Simplified Mass Balance Model Research Articles

A Simplified Kinetic Modeling of CO2 Absorption into Water and Monoethanolamine Solution in Hollow-Fiber Membrane Contactors

The absorption of CO2 from CO2-N2 gas mixtures using water and monoethanolamine (MEA) solution in polypropylene (PP) hollow-fiber membrane contactors was experimentally and theoretically examined. Gas was flowed through the lumen of the module, whereas the absorbent liquid was passed counter-currently across the shell. Experiments were carried out under various gas- and liquid-phase velocities as well as MEA concentrations. The effect of pressure difference between the gas and liquid phases on the flux of CO2 absorption in the range of 15-85 kPa was also investigated. A simplified mass balance model that considers non-wetting mode as well as adopts the overall mass-transfer coefficient evaluated from absorption experiments was proposed to follow the present physical and chemical absorption processes. This simplified model allowed us to predict the effective length of the fiber for CO2 absorption, which is crucial in selecting and designing membrane contactors for this purpose. Finally, the significance of membrane wetting could be highlighted by this model while using high concentrations of MEA in the chemical absorption process.

Prediction of Arsenic and Antimony Behaviour in MSWI Fly Ash During Co-Processing in a Cement Kiln

Municipal solid waste incinerator (MSWI) fly ash contains large amounts of arsenic and antimony. This study focuses on the incorporation and evaporation of arsenic and antimony when MSWI fly ash added to clinker raw meal. Thermal analysis was used to simulate the “single incorporation” of arsenic and antimony into clinker with HSC. Statistical analysis was acquired by cement industrial monitoring data to determine the effect of total chloride, arsenic and antimony input on the incorporation or evaporation of arsenic or antimony. A simplified mass balance model was used to evaluate the effect of cement kiln dust (CKD) recirculation on the “multiple incorporation” of arsenic and antimony in clinker and the evaporation of arsenic and antimony in waste CKD. The results indicated that arsenic and antimony was largely incorporated into the clinker as Ca2(AsO4)2(s), even in the presence of chlorides. Moreover, CKD recirculation promoted arsenic and antimony incorporation into clinker.

Using 239+240Pu atmospheric deposition and a simplified mass-balance model to re-estimate the soil erosion rate: a case study of Liaodong Bay in China

By using the mass balance model of 137Cs and introducing 239+240Pu atmospheric deposition, a simplified mass balance model of 239+240Pu was developed and the soil erosion rate was re-estimated. The results indicated that the reference inventory of 239+240Pu was estimated to be 88.4 Bq/m2 in Liaodong Bay. In addition, the atomic ratios of 240Pu/239Pu in all core samples were approximately 0.18, which indicated that the major source of Pu was the global fallout. Statistical analysis of the erosion rates derived from the model demonstrates that the 239+240Pu atmospheric deposition is a feasible way to estimate the soil erosion rate and further improve tracer technique to assess the soil erosion rate.

Evaluation of Cesium-137 Conversion Models and Parameter Sensitivity for Erosion Estimation

The Cs technique has been widely used to provide soil redistribution estimates since the 1970s. However, most Cs-conversion models remain theoretical and largely unvalidated. Our objectives were to validate the four widely used conversion models, examine model parameter sensitivity, and evaluate the potential of using kriging to improve soil redistribution estimation. Soil loss was measured from a 1.6-ha plot since 1978. Winter wheat ( L.) was grown primarily under conventional tillage. Soil samples in a 10-m grid were taken from the plot to estimate the Cs inventory. Soil redistribution rates were estimated using four models and were further interpolated using ordinary kriging. The parameter sensitivity analyses at the 95% confidence limits showed that reference inventory had the most impact on estimated water erosion, followed by particle size correction for erosion and tillage depth, with minimal impacts from mass depth, bulk density, and particle size correction for deposition. Compared with the measured water erosion, the relative errors of the mean net water erosion estimates across the entire plot without and with kriging were 28 and -17% for the proportional model (PM), 141 and 106% for the simplified mass balance model, 133 and 100% for the improved mass balance model (MBM2), and 109% for the extended MBM2 with tillage erosion (MBM3). Results indicated that the PM performed better than the mass balance models under the study conditions and that kriging improved mean soil redistribution estimates. However, the full potential of the MBM2 and MBM3 needs to be further evaluated under conditions where loss of newly deposited Cs exists.

Application of 137Cs technique for evaluation of erosion and deposition rates within cultivated fields of Salihli region, Western Turkey

Soil erosion by wind and water is an important problem for Salihli region in Western Turkey. There are several vineyards on the cultivated soils of this region, which is a significant economic income source for the residents. This study focuses on the cultivated soils in these areas to quantify spatial distribution of 137Cs using 3-D graphic method and eventually to estimate erosion and deposition using the results of 137Cs spatial distribution obtained. The erosion and deposition rates were estimated using proportional and simplified mass balance models. Results obtained using simplified mass balance model gave slightly higher values than those found using proportional model. Erosion and deposition rates derived from proportional model varied from −16.02 to −19.40 t ha-1y−1 and from +6.80 to +9.62 t ha-1y−1, respectively. On the other hand, values determined using simplified mass balance model ranged from −17.52 to −21.10 t ha-1y−1 and from +7.21 to +11.31 t ha-1y−1. The comparison of the results obtained via these models revealed a good agreement within the range of 30 t ha-1y−1 soil loss and gain.

An evaluation of the role of hillslope components and land use in soil erosion using 137Cs inventory and soil organic carbon stock

Land use and geomorphology of hillslope play important roles in influencing soil water erosion which is the primary factor for the depletion or restoration of soil organic carbon stock (SOCS). Reliable information on the impact of erosion/deposition dynamics on SOCS is required for effective accounting of the carbon flux that indirectly influences management of climatic change. The main objectives of this study were to determine soil redistribution on the basis of the variation of 137Cs radionuclide activity under different land uses and hillslope components in a mountainous catchment of western Iran. Also, the relationship between soil erosion and deposition rates, using 137Cs inventory-conversion models and storage and loss of soil organic carbon stocks was examined. To do this, 137Cs activity and SOCS were measured in thirty-two sample sites from different hillslope components in cultivated and forested areas. The simplified mass-balance model and diffusion and migration model estimated very high erosion rates of 6.43 and 40.3tha−1yr−1 in the shoulder component of forest and cultivated areas, respectively. In both disturbed (cultivated) and undisturbed (forested) soils, positive and statistically significant relationships were found between the SOCS and 137Cs inventory. Consequently, 137Cs could be used directly for quantifying dynamics of SOC in soil redistribution relationship as affected by soil erosion. Statistical analyses also indicated that the 137Cs activity and inventory, SOCS and erosion/deposition were significantly affected by landform components and land use types.

Estimation of soil erosion in the Xihanshui River Basin by using 137Cs technique

The Cesium-137 technique was used to estimate soil erosion in the Xihanshui River Basin. More than 100 samples were taken from 10 sites and 20 hillslopes with a 10cm diameter hand-operated core driller. Each sample was 60 cm long. The 137Cs activity was analyzed by gamma spectrometry. The simplified mass balance model and the profile distribution model were used to calculate soil erosion and deposition rate. The local 137Cs reference ranged from 1,600 to 2,402 Bq m−2. The data shows an exponential decrease of mass concentration and amount with depth in an undisturbed soil profile. Soil erosion in the river basin is moderate or severe on cultivated land with annual erosion rates of 2,000–6,000 t km−2 yr−1. In general, very severe or severe soil erosion occurred at the upper slope sections, moderate or severe soil erosion at the middle section, and moderate or slight soil erosion at the lower slope sections. On the slopes with natural vegetation, consisting of herbaceous and wood species, the erosion rate is much lower or not detectable. On the lower section of slopes with well-developed vegetation however, there was no soil loss, instead deposition occurred at a rate of more than 300 t km−2 yr−1. The slope gradient and vegetation cover affected soil erosion and deposition rates. In general, the rate of soil erosion was proportional to the slope gradient and inversely proportional to the degree of vegetative cover.

Soil redistribution rate and its relationship with soil organic carbon and total nitrogen using 137Cs technique in a cultivated complex hillslope in western Iran

The spatial pattern of soil redistribution rate was investigated using cesium-137 ( 137Cs) within a cultivated complex hillslope in western Iran. The relationship between soil redistribution rate and soil organic carbon and total nitrogen pattern were studied using co-regionalization analysis. Ninety-one soil cores were sampled for 137Cs, total nitrogen, and soil organic carbon measurements. The simplified mass balance model estimated a gross erosion rate of 29.8 t ha −1 yr −1 and a net soil deposition rate of 21.8 t ha −1 yr −1; hence, a net soil loss rate of 8 t ha −1 yr −1. This magnitude of soil erosion rate is higher than the acceptable rate in semiarid regions. Co-regionalization analysis and co-dispersive coefficients among the selected variables showed that only a small fraction of the variability in total nitrogen and soil organic carbon could be explained by soil redistribution and that the remaining might be the result of different management practices by local farmers.

Soil erosion determinations by using 137Cs technique in the agricultural regions of Gediz Basin, Western Turkey

Gediz Basin is one of the regions where intense agricultural activities take place in Western Turkey. Erosion and soil degradation have long been causing serious problems to cultivated fields in the basin. This work describes the application of two different 137Cs models for estimating soil erosion rates in cultivated sites of the region. Soil samples were collected from five distinct cultivated regions subject to soil erosion. The variations of 137Cs concentrations with depth in soil profiles were investigated. Soil loss rates were calculated from 137Cs inventories of the samples using both proportional model (PM) and simplified mass balance model (SMBM). When PM was used, erosion and deposition rates varied from −15 to −28 t ha−1 year−1 and from +5 to +41 t ha−1 year−1, respectively; they varied from −16 to −33 t ha−1 year−1 and from +5 to +55 t ha−1 year−1 with SMBM. A good agreement was observed between the results of two models up to 30 t ha−1 year−1 soil loss and gain in the study area. Ulukent, a small representative agricultural field, was selected to compare the present data of 137Cs techniques with the results obtained by universal soil loss equation (USLE) applied in the area before.

Estimates of soil erosion using cesium-137 tracer models

The soil erosion was studied by 137Cs technique in Yatagan basin in Western Turkey, where there exist intensive agricultural activities. This region is subject to serious soil loss problems and yet there is not any erosion data towards soil management and control guidelines. During the soil survey studies, the soil profiles were examined carefully to select the reference points. The soil samples were collected from the slope facets in three different study areas (Kirtas, Peynirli and Kayisalan Hills). Three different models were applied for erosion rate calculations in undisturbed and cultivated sites. The profile distribution model (PDM) was used for undisturbed soils, while proportional model (PM) and simplified mass balance model (SMBM) were used for cultivated soils. The mean annual erosion rates found using PDM in undisturbed soils were 15 t ha(-1) year(-1) at the Peynirli Hill and 27 t ha(-1) year(-1) at the Kirtas Hill. With the PM and SMBM in cultivated soils at Kayişalan, the mean annual erosion rates were obtained to be 65 and 116 t ha(-1) year(-1), respectively. The results of 137Cs technique were compared with the results of the Universal Soil Loss Equation (USLE).

Distribution characteristics of 137Cs in wind-eroded soil profile and its use in estimating wind erosion modulus

Due to its inert reaction in soil system and distinctive vertical distribution in soil profile, caesium-137 (137Cs) has been used as a tracer to assess wind erosion. In this study, 62 soil samples were collected from 4 sampling sites in Taipusi County, Inner Mongolia; Caesium-137 activities for those soil samples were measured using a gamma-ray spectrometry in Sichuan University, Chengdu. Distribution pattern of 137Cs in vertical soil profile was different for different land use and land cover types. Caesium-137 was distributed homogeneously in plow layer of cropland, and negatively exponential in low to medium cover grassland. Distribution pattern in high covered grassland was represented by a peak at 2–4 cm soil depth followed by a negative exponential curve. Based on those findings, simplified mass balance model was chosen to estimate the rate of wind erosion for cropland, while profile distribution model was used for grassland. Estimated wind erosion rates were 7990, 4270 and 1808 Mg·km−2·a−1 for cropland, low cover grassland and medium cover grassland, respectively. Wind erosion intensity correlated negatively with plant cover.

Assessment of soil erosion on arable land using [formula omitted] measurements: a case study from Jaslovske Bohunice, Slovakia

This study was carried out to obtain a representative set of data on long-term erosion rates from a pilot area located close to the Jaslovske Bohunice village, in western Slovakia using the 137 Cs -method. The study area chosen was representative of the hilly loess cultivated areas of Slovakia. The sampling strategy was based on a multiple transect approach. Analyses of the samples for 137 Cs activity were made at the Nuclear Power Plant Research Institute, Jaslovske Bohunice. The 137 Cs -method was used to obtain long-term estimates of soil erosion in the Jaslovske Bohunice site, a representative hilly loess cultivated area of Slovakia. The estimated reference 137 Cs inventory was 2910 Bq m −2, with a coefficient of variation of 4.3%. Examination of the 137 Cs redistribution in relation to the topography of the study area revealed that, within individual transects the 137 Cs inventories were closely related to major landforms. The 137 Cs inventories were considerably lower on the slopes than on the plateau and they were highest in the valley. However, when plotted against a selection of individual quantitative slope parameters, i.e. the S and the LS factors of the USLE or slope inclination, the correlations obtained were weak. Three conversion models, i.e. the proportional model (PM), the simplified mass balance model (MBM1) and the standard mass balance model (MBM2), from the set of models developed at Exeter University, Great Britain were selected to interpret the resulting 137 Cs measurements into soil erosion/deposition rates. The mean erosion rates estimated with the PM were 22.4, 35.6 with MBM1 and 17.3 t ha −1 per year with MBM2. There was a good agreement between the average of these mean erosion rates (25.1 t ha −1 per year) for the Jaslovske Bohunice site and the estimated mean soil erosion rate obtained for small erosion plots (15 t ha −1 per year) for conditions similar to the study site. Nevertheless, further research on the application of the 137 Cs -method, in particular the independent validation of the results obtained, is needed. Several issues requiring further study have been highlighted.

Use of 137Cs technique for soil erosion study in the agricultural region of Casablanca in Morocco

Accelerated erosion and soil degradation currently cause serious problems to the Oued El Maleh basin (Morocco). Furthermore, there is still only limited information on rates of soil loss for optimising strategies for soil conservation. In the present study we have used the 137Cs technique to assess the soil erosion rates on an agricultural land in Oued el Maleh basin near Casablanca (Morocco). A small representative agricultural field was selected to investigate the soil degradation required by soil managers in this region. The transect approach was applied for sampling to identify the spatial redistribution of 137Cs. The spatial variability of 137Cs inventory has provided evidence of the importance of tillage process and the human effects on the redistribution of 137Cs. The mean 137Cs inventory was found about 842 Bq m −2, this value corresponds to an erosion rate of 82 tha −1 yr −1 by applying simplified mass balance model in a preliminary estimation. When data on site characteristics were available, the refined mass balance model was applied to highlight the contribution of tillage effect in soil redistribution. The erosion rate was estimated about 50 tha −1 yr −1. The aspects related to the sampling procedures and the models for calculation of erosion rates are discussed.

Assessing soil erosion in a small Sicilian basin by caesium-137 measurements and a simplified mass balance model

The caesium-137 technique affords both an alternative to conventional measurement methods and an effective quantitative estimate of soil redistribution at the basin scale. Among the available calibration relationships which link the degree of increase or depletion of the 137Cs activity relative to the baseline 137Cs input and sediment yield, the mass balance approach has received increased application for its physical basis. First, the applicability of the refined simplified point-based mass balance (RSPMB) model of Zhang et al. (1999) at the scale of the morphological unit is proposed herein. The 137Cs spatial distribution measured in a small Sicilian basin and the spatial distribution of the sediment yield calculated by a sediment delivery distributed approach are used to estimate values of the two key parameters of the RSPMB model, φ1 and φ2, the fraction of 137Cs fallout incorporated into soil and a particle size correction factor, respectively. Finally, the best procedure for experimental testing of a distributed sediment yield model by using caesium-137 measurements is investigated.

Simplified mass balance models for assessing soil erosion rates on cultivated land using caesium-137 measurements

Soil erosion on agricultural land has become a global environmental problem and information on rates of soil loss is an important requirement both for quantifying the problem and for developing improved land management and soil conservation practices. The use of fallout 137Cs measurements overcomes many of the difficulties facing traditional approaches to erosion monitoring and affords an effective means for obtaining estimates of soil redistribution rates on cultivated land. A number of empirical functions and theoretical models have been developed to establish the relationship between the change in the soil 137Cs inventory relative to the local 137Cs fallout input and the rate of soil redistribution. Of these approaches, physically-based mass balance models have received increasing emphasis, but their application may be hampered by their complexity and the need to specify values for a number of parameters. This paper presents a refined simplified point-based mass balance model for deriving estimates of soil redistribution rate from soil 137Cs data for individual sampling points. This model incorporates a number of important factors which are included in more comprehensive mass balance models. A spatially-averaged mass balance approach is also presented. This can be used to estimate water-induced soil erosion rates at different spatial scales in situations where detailed information on within-field variation of soil redistribution rates is not needed but information on net erosion rates or sediment output from a field is required.

Modelling phytoplankton abundance in a small enclosed bay used for salmon farming

. A simplified mass balance model was used to predict spatially averaged nitrogen and chlorophyll concentrations in Big Glory Bay, Stewart Island, New Zealand. The bay is used for salmon fanning and during January 1989 supported a dense bloom of Heterosigma alcashiwo which killed 600t of fish. Nutrient concentrations in the bay arc affected by inputs from bottom sediments, catchment run-off, rainfall, salmon farms and water exchange with Paterson Inlet (into which Big Glory Bay drains). The nitrogen model was calibrated using field data collected on 11–27 February 1988 and successfully predicted the mean nitrogen concentration of the bay during the 1989 bloom. Nitrogen concentrations in the bay were most affected by the nitrogen concentration in Paterson Inlet, which appears to vary year-to-year as a result of the incursion into Fouveaux Strait of highly fertile oceanic water. The marginal effect of the salmon farms was to increase the mean nitrogen concentration of Big Glory Bay by about 30%. The nitrogen model was combined with a logistic phytoplankton growth model to examine the effects of nitrogen availability and hydraulic flushing on phytoplankton yields (measured as chlorophyll a). The spatially averaged chlorophyll concentration of Big Glory Bay was reliably predicted during the 1989 study, when there was strong evidence that phytoplankton were nitrogen limited. The model indicated that nitrogen inputs from the salmon farms increased the mean chlorophyll concentration of the bay by about 33%. The model was less successful in predicting chlorophyll concentrations in February 1988 when phytoplankton growth was not restricted by nitrogen, but may have been controlled by zooplankton grazing or sedimentation (which were not included in the model). The use of mo re complex three-dimensional models is advocated to describe the observed‘patchiness’in Heterosigma distribution.

A COMPARISON OF MODELS PREDICTING GROUND WATER LEVELS ON HILLSIDE SLOPES1

ABSTRACT: A comparative study of ground water level predictions on hillside slopes using two models is presented. The models are a simplified mass balance model that has components for evapotran‐spiration, recharge, and drainage; and a two‐dimensional finite difference model that employs kriging to estimate soil parameters and accounts for non‐uniform thickness of the soil layer. These models are representative of a wide range of modeling capabilities and are used to illustrate the sensitivity of ground water level predictions to the sophistication of the modeling techniques. The drainage and recharge components of the two models are evaluated and the importance of unsaturated flow in recharge computations is underscored. Piezometric observations in a small drainage depression on the slope of Kennel Creek Valley in Tongass National Forest, Alaska, were used to evaluate the two models. The results show that, although the predictions differ from the field observations, the simple physically‐based mass balance model predicts the ground water levels as well as the two‐dimensional model. It is suggested that caution should be exercised in using complex models to validate simpler models.