North-south Transect Research Articles

The Amazon river is a suture zone for a polyphyletic group of co‐mimetic heliconiine butterflies

The Amazon basin contains few obvious geographic barriers, yet it is the most biodiverse region on Earth. One hypothesis to explain its diversity is that the very large rivers promote allopatric divergence. Consistent with this, maps of heliconiine butterflies made from museum specimens show high subspecies richness close to the Amazon river, suggesting that it may produce or maintain intra‐specific phenotypic variability. However, museum data are subject to strong spatial biases (the ‘Wallacean shortfall' of distribution data), raising the possibility that this pattern is a sampling artefact. To test this, we systematically collected along a ~900 km north–south transect running through central Amazonia. We found a significant association between phenotypic diversity and major rivers, with distance from the Amazon river explaining 61% of the variance in the mean polymorphism of 25 species. This association is partly because many species exhibit different phenotypes on either side of the river. Nonetheless, we also find sites with high polymorphism close to the river, indicating continual cross‐river dispersal. Our results strongly suggest the presence of a suture zone (a region where multiple species have hybrid zones) near the city of Manaus. However, the effect of the river on spatial patterns of intra‐specific phenotypic diversity depends on a species' mimetic phenotype. Rather than being absolute barriers, our results support the idea that rivers can act as partial barriers that trap moving hybrid zones, resulting in a suture zone. As such, the wide Amazonian rivers help generate and maintain colour pattern diversity, but to date there is no evidence that they lead to speciation in our study group.

Stable isotopes of precipitation in Nepal Himalaya highlight the topographic influence on moisture transport

The Nepal Himalaya is a transition zone for pollutants transport from the South Asia onto the Tibetan Plateau, with the moist convection identified as dominating the chemical composition that would be transported onto the Plateau. Yet little is known regarding the atmospheric water vapor transport over this region, and how the summer monsoon flows would interact with local topography, with traces detectable from ground sample and observations. The stable oxygen and hydrogen isotopes in precipitation (δ18Op and δDp) are important tracers for understanding various hydrological processes. This study reports, for the first time, stable isotope data in daily precipitation at five stations along a north-south transect on the southern slope of Himalaya, with altitudes ranging from 102 m to 5050 m above sea level (a.s.l). The altitude effect of δ18Op across the region of interest is apparent with an altitudinal lapse rate as 0.17‰/100 m. Seasonal trends in δ18Op and δDp show low values during June–September and higher values during October–May at all of the study sites, with the noticeable decrease of δ18Op during summer indicative of the presence of the Indian monsoon over the eastern Nepal Himalaya. The average d-excess values in the summer precipitation increase with altitudes til 3800 m a.s.l before decreasing afterward to 5050 m a.s.l. This corroborates with previous meteorological discovery in the region, and probably confirms the replacement of prevailing westerly by the southerly monsoon flows during summer monsoon season.

Effects of mountain urbanization on greenhouse gas emissions from municipal solid waste management practices in Southwest China.

Urbanization is occurring globally at an unprecedented rate. The byproduct of this mounting urbanization is an increase in municipal solid waste (MSW), which has a significant effect on population health and the surrounding environment. This trend poses a challenge to the cities responsible for managing waste in a socially and environmentally acceptable manner. Effective waste management strategies depend on local waste characteristics, which vary under different cultural, climatic, and socioeconomic conditions. It is important to note that MSW disposal represents one of the largest sources for anthropogenic greenhouse gas (GHG) emissions. This study found a direct proportional urban and rural gradient between household income and GHG emissions under a typical urban household size. The distribution of GHG is U-shaped. This study found that urbanization exhibited a pattern of continuous growth, and the effect of urbanization was less than the effect of the population in magnitude. The correlation between GHG and income level in recent urban sprawl along a north-south transect was lower than during the period of early urban expansion.

Twenty years of European mountain permafrost dynamics—the PACE legacy

This paper reviews and analyses the past 20 years of change and variability of European mountain permafrost in response to climate change based on time series of ground temperatures along a south–north transect of deep boreholes from Sierra Nevada in Spain (37°N) to Svalbard (78°N), established between 1998 and 2000 during the EU-funded PACE (Permafrost and Climate in Europe) project. In Sierra Nevada (at the Veleta Peak), no permafrost is encountered. All other boreholes are drilled in permafrost. Results show that permafrost warmed at all sites down to depths of 50 m or more. The warming at a 20 m depth varied between 1.5 °C on Svalbard and 0.4 °C in the Alps. Warming rates tend to be less pronounced in the warm permafrost boreholes, which is partly due to latent heat effects at more ice-rich sites with ground temperatures close to 0 °C. At most sites, the air temperature at 2 m height showed a smaller increase than the near-ground-surface temperature, leading to an increase of surface offsets (SOs). The active layer thickness (ALT) increased at all sites between c. 10% and 200% with respect to the start of the study period, with the largest changes observed in the European Alps. Multi-temporal electrical resistivity tomography (ERT) carried out at six sites showed a decrease in electrical resistivity, independently supporting our conclusion of ground ice degradation and higher unfrozen water content.

Isotope hydrology and hydrogeochemical modeling of Troodos Fractured Aquifer, Cyprus: The development of hydrogeological descriptions of observed water types

The origin of groundwater recharge and subsequent flow paths are often difficult to establish in fractured, multi-lithological, and highly compartmentalized aquifers such as the Troodos Fractured Aquifer (TFA). As the conjunctive use of stable isotopes and hydrogeochemical data provides additional information, we established a monitoring network for stable isotopes in precipitation in Cyprus. The local meteoric water line, altitude effect and seasonal variation of stable isotopes in precipitation are derived from monitoring data. Stable isotopes and hydrogeochemical data are combined to model water-rock interactions and groundwater evolution along a complete ophiolite sequence. As a result a generic hydrogeologic description for the observed water types is developed. Isotope hydrology was applied in conjunction with hydrogeochemical modelling in Kargiotis Watershed, a major north-south transect of the TFA. PHREEQC was used for hydrogeochemical modelling to establish generic descriptions for observed water types. Mean precipitation-weighted values from 16 monitoring stations were used to calculate the Local Meteoric Water Line (LMWL), which was found to be equal to δ2H = (6.58 ± 0.13)*δ18O + (12.64 ± 0.91). A general decrease of 1.22‰ for δ2H and 0.20‰ for δ18O in precipitation was calculated per 100 m altitude. A generic groundwater evolution path was established: 1. Na/MgClHCO3, 2. MgHCO3, 3. Ca/MgHCO3, 4. Ca/MgNaHCO3, 4a. MgNa/CaHCO3/Cl, 5. NaMg/CaHCO3/Cl, 6. NaHCO3, 7. Na/MgHCO3SO4, 8. NaSO4Cl/HCO3. Hydrogeologic descriptions, consisting of groundwater origin, flow path and possible active water-rock processes, have been realised for the observed water types. The first two water types occur in serpentine and ultramafic-gabbro springs. Type 3 waters represent early stages of recharge and/or short flow paths, in gabbro whereas types 4 and 5 are typical for further percolating waters in gabbro and diabase. Water types 6 and 7 occur both in diabase and in the basal group and represent the regional flow. Water type 8 is the end member of regional, upwelling groundwater in the basal group. The presented descriptions and methods have practical applications in groundwater exploration, characterization, and protection. The methodology can be applied in other complex aquifer systems.

Decoupled diversity patterns in microbial geographic distributions on the arid area (the Loess Plateau)

Soil microbes are essential to biogeochemical cycling, soil organic matter decomposition and climate regulation in terrestrial ecosystems. The biogeography of soil bacteria and fungi lags behind in animals and plants, especially in arid areas with alkaline conditions. Understanding the biogeographic of soil microbes and the interactions with environmental factors will provide new insights into the ecosystem functions and services droved by soil bacteria and fungi. Therefore, we chose 48 dryland sites from two transects (north-south and east-west transects) on the Loess Plateau (an arid area) to determine soil bacterial and fungal diversity and community compositions in response to environmental factors and geographic distance. The results showed that soil organic carbon enhanced soil fungal diversity rather than soil bacterial diversity, while soil bacterial diversity was not affected by the environmental factors on the Loess Plateau. The significant associations between the abundance of main bacteria and fungi and soil pH, suggesting that soil pH was the predominant factor affecting soil microbial community structure. In the alkaline soils (pH = 7.4–9.1), soil bacterial community compositions were limited by soil pH, while soil fungal community composition was less sensitive in response to the alterations in soil pH, revealing soil fungi has a wider optimal pH range than bacteria. Compered to historical contingencies, local environment mainly controlled the geography of bacteria and fungi in soils. On the Loess Plateau, soil microbial communities diverge most by soil pH, especially for soil bacteria. These results provide a well understanding of soil microbial geography and associated biogeochemical cycling in arid areas with higher soil pH.

The seasonal imperative: Environmental drivers of livestock mobility in East Darfur, Sudan

At their furthest extent, the livestock migrations examined in this paper traverse a distance of 400 km or more along a north-south transect, crossing up to half a dozen distinct ecological zones and, upon occasion, the international border between Sudan and South Sudan. Official Sudanese recognition of the value of migratory livestock production has led in recent years to policy and legal changes that support pastoral mobility, but there remains a gap in the scientific evidence that can be called upon to inform this emerging awareness. This paper uses remotely sensed livestock tracking data to document pastoral behaviour in relation to some of the biophysical factors that are important for livestock survival and production. This research supports several policy-relevant conclusions:1. In East Darfur, long-distance migratory livestock production is remarkably resilient to rainfall fluctuations, including drought and flooding, because movement cycles are already designed to accommodate this kind of variability.2. Mobile livestock producers are exposed to human-generated disruption and increasing pressures on their mobility from expanding farms, localized conflict and insecurity, and a new international border.3. Pastoralists need sympathetic governance to mediate their interactions with other forms of land use, which is unlikely to happen unless authorities appreciate the technical sophistication and economic advantages of migratory systems.4. Migratory production in East Darfur uses locally available resources which leaves livestock owners and government free to expend cash reserves on other kinds of inputs, investments or activities.

Connection, isolation and reconnection: Quaternary climatic oscillations and the Andes shaped the phylogeographical patterns of the Patagonian beeCentris cineraria(Apidae)

AbstractThe joint effect of the Andes as a geographical barrier and the Quaternary glaciations as promoters of genetic divergence remains virtually unexplored in southern South America. To help fill this knowledge gap, in this study we investigated the demographic history of Centris cineraria, a solitary bee mainly distributed in Patagonia. We used mitochondrial and nuclear markers and performed phylogeographical and dating analyses, adjusted spatio-temporal diffusion and species distribution models, and used Approximate Bayesian Computation to identify likely historical demographic scenarios. Our results revealed that during glacial periods the Andes represented a barrier due to the extent of the ice-sheets and the occurrence of unsuitable habitats, while interglacials allowed for gene flow across the Andes. Secondary contact between previously isolated lineages was evident across at least two low-altitude Andean areas, the northern one being a putative glacial refugium. Our findings also suggest that C. cineraria has persisted in situ in four periglacial refugia located along a north–south transect, congruent with the maximum extent of the ice sheet during the Greatest Patagonian Glaciation. As the first phylogeographical study of Patagonian insects, our work reveals that the interaction between Quaternary climatic oscillations and the Andes as a barrier was the main driver of the spatial and demographic history of C. cineraria.

Thermochronology of the highest central Asian massifs (Khan Tengri - Pobedi, SE Kyrgyztan): Evidence for Late Miocene (ca. 8 Ma) reactivation of Permian faults and insights into building the Tian Shan

Geological study of the Khan Tengri and Pobedi massifs highlights two phases of compressional fault displacements. A Late Permian/Triassic displacement phase is highlighted (1) by biotite 40Ar/39Ar ages of 265–256 Ma, suggestive of cooling of Pobedi mid-crustal granulites during > 8 km of top-to-the-north motion of the Pobedi Thrust; (2) by 40Ar/39Ar dating of syn-kinematic phengite at 249–248 Ma, which suggests a crystallization age during top-to-the-south motion of the Khan Tengri Thrust shear zone; (3) by Apatite Helium (AHe) ages of 280–240 Ma on the crystalline basement below the Mesozoic peneplain, which gives insight into the final exhumation stage. Cenozoic reactivation of the Pobedi Thrust is indicated by AHe thermochronology with a mean age of 8.3 ± 2.5 Ma, in agreement with ~3 km exhumation and ~4.2 km of top-to-the-north motion in the Late Miocene. Along a north–south transect of the west Tian Shan range from Issyk-Kul Lake to Tarim Basin, compiled thermochronological data outline out-of-sequence deformation beginning with the activation of north-directed crustal-scale faults at 22–15 Ma along the northern margin of the north Tian Shan, followed by 20–10 Ma motion at the boundary between the Middle and the South Tian Shan, and ending with the < 10 Ma reactivation of the Pobedi Thrust in the South Tian Shan. This latter coincided with south-directed motion on the South Tian Shan Front (the Maidan Fault) and fold and thrust belt propagation towards the Tarim Basin.

Hydrogen isotope fractionation in modern plants along a boreal-tundra transect in Alaska

An increasing number of studies from high latitude settings use the stable hydrogen isotope ratio (δ2H) of plant leaf waxes to quantify changes in past precipitation. Calibration of modern vegetation and source water use from these landscapes is important to more accurately reconstruct past hydroclimate variability using sedimentary leaf wax δ2H values. Here, we determine plant-water fractionations from 12 sites along a south-north transect in central Alaska, from Fairbanks to Deadhorse (64-70°N). We characterize the δ2H values of n-alkanes and n-alkanoic acids from modern plants and their xylem and leaf water δ2H values, as well as plant source water using surface soils, a soil core, and previously collected meteoric water data from the region. We find both transpiration (εLW/XW) and biosynthetic (εwax/LW) fractionation are sensitive to environmental controls with latitude, with increased leaf transpiration and biosynthetic fractionation to the north, potentially due to increased summer sunlight hours. Soil water δ2H values show near linear 2H enrichment toward the surface associated with evaporation, with the δ2H value ∼40 cm matching mean annual precipitation (MAP). Average net fractionation was calculated using xylem water and chain length weighted wax δ2H values (εwax/XW) and we find nearly the same mean values for both n-alkanes, −112 ± 27‰, and n-alkanoic acids, −110 ± 23‰, from 12 common high latitude vascular plants. To provide the range of likely net fractionations along this transect, we also calculate the average net fractionation using MAP, finding values are less negative than using xylem waters (εwax/MAP, −89 ± 28‰ for n-alkanes, and −86 ± 24‰ for n-alkanoic acids). To compare across studies, we determined the average εwax/MAP of n-alkanes from all available high latitude calibration studies and found more 2H enriched (smaller fractionations) for C27 (-87 ± 29‰), C29 (-87 ± 32‰), and C31 (-91 ± 31‰) than those of global εwax/MAP homolog averages. This new work in Alaska contributes to our growing understanding of plant water-wax fractionation in the high latitudes and is potentially important for the use of sedimentary δ2H values for paleoprecipitation estimates.

Observation of a mesoscale eddy dipole on the northern Madagascar Ridge: Consequences for the circulation and hydrography in the vicinity of a seamount

Based on satellite and in situ data, the dynamic characteristics and vertical structure of a surface intensified mesoscale eddy dipole recently expelled from the South East Madagascar Current (SEMC) is described for the first time. The dipole was surveyed 250 nautical miles south of Madagascar between 14 and 23 November 2016, during west-east and south-north transects carried out over the northern Madagascar Ridge. The dipole consisted of two counter-rotating vortices of similar size (100 km) and intensity (0.7 f), and an intense southwestward jet (150 cm s-1) in the frontal region between the two eddies. The cyclonic eddy was lying on the western side of the anticyclonic eddy. With azimuthal velocities reaching 100 cm s-1 at the surface and decreasing slowly with depth (40 cm s-1 at -600 m), this dipole was defined as a highly non-linear (Ro ~ 0.7) isolated eddy-type structure (cβ ~ 11 cm s–1 and U/cβ ~ 0.7) capable of trapping and advecting water masses over large distances. The enhanced concentration of chlorophyll-a found in the cyclone relative to the anticyclone could be tracked back to the spin-up phase of the two eddies and attributed to eddy-pumping. The eddy cores were located above the pycnocline (1026.4 kg m-3), within the upper 600 m, and consisted of varieties of Subtropical Underwater (STUW) found within the SEMC. The STUW found in the anticyclone was more saline and oxygenated than in the cyclone, highlighting mixing with the inshore shelf waters from the southeastern coastal upwelling cell off Madagascar. Observations suggest that the dipole interacted strongly with the chaotic bathymetry of the region, characterized by a group of five seamounts lying between -240 m and -1200 m. The bathymetry blocked its westward advection, trapping it in the vicinity of one shallow seamount for more than 4 weeks, so enhancing the role of the eddy-induced velocities in stirring the surrounding water masses. Squeezed between the southern Madagascan shelf and the northern flank of the anticyclone, two filament-like dynamic features with very different water-mass properties could be observed on the south-north transect: i) one filament highly concentrated in chlorophyll-a demonstrating the capacity of the eddy to export shelf water offshore; ii) intrusions of southern-type STUW generally found south of the South Indian Counter Current (SICC) recirculating on the external flanks of the anticyclone. Although the observed circulation and hydrography were largely constrained by the presence of the mesoscale eddy dipole, unmistakable fine-scale dynamics were also observed in the vicinity of the MAD-Ridge seamount, superimposed onto the mesoscale eddy flow.

Molecular Distributions and Compound-Specific Stable Carbon Isotopic Compositions of Plant Wax n-Alkanes in Marine Aerosols along a North–South Transect in the Arctic–Northwest Pacific Region

A geographical source of n-alkanes in marine aerosols was assessed along a North–South transect in the Arctic–Northwest Pacific region. Marine aerosol samples were collected during the ARA08 cruise with the R/V Araon between 28 August and 28 September 2017. We investigated molecular distributions of n-alkanes (homologous series of C16 to C34) and compound-specific stable carbon isotopes (δ13C) of n-C27, n-C29, and n-C31. Unresolved complex mixtures (UCM) showed a latitudinal trend from the Arctic Ocean to the northwest Pacific Ocean, highlighting an increasing influence of the plume of polluted air exported from East Asian countries. The anthropogenic input was further evidenced by high U/R ratios (&gt;5) and low CPI17–23 (0.6–1.4). The occurrence of high molecular weight (HMW) n-alkanes with high CPI27–31 (&gt;3) indicated the biogenic input of terrestrial higher plant leaf waxes in all studied samples. The δ13C of HMW n-alkanes was influenced by both the relative contributions from the C3/C4 plant sources and from fossil fuel combustions. The back-trajectory analyses provided evidence that changes in molecular distributions and δ13C of n-alkanes were due to the long-range atmospheric transport of anthropogenic and biogenic organic materials from North American and East Asian countries to the Arctic Ocean and the remote northwest Pacific Ocean, respectively.

Components of leaf-trait variation along environmental gradients.

Leaf area (LA), mass per area (LMA), nitrogen per unit area (Narea ) and the leaf-internal to ambient CO2 ratio (χ) are fundamental traits for plant functional ecology and vegetation modelling. Here we aimed to assess how their variation, within and between species, tracks environmental gradients. Measurements were made on 705 species from 116 sites within a broad north-south transect from tropical to temperate Australia. Trait responses to environment were quantified using multiple regression; within- and between-species responses were compared using analysis of covariance and trait-gradient analysis. Leaf area, the leaf economics spectrum (indexed by LMA and Narea ) and χ (from stable carbon isotope ratios) varied almost independently among species. Across sites, however, χ and LA increased with mean growing-season temperature (mGDD0 ) and decreased with vapour pressure deficit (mVPD0 ) and soil pH. LMA and Narea showed the reverse pattern. Climate responses agreed with expectations based on optimality principles. Within-species variability contributed <10% to geographical variation in LA but >90% for χ, with LMA and Narea intermediate. These findings support the hypothesis that acclimation within individuals, adaptation within species and selection among species combine to create predictable relationships between traits and environment. However, the contribution of acclimation/adaptation vs species selection differs among traits.

Benthic foraminifera as tracers of brine production in the Storfjorden “sea ice factory”

Abstract. The rapid response of benthic foraminifera to environmental factors (e.g. organic matter quality and quantity, salinity, pH) and their high fossilisation potential make them promising bio-indicators for the intensity and recurrence of brine formation in Arctic seas. Such an approach, however, requires a thorough knowledge of their modern ecology in such extreme settings. To this aim, seven stations along a north–south transect across the Storfjorden (Svalbard archipelago) have been sampled using an interface multicorer. This fjord is an area of intense sea ice formation characterised by the production of brine-enriched shelf waters (BSW) as a result of a recurrent latent-heat polynya. Living (rose bengal-stained) foraminiferal assemblages were analysed together with geochemical and sedimentological parameters in the top 5 cm of the sediment. Three major biozones were distinguished. (i) The “inner fjord” zone, dominated by typical glacier proximal calcareous species, which opportunistically respond to fresh organic matter inputs. (ii) The “deep basins and sill” zone, characterised by glacier distal agglutinated fauna; these are either dominant because of the mostly refractory nature of organic matter and/or the brine persistence that hampers the growth of calcareous species and/or causes their dissolution. (iii) The “outer fjord” zone, characterised by typical North Atlantic species due to the intrusion of the North Atlantic water in the Storfjordrenna. The stressful conditions present in the deep basins and sill (i.e. acidic waters and low food quality) result in a high agglutinated ∕ calcareous ratio (A∕C). This supports the potential use of the A∕C ratio as a proxy for brine persistence and overflow in Storfjorden.

Analysis of soil-forming factors and soil classification using soil taxonomy system: A case study of Baraka District, Enrekang Regency

The difference in the soil-forming factors can affect the nature of the soil formed. The method was used in this research is quantitative descriptive based on primary and secondary data. The field survey was conducted using the random stratified method at 15 soil profile divided into four north-south transects. The determination of soil characteristics value were adjusted by the Soil Survey Laboratory Manual method, while the determination of dominant soil minerals used the Fourier Transform Infra-Red (FTIR). Determination of soil type used the soil taxonomy system, which refers to the 12th edition of the soil taxonomy key book. The results of the study showed that there are two soil orders in the Baraka district, Enrekang Regency that is Alfisols and Inceptisols. Alfisols was found in the six soil profile that classified as Typic Paleustalfs (subgroup) mixed family of Isohypethemic Typic Paleustalfs, Kaolinitic with Isohypethemic Typic Paleustalfs, while Inceptisol was found in the nine soil profile that classified as Lithic Haplustepts, Dystic Haplustepts, Typic Dystrudepts and on the family category that is clay mixture Isohypethemic Typic Dystrustepts, clay mixture Isohypethemic Dystric Haplustepts, clay mixture Isohypethemic Lithic Haplustepts, Carbonatic compound Isohypethemic Dystric Haplustepts. The results of this research also indicate that the dominant soil-forming factors in the Baraka District, Enrekang Regency are the parent material, vegetation, and slopes.

Northern limit of Gondwana in northwestern Mexico from detrital zircon data

UPb geochronology along a north-south transect from central Sonora to northern Sinaloa in northwestern Mexico indicates several changes in provenance sources through time and space. Lower Cambrian arenites of the Proveedora Quartzite yield a single main age peak at 1075 Ma with minor Paleoproterozoic contribution. Arenites from the Sonobari Complex of southwestern Sonora-northwestern Sinaloa, purportedly assigned to the early Paleozoic, yield main peaks at 1424, 1662, and 1736 Ma, probably derived from the Yavapai and Mazatzal provinces, which are pervasively intruded by early Mesoproterozoic granites coeval to those forming the Granite-Rhyolite Province. Lower to Upper Ordovician units deposited on shelf, slope, and abyssal environments display very similar zircon age patterns, with main peaks ca. 2700 and 1850 Ma, indicating a large drainage system arising from the Archean cratons of Laurentia such as the Wyoming or Superior Provinces, and Paleoproterozoic sources similar to the Trans-Hudsonian orogen, which are older than the Yavapai Province. The Río Fuerte quartzites from southern Sonora-northern Sinaloa contain main peaks at 534, 542, and 637 Ma whose sources may be peri-Gondwanan blocks similar to Avalonia or Carolina terranes. A minor peak at 475 Ma suggests input from igneous suites reported from the Acatlán Complex in southern Mexico. UPb geochronology permit inference of a late Paleozoic collisional orogen in northwestern Mexico that was originated by the collision of Gondwanan blocks against southern Laurentia and outline the boundary between terranes related to continental blocks in the Pangaea supercontinent.

Cloud condensation nuclei properties of South Asian outflow over the northern Indian Ocean during winter

Abstract. Extensive measurements of cloud condensation nuclei (CCN) and condensation nuclei (CN) concentrations in the South Asian outflow to the northern Indian Ocean were carried out on board an instrumented research vessel, as part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) during the winter season (January–February 2018). Measurements include a north–south transect across the South Asian plume over the northern Indian Ocean and an east–west transect over the equatorial Indian Ocean (∼2∘ S), which is far away from the continental sources. South Asian outflow over the northern Indian Ocean is characterized by the high values of CCN number concentration (∼5000 cm−3), low CCN activation efficiency (∼25 %) and a steep increase in CCN concentration with the increase in supersaturation. In contrast, low CCN concentration (∼1000 cm−3) with flat supersaturation spectra was found over the equatorial Indian Ocean. The CCN properties exhibited significant dependence on the geometric mean diameter (GMD) of the aerosol number size distribution, and CCN activation efficiency decreased to low values (&lt;20 %) at the time of new-particle formation events over near-coastal and remote oceanic regions. The analysis of the activation efficiencies for the “similar” aerosol size distributions over the northern Indian Ocean indicated the primary role of aerosol number size distribution on CCN activation efficiency. The dependence of CCN properties and activation efficiency on size-segregated aerosol number concentration, especially during the ultrafine (&lt;100 nm) particle events, is investigated in detail for the first time over the region.

Summer maize growth under different precipitation years in the Huang-Huai-Hai Plain of China

Maize (Zea mays L.) is one of the important crops for meeting the high food demand for both humans and animals in the world. Promptly monitoring and accurately assessing growth of summer maize, a major crop in the Huang-Huai-Hai Plain (the HHH Plain) in China, is regularly conducted for estimating national yield and assessing food security. In this study, the process-based Remote-Sensing-Photosynthesis-Yield Estimation for Crops (RS-P-YEC) model, driven by remote sensing products, meteorological observations, phenophases of summer maize, and some auxiliary parameters, was used to simulate daily net primary productivity (NPP) of summer maize in the HHH Plain from June to September in 2000–2017. Summer maize growth at the county scale level (characterized by NPP) under different precipitation years was evaluated along West-East, North-South, and Northwest-Southeast transects in the HHH Plain. Results showed that with increasing accumulative precipitation during the summer maize growing season, maize growth exhibited the characteristics of a downward opening parabolic curve for a dataset including all site-years and for single year datasets. The best simulated maize growth and actual observed yield generally occurred when accumulative precipitation during the summer maize growing season was between 300 and 500 mm. Furthermore, summer maize growth was reduced in years with growing season accumulative precipitation less than 300 mm or greater than 500 mm as seen in the analysis of data from several stations under different precipitation levels along the three transects. This study confirmed that NPP simulated with the RS-P-YEC model, driven by remote sensing products and ground-based meteorological observations, is a good indicator for monitoring and evaluating summer maize growth under different precipitation levels in the HHH Plain. As such, the evaluation results will be helpful for forecasting yield across broad geographical areas, and for assessing national food security.

Land use/land cover change and land surface temperature of Ibadan and environs, Nigeria.

Rapid urbanization is having a considerable impact on various aspects of living, thereby altering the biophysical environment. This study adopted the use of remote sensing technique and geographical information system (GIS) to analyse the relationship between changing land use/land cover and land surface temperature in a rapidly urbanizing tropical cityof Ibadan between 1984 and 2019. Landsat series TM, ETM+, and OLI satellite imageries of Ibadan region city for 1984, 2002, and 2019, respectively, were obtained from the US Geological Survey (USGS) Landsat series of Earth Observation satellites accessible on the Google earth engine (GEE) platform. Supervised classification was done using a random forest (RF) machine learning classifier in the GEE platform. Surface emissivity maps were obtained from the normalized difference vegetation index (NDVI) thresholds method and land cover information. The surface emissivity based on NDVI classes was used to retrieve land surface temperature (LST). The results showed an increase in urban cover from 341.72km2 in 1984 to 520.58km2 in 2019 with an average increase in land surface temperature from 17°C to 38°C, respectively. Temperature sampling in the north-south and west-east transect revealed that highly urbanized areas located at the city centre of Ibadan have the highest LST of about 38°C. It dissipates to about 19°C at the suburb that is less built up. A significant negative relationship exists between the health condition of vegetation (NDVI) and LST with a correlation coefficient of r = - 0.95. The study confirms the potential application of GIS and remote sensing for detecting urban growth as well as relates growth impact to LST, thereby suggesting that fitting strategies will be important for the sustainable management of the urban areas.

Greenhouse gas-producing soil biological activity in burned and unburned forests along a transect in European Russia

It is not clear which mechanisms are responsible for changing soil biological activity following a fire. To address this knowledge gap, we measured such parameters of soil biological activity as flux rates of CH4, and CO2 and identified key environmental parameters that can influence soil biological activity. Soil samples were collected in burned and adjacent unburned control forests, along a 3000 km-long north-south transect in European Russia. A raw biological activity of tested soil samples varied significantly between forest types, but not between burned and control forest stands. Linear mixed effect modeling demonstrated a striking contrast in the importance of different drivers in sustaining a soil biological activity in the burned and control forests. The optimal model of basal soil respiration consisted of: “Soil moisture” (26%), “Fire treatment × Soil moisture × Labile soil N:P ratio” (21%), and “Fire treatment × Labile soil C × Labile soil N:P ratio” (13%). The model for CH4 in turn was defined by interactions of bulk and labile soil C with soil moisture and other factors. Our study clearly demonstrated that forest fires affect soil biological activity rather indirectly through modifying soil properties. The results enable forecasting post-fire effects on soil functioning in a changing climate under varied fire regimes.