Effect of Particle Size on Droplet Infiltration into Hydrophobic Porous Media As a Model of Water Repellent Soil

The wettability of soil is of great importance for plants and soil biota, and in determining the risk for preferential flow, surface runoff, flooding,and soil erosion. The molarity of ethanol droplet (MED) test is widely used for quantifying the severity of water repellency in soils that show reduced wettability and is assumed to be independent of soil particle size. The minimum ethanol concentration at which droplet penetration occurs within a short time (≤10 s) provides an estimate of the initial advancing contact angle at which spontaneous wetting is expected. In this study, we test the assumption of particle size independence using a simple model of soil, represented by layers of small (0.2–2 mm) diameter beads that predict the effect of changing bead radius in the top layer on capillary driven imbibition. Experimental results using a three-layer bead system show broad agreement with the model and demonstrate a dependence of the MED test on particle size. The results show that the critical initial advancing contact angle for penetration can be considerably less than 90° and varies with particle size, demonstrating that a key assumption currently used in the MED testing of soil is not necessarily valid

Effects of water withdrawals on macroinvertebrate emergence: Unexpected results for three holometabolous species

Small, low-head diversion dams are capable of withdrawing much of the flow of a river, often resulting in elevated water temperatures. Accelerated growth and development of aquatic invertebrates has been demonstrated in warmer temperatures, suggesting that the timing of insect emergence and adult body size may be significantly altered by water withdrawals. To examine the influence of summer water withdrawals on aquatic invertebrate life histories, emergence timing and adult body mass of three holometabolous species were monitored continuously for 9–10 weeks on the Umatilla and Walla Walla Rivers in arid northeastern Oregon. On each river, multiple sample sites were located along gradients of decreasing discharge and increasing water temperatures caused by successive diversions. Despite reductions in discharge of up to 93% and increases in average water temperature of up to 4.6°C from upstream to downstream, timing of median emergence was unaltered for Helicopsyche borealis, Petrophila confusalis and Glossosoma traviatum. However, in a laboratory experiment, higher temperatures led to earlier emergence for H. borealis. Water temperature in the field study was not significantly correlated with reduced adult body size of these species, though female P. confusalis were 31% smaller at the warmest sample site. Holometabolous life histories and high temperature tolerances are possible explanations for the observed resistance of these species to life history alteration.Keywords: water abstraction, Petrophila, life history, agriculture, Glossosoma, Helicopsyche, discharge, temperatur

Short-term responses of native bees to livestock and implications for managing ecosystem services in grasslands

Rangelands are significant providers of ecosystem services in agroecosystems world‐wide. Yet few studies have investigated how different intensities of livestock grazing impact one important provider of these ecosystem services—native bees. We conducted the first large‐scale manipulative study on the effect of a gradient of livestock grazing intensities on native bees in 16 40‐ha pastures in the Pacific Northwest Bunchgrass Prairie. Each pasture was exposed to one of four cattle stocking rates for two years and grazing intensity was quantified by measuring utilization. We measured soil and vegetation characteristics related to floral and nesting resources as well as several metrics of the bee community. Increased grazing intensity significantly reduced vegetation structure, soil stability, and herbaceous litter and significantly increased soil compaction and bare ground. Native bees responded with changes in abundance, richness, diversity, and community composition. Responses varied with taxa and time of season. Bumble bees were sensitive to grazing intensity early in the season, showing reduced abundance, diversity, and/or richness with increased intensity, potentially because of altered foraging behavior. In contrast, sweat bees appeared unaffected by grazing. These results show that native bee taxa vary in their sensitivity to livestock grazing practices and suggest that grazing may potentially be a useful tool for managing pollination services in mosaic agroecosystems that include rangelands

Phylogenetic Constraints Do Not Explain the Rarity of Nitrogen-Fixing Trees in Late-Successional Temperate Forests

Symbiotic nitrogen (N)-fixing trees are rare in late-successional temperate forests, even though these forests are often N limited. Two hypotheses could explain this paradox. The 'phylogenetic constraints hypothesis' states that no late-successional tree taxa in temperate forests belong to clades that are predisposed to N fixation. Conversely, the 'selective constraints hypothesis' states that such taxa are present, but N-fixing symbioses would lower their fitness. Here we test the phylogenetic constraints hypothesis.Using U.S. forest inventory data, we derived successional indices related to shade tolerance and stand age for N-fixing trees, non-fixing trees in the 'potentially N-fixing clade' (smallest angiosperm clade that includes all N fixers), and non-fixing trees outside this clade. We then used phylogenetically independent contrasts (PICs) to test for associations between these successional indices and N fixation. Four results stand out from our analysis of U.S. trees. First, N fixers are less shade-tolerant than non-fixers both inside and outside of the potentially N-fixing clade. Second, N fixers tend to occur in younger stands in a given geographical region than non-fixers both inside and outside of the potentially N-fixing clade. Third, the potentially N-fixing clade contains numerous late-successional non-fixers. Fourth, although the N fixation trait is evolutionarily conserved, the successional traits are relatively labile.These results suggest that selective constraints, not phylogenetic constraints, explain the rarity of late-successional N-fixing trees in temperate forests. Because N-fixing trees could overcome N limitation to net primary production if they were abundant, this study helps to understand the maintenance of N limitation in temperate forests, and therefore the capacity of this biome to sequester carbon

Sediment source fingerprinting: benchmarking recent outputs, remaining challenges and emerging themes

Abstract: Purpose: This review of sediment source fingerprinting assesses the current state-of-the-art, remaining challenges and emerging themes. It combines inputs from international scientists either with track records in the approach or with expertise relevant to progressing the science. Methods: Web of Science and Google Scholar were used to review published papers spanning the period 2013–2019, inclusive, to confirm publication trends in quantities of papers by study area country and the types of tracers used. The most recent (2018–2019, inclusive) papers were also benchmarked using a methodological decision-tree published in 2017. Scope: Areas requiring further research and international consensus on methodological detail are reviewed, and these comprise spatial variability in tracers and corresponding sampling implications for end-members, temporal variability in tracers and sampling implications for end-members and target sediment, tracer conservation and knowledge-based pre-selection, the physico-chemical basis for source discrimination and dissemination of fingerprinting results to stakeholders. Emerging themes are also discussed: novel tracers, concentration-dependence for biomarkers, combining sediment fingerprinting and age-dating, applications to sediment-bound pollutants, incorporation of supportive spatial information to augment discrimination and modelling, aeolian sediment source fingerprinting, integration with process-based models and development of open-access software tools for data processing. Conclusions: The popularity of sediment source fingerprinting continues on an upward trend globally, but with this growth comes issues surrounding lack of standardisation and procedural diversity. Nonetheless, the last 2 years have also evidenced growing uptake of critical requirements for robust applications and this review is intended to signpost investigators, both old and new, towards these benchmarks and remaining research challenges for, and emerging options for different applications of, the fingerprinting approach

Rethinking soil water repellency and its management

Soil water repellency (SWR) is a widespread challenge to plant establishment and growth. Despite considerable research, it remains a recalcitrant problem for which few alleviation technologies or solutions have been developed. Previous research has focused on SWR as a problem to be overcome, however, it is an inherent feature of many native ecosystems where it contributes to ecosystem functions. Therefore, we propose a shift in the way SWR is perceived in agriculture and in ecological restoration, from a problem to be solved, to an opportunity to be harnessed. A new focus on potential ecological benefits of SWR is particularly timely given increasing incidence, frequency and severity of hotter droughts in many regions of the world. Our new way of conceptualising SWR seeks to understand how SWR can be temporarily alleviated at a micro-scale to successfully establish plants, and then harnessed in the longer term and at larger spatial scales to enhance soil water storage to act as a “drought-proofing” tool for plant survival in water-limited soils. For this to occur, we suggest research focusing on the alignment of physico-chemical and microbial properties and dynamics of SWR and, based on this mechanistic understanding, create products and interventions to improve success of plant establishment in agriculture, restoration and conservation contexts. In this paper, we outline the rationale for a new way of conceptualising SWR, and the research priorities needed to fill critical knowledge gaps in order to harness the ecological benefits from managing SWR

Influence of Spanish goats on vegetation and soils in Arizona chaparral

The key to managing Arizona chaparral depends on creating and maintaining brush-free or savanna-like habitats. Brush control using fire, chemicals, and mechanical methods has been tested previously; but limited information is available on goats. This study evaluated the effect of 4 goat-stocking levels in a short duration grazing system and mechanical brush crushing on chaparral shrubs, herbaceous vegetation, litter, and soils. After 4-1/2 years, percent total shrub cover was lower (P<0.05) on paddocks stocked at 1.4, 2.4, and 4.2 Spanish goats/ha (35, 39, and 382, respectively) compared to unstacked controls (51%). Crushing brush increased the effectiveness of goats; mean total shrub cover was lower (P<0.05) on paddocks where brush was crushed vs not crushed (33 and 50% respectively). Shrubs least preferred by goats were not affected, while preferred browse was impacted at all stocking levels. Goat stocking and brush treatments did not affect perennial herbs, while annuals were generally increased by soil disturbance. Less litter (P<0.05) accumulated under shrubs subjected to heavy stocking levels compared to unbrowsed paddocks. Concentrations of N and P in the soil were also affected (P<0.05) under desert ceanothus (Ceanothus greggii Gray) where the soil bulk density was also increased (P<0.05). While goats can reduce total shrub cover, problems may result. Perennial herbaceous vegetation did not respond. Shrubs preferred by goats were also preferred by native deer. Reduced forage diversity and nutritional stress could result if these species were eliminated from the stand. Also, trampling disturbance by goats affected nitrogen accumulation in the litter and soil, but more importantly heavy browsing may eliminate nitrogen-fixing shrubsThis material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202