The Role of Leaf Decomposition in Macroinvertebrate Colonization

Decomposition plays an important ecological role in carbon and nutrient cycling that supply food and energy resources to food webs. This study investigates the potential role that leaf decomposition of different leaf species may play in macroinvertebrate assemblages in upper Midwest streams. We hypothesized that the different decomposition rates experienced with different leaf species and in different streams would have an effect on invertebrate colonization due to the variance in nutrient availability. Due to altered fire regimes and other influences, forests are experiencing declines in fire-adapted, heliophytic species such as oaks and compositional shifts toward shade-tolerant, mesophytic species such as maples. This compositional shift in forest species, also known as Mesophication, may have implications for macroinvertebrate communities. Sugar Maple (Acer saccharum) and Bur Oak (Quercus macrocarpa) leaves were chosen to test the effect of their decomposition on invertebrates due to their prevalence in the Midwest, research supporting their expected difference in decomposition rates, and implications for Mesophication. Dried leaves were placed into 60 mesh bags (30 of each leaf species) with a starting dry mass of 5g ± 0.1, into three different streams for 22 days. Mass loss was measured to quantify decomposition rates and macroinvertebrates within each mesh bag were collected and identified to the family level. In agreement with past research, Sugar Maple leaves decomposed significantly faster than Bur Oak leaves. Leaf decomposition rate varied significantly across the experiment (ANOVA, F= 55.428, p= 0.000) and was strongly impacted by leaf type (ANOVA, F=264.449, p=0.000) and by stream (ANOVA, F=5.640, p=0.006) . However, contrary to our hypothesis, leaf type did not have an effect on invertebrate communities observed in the leaf bags in terms of abundance, Simpson’s diversity, Shannon’s diversity, or Family Biotic Index. Likewise, stream did not have an effect on macroinvertebrate indices, except for richness (ANOVA, F=5.047, p=.010). Invertebrate assemblages in all streams were dominated by predator and collector/gatherer taxa. Overall, leaf type did not have a significant effect on macroinvertebrate communities found colonizing the leaf packs despite the leaf types significant difference in decomposition rates. A possible explanation for this lack of effect is that the numerically dominant predator and collector/gatherer taxa may rely on leaf types for habitat or protection from predators as opposed to being directly involved in the decomposition process like shredders (which were rare in all streams). Further research might include allowing for a longer decomposition time to look for the impact of later colonizing species or species that may differ in preference once the difference between leaf types becomes more pronounced later in decomposition

Identifying robust response options to manage environmental change using an ecosystem approach:a stress-testing case study for the UK

A diverse range of response options was evaluated in terms of their utility for sustaining ecosystem services in the UK. Robustness of response options was investigated by applying a ‘stress-testing’ method which evaluated expected performance against combined scenarios of socioeconomic and climate change. Based upon stakeholder feedback, a reference scenario representing current trends in climate and socioeconomic drivers (‘business-as-usual’) was used as a dynamic baseline against which to compare results of other scenarios. The robustness of response options was evaluated by their utility in different environmental and social contexts as represented by the scenarios, and linked to their adaptability to adjust to changing conditions. Key findings demonstrate that adaptability becomes increasingly valuable as the magnitude and rate of future change diverges from current trends. Stress-testing also revealed that individual responses in isolation are unlikely to be robust meaning there are advantages from integrating cohesive combinations (bundles) of response options to maximise their individual strengths and compensate for weaknesses. This identifies a role for both top-down and bottom-up responses, including regulation, spatial targeting, incentives and partnership initiatives, and their use in combination through integrated assessment and planning consistent with the adoption of an Ecosystem Approach. Stress-testing approaches can have an important role in future-proofing policy appraisals but important knowledge gaps remain, especially for cultural and supporting ecosystem services. Finally, barriers and enablers to the implementation of more integrated long-term adaptive responses were identified drawing on the ‘4 Is’ (Institutions, Information, Incentives, Identity) conceptual framework. This highlighted the crucial but usually understated role of identity in promoting ownership and uptake of responses

Drivers of Macroinvertebrate Community Integrity Within Mixed Urban and Agricultural Dominated Mississippi Tributary Watersheds

The “urban stream syndrome” refers to a multitude of impacts caused by urbanization including flashier hydrograph, elevated concentrations of nutrients and contaminants, altered channel morphology and stability, reduced biotic richness, with increased dominance of tolerant species, reduced base flow and increased suspended solids. The drivers of these “symptoms” include impervious surfaces, piping in stormwater drainages, habitat and forest loss, water supply and sewer leaking, and direct alterations to channel morphology and flow. The goal of this study was to assess the integrity of the macroinvertebrate community and determine the most significant drivers of such integrity at the catchment, riparian zone, and reach scales. The study area included eight mixed land use (urban & agricultural) watersheds in Rock Island County, IL and Scott County, IA. Watersheds were delineated using Arc-GIS. Forty-one sampling sites were identified to capture the maximum variation in known drivers of watershed degradation. Macroinvertebrates were sampled using standard dip-netting techniques, with staples apportioned to different in-stream habitats weights by habitat abundance. Water quality data was collected monthly for the following parameters: total dissolved solids (TDS), total suspended solids (TSS) dissolved oxygen (DO), phosphate, and discharge. Sub-catchment basins above each sampling site were then delineated and used to quantify upstream landscape characteristics using available geospatial data including land cover, total impervious surface and within a 5m buffer of streams, etc. The family biotic index (FBI), a measure of integrity in relation to organic pollution tolerance was calculated

Polarization-Engineering in III-V Nitride Heterostructures: New Opportunities For Device Design

The role of spontaneous and piezoelectric polarization in III-V nitride heterostructure devices is discussed. Problems as well as opportunities in incorporating polarization in abrupt and graded heterojunctions composed of binary, ternary, and quaternary nitrides are outlined.Comment: 7 pages, 5 figure

Validation of an arterial constitutive model accounting for collagen content and crosslinking

During the progression of pulmonary hypertension (PH), proximal pulmonary arteries (PAs) increase in both thickness and stiffness. Collagen, a component of the extracellular matrix, is mainly responsible for these changes via increased collagen fiber amount (or content) and crosslinking. We sought to differentiate the effects of collagen content and cross-linking on mouse PA mechanical changes using a constitutive model with parameters derived from experiments in which collagen content and cross-linking were decoupled during hypoxic pulmonary hypertension (HPH). We employed an eight-chain orthotropic element model to characterize collagen’s mechanical behavior and an isotropic neo-Hookean form to represent elastin. Our results showed a strong correlation between the material parameter related to collagen content and measured collagen content (R2 = 0.82, P < 0.0001) and a moderate correlation between the material parameter related to collagen crosslinking and measured crosslinking (R2 = 0.24, P = 0.06). There was no significant change in either the material parameter related to elastin or the measured elastin content from histology. The model-predicted pressure at which collagen begins to engage was ∼25 mmHg, which is consistent with experimental observations. We conclude that this model may allow us to predict changes in the arterial extracellular matrix from measured mechanical behavior in PH patients, which may provide insight into prognoses and the effects of therapy

Reviews

Reviews of Unions on the board, The social organisation of industrial conflict: control and resistance in the workplace, Good industrial relations: theory and practice, Industrial conflict and den1ocracy : the last chance, The nature of work: an introduction to debates on the labour process, Cul de sac : The question of New Zealand's future, Innovation and Australian industrial relation

Hop: Heterogeneity-Aware Decentralized Training

Recent work has shown that decentralized algorithms can deliver superior performance over centralized ones in the context of machine learning. The two approaches, with the main difference residing in their distinct communication patterns, are both susceptible to performance degradation in heterogeneous environments. Although vigorous efforts have been devoted to supporting centralized algorithms against heterogeneity, little has been explored in decentralized algorithms regarding this problem. This paper proposes Hop, the first heterogeneity-aware decentralized training protocol. Based on a unique characteristic of decentralized training that we have identified, the iteration gap, we propose a queue-based synchronization mechanism that can efficiently implement backup workers and bounded staleness in the decentralized setting. To cope with deterministic slowdown, we propose skipping iterations so that the effect of slower workers is further mitigated. We build a prototype implementation of Hop on TensorFlow. The experiment results on CNN and SVM show significant speedup over standard decentralized training in heterogeneous settings

Double Averaging Analysis Applied to a Large Eddy Simulation of Coupled Turbulent Overlying and Porewater Flow

Freestream turbulence in rivers is a key contributor to the flux of dissolved nutrients, carbon, and other ecologically important solutes into porewater. To advance understanding of turbulent hyporheic exchange and porewater transport, we investigate flow over and through a rough bed of spheres using large eddy simulation (LES). We apply double averaging (combined space and time averaging) to the LES results to determine the mean velocity distribution, momentum balance, and drag forces. Our simulations show large-scale freestream structures interacting strongly with vortices generated at the surfaces of individual spheres to control turbulent momentum fluxes into the bed. The transition between turbulent flow and Darcy flow occurs over the first row of spheres, where turbulence decays rapidly and turbulent kinetic energy, Reynolds stress, and drag forces peak. Below this region, turbulence is only present in the high-velocity flow in open pore throats. Experimental observations suggest that minimum mean porewater velocity occurs in the first open pore space below the transition region, but our results show that the minimum occurs between the first and second pore spaces. The simulation mean porewater velocities are approximately half those captured in measurements because the model resolves the entire flow continuum while measurements can access high-velocity fluid in open pores. The high-resolution dual time-space averaging of the LES resolves both turbulent and mean flow features that are important to interfacial solute and particle fluxes, providing a means to include turbulent hyporheic exchange in upscaled river models, which has not been achieved to date