Avaliação de condicionadores em solo para uso em telhados verdes com vistas à retenção hídrica.

Abstract

Floods are natural phenomena that occur due to the large magnitude of rains, aggravated in urban areas by soil sealing and inefficient drainage systems. Green roofs emerge as a structural compensatory measure may retain part of the precipitated water, delaying the peak flow. The objective of this study was to develop a combination of soil and conditioners for green roof, promote a significant increase in water retention capacity and greater postponement of the peak stormwater runoff. This study was divided into two stages. In Step 1, were analyzed by percolation columns three conditioners in the following concentrations: Gel STOCKOSORB® retainer (2; 4; 6 g / dm3) Osmocote® slow-release fertilizer (4,7; 7,1; 9, 0 g / dm3) and zeolite (30; 50; 70 g / dm3), three events (watering) consecutive simulated rainfall intensity of 57 mm / hr. Evaluation of the most suitable among the concentrations tested for each condition was based on the analyzes for water retention (when the medium after watering, the flow delay time; mm retained; intensity of percolated water in mm / min) and the quality of percolated water (pH, dissolved oxygen, turbidity and solids). In Step 2, was evaluated in pots, the effect of the presence of three species of plants (Arachis pintoi, Raphanus sativus, Lavandula angustifolia) in two types of medium: no soil conditioners; best soil conditioners in concentrations indicated in Step 1, only one being simulated rainfall event of 57 mm / hr. Biological parameters were analyzed (germination, surviving plants, stem and root length, stem biomass and root weight); Water retention (after half the time of irrigation, the flow delay time; mm retained; intensity of percolated water in mm / min); quality of soil solution (pH, dissolved oxygen, turbidity, solids, nitrate, ammonia, total phosphorus). The Step 1 results indicated that the gel significantly promoted an increase in water retention, and delayed the start of the percolation of water, and promote slight increase of pH in soil solution. The addition of zeolite resulted in significant improvement of water retention, not as much as the retaining gel. The addition of fertilizers did not cause changes in the quality of the soil solution. In Step 2, only the effect of the presence of A. pintoi (higher biomass of root and stem) and R. sativus were evaluated. The presence of conditions on the ground provided a significantly better performance in relation to water retention (substrate height and postponement of peak rainfall) and quality of the soil solution (pH and turbidity) when compared to tests carried out in the presence only of soil. However, the influence on the high fertilizer concentrations of nutrients (nitrogen and phosphorus) in water leachate in the results, it is concluded that the presence of the gel on the substrate, resulting in a higher water retention ability, and therefore in delaying the peak intensity rain. Thus, the application of the gel is recommended for further studies to green roofs outdoors.