Beginning Of Rain Event Research Articles

Atmospheric deposition of organochlorine pesticides by precipitation in a coastal area.

Wet deposition fluxes of organochlorine pesticides (OCPs) were determined for rain samples collected in a coastal area of Turkey. Seventeen precipitation samples were collected over a 1-year period from 2008 to 2009. Rainwater was accumulated at the beginning of rain events using real time monitoring. Atmospheric concentrations were also measured in parallel with deposition samples. Both atmospheric concentrations and deposition fluxes were determined as particle and gas phases. The particle phase and dissolved phase deposition fluxes were 794.26 ± 756.70ngm-2day-1 and 800.77 ± 672.63ngm-2day-1, respectively. The washout ratios for OCP compounds were calculated separately for the particle and dissolved phases using the atmospheric concentrations and rain concentrations. The minimum washout ratio for the particle phase was 2339.47 for Endrin aldehyde, whereas the maximum washout ratio was 497593.34 for Methoxychlor. The maximum washout ratio for the dissolved phase was 247523.89 for Endosulfan beta, whereas the minimum washout ratio was 10169.69 for p,p'-DDT. The dry deposition velocities ranged from 0.01 to 1.67cms-1. The partitioning of wet deposition between the particle and dissolved phases was 50% in terms of total OCP deposition.

Dracaena marginata biofilter: design of growth substrate and treatment of stormwater runoff

ABSTRACTThe purpose of this research was to investigate the efficiency of Dracaena marginata planted biofilters to decontaminate urban runoff. A new biofilter growth substrate was prepared using low-cost and locally available materials such as red soil, fine sand, perlite, vermiculite, coco-peat and Sargassum biomass. The performance of biofilter substrate was compared with local garden soil based on physical and water quality parameters. Preliminary analyses indicated that biofilter substrate exhibited desirable characteristics such as low bulk density (1140 kg/m3), high water holding capacity (59.6%), air-filled porosity (7.82%) and hydraulic conductivity (965 mm/h). Four different biofilter assemblies, with vegetated and non-vegetated systems, were examined for several artificial rain events (un-spiked and metal-spiked). Results from un-spiked artificial rain events suggested that concentrations of most of the chemical components in effluent were highest at the beginning of rain events and thereafter subsided during the subsequent rain events. Biofilter growth substrate showed superior potential over garden soil to retain metal ions such as Al, Fe, Cu, Cr, Ni, Zn, Cd and Pb during metal-spiked rain events. Significant differences were also observed between non-vegetated and vegetated biofilter assemblies in runoff quality, with the latter producing better results.

Modelling the impact of retention-detention units on sewer surcharge and peak and annual runoff reduction.

Stormwater management using water sensitive urban design is expected to be part of future drainage systems. This paper aims to model the combination of local retention units, such as soakaways, with subsurface detention units. Soakaways are employed to reduce (by storage and infiltration) peak and volume stormwater runoff; however, large retention volumes are required for a significant peak reduction. Peak runoff can therefore be handled by combining detention units with soakaways. This paper models the impact of retrofitting retention-detention units for an existing urbanized catchment in Denmark. The impact of retrofitting a retention-detention unit of 3.3 m³/100 m² (volume/impervious area) was simulated for a small catchment in Copenhagen using MIKE URBAN. The retention-detention unit was shown to prevent flooding from the sewer for a 10-year rainfall event. Statistical analysis of continuous simulations covering 22 years showed that annual stormwater runoff was reduced by 68-87%, and that the retention volume was on average 53% full at the beginning of rain events. The effect of different retention-detention volume combinations was simulated, and results showed that allocating 20-40% of a soakaway volume to detention would significantly increase peak runoff reduction with a small reduction in the annual runoff.

Pilot-scale evaluation of green roofs with Sargassum biomass as an additive to improve runoff quality

Green roofs have the potential to be used as a pollutant-sink in urban environments. Unfortunately, until now no systematic study has been conducted to enhance the runoff quality from green roofs. The present work investigates the viability of using low-cost aggregates along with a biosorbent (Sargassum biomass) to prepare substrate mix for extensive green roofs to improve runoff quality. We have used (on a volume basis) 30% perlite, 20% vermiculite, 10% sand, 20% crushed brick, 10% coco-peat and 10% Sargassum biomass to prepare green roof substrate. The developed green roof substrate was found to have low bulk density (487kg/m3), high water retention capacity (58.5%), air filled porosity (19.5%), and hydraulic conductivity (4195mm/h). Through laboratory packed column study, we identified superior sorption capacity of green roof substrate towards various metal ions such as Al, Fe, Cr, Cu, Ni, Zn, Cd and Pb. Roof-top experiments in pilot-scale green roof assemblies with Portulaca grandiflora as vegetation were conducted for several artificial rain events (unspiked and metal-spiked). Results based on unspiked artificial rain events suggested that concentrations of most of the chemical components in runoff were highest during the beginning of rain events and thereafter subsided during the subsequent rain events. Metal-spiked artificial rain events revealed that green roofs acted as a sink for various metal ions and generated better runoff, whose quality was significantly less than fresh water standards. Green roofs also showed the potential to neutralize the acidic nature of inlet water and delay runoff generation. Significant differences were also observed between non-vegetated and vegetated green roof assemblies in runoff quality and quantity, with the latter producing better results.

Differences between coarse woody debris and leaf litter in the response of heterotrophic respiration to rainfall events

Heterotrophic respiration strongly influences carbon cycles at the ecosystem and global scales. We used an automated chamber system to measure the heterotrophic respiration of coarse woody debris (CWD) and leaf litter in a secondary broadleaved forest in southern Kyoto Prefecture. This system, which targeted only organic matter, could detect heterotrophic respiration responses to changes in environmental factors, especially rainfall events. The temporal trends and responses of respiration to environmental factors differed dramatically between CWD and leaf litter. CWD respiration showed a clear diurnal change corresponding to changes in CWD temperature and a clear decrease during rainfall events. Leaf litter respiration did not change clearly but increased at the beginning of rain events and returned to pre-rain rates when soil water content declined. The temporal patterns of the residuals between the observed respiration and baseline respiration, developed from the temperature–response curves under pre-rain conditions, differed between CWD and leaf litter respiration. The typical trend in CWD respiration response to rainfall events was a clear decrease and then gradual increase in the residuals after the event. The response of leaf litter respiration to wetting was an increase in the residuals during rainfall events and then a gradual decrease during drying. The difference in the responses of these respirations to wetting and drying processes are likely caused by differences in the physical characteristics of the CWD and the leaf litter layer. Measurements targeting only organic matter using an automated chamber system could detect the responses of heterotrophic respiration to environmental factors.

A field study to evaluate runoff quality from green roofs

Green (vegetated) roofs are emerging as practical strategies to improve the environmental quality of cities. However, the impact of green roofs on the storm water quality remains a topic of concern to city planners and environmental policy makers. This study investigated whether green roofs act as a source or a sink of various metals (Na, K, Ca, Mg, Al, Fe, Cu, Cd, Pb, Zn, Mn, Cr, Ni, Li and Co), inorganic anions ( NO 3 − , NO 2 − , PO 4 3 − , SO 4 2 − , Cl −, F − and Br −) and cation ( NH 4 + ). A series of green roof assemblies were constructed. Four different real rain events and several artificial rain events were considered for the study. Results showed that concentrations of most of the chemical components in runoff were highest during the beginning of rain events and subsided in the subsequent rain events. Some of the important components present in the runoff include Na, K, Ca, Mg, Li, Fe, Al, Cu, NO 3 − , PO 4 3 − and SO 4 2 − . However, the concentration of these chemical components in the roof runoff strongly depends on the nature of substrates used in the green roof and the volume of rain. Based on the USEPA standards for freshwater quality, we conclude that the green roof used in this study is reasonably effective except that the runoff contains significant amounts of NO 3 − and PO 4 3 − .

Chemistry of rain events in West Africa: evidence of dust and biogenic influence in convective systems

Abstract. This paper documents the chemical composition of 7 rain events associated with mesoscale convective systems sampled at the supersite of Banizoumbou, Niger, during the first special observation periods (June–July 2006) of the African Monsoon Multidisciplinary Analyses (AMMA) experiment. Time-resolved rain sampling was performed in order to discriminate the local dust scavenged at the beginning of rain event from the aerosol particles incorporated in the cloud at the end of the rain. The total elemental composition is dominated by Al, Si, Fe and Ca, indicating a high influence of dust and limited marine or anthropogenic contribution. After the aerosol wash-out, the elemental concentrations normalized to Al and the microscopic observations of diatoms, a tracer of the Bodélé depression, both indicate that the total elemental composition of rainwater is controlled by dust originating from North-eastern Saharan sources and probably incorporated in the convective cloud from the Harmattan layer. The low variability of the rain composition over the measurement period indicates a regional and temporal homogeneity of dust composition in the Harmattan layer. In the dissolved phase, the dominant anions are nitrate (NO3−), sulphate (SO42−) and chloride (Cl−). However, between June and July we observe an increasing contribution of the organic anions (formate, acetate, oxalate) associated with biogenic emissions to the total ion composition. These results confirm the large influence of biogenic emissions on the rain composition over Sahel during the wet season. The paper concludes on the capacity of mesoscale convective systems to carry simultaneously dust and biogenic compounds originating from different locations and depose them jointly. It also discusses the potential biogeochemical impact of such a phenomenon.

Hydrological and geochemical factors controlling the leaching of cemented MSWI air pollution control residues: A lysimeter field study

A pilot landfill (area, 16 m 2; depth 1.5 m) containing cement-stabilized air pollution control (APC) residues from municipal solid waste incinerators (MSWI) was investigated in order to determine the hydrological and geochemical factors that control the leaching process. Between May and August 1996, 3 rain events were investigated. Rainfall and discharge were monitored and leachate samples taken for the analysis of major components. It was found that water from the rain events took 2–3 days to pass through the lysimeter. Leachate dilution at the beginning of rain events indicated that rainwater passed through the lysimeter as preferential flow. The change in the concentration of leachate components with time was found to be almost identical for most components. Conductivity, dominated by Na + and OH −, also positively correlated with the concentrations of Al, Cs, K, Si, sulfate, chloride, carbonate and organic substances in the drainage discharge. The Ca concentrations were not influenced by the rain events, indicating that this component was leached by rainwater from the lysimeter cover layer. This was also found to apply to observed changes in Sr concentrations. Both conductivity and Sr were used as tracers for rainwater in the leachate and results agreed well. The solubility of the main constituents, Ca, Si, and Al could be explained by thermodynamic equilibrium with the solids calcium silicate hydrate, ettringite and possibly K-feldspar. The results indicate that the leaching process (within the first 5 years) is dominated by pore waters between the cement blocks that are in equilibrium with the cement-stabilized APC residues (thus explaining the constant composition of the leachate) and is flushed out by rain events.

Behavior of Heavy Metals, Nutrients, and Major Components during Roof Runoff Infiltration

The behavior of heavy metals (Cd, Cu, Zn, Cr, Pb), nutrients (organic C, P, and N parameters), and major ions was investigated during percolation of roof runoff water through an artificial infiltration site. The concentrations of the various components were determined in rainwater, roof runoff, and infiltrating water at various depths in the soil. The concentrations of most parameters in roof runoff were highest during the “first flush” at the beginning of rain events. Despite rapid infiltration caused by strong preferential flow, differences were still observed in infiltration behavior between individual compounds. Cl-, NO3-, SO42-, ortho-phosphate, and the major part of DOC behaved essentially conservatively during infiltration, whereas NH4+ concentration decreased probably as a consequence of nitrification. The concentrations of Ca, Mg, Na, K, and alkalinity were regulated by dissolution of soil material. The change in concentrations of Cu, Cd, and Cr during infiltration was mostly due to the concentra...