Deposition Gradient Research Articles

The effect of nitrogen deposition on the vegetation of wet heathlands

The statistical modelling of joint species abundance is currently receiving increasing attention in the ecological literature because it complements earlier descriptive accounts of the effect of disturbance on community change with quantitative measures of spatial covariation among species at different spatial scales. Using a hierarchical Bayesian approach, we fitted both temporal and spatial plant cover data to a joint distribution model of plant abundance of the dominant plants in wet heathlands (Erica tetralix, Calluna vulgaris and Molinia caerulea) undergoing nitrogen deposition over several decades. The spatial analysis was based on pin-point cover data from 114 Danish sites with a total of 1509 randomly placed plots along a nitrogen deposition gradient. The temporal analysis was based on pin-point cover data from 22 sites with a total of 986 observations from plots that had been resampled at least three times since 2007. The spatial variation was partially explained by nitrogen deposition, as the cover of Erica decreased significantly with nitrogen deposition, whereas the cover of both Calluna and Molinia increased (albeit non-significantly) with nitrogen deposition. There was a strong and significant positive spatial covariation between Erica and Calluna. Oppositely, there was a strong and significant negative spatial covariation between Calluna and Molinia. The spatial covariation between Erica and Molinia was not significantly different from zero. There were no significant changes in the cover of any of the three species since 2007. However, by including data from 2004, the previously reported result of a significant decreasing cover of Erica was confirmed, and the cover of Calluna increased significantly. We conclude that the statistical modelling of joint species abundance is a potentially powerful tool to understand the effect of the alteration of nitrogen dynamics on community composition. This is essential to design management practices aligned with the predicted effects of varying levels of nitrogen deposition on community structure. The study also demonstrated the insight gained on the community dynamics by the use of hierarchical Bayesian models.

Chronology of the Fram Slide Complex offshore NW Svalbard and its implications for local and regional slope stability

The best known submarine landslides on the glaciated NW European continental margins are those at the front of cross-shelf troughs, where the alternation of rapidly deposited glycogenic and hemi pelagic material generates sedimentary overpressure. Here, we investigate landslides in two areas built of contourite drifts bounded seaward by a ridge-transform junction. Seismic and bathymetric data from the Fram Slide Complex are compared with the tectonically similar Vastness area ~120km to the south, to analyze the influence of local and regional processes on slope stability. These processes include tectonic activity, changes of climate and oceanography, gas hydrates and fluid migration systems, slope gradient, toe erosion and style of contourite deposition. Two areas within the Fram Slide Complex underwent different phases of slope failures, whereas there is no evidence at all for major slope failures in the Vastness area. The comparison cannot reveal the distinct reason for slope failure but demonstrates the strong impact of variation in the local controls on slope stability. The different failure chronologies suggest that toe erosion, which is dependent on the throw of normal faults, and the different thickness and geometry of contourite deposits can result in a critical slope morphology and exert pronounced effects on slope stability. These results highlight the limitations of regional hazard assessments and the need for multi-disciplinary investigations, as small differences in local controlling factors led to substantially different slope failure histories.

Atmospheric transport of trace elements and nutrients to the oceans

This paper reviews atmospheric inputs of trace elements and nutrients to the oceans in the context of the GEOTRACES programme and provides new data from two Atlantic GEOTRACES cruises. We consider the deposition of nitrogen to the oceans, which is now dominated by anthropogenic emissions, the deposition of mineral dust and related trace elements, and the deposition of other trace elements which have a mixture of anthropogenic and dust sources. We then consider the solubility (as a surrogate for bioavailability) of the various elements. We consider briefly the sources, atmospheric transport and transformations of these elements and how this results in strong spatial deposition gradients. Solubility of the trace elements also varies systematically between elements, reflecting their sources and cycling, and for some trace elements there are also systematic gradients in solubility related to dust loading. Together, these effects create strong spatial gradients in the inputs of bioavailable trace elements to the oceans, and we are only just beginning to understand how these affect ocean biogeochemistry.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Responses of soil N-fixing bacteria communities to invasive species over a gradient of simulated nitrogen deposition

Soil N-fixing bacteria (SNB) play an important role in the invasion by invasive plant species (IPS). Meanwhile, progressive increases in the level of anthropogenic N deposition can change both soil physicochemical properties and the ecological characteristics of soil microbial communities, with particular impact on SNB. This can impact the soil micro-ecological mechanisms of invasion. This study used new-generation high throughput sequencing technology to determine the effects of invasive plant species Amaranthus retroflexus L. on the structure and diversity of SNB communities over a gradient of simulated N deposition (SND). The study found that soil pH decreased but soil electrical conductivity increased under A. retroflexus invasion. The diversity and richness of SNB decreased under A. retroflexus invasion, due to the altered soil nutrient content mediated by the root exudates released from A. retroflexus, and/or the decreased soil pH triggered by the invasion of A. retroflexus. SND at low levels (2.5–25gNm−2yr−1) decreased soil pH but SND at high levels (50gNm−2yr−1) increased soil pH significantly via soil secondary salinization. Thus, atmospheric N deposition may exert soil acidification at levels of atmospheric N deposition below critical values but soil alkalization when the level of N exceeds a critical threshold. To a certain extent, SND can increase the species number and the richness of SNB. SND at high levels (50gNm−2yr−1) significantly increased the diversity of SNB but significantly decreased the dominance of SNB. Amaranthus retroflexus invasion with SND can decrease the species number, diversity, and richness of SNB and increase the dominance of SNB. The interaction of these effects can produce a neutralizing effect on the diversity and richness of SNB. Thus, the invasion of A. retroflexus may be reduced under SND as a result of the decreased diversity and richness of SNB.

Atmospheric deposition of soluble trace elements along the Atlantic Meridional Transect (AMT)

We briefly review the role of atmospheric deposition measurements within the Atlantic Meridional Transect (AMT) programme and then go on to present new data on the soluble concentrations of a range of trace metals (Fe, Al, Mn, Ti, Zn, V, Ni and Cu) and major ions in aerosols collected along the AMT transect. The results allow us to identify emission sources of the trace metals particularly in terms of the relative importance of anthropogenic versus crustal sources. We identify strong gradients in concentrations and deposition for both crustal and anthropogenically sourced metals with much higher inputs to the North Atlantic compared to the South Atlantic, reflecting stronger land based emission sources in the Northern Hemisphere. We suggest anthropogenic sources of Ni and V may include an important component from shipping.We consider the extent to which these gradients are reflected in surface water concentrations of these metals based on the GEOTRACES water column trace metal data. We find there is a clear difference in the concentrations of surface water dissolved Al and Fe between the north and south Atlantic gyres reflecting atmospheric inputs. However for Mn, V or Ni, higher inputs to the North Atlantic compared to the South Atlantic are not clearly reflected in their water column concentrations.

Long-term temporal relationships between environmental conditions and xylem functional traits: a meta-analysis across a range of woody species along climatic and nitrogen deposition gradients.

The objectives of this study were to provide a quantitative description of the long-term effects of environmental variability on xylem functional traits, in order to better assess xylem capacity to change in response to climate change. Twenty-six sites throughout the world, primarily in Europe, were chosen where results from long-term measurements of anatomical traits were previously published. Published data on long-term xylem anatomy (conduit size and density) and ring width variability were compiled across a range of tree species, which was subsequently related to variability in temperature, precipitation and nitrogen deposition rates across the study sites using generalized additive models and Bayesian methods. We found some appreciable relationships between xylem traits (conduit area Ac and conduit density Dc) and environmental variables; whereas combined trait indices (lumen fraction: Ac × Dc and vessel composition: Ac/Dc) were found to be rather constant across a wide range of environmental conditions and to be decoupled from tree growth rates. Overall, results suggested xylem traits coordinated towards a homeostasis in xylem function, which appeared to act across a wide range of environmental conditions. Results showed also nitrogen deposition was associated with xylem traits and vessel composition: increased nitrogen availability due to nitrogen deposition might facilitate construction of a xylem structure efficient for water transport, and concurrently provide capacity to withstand the risks of drought-induced embolism.

Synchronous diversification of Laurentian and Baltic rhynchonelliform brachiopods: Implications for regional versus global triggers of the Great Ordovician Biodiversification Event

Abstract The profound global impact of marine radiations during the Great Ordovician Biodiversification Event (GOBE) is widely appreciated; however, diversification varied among paleocontinents and these individual trajectories are less understood. Here we present a new species-level diversity curve for rhynchonelliform brachiopods from midcontinental Laurentia based on bed-by-bed analysis of the Simpson Group of Oklahoma (USA). Diversity and abundance data span the Dapingian through Sandbian Stages, which encompass the interval of maximum global diversification. A rapid, statistically significant increase in brachiopod diversity was observed in the early Darriwilian Histiodella holodentata Biozone. We interpret this as a biological signal because the increase cannot be explained by sampling intensity, facies types, or position along depositional gradient. Diversifications on Laurentia and Baltica were temporally synchronous at the biozone level, and cumulative diversity curves for the regions show similar patterns, suggesting a global driver for the radiations. The taxonomic composition of the brachiopod faunas, however, differs substantially, highlighting the importance of regional controls on diversification. Thus both global and local factors controlled diversity increase during the GOBE.

Relative importance of local- and large-scale drivers of alpine soil microarthropod communities.

Nitrogen (N) deposition and climate are acknowledged drivers of change in biodiversity and ecosystem function at large scales. However, at a local scale, their impact on functions and community structure of organisms is filtered by drivers like habitat quality and food quality/availability. This study assesses the relative impact of large-scale factors, N deposition and climate (rainfall and temperature), versus local-scale factors of habitat quality and food quality/availability on soil fauna communities at 15 alpine moss-sedge heaths along an N deposition gradient in the UK. Habitat quality and food quality/availability were the primary drivers of microarthropod communities. No direct impacts of N deposition on the microarthropod community were observed, but induced changes in habitat quality (decline in moss cover and depth) and food quality (decreased vegetation C:N) associated with increased N deposition strongly suggest an indirect impact of N. Habitat quality and climate explained variation in the composition of the Oribatida, Mesostigmata, and Collembola communities, while only habitat quality significantly impacted the Prostigmata. Food quality and prey availability were important in explaining the composition of the oribatid and mesostigmatid mite communities, respectively. This study shows that, in alpine habitats, soil microarthropod community structure responds most strongly to local-scale variation in habitat quality and food availability rather than large-scale variation in climate and pollution. However, given the strong links between N deposition and the key habitat quality parameters, we conclude that N deposition indirectly drives changes in the soil microarthropod community, suggesting a mechanism by which large-scale drivers indirectly impacts these functionally important groups.

Vegetation community change points suggest that critical loads of nutrient nitrogen may be too high

It is widely accepted that elevated nitrogen deposition can have detrimental effects on semi-natural ecosystems, including changes to plant diversity. Empirical critical loads of nutrient nitrogen have been recommended to protect many sensitive European habitats from significant harmful effects. In this study, we used Threshold Indicator Taxa Analysis (TITAN) to investigate shifts in vegetation communities along an atmospheric nitrogen deposition gradient for twenty-two semi-natural habitat types (as described under Annex I of the European Union Habitats Directive) in Ireland. Significant changes in vegetation community, i.e., change points, were determined for twelve habitats, with seven habitats showing a decrease in the number of positive indicator species. Community-level change points indicated a decrease in species abundance along a nitrogen deposition gradient ranging from 3.9 to 15.3 kg N ha−1 yr−1, which were significantly lower than recommended critical loads (Wilcoxon signed-rank test; V = 6, p < 0.05). These results suggest that lower critical loads of empirical nutrient nitrogen deposition may be required to protect many European habitats. Changes to vegetation communities may mean a loss of sensitive indicator species and potentially rare species in these habitats, highlighting how emission reductions policies set under the National Emissions Ceilings Directive may be directly linked to meeting the goal set out under the European Union’s Biodiversity Strategy of “halting the loss of biodiversity” across Europe by 2020.

Geochemical pattern of soils in Bobovdol valley, Bulgaria. Assessment of Cd and Co contents

The chemical composition of soils spread in the Bobov dol valley was studied in order to reveal the natural and anthropogenic patterns of Cd and Co spatial distribution. A sampling procedure based on the irregular grid of points and validated analytical methods were used in the field and laboratory studies. It is found that Cd content varies from 0.21 to 0.90 mg kg -1 in studied soils and the average value of 0.55 mg kg -1 coincides with concentration demarcating soil pollution (0.5 mg kg -1 ). Co content ranges from 2.22 to 15.76 mg kg -1 and in 70 % of sampled points exceeds the natural background content of 7.8 mg kg -1 found in local rocks. Still, Cd enrichment of studied soils is more significant than Co’s with coefficient of Clarke concentration of 3.67. Hence, the secondary deposition of studied elements as a result of the Bobov dol Thermal power plant air emissions is verified by results obtained. The spatial distribution of Cd and Co is featured with an altitudinal gradient in deposition and a trend of quantitative depletion in the South of Plant. Soil organic matter and pH have no influence on the content and spatial distribution of studied elements. Elements iron affinity governs their geochemical linkage in soils although cobalt occurs allied with aluminum and titanium.

Applicability of a drift-flux model of aerosol deposition in a test tunnel and an indoor heritage environment

Near-wall turbulence associated with air flows parallel to walls can promote aerosol deposition. In indoor environments, where this kind of flow is frequently present, this results in local deposition gradients near ventilation inlets and outlets. This phenomenon is of special interest to the heritage field, which is often concerned about the spatial distribution of deposition and its links to environmental management. In this paper we investigate the capability of a drift-flux model of particulate matter deposition to describe this mechanism. This model has often been validated using decay rates of particulate matter concentration; however, in several indoor applications the interest is not in concentration but in the spatial distribution of the deposition flux. To test the model, we use untreated atmospheric aerosols in two different cases: an experimental tunnel designed to induce near-wall velocity gradients and an actual indoor room with various ventilation regimes. Both systems exhibit significantly inhomogeneous deposition distributions. While the first system is operated under controlled laboratory conditions, the second yields data collected in-situ during a six-month monitoring campaign. In either case the model reproduces the experimental values with enough accuracy to allow understanding how the environment behaves. This work confirms the usability of the drift-flux approach as an analysis tool for particle deposition in complex environments in a wide range of geometries.

How long do ecosystems take to recover from atmospheric nitrogen deposition?

Atmospheric nitrogen (N) deposition is a considerable threat to biodiversity and ecosystem function globally. Many experimental N additions and studies using gradients of ambient deposition have demonstrated impacts on plant species richness, diversity and composition in a broad range of habitats together with changes in soil biogeochemistry. In the last two decades levels of N deposition have begun to decline in some parts of Europe but it is currently difficult to assess the extent to which reductions in N deposition will result in recovery within semi-natural habitats. There have been a number of investigations using the cessation of N additions in long-term experiments, monitoring in areas where ambient deposition has declined, transplants to situations with lower N inputs and roof experiments where rain is collected and cleaned. This review collates evidence from experiments in grasslands, forests, heathlands and wetlands where N additions have ceased or where N inputs have been reduced to assess how likely it is that habitats will recover from N deposition. The results of the majority of studies suggest that vegetation species composition, below-ground communities and soil processes may be slow to recover whereas some soil variables, such as nitrate and ammonium concentrations, can respond relatively rapidly to reductions in N inputs. There are a number of barriers to recovery such as continued critical load exceedance and lack of seed bank or local seed source, and there is the potential for vegetation communities to reach an alternative stable state where species lost as a consequence of changes due to N deposition may not be able to recolonise. In these cases only active restoration efforts can restore damaged habitats.

Vegetation community change in Atlantic oak woodlands along a nitrogen deposition gradient

Atlantic old sessile oak woodlands are of high conservation importance in Europe, listed in the European Union (EU) Habitats Directive Annex I, and known for their rich bryophyte communities. Their conservation status ranges from unfavourable to bad across their known distribution, which is predominantly within the UK and Ireland, but also extends into Iberia and Brittany. The objectives of this study were to determine if nitrogen (N) deposition, a known driver of terrestrial biodiversity loss, was a significant predictor of community composition in old sessile oak woodlands (i.e., EU Habitats Directive Annex I class: 91A0), and to identify significant changes in individual plant species and community-level abundance (i.e., change points) along an N deposition gradient. Relevé data from 260 Irish oak woodland plots were evaluated using Canonical Correspondence Analysis (CCA) and Threshold Indicator Taxa ANalysis (TITAN). Nitrogen deposition accounted for 14% of the explainable variation in the dataset (inertia = 0.069, p < 0.005). A community scale change point of 13.2 kg N ha−1 yr−1 was indicated by TITAN, which falls within the current recommended critical load (CL) range for acidophilous Quercus-dominated (oak) woodlands (10–15 kg N ha−1 yr−1). The results suggest that the current CL is sufficient for maintaining a core group of indicator species in old sessile oak woodlands, but many nutrient sensitive species may disappear even at the CL range minimum.

Overprint of neotectonism along the course of River Chel, North Bengal, India

This paper aims to unveil neotectonic imprints in topography, drainage and sediments in the 46.25 km long course of the River Chel from its source down to its alluvial fan at the base of the Himalayan Mountain Front in the Darjeeling–Jalpaiguri districts of India. A semi-circular ridge delimits its primary catchment. Within confinement of this watershed basin the drainage pattern is composite being convergent along the periphery and divergent on a butte inside. All these geomorphic neotectonic imprints are accompanied by ramp and flat structures and spectacular mylonitization of rocks.High hypsometric index and convex shape of the hypsometric curve derived from the central near-straight course of the river between the primary catchment and the Main Frontal Thrust (MFT) also reflects tectonic youthfulness of the river course. It is well manifested also in widely variable stream index and stream gradient index ratios (SL/K) often exceeding 2. In response to neotectonism, this river course as a whole shifted westward between 1962 and 2007. Maximum reduction of the stream gradient on top of the MFT is eloquent enough about recent uplift of the thrust ridge. The high average slope gradient of canyon wall about 45.68° is well consistent with this uplift. Very low channel-width/valley-height ratio along the river further corroborates the uplift.The alluvial fan system of the River Chel is comprised of five morphogenetic fans stacked one above another with a tendency to shrink and shift progressively upslope. They differ from each other in terms of tilt, axial orientation, primary depositional surface gradient and convexity in transverse section and thus present a writ of ongoing tectonism. Progressive upward increase in the share of distal crystalline rocks in clast composition within alluvial fan package is a clear proxy for southerly advancement of the MFT. Concomitant increase in maximum clast size is in good agreement with sediment source uplift. All the five fans are, however, dormant now. Present-day River Chel deeply incises through all of them and suggests further basement uplift in the context of frequent evidences of neotectonism all around, although the role of climate remains uncertain in absence of adequate data.

Conditional vulnerability of plant diversity to atmospheric nitrogen deposition across the United States

Atmospheric nitrogen (N) deposition has been shown to decrease plant species richness along regional deposition gradients in Europe and in experimental manipulations. However, the general response of species richness to N deposition across different vegetation types, soil conditions, and climates remains largely unknown even though responses may be contingent on these environmental factors. We assessed the effect of N deposition on herbaceous richness for 15,136 forest, woodland, shrubland, and grassland sites across the continental United States, to address how edaphic and climatic conditions altered vulnerability to this stressor. In our dataset, with N deposition ranging from 1 to 19 kg N⋅ha(-1)⋅y(-1), we found a unimodal relationship; richness increased at low deposition levels and decreased above 8.7 and 13.4 kg N⋅ha(-1)⋅y(-1) in open and closed-canopy vegetation, respectively. N deposition exceeded critical loads for loss of plant species richness in 24% of 15,136 sites examined nationwide. There were negative relationships between species richness and N deposition in 36% of 44 community gradients. Vulnerability to N deposition was consistently higher in more acidic soils whereas the moderating roles of temperature and precipitation varied across scales. We demonstrate here that negative relationships between N deposition and species richness are common, albeit not universal, and that fine-scale processes can moderate vegetation responses to N deposition. Our results highlight the importance of contingent factors when estimating ecosystem vulnerability to N deposition and suggest that N deposition is affecting species richness in forested and nonforested systems across much of the continental United States.

Neonicotinoid insecticide systemicity in soybean plants and its effect on brown stink bugs

ABSTRACT During the application of pesticides on soybean fields, a vertical deposition gradient of the product can occur throughout the canopy, resulting in difficulties for controlling stink bugs that are in the middle and lower thirds of plants. This study aimed at evaluating the systemicity of thiamethoxam insecticide in different soybean phenological stages, using brown stink bugs as bioindicators of the pesticide efficacy. The study combined product application sites (lower, middle and upper third) and stink bugs infestation areas at five soybean phenological stages (R2, R3, R4, R5.2 and R6). For the R2 and R5.2 stages, plants presented acropetal translocation of the product, being the effect more evident in the R2 stage. For the R3, R4 and R6 stages, the product translocation was not sufficient for controlling the stink bugs. In all stages, for treatments with direct exposure (same infestation and spraying place), stink bugs were satisfactorily controlled.

Mass-transport and slope accommodation: Implications for turbidite sandstone reservoirs

Mass-transport events are virtually ubiquitous on the modern continental slope and are also frequent in the stratigraphic record, but the potential they create for stratigraphic trapping within the sea-floor topography is not generally appreciated. Given the abundance of mass-transport deposits (MTDs), we should expect that many turbidite systems are so affected. The MTDs may be very large (volumes > 103 km3 [∼250 mi3], areas > 104 km2 [∼6250 mi2], thicknesses > 102 m [∼330 ft]), and they extensively remold sea-floor topography on the continental slope and rise. Turbidity currents are highly sensitive to topography; thus, turbidite reservoir distribution and geometry on the slope and rise are often significantly affected by subjacent MTDs or their slide scars. Turbidites may be captured within slide scars and on the trailing edges, margins, and rugose upper surfaces of MTDs; developed in accommodation when the mass movement comes to rest; or subsequently resulting from compaction or creep. The filling of such accommodation depends on the properties of the turbidity currents, their depositional gradient, and how they interact with basin floor topography. The scale of accommodation on top of MTDs is determined largely by the dynamics of the initial mass flow and internal structure of the final deposit, and it typically has a limited range of length scales. We present interpretations of a range of previously published and original case studies to illustrate the range of accommodation styles associated with MTD-related topography within the evacuated space of the slide scar, around and on top of the deposits themselves. In fact, several well-known deep-water outcrops probably represent examples of sedimentation influenced by MTDs. Hydrocarbon reservoirs in many slope settings may be controlled by the accommodation related to MTD topography. At the exploration scale, entire shelf margin and slope depositional systems may be contained within the scars evacuated on the upper slope by mass failure, whereas at the production scale, the rugosity on the top of MTDs creates widespread potential for stratigraphic trapping. The location, geometry, and property distribution of such reservoirs are closely controlled by the interaction of turbidity currents with the topography; thus, an understanding of these processes and their impact on slope stratigraphy is vital to reservoir prediction.

Effects of nitrogen deposition on nitrogen acquisition bySarracenia purpureain the Adirondack Mountains, New York, USA1

Abstract Human generated emissions to the atmosphere have historically increased inorganic nitrogen (N) deposition throughout the Adirondack Mountains of New York. Nitrogen is generally a limiting nutrient for the purple pitcher plant (Sarracenia purpurea L.). Our objective was to determine the dependence of S. purpurea on atmospherically deposited and insect-derived N sources across an increasing nitrogen deposition gradient. Sampling was conducted at 10 sites, with 104 S. purpurea plants sampled. The effects of increasing nitrogen deposition on morphological characteristics and organic N content of S. purpurea and a noncarnivorous reference plant, Chamaedaphne calyculata L. Moench, Leatherleaf, were examined. Sarracenia purpurea flower and C. calyculata leaf tissues were analyzed for stable nitrogen isotope (δ15N), and foliar N content. Increased nitrogen deposition up to 4.1 kgN*ha−1*yr−1 was correlated with increased plant size and δ15N values of S. purpurea. However, deposition exceeding these levels...

Novel Pattern of Iron Deposition in the Fascicula Nigrale in Patients with Parkinson’s Disease: A Pilot Study

Background and Purpose. To determine whether the pattern of iron deposition in the fascicula nigrale in patients with Parkinson's disease would be different from age-matched controls by utilizing quantitative susceptibility mapping to measure susceptibility change. Methods. MRIs of the brain were obtained from 34 subjects, 18 with Parkinson's disease and 16 age- and gender-matched controls. Regions of interest were drawn around the fascicula nigrale and substantia nigra using SWI mapping software by blinded investigators. Statistical analyses were performed to determine susceptibility patterns of both of these regions. Results. Measurements showed significantly increased susceptibility in the substantia nigra in Parkinson's patients and an increased rostral-caudal deposition of iron in the fascicula nigrale in all subjects. This trend was exaggerated with significant correlation noted with increasing age in the Parkinson group. Conclusion. The pattern of an exaggerated iron deposition gradient of the fascicula nigrale in the Parkinson group could represent underlying tract dysfunction. Significant correlation of increasing iron deposition with increasing age may be a cumulative effect, possibly related to disease duration.

Fabrication of high aspect ratio self-aligned stepped polysilicon electrode for single-crystal silicon microstructure

This paper reports a self-aligned process for the fabrication of a high aspect ratio stepped polysilicon electrode with sub-micron capacitive gaps, which increases the coupling factor in capacitive driving and sensing. In contrast to the previous works, the polysilicon electrodes, which are formed by refilling the trenches and etching back, are anchored on the surfaces of steps in the trenches and etched by two-step deep reactive ion etching. The polysilicon electrodes are self-aligned and perfectly symmetric. Because of the `U'-shaped profile produced by the refilling process, the polysilicon electrode is less sensitive to a stress gradient in Low-pressure chemical vapor deposition (LPCVD) polysilicon layer. A thin layer of heavily doped polysilicon and a low-stress polysilicon layer, instead of uniform, heavily doped polysilicon, are used to form the polysilicon electrodes without sacrificing the electrical performance, which decreases the deposition time for LPCVD significantly due to the much faster deposition of normal low-stress polysilicon. To validate the study, a single-crystal silicon length extensional mode resonator with a 300-nm capacitive gap is fabricated based on this process. The frequency of the resonator is measured to be 25.5955 MHz, with a quality factor of 67,656 under 20 Pa.