Infiltration Coefficient Research Articles

Sensitivity analysis of SWAT streamflow and water quality to the uncertainty in soil properties generated by the SoLIM model

Hydrological models are essential tools for understanding natural processes, yet they often encounter with uncertainties due to limited input data and simplified assumptions. Soil data is a crucial input parameter for hydrological models, but it faces cartographic challenges due to lack of standardized soil mapping methods. To explore the applicability of soil datasets derived from the Third Law of Geography in hydrological models, the Soil Landscape Inference Model (SoLIM) based on this principle is used to generate a soil dataset. This dataset is then utilized as input data for a semi-distributed hydrological model (Soil and Water Assessment Tool, SWAT) to assess the impact of soil dataset uncertainty on performance of the hydrological model. This study, utilized the Fengyu River Watershed in Yunnan Province, China as an example, showed that: 1) Although the integration of SoLIM-generated soil data into the SWAT model introduces sensitivity in sediment yield, the overall results remain reliable. This suggests that soil datasets based on the Third Law of Geography can serve as input for semi-distributed hydrological models. 2) Uncertainty introduced by SoLIM-generated soil data affects parameters such as evaporation, total porosity of the soil layer (Φd), and groundwater infiltration coefficient (Ksat). These variations influence the sensitivity of SWAT’s predictions regarding streamflow and water quality. 3) Factors influencing model outcomes include steeper slopes in certain areas, which enhance streamflow velocity and flow rates, resulting in more dynamic and non-linear responses. Additionally, soil water dynamics exhibit higher temporal and spatial variability in forests compared to pasture and rice paddy fields, where vegetation tends to be more uniform, maintaining stable soil water loss pathways and reducing uncertainty in streamflow predictions. The study provides a foundation for studies addressing the difficulties in acquiring high-precision soil datasets for such models.

Impact of ventilation system retrofitting on indoor air quality in a single-family building

Due to prolonged human occupancy within indoor environments, the quality of indoor air holds significant importance. This study evaluates the impact of retrofitting a ventilation system from natural to mechanical on indoor air quality (IAQ) in a bedroom during heating seasons in 2017/18 and 2020/21. Measurements were conducted before and after modernization to assess CO2 concentrations, temperature, humidity, particulate matter (PM) and bacterial and fungal aerosols levels indoors and outdoors. Results show a significant decrease in CO2 concentration (from 1000 ± 240 ppm to 806 ± 165 ppm) and relative humidity (from 53.0 ± 3.6 % to 28.2 ± 4.1 %) post-modernization. Notable reduction in CO2 concentrations averaging 20 % was recorded, thereby elevating air quality category from IDAIII to IDAII. Additionally, the study determined the infiltration coefficient for PM2.5, which increased from 0.48 under natural ventilation to 0.63 after retrofitting. PM2.5 concentrations increased indoors (from 23.49 ± 11.21 μg/m3 to 56.68 ± 13.47 μg/m3) due to higher infiltration rates with mechanical ventilation. Bioaerosol measurements indicate fluctuating concentrations, with bacterial aerosols peaking in the evening. The use of mechanical ventilation led to increased transport and dispersion of bacterial bioaerosols indoors. In contrast, this was not observed for fungal aerosols. Additionally, the study highlights limitations in ventilation filtration efficiency and recommends the installation of PM2.5 sensors to regulate airflow during periods of high outdoor PM2.5 concentrations. Overall, while mechanical ventilation improved some IAQ parameters, it posed challenges in controlling particulate matter infiltration, emphasizing the need for comprehensive ventilation strategies to ensure indoor air quality and occupants' well-being.

Estimation of soil infiltration coefficient in the furrow irrigation using the combination of the hydrodynamics model and Richard's equation

Present study optimizes the coefficients of the Kostiakov-Lewis infiltration Eq. and estimates water infiltration in the soil with the help of simulation of the advancing phase using the numerical solution of the Saint-Venant equations. In order to validate the numerical model, two series of field data measured in two regions of Iran were used and the results of the simulation were compared with actual field results. Also, using the Richards' Eq., the HYDRUS-1D software, the Hydrus-2D software, and a combination of the Hydrodynamics model with each of the mentioned methods the infiltration simulation and prediction of coefficients of the Kostiakov-Lewis infiltration Eq. were provided. The criteria for the accuracy of the methods were considered the comparison between the infiltration volumes of the water (calculated from each method) and the actual infiltration volume of the water in Furrow irrigation. The results illustrated that the combination of the Hydrodynamics model with each of the HYDRUS-1D, HYDRUS-2D software and the numerical solution of the Richards' Eq. increased the accuracy of the estimation process of the coefficients of the Kostiakov-Lewis's infiltration equation and the infiltration volume. So, the best and worst methods for simulating water infiltration through the soil has been introduced based on the less error between numerical and observed values of the infiltration volume as the combined method of the Hydrodynamics- HYDRUS 2D with NRMSE = 17.62% and numerical solution of the Richard's Eq. with NRMSE = 36.02%, respectively. The results illustrated that the error of the Hydrodynamics- HYDRUS-2D compared with the numerical solution of the Richard's Eq. (t(10) = −3.018) was significantly less value.

Reliability of reservoir inflow for supporting the operation simulation model of multi reservoir

This research intends to analyze the inflow reliability of the Tugu-Bagong multi-reservoir. The utilization of Tugu Dam is as follows: for fulfilling the irrigation water need of Ngasinan Irrigation Area an area is 1,200 ha, supplying 12 l/s of raw water, controlling the yearly flood in Trenggalek Regency with the discharge is 76.21 m3/s, as the potency of mini-hydro electrical generation (PLTM) in the amount of 0.40 MW, and as the tourism means. However, Bagong Dam, besides being utilized for flood control, is also utilized for supplying raw water, irrigation, and domestic water; for water resources conservation; and recreation or tourism. The methodology consists of collecting the rainfall data and watershed parameters like watershed area, infiltration coefficient each for dry and rainy seasons, retention coefficient, SMC value, etc.; to analyze the dependable discharge due to the rainfall analysis input in 4 discharge conditions: dry season discharge, low water discharge, normal water discharge, and sufficient water discharge. The result of inflow reliability is hoped to be able to support the operation simulation modeling of the Tugu-Bagong multi-reservoir.

Quantitative Groundwater Modelling under Data Scarcity: The Example of the Wadi El Bey Coastal Aquifer (Tunisia)

The Grombalia aquifer constitutes a complex aquifer system formed by shallow, unconfined, semi-deep, and deep aquifers at different exploitation levels. In this study, we focused on the upper aquifer, the Wadi El Bey coastal aquifer. To assess natural aquifer recharge, we used a novel physiography-based method that uses soil texture-dependent potential infiltration coefficients and monthly rainfall data. The developed transient flow model was then applied to compute the temporal variation in the groundwater level in 34 observation wells from 1973 to 2020, taking into account the time series of spatially variable groundwater recharge, artificial groundwater recharge from 5 surface infiltration basins, pumping rates on 740 wells, and internal prescribed head cells to mimic water exchange between the wadis and aquifer. The quantified deviations in the computed hydraulic heads from measured water levels are acceptable because the database used to construct a scientifically sound and reliable groundwater model was limited. Further work is required to collect field data to quantitatively assess the local inflow and outflow rates between surface water and groundwater. The simulation of 12 climate scenarios highlighted a bi-structured north‒south behaviour in the hydraulic heads: an increase in the north and a depletion in the south. A further increase in the pumping rate would, thus, be severe for the southern part of the Wadi El Bey aquifer.

Determination of snowmelt infiltration coefficients for seasonally frozen regions requires considering the response of the groundwater table to the freeze–thaw process

Atmospheric precipitation is an important recharge source for groundwater resources and the precipitation infiltration recharge coefficient (PIRC) is key to accurately assessing the amount of groundwater resources. However, the freeze–thaw process in seasonally frozen areas can significantly reduce the soil infiltration capacity and affect the snowmelt infiltration process, thus changing PIRC during the snowmelt period. Currently, in the calculation of PIRC for snowmelt period, the same method as that used for the flood period is generally adopted, which may cause significant bias in groundwater recharge evaluation results. To resolve these issues, this study performed a method for determining the snowmelt infiltration coefficient based on groundwater level variation with a simplified process, high accuracy, and produces stable results. The results of this study showed that: (1) The groundwater level variation ΔH caused by snowmelt recharge should be determined by considering the water exchange within the unsaturated zone and groundwater caused by the freeze–thaw process of the soil. (2) The total amount of meltwater infiltration recharge P cannot be a simple addition of precipitation during the freeze–thaw period. It is suggested that the actual infiltrated meltwater recharge should be calculated using the improved degree-day model, which improves the accuracy by 50.3 %–66.4 % compared with the existing algorithm. (3) The snowmelt infiltration coefficient determined in this study can improve the calculation accuracy of groundwater recharge resource in a seasonally frozen zone by 8.8 %–15.0 % by considering its seasonal dynamic characteristics. The research results provide a theoretical basis for understanding the recharge potential of winter snow cover in seasonally frozen areas and improving the accuracy of groundwater resource evaluation in such regions.

A framework for parameter estimation, sensitivity analysis, and uncertainty analysis for holistic hydrologic modeling using SWAT+

Abstract. Parameter sensitivity analysis plays a critical role in efficiently determining main parameters, enhancing the effectiveness of the estimation of parameters and uncertainty quantification in hydrologic modeling. In this paper, we demonstrate an uncertainty and sensitivity analysis technique for the holistic Soil and Water Assessment Tool (SWAT+) model coupled with new gwflow module, spatially distributed, physically based groundwater flow modeling. The main calculated groundwater inflows and outflows include boundary exchange, pumping, saturation excess flow, groundwater–surface water exchange, recharge, groundwater–lake exchange and tile drainage outflow. We present the method for four watersheds located in different areas of the United States for 16 years (2000–2015), emphasizing regions of extensive tile drainage (Winnebago River, Minnesota, Iowa), intensive surface–groundwater interactions (Nanticoke River, Delaware, Maryland), groundwater pumping for irrigation (Cache River, Missouri, Arkansas) and mountain snowmelt (Arkansas Headwaters, Colorado). The main parameters of the coupled SWAT+gwflow model are estimated utilizing the parameter estimation software PEST. The monthly streamflow of holistic SWAT+gwflow is evaluated based on the Nash–Sutcliffe efficiency index (NSE), percentage bias (PBIAS), determination coefficient (R2) and Kling–Gupta efficiency coefficient (KGE), whereas groundwater head is evaluated using mean absolute error (MAE). The Morris method is employed to identify the key parameters influencing hydrological fluxes. Furthermore, the iterative ensemble smoother (iES) is utilized as a technique for uncertainty quantification (UQ) and parameter estimation (PE) and to decrease the computational cost owing to the large number of parameters. Depending on the watershed, key identified selected parameters include aquifer specific yield, aquifer hydraulic conductivity, recharge delay, streambed thickness, streambed hydraulic conductivity, area of groundwater inflow to tile, depth of tiles below ground surface, hydraulic conductivity of the drain perimeter, river depth (for groundwater flow processes), runoff curve number (for surface runoff processes), plant uptake compensation factor, soil evaporation compensation factor (for potential and actual evapotranspiration processes), soil available water capacity and percolation coefficient (for soil water processes). The presence of gwflow parameters permits the recognition of all key parameters in the surface and/or subsurface flow processes, with results substantially differing if the base SWAT+ models are utilized.

Estimativa da infiltração e afluxo devido à precipitação em uma bacia de esgotamento sanitário

Abstract Extraneous flows to sewer networks can occur underground (infiltration) or in the routing of rainwater (inflow). Infiltration in these networks is often inevitable, leading to system overloads and causing overflows. The range of values suggested by the Brazilian standard for the infiltration coefficient is quite broad, which may result in the adoption of elevated or inaccurate values, leading to imprecise sizing and consequent expenses and problems that could be predicted or avoided. Sizing problems can lead to chronic operational issues. The application of methodologies for estimating infiltration and inflow due to precipitation (IDP) presents itself as an important tool in addressing these challenges. The objective of this work was to propose and test a methodology to estimate infiltration and IDP in a sewage basin in a coastal region (Florianópolis, Santa Catarina, Brazil). This methodology was developed based on the operational conditions available at the sanitation company. The aim was to use what was available, without costly acquisitions, and thus quantify these elements. For this, two distinct methodologies were applied: one for the quantification of the inflow and the other for the measurement of underground infiltration and determination of the infiltration coefficient. The results showed a directly proportional relationship between rainfall intensity and IDP value. The measured infiltration coefficients resulted in values higher than those adopted in the project. It is expected that this research will contribute to reducing network overload and improving local sanitation management.

Water availability of Akelamo River, Obi Island, South Halmahera

The nickel mining industry’s activities are not spared from the high quantity of water demand, such as those of Harita Nickel Indonesia, a company located in Obi Island, South Halmahera. As one of the largest nickel mining companies that uphold environmental conservation, Harita Nickel Indonesia conducted this study to identify and analyze water availability to ensure the company’s and local residents’ water needs. One of the water resources in this study is Akelamo River, which has a 254.99 Km2 catchment area (covering the catchment area of Karo Lake upstream). Referring to SNI 6738:2015, water availability can be indicated by the amount of dependable flow based on an 80% probability of occurrence. This calculation is carried out using F.J. Mock method that heavily relies on six (6) defining variables: Reflection coefficient (r), Exposed surface (m;%), Soil moisture capacity (ISMC), Infiltration coefficient (if), Flow recession constant (k), and Percentage factor (PF). Based on the method and conditions of this location, it is calculated that the dependable flow Q80 of the Akelamo River is 6.2 m3/sec. It should be noted that this figure only represents overflow discharge and does not include the amount of water currently stored in the water body. This availability study can be continued with a water balance analysis according to the planned water demand or even as a consideration in hydrological infrastructure planning such as dams.

Study of seepage patterns and calculation of infiltration coefficients of loose stacked layers on slopes under rainfall action

Rainfall is one of the most important factors inducing landslide occurrence, and previous researchers have carefully studied the stages of rainfall infiltration as well as the factors that affect infiltration (e.g., rainfall intensity, rainfall duration, initial water content and dry density). However, previous studies using homogeneous soils were overly idealised and ignored the effects of water content and dry density on infiltration, which vary with depth. In this paper, based on indoor rainfall infiltration tests under the above initial conditions and influencing factors, the following patterns were found: (1) dry density and water content of natural soils tend to increase along the direction of gravity under long-term gravity and repeated rainfall evapotranspiration; (2) stepped dry density increases infiltration resistance, which increases the total response time; stepped initial water content decreases infiltration water volume, which decreases the total response time; stepped dry density and water content have the shortest total response time;(3) The increase in dry density delayed the sudden change point in the permeability coefficient, and the initial moisture content had little effect on the sudden change point.

Rainfall–runoff process and sediment yield in response to different types of terraces and their characteristics: A case study of runoff plots in Zhangjiachong watershed, China

AbstractA field experiment was conducted in the Zhangjiachong watershed to analyze the characteristics of rainfall–runoff process and sediment yield under different types of terraces. Various runoff plots were utilized, and a two serial tank model was employed to simulate runoff generation and concentration processes, taking into account vegetation interception. A soil erosion model incorporating raindrop erosion and sheet erosion was established to replicate sediment yield and concentration process. The parameters of the rainfall–runoff model and soil erosion model were calibrated and validated using observed runoff and sediment yield data. The controlling factors on runoff and sediment yield were explored and compared. The results indicate that both calibration and validation outcomes were acceptable. The earth‐banked terraces–citrus demonstrated the largest coefficients of upper and lower surface runoff, while its upper runoff threshold of the upper tank and the runoff threshold of the lower tank were the lowest, suggesting that it was more likely to produce surface and subsurface runoff. On the other hand, the stone dike terraces–crops exhibited the smallest coefficients of upper and lower surface runoff, while its upper runoff threshold of the upper tank was the highest. The lower runoff threshold of the upper tank was the same across different types of terraces. Compared to the earth‐banked terraces, the stone dike terraces have a larger infiltration coefficient in the upper tank and a smaller infiltration coefficient in the lower tank. Sensitivity analysis indicates that the most sensitive factors affecting runoff simulation results are the runoff threshold and the infiltration coefficient of the lower tank. Terraces, whether constructed with earth banks or stone dikes, are effective in reducing soil erosion. However, during storm rainfall events, these terraces may be partially destroyed, resulting in a higher sediment yield than that of the same vegetation cover on slope land. Terraces with hedgerows have a more significant effect on reducing runoff and sediment than those without hedgerows.

Division Method of Dynamic Flow Units in Fluvial Reservoir at Ultra-high Water Cut Period

The heterogeneity of fluvial sedimentary reservoir is serious. The division of flow units in the early stage of development can provide a good guidance in the well pattern distribution and reservoir production. Due to the huge changes in the oil-water system in the long-term development reservoir, the flow units divided at the initial stage are difficult to guide the production when entering the ultra-high water cut period. Therefore, it is necessary to redefine the division indicators and methods of flow units, so as to provide support for the formulation of efficient regulation and control technology. Starting from the definition of flow unit, this paper establishes the percolation coefficient as the characteristic index of percolation capacity. Combined with the percolation characteristics of fluvial reservoir, the dynamic flow unit division method with percolation coefficient and water cut as division parameters is established. Through the division results of typical models of fluvial reservoir, it can be seen that the four types of flow units divided by the dynamic flow unit method in this paper can play a great guiding role in the later formulation of regulation and control measures. The verification of reservoir examples shows that the division results of dynamic flow units of fluvial facies can well reflect the remaining oil enrichment areas in the reservoir and classify the remaining oil enrichment areas. At the same time, the dynamic flow unit changes continuously with the development process, which can more clearly show the producing degree of each remaining oil enrichment area after the regulation and control measures. This provides a key support for formulating targeted and efficient reservoir development technique.

Effect of Different Irrigation Managements on Infiltration Equations and Their Coefficients

The main aim of this paper was to analyze the sensitivity of the five infiltration equations (Kostiakov, Kostiakov–Lewis, Philip, Horton and SCS) and their coefficients to various ponding depths and initial soil moisture under different irrigation managements. The treatments included three qualities of water (electrical conductivity = 6, 3 and 0.6 dS/m), two managements of irrigation (intermittent irrigation and daily irrigation) and three irrigation periods (100, 45 and 8 days). The HYDRUS-1D model was calibrated to simulate infiltration in various initial soil moistures and ponding depths. Evaluating the performance of infiltration equations showed that the Horton and Kostiakov–Lewis had better accuracy and Kostiakov and SCS had less accuracy than the other equations. The empirical coefficients of SCS and Kostiakov had the most and least sensitivities, respectively. Furthermore, Horton was the most sensitive equation, while SCS was the least sensitive one. The output parameters under daily management were the most sensitive to variations in infiltration coefficients, especially when the salinity and sodium contents of water and soil were higher. The results also showed that the effect of the initial soil moisture on the infiltration coefficient in high permeable soil (arising from daily management) was greater; but in low permeable soil (arising from intermittent management), the ponding depth was more effective. It is concluded that the infiltration equations (specifically the SCS equation) and their coefficients (specifically coefficient c) should be calibrated relative to the initial soil moisture, ponding depth, soil solution and water irrigation quality. Particularly in areas with high permeable soil (in the daily management), the calibration of the infiltration equation should be conducted with the initial soil moisture. In these areas, the irrigation period should be controlled. In areas with low permeable soil (in intermittent management), calibration should be carried out relative to the ponding depth. In these areas, the inflow rate should be controlled.

Developing a simple method for estimating soil infiltration in furrow and border irrigation using advance, recession and runoff data

AbstractEstimating soil infiltration is important in designing and managing surface irrigation systems. To date, various methods have been proposed to estimate infiltration coefficients. In this research, a simple method for estimating the coefficients of the Kostiakov–Lewis infiltration equation in surface irrigation is presented. Then, the performance of this method is compared with other similar methods, including the Elliott–Walker two‐point, IPARM and Merriam–Keller methods, using eight furrow irrigation datasets and six border irrigation datasets. The proposed method calculates the coefficients of the infiltration equation through the comparison between the measured and calculated infiltrated water amount by an optimization method, the normal decreasing gradient algorithm, using advance and recession data. The mean relative errors in estimating the infiltrated water volume were 13.63, 3.92, 0.005 and 0.00 for the two‐point, IPARM, Merriam–Keller and proposed methods for border irrigation, respectively. Similarly, the respective mean relative error values were 14.35, 6.31, 1.90 and 0.00 for furrow irrigation. In addition, to ensure the optimality of the obtained coefficients, response surfaces were drawn. The coefficients obtained from the proposed method are located in the minimum place of the response surface, while no similar behaviour was observed in the other methods. These results prove the effectiveness of the proposed method in addition to its simplicity.

Determining Kostiakov–Lewis infiltration coefficients using the water advance relationship and optimization

AbstractTwo exponential relationships ([1] from the beginning to the midpoint of the field, [2] from the beginning to the endpoint of the field) were considered for the advance curve of surface irrigation water along a field. The constant coefficients of these advance relationships were determined using the least squares optimization method. These relationships were compared with the advanced relationships obtained by the Elliott and Walker method (EW) using the advanced data related to 14 irrigation events and using root mean square error deviation (dRMS) and Nash–Sutcliffe (NSE) indices. The results of this evaluation showed that the advanced relationships obtained from the method presented in this research (TR) have better accuracy, with average values of 7.05 min and 0.984 for dRMS and NSE, respectively. Then, using the TR method for deriving the advance relationships and using the volume balance method, the coefficients of the Kostiakov–Lewis infiltration relationship were determined. The infiltration relationships derived from the TR method were compared with the infiltration relationships obtained from the two‐point method of EW. The results of this investigation showed that the TR method predicts the average infiltration depth with an average absolute relative error of 6%, which is more accurate than that of EW.

Using geophysics to guide the selection of suitable sites for establishing sustainable earthen fishponds in the Niger-Delta region of Nigeria

Water retention in earthen fishponds throughout a fish farming cycle is challenging due to climate-induced water loss via evapotranspiration, seepages, and lowering of the groundwater table. These processes depend on the soil hydrostratigraphic condition and constitute a major challenge for fish farmers in the Niger-Delta region of Nigeria, where seasonal variations cause groundwater levels to fluctuate. This study assesses the use of non-invasive geophysical methods, including electrical resistivity and induced polarization, to guide the selection of sites with appropriate hydrostratigraphic conditions for establishing earthen fishponds. We combined measurements of electrical resistivity and chargeability distributions to assess the subsurface of two earthen fishpond sites at Ugono-Abraka and Agbarha-Otor areas in the Niger-Delta region of Nigeria. Electrical soundings were acquired at ten locations, while two-dimensional electrical resistivity and Induced polarization were acquired across five transects using Schlumberger and dipole-dipole electrode configurations. The field data were inverted using IP2win, and Diprowin software. The geophysical models were combined with lithological data from soil cores to characterize the subsurface stratigraphy, while measured clay contents were used to estimate infiltration coefficients relying on established petrophysical relationships. The delineated subsurface properties at Ugono-Abraka and Agbarha-Otor show higher variations than assumed by practitioners. The complementary results of low resistivity (20–140 Ωm) and high chargeability (10–50 msec) revealed areas with clay-rich sediments. Soil samples confirmed higher clay contents of up to 10% at Ugono-Abraka and low values of 2% at Agbarha-Otor. Estimated infiltration coefficients are lower at the Ugono-Abraka site (1.6 m/day) compared to Agbarha-Otor (8.4 m/day). This implies variable water loss in the earthen fishponds; hence, we recommend characterizing these variations using non-invasive geophysical methods before establishing medium to large-scale earthen fishponds in the area.

Influence of hydrogeological and geochemical parameters on N2O in the groundwater in the irrigation area of lower reaches of Yellow River

The plains of the lower reaches of rivers are important areas for food production. In the groundwater of irrigated agricultural areas of these regions, the N2O concentration was generally observed to be higher than that of the water–gas equilibrium. Due to the complexity and uncertainty of the aquifers, the mechanisms by which groundwater N2O are affected by groundwater hydrogeology and geochemistry remain unexplored. In this study, 41 groundwater samples were collected from three zones of the irrigation area of the lower reaches of Yellow River (i.e., piedmont plain, coastal plain, and central plain), and the hydrogeological parameters of these three areas were characterized. The results showed significant differences of the N2O concentration in the groundwater of the three zones of the lower reaches of Yellow River plain, which was 14.1 ± 13.1 µg/L, 1.84 ± 1.48 µg/L, and 36.5 ± 40.5 µg/L for the piedmont plain, central plain, and coastal plain, respectively. The differences were attributed to different groundwater N input and hydrogeological parameters in the three zones. The infiltration coefficient of precipitation was found to be the most important hydrogeological parameter affecting groundwater N2O. This study also evaluated the indirect N2O emission factor in the irrigation area of the lower reaches of Yellow River. The N2O emissions induced by groundwater exploitation in the irrigation area of the lower reaches of Yellow River were found to be 1.87 g hm−2 year−1. These findings provide a foundation to develop strategies to reduce N2O production and emissions in the agricultural area of the lower reaches of rivers.

Effect of simultaneous variations of Kostiakov–Lewis infiltration coefficients equation in irrigation management on SIRMOD model outputs

Effect of simultaneous variations of Kostiakov–Lewis infiltration coefficients equation in irrigation management on SIRMOD model outputs

Runoff and Infiltration responses of revegetated slopes to clipping management on the northern Loess Plateau

Large-scale vegetation restoration can reduce local watershed water yield, limit vegetation establishment and subsequent growth, and influence regional ecosystem functions. Clipping management by reducing aboveground parts of grassland was gradually recommended and adopted in Grain-for-Green project management to offset these additional issues. Thus, scientific evaluation of the effectiveness of clipping management on infiltration and runoff processes is necessary for maintaining the stability of the surface water system and the sustainability of vegetation restoration in semi-arid regions. A field simulated rainfall experiment was conducted with four managed clipping grasslands (mainly bunge needlegrass and Stipa grandis), including no clipping, light clipping, heavy clipping, and complete clipping under three slope gradients (10, 20, and 30°) and three rainfall intensities (60, 90, and 120 mm/h) to explore the mechanism of runoff and infiltration responses to clipping using structural equation modeling and variation partitioning based on an SCS-CN model. The results showed the runoff coefficient of the light clipping, heavy clipping, and complete clipping plots were 1.33, 2.22, and 4.22 times that of the no clipping plot. The light clipping, heavy clipping, and complete clipping plots decreased the infiltration coefficients by 0%, 5%, and 26% relative to the no clipping plot. Rainfall intensity dominated runoff and infiltration amounts, and clipping intensity's total effect was stronger than slope gradient. Clipping intensity and slope gradient were more influential on runoff with increasing rainfall intensity. The mutual inhibition effect was between clipping intensity and slope gradient on runoff. In order to maintain the sustainability of restoration, a 25–50% vegetation coverage after clipping maximizes the benefits of increasing runoff and maintaining enough soil water supply that prevents possible soil drought. We propose that future vegetation restoration policies should evaluate the appropriate clipping intensity; meanwhile, local physiographic and climate conditions should be considered. These findings may offer guidance for the development of measures for runoff regulation and ecosystem functions of the watershed during vegetation restoration on the northern Loess Plateau.

Hidden hydrosphere under the Caspian Sea: Geophysical evidence and sea-level influence

We analyzed geologic-geophysical data, both from archives and collections in recent expeditions by the Shirshov Institute of Oceanology of Russian Academy of Sciences, and revealed many anomalies in the seismoacoustic wavefield. Anomalies are of two types: horizontal disturbed layers and vertical pipes. Anomalies form associations — pipes (chimneys) are rooted in disturbed layers and go through sediments up to the seafloor and form pockmarks. We consider all specified seismic anomalies and bottom microrelief as a possibility of vertical migration of gas and water via sediments (fluid from sediments to water and from seawater to sediments). It is expected that the fluids form a huge underground hydrosphere below the Caspian Sea. To test the fluid flow, we made a mathematical model of fluid discharge and absorption in bottom sediments. We hypothesize that the Caspian Sea level fluctuates, at least partially, due to cycles of the submarine ground water discharge and sea water absorption back into the sediments. This cyclicity of fluid discharge and absorption correlates with regional seismic events. The earthquakes cause tectonic relaxation, triggering the absorption process, and sea-level drop due to reverse flow into sediments. In other periods, the tectonic tension causes sediment compression and fluid discharge to sea water, which causes sea-level rise. The model was tested on the recent (past 100 years) sea-level change curve. As a result, we got a distribution of the general volume of fluid flows depending on the infiltration coefficient. The real change in the Caspian Sea volume is at the lower range of the calculated values, so we cannot neglect the effect of “gas pipes” (“chimneys”) on the Caspian Sea-level change.