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1

Experimental and numerical investigation on runoff reduction and water stress of green roofs with varying soil depth and saturated water content under dry–wet cycles

Ma Ming, Wang Jun, Garg Ankit, Mei Guoxiong

Acta Geophysica

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2023

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Vol. 71, no. 2

893--903

EN

The soil layer is the most important structure for green roof runoff reduction and vegetation growth. The mechanisms of runoff reduction and water content of green roofs with varying soil depth and saturated water content (θs) under dry–wet cycles are not well understood. Field and numerical methodologies were adopted for investigation in this study. The green roof drainage and water content were observed for a given period (i.e., August 2020 to July 2021). A numerical model was calibrated and validated for the analysis of annual runoff reduction and water stress with different θs and soil depths. Based on climate in southern China, the green roof's annual runoff reduction rate (ARR) (100 mm soil) was 33%, and the annual water stress was 168 days. With an increase in θs by 0.1 mm3 /mm3 , the ARR of green roofs increased by an average of 5% while the water stress was reduced by an average of 32 days. With an increase in soil depth by 100 mm, the average ARR increased by 4%, whereas the average water stress was reduced by 6 days. It was shown that the runoff reduction is enhanced with an increasing θs and soil depth during a longer antecedent dry weather period, but it had no significant effect on runoff reduction during back-to-back rainfall events. Increasing soil depth had no significant improvement in runoff reduction and water stress beyond a certain point. Consequently, the optimal structural configuration of green roofs was considered as a soil depth of 200 mm (θs of 0.5 mm3 /mm3 ).

2

Moisture management in biochar amended green roofs planted with Ophiopogon japonicus under different irrigation schemes: an integrated experimental and modeling approach

Liu Jiaqin, Garg Ankit, Wang Hao, Huang Shan, Mei Guoxiong

Acta Geophysica

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2022

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Vol. 70, no 1

373--384

EN

Green roof constantly suffers from the water stress that is developed during prolonged drought seasons. In general, periodical irrigation is required to ensure plant growth and hence serviceability of green roofs. Biochar, a carbon sink material, has been proposed as a substrate amendment in green roofs for enhancing water retention ability of soils. This study aims to conduct an assessment of the irrigation efficiency of green roofs with different biochar additions (0%, 5%, 10%, 15% and 20%; v/v) under sub-tropical climatic conditions. In order to achieve this objective, outdoor monitoring as well as numerical modeling using HYDRUS-1D was conducted. Soil columns mixed with different proportion of biochar were prepared. These columns were subjected to different irrigation schemes (three irrigation frequencies were assessed (i.e., per 3, 7 and 10 days after irrigation or rainfall); moreover, three irrigation amounts for the three irrigation frequencies were considered (i.e., to a fixed amount (FA10mm), to Field water holding capacity (FC) and to Saturated moisture content (SR))). As suggested from the results: (1) Biochar significantly improved water holding capacity and plant available water. 20% biochar delayed the onset of the significant plant wilting phenomenon by approximately 3 days and maintained the maximal transpiration rate of vegetation in the dry period. (2) As compared to irrigation scheme A (irrigation to FC per 7 days), the efficiency of scheme B (irrigation to SR per 10 days) was more vulnerable to the biochar amendment. Moreover, the total irrigation water and days of water stress decreased with an increase in the biochar addition. Furthermore, the combination of 20% biochar and irrigation scheme B could be the optimal choice for maintaining the health of the green roofs and water conservation. The present study helps to obtain desired outcomes in green roofs, e.g., stormwater management, cost reduction as well as providing greening.

3

Estimation of unsaturated hydraulic conductivity function: implication of low to high suction measurements

Saha Abhisekh, Sekharan Sreedeep

Acta Geophysica

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2021

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Vol. 69, no. 2

547--559

EN

Establishment of the relationship between soil suction and water content, commonly termed as soil–water characteristic curve (SWCC), is of prime importance in the feld of unsaturated soil mechanics. There are several instruments available that can be used to measure the SWCC of soil, but every suction measuring device has its own limitations in terms of its suction measurement range. Therefore, the preciseness of the estimated unsaturated soil properties largely depends on the range of suction measurements and the type of instruments used. The primary objective of this study is to quantify the error that can occur during the estimation of unsaturated hydraulic conductivity function (UHCF) from SWCC for low plastic soils. Experiments were performed to investigate the infuence of diferent suction measurement devices on the estimated UHCF for four diferent soils with varying clay content. A dew point potentiometer (WP4) and a miniature tensiometer (T5) have been used in this study for the suction measurement. The SWCC of the selected soils were predicted mathematically using a commonly used pedo-transfer function (PTF). The experimental results clearly indicated that the sole use of WP4 overestimated the SWCC parameters, as well as UHCF (overestimation in the conductivity value is in order of 104 times). Rather, a combination of T5 and WP4 data, within their accurate range, provides a more precise estimation of UHCF. Further, the accuracy of the PTF was found very efective for low plastic soils with a relatively low percentage of clay (% clay < 10), in the absence of any experimental data.

4

Nitrogen Transportation and Transformation Under Different Soil Water and Salinity Conditions

Zeng W. Z., Ma T., Huang J. S., Wu J. W.

Ecological Chemistry and Engineering. S

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2016

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Vol. 23, nr 4

677--693

EN

Soil nitrogen transportation and transformation are important processes for crop growth and environmental protection, and they are influenced by various environmental factors and human interventions. This study aims to determine the effects of irrigation and soil salinity levels on nitrogen transportation and transformation using two types of experiments: column and incubation. The HYDRUS-1D model and an empirical model were used to simulate the nitrogen transportation and transformation processes. HYDRUS-1D performed well in the simulation of nitrogen transportation and transformation under irrigated conditions (R2 as high as 0.944 and 0.763 for ammonium and nitrate-nitrogen simulations, respectively). In addition, the empirical model was able to attain accurate estimations for ammonium (R2 = 0.512-0.977) and nitrate-nitrogen (R2 = 0.410-0.679) without irrigation. The modelling results indicated that saline soil reduced the rate of urea hydrolysis to ammonium, promoted the longitudinal dispersity of nitrogen and enhanced the adsorption of ammonium-nitrogen. Furthermore, the effects of soil salinity on the nitrification rate were not obviously comparable to the effects of the amount of irrigation water. Without irrigation, the hydrolysis rate of urea to ammonium decreased exponentially with the soil salinity (R2 = 0.787), although the nitrification coefficient varied with salinity. However, the denitrification coefficient increased linearly with salinity (R2 = 0.499).

5

Effects of different irrigation strategies on soil water, salt, and nitrate nitrogen transport

Xu C., Zeng W. Z., Wu J. W., Huang J. S.

Ecological Chemistry and Engineering. S

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2015

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Vol. 22, nr 4

589--609

EN

Intermittent irrigation has attracted much attention as a water-saving technology in arid and semi-arid regions. For understanding the effect of intermittent irrigation on water and solute storage varied from irrigation amount per time (IRA), irrigation application frequency (IRAF), irrigation intervals (IRI) and even soil texture (ST), intermittent irrigation experiment was carried out in 33 micro-plots in Inner Mongolia, China. The experiment results were used for the calibration and validation of HYDRUS-1D software. Then 3 ST (silty clay loam, silty loam, and silty clay), 5 IRA (2, 4, 6, 8, and 10 cm), 4 IRAF (2, 3, 4, and 5 times) and 4 IRI (1, 2, 3, and 4 days) were combined and total 240 scenarios were simulated by HYDRUS-1D. Analysis of variance (ANVOA) of simulated results indicated that ST, IRA, and IRAF had significant effect on salt and nitrate nitrogen (NO3−-N) storage of 0-40 cm depth soil in intermittent irrigation while only ST affected soil water storage obviously. Furthermore, salt leaching percentage (SLP) and water use efficiency (WUE) of 0-40 cm depth were calculated and statistical prediction models for SLP were established based on the ANOVA using multiple regression analysis in each soil texture. Then constraint conditions of soil water storage (around field capacity), salt storage (smaller than 168 mg·cm−2), WUE (as large as possible) in 0-40 cm depth and total irrigation water amount (less than 25 cm) were proposed to find out the optimal intermittent irrigation strategies. Before sowing, the optimal irrigation strategy for silty clay loam soil was 6 cm IRA, 3 times IRAF, and 2 days IRI respectively. For silty loam and silty clay soils, IRA, IRAF, and IRI were 8 cm, 3 times, and 2 days respectively.

PL

Nawadnianie przerywane zwraca uwagę jako technologia oszczędnego użycia wody w regionach suchych i półpustynnych. Dla zrozumienia wpływu parametrów nawadniania przerywanego, takich jak czas (IRA), częstotliwości stosowania nawadniania (IRAF), odstępy czasu nawadniania (IRI), a także struktury gleby (ST) na magazynowanie wody i substancji rozpuszczonych, przeprowadzono eksperyment przerywanego nawadniania na 33 mikropoletkach w Mongolii Wewnętrznej, w Chinach. Wyniki doświadczeń użyto do kalibracji i walidacji oprogramowania HYDRUS-1D. Następnie 3 ST (mulisty piasek gliniasty, muliste iły i gliny pylaste), 5 IRA (2, 4, 6, 8 i 10 cm), 4 IRAF (2, 3, 4 i 5 razy) i 4 IRI (1, 2, 3 i 4 dni) połączono ogółem w 240 scenariuszy symulowanych przez HYDRUS-1D. Analiza wariancji (ANVOA) symulowanych wyników wykazała, że ST, IRA i IRAF miały znaczący wpływ na sól i azot azotanowy (NO3–-N), składowane na głębokości 0-40 cm gleby w nawadnianiu przerywanym, podczas gdy ST wpływał tylko na magazynowanie wody w glebie. Ponadto, procentowe ługowanie soli (SLP) i efektywność wykorzystania wody (WUE) zostały obliczone dla głębokości 0-40 cm i statystyczne modele predykcyjne dla SLP zostały ustalone na podstawie analizy wariancji i za pomocą analizy regresji wielokrotnej w każdej strukturze gleby. Aby określić optymalną strategię sporadycznego nawadniania, zaproponowano ograniczenie warunków magazynowania wody w glebie (około pojemności polowej), magazynowania soli (mniejsze niż 168 mg · cm–2), WUE (jak największa) w 0-40 cm głębokości i całkowitej ilości wody do nawadniania (mniej niż 25 cm). Przed siewem optymalna strategia nawadniania gleb mulistych gliniastych zakładała odpowiednio 6 cm IRA, 3 razy IRAF i 2 dni IRI. Dla gliny pylastej i ilastych gleb gliniastych założono IRA, IRAF i IRI odpowiednio 8 cm, 3 razy i 2 dni.