Reclamation and Restoration of Disturbed Systems

Chapter 20

Reclamation and Restoration of Disturbed Systems M.L. Brusseau, E.P. Glenn and I.L. Pepper

Cover Art: The Cienega de Santa Clara, a human-made wetland in the delta of the Colorado River where it enters the Gulf of California in Mexico. This wetland is formed by the discharge of agricultural wastewater onto salt flats (visible in background) in the intertidal zone. It supports tens of thousands of resident and migratory water birds and endangered fish and bird species. Photo courtesy E.P. Glenn.

20.1 INTRODUCTION Many different types of human activities can lead to disturbances that impair ecosystems and their functions, as covered in Chapters 14–17, and 25. Major impacts include degraded soil quality, water and air pollution, scenic impairment, and habitat destruction. These disturbances occur over a vast range of scales, from a single site such as a manufacturing plant, mine, or agricultural field, to watershed systems, to entire regions (such as deforestation of the Amazon rainforest). Different approaches are used to address these different scales of problems. This chapter will focus primarily on disturbances associated with single sites, or what may be referred to as local-scale disturbances. Methods for dealing with regional and global-scale issues are discussed in Chapter 32.

Environmental and Pollution Science. https://doi.org/10.1016/B978-0-12-814719-1.00020-3 Copyright © 2019 Elsevier Inc. All rights reserved.

The first step in addressing disturbed systems is to understand the “four Rs”—reclamation, remediation, rehabilitation, and restoration (Information Box 20.1). The objective of Reclamation is to return the site to a productive use. It is focused primarily on conditions of the land surface and the ability to use the site for a particular land use activity (redevelopment). Remediation is focused on removing or treating soil, air, and water contamination to reduce or eliminate risks to the health of humans and other lifeforms. Remediation methods are covered in Chapter 19. Reclamation and Remediation do not focus on the broader aspects of ecological conditions and ecosystem functions. However, reclamation and/or remediation actions may be implemented in support of larger scale ecosystem restoration efforts. Rehabilitation is focused on improving site conditions so that an impaired ecosystem service can be recovered. For example, an impaired wetland may be rehabilitated to recover its ability to naturally filter and treat water pollution. Restoration is a general term that is often used to represent any type of activity conducted to improve site conditions. Thus Reclamation, Remediation, and Rehabilitation are subsets of Restoration. Ecological or Ecosystem restoration is formally defined by The Society for Ecological Restoration as “assisting the recovery of an ecosystem that has been degraded, damaged or destroyed.” This comprises a range of activities designed to initiate or accelerate the recovery of an ecosystem with respect to its health, integrity, and sustainability. Ecological restoration is focused on the entire ecosystem, including flora, fauna, and overall ecosystem functioning, and not just on soil, air, and water quality. Generally, the goal of ecological restoration is to support recovery to a natural state. Remediation and Reclamation are primarily concerned with improving site conditions to reduce human health risk and to support future human activities. In addition, Rehabilitation is often focused on improving ecosystem services for human well-being. In other words, they are human-centric focused. Conversely, ecological restoration is focused on

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INFORMATION BOX 20.1 Restoration Terminology Reclamation: repairing some or most of the damage done to land so that it can serve some productive function; returning it to a useful state. For example, salinized farmland, unable to support native plants, can be planted with salt-tolerant plants (halophytes) to prevent erosion and provide wildlife habitat. Rehabilitation: reinstating a level of ecosystem functionality where complete ecological restoration is not sought, but rather with the objective of recovering ecosystem services. For example, adding organic amendments to a plot of degraded soil to support planting of crops and resultant food production. Remediation: removing or treating site contamination (site cleanup) in order to protect human health and the environment. This has a specific meaning for hazardous waste sites (see Chapter 19). Examples include excavation of contaminated soils, pump and treat of contaminated groundwater, and soil vapor extraction for volatile organic contaminants in the vadose zone. Restoration: A general term for any and all activities conducted at the site to improve conditions. Reclamation and Remediation are subsets of Restoration. Ecological Restoration (also called ecosystem restoration): is formally defined by The Society for Ecological Restoration as assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed; an intentional activity that initiates or accelerates the recovery of an ecosystem with respect to its health, integrity, and sustainability.

the ecosystem itself, its functioning and overall health. Keep in mind however that reclamation, remediation, and rehabilitation efforts may be implemented as part of an ecosystem restoration project. This chapter will focus on reclamation and ecological restoration separately. As previously noted, remediation is covered in Chapter 19.

20.2 20.2.1

PROJECT DESIGN Planning and Site Assessment

The components and overall restoration process is shown in Fig. 20.1. A conceptual plan for the restoration project begins with a detailed history of the site, where information is collected to determine the disturbance and associated changes that have led to the current state of degradation. This information is cross-referenced against historical and current topographic, geologic, and vegetation maps to determine what changes have occurred spatially and temporally. Information on the environmental and ecological properties of the site prior to the disturbance is collected to determine the natural-condition state and evaluate the restoration potential of the area. If this information is not available for the site in question, nearby natural reference sites are used.

FIG. 20.1 Components of a restoration project. (From Environmental Monitoring and Characterization, Elsevier, 2004.)

Once a complete history of the site has been compiled and it has been determined that the restoration project is feasible, a thorough site assessment of abiotic and biotic conditions takes place. This step is one of the most important in any restoration project, since it not only provides baseline measurements on such parameters as hydrologic features, soil and water conditions, and biological information, but it also serves as the benchmark upon which to evaluate project performance through time. This step first involves placing the site in the context of the regional ecosystem type (or ecoregion) prevalent for that area. This is critical to make sure that the objectives and outcomes selected for the planned restoration effort will be compatible with the prevalent ecological conditions of the region. After the ecoregion evaluation, site investigations are conducted to characterize specific conditions such as habitat fragmentation, disconnected surface and subsurface hydrologic flows, water quality issues, physical and chemical properties of the soil, and plant and animal inventories. In assessing a site, it is important to determine which basic ecological functions are damaged or fragmented, since this often sets the restoration priorities and ultimately the success of the project over time. Specific site characterization activities are conducted to determine the presence or absence of toxic constituents such as heavy metals, organic compounds, and radioactive waste in soil, water, and air. These are done as described in Chapter 10. It is worth noting that the soil conditions and water quality in a given area generally dictate the type of vegetation cover and thus the biodiversity of biotic components. Therefore extra care should be taken in analyzing and describing these two elements both horizontally and vertically across the landscape. Plants provide valuable information about site conditions. The occurrence and relative abundance of certain plant

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species and their physiological and ecological tolerances provide evidence of environmental conditions that are of importance for understanding the nature of the site, potential human health and ecological risks, and the feasibility of different restoration alternatives. Typically, plant ecology investigations include four types of studies: (1) plant species survey; (2) estimates of the percent cover and age structure of dominant, perennial plant species; (3) evaluation of the composition, relative abundance, and distribution of plant associations; and (4) vegetation mapping. The plant species survey is conducted by traversing a site, usually on foot, and noting each species present. The percent cover study attempts to quantify the percent of the site that is covered by bare soil or individual plant species utilizing a line intercept method. First, the plant community to be described is delineated on a map and then 30-m transect lines are randomly chosen where actual plant counts will take place. In the field, a 30-m tape is stretched out and the total distance intercepted by each plant species is recorded and used to calculate the percent cover of each species. For example, a transect might consist of 12% fourwing saltbush, 10% black greasewood, and 78% bare soil. Plant associations and ultimately vegetation mapping are used to delineate land management units for future revegetation efforts. Recently, surveys of microbial communities associated with the soil have become more common for site characterization. They can provide information regarding, for example, overall soil health, the ability to support plant growth, predominant biogeochemical nutrient cycles, and the potential for natural attenuation of contaminants. See Chapters 5 and 9 for more information on this topic. Surveys of animal species are also conducted. This information is used to determine the trophic structure of the system and to identify if certain species are threatened.

20.2.2

Objectives and Approaches

A key component for any successful restoration effort is the identification of clear objectives. There are several reasons for defining objectives for restoration projects, including: l

l

l

l

Focus and sharpen thinking about the desired state or condition of the restored site; Describe to others the desired condition of the restored site; Provide a desired outcome that serves as a metric for assessing restoration success; and Provide direction for the appropriate type of performance monitoring.

Restoration objectives that are inadequately defined lead to ambiguity as to whether a project was successful. The SMART acronym can be used to help design effective

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objectives: Specific, Measurable, Achievable, Relevant, and Time bound (USGS, 2011). As noted previously, restoration projects range from limited activities that restore some beneficial land use, to contamination cleanup, to focused efforts to restore a particular ecosystem service, to full-scale ecosystem restoration efforts. The objectives selected to guide a restoration project need to be consistent with the degree of restoration that is feasible for the site. The restoration feasibility as well as the methods chosen for the restoration of a particular site are determined by: l l l l

the nature of the site and surrounding environment, the nature and magnitude of disturbance and degradation, the desired outcome, and the planned future land use.

For example, the site may be contaminated or disturbed to such an extent that it would be cost prohibitive to attempt to fully restore the site (complete ecological restoration). In this case, remediation and reclamation activities would be conducted to return the site to a state that would support alternative land uses. In addition, the extent of reclamation would depend upon the intended land use, with lesser degrees applied for an industrial use versus a site planned for a housing development for example. It is important to recognize that ecosystems are dynamic, such that they change and evolve over time through the course of natural events. Thus it may not be feasible to restore the site to the original natural state, as it would not be consistent with the current natural status of the region. Therefore the focus of the project should be on the desired characteristics of the ecosystem in the future, rather than on the characteristics that were previously there.

20.2.3 Project Completion and Performance Monitoring A critical component of all restoration projects is monitoring site conditions over time to evaluate success or failure of the project, which is termed performance monitoring or postproject assessment. Effective performance monitoring efforts require development of clearly articulated objectives. In addition, it requires identification of informative indicators or metrics. Examples of metrics would be a reduction in suspended sediment load in lake water, a reduction in erosion of a slope, or an increase in plant density. Most restoration performance assessments are based on short-term monitoring, perhaps completed several months or a few years after project completion. This is due to a number of reasons—project funding sources typically require a specific project completion time frame, sponsors want to see the results of their investments, and the public expects rapid results. Many reclamation

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projects can be successfully completed in the span of months to a few years, which is compatible with the short-term focus. Conversely, many remediation and ecological restoration projects can take many years or decades to complete, a time span that is not compatible with the previously stated desires. Monitoring programs are based on the periodic collection of data. This includes collecting soil, plant, surface water, and groundwater samples and conducting plant and animal inventories. Until recently, these data were collected using standard labor-intensive field sampling techniques. However, with increased computing power and sophisticated data collecting techniques, real-time data can more easily be obtained without additional personnel. This can provide larger, higher resolution data sets that can improve performance assessments. Site monitoring methods are discussed in Chapter 10.

Slope stability design is based on the angle of repose. Slopes with angles larger than the angle of repose are susceptible to slumping or mass wasting (see Fig. 20.2). The angle of repose is a function of the material properties and can be influenced by environmental conditions (water infiltration, erosion, external disturbances). Generally, slopes are designed to less than 3:1 or 33% (a change of three horizontal length units for each vertical unit), which is equivalent to an angle of 18 degrees. Infiltration and erosion control measures can be implemented to help maintain slope integrity. These include application of drainage systems, surface covers, and revegetation, all of which are discussed in forthcoming sections. Surface contouring involves reshaping of the land surface. It is conducted following these general principles: l l

20.3

LAND RECLAMATION METHODS

Major methods used to reclaim disturbed land surfaces and soil quality will be covered in this section. These include: l l l l

Surface grading and contouring, Surface covers and caps, Revegetation, and Soil treatment for various purposes.

20.3.1

Surface Grading and Contouring

A primary approach used in the initial stages of most reclamation projects is grading and contouring of the land surface. This is done for a number of reasons, including improving slope stability, controlling water flow, reducing wind and water erosion, preparing the surface for planned infrastructure, and to enhance aesthetics. The nature and extent of this work will depend on the project objectives. FIG. 20.2 Slumping of an unstable slope. (From Unsafe Ground: Landslides and Other Mass Movements; Available from: http://slideplayer.com/slide/4565885/.)

l l

Create a geomorphically mature landscape. Create a robust landscape that improves in stability with time. Create a landscape that mimics natural systems in the area. Use best available demonstrated control technology.

Generally, it is most desirable to produce land forms that mimic natural conditions present in the region. This concept is illustrated in Fig. 20.3. An example of employing natural contouring for reclamation of a mining site in Pennsylvania is given in Fig. 20.4.

20.3.2

Surface Covers and Capping

Different types of covers or caps can be applied to the land surface to achieve a range of objectives. The objectives and types of covers are presented in Information Box 20.2. An example of geomembrane application is presented in Fig. 20.5. The type of cover to use depends on several factors:

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FIG. 20.3 Concept of contouring land surfaces to natural forms. (From Landforming: An Environmental Approach to Hillside Development, Mine Reclamation and Watershed Restoration. Horst J. Schor, Donald H. Gray, John Wiley & Sons, 2007.) FIG. 20.4 Example of natural contouring for mine site reclamation. (From https://en.wikipedia.org/wiki/Mine_reclamation#/media/File: Northeast_from_Providence_Quaker_Chapel.jpg.)

– Site conditions—material properties, climate (rainfall, wind) – Source of borrow material (is there a source of soil nearby) – Planned land use – Site location (nearby human populations?) Several factors need to be considered when designing the cover system. These include: – Drainage layers or devices: layers (sand and gravel) or devices (drainage pipe) to manage seepage flow – Stormwater control: structures such as drainage channels and retention ponds to manage runoff

– Institutional controls: fencing, driving restrictions, no-access signage – Long-term monitoring and maintenance Examples of surface water control are presented in Fig. 20.6A and B. In addition to large-scale covers, additional measures are available to control water erosion. Permeable barriers made of straw bales or woven fabrics can be used to slow water and reduce its ability to carry sediments. Runoff water can be trapped in settling ponds in which water velocity is eliminated or greatly reduced, allowing suspended particles to settle out, and reducing sediment loads

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INFORMATION BOX 20.2 Objectives and Types of Surface Covers The objectives of covers include: – Limit water infiltration – Control air entry (oxygen) – Reduce erosion by wind and water – Support vegetation – Contain contamination General types of covers: Soil caps: soil spread on surface. Geotextiles: Geotextiles are permeable fabrics that allow passage of water through the material but prevent soil from moving through to lower layers. Impermeable caps: Engineered, impermeable barrier caps, to prevent percolation into underlying layers. These layers are typically composed of clay or geosynthetic membranes. Hardened cover: Typically composed of rock, screened to an appropriate size, to reduce erosion and improve stability. Vegetative cover: Vegetation planted on surface.

Wind erosion is reduced by a rough soil surface. Surface roughness can be controlled by creating ridges or a rough surface with tillage implements. Ridges 5–10 cm in height are most effective for controlling wind erosion. Soil surface can also be protected by providing vegetative or other surface cover, such as straw, hay, waste residues such as manure, and gravel or rocks. The soil water erosion control measures discussed earlier also provide effective wind erosion control. Various amendments that help bind soil particles together, including calcium chloride (CaCl2), soybean feedstock processing by-products, calcium lignosulfate, polyvinyl acrylic polymer emulsion, polyacrylamide, and emulsified petroleum resin are applied to unpaved roads to reduce particulate emissions. Unpaved roads can also be covered in gravel or similar nonerodible surfacing materials. However, most of these treatments generally offer only temporary dust control and must be periodically repeated.

20.3.3 before overflow water is released. If suspended colloids are in a dispersed condition, flocculating agents may be added to aggregate particles into larger assemblages that rapidly settle out of suspension. Gabions or wire mesh containers filled with rocks can also be used to control water erosion in gullies and drainage ways (Fig. 14.7). Wind velocity, a major factor in soil wind erosion, can be decreased with windbreaks. These may be living windbreaks of planted trees, shrubs, or grasses, or they can be constructed material such as fences or screens. Windbreaks are most effective when placed perpendicular to the direction of the prevailing wind. Effects of windbreaks extend to as much as 40–50 times the height of the windbreak; however, the area adequately protected by the windbreak is usually smaller. Effective control is usually considered to extend to about 10 times the height of the windbreak. FIG. 20.5 Example of applying a geomembrane cap. (From: https://commons.wikimedia.org/wiki/File:Geomembrane_instal lation.jpg.)

Revegetation

Many reclamation and restoration projects involve some type of revegetation of the land surface. Revegetation serves to accomplish multiple objectives, including: – – – – –

Limit water infiltration (evapotranspiration barrier) Reduce erosion by wind and water Reduce contaminant migration Restore habitat Enhance aesthetics

The types of plants to employ for revegetation depends on the site conditions and intended land use (Table 20.1, Heikkinen et al., 2008). Special consideration needs to be given to assessing the potential ability of the plant to prosper under the site conditions. This can often be enhanced by selecting species that are native to the region. Another consideration is the potential impact of soil contamination on the

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(A)

(B) FIG. 20.6 Surface water control. (A) Drains, from mining waste treatment technology selection, interstate technology and regulatory council (www. itrcweb.org), (B) trench, (From Heikkinen, P.M., Noras, P., Salminen, R. (Eds.), 2008. Mine Closure Handbook. Vammalan Kirjapaino Oy, Helsinki. ISBN 978.952-217-055-2.)

vegetation. Some plants sequester contaminants such as metals and organic compounds into their leaves and stems. This is termed phytoextraction. If this occurs, there is potential for foraging wildlife to become exposed to the contaminants. Soil quality is another primary factor to consider for revegetation. The soil quality at many disturbed sites may be impaired to such a degree that it cannot support plant growth. In these cases, soil treatment methods need to be employed prior to revegetation. Soli treatments typically involve addition of one or more amendments such as lime for pH modification, organic matter, and nutrients. Soil

remediation may be required if contaminants are present. Soil treatment methods are covered in the next sections. In semiarid and arid areas of the world, where water is scarce, it is often problematic to include long-term irrigation in the revegetation project design. Hence, it is best to design the project so that the naturally occurring precipitation is sufficient to support vegetation and therefore irrigation is not required. In some cases, irrigation may be needed for the initial application stage, but not over the long term. Low-cost techniques can be used to capture and retain precipitation where it falls to support the revegetation effort. The simplest and cheapest methods involve placing logs, rocks, or mulch

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TABLE 20.1 Revegetation Strategy as a Function of Intended Land Use Type of Land Use

Revegetation Strategy

Plantation forestry

Recommended, if intention is economically viable forest production Fast growing plants with high yield

Recreation

Plants resistant to physical impact, such as turf for sportsgrounds and playing fields Slow-growing ground cover species

Agriculture or grazing

Requires careful risk assessment and monitoring during and after rehabilitation Plants susceptible to uptake of toxic compounds

Natural landscape with no specific commercial or conservation objectives

Facilitate rapid colonization of vegetation by endemic species

No specifically defined land use

Species that rapidly stabilize the site, including commercial grass varieties

Nature conservation

Maximize floral diversity in accordance with original ecosystem

From Heikkinen, P.M., Noras, P., Salminen, R. (Eds.), 2008. Mine Closure Handbook. Vammalan Kirjapaino Oy, Helsinki. ISBN 978.952-217-055-2.

on bare ground to capture moisture, nutrients, seeds, and soil from the surrounding area. Contour furrows, pits, and small depressions in surface soils play the same role in capturing essential elements for plant establishment. It is important to recognize that most reclamation projects will incorporate more than one method. Thus surface grading and contouring, capping, and revegetation may all be applied for one project. An example of integrated reclamation for mine sites is presented in Fig. 20.7. Reforestation is a specific type of revegetation strategy for returning trees to a deforested ecosystem. Trees are removed for a variety of reasons. Tropical rainforests are cleared for agriculture, but often the farms fail due to lack of soil nutrients. Temperate zone forests are often clear-cut for timber. Dryland forests in the subtropics are often denuded due to overgrazing of livestock and harvesting of trees for charcoal and firewood. Forests prevent soil erosion, protect against floods, store carbon, and are sites of biodiversity. Hence, efforts are underway to restore forests on a global scale. A wide variety of techniques have FIG. 20.7 Integrated mine site reclamation mine tailings in Globe AZ. (Courtesy of J. Fehmi, Univ of Arizona.)

been developed for reforestation. The least expensive method is direct sowing of tree seeds, but the success rate is low. Tree nurseries set up near the site of disturbance can be used to grow juvenile trees for transplanting, a more successful method than direct seeding. Reforestation can use either native or exotic tree species. Fast-growing Eucalyptus trees from Australia have been planted over vast areas of the world to replace native forests that were cleared by humans. Native trees may be more difficult to grow than exotics. However, there is a trend to use native species where possible, because they usually provide greater ecological benefits than exotic species.

20.3.4

Soil Treatment for Acidic Soils

The optimum pH of soils for plant growth is generally between pH 6 and 8. However, agricultural crop production over a period of several years can result in a decreased soil pH or the production of acidic soils (pH < 6).

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INFORMATION BOX 20.3 Adverse Effects of Soil Acidity on Plant Growth  Aluminum toxicity  Calcium deficiency  Manganese toxicity  Phosphorus deficiency  Heavy metal toxicity  Molybdenum deficiency Biological effects  Disturbance and/or decreased microbial activity.

In many areas of the world, as for example in the U.S. Midwest and several parts of Europe, agricultural crop production is carried out in environments where rainfall exceeds the amount of water used by the plants. This excess water results in the leaching of basic cations through the soil profile. In essence, these basic cations are replaced from cation exchange sites (see Chapter 2) by H+ ions that are produced during the degradation of plant residues and organic matter. In addition, applications of ammonium-based fertilizers can also result in increased soil acidity following nitrification. The decreased soil pH can adversely influence plant growth in a number of ways (Information Box 20.3). Although some crops such as pineapples (grown in Hawaii) or azaleas can tolerate and even grow well at soil pH values of 4.5–5.0, most crops do not grow well. Therefore soil treatment must be conducted to allow viable crop production. To correct soil acidity, lime amendments are recommended. The liming materials are frequently calcific limestone, which consists of calcium carbonate, or dolomitic limestone, which is a mixture of calcium and magnesium carbonates. There are many factors that influence the amount of lime to be added which include initial soil pH, final target pH, cation exchange capacity, and other soil characteristics that are site specific. Many states in the United States have specific recommendations for lime requirements issued through the land grant universities or the United States Department of Agriculture (USDA). As an example, however, approximately 10 tonne ha
1 of ground limestone might be necessary to raise the pH of a Midwest agricultural soil from pH 6.2 to pH 7. In contrast, once the soil pH falls below 5.0, the amount of lime required increases dramatically. Hence, the same soil at a pH of 5.6 might need 20 tonne ha
1 to bring it back up to 7.0. In general, smaller amounts of lime are added more frequently to agricultural land to maintain the pH between 6.0 and 7.0.

20.3.5 Soil Treatment for Saline and Sodic Soils In contrast to soil acidity problems, agricultural crop production can also result in the build up of salts in high pH

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soils. The original source of salts in soils is derived from the primary minerals found in soils including various proportions of the cations—sodium, calcium, and magnesium, and the anions—chloride and sulfate. In humid regions with adequate rainfall, these salts are transported or leached downwards into groundwater or streams, and carried to the oceans. Therefore salt accumulations in soils of the humid regions are rare. In arid areas where rainfall is limited, there is no such mechanism to remove salts, and salt concentrations can increase. However, for salt concentrations to increase to problematic levels, additional sources of salts are necessary. Irrigation water used for crop production in arid regions can be a source of such salts. In hot arid areas, evaporation of applied irrigation water from soils, and evapotranspiration of water from plants, removes water from the land, but retains the salts. Therefore over time, salt concentrations will increase. This situation can be compounded in low-permeability soils with poor drainage characteristics. In addition, if sodium is the dominant cation, it will replace calcium and magnesium, and result in cation exchange sites dominated by sodium. Therefore salt-affected soils can be separated into three groups: saline, saline-alkali, and nonsaline alkali or sodic soils. The characterization of these three groups is based on: (1) the electrical conductivity in mmhos (mho is a conductance unit that is the reciprocal of resistance measured in ohms), (2) the percent of cation exchange sites occupied by sodium, and (3) the soil pH (Information Box 20.4). Saline soils are generally flocculated and have reasonable drainage characteristics. These soils can adversely affect plant growth due to high and often toxic amounts of salts. In contrast, sodic soils are frequently dispersed and have poor drainage characteristics. Plant growth in sodic soils may be restricted by both high pH and toxic amounts of sodium. Saline-alkali soils can have the adverse characteristics of both saline and sodic soils. Soil treatment procedures have been developed to remedy the conditions that produce the poor plant growth and decreased yields associated with the three groups of impacted soils. First, large amounts of irrigation water can be used to leach excess salts through the soil profile

INFORMATION BOX 20.4 Characteristics of Salt Affected Soils

Soil

pH

Electrical Conductivity (mmhos cm21)

Exchangeable Sodium Percentage

Saline SalineAlkali Sodic

<8.5 8.5

>4 >4

<15 >15

>8.5

<4

>15

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and out of the root zone. This is appropriate for reclamation of saline soils. This can only be accomplished if the soil has adequate drainage characteristics. For sodic soils, drainage can in turn be improved by amending the soil with calcium amendments, which replace sodium on the exchange sites and cause flocculation of soil particles with increased pore space (see Chapter 2). The most frequently used amendments are limestone (CaCO3) and gypsum (CaSO4  2H2O). Sodic or saline alkali soils may require up to 15–20 tonne ha
1 to reduce the exchangeable sodium content to acceptable levels. Finally, elemental sulfur is also used as a soil amendment to reduce soil pH when values are initially in excess of 8.5. Elemental sulfur is oxidized by autotrophic bacteria such as Thiobacillus thiooxidans, resulting in the production of sulfuric acid and a concomitant soil pH decrease (see also Chapter 5). Sulfur amendments can be in the range of 1–3 tonne ha
1. In the desert southwest, commercial nitrogen fertilizers frequently have sulfur included to maintain soil pH values within the neutral zone. Overall, the strategies employed to reclaim saline and/or sodic soils can be summarized as: (1) improving drainage by replacing sodium on exchange sites with calcium, (2) leaching soluble salts via applying large volumes of irrigation water, and (3) decreasing soil pH via sulfur amendments.

TABLE 20.2 Problems Related to Low Organic Matter in Soil and Other Surface Material Parameter

Problem

Poor aggregation of primary particles

Compaction Low infiltration rates Low water holding capacity Limited aeration

Low nutrient status

Infertile soils Low microbial populations

Extreme pH

Affect chemical and biological properties

High metal concentrations

Toxicity

From Environmental Monitoring and Characterization, Elsevier Academic Press, San Diego, CA, © 2004.

INFORMATION BOX 20.5 Sources of Organic Materials for Ecosystem Restoration Human and Animal Waste

Animal manures

20.3.6 Soil Treatment Using Organic Amendment Highly disturbed sites often result in surface soils being devoid of organic matter. This can occur from a variety of human activities including strip mining, where the surface top soil is removed and mine tailings are deposited over existing topsoil, soil erosion, and overuse. In all cases, organic matter is sparse or entirely absent, which reduces the ability of the soil to support plants. It is common for these sites to have extremely low microbial populations, extreme pH, low soil permeabilities, and high soluble metal concentrations. These conditions are not suitable for sustainable plant growth, and they generally require some form of organic amendment to jump-start the revegetation process. Problems that occur due to low organic materials are presented in Table 20.2, and common sources of organic materials used to enhance ecosystem restoration are illustrated in Information Box 20.5. The concept of organic amendments to enhance plant growth has been used for centuries as in the application of “night soil” (human feces and urine) to agricultural land. The use of raw waste material can spread disease, but in the United States, the solid material (biosolids) left after treatment of municipal sewage is further refined to largely eliminate potential pathogens before being applied to agricultural land (see Chapter 23). Biosolids have been successfully applied to mine tailings or smelters that contain high

Biosolids Composted wastes

Industrial Waste

Paper mill sludges Sawdust Wood chips

Agricultural Waste

Mulch

or even phytotoxic levels of heavy metals. Biosolids that have undergone lime stabilization are particularly useful for such restoration, since the increase in pH reduces the bioavailability of metals to plants. Biosolids and composts have also been used to restore diverse ecosystems such as mountain slopes in the Washington Cascades or stabilize sand dunes in southeastern Colorado. In addition to pathogens, there is potential concern over other contaminants that may be present in the organic material. These include constituents such as salts, metals, nanoparticles, and hazardous organic compounds. The presence of physical, chemical, and biological contaminants needs to be assessed prior to use of the organic material as an amendment. In all cases of organic amendment added to restore soils, the critical parameter appears to be the magnitude of organic material applied. This is particularly important in desert ecosystems, where high temperatures result in rapid decomposition and mineralization of organic materials. If insufficient organic matter is added to a disturbed site, the beneficial effect is not maintained for a sufficiently long time to allow stable revegetation to occur. An example of organic amendment application for revegetation of mine tailings is presented in Case Study 20.1.

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Case Study 20.1 Mission Copper Mine, Arizona: Reclamation and Revegetation of Mine Tailings Using Biosolids Amendment In the United States, mining is a large industry that provides valuable raw material and creates economic benefit for local communities. However, the environmental damage incurred from this industry range from unsightly mine tailings to the generation of dust, to the leaching of toxic elements into nearby waterways and aquifers. Mine tailings are formed during the extraction and processing of the ore. Typically these materials are disposed of into large tailings piles that are 30– 40 m high. The physiochemical characteristics of mine tailings are totally unlike the displaced topsoil that once supported vegetation in any given area. By removing and crushing bedrock from the mines and placing it on the surface, minerals will oxidize when exposed to the atmosphere. For example, pyrite (FeS2) is a common mineral at many mines, and it oxidizes to form acid mine drainage. Leachate from tailings can then contaminate surface and groundwaters in addition to increasing the solubility of toxic metals. Mine tailings are a very inhospitable medium in which to grow plants. The material has poor structure; there is no organic material; the cation exchange capacity (CEC) is very low; the water holding capacity of the material is poor to nonexistent; and there are few macronutrients (NPK) available for the plants. Soil biota, in the form of bacteria and fungi, are present only in low numbers, and finally, the pH is usually low, which increases the likelihood that toxic metals could be taken up by the plants. Therefore the material needs to be treated to provide a conducive environment for plant growth. This is typically done by the addition of amendments, one major type of which is organic amendments (Information Box 20.5). In 1994, the Arizona Mined Land Reclamation Act was passed that required reclamation of all mining disturbances on private land to a predetermined postmining use, and in 1996 the Arizona Department of Environmental Quality (ADEQ) adopted new rules allowing for the use of biosolids to support this reclamation. The Arizona Mining Association (AMA) has estimated that there are 13,360 ha of active mine sites in Arizona that can be reclaimed with the use of biosolids. Current ADEQ regulations limit the lifetime loading rate of biosolid applications to mine tailings to 333 metric tons/ha (dry weight). Here we describe a case study illustrating the use of biosolids to restore and stabilize mine tailings derived from copper mining. The Overall Objective of the project was to evaluate the efficacy of dried biosolids as a mine tailing amendment to enhance site stabilization and revegetation. Experimental Plan Study Site

A 5-acre copper mine tailing plot located near Mission Mine, south of Tucson, Arizona was designated for this study. Biosolids were applied at a rate of 200 to 300 (70,100 dry tons/acre) across the site in December 1998. Supplemental irrigation was not used in this experiment. This is an important component, as it is not desirable to design projects that require irrigation for sites in arid environments.

Soil Microbial Response to Biosolids

Pure mine tailings contain virtually no organic matter and very low bacterial populations of approximately 103 per gram. A large population of heterotrophic bacteria is essential for plant growth and revegetation, and therefore, monitoring soil microbial populations gives an insight into the probability of revegetation prior to plant growth. Biosolids routinely contain very high concentrations of organic matter, including the macroelements carbon and nitrogen, which are essential for promoting microbial growth and metabolism. Following biosolid amendment of the mine tailings, heterotrophic bacterial populations increased at the surface to around 107 per gram. Bacteria decreased with increased depths from the surface, indicating the influence of the biosolid surface amendment on bacterial growth. Overall, the microbial monitoring data showed the success of biosolid amendment in changing mine tailings into a true soil-like material. Physical Stabilization

One of the main objectives in reclaiming mine tailings is erosion control through wind and water erosion. This is generally best accomplished through a revegetation program, since the root structures of the plants help to hold soil particles in place. In this experiment, the application of biosolids and the subsequent growth of plants promoted site stabilization. In the desert Southwest, high summer temperatures and limited rainfall are normal; however, despite these extreme conditions, grasses have become established on these tailings. Vegetation transects surveys were conducted on this site 14 months, 21 months, and 33 months after initial seeding. The vegetation cover increased from 18% at the 14month survey to 78% after 33 months. At 14 months, the predominant plant species were bermuda grass (Cynodon dactylon), and the invasive weed, Russian thistle or tumbleweed (Salsola tragus), but by the 33rd month, buffelgrass (Pennisetum ciliare), and Lehmann lovegrass (Eragrostis lehmanniana) had replaced the Russian thistle. Fig. 20.8 A–C show the progressive increase of vegetation on this site over time. In this case, the use of biosolids for enhanced revegetation and stabilization of mine tailings would be considered a success. Soil Nitrate and Metal Concentrations At Site 1, soil nitrate and total organic carbon (TOC) are very high at the surface, but decrease to the levels found in pure mine tailings at lower depths. The fact that nitrate and TOC concentrations are correlated is important, since it creates substrate and terminal electron acceptor concentrations suitable for denitrification (see also Chapter 5). Nitrate concentrations increased during the monsoon rainy season of 2000, most likely due to enhanced ammonification and subsequent nitrification. However, within the soil profile, nitrate concentrations decreased with depth. By the winter and spring of 2001, the nitrate concentrations at all soil depths

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had decreased. There was no evidence of the leaching of nitrate since concentrations at the 30 —40 depth were always minimal. Therefore the most likely explanation for decreased nitrates within the soil profile is the process of denitrification. Soil nitrate concentrations became extremely high at both sites in the summer of 2001, again most likely due to nitrogen mineralization and seasonal nitrogen cycling. Specifically during the warmer summer months, rainfall events appear to have triggered microbial mineralization of nitrogen as nitrate. The application of biosolids to a project site brings some concern about the introduction of heavy metals to the environment. However, data from this study showed that metal concentrations were fairly consistent with soil depth, indicating that the tailings were the major source of metals, not

20.3.7 Soil Treatment for Metals and Organic Contaminants Special efforts are needed to treat soils contaminated by metals or organic compounds. A standard approach is excavation and replacement. This is an effective method, particularly for relatively small areas with shallow (<3 m deep) contamination. Soil washing can also be used, wherein for example a surfactant solution (detergent) is applied to the contaminated soil to enhance removal of the contaminants. This can be accomplished either in aboveground reactors, by excavating the soil, or in situ by injecting the solution followed by extraction back to the surface. Biological or chemical treatment methods can also be used to degrade organic contaminants. Phytoremediation can be used to remove metals and organics. These and other methods are covered in Chapter 19.

the biosolids. Further evidence of this is shown by the high molybdenum and copper values typical of mine tailings. At this site there was little evidence of metals leaching through the soil profile. Summary This study on the application of biosolids to mining tailing at the Mission Mine in Arizona shows that soil stabilization has been encouraged through revegetation techniques and that the leaching of nitrate and heavy metals to important water resources has not been observed. This case study gives an indication of the extensive monitoring that is necessary to understand and assess the performance of the restoration process, and the necessary duration of the monitoring effort.

“site” may comprise 100’s to 1000’s of acres for example. Methods used for reclamation and restoration therefore need to be cost effective over those large scales. Because of the cost and complexity of restoring degraded rangeland, sustainable management of rangelands is particularly critical to reduce the advent of pollution and other disturbances.

20.4 AQUATIC RECLAMATION METHODS Major methods used to reclaim disturbed aquatic systems and improve water and sediment quality will be covered in this section. These include: l

l l

20.3.8

Rangeland Restoration

Roughly a third or more of the earth’s land surface can be classified as rangelands, which includes such fragile ecosystems as grasslands, shrublands, wetlands, and deserts. These environments are particularly vulnerable to the impacts of global climate change. Rangelands in many regions of the world are often used to support pastoral farming—animal production conducted to provide food and fiber for humans. Hence, they are critical for human well-being. Rangelands also provide critical habitat for many plant and animal species, supporting healthy wildlife populations. Rangelands suffer from many issues that can impair their functioning. Loss of soil quality through pollution or overuse, loss of soil quantity through erosion or desertification, and the advent of invasive species are primary examples of issues that can degrade rangeland quality. The restoration and management of rangelands is very complex due to the nature and size of rangelands. A single rangeland

l l

Physical actions (shoreline stabilization, stream channel modification, dredging) Water treatment, Sediment treatment, Aquatic plant management, and Biomanipulation.

Aquatic systems span a wide variety of environments: l l l l l

Streams Lakes Wetlands Estuaries Marine (coastal and open ocean)

The objectives of and methods used for restoration may vary for these different types of aquatic systems.

20.4.1

Physical Actions

The stabilization of shorelines—the banks of streams and lakes—is accomplished using grading and contouring, capping, and revegetation. General aspects of these methods were covered in Section 20.3. There are special types of actions used for aquatic systems. For example,

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FIG. 20.8 Mine tailings plot during a revegetation project. (A) prior to biosolid amendment; (B) 2 years after biosolid application; (C) 3 years after biosolid application. (From Environmental Monitoring and Characterization, Elsevier Academic Press, San Diego, CA, 2004.)

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(A)

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8- to 12-foot length

Rootwad Baseflow Streambed

Thalweg channel Diameter of log = 16-in min.

Footer log

Boulder 1 1/2 times diameter of log

(A)

(B) FIG. 20.9 Root wads for shoreline stabilization, (A) diagram illustrating implementation, (B) photograph of root wad deployment. (Available from: USDA, https://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/water/manage/restoration/?cid¼stelprdb1044678.)

one special type of surface cover is called Root Wads, which are the stumps of large dead trees. These are placed on the edge of the shoreline along with boulders, as shown in Fig. 20.9. Another type of cover method is Staking, which involves the use of wooden stakes driven into the ground to help anchor live vegetation (Fig. 20.10). A third approach is to use Fascines, which are rough bundles of

brushwood or other material (Fig. 20.11). Rock riprap is a fourth type of cover used for bank stabilization (Fig. 20.12). A special consideration for streams is the properties and condition of their channel. This influences many aspects of the ecosystem, including stream water velocity, erosion potential and sediment load, flooding potential, and the

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Dead stout stake Wire secured to stakes

Brush mattress

Live and dead stout stake spacing 2 feet on center 16 Gauge wire Branch cuttings

t 2f

Live stake

Baseflow Streambed

Live fascine bundle Live stake Geotextile fabric

Dead stout stake driven on 2-foot centers each way, minimum length 2 1/2 feet

FIG. 20.10 Schematic illustrating the principles of the staking method for shoreline stabilization. (Available from: USDA, https://www.nrcs.usda.gov/ wps/portal/nrcs/detail/national/water/manage/restoration/?cid¼stelprdb1044678.)

FIG. 20.11 Using fascinces for shoreline stabilization. A single fascine is shown on the left side of the figure. (Source: Available from: https://www. ernstseed.com/products/bioengineering-materials/). Rows of fascines deployed on a shoreline are shown on the right side (Source: Available from: USDA, https://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/water/manage/restoration/?cid¼stelprdb1044678.)

types of habitats and associated wildlife present. Therefore stream channel modification can be a significant component of restoration activities. The first step in channel modification efforts to repair a disturbance and restore function is to determine the optimal conditions to which to restore the channel. This depends on the ecoregion in which the sites resides and the type of stream. For example,

the properties and behavior of a stream located in the headwaters of a watershed are different from those of a stream located in the discharge or outflow zone of the watershed (Fig. 20.13). Thus the types of landforms and habitats present will be different. A large-scale factor to consider is the Sinuosity or Meander Ratio, which is the length of the stream divided

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by the length of the valley (Fig. 20.14). For example, a linear stream has a MR of 1. Ideally, one would restore the stream channel pattern to a condition that is compatible with current environmental conditions so that it will remain stable. Large-scale construction work is implemented to make alterations in stream channel patterns. This may include creating artificial meanders and shifting the location of sections of the stream. At smaller scales, flow changing devices are a broad category of physical devices used to divert stream flow away from eroding banks. These include devices known as deflectors, bendway weirs, vanes, spurs, kickers, and barbs. In essence, they are structures that project from a streambank and oriented upstream to redirect streamflow away from an eroding bank and to alter secondary currents. These treatments are typically constructed of large boulders and stone, but timber and brush have also been used. Dredging of sediment is a standard method used for restoration of aquatic systems. Dredging may be implemented for several reasons, including: l l l l l

FIG. 20.12 Rock riprap for shoreline stabilization. (Available from: USDA, https://www.fs.usda.gov/detail/hoosier/about-forest/?cid¼ fsbdev3_017633.)

Mountain headwater streams flow swiftly down steep slopes and cut a deep V-shaped valley. Rapids and waterfalls are common

Deepen and increase lake/river volume Control excessive plant growth Remove excess nutrient-rich muck Remove resting cysts of noxious algae Remove contaminants

Dredging is conducted under either dry or wet conditions. The water body must first be drained for dry dredging.

Low-elevation streams merge and flow down gentler slopes. The valley broadens and the riveer begins to meander

At an even lower elevation a river wandeers and meanders slowly across a broad, nearly flat valley. At its mouth it may divide into many separate channels as it flows across a delta built up of riverborne sediments and into the sea

Zone 1 Head wate rs

Zone 2 Trans fer zo n

e Zone 3 Depo sition al

zone

FIG. 20.13 Zones of a stream. (Available from: USDA, https://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/water/manage/restoration/? cid¼stelprdb1044678.)

Reclamation and Restoration of Disturbed Systems Chapter

FIG. 20.14 Example of a meandering stream. (Available from: USDA, https://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/water/manage/ restoration/?cid¼stelprdb1044678.)

Standard excavation equipment are used for this purpose. Dry dredging may be more disruptive and expensive due to the need to drain the water body, but it provides direct access to the sediment, often resulting in highly effective results. Wet dredging is conducted while the water remains in the water body. In this case, the dredging equipment are placed on the shoreline or on a barge or ship. There are two general types of wet dredging—mechanical and hydraulic/pneumatic. Mechanical dredging uses a bucket or clamshell device to physically remove sediment (Fig. 20.15). Conversely, hydraulic dredging uses strong suction to remove water and sediment (Fig. 20.16). Pneumatic dredging is similar to hydraulic, except that air rather than water is used. While dredging can be an effective method, there are several potential concerns. One is the temporary loss of water clarity due to suspension of sediment. Another concern is the mobilization of contaminants and nutrients stored in the sediment. Lastly, a major longer term concern is the potential impact on the benthic habitat and associated wildlife. Another factor is that the sediment will require treatment if it is contaminated. Dredging is typically relatively expensive compared to other restoration methods.

20.4.2

Water and Sediment Treatment

Various methods are available to treat surface water, depending upon the issue. A chemical coagulant can be added, for example, to reduce phosphorus concentrations. Aluminum, iron, or calcium salts are added to form floc (small aggregated particles) that sequester P. The floc settles out of of the water column, reducing the P load. Algicides can be added to the water to eradicate algal buildups. Aeration devices can be used to provide oxygen to the water column.

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Biomanipulation is another option for treating water quality issues. This is the process of purposefully adding or removing an organism from the system. For example, zooplankton such as water fleas can be added to a lake to feed on algae, and thereby reduce algal blooms. Implementing a biomanipulation action requires consideration of how the planned addition or subtraction will affect the overall food web of the system. As noted before, dredging is a standard method used to remove contaminated sediments. One alternative to dredging is to cap the sediment with clean sediment and/ or a synthetic geomembrane. The cap can stabilize the surface, isolate the contamination, and separate the benthic community from the contamination. Another alternative is to treat the sediment in place. One example currently being investigated is mixing activated carbon into the surface layer of the sediment. The objective is for organic contaminants present in the sediment to adsorb to the carbon, which removes them from the sediment. Reactive media such as oxidants or reductants could be added to destroy the contaminants. Alternatively, methods could be implemented to promote biotransformation of the contaminants. These latter approaches were discussed in Chapter 19. One common issue for many aquatic systems is excessive vegetation, particularly weeds. Mechanical methods can be used to remove unwanted vegetation. The water level can be manipulated to remove the water source for the vegetation. Herbicides can be added to eradicate the vegetation. The use of herbicides has several associated concerns that must be considered before use.

20.5

ECOLOGICAL RESTORATION

20.5.1 Natural Versus Active Ecological Restoration Natural restoration is essentially the process of allowing the ecosystem to heal itself without active management or human interference. Depending on site-specific characteristics, natural restoration may not be a viable alternative. Natural or passive ecological restoration projects primarily apply to systems that are still functionally intact, but that have lost vegetative cover and biodiversity from such activities as overgrazing or habitat fragmentation. The implicit goals of these projects are to reduce or eliminate the causes of degradation, often through institutional actions, while encouraging the growth of indigenous plants to increase the productivity of the area in a sustainable way. In general, minimal soil preparation is needed, soil amendments and irrigation are not required, and seeds are simply broadcast in a designated area. Restoration under these conditions is usually coupled with land conservation objectives.

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2

3

Transport barge 4

Grab dredge

Water

Stabilization spud Underwater silt screen

Existing bottom of waterway 1 Design waterway elevation 1

Dislodging of in situ sediment

2

Raising of dredged material to the surface

3

Horizontal transport

4

Placement or further treatment

Sediment disturbance zone New bottom of waterway

(A)

(B) FIG. 20.15 Mechanical wet dredging, (A) Schematic (Available from: https://instrumentalism.wordpress.com/2011/11/06/dredge-landscape-taxon omies/), (B) example rig (Available from: https://www.fema.gov/media-library/assets/images/71444).

Active ecological restoration is necessary for sites where the abiotic and biotic functions of an ecosystem have been impaired to an extent beyond their ability to recover naturally. Active restoration is obviously much more expensive than passive. The cost of restoration will generally rise in proportion to the damage incurred. The restoration goals and objectives developed for a project

compared to the existing site conditions will specify the degree of work necessary to achieve the specified goals. Active ecological restoration employs any and all of the methods discussed in the preceding sections for land and aquatic reclamation, and also remediation methods discussed in Chapter 19. These methods are employed to make the environment suitable to support flora and fauna and to

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4 3 Upland disposal site with containment dike Hydraulic pipeline Hydraulic dredge Underwater silt screen Water

2

Sediment disturbance zone

1 New bottom of waterway

Design elevation

1 Dislodging of in situ sediment 2 Raising of dredged material to the surface 3 Horizontal transport 4 Placement or further treatment FIG. 20.16 Hydraulic wet dredging schematic. (Available from: https://instrumentalism.wordpress.com/2011/11/06/dredge-landscape-taxonomies/.)

support proper ecosystem functioning. In addition to reclamation and remediation methods, efforts are often made to restore threatened or displaced plant and animal species.

20.5.2

Best Practices

Guiding principles and best practices have been developed for ecological restoration by the Society for Ecological Restoration. These are summarized in Information Box 20.6.

One key concept is to first remove the source of the impairment or disturbance. If this step is not carried out, it is likely that the restoration project will fail because the disturbance will occur again. Another key concept is the use of natural (native) reference ecosystems. A reference system represents what the disturbed site’s ecosystem would be like had degradation not occurred, while incorporating capacity for the ecosystem to adapt to existing and anticipated environmental change. It is used to inform the objectives and target outcomes for the restoration project. A third concept

INFORMATION BOX 20.6 Values and Principles That Underpin Effective Ecological Restoration Restoration Should Be Effective, Efficient, and Engaging Effective ecological restoration reestablishes and maintains values. Efficient ecological restoration maximizes beneficial outcomes while minimizing costs in time, resources and effort. Engaging ecological restoration collaborates with partners and stakeholders, promotes participation and enhances experience. Effective Ecological Restoration

Supports and is modeled on existing native ecosystems and does not cause further harm. Examples of relatively intact land and water ecosystems remain across the globe, which represent an invaluable natural heritage. Appreciation of the long history of evolution of organisms interacting with their natural environments underlies the ethic of ecological restoration. Is aspirational. The ethic of ecological restoration is to seek the highest and best conservation outcomes. Even if it takes long time frames, full recovery should be the goal wherever it may be ultimately attainable and desirable. Where full recovery is

clearly not attainable or desirable, at least partial recovery and continuous improvement in the condition of ecosystems to provide substantial expansion of the area available to nature conservation is encouraged. This ethic informs and drives high quality restoration. Is universally applicable and practiced locally with positive regional and global implications. It is inclusive of aquatic and terrestrial ecosystems, with local actions having regional and global benefits for nature and people. Reflects human values but also recognizes nature’s intrinsic values. Ecological restoration is undertaken for many reasons including our economic, ecological, cultural, and spiritual values. Our values also drive us to seek to repair and manage ecosystems for their intrinsic value, rather than for the benefit of humans alone. In practicing ecological restoration, we seek a more ethical and satisfying relationship between humans and the rest of nature. Is not a substitute for sustainably managing and protecting ecosystems. The promise of restoration cannot be invoked as Continued

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INFORMATION BOX 20.6

—cont’d

a justification for destroying or damaging existing ecosystems because functional natural ecosystems are not transportable or easily rebuilt once damaged, and the success of ecological restoration cannot be assured. Efficient Ecological Restoration Depends Upon

Addressing causes at multiple scales to the extent possible. Degradation will continue to undermine restoration inputs unless the causes of degradation are addressed or mitigated. Recognizing that restoration facilitates a process of recovery carried out by the organisms themselves. Reassembling species and habitat features on a site invariably provides just the starting point for ecological recovery; the longer term process is performed by the organisms themselves. Taking account of the landscape/aquatic context and prioritizing resilient areas. Sites must be assessed in their broader context to adequately assess complex threats and opportunities. Applying approaches best suited to the degree of impairment. Many areas may still have some capacity to naturally regenerate, at least given appropriate interventions; while highly damaged areas might need rebuilding “from scratch.” It is critical to consider the inherent resilience of a site (and trial interventions that trigger and harness this resilience) prior to assuming full reconstruction is needed. Addressing all biotic components. Terrestrial restoration commonly starts with reestablishing plant communities but must integrate all important groups of biota including plants and animals (particularly those that are habitat forming) and other biota at all levels from micro- to macro-organisms. Drawing rigorous, relevant, and applicable knowledge from a dynamic interaction between science and practice. All forms of knowledge, including knowledge gained from science, nature-based cultures, and restoration practice are important for designing, implementing, and monitoring restoration projects and programs. Knowing your ecosystems and being aware of past mistakes. Success can increase with increased working knowledge of the ecosystem and of appropriate restoration methods.

is to evaluate the site according to the six key attributes listed in Information Box 20.7. Another key concept is to recognize that full restoration may not always be achievable, and that large magnitudes of recovery may take many years to decades. This concept is captured by the five-star recovery ranking system (Information Box 20.8).

20.5.3

The Invasive Species Problem

As discussed in Chapter 14, due to increases in global trade and travel, alien plant and animal species have been introduced into native ecosystems around the world. Most of these species quickly die out in the new environment, while others become permanent, but minor components of the ecosystem. A few (less than 1%) may become

Taking an adaptive (management) approach. Ecosystems are often highly dynamic, particularly at the early stages of recovery and each site is different. This not only means that specific solutions will be necessary for specific ecosystems and sites; but also that solutions may need to be arrived at after trial and error. It is therefore useful to plan and undertake restoration in a series of focused and monitored steps, guided by initial prescriptions that can be modified as the project develops. Identifying clear and measurable targets, goals, and objectives. In order to measure progress, it is necessary to identify at the outset how restoration outcomes will be assessed. This will not only ensure that a project collects the right information but that it can also better attune the planning process to devise strategies and actions more likely to end in success. Adequate resourcing and long-term management arrangements. Engaging Ecological Restoration Depends Upon

Establishing effective communication and outreach to and with stakeholders. Successful restoration projects have strong engagement with stakeholders including local communities, particularly traditional communities and Indigenous peoples who retain traditional ecological knowledge. This communication and outreach is best achieved if the involvement commences at the planning stage and continues throughout the project and after restoration works are completed. Involving stakeholders in the development of solutions for improved management and restoration of sites. Ecological restoration outcomes are often more effective and efficient if stakeholders are engaged in assessing problems and devising solutions. The outcome of restoration is also more secure when there are appreciable benefits or incentives available to the stakeholders; and where stakeholders are themselves engaged in the restoration effort, building “ownership” into local cultures.

(Source: From Society for Ecological Restoration, 2016.)

invasive, spreading over large areas and disrupting ecosystem functions. They may also become pests in humanmanaged systems such as farms and rangelands. Examples of invasive plants are purple loosestrife and salt cedar, two introductions that have come to dominate many wetland and riparian ecosystems in North America. An example of an invasive animal is the zebra mussel, which clogs the intakes of power plants and depletes the water of phytoplankton that form the base of the native food chain. Over a hundred invasive species have been recognized as causing damage on an ecosystem-wide scale. Invasive species are a special problem in restoration work, because human-disturbed ecosystems are especially prone to invasion. For example, abandoned farmland in the western United States is often saline and high in

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INFORMATION BOX 20.7 Key Ecosystem Attribute Categories and Examples of Broad Goals for Each Attribute Category in a Restoration Project

Attribute

Absence of threats

Physical conditions Species composition Structural diversity Ecosystem functionality

External exchanges

Examples of broad goals—for which more specific goals and objectives appropriate to the project would be developed

Cessation of threats such as overutilization and contamination; elimination or control of invasive species Reinstatement of hydrological and substrate conditions Presence of desirable plant and animal species and absence of undesirable species Reinstatement of layers, faunal food webs, and spatial habitat diversity Appropriate levels of growth and productivity, reinstatement of nutrient cycling, decomposition, habitat elements, plant-animal interactions, normal stressors, on-going reproduction and regeneration of the ecosystem’s species Reinstatement of linkages and connectivity for migration and gene flow; and for flows including hydrology, fire, or other landscape-scale processes

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INFORMATION BOX 20.8 Five-Star Recovery Rating System Number of stars

«

««

«««

««««

(Source: From Society for Ecological Restoration, 2016.)

nutrients. These conditions favor the establishment of Russian thistle (tumbleweed), an annual plant that completes its life cycle on very little water and releases large amounts of seeds into the soil to germinate in subsequent years. Projects that attempt to reintroduce native plants on abandoned farmland often just stimulate the growth of even more tumbleweed. As another example, western U. S. rivers have been dammed and their flow regulated to prevent the occurrence of normal spring floods. Their floodplains have been invaded by salt cedar, which thrives on the saline soil that develops when the floods are disrupted. By contrast, native cottonwood and willow trees are not salt tolerant, and they have become rare on western rivers. There is no simple answer to the control of invasive plant species. However, some guiding principles are emerging from restoration studies. First, invasive species tend to be early successional plants, dominating an ecosystem just after it is disturbed. For example, tumbleweed often dominates for five years after a soil is disturbed, but during that time it adds organic matter to the soil, and conditions the soil to eventually become habitable by native species. Hence, patience is necessary in restoration work.

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«««««

Summary of Recovery Outcome (Note: Modelled on an appropriate local native reference ecosystem)

Ongoing deterioration prevented. Substrates remediated (physically and chemically). Some level of native biota present; future recruitment niches not negated by biotic or abiotic characteristics. Future improvements for all attributes planned and future site management secured. Threats from adjacent areas starting to be managed or mitigated. Site has a small subset of characteristic native species and low threat from undesirable species onsite. Improved connectivity arranged with adjacent property holders. Adjacent threats being managed or mitigated and very low threat from undesirable species onsite. A moderate subset of characteristic native species are established and some evidence of ecosystem functionality commencing. Improved connectivity in evidence. A substantial subset of characteristic biota present (representing all species groupings), providing evidence of a developing community structure and commencement of ecosystem processes. Improved connectivity established and surrounding threats being managed or mitigated. Establishment of a characteristic assemblage of biota to a point where structural and trophic complexity is likely to develop without further intervention. Appropriate cross boundary flows are enabled and commencing and high levels of resilience is likely with return of appropriate disturbance regimes. Long term management arrangements in place.

(Source: From Society for Ecological Restoration, 2016.)

Second, eradication of invasive species by physical or chemical means is often ineffective. Unless the physical environment is restored, the invasive species simply returns. A more successful approach is to attempt to restore the environment to one favoring establishment of native species. For example, native cottonwood and willow trees along western U.S. rivers can be restored even in the presence of invasive salt cedar if a pulse flood regime is returned to the river channel. The floods wash salts from the floodplain soil and germinate native trees, which then overtop the salt cedar and shade them out. Third, invasive species may come to play a positive role in the ecosystem.

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Animals that formerly depended on native species may adapt to use the invasive species as a source of food or shelter. Therefore a viable restoration goal might be to aim for a mix of native and introduced species that still can fulfill ecosystem functions. Invasive species can also be attacked by using biological control agents. Typically, these are insects from the native range of the invasive plant that are introduced into its new habitat to control its spread. For example, Asian beetles that feed on salt cedar are being tested as possible control agents for salt cedar on western U.S. rivers. Extensive research is needed before the release of a biocontrol agent to ensure that it is effective and will not become a pest for native plants as well as the introduced species.

20.6 REDEVELOPMENT AND REVITALIZATION The presence of an abandoned or otherwise impaired property is often a blight for the local community. Thus there is often great interest in redeveloping such properties for a number of reasons. These include increasing the local tax base, facilitating job growth, lessening development pressures on undeveloped, open land (urban infill), improving environmental quality, and invigorating the local community. The redevelopment of impaired properties is often constrained by the presence of contamination or other risk issues. We learned about the four “Rs” used to repair such sites—Reclamation, Remediation, Rehabilitation, and Restoration. A fifth R, Revitalization, connotes the sustainable redevelopment of impaired sites. Many abandoned properties are classified as brownfield sites, which is defined as a property whose expansion, redevelopment, or reuse may be complicated by the presence or potential presence of a hazardous substance. The EPA estimates that there are approximately 450,000 brownfields in the United States. Specific legislation was passed in the United States in 2002 to address these sites (see Chapter 30). Additional types of sites exist that may not be classified as a brownfield site but whose redevelopment is constrained by pollution or related issues. Examples of brownfield and other such sites include abandoned industrial or commercial properties (manufacturing plants, service stations, dry cleaners), unused agricultural fields, closed landfills, closed golf courses, and closed military bases. Sites may be redeveloped to many different uses, depending upon site conditions, surrounding land uses, and community wishes. Examples of common redevelopment uses include open green spaces (parks), community

centers, and commercial uses (hotels, business parks). Successful revitalization efforts require cooperation among all stakeholders in the process.

QUESTIONS AND PROBLEMS 1. Differentiate among: (a) rehabilitation; (b) revegetation; and (c) reclamation. 2. Discuss the different types of surface covers and identify under what conditions each type would be preferred. 3. Discuss why it is important to have clearly defined objectives for a restoration project. 4. What factors primarily determine whether active or passive ecological restoration should be undertaken? 5. What is the influence of organic amendments on soil physical and chemical properties? 6. Discuss the issues that need to be overcome to support a successful revegetation project. 7. What are major issues to deal with for restoration of streams?

REFERENCES Heikkinen, P.M., Noras, P., Salminen, R., 2008. Mine Closure Handbook. Vammalan Kirjapaino Oy, Helsinki. ISBN 9789522170552. United States Geological Survey (USGS), 2011. Monitoring habitat restoration projects: U.S. fish and wildlife Pacific region partners for fish and wildlife program and coastal program protocol. In: Chapter 11 of Section A, Biological Science, Book 2, Collection of Environmental Data. Available from: https://pubs.usgs.gov/tm/tm2a11/pdf/tm2a11.pdf.

FURTHER READING Artiola, J.F., Brusseau, M.L., Pepper, I.L., 2004. Environmental Monitoring and Characterization. Academic Press, San Diego, CA. Hobbs, R.J., Harris, J.A., 2001. Restoration ecology: repairing the earth’s ecosystems in the new millennium. Restor. Ecol. 9, 239–246. McDonald, T., Gann, G.D., Jonson, J., Dixon, K.W., 2016. International Standards for the Practice of Ecological Restoration—Including Principles and Key Concepts. Society for Ecological Restoration, Washington, DC. Middleton, N., Thomas, D. (Eds.), 1997. World Atlas of Desertification. Arnold Press, London, England. Pfadenhauer, J., Grootjans, A., 1999. Wetland restoration in Central Europe: aims and methods. Appl. Veg. Sci. 2, 95–106. United Nations FAO, Aquatic restoration website document. Available from: http://www.fao.org/docrep/008/a0039e/ a0039e00.htm#Contents.