Benefit of Sponge City monetization based on "water footprint theory": cases of Xi'an and Guyuan.

China has proposed to build "Sponge City" to alleviate the problems of urban waterlogging, water shortage, ecological degradation, and water pollution. The benefits of Sponge City construction have become a focus of attention because of the considerable investment and the extensive participation of all sectors of society. This paper develops a model for monetizing urban, river, and regional benefits, by taking city and river areas as the research objects. This model is based on the regional water balance, water footprint theory, and the shadow price of water. This model monetizes the potential benefits of a Sponge City before construction. Our case study is Xi'an and Guyuan. Applying the benefits calculated at the 7% discount rate, the benefit/cost (B/C) ratios of the two locations are 3.86 and 0.93 times, respectively. Also, applying the benefits calculated at the 5% discount rate, the B/C ratios of the two locations are 5.41 and 1.31 times, respectively. In terms of urban benefits, the static payback periods of Xi'an and Guyuan are about 3.7 years and 15.3 years, respectively. In terms of regional benefits, they are about 4.0 years and 16.2 years, respectively. According to the results, the return of Sponge City construction in Xi'an and Guyuan is much higher than the investment but with some risks in the investment for social investors in Guyuan. In this paper, the model and the research results can provide some references for the research on the monetization of Sponge City benefits.

Quantitative assessment of non-point source pollution load of PN/PP based on RUSLE model: a case study in Beiluo River Basin in China.

The runoff-sediment relationship in the Yellow River Basin of China is still grim. People pay more and more attention to non-point source (NPS) pollution caused by surface pollutants migrating into the receiving water body with rainfall runoff. The particulate load of pollutants adsorbed in the soil and sediment by erosion and denudation and migration into water is also quite serious. It is necessary to deeply analyze the quantitative relationship between particulate nitrogen and phosphorus (PN/PP) load and soil loss. The soil erosion estimation of different administrative units in the study basin is obtained by the revised universal soil loss equation (RUSLE). The spatial distribution and the variation characteristics at different slopes and different land use of PN/PP load are discussed. An empirical equation of particulate organic load is used to calculate the PN/PP load. The results show that the multi-annual average erosion modulus of the basin is 358.33 t/(km2∙a); the multi-annual average soil erosion reaches 9.62 million tons. The PN/PP load caused by soil loss reaches 11,107.1 t and 7909.3 t, and the export coefficients are 4.13 kg/hm2 and 2.94 kg/hm2, respectively. Spatial distribution of the PN/PP load is in step with the soil erosion distribution. Soil erosion is prone to occur in the region under the slope of 8 ~ 25°, the NPS load of PN/PP are relatively large, and the average export coefficients of PN/PP are 7.17 kg/hm2 and 5.06 kg/hm2. With the increase of the slope, the PN/PP load export coefficient increases first and then decreases. Agricultural land (AGRL), forest land (FRST), and pasture (PAST) are the land use types that contribute the most to the PN/PP load and soil erosion, and the average export coefficients of PN/PP are 4.54 kg/hm2 and 3.23 kg/hm2, respectively. The variability of natural elements, the unevenness and heterogeneity of spatial distribution, and the heavy involvement of human activities will have a conspicuous impact on the soil erosion and NPS pollution processes in the basin. The research on the influence of single factor and combined factors on NPS pollution process can be strengthen and provides scientific theoretical basis for formulating reasonable and efficient water and soil conservation measures and NPS pollution control scheme, so as to achieve effective control and scientific management of environment pollution.

Improvement and application research of the SRM in alpine regions.

The simulation of snowmelt runoff in alpine mountainous areas is of great significance not only for the risk assessment of snowmelt flood in spring and summer, but also for the development and management of water resources in the basin. An improved snowmelt runoff model (SRM) is constructed based on the analysis of change characteristics of climate, runoff, and snow and ice cover in the middle and upper reaches of the Taxkorgan River in Xinjiang Province, China. Because of the large evaporation in the study basin, the evaporation loss is added to the model. The SRM and the improved SRM are calibrated and verified by using data such as temperature, precipitation, water vapor pressure, and snow-covered area (SCA) ratio in the study basin from 2002 to 2012. The results show that, compared with the SRM, the average Nash-Sutcliffe coefficient (NSE) of annual runoff simulation increases from 0.80 to 0.86 in the calibration and increases from 0.74 to 0.83 in the validation through the improved model, and the average runoff error reduces from - 12.8 to 1.32% in the calibration and reduces from - 20.0 to - 11.51% in the validation. After adding the measured flow rate for real-time correction, the average NSE of annual runoff simulation increases from 0.91 to 0.93 and the average annual runoff error reduces from - 7.76 to - 3.91% in the calibration. The average NSE increases from 0.85 to 0.89 and the average runoff error reduces from - 12.35 to - 2.76% in the validation. It indicates that the SRM structure with increased evaporation loss is more in line with the actual situation. The short-term simulation effect of the model is greatly improved by adding the measured flow rate for real-time correction. At the same time, the improved SRM and the hypothetical climate change scenario are used to analyze the impact analysis of the snowmelt runoff simulation in the partial wet year. The results show that in the case of rising temperature, the ice and snow ablation period is prolonged, and the annual runoff also changes significantly in time distribution. It is of guiding significance for the influence of climate change on the runoff of recharged rivers with ice-snow meltwater in the other alpine regions.

Filler improvement and purification effects of constructed rapid infiltration facility.

Purification effects of constructed rapid infiltration system with two main fillers (coarse sand or medium coarse sand) and different addition proportion (5%, 10%, or 15%) modifiers (sponge iron, blast furnace slag, or zeolite) on rainwater runoff were studied through filter column tests. A set of constructed rapid infiltration system test device was designed, which included 9 rainwater filter columns. The test results showed that the permeability of artificial fillers blended with modifiers could have the promotion with varying degrees. There were differences in the characteristics of the modifiers, so the artificial fillers blended with different modifiers had a significant difference for the purification effects on each pollutant. In view of the overall situations, the pollutant removal effects of artificial fillers with two or more modifiers had a smaller gap, and the reduction effects were good, ranging from 38.95 to 46.25% when the main filler is coarse sand and from 46.29 to 49.46% while main filler is medium coarse sand. It was worth noting that the artificial fillers blended with sponge iron showed a slight harden after prolonged used; however, it had little influence on the permeability and water purification effects.

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We examined root fractal parameters, root length, root quantity, root mass, root-shoot ratio of 3-year-old seabuckthorn in the Pisha sandstone area of Inner Mongolia, using the fractal theory and statistical method. The results showed that soil moisture had the most significant effect on the root architecture, followed by slope. Slope position had the least effect on the root architecture. The seabuckthorn in the Pisha sandstone area was suitable for planting on slope bottom or mid-slope with a soil moisture of about 8%. Mid-slope with a slope of 30°-35° was recommended. The root-shoot ratio of seabuckthorn decreased with increasing soil moisture. It increased at first and then decreased with increasing slope and slope position. Seabuckthorn with the characters of developed root and high root-shoot ratio in arid and barren midslope meets the basic requirements of tree species for soil-fixing and slope-protection.

Design parameters and treatment efficiency of a retrofit bioretention system on runoff nitrogen removal.

Mixed media design is key factor that affects the operation of bioretention systems. In this study, four types of modifiers, namely, water treatment residual (WTR), green zeolite, fly ash, and coconut bran, were mixed with traditional bioretention soil (65% sand + 30% soil + 5% sawdust, by mass). Consequently, four kinds of modified media were obtained. Ten pilot-scale bioretention basins were constructed by setting different configurations. The steady infiltration rates of the modified packing bioretention systems were 3.25~62.78 times that of plant soil, which was 2.88~55.75 m/day. Results showed that the average concentration removal (ACR) of both mixed and layered fly ash and WTR were better than those of the other media, and the effects could reach over 61.92%. In the bioretention basins with WTR as the modifier, the treatment efficiency of nitrogen under the submerged zone height of 150 mm was relatively optimal, and ACR could reach 65.46%. Outflow total nitrogen (TN) load was most influenced by inflow load, and the correlation coefficient was above 0.765. Relative to the change of inflow concentration (IC), the change of recurrence interval (RI) and discharge ratio (DR) was more sensitive to TN load reduction. The reduction rate of TN load decreased by approximately 15% when the recurrence interval increased from 0.5 to 3 years. It decreased by approximately 12% when the discharge ratio increased from 10 to 20. This study will provide additional insights into the treatment performance of retrofit bioretention systems, and thus, can guide media and configuration design, effect evaluation, and related processes.

[Impact analysis of Xi'an to the water quality of Weihe River].

Based on the water quality inspection results of Weihe River in the Xi'an section and the runoff at the watershed in different representative years, it was found through the pollution load calculated from the mean concentration method that Weihe River's main stream was dominated by point source pollution and non-point source pollution was more serious in tributaries. The input amount of pollutant to Weihe River' main stream from Xi'an which is located within the Xianyang and Lintong section was calculated from the material balance algorithm based on the pollutant concentrations measured in 2009 and 2011. The percentage of the pollution load of Xi'an area on Lower reaches' monitoring section of Lintong was analysed and the impact of Xi'an area on the water quality of Weihe River was quantified. The computational results showed that the upstream of the Xianyang section was the main source of the pollution load of the Lintong section in Weihe River, followed by Xi'an area. More than 40% of TN, COD and NH4+ -N of the Lintong section came from the upstream of the Xianyang section and more than 30% came from Xi'an area, in addition, 53% of TP came from Xi'an area. The non-point source pollution in Xi'an was more serious than in its upstream and downstream areas while point source pollution load accounted for 63% of the total.

[Study on water quality monitoring scheme based on non-point source pollution].

In order to improve standardization and normalization of non-point source pollution monitoring, this paper summarized the non-point source pollution monitoring scheme that based on conventional technology condition. The scheme firstly emphasized the preparation work before monitoring, including situation investigation and index selection of the monitoring area and so on; In the process of establishing monitoring scheme, the monitoring area was divided into three types: city, agriculture and watershed. Take urban area monitoring scheme for Xi'an as an example, through dividing function zone setting sampling point, summarized sampling time interval, frequency and sampling methods during a rainfall process. An irrigation district was an example for agricultural monitoring scheme, through unit division, setting sampling point at the approach channel and drain channel, introduced sampling times, interval time and so on in the process of irrigation. Watershed monitoring scheme's example was the Weihe GuanZhong section, raised the setting principle of each sample section, and analyzed each section's sampling law in the process of rainfall. Finally the principal character of different non-point source pollution monitoring areas was discussed, and concluded that non-point source pollution monitoring scheme is the base of non-point source pollution study and control.

[Monitoring and analysis on evolution process of rainfall runoff water quality in urban area].

In order to find the water quality evolution law and pollution characteristics of the rainfall runoff from undisturbed to the neighborhood exit, 6 times evolution process of rainfall runoff water quality were monitored and analyzed from July to October in 2011, and contrasted the clarification efficiency of the grassland to the roof runoff rudimentarily at the same time. The research showed: 1. the results of the comparison from "undisturbed, rainfall-roof, rainfall runoff-road, rainfall-runoff the neighborhood exit runoff " showed that the water quality of the undisturbed rain was better than that from the roof and the neighborhood exist, but the road rainfall runoff water quality was the worst; 2. the average concentrations of the parameters such as COD, ammonia nitrogen and total nitrogen all exceeded the Fifth Class of the Surface Water Quality Standard except for the soluble total phosphorus from undisturbed rainfall to the neighborhood exit; 3. the runoff water quality of the short early fine days was better than that of long early fine days, and the last runoff water quality was better than that of the initial runoff in the same rainfall process; 4. the concentration reduction of the grassland was notable, and the reduction rate of the grassland which is 1.0 meter wide of the roof runoff pollutants such as COD and nitrogen reached 30%.

[Simulation and application of the agricultural non-point source pollutants in drainage ditch].

Drainage ditch system is the transitional zone between yield in the field and receiving waters for agricultural non-point source pollutants. Based on the brief analysis of the migration and transformation process of agricultural non-point source pollutants in drainage ditch system, the one-dimensional transport model of agricultural non-point source pollutants in drainage ditch system was constructed on the basis of the equation of continuity of flow and pollutants migration transform. Taking the Di Yi drainage ditch system, in the Qing-Tong-Xia irrigation district at the Yellow River upstream, as an example, combining with actual situation, the drainage discharge and concentration of nitrate nitrogen and total phosphorus were simulated by this model. The results show that the simulated drainage discharge accords with measured data approximately and Nash-Suttcliffe coefficient is 0.82, the simulated concentration of nitrate nitrogen and total phosphorus in farmland drainage was reasonable.

[Experimental research on migration characteristics of nitrogen and phosphorus in Qingtongxia irrigation district].

Taking the Qingtongxia irrigation district at the Yellow River upstream as an example, based on the monitor experiment material, this paper has analyzed the migration characteristics of nitrogen and phosphorus in the water conveyance system, the field system and the drainage system in the irrigations district. The results showed that, the concentrations of nitrogen and phosphorus showed increasing tendency in the water conveyance system and the increasing extent related to the channel substrate and content of nitrogen and phosphorus. In the field system, the fertilizer application process has a great influence on the concentration of nitrogen and phosphorus in farmland irrigation drainage and soil. During the crop growing period, nitrogen content in the soil above 60 cm changes greatly, total phosphorus content in the soil changes slightly correspondingly. In the drainage system, the concentrations of nitrogen and phosphorus showed decreasing tendency, from the end of farm ditch to outlet of agricultural drain, the concentration of ammonia nitrogen, nitrate nitrogen and total phosphorus in the agricultural drain decreased by 25%, 41% and 45% respectively. Affected by livestock and poultry breeding pollution and so on, the concentration of nitrogen showed increasing tendency in mainstay drainage ditch.

[Study on simulation of clarification for Vegetative Filter Strips by VFSMOD Model].

The functions and mechanism of Vegetative Filter Strips Model (VFSMOD) had been introduced in this paper, and the applicability and performance ability of this model have been tested by plot experiment data. The results show that the relative deviations between simulated values and measured values of outflow quantity are within +/- 15%, while with the concentration of SS, the relative deviations are within +/- 20%, and the determination coefficients between simulated values and measured values for outflow and SS are 0.995 and 0.889 respectively. Therefore, the simulation precision of this model is satisfactory, the model can be used as a tool for the design of VFS.

[Establishment and application of the estimation model for agricultural non-point source pollution in the field].

The quantitative research on pollution loads is the basis of control, evaluation and management of non-point source pollution. The estimation of agricultural non-point source pollution loads includes two steps: evaluation of water discharge and prediction of pollutant concentration in agricultural drain. Water discharge was calculated by DRAINMOD model based on the principle of water balance on farmland. Meanwhile, the synthesis of fertilization and irrigation is used as an impulse input to the farmland, the pollutant concentration changes in agricultural drain is looked as the response process corresponding to the impulse input, the complex migratory and transforming process of pollutant in soil are expressed implied by Inverse Gaussian Probability Density Function. Based on the above, the estimation model of agricultural non-point source pollution loads at field scale was constructed. Taking the typical experimentation area of Qingtongxia Irrigation District in Ningxia as an example, the loads of nitrate nitrogen and total phosphorus in paddy-field drain was simulated by this model. The results show that the simulated accorded with measured data approximately and Nash-Suttcliffe coefficient is 0.963 and 0.945 respectively.

[Continuously modeling research on the transfer and transform processes of phosphorus in Heihe River watershed].

Taking supply water source of Xi'an city as an example, by the help of Matlab software, using fill and yield model, the Inverse-Gauss flow concentration model, runoff-sediment relation model and Viney model, the transfer and transform processes of phosphorus from 1981 to 1990 were modeled continuously. Phosphorus pollution loads of Heihe River were also estimated. The result shows that the continuous modeling result accorded with the generic law of phosphorus loss. The relative error between modeling result and monitor interpolation result was not more than +/-30%. So the modeling method proposed in this paper could be used to model continuously the transfer and transform processes of phosphorus in Heihe river watershed. This study was only primary attempt to non-point source pollution continous model, therefore, the modeling method needed to be improved and perfected further.

[Runoff loss of soil mineral nitrogen and its relationship with grass coverage on Loess slope land].

In a simulated rainfall experiment on Loess slope land, this paper determined the rainfall, surface runoff and the effective depth of interaction (EDI) between rainfall and soil mineral nitrogen, and studied the effects of grass coverage on the EDI and the runoff loss of soil mineral nitrogen. The results showed that with the increase of EDI, soil nitrogen in deeper layers could be released into surface runoff through dissolution and desorption. The higher the grass coverage, the deeper the EDI was. Grass coverage promoted the interaction between surface runoff and surface soil. On the slope land with 60%, 80% and 100% of grass coverage, the mean content of runoff mineral nitrogen increased by 34.52%, 32.67% and 6.00%, while surface runoff decreased by 4.72%, 9.84% and 12.89%, and eroded sediment decreased by 83.55%, 87.11% and 89.01%, respectively, compared with bare slope land. The total runoff loss of soil mineral nitrogen on the lands with 60%, 80%, and 100% of grass coverage was 95.73%, 109.04%, and 84.05% of that on bare land, respectively. Grass cover had dual effects on the surface runoff of soil mineral nitrogen. On one hand, it enhanced the influx of soil mineral nitrogen to surface runoff, and on the other hand, it markedly decreased the runoff, resulting in the decrease of soil mineral nitrogen loss through runoff and sediment. These two distinct factors codetermined the total runoff loss of soil mineral nitrogen.