Evaporation Ratio Research Articles

Evaluating the role of watershed properties in long‐term water balance through a Budyko equation based on two‐stage partitioning of precipitation

AbstractIn this paper, a four‐parameter Budyko equation is derived for mean annual water balance by applying the proportionality relationship to a two‐stage partitioning of precipitation. The four dimensionless parameters include the Horton index (H, defined as the ratio of evaporation to total wetting) and λ (the ratio of initial evaporation to total wetting) for slow runoff, and β (the ratio of initial wetting to total wetting) and γ (the ratio of total wetting to its potential) for fast runoff. The derived four‐parameter equation balances model parsimony and representation of dominant hydrologic processes and provides a framework to disentangle the roles of climate variability, vegetation, soil, and topography on long‐term water balance in gauged watersheds. The four parameters are determined for 165 watersheds by using observations of precipitation, potential evaporation, streamflow, and soil properties. Based on the principal component regression analysis, average time interval between rainfall events, slope, normalized difference vegetation index, and wilting point are identified as the dominant controlling factors on H and λ; saturated hydraulic conductivity and the difference between field capacity and residual soil moisture are identified as the dominant controlling factors on β; and γ is controlled by effective soil water storage capacity, frequency of rainfall events, and climate seasonality. The combination of four‐parameter Budyko equation and the principal component regression equations provides a model to assess the long‐term responses of evaporation and runoff to climate and watershed property changes in ungauged watersheds.

Effect of tillage practices on least limiting water range in Northwest India

Abstract Tillage practices affect mechanical and hydrological characteristics of soil and subsequently the least limiting water range. This quality indicator under the wheat-maize system of northwest India has not been studied yet. The treatments included four tillage modes, namely conventional tillage, no-tillage without residue, no-tillage with residue, and deep tillage as well as three irrigation regimes based on the irrigation water and pan evaporation ratio i.e. 1.2, 0.9, and 0.6. The experiment was conducted in a split plot design with three replications. At the end of cropping system, the mean least limiting water range (m3 m-3) was found to be highest in deep tillage (0.26) and lowest in notillage without residue (0.15). The field capacity was a limiting factor for the upper range of the least limiting water range beyond soil bulk density 1.41 Mg m-3 and after that 10% air filled porosity played a major role. However, for the lower range, the permanent wilting point was a critical factor beyond soil bulk density 1.50 Mg m-3 and thereafter, the penetration resistance at 2 MPa becomes a limiting factor. Thus, deep tillage under compaction and no-tillage with residue under water stress is appropriate practice for achieving maximum crop and water productivity.

Lake sedimentological and ecological response to hyperthermals: Boltysh impact crater, Ukraine

AbstractThe Boltysh meteorite impact crater, Ukraine, formed at the Cretaceous–Palaeogene boundary at ca 65·2 Ma. A borehole drilled in the central part of the crater cored a >400 m thick high‐resolution lacustrine succession that covers the Dan‐C2 hyperthermal event associated with a negative carbon isotope excursion. Continuous terrestrial records of past hyperthermals are of limited availability, which makes this record a unique case study of the continental impact of rapid climate warming. This study uses high‐resolution sedimentological core log data together with thin‐section, X‐ray diffraction, microprobe and palynological analyses to: (i) reconstruct lake sedimentological and ecological development across the carbon isotope excursion; and (ii) assess the environmental effect of hyperthermals on terrestrial ecosystems. Based on detailed facies analysis, five gradual stages of lake formation are identified, which show a strong relationship to carbon isotope shifts and associated climatic trends. Initially, sediment supply into the Boltysh lake was controlled by crater morphology. During later lake stages, sediment supply was increasingly controlled by changes in inflow–evaporation ratios which affected seasonal stratification patterns and longer term lake levels. An inferred increase in atmospheric pCO2 related to the carbon isotope excursion, together with increasing mean annual temperatures, was probably responsible for periodic increases in biological activity of photosynthesising organisms and biomass production. These fluctuations in facies and lake settings largely correspond to orbital‐paced moisture availability oscillations. The gradual reduction in sediment supply commencing during early lake formation prior to carbon isotope excursion inception suggest that the Dan‐C2 event did not initiate sedimentary changes, but intensified sedimentary response to orbital controlled climate change.

Modeling evapotranspiration of greenhouse tomato under different water conditions based on the dual crop coefficient method

An experiment was conducted to investigate soil evaporation (E), crop transpiration (T), evapotranspiration (ET) and the ratio of evaporation to evapotranspiration (E/ET) of drip-irrigated tomato, which was planted in a typical solar greenhouse in the North China, under different water conditions [irrigation amount was determined based on accumulated pan evaporation (Ep) of 20 cm pan evaporation, and two treatments were designed with full irrigation (0.9Ep) and deficit irrigation (0.5Ep)] at different growth stages in 2015 and 2016 at Xinxiang Comprehensive Experimental Station, Chinese Academy of Agricultural Sciences. Effects of deficit irrigation on crop coefficient (Kc) and variation of water stress coefficient (Ks) throughout the growing season were also discussed. E, T and ET of tomato were calculated with a dual crop coefficient approach, and compared with the measured data. Results indicated that E in the full irrigation was 21.5% and 20.4% higher than that in the deficit irrigation in 2015 and 2016, respectively, accounting for 24.0% and 25.0% of ET in the whole growing season. The maximum E/ET was measured in the initial stage of tomato, while the minimum obtained in the middle stage. The Kc the full irrigation was 0.45, 0.89, 1.06 and 0.93 in the initial, development, middle, and late stage of tomato, and 0.45, 0.89, 0.87 and 0.41 the deficit irrigation. The Ks the deficit irrigation was 0.98, 0.93, 0.78 and 0.39 in the initial, development, middle, and late stage, respectively. The dual crop coefficient method could accurately estimate ET of greenhouse tomato under different water conditions in 2015 and 2016 seasons with the mean absolute error (MAE) of 0.36-0.48 mm·d-1, root mean square error (RMSE) of 0.44-0.65 mm·d-1. The method also estimated E and T accurately with MAE of 0.15-0.19 and 0.26-0.56 mm·d-1, and with RMSE of 0.20-0.24 and 0.33-0.72 mm·d-1, respectively.

Canopy hydrometeorological dynamics across a chronosequence of a globally invasive species, Ailanthus altissima (Mill., tree of heaven)

Many mechanisms aid invasive plants’ competitive interactions. Yet, the extent to which invasive plants alter canopy hydrometeorological mechanisms determining the quantity and distribution of rainwater resources to soils have never been assessed. We examine these mechanisms for a global invader, Ailanthus altissima, across an invasion chronosequence (stands aged 20, 30, 40 years) for 99 storms, each with ∼200 net rainfall observations. With age woody area index, ratio of wet canopy evaporation and rainfall rates, and stem drainage coefficient increased; while leaf area index, canopy water storage, and gap fraction declined. This corresponded to increased stemflow and decreased throughfall across annual, seasonal, and interstorm scales. Promotion of stemflow may be advantageous to the invasive species as it increases water supply to roots and may help distribute allelopathic chemicals through the soil. Further research is needed on relationships between canopy hydrometeorological changes during invasion and redistribution of water to soils.

Estimating the contribution of glacial meltwater to Ranwu Lake, a proglacial lake in SE Tibet, using observation data and stable isotopic analyses

It is important for both current monitoring and paleoenvironmental research conducted on proglacial lakes and their adjacent glaciers to clarify the hydrological processes operating on these lakes. However, in remote regions with limited accessibility it may be difficult to study hydrological processes by direct monitoring. In this study, we use measurements of stable isotopic compositions to trace the multiple water sources contributing to Ranwu Lake, a proglacial lake in south-eastern Tibet. Using stable isotopic data from precipitation, inflowing rivers and the lake water, a water and isotope mass balance modelling method was used to calculate the ratio of evaporation to input. Subsequently, using hydrological and climatic data for the outflow, the largest inflow and precipitation, other hydrological elements of the lake water balance were also calculated. The results demonstrate that the ratio of evaporation to inflow is as low as 0.009, the lowest value observed for the Tibetan Plateau, indicating that Ranwu Lake is a through-flow lake with a very short retention time. Glacial meltwater accounts for at least 55% of total runoff, the highest value observed for the Tibetan Plateau, indicating that the sediments of Ranwu Lake may have considerable potential for reconstructing variations in the activity of the local glaciers. Finally, we note that it may be inappropriate in this glacier-fed lake to use the intersection of the local meteoric water line with the lake water line for determining the isotopic composition of the input water, and this possibility must be carefully considered when stable isotope mass modelling is used in proglacial lakes.

Biomarkers in Lake Van sediments reveal dry conditions in eastern Anatolia during 110.000–10.000 years B.P.

AbstractLipid biomarkers were analyzed in Lake Van sediments covering the last 600 ka, with a focus on the period between 110 and 10 ka, when a broad maximum in pore water salinity as a relict from the past suggests dry conditions. The occurrence and distribution of biomarkers indicative for terrestrial plants (long‐chain n‐alkane C29), haptophyte algae (methyl alkenones C37) and halophilic archaea (archaeol) all point toward a dry climate in Lake Van region during this time interval. The hydrogen isotopic composition of C29 n‐alkanes (δDC29) and C37 alkenones (δDC37) is enriched between MIS 4 and MIS 2, which is interpreted as a decrease in the regional ratio of precipitation to evaporation. Similarly, the low abundance of the acyclic glycerol dialkyl glycerol tetraether GDGT‐0 relative to archaeol, quantified by the Archaeol and Caldarchaeol Ecometric (ACE) is assumed to reflect the presence of halophilic euryarchaeota adapted to high salinity water. The climate around Lake Van appears in phase with the Yammouneh basin 800 km southwest and Lake Urmia 250 km southeast of Lake Van over the last two glacial periods. The results highlight the potential of combining ACE, δDC29, and δDC37 for reconstructing salinity changes and regional precipitation to evaporation ratio from lake sediments.

Quantifying the economic water savings benefit of water hyacinth (<i>Eichhornia crassipes</i>) control in the Vaalharts Irrigation Scheme

Global freshwater resources are threatened by an ever-growing population and continued economic development, highlighting the need for sustainable water management. Sustainable management must include the control of any additional factors that may aggravate water scarcity, such as invasive alien plants. Water hyacinth ( Eichhornia crassipes ), one of the world’s most destructive invasive plants, presents a direct threat to economically productive water resources. Through high levels of evapotranspiration, water hyacinth leads to substantial water losses that could otherwise be used more productively, thereby creating an externality on water-dependent industries, such as irrigation-fed agriculture. This study provides an economic valuation of the water-saving benefit of water hyacinth control, using Warrenton Weir on the Vaalharts Irrigation Scheme as a case study. A Residual Value Method was employed to estimate the average production value of irrigation water, based on water’s relative proportion of total costs (TC), to serve as a proxy for the value of water lost via evapotranspiration by water hyacinth. Three evapotranspiration to evaporation ratios, derived from the literature, at three levels of invasion (100; 50 and 25% cover), were used to estimate the annual water loss at Warrenton Weir. The average production value of irrigation water was estimated to be R38.71/m 3 , which translated into an annual benefit of between R54 million and R1.18 billion. These results highlight the need for invasive plant control, particularly in economically productive water resources. An alien plant control policy should prioritise invasions of this nature, as they present significant costs to the economy and threaten the sustainability of freshwater resources. Keywords : sustainability, water resources, water hyacinth, water loss, externality, benefit, control

Modeling and Partitioning of Regional Evapotranspiration Using a Satellite-Driven Water-Carbon Coupling Model

The modeling and partitioning of regional evapotranspiration (ET) are key issues in global hydrological and ecological research. We incorporated a stomatal conductance model and a light-use efficiency-based gross primary productivity (GPP) model into the Shuttleworth–Wallace model to develop a simplified carbon-water coupling model, SWH, for estimating ET using meteorological and remote sensing data. To enable regional application of the SWH model, we optimized key parameters with measurements from global eddy covariance (EC) tower sites. In addition, we estimated soil water content with the principle of the bucket system. The model prediction of ET agreed well with the estimates obtained with the EC measurements, with an average R2 of 0.77 and a root mean square error of 0.72 mm·day−1. The model performance was generally better for woody ecosystems than herbaceous ecosystems. Finally, the spatial patterns of ET and relevant model outputs (i.e., GPP, water-use efficiency and the ratio of soil water evaporation to ET) in China with the model simulations were assessed.

Effect of Mulching, Cumulative Pan Evaporation Ratio and Nutrient Levels on Yield, Nutrient Content and Uptake of Linseed

Effect of Mulching, Cumulative Pan Evaporation Ratio and Nutrient Levels on Yield, Nutrient Content and Uptake of Linseed

Deuterium‐excess determination of evaporation to inflow ratios of an alpine lake: Implications for water balance and modeling

AbstractThe numerous lakes on the Tibetan Plateau play an important role in the regional hydrological cycle and water resources, but systematic observations of the lake water balance are scarce on the Tibetan Plateau. Here, we present a detailed study on the water cycle of Cona Lake, at the headwaters of the Nujiang‐Salween River, based on 3 years (2011–2013) of observations of δ18O and δ2H, including samples from precipitation, lake water, and outlet surface water. Short‐term atmospheric water vapor was also sampled for isotope analyses. The δ2H–δ18O relationship in lake water (δ2H = 6.67δ18O − 20.37) differed from that of local precipitation (δ2H = 8.29δ18O + 12.50), and the deuterium excess (d‐excess) in the lake water (−7.5‰) was significantly lower than in local precipitation (10.7‰), indicating an evaporative isotope enrichment in lake water. The ratio of evaporation to inflow (E/I) of the lake water was calculated using both d‐excess and δ18O. The E/I ratios of Cona lake ranged from 0.24 to 0.27 during the 3 years. Observations of atmospheric water vapor isotopic composition (δA) improved the accuracy in E/I ratio estimate over a simple precipitation equilibrium model, though a correction factor method provided nearly identical estimates of E/I ratio. The work demonstrates the feasibility of d‐excess in the study of the water cycle for lakes in other regions of the world and provides recommendations on sampling strategies for accurate calculations of E/I ratio.

The Budyko functions under non-steady-state conditions

Abstract. The Budyko functions relate the evaporation ratio E ∕ P (E is evaporation and P precipitation) to the aridity index Φ = Ep ∕ P (Ep is potential evaporation) and are valid on long timescales under steady-state conditions. A new physically based formulation (noted as Moussa–Lhomme, ML) is proposed to extend the Budyko framework under non-steady-state conditions taking into account the change in terrestrial water storage ΔS. The variation in storage amount ΔS is taken as negative when withdrawn from the area at stake and used for evaporation and positive otherwise, when removed from the precipitation and stored in the area. The ML formulation introduces a dimensionless parameter HE = −ΔS ∕ Ep and can be applied with any Budyko function. It represents a generic framework, easy to use at various time steps (year, season or month), with the only data required being Ep, P and ΔS. For the particular case where the Fu–Zhang equation is used, the ML formulation with ΔS ≤ 0 is similar to the analytical solution of Greve et al. (2016) in the standard Budyko space (Ep ∕ P, E ∕ P), a simple relationship existing between their respective parameters. The ML formulation is extended to the space [Ep ∕ (P − ΔS), E ∕ (P − ΔS)] and compared to the formulations of Chen et al. (2013) and Du et al. (2016). The ML (or Greve et al., 2016) feasible domain has a similar upper limit to that of Chen et al. (2013) and Du et al. (2016), but its lower boundary is different. Moreover, the domain of variation of Ep ∕ (P − ΔS) differs: for ΔS ≤ 0, it is bounded by an upper limit 1 ∕ HE in the ML formulation, while it is only bounded by a lower limit in Chen et al.'s (2013) and Du et al.'s (2016) formulations. The ML formulation can also be conducted using the dimensionless parameter HP = −ΔS ∕ P instead of HE, which yields another form of the equations.

Comparison of ET partitioning and crop coefficients between partial plastic mulched and non-mulched maize fields

The ratio of evaporation to evapotranspiration (E/ET) and crop coefficients (Kc) are important parameters for evaluating the water-saving potentials of agronomic technologies and they may vary with different practices of dryland cultivation. This study synchronously investigated changes of E/ET and Kc for three years using two eddy covariance systems and multi-microlysimeters under two cultivation methods—conventional flat planting without mulching (CK) and a furrow-ridge system with plastic film partially mulching (MFR)—on the semiarid Loess Plateau of China. Due to an increase of vapor diffusion resistance at the soil-air interface partially mulched by plastic film, the average E and ET of MFR were lower than those of CK by 38.1% and 9.3%, respectively, for the three growing seasons. Thus, the average E/ET in MFR decreased by 11.2 percentage points compared with CK. E/ET showed a significant logistic function with the green leaf area index (GLAI) under both treatments during the three growing seasons. The seasonal Kc varied with GLAI following a step function curve for both treatments, and was linearly correlated to GLAI with significance levels when GLAI was below the thresholds of 3.0 and 3.2–3.4 for CK and MFR, respectively. Maximum Kc values were 1.01±0.05 and 0.91±0.09 for CK and MFR, respectively, at the middle crop growth stage. These results suggest that MFR can significantly reduce E/ET and maximum Kc, which help to improve yield and water use efficiency in rainfed spring maize fields. Consequently, MFR enhanced the average grain yield and crop water use efficiency by 12.5% and 24.6%, which amounted to 11527kg/ha and 3.36kg/m3, respectively. Therefore, MFR promoted crop water productivity and is an effective approach to solve water crises in dryland regions.

Gumleaf skeletoniserUraba lugens(Lepidoptera: Nolidae) larval outbreaks occur in high rainfall Western Australian jarrah (Eucalyptus marginata) forest after drought

Larvae of the gumleaf skeletoniser Uraba lugens Walker can be a severe defoliator of jarrah (Eucalyptus marginata) forest in southwest Western Australia. Extensive outbreaks that developed in the summer of 2010/2011 affected more than 250 000 ha. Rainfall or temperature anomalies correlated over large distances can be a lead to regionally synchronous population dynamics of species. These are known as Moran effects and can result in extensive outbreaks. The effects of spatial variation in regional climate (as measured by dryness index, the ratio of annual pan evaporation and annual rainfall) on the magnitude of outbreak and equilibrium populations of U. lugens were examined using long-term monitoring data. The effects of temporal variation in regional temperature and rainfall anomalies on populations were examined. The coincidence of regional rainfall and temperature anomalies with regional outbreaks was investigated using permutation multivariate analysis of variance and canonical analysis of principal coordinates. Outbreaks resulting in severe defoliation are restricted to high rainfall areas of the southern jarrah forest region in southwest Western Australia. Outbreak years were warmer than years of no known outbreak, yet temperature anomalies were a poor predictor of known multiple outbreaks. Synchronous U. lugens outbreaks coincided with a combination of long-term (seven-year) drying trends and autumn and winter drought. Canonical analysis of principal coordinates analysis using rainfall anomalies correctly predicted multiple outbreaks in 70% of cases. While the mechanisms behind drought as a driver of U. lugens outbreaks are unresolved, U. lugens outbreak may be an early indicator of future lethal stress in jarrah forest. Early insect indicators of stress are likely to allow latitude for early management responses to ameliorate effects of long-term drought on economically and ecologically important tree species.

Rescaling the complementary relationship for land surface evaporation

AbstractRecent research into the complementary relationship (CR) between actual and apparent potential evaporation has resulted in numerous alternative forms for the CR. Inspired by Brutsaert (2015), who derived a general CR in the form y = function (x), where x is the ratio of potential evaporation to apparent potential evaporation and y is the ratio of actual to apparent potential evaporation, an equation is proposed to calculate the value of x at which y goes to zero, denoted xmin. The value of xmin varies even at an individual observation site, but can be calculated using only the data required for the Penman (1948) equation as expressed here, so no calibration of xmin is required. It is shown that the scatter in x‐y plots using experimental data is reduced when x is replaced by X = (x − xmin)/(1 − xmin). This rescaling results in data falling along the line y = X, which is proposed as a new version of the CR. While a reinterpretation of the fundamental boundary conditions proposed by Brutsaert (2015) is required, the physical constraints behind them are still met. An alternative formulation relating y to X is also discussed.

Delineation of Environmental Units by Multivariate Techniques in the Duero River Watershed, Michoacán, Mexico

Environmental or hydrological landscape units can integrate various environmental characteristics to support proper management of natural resources. To delineate these units, quantitative methods such as ordination, clustering, and classification of abiotic factor information are used. In the present work, environmental units were delineated in the Duero River watershed of Michoacan, Mexico. This will enhance understanding of the hydrologic landscape, which is a fundamental to natural resource management. A digital elevation model was used to generate sub-basins. Climatic data were obtained from 16 meteorological stations. Sixty-nine soil and 150 water samples were collected and analyzed in the laboratory. Geostatistical methods for spatial prediction of the environmental variables were used. Mean data for each sub-basin were obtained from the environmental variable grids, generating an abiotic factor data matrix. A multivariate analysis was conducted. Exponential, linear, spherical, and Gaussian models were fit to an empirical variogram. Spatial prediction of the environmental data was done via universal and ordinary kriging. Based on principal component analysis, abiotic factors evaporation, total nitrogen, soil pH, and sodium absorption ratio of water were selected for cluster analysis. Five environmental units were delineated in the Duero watershed. One environmental unit (number 4) provided greater than 50 % of the payment for ecosystem services. The general trend is an increase of urban area. The urban surface in 1983 and 2014 was 1724 and 4750 ha, respectively, an increase of 275 %. Environmental unit 1 showed the greatest urban area growth (1336 ha) during the latter period.

Transient transport of heat, mass, and momentum in paperboard including dynamic phase change of water

A theory to describe deforming moist paperboard in environments where both temperature and pressure change significantly during a short period of time is presented. Paperboard is viewed as an orthotropic triphasic porous medium consisting of fibers, bound water and moist air. Furthermore, the moist air is considered as a mixture of two miscible gases, namely dry air and water vapor. A two–scale hybrid mixture theory is adopted in a large strain setting and balances of mass, linear momentum, and energy are presented on the macroscale. Constitutive relations are derived on the macroscale through exploitation of the dissipation inequality. Mass exchange between bound water and water vapor is included as a dynamic process. Mass transportation processes include chemical potential driven diffusion and nonlinear seepage flow. The elasto–plastic stress–strain response of the fiber network is described by assuming a multiplicative split of the deformation gradient associated with the motion of the fiber network. The dynamics related to the mass exchange between bound water and water vapor is illustrated by changes of pressure, relative humidity, moisture ratio, and rate of evaporation during rapid heating of a moist paperboard.

Partitioning Evapotranspiration into Soil Evaporation and Canopy Transpiration via a Two-Source Variational Data Assimilation System

Abstract The primary objective of this study is to assess the accuracy of the two-source variational data assimilation (TVDA) system for partitioning evapotranspiration (ET) into soil evaporation (ETS) and canopy transpiration (ETC). Its secondary aim is to compare performance of the TVDA system with the commonly used two-source surface energy balance (TSEB) method. A combination of eddy-covariance-based ET observations and stable-isotope-based measurements of the ratio of evaporation and transpiration to total evapotranspiration (ETS/ET and ETC/ET) over an irrigated cropland site (the so-called Daman site) in the middle reach of the Heihe River basin (northwestern China) was used to investigate these objectives. The results indicate that the TVDA method predicts ETS and ETC more accurately than TSEB. Root-mean-square errors (RMSEs) of midday (1300–1500 LT) averaged soil and canopy latent heat flux (LES and LEC) estimates from TVDA are 23.1 and 133.0 W m−2, respectively. Corresponding RMSE values from TSEB are 41.9 and 156.0 W m−2. Compared to TSEB, the TVDA method takes advantage of all of the information in land surface temperature observations in the estimation period by leveraging a dynamic model (the heat diffusion equation) and thus can generate more accurate LES and LEC estimates.

Reconstruction of Holocene paleohydrological and sedimentological characteristics of Umm Ar-Rimam basin (northern Kuwait)

The paleohydrological and sedimentological characteristics of a playa lake in northern Kuwait (Arabian Gulf) are reconstructed using sedimentological, geochemical, and isotopic techniques. The sequence consists of up to 8 cycles of S-poor, alluvial sediments capped by a thin organic soil interbedded with gravity-fall calcrete sediments. The succession is locally derived from mainly Quaternary sediments and is regressive with upsection filling of the subsiding basin by cycles of sheetwash flow in response to climatic change. There is no natural, open-water lake water as indicated by low total organic carbon (TOC) data, but the presence of incised calcrete yardangs suggests that more extensive open-water conditions were operative in the past. Stable isotope (δ18O‰ and δ13C‰) values of the authigenic carbonates indicate the following three distinct processes: evaporation, meteoric fluid infiltration, and rapid per-descensum flow (rapid downward movement of water and playa sediment through pipes) through a porous, clastic sequence. Because evaporites are scarce, other factors besides evaporation action control chemical and isotopic compositions of the per-decensum lake fluids. Consequently, the isotopic composition cannot be interpreted exclusively as an indicator of salinity or evaporation ratio. The degassing of CO2 during groundwater discharge may explain the enriched carbon isotope values for the authigenic carbonates precipitated in the sediments. Hydrologically closed lake water bodies tend to show low negative carbonate oxygen and carbon isotopic signatures. Isotopically negative δ13C values imply a strong input of soil-zone carbon to the groundwater of the top 60 cm of the sediment. Lakes that are hydrologically closed and evaporate or equilibrate with atmospheric CO2 will tend to have low negative δ18O and δ13C values in the carbonates as reported by Talbot (Chem Geol: Isotope Geosci Sect 80(4):261–279, 1990). Biologically active lakes will tend toward lower δ13C of dissolved carbon due to the photosynthetic effects of 12C withdrawal as reported by Dunagan and Driese (J Sed Res 69:772–783, 1999). Increased biological activity during sedimentation may account for low carbon isotope values where plants were abundant, but in shrinkage-dominated systems (those of clay-rich soil subjecting to wet-dry conditions), carbon isotopes will be largely inherited from the calcretic limestones in the land extending landward of the coast and not influenced by coastal processes (known as hinterland), such as Umm Ar-Rimam depression. This basin does not fit the classic shallow playa-type basins of the Arabian Peninsula but rather the recharge playas of the southwestern USA.

Kinetics of Na2O evaporation from CaO–Al2O3–SiO2–MgO–TiO2–Na2O slags

The present work is carried out to study the evaporation of Na2O from CaO–Al2O3–SiO2–TiO2–MgO–Na2O slags with high basicity and high alumina in the temperature range of 1500–1560°C. The ratio of evaporation was determined by monitoring the Na2O content change of the slag melt under isothermal reduction conditions. The results show that the evaporation ratio increases with increasing the temperature. Higher basicity and increasing concentrations of Na2O, Al2O3 are also found to increase the evaporation ratio of Na2O, while MgO addition only slightly enhances the evaporation ratio. With TiO2 content increasing, the evaporation ratio first increases and then decreases. The evaporation rate of Na2O appears to be controlled by chemical reaction at the slag/gas interface in the beginning, followed by a mixed reaction-mass transfer regime, and finally a liquid-phase mass transport step. The apparent activation energy is 134.74 kJ mol−1 for the chemical reaction regime and 268.53 kJ mol−1 for the liquid-phase mass diffusion step.