Valuation of ecosystem services in South Africa, 2001–2019

Please read abstract in the article.The Department of Environmental Affairs (South Africa) and the joint National Research Foundation (NRF) of South Africa and the National Natural Science Foundation of China (NSFC).https://www.mdpi.com/journal/sustainabilityam2022Agricultural Economics, Extension and Rural Developmen

Surfactant and irrigation effects on wettable soils: runoff, erosion, and water retention responses

Surfactants are chemical compounds that change the contact angle of water on solid surfaces and are commonly used to increase infiltration into hydrophobic soil. Since production fields with water-repellent soil often contain areas of wettable soil, surfactants applied to such fields will likely be applied to wettable soil, with unknown consequences for irrigation-induced erosion, runoff, or soil water relations. We evaluated surfactant and simulated sprinkler irrigation effects on these responses for three wettable, Pacific Northwest soils, Latahco and Rad silt loams and Quincy sandy loam. We studied three surfactants: an alkyl polyglycoside in solution at a concentration of 18 g a.i./kg, a block copolymer at 26 g/kg, and a blend of the two at 43 g/kg. From 2005 to 2009 in the laboratory, each surfactant was sprayed at a rate of 46.8 L/ha onto each soil packed by tamping into 1.2- by 1.5-m steel boxes. Thereafter, each treated soil was irrigated twice at 88 mm/h with surfactant–free, well water. Runoff and sediment loss were measured for each irrigation and soil samples were collected after each irrigation. While measured properties differed among soils and irrigations, surfactants had no effect on runoff, sediment loss, splash loss, time to runoff, or tension infiltration, compared to controls. Across all soils, however, the alkyl polyglycoside increased volumetric water contents by about 3% (significant at P less than or equal to 0.08) at matric potentials from 0 to -20 kPa, compared to controls. With a decrease in the liquid-solid contact angle on treated soil surfaces, surfactant–free water appeared able to enter, and be retained in pores with diameters greater than or equal to 15 mm. All in all, surfactants applied at economic rates to these wettable Pacific Northwest soils posed little risk of increasing either runoff or erosion or harming soil water relations. Moreover, by increasing water retention at high potentials, surfactants applied to wettable soils may allow water containing pesticides or other agricultural chemicals to better penetrate soil pores, thereby increasing the efficacy of the co-applied materials

On the use of surrogate-based modeling for the numerical analysis of Low Impact Development techniques

Mechanistic models have proven to be accurate tools for the numerical analysis of the hydraulic behavior of Low Impact Development (LIDs) techniques. However, their widespread adoption has been limited by their computational cost. In this view, surrogate modeling is focused on developing and using a computationally inexpensive surrogate of the original model. While having been previously applied to various water-related and environmental modeling problems, no studies have used surrogate models for the analysis of LIDs. The aim of this research thus was to investigate the benefit of surrogate-based modeling in the numerical analysis of LIDs. The kriging technique was used to approximate the deterministic response of the widely used mechanistic model HYDRUS-2D, which was employed to simulate the variably-saturated hydraulic behavior of a contained stormwater filter. The Nash-Sutcliffe efficiency (NSE) index was used to compare the simulated and measured outflows and as the variable of interest for the construction of the response surface. The validated kriging model was first used to carry out a Global Sensitivity Analysis of the unknown soil hydraulic parameters of the filter layer, revealing that only the shape parameter α and the saturated hydraulic conductivity Ks significantly affected the model response. Next, the Particle Swarm Optimization algorithm was used to estimate their values. The NSE value of 0.85 indicated a good accuracy of estimated parameters. Finally, the calibrated model was validated against an independent set of measured outflows with a NSE value of 0.8, which again corroborated the reliability of the surrogate-based optimized parameters

Effect of Interstitial Velocity on the Adsorption of Bacteria onto Soil

The adsorption of bacteria onto soil is affected by the physical and chemical characteristics of the soil and water, the size and morphology of the bacterial cells, and the water-flow characteristics in the soil. The present study focuses on the latter factor by investigating the effect of the interstitial velocity on the adsorption of bacteria onto soil. Columns of 10 cm diameter and 130 cm height, respectively, were packed with a sandy soil. The columns were saturated with water containing nalidixic acid-resistant Escherichia coli as a bio-tracer at three different pH levels. The columns were maintained at 20°C for 24 h before connecting the column outlet to its inlet by a pump in a closed loop. Water containing the biotracer was re-circulated through the column for another 24 h at three different interstitial velocities. Water samples were taken from a sampling tap connected to the pump at 4-h intervals. These samples were analyzed to determine the biotracer concentration. The results show that more biotracer cells were retained in the soil at the lower interstitial velocity. The higher interstitial velocity resulted in higher shear forces which caused more desorption of the biotracer cells from the surfaces of the soil particles. Bacterial adsorption was higher at the acidic pH value. The survival of the biotracer cells in soil solution was also tested at three different pH levels. The results show that no decline in the biotracer concentration occurred during the test period

Urban Rainfall Harvesting to Alleviate Water Shortages and Combat Desertification in the Arid Land of Jordan

Abstract: Water harvesting can alleviate the chronic water supply shortages in Jordan, increase cropping land area, improve the livelihood of population and eventually combat desertification. A systematic study was undertaken to evaluate the use of rooftop rainfall harvesting in urban areas, study the socioeconomic value, determine the optimum rainfall collection tank volume and the potential contribution of rainfall harvesting to the national domestic water supply budget. The potential water supply volume from rooftop rainfall harvesting can reach 14.7 million m 3 /year, comprising of about 6% of the domestic national water supply. Analysis of domestic water supply rate in relation to average rainfall depth and number of cisterns in each governorates indicated that the public water supply rate decreased in governorates with high rainfall depth and large number of cisterns. Cistern number among governorates increased with rainfall depth indicating a good adaptation behavior to water shortages. Optimum cistern volume charts were constructed for some governorates as a function of family consumption rate and house roof area. These charts can be used as tool to determine the optimum rainfall cistern volume as related to consumption rate and rooftop area. An immediate and nationwide awareness and legislative program is needed to spread rooftop rainfall harvesting among the whole population of Jordan and region with similar climates

Field evaluation of sand-ditch water harvesting technique in Jordan

Water harvesting is viable alternatives for rainfed agricultural production in semiarid lands. A field experiment was conducted to evaluate the efficiency of a relatively new water harvesting technique, called sand ditch, for moisture and soil conservation. Twelve field plots of 10 m x 2 m were constructed in two adjacent fields having silt loam soils but varied in soil depth, 0.75 m and 2 m, and slope of 10% and 12%. A 130 L barrel was installed at the downslope end of the plots to collect water and sediments at the end of each rainstorm along the rainy season. Three types of treatments were used in duplicates (12 plots in total); sand-ditch plots in which a ditch of 2-m long, 1 m wide and 0.8 m deep was constructed in the middle of plots across the slope (2 in each field), two compacted plots and two plots covered with plastic mulch in addition to four control plots, 2 in each field. The total amount of runoff, sediment concentration, total infiltration and sediment loss for the experimental plots were measured or calculated after each storm during the winter season 2004/2005. Experimental results showed that sand-ditch technique significantly reduced runoff and sediment loss and increased infiltration and soil moisture compared to control or compacted plots. The overall average runoff and sediment reductions in the sand-ditch plots were 46% and 61% compared to control plots. Sediment losses from compacted plots were about 2.2 and 6 folds higher than control and sand-ditch plots, respectively making soil compaction unsuitable technique for rainfall harvesting under the current experimental and climatic conditions. Construction of sand ditch also increased the dry matter yield of native grass by an average of 62% and 40% in the two experimental fields compared to control.Runoff Soil loss Rainfall harvesting Soil moisture Semi-arid land