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About UNEP
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United Nations Environment Programme
Division of Technology, Industry and Economics
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Newsletter and Technical Publications
Freshwater Management Series No. 5

Guidelines for the Integrated Management of the Watershed
- Phytotechnology and Ecohydrology -


O. Phytotechnologies for reducing soil erosion and nutrient losses to aquatic systems

As noted above, phytotechnologies can be utilised to minimise erosion by wind and water from the land surface. Plants can be used to bind contaminants, limiting their availability for transport into surface and ground waters. The degree to which plants can reduce soil and nutrient losses is a function of the type and density of plant cover; site hydrology and hydraulics; and the distribution of plants within or along a site.

Vegetative cover

Vegetative cover refers to the long-term, self-sustaining community of plants growing in and/or over the land surface. When this concept is applied to phytotechnologies, it refers specifically to plant communities associated with materials that pose an environmental risk. Use of vegetative cover may reduce that risk to an acceptable level. Vegetative alternatives generally require minimal maintenance. There are two types of vegetative cover:

  • Evapotranspiration cover that is composed of the soil and plant system engineered to maximise the available storage capacity of the soils, evaporation rates, and the transpiration process of the plants to minimise water infiltration. An evapo- transpiration cap, commonly used at sealed landfill sites, is a form of hydraulic control by plants that reduces environmental risk by limiting the human or wildlife exposure to contaminants and reducing leachate formation and movement.
  • Phytoremediation cover consists of a soil and plant system designed to minimise infiltration of water into a contaminated site, thereby aiding in the degradation of the underlying waste. Risk reduction relies on the degradation of contaminants, the isolation of contaminants to prevent human or wildlife exposure, and the reduction of leachate formation and movement.

Hydraulic controls

Hydraulic controls use plants to remove groundwater through uptake and consumption in order to contain or control the migration of contaminants. Hydraulic control is also known as phytohydraulics or hydraulic plume control. Trees such as the willow are often utilised for hydraulic control purposes since these trees have an high water demand.

Buffer zones

Buffer zones are generally applied along streams and river banks to control and treat contaminated surface runoff and groundwater moving into the river. These systems can also be installed to prevent downgradient migration of contamination plumes in groundwater systems. Often these systems are utilised in projects that encourage phytodegradation of contaminants in a plume.

P. Selection criteria for phytoremediation

The main consideration in the evaluation of phytoremediation alternatives in the remediation of contaminated sites is related to the type of soil media and water source, the concentration of the contaminant(s) of interest, and the potential for effective vegetation growth at the site.

The decision-making process for evaluating whether or not phytoremediation are viable options is summarised in the following outline:

  • Define the problem
    • conduct a site characterisation,
    • identify the problem: media and/or contaminant,
    • identify regulatory requirements,
    • identify remedial objectives,
    • establish criteria for defining the success of the phytoremediation system.
  • Evaluate the site for potential application of phytoremediation
    • perform a phytoremediation -oriented site characterisation and risk assessment
    • identify appropriate phytoremediation that address the media/ contaminant/goals,
    • determine the most appropriate plant species to be used, based upon consideration of the site conditions, pollutant(s) involved, and the ability of the plant(s) to absorb or translocate significant levels of the contaminant(s),
    • review known information about the identified phytoremediation,
    • identify potential plants and sources of plants (local plants are best).
  • Conduct preliminary studies and make a decision
    • conduct screening studies,
    • perform optimisation studies to determine optimal planting densities and types,
    • conduct field plot trials prior to full-scale implementation,
    • revise the selection of plants for use with the phytoremediation, if necessary.
  • Evaluate a full-scale phytoremediation system
    • design the system, including measures to limit flooding, control erosion, and dispose of harvested plant materials,
    • construct the system,
    • maintain and operate system for at least one full growth cycle,
    • evaluate and modify the system,
    • evaluate system performance.
  • Continue to achieve the objectives
    • perform quantitative measurements to monitor system operation and performance,
    • review the degree to which the technology has met the criteria for success.

Q. Summary

One of the fundamental tenets of the concept of sustainable development is the maintenance of a homeostatic equilibrium within the ecosystem. Over-exploitation of the ecosystem, or degradation of its biotic structure, alters ecosystem processes to the point whereby the ability of the ecosystem to meet desired conditions is seriously diminished. Water is the medium for all ecological processes, from the molecular to the global scales. The physical quantification of ecological processes, in terms of water and energy, is fundamental to the scientific investigations that should underpin a programme of sound ecosystem management.

The most appropriate scale for measuring and quantifying energy and nutrient dynamics in aquatic ecosystems is the mesocycle within a basin, which forms the basic geographic unit within which to determine and quantify the interconnected processes that comprise the ecosystem and provide a framework for the interactions between its biotic, physical and chemical elements.

The degradation of freshwater ecosystems can be characterised in terms of two dimensions; namely, pollution, which can be reduced to a significant extent using known technologies, and the degradation of established water and nutrient cycles within the ecosystem as a whole. This second dimension is much more complex. A new tool for resolving ecosystem-scale problems is the application of ecohydrological principles and phytotechnologies. Our progressive understanding of the range of anthropogenically-induced degradation of hydrological, biogeochemical, and biological processes within water basins indicates an urgent need to control and regulate nutrient and water dynamics by increasing plant biomass and diversity. Phytotechnologies can be viewed as a tool for increasing ecosystem carrying capacity and enhancing the resilience and functionality of ecosystems at the basin scale. Phytotechnologies form the medium by which to implement ecohydrological principles.

An interdisciplinary, holistic approach, based on an understanding of the role of plant biomass in the control of water and biogeochemical cycles (i.e., "green feedback", should lead to improved water quality, enhanced biodiversity and agricultural production, and sustainable bioenergy generation, as well as increased employment opportunities.

Acknowledgements

Preparation of this chapter has been supported by Polish State Committee for Scientific Research grant no KBN 6P04 611220.

INTERNET SOURCES

Advanced Applied Technology Demonstration Facility (AATDF) http://www.ruf.rice.edu/~aatdf
Air Force Center for Environmental Excellence(AFCEE) http://www.afcee.brooks.af.mil
Alternative Treatment Technology InformationCenter (ATTIC) http://www.epa.gov/attic
Brownfieldstech Internet web site http://www.brownfieldstech.org
CLU-IN: Hazardous Waste Clean-Up Information http://clu-in.org
Environmental Security Technology Certification Program (ESTCP) http://www.estcp.org
Federal Remediation Technologies Roundtable http://www.frtr.gov
GNET: The Global Network of Environment and Technology http://www.gnet.org
Great Plains/Rocky Mountain Hazardous Substance Research Center http://www.engg.ksu.edu/HSRC
Ground Water Remediation Technologies Analysis Center http://www.gwrtac.org
Innovative Treatment Remediation Demonstration (ITRD) http://www.em.doe.gov/itrd
Interstate Technology and Regulatory Co-operation Working Group http://www.sso.org/ecos/itrc
PHYTONET - Phytoremediation Electronic Newsgroup Network http://www.dsa.unipr.it/phytonet
Remediation Technologies Development Forum (RTDF)  
Phytoremediation of Organics Action Team http://www.rtdf.org/public/phyto
Strategic Environmental Research and Development Program http://www.serdp.gov
U.S. Army Corps of Engineers Phytoremediation Research http://www.wes.army.mil/EL/phyto
U.S. Army Environmental Center (USAEC) http://aec-www.apgea.army.mil:8080
U.S. Department of Agriculture (USDA) http://www.usda.gov

 

LIST OF ACRONYMS
 

BTEX Benzene, toluene, ethylbenzene, and xylene
PAH Polycyclic aromatic hydrocarbons
PCB Polychlorinated biphenyl
PCP Pentachlorophenol
TCA Trichloroethane
TCE Trichloroethylene
TNT Trinitrotoluene
TPH Total petroleum hydrocarbons

 

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