Water quality impacts of young green roofs in a tropical city: a case study from Singapore

This study examined the effects of two substrates (SOIL and COMMERCIAL) and grass on the green roof runoff quality in Singapore. Ten events were sampled over a 9-month period. Rainfall and green roof runoff from grass and bare experimental configurations were tested for total organic carbon (TOC), nitrogen and phosphorus nutrients (N, NH4+-N and PO43−-P), cations/anions and trace metals (Fe, Cu, Zn, Cd and Pb). All configuration units neutralised acid rainfall and removed metals except Fe despite their proximity to an industrial area. Concentrations decrease over the monitoring period for most water quality variables. The COMMERCIAL (COM) configurations elevated Cl− (3.8–10.8 ppm), SO42− (1.5–32.4 ppm), NO3−-N (7.8–75.6 ppm) and NH4+-N (22.0–53.1 ppm) concentrations in the runoff. Concentrations of NO3−-N (4.5–67.7 ppm) and NH4+-N (14.7–53.0 ppm) remained high at the end of the monitoring period for the COMgrass configuration, even with dilution from monsoon rainfall, making it suitable as an irrigation water source and a fertiliser substitute. The SOIL substrate retained N-nutrients, TOC and trace metals with concentrations comparable or below rainfall inputs. This substrate is suitable for widespread green roof applications in Singapore and other tropical cities. We recommend substrate testing before their approval for use on green roofs and encourage the long-term monitoring of these systems.

Release of Heavy Metals and Metalloids from Two Contaminated Soils to Surface Runoff in Southern China: A Simulated-Rainfall Experiment

The release of heavy metals and metalloids (HMs), including Pb, Zn, Cd, As, and Cu, from two typical contaminated soils with different properties, namely red soil and limestone-dominated soil, was characterized through simulated-rainfall experiments in order to investigate the effects of soil properties on HM release. Significant differences in the HM concentrations between the two soils resulted in various concentrations of dissolved and particulate HMs in the runoff. Differences in the dissolved HM concentrations in the runoff were inconsistent with the HM concentrations in the soils, which is attributed to the variable solubilities of HMs in the two soils. However, the HM enrichment ratios were not significantly different. The strong correlation between dissolved organic carbon and dissolved HMs in the runoff, and between the total organic carbon and particulate HMs in sediments, were observed, especially in the limestone-dominated soil. The specific surface area and HM concentrations in sediments were weakly correlated. Acid-rainfall experiments showed that only the limestone-dominated soil buffered the effects of acid rain on the runoff; the concentrations of dissolved Pb, Zn, Cd, and Cu increased in the red soil under acid rainfall and were 60, 29, 25, and 19 times higher, respectively, than under the neutral conditions. The results contribute to the understanding of HM behavior in the two typical soils in southern China, exposed to frequent storms that are often dominated by acid rainfall.

Corrosion of Concrete Using Portland Composite Cement and Rice Husk Ash under Simulated Acid Rain Environment

Cement production, which results in higher CO2 levels, has a negative impact on environment. This phenomenon has caused the emergence of a new type of environmentally friendly cement, such as Portland Composite Cement (PCC). On the other hand, rainfall becomes high acidity level. This will be an issue in the construction of concrete, which causes concrete deterioration if value of pH is below 6. The purpose of this study is to investigate corrosion caused by acid rainfall when used PCC cement mixed with RHA. RHA replacement level of 5%, by weight of cement was used in this study. The compressive strength design was 30 MPa. The simulated acid rain solution was prepared by mixing solution of H2SO4 and HNO3 to reach value pH of 4. The deterioration was measured by the number of corrosion product using SEM test. The results indicate a decrease in the number of component corrosion that occurs by using ASP.

Laboratory assay of aluminium transport through intact soil sample under controlled conditions

Aluminium (Al) mobilisation in the forest soils is a serious problem due to the soil acidification. The rate and magnitude of leaching of Al and other elements and compounds from soils can be examined by means of percolation experiments. Aluminium elutriation was studied under laboratory conditions using undisturbed samples of forest topsoil from the Paličník area in the Jizera Mountains (Czech Republic), which originated under two different vegetation covers: European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Ponding infiltration was performed using three subsequently applied solutions. KCl solution was used to simulate the soil solution. Solutions with sulphates and nitrates addition (of two different pH values) were used to simulate acid rainfall. Passing liquid phase was analysed with respect to Al content and aluminium speciation. Differences were found in Al content and transport between different soils under spruce and beech covers. The soil sample under the spruce forest (SF sample) had a higher initial Al content than the soil sample under the beech forest (BF sample). As a result, the aluminium leaching from the spruce soil sample and the final content of water-extractable Al in the soil (Al content after the leaching experiment) were higher compared to the beech soil sample. This suggests that Al mobility and potential toxicity in the beech forest are grater than those in the spruce monoculture when studied in the acidification endangered areas.

Experimental Modelling of the Radionuclides Diffusion Process in Uranifer Tailing Dum

Generally, the uranifer tailings dump are not protected. During the time appear chemical and physical modifications which favour spreading of the radioactive contaminant into the environment, because of the waters provided from precipitations with pH variation (acid rainfall, snow), solar radiance, variation of temperature and humidity, interaction of different minerals from the waste rock with infiltration water during the flow, leading to precipitations phenomenon, ionic exchange, adsorption and re-dissolving [2]. As a rule, the speed of radionuclides diffusion from radioactive tailings dump depends on each of these factors and is very specific to the hydro and geochemistry of the nearest rocks [7]. Because of that, the scientific research is very difficult and will obliges us to study through the simplified physical systems but maintaining the important parameters which are influencing the diffusion process of the contaminant in the environment. The main objective of this paper is to characterize hydro and geochemistry properties controlling the migration of radionuclides extracted from tailings dump into the environment, including the processes of sorption and adsorption and neglecting other physical processes as precipitation, ion exchange or some other geochemical interactions within the system. For this purpose we made studies on 226Ra and Unat extraction from uranifer tailings dump analyzed in pure water in dynamic system, studies about the influence of clay presence on speed of diffusion process in sorption and adsorption phenomenon. Finally we made a prediction for long term about variation of concentrations of 226Ra and Unat based on experimental data using some software programs from literature [8].

Nutrient leaching from Acerrubrum leaves by experimental acid rainfall

Freshly collected Acerrubrum L. leaves from a regenerating forest stand at the Coweeta Hydrologic Laboratory, North Carolina, were washed with experimental acid rainfall (pH 4.6). Nutrient leaching rates from undamaged leaves were significant for SO42−, K+, Ca2+, and Mg2+, whereas NO3−-N was absorbed from rainfall. Significantly greater leaching of SO42−, K+, Ca2+, and Mg2+, and significantly greater absorption of NO3−-N and NH4+-N, occurred in artificially damaged leaves than in undamaged leaves. Comparisons between leaching transfers and foliar nutrient pools showed that base cation (K+, Ca2+, and Mg2+) leaching losses account for up to 25% of foliar pools, whereas absorption of NO3−-N and NH4+-N from precipitation can increase total foliar N by almost 2%. Projected growing season cation leaching losses (expressed as a percentage of foliar pools) from damaged leaves were in agreement with previously reported whole-canopy leaching fluxes based on analysis of throughfall at the field site. These results suggest that nutrient leaching losses from young, rapidly growing tree leaves are lower than previously published leaching fluxes for more mature forest stands.