogeneity within experimental units, we also utilized a categorical soil factor (termed Edaphic Habitat Types or EHT), determined by characterizing soil depth, texture, and rock fragment content at sample sites. Stocking rate did not affect extent of bare ground or soil aggregate stability. Stocking rate had a significant effect on penetration resistance, which was greatest at the high stocking rate (1.6 J · cm−1 ± 0.1 SE) and lowest in the control (1.1 J · cm−1 ± 0.1 SE). For litter cover, the effects of stocking rate and EHT interacted. In two rocky EHTs, litter cover was highest in the controls (60% ± 6 SE; 50% ± 3 SE) and ranged from 27% ± 3 SE to 33% ± 6 SE in the stocking rate treatments. Measures of penetration resistance, aggregate stability, and bare ground were different across EHTs regardless of stocking rate, but did not interact with stocking rate. Our study demonstrates that response of dynamic soil properties to stocking rates should be considered as a useful and accessible approach for monitoring effects of livestock management decisions on rangeland conditions.

DEVELOPMENT OF A GIS DATABASE FOR GROUND-WATER RECHARGE ASSESSMENT OF THE PALOUSE BASIN

The advent of Geographic Information Systems (GIS) is bringing about the expansion of soil survey data into interdisciplinary research projects. A GIS database was developed for the Palouse Basin in northern Idaho and eastern Washington to identify areas where soil and geologic features are likely to impact ground-water recharge. Using GeoProcessing operations in ArcView, 1:24,000 soil survey data and surficial geology were combined. The resulting ArcView-based GIS coverage was used to delineate recharge mechanisms and classify recharge potential in the Palouse Basin. A database was developed using binary weighting and index overlay modeling methods to assign values to soil map units based on selected soil characteristics, including permeability rates, depth to bedrock, and the presence of perched water tables. These data were then linked to Basin recharge mechanisms to produce maps indicating the potential for deep percolation through soil and subsequent recharge to the local aquifer system. Results indicate that recharge through loess is the most spatially extensive recharge mechanism, operating over 71% of the total study area. Of this, approximately 2300 ha have high potential for recharge. Recharge through stream loss operates over 16% of the total study area, whereas percolation through localized fractures in bedrock is the least extensive recharge mechanism, operating over just 13% of the total study area. Although stream loss and infiltration along Basin margins occupy a limited spatial extent they have more land area rated as ‘high potential’ for recharge. There is lower recharge potential in the eastern portion of the Basin because of the presence of extensive hydraulically restrictive subsoil horizons.

BEIDELLITE IN E HORIZONS OF NORTHERN IDAHO SPODOSOLS FORMED IN VOLCANIC ASH

While soils formed in tephra are typically dominated by poorly crystalline clay minerals, the occurrence of smectite in E horizons of podzolized soils (Spodosols) has been well-documented. We have observed a well-crystallized smectite mineral dominating the clay fraction of E horizons in tephra-derived soils of northern Idaho. This study was initiated to examine properties and distribution of this mineral along a developmental sequence of high-elevation, forested Spodosols formed in 6800-yr-old Mazama tephra. Three soils exhibiting strong, moderate, and weak E horizon development were sampled along an elevational and climatic gradient. The smectite mineral was identified as beidellite based on expansion and layer charge characteristics. Heated, Li-saturated samples from the most strongly developed E horizon exhibited relatively complete expansion to 1.8 nm with glycerol solvation and mean layer charge was calculated to be 0.44 molc/formula unit using sorption characteristics of alkylammonium ions. Apparent crystallinity and relative abundance of the beidellite in clay fractions decrease with decreasing E horizon development. The more poorly crystalline beidellite is associated with a non-expansive 1.4-nm mineral with considerable Al-hydroxy interlayering. Beidellite was not detected in underlying glacial drift or in a thin layer of 200-yr-old ash that mantles these soils, suggesting it is not inherited from these materials. Rather, our results indicate that beidellite forms in these soils in an environment characterized by low pH and a large flux of organic metal-complexing agents.

Chloride Distributions as Indicators of Vadose Zone Stratigraphy in Palouse Loess Deposits

Chloride is often used as a conservative tracer to estimate groundwater recharge rates in arid and semiarid regions. Relationships between Cl− depth profiles and vadose zone stratigraphy have revealed new information on the behavior of this dissolved constituent in pore waters of heterogeneous materials. We measured pore-water Cl− in loess deposits of the eastern Palouse region in northern Idaho, where multiple sequences of buried soils extend to ∼20 m depth. Three cores were collected to bedrock at summit, side slope, and valley positions. Pore-water Cl− distribution, clay content, soil strength, and secondary Mnd/Fed ratios were measured to identify relationships between natural tracer migration and vadose zone stratigraphy. Characterization of deep strata revealed complex sequences of extremely dense paleosol fragipans interstratified with less dense leached horizons. Abrupt changes in Cl− concentration reflect boundaries between these stratigraphic units that display contrasting physical and morphological properties. Results illustrate that loess stratigraphy influences vadose zone water movement in the Palouse. In addition, Cl− depth profiles can be used as indicators of deep stratigraphy across various landscape positions.

XAS STUDY OF Fe MINERALOGY IN A CHRONOSEQUENCE OF SOIL CLAYS FORMED IN BASALTIC CINDERS

The characterization of poorly crystalline minerals formed by weathering is difficult using conventional techniques. The objective of this study was to use cutting-edge spectroscopic techniques to characterize secondary Fe mineralogy in young soils formed in basaltic cinders in a cool, arid environment. The mineralogy of a chronosequence of soils formed on 2, 6, and 15 thousand year old basaltic cinders at Craters of the Moon National Monument (COM) was examined using synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy in combination with selective extractions. Fe K-edge XAFS is useful for determining speciation in poorly crystalline materials such as young weathering products. Over 86% of Fe in the soil clay fractions was contained in poorly crystalline materials, mostly in the form of ferrihydrite, with the remainder in a poorly crystalline Fe-bearing smectite. The XAFS spectra suggest that ferrihydrite in the 15 ka soil clay is more resistant to ammonium oxalate (AOD) extraction than is ferrihydrite in the younger materials. Fe in the poorly crystalline smectite is subject to dissolution during citrate-bicarbonate- dithionite (CBD) extraction. The results indicate that relatively few mineralogical changes occur in these soils within the millennial time frame and under the environmental conditions associated with this study. Although the secondary mineral suite remains similar in the soils of different ages, ferrihydrite crystallinity appears to increase with increasing soil age.

Hydrologic processes in valley soilscapes of the eastern Palouse basin in northern Idaho

Vadose zone hydrology in the eastern Palouse Basin of northern Idaho is poorly understood because loess deposits often contain multiple hydraulically restrictive horizons that impede water flow. Valley soilscapes are of particular interest from a hydrologic perspective, because during the winter months, most of the precipitation is redistributed as runoff and throughflow into these landscape positions. Understanding the relationship between near-surface perched water table dynamics and vadose zone hydraulic processes in valley soilscapes is necessary to assess the sustainability of the groundwater resource. We implemented a combined approach to assess hydrologic processes in valley positions using hydrometric measurements, natural tracers, and stratigraphic observations. Hydrographs of near-surface monitoring wells indicate that valley positions maintain a thicker zone of saturation for longer duration compared with adjacent upland positions. Deep tensiometers demonstrate that multiple zones of seasonal saturation develop within the vadose zone of valley soilscapes in response to paleosol fragipan horizons and sediments of contrasting hydraulic conductivity. In some instances, the saturated thickness of vadose zone water tables was greater than 2.0 m and, because they are confined, displayed a positive pressure head. On adjacent uplands, seasonal saturation occurs only above the uppermost fragipan. Eluvial horizons having low Mnd correspond to zones of saturation, whereas aquitards reflect Mnd maxima. The recharge rate calculated using natural Cl− mass balance was 2.4 mm y−1 and did not correspond to measurements of saturated thickness by tensiometers. In addition, natural chloride profiles of other valley soilscapes display differences in recharge rates according to regional patterns in soil development. Together, deep tensiometer readings, secondary Mn distributions, and Cl− profiles suggest that groundwater recharge does not occur via piston flow. Detailed stratigraphic analysis illustrates that preferential flow is a possible recharge mechanism. Results suggest that valley soilscapes play an important role in both surficial and deep regolith hydrological processes in the Palouse Basin.