«Proceedings of the th 14 National Street Tree Symposium 2013 ISBN: 978-0-9806814-1-3 TREENET Proceedings of the 14th National Street Tree Symposium ...»
Toxic effects of chloride on plants Chloride is an essential micro-nutrient required in small quantities by all plants (Stevens et al., 2008). It is also one of the most common phytotoxins which is typically absorbed through the roots of the plant. It can also be absorbed through the plant leaves, and this speeds up the rate of toxic accumulation of the ion (Lazarova and Bahri, 2005). The toxicity level of chloride ions will be specific to each plant or plant group, and should be considered on an individual basis. Visible symptoms of chloride toxicity usually appear before those of sodium or boron (Azza Mazher et al., 2007). These symptoms include marginal chlorosis of the older leaves, followed by extensive leaf scorching, wilting and eventually defoliation (Fig.4). An indirect effect of excessive chloride levels is the prevention of absorption of essential nutrients such as nitrate and phosphates (Stevens et al., 2008). Figure4. Evidence of chloride toxicity in an aspen (Goodrich and Jacobi, 2007/2008) Toxic effects of boron on plants Boron is an element that is actually required for good plant growth (Lazarova and Bahri,2005). The range between acceptable and toxic levels of Boron is quite small (Stevens et al., 2008) and plants respond differently to specific levels of boron. These toxic levels do not often occur in arable soil, making it necessary to ensure the water used has minimal levels of boron.
The 14th National Street Tree Symposium 2013 Glenelg wastewater for Adelaide parklands Urban land scapes impact on the microclimate, hydrological cycle, biodiversity, water quality, air pollution, removing significant amounts of pollutants such as nitrogen, phosphorus and fine sediments and in general have environmental, social and economic benefits. There is currently a lack of adequate information specific to the Adelaide Park Lands vegetation, their tolerance to salinity and toxicity and their threshold levels. There is little research to investigate water requirements of mixed vegetation in urban landscapes such as plantings in the parkland systems. However, currently a research using WOCULS approach for estimating parkland plants water requirement is curing out at UniSA. Adelaide Park Lands, with an area of 720 ha are a core component of Adelaide, brings environmental, social, cultural and financial benefits for the people of Adelaide.
The average main element concentrations in the Glenelg recycled wastewater is Figure6. Leaf damage as a given in Table 2. The variation of concentration of these elements, coupled with result of water logging irrigation application rate and the other management measures are important for (Manitoba Agriculture Food long term sustainable irrigation management. and Rural Initiatives,n.d.) Table 2. Annual average concentration of some main elements in Glenelg recycled wastewater (REM et al., 2008)
The annual average salt concentration in the Glenelg recycled wastewater is nearly 1.8dSm-1. Although the salinity variation in usual irrigation water is expected to vary up to 3 dS/m, irrigation with Glenelg recycled wastewater with an annual application rate of 4500m3ha-1 would cause annual accumulation of nearly 9 tha-1 salts to the soil. In the lack of efficient irrigation management salinity build up hazard would be problematic in the long term. Toxicity often accompanies or complicates a salinity or infiltration problem although it may appear even when salinity is low. The toxic ions sodium and chloride can also be absorbed directly into the plant. In cases where the toxicity problem is not too severe, relatively minor changes in farm cultural practices can minimize the impact. An alternative water supply may be available to blend with a poorer supply to lower the hazard from the low quality water (Ayers and Westcot, 1994). A good indicator of sodium tolerance would be the presence of low sodium content in the plant leaves, in combination with high potassium content in the roots, stems and leaves (Adrover et al., 2008). Plant species that have high tissue calcium content in their leaves and stems would also be sodium-tolerant as calcium has been shown to neutralise the deleterious effects of various salts (Kozlowski, 1997).Typical toxicity symptoms are leaf burn, scorch and dead tissue along the outside edges of leaves in contrast to symptoms of chloride toxicity which normally occur initially at the extreme leaf tip. The average sodium level in the Glenelg recycled wastewater is 261mgl-1 and the amount of SAR is 7 (REM and SRHS, 2007). However, the sodium concentration in usual irrigation water is expected to be 0-920 mgl-1. This shows that the sodium concentration in the Glenelg recycled wastewater is considerably below the maximum allowable level. However, it does not mean that accumulation of this toxic ion in the long term without considerable attention to sustainable irrigation management would not be a hazard for Adelaide Park Land plants, particularly for those that are sensitive to sodium. Wu et al. (1995) gathered experimental evidence from a number of landscape plants and suggests that plants with high concentrations of tissue calcium exhibit tolerance to chloride. Therefore, chloride-tolerance is positively correlated to tissue calcium percentages. Not much research has been done on Australian landscape plants and it is important to have knowledge specific to each plant species, before assuming chloride tolerance.
Chloride toxicity Boron toxicity management Tolerances to chloride are not nearly so well documented as crop tolerances to salinity. Chloride moves readily with the soil-water, is taken up by the crop, and accumulates in the leaves. If exceeds the tolerance of the crop, injury symptoms develop such as leaf burn or drying of leaf tissue. With sensitive crops, the symptoms occur when leaves accumulate from 0.3 to 1.0 % chloride on a dry weight basis. Many tree crops, for example, begin to show injury above 0.3 % chloride. Chloride toxicity can occur by direct leaf absorption The 14th National Street Tree Symposium 2013 through leaves wet during overhead sprinkler irrigation. (Ayers and Westcot, 1994). Toxic levels of boron are usually related to soil types associated with low rainfall areas. As with sodium and chloride, boron-tolerance is specific to individual species and water application method. Research suggests that boron tolerance is at a genetic and cellular level (Nable et al., 1997). For example, differences in phloem mobility result in different accumulations of boron in the leaves, fruit and cambial tissue of a plant (Nable et al., 1997). It is therefore difficult to identify boron-tolerant plants from any physiological attribute. The allowable level of boron in the irrigation water is between 0-2 mgl-1. The level of boron in the class A Glenelg recycled wastewater is 0.4 mgl-1 (REM and SRHS, 2007). Boron therefore is not a concern in the Glenelg recycled wastewater at least in the short term.
Conclusion A wide variety of plants are used in the Adelaide Park Lands, each with a specific tolerance for high levels of salinity, sodium, chloride and boron. This further complicates the task of providing the correct amount of water without causing toxic levels of any of the above mentioned elements. It is important, therefore, to provide irrigation water that has salt concentrations suitable to a large number of plant species (Wu et al., 2001). Using recycled wastewater is a sustainable option for irrigation of the Adelaide Park Lands. It is however important to maintain a healthy and diverse collection of plants within the parklands in order to achieve one of the goals of creating habitat for native fauna. To this end, it is important to understand the nutrient requirements and characteristics for each species found within the parklands and to manage the care of the parklands accordingly. The amount of nutrient loadings using recycled water should be taken into consideration by monitoring the amount of nutrients are loaded by recycled water and are taken up by the plants. Previous reports have developed adaptive management frameworks designed to address the potential impacts of using recycled wastewater from Glenelg Wastewater Treatment Plant. A plant’s salt tolerance is variable depending on the climate, weather, genetic variation, soil health, texture and structure and irrigations methods and frequency (Wu et al., 2001). Investigation undertook in a study (Hassanli and Kazemi, 2012) indicates that the average level of three main plant toxic elements, sodium, chloride and boron is lower than the maximum allowable level recommended in the guidelines in Water Quality for Agriculture developed by FAO (Ayers and Westcot, 1994). The average Na+ and Cl- level in the Glenelg recycled in 2005 was 242 and 364 mgl-1, respectively (REM and SRHS, 2007). This shows that the Na+ and Cl- concentration in the Glenelg recycled wastewater is below the maximum allowable level. However, it does not mean that accumulation of these two toxic ions in the long term without considerable attention to sustainable irrigation management would not be a hazard for the Adelaide Park Land plants particularly those that are sensitive to toxicity of these elements.
Findings suggest that further research would be needed to clarify the benefits of the irrigation of urban green spaces by recycled water and improve irrigation management to mitigate the possible inverse impacts of recycled water for a sustainable environment to ensure having a healthy plant, soil and water system across the Adelaide Parklands.
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Abstract This paper details water sensitive urban design (WSUD) in practice in the City of Salisbury including the TREENET inlet system.
In collaboration with Uni SA and TREENET, the City of Salisbury is planning and implementing a range of research projects to provide evidence required to support the adoption of the technologies as standard practice for the city engineers and arborists.
The demands for onsite storm water retention, the need to defer capital expenditure on kerb and channel replacement and the much needed regeneration of an aging urban forest provided the incentive for Salisbury Council investigate putting WSUD to the test. It is anticipated that there will be significant savings in expenditure on repairing uplifted kerbs and footpaths as the root systems are naturally redirected away from this infrastructure in response to the relocation of water resources to the driest and thirstiest zone currently in the urban environment, the curiously named universal “nature strip”.