At the time of this study, the trees in the control and treatment bioswales were fully established and approaching mature size. Measurements recorded the differences in surface runoff dynamics and pollutant reduction rates, as well as tree and shrub growth. This study provides new information on the long-term effectiveness of engineered bioswales in a region with a Mediterranean climate. The water collection system was installed in 2007 to collect composited samples from natural runoff . In this study, surface runoff samples from the control site were collected at a high frequency using grab samples to better observe pollutant concentration dynamics for each experiment throughout a storm hydrograph. A test run was conducted on 10 October 2013 to determine the optimal runoff sampling time intervals and the number of samples needed to capture the peak and total loadings. For the test run, the water soluble fertilizer was applied to both of the sites at a rate of 2.24 g m−2 . Grab samples were collected at a 10-min frequency over a two hour irrigation period from the control site. Water samples were collected immediately before the runoff was directed to the underground tank.
The water samples were coarse filtered during sample collection with coffee filters to remove large tree leaves,square plant pots grass clippings and large soil particles. Based on the results of the test run, the water sampling frequency for subsequent trials was extended to six hours with a variable sampling interval to better characterize the runoff pollutant pattern. The composite water sample from the treatment site was used for calculating the total loading of the treatment site where little surface runoff occurred in this study. A 5.1 cm diameter and 0.9 m long PVC drainage pipe was vertically installed into the middle of the treatment bioswale to collect a representative water sample for monitoring pollutants concentration dynamics in the bioswale. The treatment site water samples were not affected by successive flow from the control site because the treatment site was located upslope of the control site. The water sample collected from the control site was surface runoff, which was not affected by subsurface flow of the treatment site because of the site’s relatively flat surface. The pH ranged from 7.90 to 8.24 for the control site and 8.07 to 8.20 for the treatment site. The relatively high pH values indicate that alkalinity was not elevated by the ESM used in this bioswale. The high pH and alkalinity results from the relatively poor quality of the irrigation water originating from groundwater. The groundwater sources are from marine sedimentary rocks of the Coastal Range, which have high salt and carbonate levels.
The irrigation water supply had an average pH value of 8.79, and its hardness was as high as 890 ppm. Another factor that contributed to the accumulation of salts in the soil was the 2013–2014 drought, which resulted in very little soil leaching in the year prior to this study . Without leaching from winter precipitation, the salts accumulated in the surface soil layer. The cations were mainly Na+ , Ca2+, and Mg2+, and the anions were mainly Cl−, SO4 2−, and HCO3 −. Concentrations of these major cations and anions did not show significant variation from sample to sample, indicating that their dominant source is the irrigation water. The high TIC in all water samples reflects the high carbonate concentrations of the groundwater used for irrigation. On average, the bioswale with ESM reduced pollutants carried in surface runoff by more than 99.5%. The average pollutant loading reduction rate was 99.6% , 99.5% , and 99.4% for the LPL, MPL, and HPL experiments, respectively . This treatment bioswale had slightly higher pollutant reduction rates as compared to the bioswale with ESM installed adjacent to a parking lot in a previous study. The parking lot bioswale reduced the nutrients by 95.3% and organic carbon by 95.5%. The peak pollutant concentration reduction rates found in this study were a minimum of 53% higher than those reported in the parking lot study. One possible explanation for this difference is that the trees and shrubs in the bioswale were more extensive and older than the tree in the parking lot site. Tree and shrub roots can function as a biofilter, where pollutants are immobilized, transformed, or degraded.
Although data were not available for below ground biomass, a more extensive rooting system and associated microorganisms in this study’s bioswale could be partially responsible for its improved performance. Another possible explanation is the difference in pollutant inflows. The primary pollutant source in the parking lot study was from atmospheric deposition, with lower concentrations when compared to the fertilizer rates applied in this study. Storm water BMPs, such as bioswales, are reported to have higher removal rates when treating storm water with high inflow concentrations. Concentration of Zn, Cd, Ni, Cu, and Pb are key water quality concern parameters. They were excluded from this analysis because their concentrations were below detection levels in the irrigation source waters and these metals are not identified as impairments in the study area.The interpretation of results from this study is subject to some limitations. Pollutants can leave the system via infiltration deeper into the soil and potentially enter the groundwater. Deep leaching can be an important flow path affecting the fate of pollutants, and was not included in the scope of this study. Caution should be taken regarding the potential for groundwater contamination when considering the use of ESM in bioswale projects. In this experiment, the trees were eight years old and their root systems were well established. Trees received excess surface irrigation runoff during the hot/dry summer. Because the ESM in this study was 75% lava rock it may not retain enough moisture for tree roots during long dry periods. Trees in bioswales with ESM may require more irrigation than trees in native soils, especially for establishment. In this study, the pollutants were artificially added to the system by using dissolved fertilizer. Actual storm runoff includes pollutants from atmospheric deposition and has a more complex mixture of pollutants. These factors introduce uncertainty in extrapolating the pollutant reduction efficiency of the bioswale to other sites. It is unclear whether all of the pollutants retained by the bioswale were fully retained by the vegetation and soil, or if a portion of these pollutants were only temporarily immobilized in the system by the soil-tree root system. The bioswale system tested in this study was eight years old, relatively young when compared to its 20 to 30 year life expectancy. Long-term monitoring of system performance is needed to document bioswale performance over longer time periods typical of urban green infrastructure. Additional research is needed that follows the fate and transport of pollutants after infiltration. In particular, chemical analyses of soil and tree samples are needed to understand the fate and transport of the pollutants in the bioswale system. The length of lifespan of a particular normal cell of any organism is predetermined.
Similarly, the length of lifespan of all organisms is pre-determined by their genetic makeup and their external and internal environments and diet-related factors specific to an organism. Therefore, the length of lifespan can be increased or decreased by manipulating the environment, diet and genetic factors only by small extent. The length of lifespan of the organisms can also be impacted by differential rates of senescence of cells and organs that ultimately lead to the death of the organisms. The differential rates of cellular senescence are influenced by several confounding factors,plastic potting pots such as external and internal environments, diet and genetic factors. Because of these confounding factors that can impact rates of progression of degenerative changes in the organs, it is almost impossible to study aging in the absence of organ pathology. Based on numerous studies on aging in vertebrates and invertebrates, a recent informative review has suggested that oxidative stress theory of aging can only be applied to conditions in which age associated pathologies are included. Furthermore, it was suggested that in environment with minimal stress, oxidative damage plays little role in aging. This suggestion can be argued on the fact that little oxidative damage may take longer time to deregulate protective transcription factors, adaptive responses to stressors, and repair mechanisms, and thereby extending the lifespan of the organisms more than that produced by higher oxidative damage which can deregulate above biological functions in shorter time. Using vertebrate and invertebrate models, some major biochemical and genetic factors that are associated with aging processes have been identified. They include increased oxidative stress and chronic inflammation, decreased adaptive response to stressors, post-translational protein modifications, mitochondrial dysfunction, decreased of proteasome and lysosomal-mediated proteolytic activity, shortening of telomeres and transcriptional deregulation. Among these, the theory of oxidative stress is most extensively investigated in various experimental models, using pharmacological agents, antioxidants, anti-inflammatory agents and deletion of one or more antioxidant enzymes as well as of mitochondrial complexes. Depending upon the experimental models, experimental designs, and substrate used to assay oxidative stress and criteria of oxidative stress, the role of oxidative stress in aging has been substantiated or questioned. We hypothesized that increased oxidative stress may be one of the primary early events that causes chronic inflammation, transcriptional deregulation, post-translational protein modifications, mitochondrial dysfunction, decreased of proteasome and lysosomal-mediated proteolytic activity and shortening of telomeres. Invertebrate models, such as Caenorhabditis elegans has been extensively used to evaluate the role of oxidative stress in aging primarily due to shorter lifespan of about 3 days and ease of genetic manipulation. This review analyzes recent published studies on C. elegans on the role of oxidative stress in determining the length of lifespan by generating mutants that show suppression of mitochondrial function or lack of superoxide dismutase .
Caenorhabditis elegans has been extensively used to investigate the role of oxidative stress in aging by measuring the length of lifespan. Mitochondria are considered the major sites for the production Reactive oxygen species , although ROS are also produced outside the mitochondria. In order to demonstrate the impact of oxidative stress, several mutants of C. elegans were generated. They include mutations in four clock genes , mutation in the iron sulfur protein of mitochondrial complex III, mutation in the gene NUO-6 and mutation in the gene daf-2. The effects of mutations on oxidative stress and lifespan are summarized in Table 1. The clk-1 gene encodes an enzyme that is necessary for the biosynthesis of ubiquinone that is required by the mitochondria to generate energy. Mutation in the clk-1 gene increases the life span by slowing down mitochondrial activity due to reduced availability of ubiquinone. This slowing of the electron transport chain would reduce oxidative stress. The role of reduced oxidative stress in extending the lifespan is further supported by the fact that overexpression of clk-1 gene in wild-type C. elegans increased mitochondrial activity and shortened the lifespan. A mutation in the iron sulfur protein of mitochondrial complex III causes low oxygen consumption, reduced oxidative stress and increased lifespan. Mutation in the daf-2 gene which codes for a member of insulin receptor family increased lifespan and enhanced resistance to oxidative stress. In this daf-2 mutant, expression of the SOD-3 gene, which encodes mitochondrial Mn-superoxide dismutase, was much higher than in the wild type. This implies that the increased levels of SOD-3 in the daf-2 mutant reduced oxidative stress and thereby increased lifespan. Mutation in the gene NUO-6 which encodes complex I of mitochondria increases life span of C. elegans by decreasing the mitochondrial function. Mutation in the age-1 increased lifespan by two folds. This mutant worm had increased catalase and Cu/Zn SOD activities which may account for the increased resistance to the paraquat, a superoxide generating chemical. The mutants C. elegans support the view that the levels of oxidative stress is one of the important determinant factors in determining the length of lifespan.Superoxide anions are produced enzymatically outside the mitochondria by different oxidases and nonenzymatically inside the mitochondria. SOD detoxifies superoxide to hydrogen peroxide , which is converted to water and oxygen by catalase. There are five superoxide dismutase isoforms SOD-1, SOD-2, SOD-3, SOD-4 and SOD-5 in C. elegans. However, in most organisms there are only 3 SODs. SOD-1 is present in the cytoplasm and represents the majority of SOD activity, whereas SOD-2 and SOD-3 are present in mitochondria.