Phyto-remediation: Healing Urban Landscapes

Aspects of Phytoremediation

by Marti Gil 

There is no doubt that we, as humans, contaminate our environment by activities related to our lifestyle. For instance, the production of energy, food, clothes, infrastructure, and industries produce a concentration of substances that enter the Earth, affecting the conditions of the air, water, and soil ecosystems.

There are many procedures to eliminate these contaminants from the environment. One especially interesting method is the use of living organisms or bioremediation such as bacteria, mushrooms, algae, protozoa, and plants. Through this procedure the concentrations of the pollutants are decreased, taking advantage of their capacity to degrade these elements.

In a Landscape Architects Network article titled “Phytoremediation: Healing Urban Landscapes”  Yuliya approached the subject by using a great theoretical example from the Netherlands and this article begins by explaining how the healing of an environment with plants functions and the types of plants that we should use in order to eliminate specific contaminants.

Active Modular Phytoremediation Wall System, CASE

Phytoremediation is a set of methods, performed by plants that degrade, detoxify, assimilate, or metabolize contaminants deposited in the soil, water, or in the atmosphere. These contaminants are: pesticides, metals, organic compounds, herbicides, explosives, and other compounds that in many cases, cannot be degraded, but can be assimilated by the harvestable part of a plant.

The advantages are that this process is cost-effective because it is a natural process that uses solar energy and it is in situ. Furthermore, it can be an excellent method to implement in large areas, and it has been widely accepted by society and can be performed in an aesthetic manner. Some of the limitations are that it requires lengthy periods of time. Additionally, the contaminants cannot exceed the maximum level that the plants can assimilate. Phytoremediation does not work on profound soils or water due to the size of the plant’s roots and lack of research on a particular topic.

Living Machine

In order to select plants we need to investigate the concentration of the pollutants, the cost of the irrigation, the related maintenance, the length of time, the risk of pests, and the planting scheme. Plants that can be used to heal an ecosystem may vary depending on the characteristics of the environment, but we can generally expect healing from plants with deep roots (due to their scope), pastures (due to soil retention), legumes (due to the fixation of Nitrogen), and aquatic plants, which can be found worldwide.

According to Alejandro Mentaberry, Ph.D. from the Universidad de Buenos Aires in Argentina, there are six basic mechanisms in which plants do their work with the help of chemical and physical processes:

• Phyto-extraction: Mainly for the concentration of metals and other inorganic toxic compounds in the harvestable parts. It is important to consider plants with an important biomass, principally on the aerial part such as sunflowers, dandelions, and mustard.
• Rhizo-filtration: The roots are used to absorb, precipitate and concentrate heavy metals and organic compounds in liquid effluents. The plants should have roots that grow fast and abundant ramification like different algae and Thypha latifolia.
• Phyto-stimulation: Uses the roots exudates to promote the growth of degradation organisms like mushrooms and bacteria, efficient with organic hydrophobic compounds like oil sub products. Phreatophyte plants (with the roots in the water), trees from the genus Populus, pastures like Rye, phenol compounds producers like apple, and aquatic plants are great performers.
• Phyto-stabilization: Plants resistant to metals are used to avoid and reduce the movement both in air and to underground layers. The use of phreatophyte trees and pastures are recommended.
• In both Phyto-degradation and phyto-volatilization a transformation of the contaminants are present so the use of phreatophyte trees (Populous sp.), pastures and legumes are recommended. The plants are used to capture and metabolize organic compounds to produce less or non-toxic sub products in the degradations, and to collect heavy metals and organic compounds releasing them into the atmosphere through transpiration on the volatilization.

All these techniques and technologies are improving daily and becoming more efficient.  It is important to consider that collectively they can be part of a system that combines different kinds of mechanisms to heal our ecosystems improving the results.

Shanghai Houtan Park, Turenscape

Of course, it does not mean that we can continue polluting without remorse just because we have found a way to clean the world naturally. It means that we can change what we, as humans, have done and begin to produce more environmentally friendly methods of eliminating contaminants not only in big, gray facilities, but in projects such as the Shanghai Houtan Park, which maintains a beautiful landscape with a practical use.

http://landarchs.com/aspects-phytoremediation/