Seasonal variations of diffuse solar radiation at Ilorin (8°32′N,4°46′E), Nigeria

Hourly diffuse solar irradiance (H_d) and the corresponding global irradiance (H) falling on a horizontal surface at Ilorin (8°32N,4°46E), Nigeria has been measured for a period of fifteen months commencing from February, 1993. As expected, each monthly mean diurnal variation of H_d exhibits a mid-day maximum, while that of the ratio H_d/H exhibits a minimum. The month to month variations of these parameters are consequent on the dominant atmospheric conditions observed in the months concerned. The monthly average daily total of diffuse radiation (H_dm) was found to be highest in February, 1994 with a value of (3347 ± 45) Wm^–2day^–1, mainly due to the effects of Harmattan haze and thin clouds, while it was found to be lowest in November, 1993 and January, 1994 with a value of about 2500 Wm^–2day^–1. Similarly, the ratio of the monthly average daily total of diffuse radiation to the monthly average daily total of global radiation (H_dm/H_m) had the lowest value of 0.49 in the relatively clear sky month of November, 1993 and the highest value of 0.74 in the mainly cloudy month of August, 1993. On an annual average, the diffuse component constituted about 60% of the global solar radiation arriving on the ground at Ilorin, Nigeria primarily due to clouds and Harmattan haze which are seasonal, in addition to the constant background of molecular scattering.     

Geochemical exploration of a Precambrian Batholith, source of a Cu-W mineralization of the tourmaline breccia in Southern Finland

The Hämeenkyrö batholith is a round-shaped plutonic body of an areal size of 147 km². It is composed of calc-alkaline to alkaline rocks that intruded previously metamorphosed Svecofennian volcanogenic and sedimentary schists 1860 Ma ago. The Cu-W bearing tourmaline breccia of the Ylörvi deposit occurs in metavolcanic rocks close to the eastern contact of the batholith.The average sampling density in the batholith was 1 sample per km², and 175 samples were analyzed for Cu, Au, Ag, Ni, Pb, Co, Zn, S by AAS for SiO₂, TiO₂, Al₂O₃, FeO, MnO, MgO, CaO, Na₂O, K₂O, As, Sn and P by X-ray fluorescence. Mo and W were determined colorimetrically. Barth mesonorms were calculated for each sample and the rock type was determined according to Streckeisen's classification. Element distributions are displayed on contour maps.The rock types of the batholith exhibit an asymmetric concentric arrangement, the order from the center towards the margin being alkali-feldspar granite, syenogranite, monzogranite, quartz monzonite, quartz syenite, alkali-feldspar, quartz syenite, syenite and alkali-feldspar syenite. Anomalously high Cu, As, Sn, S, K₂O and Na₂O contents have been found at the eastern margin of the batholith in a N—S-trending zone, which is characterized by hydrothermal alteration phenomena, propylitization, tourmalinization and scapolitization. Three anomalous areas have been defined within this zone, one of them is associated with the Ylöjärvi deposit and the other two are regarded as exploration targets.     

Geomorphological evidence of paleoseismicity: Surficial and underground structures of Pasmajärvi postglacial fault

The cyclic nature of glaciations and related postglacial faulting represents a risk for the deep geological disposal of spent nuclear fuel in areas likely to be affected by future glaciations. Seismic history was therefore studied by means of detecting geomorphological structures on airborne laser scanning digital elevation models and underground by excavating in an esker and trenching across a postglacial fault located in northern Fennoscandia. OLS dating and assessing the geomorphological structures was used for timing of the seismic history. The results suggest that the faulting of different segments in the Pasmajärvi complex is due to at least two late Weichselian events, which probably occurred both subglacially and postglacially. The most reliable input for the moment magnitude estimates was vertical slip profiles, and therefore these estimates (M_W ≈ 6.4–6.9) are suggested. © 2020 John Wiley & Sons, Ltd.     

Modern halite sedimentation processes and depositional environments,Hutt Lagoon,Western Australia

Abstract

Contemporary layered halite in the Hutt Lagoon, Western Australia, forms distinct precipitational and clastic fades, which are ascribed to seasonal ponding and playa development in the lagoon respectively. Field and laboratory documentation of the halite types and monitoring of surface water chemistry for several annual hydrologic cycles indicate that following evaporative concentration of ponded seawater halite layers, characterized by zoned and clear halite crystal varieties, are developed. During early stages of annual playa development, vadose solution and precipitation appear to be most active within and above the capillary fringe zone, causing diagenetic modification of the halite textures, fabrics and structures. Ultimately, clastic halite facies are produced by wind reworking of the earlier deposits, in response to progressive evaporative drawdown of the brine level in the main depression area of the lagoon.

The co-existence of the halite precipitates and clastites is related to a dynamic equilibrium in the water budget of the Hutt Lagoon. This equilibrium is best exemplified by limitation of brine level fluctuations to a narrow repetitive zone. Identification of similar early diagenetic features, such as vadose solution, precipitation, overgrowth, replacement and mechanical reworking of surface halite sediments, in ancient evaporite deposits may aid in a better understanding of the role of brine level fluctuation on genesis and diagenesis of subaqueous/subaerial halite.     

On the annual and monthly mean diurnal variations of diffuse solar radiation at a meteorological station in west Africa

Summary In addition to global solar radiationE ^g , the hourly diffuse componentE ^d incident on a horizontal surface has been measured from February 1993 to January 1995 at a meteorological station in tropical West Africa. The measured diffuse solar irradiance data was corrected for shadow band effects. The monthly mean diurnal variations of diffuse solar irradiance obtained for identical months in the two years have been compared and found to be generally consistent. The corresponding monthly mean hourly values ofE ^d for identical months in 1993 and 1994 agreed to within 9% while yielding correlation coefficients greater than 0.960. In addition, the monthly mean daily totals ofE ^d for identical months were found to agree mostly to within 6% and showed virtually the same annual variations in both years. The monthly mean daily total values of diffuse solar radiation for most months in the two years ranged between 7.94 MJm^–2d^–1 and 10.50 MJm^–2d^–1. The monthly mean of daily hourly maximum values ofE ^d obtained for identical months in the two years have been discussed in relation to the dominant atmospheric conditions during these months. The results been presented here have been compared with those of some investigators within and outside the Africa region.With 8 Figures     

Development of large shallow Lake Peipsi (North-Eastern Europe) over the Holocene based on the stratigraphy of phosphorus fractions

We studied high-resolution stratigraphy of phosphorus (P) forms in the Holocene sediments of large shallow Lake Peipsi (Estonia/Russia) in order to evaluate the lake ecosystem response to environmental changes and track the lake’s eutrophication history. We distinguished four main periods in the history of Lake Peipsi, each having likely different factors responsible for the distribution pattern of P fractions in the sediment record. We suggest that in the oldest period, from ca. 10.4 up to 7.3 cal ka BP, the sediment composition was mainly determined by rising water level, the second period dated 7.3–2.3 cal ka BP was governed mainly by stable hydrology and P loading, while the third period between 2.3 and 0 cal ka BP was primarily influenced by emerging anthropogenic impact. The sediments from the last period since 1950 are subject of ongoing diagenetic processes but still reflect rapid eutrophication of the lake. Comparison of the results with periods derived from other sediment proxies proved the usability of P fractions stratigraphy in reconstruction of the development of lakes.     

GHG mitigation of agricultural peatlands requires coherent policies

As soon as peat soil is drained for agricultural production, the peat starts to degrade, which causes emissions to the atmosphere. In countries with large peatland areas, the GHG mitigation potential related to management of these soils is often estimated as the highest amongst the measures available in agriculture. Although the facts are well known, the policies leading to diminished emissions are often difficult to implement. We have analysed the reasons why the mitigation potential is not fully utilized and what could be done better in national implementation of climate policies. Four cases are used to illustrate the necessary steps to reach mitigation targets: determining the amount and properties of peat soils, estimating the potential, costs and feasibility of the mitigation measures, and selecting and implementing the best measures. A common feature for all of the cases was that national and international climate policies have increased the public interest in GHG emissions from peat soils and increased the pressure for mitigation. Basically the same factors restrict the implementation of mitigation measures in all countries with significant peat soil areas. The most important of these is lack of policy coherence, e.g. ignoring climate policies when planning land use or agricultural policies. We conclude that GHG mitigation is achieved only if other policies, especially national regulations and strategies, are in line with climate policies.

Policy relevance

Agricultural peat soils could be used to help reach GHG mitigation goals in many countries, but the full potential of mitigation of peat soils is not used. Although peatland cultivation inevitably leads to loss of the whole peat layer and high emissions, there are few incentives or regulation to effectively minimize these losses. This article discusses the possibilities to reduce GHG emissions from agricultural peat soils, with specific emphasis on the barriers of implementing mitigation measures nationally. The lessons learned from the selected cases emphasize the role of all policy makers and their cooperation in planning coherent policies for achieving the goals determined by climate policies.     

Heavy metal geochemistry and dispersion pattern in coastal sediments,soil, and water of Kedron Brook floodplain area,Brisbane, Australia

Hydrochemical monitoring and heavy metal speciation by sequential extraction techniques indicate direct relationships among enrichment of the heavy metals (copper, lead, zinc, iron, manganese, and cadmium), soil acidification, and salinization in Kedron Brook floodplain area of Brisbane, Australia. Assessment of modes of occurrence and distribution pattern of the heavy metals in soil, sediment, and water environments of this coastal plain indicates that the total concentrations and reactive fractions of these metals are elevated in soil and channel bed sediments. Such geochemical signatures reflect the complex influence of sources and a combination of natural and anthropogenic processes on concentration and dispersion within the coastal zone. According to a working model presented, the enrichment of the heavy metals, like cadmium, in the soil and sediment profiles is triggered by capillary pumping during low groundwater standing levels, when the metals are in a stable form associated with dry gels. During higher groundwater levels and occasional flood events, these metals become mobilized when the gel material is transformed into soluble colloidal phase.This study indicates that the potential impacts of heavy metal pollution on the coastal ecosystems can not be assessed and managed in isolation solely by considering the natural cause-effect relationships. The complex nature of sediment-soil-water interactions in the coastal hydrodynamic zones can produce a manifold of effects, including mobilization, concentration, and/or dispersion of heavy metals at both short and longer time scales. In the case of Kedron Brook, chemical erosion due to variation in natural climatic and hydrodynamic conditions contributes significantly to concentration of heavy metals in the coastal environments. Therefore, a sound understanding of the prevailing hydrogeochemical processes is essential for prediction of the fate of heavy metals and establishment of meaningful coastal zone management strategies.