Strong Longitudinal Gradients Research Articles

Distribution patterns of marine megafauna density in the Mediterranean Sea assessed through the ACCOBAMS Survey Initiative (ASI)

The ACCOBAMS Survey Initiative (ASI) is the first synoptic large-scale survey of the entire ACCOBAMS Area and as such it plays a key role in filling the current gaps in our biological and ecological knowledge of large vertebrate species occurring in the region. Data gathered during the ASI were analyzed in a distance sampling surface-modelling framework to assess the summer distribution, densities and patterns, as well as to investigate the correlates of these parameters, for large vertebrate species and taxa in the Mediterranean Basin. Static and dynamic explanatory variables, including water depth (m), distance to depth contours (km), distance to canyons and seabed slope (km), sea surface temperature (°C), mixed layer depth (m) and levels of chlorophyll-a (mg/l), were considered to predict density and compute its variance spatially at a resolution of 10x10 km. A strong longitudinal gradient from low densities in the east to high densities in the west is shared by most taxa. In addition, several taxa also showed a less marked latitudinal gradient varying in direction according to species, and finally, a few of them exhibited patchy distributions.

Quantifying Abundance and Mapping Distribution of Loggerhead Turtles in the Mediterranean Sea Using Aerial Surveys: Implications for Conservation

In the Mediterranean, incidental captures in fishing gear contribute to the high mortality of loggerhead turtles (Caretta caretta). Understanding the effects of bycatch is complex and requires robust knowledge of baseline population parameters such as abundance and density, as well as an understanding of animals’ distribution in relation to commercial fishing efforts. Based on data collected during multi-species line transect aerial surveys conducted between 2009 and 2017, we present density and abundance estimates, corrected for availability bias, for a large sector of the central Mediterranean, discuss temporal and spatial patterns and provide Potential Biological Removal (PBR) values for the monitored areas. Sightings data were also used to evaluate the spatial and temporal usage areas. Strong latitudinal and longitudinal gradients in density, abundance and area usage emerged from the analysis, with turtles occurring in higher numbers in the deeper pelagic waters of the Tunisian Plateau, the Ionian Sea and the Gulf of Taranto, irrespective of the season. PBR values derived from this study are likely unsustainable. This paper investigates the implications of commercial fisheries for Mediterranean loggerhead turtles across an area rarely included in sea turtle monitoring and has the potential to be relevant towards informed management and conservation of this species and highlights the necessity of international collaborative efforts in the region.

Comparison of temperature and wind observations in the Tropics in a perfect‐model, global EnKF data assimilation system

Flow‐dependent errors in tropical analyses and short‐range forecasts are analysed using global observing‐system simulation experiments assimilating only temperature, only winds, and both data types using the ensemble Kalman filter (EnKF) Data Assimilation Research Testbed (DART) and a perfect model framework. The idealised, homogeneous observation network provides profiles of wind and temperature data from the nature run for January 2018 using the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) forced by the observed sea‐surface temperature. The results show that the assimilation of abundant wind observations in a perfect model makes the temperature data in the Tropics largely uninformative. Furthermore, the assimilation of wind data reduces the background errors in specific humidity twice as much as the assimilation of temperature observations. In all experiments, the largest analysis uncertainties and the largest short‐term forecast errors are found in regions of strong vertical and longitudinal gradients in the background wind, especially in the upper troposphere and lower stratosphere over the Indian Ocean and Maritime Continent. The horizontal error correlation scales are on average short throughout the troposphere, just several hundred km. The correlation scales of the wind variables in precipitating regions are half of those in nonprecipitating regions. In precipitating regions, the correlations are elongated vertically, especially for the wind variables. Strong positive cross‐correlations between temperature and specific humidity in the precipitating regions are explained using the Clausius–Clapeyron equation.

Why we should be looking for longitudinal patterns in biodiversity

Our understanding of global diversity patterns relies overwhelmingly on ecological and evolutionary correlates of latitude, and largely ignores longitude. However, the two major explanations of biodiversity patterns – energy and stability – are confounded across latitudes, and longitude offers potential solutions. Recent literature shows that the global biogeography of the Cenozoic world is structured by longitudinal barriers. In a few well-studied regions, such as South Africa’s Cape, the Himalayas and the Amazon-Andes continuum, there are strong longitudinal gradients in biodiversity. Often, such gradients occur where high and low past climatic velocities are juxtaposed, and there is clear evidence of higher biodiversity at the climatically-stable end. Understanding longitudinal biodiversity variations more widely can offer new insights towards biodiversity conservation in the face of anthropogenic climatic change.

Global Modeling of Ganymede's Surface Composition: Near‐IR Mapping From VLT/SPHERE

AbstractWe present maps of Ganymede's surface composition with almost complete longitude coverage, acquired using high spatial resolution near‐infrared (0.95–1.65 μm) observations from the ground‐based VLT/SPHERE instrument. Observed reflectance spectra were modeled using a Markov Chain Monte Carlo method to estimate abundances and associated uncertainties of water ices, acids, salts and a spectrally flat darkening agent. Results confirm Ganymede's surface is dominated by water ice in young bright terrain (impact craters, sulci), and low‐albedo spectrally flat material in older dark terrain (e.g., Galileo Regio). Ice grain size has strong latitudinal and longitudinal gradients, with larger grains at the equator and on the trailing hemisphere. These trends are consistent with the effects of the latitudinal thermal gradient and global variations in radiation driven sputtering. Sulfuric acid has a low abundance and appears potentially spatially correlated with plasma bombardment, where Ganymede's poles are exposed to the external Jovian magnetic field. Best‐estimate abundances suggest a mixture of salts could be present, although their low abundances, spectral degeneracies and associated uncertainties mean individual salt species cannot be detected with confidence. If present, sodium magnesium sulfate and magnesium chlorate appear tentatively correlated with exogenic plasma bombardment, while magnesium chloride and sulfate appear tentatively correlated with younger terrain, implying a possible endogenic origin. MCMC modeling was also performed on Galileo/NIMS data, showing comparable distributions. The high spatial resolution of SPHERE allows the precise mapping of small scale (<150 km) surface features, which could be used along with higher spectral resolution observations to jointly confirm the presence and distribution of potential species.

Spatial and temporal variation of genetic diversity and genetic differentiation in Daphnia galeata populations in four large reservoirs in southern China.

Daphnia galeata is a common and dominant species in warmer waters, and has a strong top-down effect on both phytoplankton and bacteria. The knowledge of its temporal and spatial patterns of genetic diversity is fundamental in understanding its population dynamics and potential ecological function in ecosystems. Its population genetics have been investigated at regional scales but few within regions or at smaller spatial scales. Here, we examined the fine-scale spatial genetic variation of D. galeata within four large, deep reservoirs in wet and dry seasons and the six-year variation of genetic diversity in one of the reservoirs by using cytochrome c oxidase subunit I and microsatellites (simple sequence repeat). Our study shows that fine-scale spatial genetic variation commonly occurred within the reservoirs, indicating strong environmental selection at least in the two of reservoirs with strong longitudinal gradients. Since the environmental gradients established in the dry season was largely reduced in the wet season, the fine-scale spatial genetic variation was much higher in the dry season. The dynamics of local genetic diversity did not follow the theoretical pattern of rapid erosion but peaked in mid or mid-late growth season. The local genetic diversity of D. galeata appears to be shaped and maintained not only by recruitment from resting egg banks but also by gene flow within reservoirs. The temporal and fine-scale genetic variation within a water body suggests that it is necessary to pay attention to sampling periods and locations of a given water body in regional studies.

A Galerkin Method for the Simulation of Laminar Boundary Layers on Heated Walls

This paper presents a new solution method for the calculation of laminar thermal boundary layers. The method consists of a coupling between a modal method (Galerkin method) in the direction normal to the wall and a finite volume method in the direction(s) tangential to the wall. It is similar to an integral method in the sense that only a surface mesh is required and that the unknowns are integral quantities (corresponding to the moments up to a fixed order of the temperature profile in the direction normal to the wall). A specificity of the Galerkin method used is that the domain over which the integrals are computed has a variable size that is also an unknown of the problem. Using a series of numerical tests (representative of situations that can be encountered in aeronautics in the case of a wing equipped with a thermal ice protection system), we show that the new method allows us to predict the quantities of interest with a maximum error of a few percent, while a usual integral method (with only one unknown per mesh cell) is unable to treat the case of boundary layers on heated walls with a strong longitudinal temperature gradient, as shown in the literature.

Both Dissolved Oxygen and Chlorophyll Explain the Large-Scale Longitudinal Variation of Deep Scattering Layers in the Tropical Pacific Ocean

The ecological characteristics of mesopelagic community are crucial to understand the pelagic food web, replenishment of pelagic fishery resources, and building models of the biological pump. The deep scattering layers (DSLs) and diel vertical migration (DVM) are typical characteristics of mesopelagic communities, which have been widely observed in global oceans. There is a strong longitudinal environmental gradient across the tropical Pacific Ocean. Nevertheless, the longitudinal variation of DSLs along this gradient was still largely unclear until now. We investigated the DSLs across the tropical Pacific Ocean using data of shipboard acoustic Doppler current profiler at 38 kHz from July to December 2019. The study area was divided into three sub-regions by cluster analysis of environmental variables: the western part (WP), the transition part (TP), and the eastern part (EP). The result confirmed that the longitudinal variation of DSLs and DVM: the weight migrating depth of mesopelagic organisms was reduced from 571.2 ± 85.5 m in the WP to 422.6 ± 80.8 m in the EP; while the migrating proportion was minimum in the TP (35.2 ± 12.8%), and increased to 86.7 ± 16.2% in the EP. Multiple regressions analysis showed that both the mesopelagic average oxygen and chlorophyll a concentration were significant factors which influenced the upper boundary depth and weight migrating depth, while the center mass depth was only influenced by the chlorophyll a. Since higher demand of most predators of mesopelagic animals for dissolved oxygen and light intensity, the limitations of predator behavior by environmental conditions might explain the observed spatial heterogeneity of DSLs. Combining the previous results and the findings of this study, it implied that declined biomass, shallower habituating depths, and lower migration proportion of mesopelagic animals under more extremely oligotrophic conditions with global change in future, would reduce the active carbon flux and hinder food supply to deep-sea biological communities in the tropical Pacific Ocean.

N<sub>2</sub> fixation in the Mediterranean Sea related to the composition of the diazotrophic community and impact of dust under present and future environmental conditions

Abstract. N2 fixation rates were measured in the 0–1000 m layer at 13 stations located in the open western and central Mediterranean Sea (MS) during the PEACETIME cruise (late spring 2017). While the spatial variability in N2 fixation was not related to Fe, P nor N stocks, the surface composition of the diazotrophic community indicated a strong longitudinal gradient increasing eastward for the relative abundance of non-cyanobacterial diazotrophs (NCDs) (mainly γ-Proteobacteria) and conversely decreasing eastward for photo-heterotrophic group A (UCYN-A) (mainly UCYN-A1 and UCYN-A3), as did N2 fixation rates. UCYN-A4 and UCYN-A3 were identified for the first time in the MS. The westernmost station influenced by Atlantic waters and characterized by highest stocks of N and P displayed a patchy distribution of diazotrophic activity with an exceptionally high rate in the euphotic layer of 72.1 nmolNL-1d-1, which could support up to 19 % of primary production. At this station at 1 % PAR (photosynthetically available radiation) depth, UCYN-A4 represented up to 94 % of the diazotrophic community. These in situ observations of greater relative abundance of UCYN-A at stations with higher nutrient concentrations and dominance of NCDs at more oligotrophic stations suggest that nutrient conditions – even in the nanomolar range – may determine the composition of diazotrophic communities and in turn N2 fixation rates. The impact of Saharan dust deposition on N2 fixation and diazotrophic communities was also investigated, under present and future projected conditions of temperature and pH during short-term (3–4 d) experiments at three stations. New nutrients from simulated dust deposition triggered a significant stimulation of N2 fixation (from 41 % to 565 %). The strongest increase in N2 fixation was observed at the stations dominated by NCDs and did not lead on this short timescale to changes in the diazotrophic community composition. Under projected future conditions, N2 fixation was either increased or unchanged; in that later case this was probably due to a too-low nutrient bioavailability or an increased grazing pressure. The future warming and acidification likely benefited NCDs (Pseudomonas) and UCYN-A2, while disadvantaged UCYN-A3 without knowing which effect (alone or in combination) is the driver, especially since we do not know the temperature optima of these species not yet cultivated as well as the effect of acidification.

The residual circulation profile of the Bons Sinais Estuary in central Mozambique - potential implications for larval dispersal and fisheries

The residual circulation in estuaries determines the net exchange of water, heat, salt, fine sediments and drifting biological organisms between estuarine and nearshore marine waters. The Bons Sinais Estuary in central Mozambique is ~ 30 km long with the city of Quelimane and an industrial port on the northern bank of its upper reaches. To investigate residual circulation in the estuary, seasonal (wet, dry and transition season) CTD profiling data were collected at 11 fixed stations between the upper estuary and mouth, and vertical current profiles were measured over a full tidal cycle at a fixed mid-estuary station. Strong longitudinal gradients in salinity and density indicated that the estuary was river-dominated during the wet season and tide-dominated during the dry season, but the water column remained partially mixed. Tidally averaged vertical profiles from the mid-estuary station revealed: uniform vertical temperatures, warmest during the wet season; depth-stratified salinity during the wet season, but uniform profiles during the dry and transition seasons with highest salinity during the dry season when the density was also highest. The density was uniform and somewhat lower in the transition season, and in the wet season the density was even lower, but stratified. The vertical velocity profile showed a classical two-layer circulation model, with downstream flow intensifying at the surface, and upstream flow at the bottom, during the wet and transitory seasons, when freshwater discharges into the estuary. The flow velocities obtained from a calibrated Hansen and Rattray model fitted the observed data well, confirming that a simplified modelling approach is adequate to describe the residual flow of the Bons Sinais Estuary. The residual circulation model provides insights useful for fisheries research and predicting the spread of water-borne pollutants in the estuary.

Physical forces driving chlorophyll-a variability in the South Java Sea Shelf: a spatio-temporal analysis

The wind and current are two physical forces that strongly influence the biogeochemistry in coastal waters. Both of these forces could enhance the Chlorophyll-a (Chl-a) concentration through the upwelling process. Here we examine the contribution of the wind and current to the Chl-a variability in the South Java upwelling system in terms of wind stress and bottom stress respectively using satellite-derived and reanalysis data from 2002 to 2017. Ten longitudinally cells were used for further analysis. A long-term Chl-a shows a strong longitudinal gradient of Chl-a with the highest value on the shelf. Seasonal and Inter-annual Chl-a analysis shows the evidence of the monsoonal winds and other forcing effects relevant to the previous studies. Wind stress (τwx ) has a strong seasonal variation which is upwelling- favorable during southeast monsoon coincide with higher Chl-a suggesting wind as the main forces during that time, while bottom stress (τbx ) has more complicated variations, but it’s seen that τwx mostly downwelling-favorable or eastward circulations. There were about 39.92- 52.94% of positive Chl anomalous events generated by the combination of upwelling- favourable τwx and downwelling-favorable τbx , higher than other combinations. In terms of Oceanographic drivers, the wind has a higher effect on enhancing Chl-a through a negative correlation. τwx leads the Chl-a anomalies by about 15 – 24 days with a correlation coefficient of more than 0.6.

Origins and diversity of the Bering Sea Island fauna: shifting linkages across the northern continents

We synthesize the historical biogeography of non-marine fauna (mammals, birds, fish, non-parasitic and parasitic invertebrates) occurring across Bering Sea islands, considering endemism, species with origins in both North America and Far East Asia, and the impacts of introduced species through the Bering region. Insular communities often constitute assemblages of unique evolutionary lineages that reflect both neutral and selective processes of diversification as a consequence of isolation and through responses to in situ environmental change. However, current knowledge of the basic distribution, ecology, and evolutionary identity of the majority of terrestrial species through the Bering Sea region is still generally lacking. A preponderance of scientific effort associated with these islands has instead focused on conservation and management of marine-associated species and economically viable biological resources. Given the critical role that terrestrial environments play in maintaining evolutionary and ecological linkages between land and sea, a greater understanding of existing biodiversity, and the biological processes that influence community integrity through this remote region is warranted. Resolving responses of resident insular species to rapidly warming Arctic climate and to modern human-associated disturbances provides valuable insight for effective management of future population trajectories and for revealing the dynamics of intra- and inter-specific connectivity across the northern hemisphere and between marine and terrestrial ecosystems. The location of this region at a high-latitude cross-roads has led to a preponderance of island taxa having trans-Beringian distributions. Species associated with the Palearctic or the Nearctic occur across a strong longitudinal gradient, reflecting the role of the Bering Sea as a dispersal filter between mainland areas. Aleutian oceanic islands reflect different biogeographic histories among taxonomic groups from land-bridge islands of the Bering Sea. We discuss evidence of recent biodiversity responses to modern environmental perturbations, including continued colonisations and novel species interactions, and call for increased scientific scrutiny of terrestrial fauna across these remote outposts.

Provenance versus weathering control on sediment composition in tropical monsoonal climate (South China) - 1. Geochemistry and clay mineralogy

This study presents an integrated mineralogical and geochemical database on mud and sand transported by the Pearl River (Zhujiang) and coastal rivers of SE China. Clay mineralogy and bulk-geochemistry of fluvial sediments are used to trace changes in weathering intensity across South China, a vast tropical to subtropical region characterized by a strong longitudinal rainfall gradient. The control of climate-induced weathering is manifest in the mineralogy and geochemistry of Pearl River mud, although mud and, to a greater extent, sand composition are also largely affected by the lithology of parent rocks. The depletion in mobile alkali and alkaline-earth metals increases steadily from the drier western part of the Pearl River catchment to the wetter eastern part and is most marked in easternmost tributaries of the Pearl River and in southern coastal rivers. Na and Ca are the most strongly depleted elements in Pearl River sediments, whereas the low concentration of Ca and Mg in river sand of coastal SE China also reflects the felsic character of parent rocks in the Cathaysia block. Eastward-increasing weathering conditions are most clearly highlighted by the progressive eastward increase in kaolinite across the Pearl River catchment, whereas the weathering effect in sand is blurred by quartz addition owing to widespread recycling of quartz-rich siliciclastic source rocks.This actualistic case study from a region characterized by monsoonal climate underscores the care that should be taken while inferring climatic conditions from the geochemical composition of sediments and sedimentary rocks, which is controlled by multiple geological factors including the felsic versus mafic character of parent rocks and the presence of extensive carbonate or siliciclastic covers in source areas. Most reliable indications are provided by the kaolinite/(illite+chlorite) ratio and by αAl indices for Na, Ca, Mg and Sr, which consistently increase eastward across South China thus paralleling the marked eastward increase in monsoonal precipitation towards the coast.

Spatial factors control the structure of fish metacommunity in a Mediterranean intermittent river

While in recent years intermittent rivers and ephemeral streams (IRES) are receiving increasing attention from ecologists, fish metacommunity dynamics have drawn less attention than other taxa. In this study, we explored fish metacommunity dynamics at a Mediterranean intermittent river (Evrotas River, Southern Greece) to unravel which factors (i.e. environmental and/or spatial) best explain fish metacommunity structure. To this end, we investigated fish compositional structure in perennial and intermittent sites distributed longitudinally along the river during the low flow period of a wet year (2009), following two extremely dry years (2007-2008). To disentangle the effects of spatial control versus local environmental variables in shaping fish metacommunities, asymmetric eigenvector map (AEM) analysis designed to model directional spatial processes, and variation partitioning were applied. Our results point out that fish metacommunity structure was largely explained by spatial (53%) rather than local environmental (3%) factors, whereas only a small fraction (16%) was explained by the spatial structure of the environmental variables. Irrespectively of their hydrological regime, neighboring sites harbored similar fish communities, with a strong longitudinal gradient in local community structure, suggesting a homogenizing effect of dispersal. Local environmental factors were not associated with shifts in community structure. These results differ markedly from those drawn from most perennial aquatic ecosystems, where environmental factors are prevailing. Overall, this study emphasizes the need to account for regional processes in IRES and adopt a metacommunity perspective for guiding conservation and restoration efforts, by promoting the connectivity within the river network and the protection of perennial refugia.

Littoral Benthic Communities Under Effect of Heat Wave and Upwelling Events in the Ne Baltic Sea

Paalme, T.; Torn, K.; Martin, G.; Kotta, I., and Suursaar, Ü., 2020. Littoral benthic communities under effect of heat wave and upwelling events in NE Baltic Sea. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 133–137. Coconut Creek (Florida), ISSN 0749-0208.The Baltic Sea forms a dynamic marine habitat with strong latitudinal and longitudinal gradients in many essential environmental variables. This environmental setting controls pelagic and benthic biodiversity by providing very narrow ecological niches for species displaying varying tolerances to environmental factors such as salinity, temperature and turbidity. In this study, changes in benthic communities in relation to extreme weather conditions, such as the occurrence of heat waves (HW) and coastal upwelling (CU) events, were analyzed and described in the north-eastern Baltic Sea. In the summer of 2018, the maximum water temperatures in the studied coastal sea sections varied between 20 and 25°C at 5 m depth whereby recorded values were up 7°C higher compared to that of the long-term mean. However, daily water temperature showed remarkable variation due to upwelling events occurring on multiple occasions with extreme temperature shifts of 14°C being recorded within a period of a few days. In the NE Baltic Sea, salinity gradient is up to 7 PSU in outer areas and it falls to zero in bays with riverine impact. Salinity has significant importance on benthic species abundance, richness and distribution. A rapid increase in salinity was observed during upwelling events. Extraordinarily, heat wave accompanied with upwelling event caused the increase of zoobenthic biodiversity and species-specific response of abundances. In contrast, the effect on macrovegetation species composition and proportion of opportunistic species was rather negative.

A Case Study of the Enhancements in Ionospheric Electron Density and Its Longitudinal Gradient at Chinese Low Latitudes

AbstractThe day‐to‐day variability of the ionospheric electron density and its longitudinal gradient challenges our description and understanding of the ionosphere, which is also essential for reliable applications of the Global Navigation Satellite System (GNSS). In this paper we conduct a case study of the anomalous enhancements in ionospheric electron density and its longitudinal gradient to reveal the spatial extent and related drivers of the enhancements. The ionospheric data analyzed include the vertical total electron content (TEC) by the Global Navigation Satellite System receivers, peak electron density (NmF2) and height (hmF2) of the F layer by a chain of ionosondes, and electron density profiles recorded by the Qujing incoherent scatter radar (103.8°E, 25.6°N) during the period from 29 May to 2 June 2015. Electron density enhancements are found in the region around the northern crest of equatorial ionization anomaly on the first 2 days of June 2015. It is the first time to report that, during the anomalous enhancement, the increase in electron density over Qujing depends on altitude, being stronger at higher altitudes. Further, there are strong longitudinal gradients in vertical TEC in the regions during the course of the electron density enhancements. Low latitude hmF2 and especially the equatorial electrojet become much larger on the enhancement days, implying the important role of equatorial zonal electric fields in the formation of the electron density enhancements at low latitudes.

A re-examination of the relationship between Steller sea lion (Eumetopias jubatus) diet and population trend using data from the Aleutian Islands

Prey diversity and energy density have been linked to each other and to population trends in many studies of bird and mammal diets. We re-examined these relationships in Steller sea lions (Eumetopias jubatus (Schreber, 1776)) using data collected from the Aleutian Islands, where there has been a strong longitudinal gradient in population trend. Diet diversity and energy density metrics were similar in the western Aleutians, where sea lion counts declined consistently, and in the easternmost Aleutian area, where population trends improved significantly. We compared traditional deterministic diet diversity metrics with diversity scores based on an occupancy model that accounts for differences in sample size and uncertainty in prey group detection. This analysis indicated that there was no significant change in diet diversity over the 23-year study period or any significant differences across the Aleutian Islands. These results are consistent with prey abundance data from nine groundfish bottom trawl surveys conducted over the same period. While diet studies detail what Steller sea lions eat and provide an estimate of their energy intake, they provide only limited information on the energy expended to obtain their food or the consequences of their diet and foraging ecology on individual or population fitness.

Input impedance measurement of a narrow pipe with thermal gradient.

Input impedance measurement is commonly used in the design of internal combustion engines to improve their performance. The water-cooled charge-air cooler used in supercharged engines imposes a strong longitudinal thermal gradient on the air contained in its narrow channels. To isolate the resonances caused by the thermal gradient, the input impedance of a semi-infinite narrow pipe with multiple longitudinal temperature profiles is studied experimentally using the Two-Measurement Three-Calibration method. Three known non-resonant loads are used to calibrate the test bench. The importance of using a semi-infinite pipe as a calibration load in narrow pipes is further demonstrated. In the case of this paper, the acoustic propagation is highly influenced by the presence of microphones. The calibration process helps to take into account this influence. Measurements show that the presence of a non-uniform longitudinal temperature profile in the air inside a pipe modifies its input impedance.

Linking Land Use to Atlantic Salmon Production to Guide Recovery Planning

AbstractQuantifying functional relationships between abundance and land use is critical during recovery planning for endangered freshwater and diadromous fishes. However, there is little practical guidance on how much abundance might be expected to change from specific types or magnitudes of land use, making it difficult to identify specific sites for restoration or to prioritize among remediation actions. To address these needs for endangered Atlantic Salmon Salmo salar inhabiting the Southern Upland region of Nova Scotia, Canada, we developed a suite of hierarchical models to evaluate the functional form and magnitude of response of populations to land use at two spatial scales. Juvenile distribution patterns showed a strong longitudinal gradient throughout the stream network, with higher densities occurring in headwaters, which suggests that maintaining connectivity as well as unmodified landscapes in the upper reaches of rivers should be prioritized to aid recovery. Relative to threats, there was no single type of land use that was primarily associated with changes in juvenile abundance. Instead, responses to the combined suite of land‐use types were nonlinear and did not appear dependent on spatial scale. When the proportion of natural forest cover was high, populations appeared to benefit from low levels of anthropogenic land use, declining with increasing human activity only once the average proportion of natural forest cover was low. To use threat relationships in recovery planning, we propose a simple quantitative index based on the extent of development in the vicinity of rivers to identify sites for remediation or protection. To aid future monitoring, we demonstrate why site‐specific electrofishing catchability must be estimated when evaluating population responses to landscape change.

A Simulation Study on the Latitudinal Variations of Ionospheric Zonal Electric Fields Under Geomagnetically Quiet Conditions

AbstractThe influence of zonal electric fields as well as E × B plasma drifts on the ionosphere has been widely investigated, but the latitudinal variations of zonal electric fields have not been well understood. In this study, we investigate the driving mechanisms responsible for the latitudinal variations of zonal electric fields under geomagnetically quiet conditions using the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIEGCM). A series of case‐controlled TIEGCM simulations were conducted to explore the effects of neutral wind and ionospheric conductivity on the latitudinal variations of zonal electric fields. The major results are given as follows: (1) The eastward electric field at noon increases with latitude, which is mainly associated with latitudinal changes of poleward neutral winds. (2) The prominent latitudinal variations of zonal electric fields at sunrise and sunset are attributed to the strong longitudinal gradients of zonal winds, that is, the curl‐free mechanism. (3) The changes of the zonal electric fields at a given location are affected by the dynamo effect globally, which also produces the latitudinal structure of zonal electric fields.