Semi-humid Conditions Research Articles

Evaluation of global seamless soil moisture products over China: A perspective of soil moisture sensitivity to precipitation

Accurate and timely information about soil moisture (SM) is not only critical to the study of climate change, but is also significant for agricultural production, drought monitoring, and hydrometeorological predictions. With the development of satellite remote sensing techniques, land surface models, and data assimilation techniques, a number of global seamless soil moisture products have been released with highly variable accuracy. A comprehensive evaluation of these products is necessary to select a suitable SM product for use. In this study, we provided such an evaluation of four global seamless SM products (SMAP-L4, ERA5-Land, GLDAS-Noah, and GLEAM) over China based on the stations from the automatic soil moisture observation (ASMO) system. Compared to previous studies that focused on a direct comparison between SM products and in situ SM observations, we specifically evaluated these products from the perspective of SM sensitivity to precipitation. This is because in situ precipitation observations are more spatially representative than in situ SM observations. Precipitation is a regional event, therefore in situ precipitation observations can be better scale-matched with coarse resolution SM products compared to in situ SM observations. Further, in addition to surface soil moisture (SSM), root zone soil moisture (RZSM) was evaluated in this study. The combination of all statistics illustrates that SMAP-L4 and ERA5-Land generally performed better than GLDAS-Noah and GLEAM. Regardless of the SSM or RZSM estimates, SMAP-L4 had the lowest median bias and RMSE of the four products, and ERA5-Land had the lowest median correlation coefficient (R) value. The lowest median ubRMSE was obtained by SMAP-L4 in SSM evaluation and ERA5-Land performed better than other RZSM products with the lowest median ubRMSE. From the perspective of SM sensitivity to precipitation, SMAP-L4 can capture daily precipitation dynamics most effectively, closely followed by ERA5-Land. This partially explains the superiority of SMAP-L4 and ERA5-Land over GLDAS-Noah and GLEAM for SM monitoring. The results of the metrics under different precipitation conditions varied considerably among the products. But while considering of ubRMSE alone, all products performed better under arid and humid conditions than to semi-arid and semi-humid conditions. This may be due to the fact that SM products had a limited ability to capture the SM dynamics under moderate precipitation. These findings may provide new insights into the selection of appropriate SM products and SM estimation in the future.

Geochemical constrains for unravelling the condition of sedimentation, provenance, paleoclimate variation, and metallogenic implication of the cretaceous deposits of Mayo Oulo Basin (North Cameroon, Africa)

The sediments from the Mayo Oulo intracontinental Basin, along the N–S cross section between the Gadavou and Lombel localities in central part of the basin, were investigated through major and trace elements geochemistry associated with palynological analysis to determine their condition of sedimentation, paleoclimate evolution and metallogenic implication along the Cretaceous sequence from the N–S cross section of the central part of this basin. From bottom to top of this sequence there are various types of facies with various concentrations of carbonate. Based on their major oxides compositions, the sediments were classified as Shales associated with Fe-shales, Fe-sands, Wacke and Litharenite. The CIX (Chemical Index of Alteration, 62.65 to 98.14) and PIX (Plagioclase Index of Alteration, 65.00 to 99.13) sediments underwent a various chemical weathering; little chemical weathering in the middle to the upper part of the sequence and moderate to high chemical weathering in the lower part. The discriminant function-based multidimensional tectonic diagrams indicate mainly and respectively arc-collisional and Island arc-active continental margin settings which are consistent with the Precambrian geological history of the study area. The SiO2 vs. Al2O3+K2O + Na2O, C-values, associated with trace elements plots such as Sr/Ba, and Rb/Sr, and palynological content (continental or terrestrial species exclusively, dominated by Gymnosperm pollens such as. Inaperturopollenites sp., Araucariacites sp. and Classopollis sp, associated with spores such as Cicatricosisporites sp) indicate mainly arid to semi-arid climate with periodic humid to semi-humid conditions. The Sr/Ba values ranging from 0.084 to 6.408 suggest a fluctuating and sometimes high salinity (Hypersaline milieu). The rare earth elements data show high LREE/HREE ratios (2.86–13.31); high negative and positive Eu anomaly (Eu/Eu∗ = 0.33 to 1.38) and no Ce anomaly (Ce/Ce∗ = 0.94 to 1.02); these features, together with mixed major and trace element ratios and plots such as, Al2O3/TiO2 ratios (14.31–54.26); Th/Co ratios (0.30–14.58); Ce vs La/Yb, Zr vs TiO2 and La/Sc vs Th/Co plots, indicate that the sediments are derived mainly from felsic to intermediate or mafic rock composition. Ni/Co (1.86–3.59) and U/Th (0.03–0.76) ratios are consistent with oxic conditions from bottom to top of the sequence. The Al/Si ratio shows positive correlation with CIA, Th, Zr, Hf, Na, K and negative correlation with Ca and Mg. The positive correlation with K, Hf, Na, Zr, and Th from detrital origin and negative correlation with Ca and Mg from chemical origin could suggest the geochemical composition control of grain size. According to the ternary Al–Fe–Mn diagram metallogenic classification, the studied samples are essentially terrigenous and partially weakly metalliferous, close to those from the Babouri –Figuil and Mamfe Basins (Cameroon) and contrary to those from the Sob area (Polar Urals). No marine or transitional fossil species are recorded. The presence of numerous tetrads to dyads indicate a lacustrine or swampy environment surrounded by vegetation.

Sandstones and red beds in the Lower Cretaceous Sidi Aich Formation, Chotts Basin (Southern Tunisia): facies, architecture and depositional environments

Abstract The Lower Cretaceous deposits of North Africa represent a terrestrial to shallow-marine sandstone-dominated succession often referred to as the ‘Continental Intercalaire’ and Nubian Sandstone informal groups. The upper Barremian Sidi Aich Formation of the Continental Intercalaire is distinguished throughout the Chotts basin of southern Tunisia by sandstone-dominated sequences within conglomerate, calcareous siltstone and palaeosol red bed occurrences. This paper aims to highlight: (1) the facies distribution, internal architecture and depositional environment of the sandbodies; and (2) the origin, spatial distribution and architecture of the red beds that underlined and topped sandbodies. Strata in the Zimlet El Beida anticlinal structure, Chotts basin, offer a good opportunity for detailed field observations and bed-by-bed logging of three representative lithostratigraphic sections. Detailed sedimentological investigation allows the recognition of several lithofacies grouped into three facies associations indicating tidal flat, tidal channel and tidal bar depositional settings characterizing a transgressive tide-dominated estuarine system that developed during an episode of relative sea-level fluctuations in the Early Cretaceous. The high-resolution petrographic, mineralogical and geochemical analyses of the red beds allow the differentiation of three distinct lithofacies sets including: (1) intraformational conglomerates; (2) calcareous siltstones; and (3) palaeosol. Major red beds comprise detrital grains inherited from the host or parent sediment and authigenic minerals (dolomite, calcite and hematite) precipitated during the diagenetic processes. Grain components have been partially or completely cemented and/or replaced by terrestrial phreatic dolomite. The negative δ 13 C and δ 18 O signatures of the dolomite analyses indicate that the dolomitization processes have been influenced by fluctuations of the groundwater table or climate change from semi-arid to semi-humid conditions. This study, therefore, may provide useful data for the better understanding of the internal architecture of the red beds associated with sandbodies that represent the main and significant potential reservoir within the Lower Cretaceous Continental Intercalaire sandstone-dominated groundwater aquifers of the Chotts basin.

Contribution of lakes in sustaining the Sahara greening during the mid-Holocene

Abstract. The climate impact contribution of lakes to sustain the Green Sahara in the mid-Holocene (MH, 6000 years ago) is still under debate. To assess the lake-induced climate response over North Africa, we investigated the roles of western Sahara lakes and Megalake Chad using reconstructions of MH Sahara lake maps as surface boundary conditions for the isotope-enabled atmospheric model MIROC5-iso. Our results show that the western Sahara lakes pushed the West African monsoon northward and extended it eastward by expanding Megalake Chad. This lake–climate impact was caused by the cyclonic circulation response related to the weakened African Easterly Jet and enhanced Tropical Easterly Jet. According to the Budyko aridity index, the northwestern Sahara climate region shifted from hyper-arid to arid or semi-arid with the lake expansion. Moreover, precipitation scarcity could have been reduced by up to 13 % to sustain the semi-humid conditions. Such lake–climate impacts could alleviate Sahara aridity, relying on lake positions in the monsoon regions. Our findings are promising for understanding the contribution of lakes to sustaining the Green Sahara.

Analyses of leaf morphological changes and expressed genes related to water shortage of Fagus orientalis populations in a drought gradient

Climate change models predict an increase in mean annual temperature, a decrease in precipitation and consequently a scarcity of water resources during the growing season for Iran, including the northern forests of the country. One of the consequences is increased water shortage stress during the summer season. Fagus orientalis Lipsky is one of the most important commercial broad leaf species in the Hyrcanian forests and its potential of phenotypic and genetic adaptation to the climate change is essentially vital. The present research was carried out along two precipitation gradients from very humid to semi-humid conditions on four beech populations. The results of the flexibility of the leaf morphological traits showed that the populations of dryer regions had smaller and more elongated leaves than other populations. Evaluation of the expression of seven candidate genes in response to water shortage showed that the expression of aldehyde dehydrogenase, ascorbate peroxidase, Dehydrin (DHN), early responsive to dehydration, late embryogenesis abundant and Cys/His-Type Zinc-Finger in the eastern population was higher than that in the western population, while a difference in elevation gradient was only observed in the expression of some genes. Therefore, the natural selection pressure in the past evolutionary periods in the westeast gradient seems to be higher than the elevation gradient and has led to greater resistance to drought. Principal component analysis revealed that aldehyde dehydrogenase genes (ALDH), early responsive to dehydration (ERD), late embryogenesis abundant (LEA) and DHN are the most effective genes responding to water shortage stress for Oriental beech in the Hyrcanian forests. Keywords: drought gradient, Fagus orientalis, gene expression, leaf morphology

Climate-driven paleoceanography change controls on petrology and organic matter accumulation in the upper Permian Dalong Formation, western Hubei Province, southern China

The influence of paleoclimate on shale sedimentary processes and organic matter accumulation is of great significance for reconstructing the “deep time” paleoclimate as well as for oil and gas exploration. Here, a detailed study on the Lopingian Dalong Formation organic-rich shales in the western Hubei area of the Middle Yangtze region is performed to understand how paleoclimate affects the depositional process and organic matter accumulation of shales. By combining a detailed core description and microscopic observations, along with mineralogical and geochemical analysis, two major lithological facies were identified from the H1 drilling core, including siliceous shale and clay/carbonate bearing mixed shale. The changes in depositional observations and geochemical indicators (including detritus index, Ln (Al2O3/Na2O), CuEF, ZnEF, UEF, MoEF, Cd/Mo and Co × Mn) indicate that the siliceous shale was deposited in an anoxic basin with well-developed upwelling under warm and semihumid conditions. However, the clay/carbonate bearing mixed shale was deposited in a hypoxic basin with weakly developed upwelling, and the climate was arid and hot. These deposits suggest that paleoclimates developed into hot and arid climates over time and that such climate change trends may be a response to global warming at the end of the late Permian. High temperatures inhibit the development of upwelling but increase the input of terrigenous clastic materials by enhancing weathering, and controlling the shale deposition. The average total organic carbon (TOC) content of the basin varies significantly in different lithological facies. We infer that the organic matter accumulation of clay/carbonate bearing mixed shale is comprehensively controlled by the carbonate production rate and primary productivity, while the organic matter accumulation of siliceous shale is primarily controlled by the authigenic quartz production rate. When the detrital index in the study area reaches 80 %, TOC does not increase or even decrease. Therefore, in the presence of authigenic quartz silicon, the increased silicate content is not always conducive to the accumulation of organic matter.

Improving paleoenvironment in North China aided Triassic biotic recovery on land following the end-Permian mass extinction

The driver of the Early–Middle Triassic biotic recovery on land following the end-Permian crisis is puzzling. Here, we show the biotic recovery was gradual and spanned up to 8 Myr after the end-Permian mass extinction, based on continuous, well-dated sections over large areas in the northeastern Ordos Basin, North China. Initial recovery began in the Olenekian, marked by the disappearance of microbially induced sedimentary structures and reappearance of bioturbation, and continued in the Anisian, with a bloom of plants and tetrapods and intense bioturbation. Sedimentary environments changed from Induan braided-eolian conditions to Olenekian–Anisian shallow lacustrine and meandering river systems, marking an overall deepening lacustrine system. Carbonate δ13C and geochemical proxies of weathering intensity, salinity and clayiness reveal an overall warm and semi-humid paleoclimate in the Olenekian–Anisian. This improved stable paleoenvironment of warm and semi-humid conditions likely contributed to the biotic recovery following the Permian-Triassic hyperthermal-related crisis.

Karadeniz Bölgesi İklim Koşullarına Uygun Jensen Haise Yöntemi Referans Evapotranspirasyon Tahmin Eşitliklerinin Geliştirilmesi

In this study, it is aimed to determine the usability level of the original equation (JH_original) of the Jensen Haise method in the monthly average reference evapotranspiration (ETo) estimations in the Black Sea Region conditions and to calibrate it in accordance with the local climatic conditions. First of all, the climate classification of the region was made according to the De Martonne aridity index method. Then modified Jensen Haise (JH_modified) equations were developed for each climate class, using the Microsoft Excel program solver add-on. ETo calculations were made using monthly average temperature, relative humidity, wind speed and sunshine duration data (1927 – 2020) of the cities in the region. The ETo values estimated by the JH_original and JH_modified equations were compared with the values determined using the FAO 56 Penman Monteith (PM) equation. While the eastern part of the region is in the very humid climate class, the climate has changed to humid and semi humid towards the west along the coastline. It has been observed that the semi arid – humid climate is dominant in the interior parts, which receive less precipitation compared to the coastal part in region. The annual average ETo values obtained with FAO 56 PM for very humid, humid, semi humid and semi arid – humid conditions were determined as 1.779 mm day-1, 2.349 mm day-1, 2.280 mm day-1 and 2.631 mm day-1, respectively. For the same climate classes, the values estimated with JH_original were obtained as 2.146 mm day-1, 2.697 mm day-1, 2.566 mm day-1 and 2.562 mm day-1. The values estimated using JH_modified were determined as 1.775 mm day-1, 2.319 mm day-1, 2.238 mm day-1 and 2.629 mm day-1, respectively. The MAPE for the ETo values estimated using JH_original varied between %19.357 – 45.561 on the basis of city. Although the accuracy of ETo values is “acceptable” (MAPE= 20 – 50%), JH_original performed poorly in all climate class conditions. For this equation, the MAE, which changed between 0.428 – 0.596 mm day-1 on the basis of climate class, decreased by 62.14 – 92.76% after calibration and regressed to 0.031 – 0.205 mm day-1 range for JH_modified. JH_modified showed the best and worst performances in very humid (MAPE= 2.298%) and semi humid (MAPE= 13.631%) conditions, respectively. Its performance in humid and semi arid – humid conditions was close to each other (MAPE= 8.937 – 9.012). The accuracy of the ETo values estimated using this equation was determined as “good” (MAPE= 10 – 20%) in semi humid conditions and “very good” (MAPE= ≤ 10%) in other climate class conditions. It was concluded that the JH_modified equation is a good alternative and can be used to estimate ETo in humid conditions İn the absence of sufficient data for FAO 56 PM.

Global assessment of lagged and cumulative effects of drought on grassland gross primary production

Drought has large impacts on the vegetation growth of global terrestrial ecosystems, particularly grasslands. Extensive in-situ studies have shown that the impact of drought on vegetation growth has lagged and cumulative effects, but it is not well known how grassland productivity (gross primary production or GPP) responds to drought over time at large scales. Here, we investigated the spatiotemporal patterns of lagged and cumulative effects of drought on global grassland GPP using an OCO-2 solar-induced chlorophyll fluorescence (SIF) based GPP product (GOSIF GPP) and the Standardized Precipitation Evapotranspiration Index (SPEI). The results showed that globally, 88.37% of the grassland had a lagged response to drought, with a lagged time scale of mainly 1 month. With the increase in soil water availability, the magnitude of the lagged effect gradually weakened. Grasslands in semiarid and semi humid conditions that were adaptable to periodic drought responded fastest to drought. Globally, more than three quarters (78.55%) of the grassland was affected by the cumulative effect of drought. The accumulated months occurred at longer time scales (8 ∼ 10 months) for the region at 40°N–55°N, which is relatively arid. The cumulative effect in relatively arid areas was stronger than that in relatively humid areas, indicating that grasslands in more arid areas had stronger tolerance to drought. More importantly, we found that the cumulative effect of drought on grassland GPP was stronger than the lagged effect. This study highlights the great importance of considering the legacy effect, especially the cumulative effect, of drought on grassland productivity, which would advance our understanding of the impact of climate change on the carbon and water cycles of terrestrial ecosystems.

Sedimentary environment and provenance of sandstones from the Qadir member in the Nayband Formation, Tabas block, east-central Iran

Qadir Member of Nayband Formation, located in East of Central Iran, has developed to a great extent. Investigation of the lithofacies and sedimentary environment, resulted in identification of the deltaic and marine deposits. Based on field evidence and facies features, Qadir Member consists of two lithofacies, including carbonate and siliciclastic facies. The siliciclastic facies were identified as having four sandstone facies including Sr, Sh, Sp, St, three fine-grained lithofacies, including FI, Fm, Fl (Sr) / Sr (FI) and one coal facies. Also, regarding the field, laboratory studies, and identification of lithofacies, the coastal plain, deltaic (including deltaic plain, proximal delta front, distal delta front, and prodelta) and open marine environments were identified for Qadir Member which is is under the impact of tidal currents. The chemical weathering index (71%) indicated semi-arid to semi-humid conditions and plotting the geochemical data showed the provenance of re-cycling and active continental margin and because of Chemical Index of Alteration, the weathering rate was found to be rather medium to high. The geochemical diagrams also showed a probable source of the intermediate igneous and sedimentary rocks. The active continental margin conditions for this deposit could suggest the Neotethys subduction under Iran’s plate and volcanic activity at the end of Triassic, which coincided with the early Cimmerian orogeny in Alborz and Central East Iranian Microcontinent.

Cultivation and mulching materials strategies to enhance soil water status, net ecosystem and crop water productivity of winter wheat in semi-humid regions

Different cultivation practices with mulching materials have been applied in the semi-arid areas of China. However, there is still insufficient systematic research on its eff ;ects on ecological indexes and crop water productivity. Therefore, a field trial was carried out in three consecutive study years (2015–2018) to evaluate ecological productivity, crop water productivity, and wheat production under six different treatments: CT: conventional flat tillage without mulching; TSM: conventional flat tillage with gravel mulching; TPM: conventional flat tillage with plastic film mulching; RP: ridges covered with plastic film and furrows without mulching; RSM: ridges covered with plastic film and furrows with gravel mulching; RPM: ridges and furrows covered with plastic film mulching. We found that different cultivation and mulching materials practices considerably improved soil moisture content, crop productivity, ecological eff ;ects and evapotranspiration (ET) rates. The RP cropping system with different mulching practices significantly increased soil moisture and ecosystem CO2 and NO2 emissions during the three consecutive study years. The RP cropping system with gravel or plastic film mulching on the furrows improved the dry matter per plant and LAI at the late growth stage, and it improved crop water productivity. Compared to the CT cultivation practice, the annual net primary productivity (NPP) and net ecosystem productivity (NEP) were significantly increased by 13% and 70%, respectively, with the RPM. In the RPM treatment, the CWPeco and CWPyield were significantly improved by 66% and 84%, respectively, relative to the CT cultivation practice. In addition, RPM treatment improved the spike partitioning index by 16%, maintained a fruiting efficiency that was 12% higher, increased water soluble carbohydrates (WSC) in the stem, increased apparent translocation (amount and ratio), and ultimately achieved an 89% higher grain yield. Taking into account the ecological eff ;ects, wheat production and ET rate, RPM treatment is an eff ;ective approach for saving water and improving CWP and production in semi-humid conditions.

Aridity conditions within the region of Oltenia (Romania) from 1961 to 2015

Aridity and drought assessment at a global level or within particular regions has lately gained an importance on the background of global warming, variability of rainfall amounts and, of course, their impact on social welfare. Aiming at understanding this impact, there were analysed spatial distribution (based on the data from 15 meteorological stations, generally covering the period 1961–2015) and temporal variability of three aridity indices. Thus, there were calculated De Martonne aridity index (IDM) at annual, seasonal and monthly level, Pinna combinative index (Ip) and Selyaninov’s hydrothermal coefficient (HTC). Ip indicates humid conditions all over the analysed area, with slight differences within the extra-Carpathian region, confirming thus that it does not give relevant results for the temperate region. IaDM illustrates a greater territorial differentiation, namely semi-humid conditions in the plain area and in the eastern part of the entire region, humid and very humid conditions in the Subcarpathians and the mountains. At monthly level, there are up to 5 months (in the plain area) with semiarid conditions, generally covering the summer period, as well as September and October. The same monthly pattern is highlighted by HTC, especially in the summer months, which are moderately or slightly arid, mainly in the plain area. However, if analysing the long-term trends (for IaDM), it results that there is not a statistically significant tendency of aridization in the analysed region.

Late Cretaceous paleoclimate change and its impact on uranium mineralization in the Kailu Depression, southwest Songliao Basin

Paleoclimate significantly influenced continental sandstone-type uranium mineralization. To better understand continental climate change in the Late Cretaceous and its influence on uranium mineralization, we selected four boreholes from Late Cretaceous sedimentary successions from the southwestern Songliao Basin, in northeastern China. Twenty-one samples were collected for sporopollen analyses. Based on the variations in the relative abundances of the different sporopollen taxa, we observed the four following palynological assemblages (PAs) in ascending order: the Schizaeoisporites–Classopollis–Tricolporollenites assemblage, the Taxodiaceaepollenites–Exesipollenties–Cranwellia assemblage, the Schizaeoisporites–Classopollis–Lytharites assemblage, and the Biasccate–Taxodiaceaepollenites–Aquilapollenites assemblage. Based on the geological range of several important elements and correlations between relevant assemblages from other regions, we assigned a geological age of late Turonian to early Campanian (approximately 86.7–84.4 Ma) to the four PAs. In this study, we introduced a sporopollen–climate transforming methodology, which uses the percentage of drought, hygrophilous, and thermophilic taxa to indicate stratigraphic trends of humidity and temperature. On the one hand, the percentage of thermophilic taxa was characterized by a continuously decreasing trend, but remained at a relatively high abundance along the entire sedimentary sequence. This was indicative of a hot subtropical–tropical climate with declining temperatures. On the other hand, the percentage of drought and hygrophilous taxa exhibited a cyclical fluctuation between humid and semi-arid climates. A semi-arid climate existed in the PA I, but this then changed to humid conditions in the PA II. Subsequently, the climate evolved into semi-arid and semi-humid conditions as a result of strengthened drought during the PA III. Finally, in the PA IV, the climate became humid once again. In general, the Yaojia Formation’s synsedimentary paleoclimate (i.e., the PA II and PA III) mainly had semi-humid conditions. In the Qianjiadian area, the main prospect target layer is the Yaojia Formation. Compared with the typical sandstone-type uranium deposits throughout northern China, we suggest that the humid paleoclimate was essential for uranium mineralization. The humid climate favored the formation of reduced sandstones, which provided significant geochemical reducing barriers and uranium pre-concentrations essential for epigenetic uranium mineralization.

Nitrogen mineralization indicators under semi-arid and semi-humid conditions: influence on wheat yield and nitrogen uptake

ABSTRACTThe objectives were i) to assess indicators for potential nitrogen (N) mineralization and ii) to analyze their relationships for predicting winter wheat (Triticum aestivum L.) growth parameters (yield and N uptake, Nup) in Mollisols of the semi-arid and semi-humid region of the Argentine Pampas. Thirty-six farmer fields were sampled at 0–20 cm. Several N mineralization indicators, wheat grain yield and Nup at physiological maturity stage were assessed. A principal component (PC) analysis was performed using correlated factors to grain yield and Nup. The cluster analysis showed two main groups: high fertility and low fertility soils. In high fertility soils, combining PCs in multiple regression models enhanced the wheat yield and Nup prediction significantly with a high R2 (adj R2 = 0.71–0.83). The main factors that explained the wheat parameters were associated with water availability and N mineralization indicator, but they differ according to soil fertility.Abbreviations: N: nitrogen; SOM: soil organic matter; POM: particulate organic matter; SOC: soil organic carbon; SON: soil organic nitrogen; POM-C: particulate organic carbon; POM-N: particulate organic nitrogen; Nan: anaerobic nitrogen; Nhyd: hydrolyzable N; NO3-N: cold nitrate; N205: N determined by spectrometer at 205 nm; N260: N determined by spectrometer at 260 nm; Pe: extractable P; Nup: wheat N uptake; NO3-N: inorganic N in the form of nitrate; FR: fallow rainfalls (March-Seeding rainfall); FLR: flowering rainfalls (October-December rainfall); GFR: grain filling rainfall (November rainfall); CCR: crop growing season rainfall (June-December rainfall); PCA: principal component analysis; PC: principal component; MR: multiple regression

Provenance, paleo-weathering and -redox signatures of estuarine sediments from Ghana, Gulf of Guinea

This paper discriminates the source of sediment supply (provenance), degree of chemical weathering, and redox conditions of Holocene sediments cored from the Ankobra and Pra estuaries of Ghana in the Gulf of Guinea using their geochemical characteristics. Considerable stratigraphical variations were observed in major element compositions in the sediments from both the Ankobra (Al2O3: 5.3–14.2%, SiO2: 75.9–88.2%, CaO: 0.3–1.2%, K2O: 0.5–1.2%) and the Pra (Al2O3: 7.8–16.9%, SiO2: 72.8–86.5%, CaO: 0.3–0.4%, K2O: 0.7–1.2%) estuaries. Elemental compositions were similar in both estuaries depicting similarities in their source rock characteristics. Some of the major and trace elements correlated significantly (r2 > 0.8) with Al2O3 in the Pra estuary confirming their possible hydraulic fractionation. Geochemical classification showed the sediments from both estuaries were predominantly composed of sub-arkoses with only a few litharenites. The chemical index of alteration (CIA*), Chemical index of weathering (CIW*), plagioclase index of alteration (PIA*), the Index of compositional variability (ICV), the SiO2/Al2O3 ratios and SiO2 vs. (Al2O3+K2O + NaO), suggest high degrees of chemical weathering coinciding with warm climatic conditions in the source regions as well as sub-matured to mature estuarine sediments deposited under semi-arid to semi-humid conditions. The sediment geochemistry and discrimination diagrams denote similar continental signature derivatives of the sediments from both estuaries. Both sediments are likely derived from intermediate to felsic granitoid source rocks as well as from a quartzose sedimentary provenance formed in a passive continental margin. The Ni/Co and V/Cr ratios depict sediment deposition under oxic conditions through time in both estuaries.

Effects of lateral depth and irrigation level on nitrate and Escherichia coli leaching in the North China Plain for subsurface drip irrigation applying sewage effluent

Subsurface drip irrigation is a sound method to apply sewage effluent, but there is a risk of nitrate and pathogen leaching. Field experiments were conducted during the maize growing seasons of 2014 and 2015 in the North China Plain to investigate the effects of lateral depth, irrigation level, and water quality on the deep percolation and the nitrate (NO3–N) and Escherichia coli (E. coli) leaching under semi-humid conditions. The experiments were designed with three lateral depths of 0 cm (D1), 15 cm (D2), and 30 cm (D3) beneath the soil surface along with three irrigation levels of 70% (I1), 100% (I2), and 130% (I3) of crop evapotranspiration requirements. Secondary sewage effluent and groundwater were used as irrigation water. The results indicated that the intensive rainfall caused most of the deep percolation and NO3–N leaching during the maize growing seasons. A high irrigation level usually produced more deep percolation and NO3–N leaching, but no significant difference was found among the treatments. In general, the cumulative NO3–N leaching beyond the root zone increased as lateral depth increased. In addition, the lateral depth obviously influenced the distribution of E. coli in soil, and subsurface drip irrigation usually induced E. coli contamination deeper in the soil. With relatively high nitrate and E. coli concentration, sewage effluent irrigation significantly increased the risk of NO3–N leaching beyond the root zone in the 2014 season, but imposed an insignificant influence on the presence of E. coli in soil. Furthermore, no E. coli was detected in the leachate following an irrigation event with sewage effluent or a rainfall event during the both maize growing seasons. A dripline depth of 15 cm with deficit irrigation can be conductive to reducing NO3 leaching as well as avoiding sewage effluent contact contamination during the maize growing season in the semi-humid region of the North China Plain.

Sedimentary palaeoenvironment, petrography, provenance and diagenetic inference of the Anacleto Formation in the Neuquén Basin, Late Cretaceous, Argentina

The Anacleto Formation is the uppermost unit of the Neuquén Group, which makes up the foreland stage infill of the Neuquén Basin, during Late Cretaceous. The detailed sedimentological study performed in the excellent outcrops of this formation on the eastern border of the basin allowed the identification of eight fluvial lithofacies, grouped into six facies associations. A meandering fluvial system with palaeo flows from the SW can be interpreted from distribution of facies associations, architectural framework, channel/floodplain ratio, etc. The compositional analysis of the sandstones was performed by mean of petrographic characterization and modal analysis. Sandstones of the Anacleto Fm are mainly subarkosic, arkosic, lithic arenites and, to a lesser extent, sublitoarenites (Q54-F25-R21; Q52-F24-L25). The composition suggests underlying igneous, metamorphic and sedimentary rocks in the main source area. Sedimentological and petrographic analyses, jointly with palaeocurrents orientations suggest that high areas of the North Patagonian Massif were the main source of the fluvial system. The diagenetic stages interpreted from the petrographic characters, SEM observations and X-ray diffraction determine eodiagenesis and telodiagenesis, which are consistent with the burial history of the Neuquén Group. Furthermore, palaeoclimatic considerations based on compositional analysis suggest semiarid to semihumid conditions for the deposition of the Anacleto Fm. These conditions are also supported by clay mineralogy that confirmed smectite as dominant species. A strong climatic seasonality is also deduced by the presence of calcrete levels and frequent discharge channels.

Effects of drip irrigation system uniformity and nitrogen applied on deep percolation and nitrate leaching during growing seasons of spring maize in semi-humid region

Drip system uniformity is one of the important factors affecting the deep percolation and nitrate leaching under drip-irrigated crops. Field experiments were conducted during two growing seasons of spring maize (Zea may L.) in 2011 and 2012 in North China Plain to evaluate the influence of drip irrigation system uniformity on deep percolation and nitrate leaching under semi-humid conditions. In the experiments, three Christiansen uniformity coefficients of 59, 80, and 97 % (the equivalent distribution uniformity DU values were 57, 71, and 95 %, respectively) and three levels of nitrogen applied at 0, 120, and 210 kg ha−1 were tested. The results of the study demonstrated that nitrate leaching was most importantly affected by the nitrogen applied, followed by the initial nitrogen content in the soil and the drip irrigation system uniformity. An increasing amount of nitrogen applied and initial nitrogen content increased the seasonal nitrate leaching significantly, while an improving system uniformity decreased the nitrate leaching. The conventional nitrogen application rate of 210 kg ha−1 could be reduced, and an extremely low drip uniformity of less than 60 % is not recommended to reduce the risk of deep percolation and nitrate leaching in the semi-humid region of North China Plain.

Late Palaeozoic–Early Triassic deposition and climates between Samfrau and Tethys: A review

Abstract In the period between the Westphalian and the Early Triassic, climatic conditions across Gondwana changed from the Gondwana-wide glaciation in the Late Carboniferous–Early Permian to warm to hot, semi-humid to arid conditions by the Late Permian–Early Triassic. In Afro-Arabia, glaciers advanced to 40° palaeolatitude creating a steep gradient between them and the temperate-humid environment in the vicinity of the equator. Synchronous deglaciation associated with a eustatic rise of sea level in the Early Sakmarian was followed by a flattening of the climate gradient and increased humidity, expressed by blackwater rivers and coal swamps between the South Pole and about 50° palaeolatitude and increasing aridity towards the equator. Brief poleward advances of hot aridity are evident around the Kungurian. Expansion of the hot climate zone to the south took place in the Middle Permian, commencing with a humid to semi-humid phase in the south and semi-arid to arid conditions towards the north. A short pluvial event is locally indicated at the beginning of the Triassic, but warm semi-arid to semi-humid conditions prevailed in the south and hot aridity near the equator. There are variations of that general theme in eastern Gondwana, but the fundamental changes in climate-controlled depositional environments occurred almost synchronously over the whole of Gondwana, including Antarctica. The slight drift of Gondwana towards the equator is therefore an unlikely cause for these changes, as are modifications of ocean–continent geometries or of atmospheric composition. As the main driver was temperature it is suggested that governing control, not only of global temperature but also of the intensity of geotectonic activities, was imposed on the solar system by forces emanating from our galaxy (cosmic ray flux, magnetic intensity, gravitational vectors) and their variation over the course of a galactic year (the time for the solar system to orbit the core of the galaxy).

Çanakkale’nin 2008 Yılı Büyük Orman Yangınlarının Meteorolojik ve Hidroklimatolojik Analizi (Meteorological and Hydro-Climatological Analysis of Large Forest Fires of Çanakkale in the Year of 2008)

Turkish Abstract: Subtropikal Akdeniz iklim bolgesinde yer alan Canakkale, genel olarak yarinemli, yaz doneminde ise kurak iklim ozellikleri gosterir. Yaz donemindeki kurak kosullar ve kurutucu egemen kuzey sektorlu ruzgarlar (ozellikle Poyraz), orman yanginlarinin olusmasi ve yayilmasi icin uygundur. Calismanin baslica sonuclari sunlardir: (1) Canakkale Orman Bolge Mudurlugu’nde (OBM) 2008 yilinda ucu 100 hektardan (ha) fazla alani etkileyen 30 orman yangininda 2070 ha orman alani zarar gordu. (2) Erinc kuraklik indisinin yillik degerlerine gore, Canakkale yarikurak bir iklime sahiptir. Aylik indislere gore ise, Nisan–Ekim aylari arasindaki 7 aylik surecte kurak kosullar egemendir. (3) Canakkale, UNCCD kuraklik indisine gore yillik degerlerde yarinemli, aylik degerlerde ise Mayis’tan Eylul’e kadar 5 ay kurak kosullarin etkisi altindadir. (4) 2008 yilinda Keetch-Byram kuraklik indisi (KBDI) 530 buyuklugundeki en yuksek degerine 10.08.2008 gunu ulasti. (5) Canakkale meteoroloji istasyonunun 2008 yili verilerine uygulanan KBDI degerleri, yilin hicbir doneminde kesin yangin olur seviyesine ulasmadi. (6) KBDI, 2008 yilinda Canakkale OBM’de olusan 30 orman yangininin % 76’sini yangin olasiliginin yuksek ve oldukca yuksek oldugu duzeylerde yakaladi. (7) Canakkale Intepe’de cikan Cinarli orman yangini, Turkiye’de 2008 yilinda yanan alanin en fazla oldugu 4 orman yanginindan biridir. English Abstract: Canakkale that is located in the subtropical Mediterranean climate is characterized with semi-humid climate conditions in general, and summer dryness. Drought conditions and drying prevailing northerly sector winds (e.g. Poyraz) in summer are favorable for occurrence and dispersing of the forest fires during the summer months. The major results of the study are as follows: (1) In the year of 2008, a total of 30 forest fires, three of which affected more than 100 hectares (ha) forest area, caused to have damaged about 2070 ha forest area. (2) Climate of the Canakkale district is of the semiarid according to Erinc’s annual drought index, while it is characterized with the arid climate conditions according to the monthly results of 7 months between April and October. (3) Canakkale district, on the other hand, is dominated by the semi-humid conditions annually and by the 5-month drought conditions during the warm months from May to September according to the UNCCD aridity index. (4) Keetch-Byram drought index (KBDI) reached the highest value on the day of 10.08.2008 with an index value of 530. (5) KBDI applied to the 2008 data of the Canakkale meteorological station did not reach the definite fire level within that year. (6) In 2008, the KBDI caught the 76% of the 30 forest fires occurred in the responsibility area of the Canakkale Regional Forest Service with a high and very high probability level of fire. (7) The area burned in the Intepe - Cinarli forest fire of Canakkale was one of the largest four forest fires occurred in Turkey during the year of 2008.