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2 Ecological and Ecosystem Engineering for Economic‐Environmental Revitalization

       Bruno Barbosa1,2 and Ana Luísa Fernando1

       1 MEtRICs, Departamento de Ciências e Tecnologia da Biomassa, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, Caparica, Portugal

       2 Universidade Feevale, Novo Hamburgo – RS, Brazil

2.1 Introduction

      A variety of factors can confer marginality to a particular soil [1–3]. This fact is reflected in the number of scientific publications related to ecological and ecosystem engineering. In a brief search of the literature, it is simple to find many published articles containing results from soils contaminated with heavy metals or organic compounds, or describing other chemical, physical, and biological properties that are unfavorable to the proper functioning and balance of soil ecosystems [4–8]. In a particular degraded soil, multiple disturbances in physical, environmental, and biological factors can be found. Indeed, soils may be marginal due to factors such as temperature, waterlogging, unfavorable soil texture and stoniness, dryness, shallow rooting depth, poor chemical properties of the soil (salinity and sodicity), steep slopes, soil layer restrictions, low biological production, acidity and alkalinity, the presence of organic and inorganic contaminants, and so on [9, 10]. Emergent contaminants, such as microplastics, can also confer marginality to soils [11, 12]. Likewise, socioeconomic factors may influence the marginality of a given soil [13, 14].

      Physical factors such as soil compaction can interfere with soil drainage, the depth of plant roots, soil porosity, soil aeration, and gas transport properties, factors that together can also induce changes in the soil microbial composition and increase the emissions of greenhouse gases such as N₂O [15]. Such physical disturbance of soil can lead to a scarcity of oxygen at the root level, limiting plant growth and nutrition and creating conditions that may lead to the development of soil pathogens [10]. These changes in soil may also cause low rates of water infiltration and low hydraulic conductivity, which in turn will lead to lower gas diffusivities and air permeability, increasing the risk of developing anaerobic conditions in compacted soils [16, 17]. Such events and consequences induced by altering a single soil factor show the complex level of disturbance that can occur when more than one soil factor is changed. The same thing can occur with other physical factors at the chemical and biological/environmental levels.

Inorganic and organic compounds can alter soils' chemical conditions, constituting chemical factors that provoke marginality in soil environments to different degrees. Organic and inorganic soil contaminants pose numerous risks for the soil environment, producing ecological dysfunctions, disorders in the structure and functioning of soil microbial communities and soil biota in general, and animal and human health [18]. For example, heavy metals in soils can lead to toxicosis in both animals and plants [19, 20]. These soil contaminants can impact biochemical processes in plants related to the production of enzymes and antioxidants involved in protein mobilization and in the photosynthetic process [21], also impacting plant growth parameters, yields, and water and nutrient balances [22, 23]. Indeed, heavy metals can cause disturbances and dysfunctions in plant organisms not only in their biochemical processes, but also in their physiological and metabolic processes, including the absorption and assimilation of nitrogen [24]. Soil microorganisms play different roles in the biogeochemical process of the soil, but they can be severely affected by the presence of heavy metals in soils [25, 26]. Long‐term exposure to heavy metals can alter the richness, diversity, and structure of soils' microbial communities. Factors like soil pH, which can be changed by heavy metals in the soil environment, can also alter the fungal community [27]. These are just some examples of how physical and chemical factors can affect soils. Most of the time, these factors act simultaneously on soil biota and soil properties: multiple restricting factors act synergistically, either positively (leading to soil revitalization) or negatively (increasing marginality) [10]. For example, despite having recorded losses in biodiversity caused by heavy metals, other authors have not registered any negative effect on the soil's microbial functional stability [28]. So, how can we control the path and direction of these synergies? Can engineering interventions predict and induce soil ecosystems in the direction of revitalization? Have we any control over the impacts resulting from our interventions?

      Ecological and environmental engineering approaches that encompass physical and chemical technologies and operations to improve soil properties together with ecosystem engineering technologies – meaning the application of bioremediation, dendroremediation, phytoremediation, mycoremediation, and associated processes – with a goal of modifying, restoring, maintaining, and/or (re‐)creating functional ecosystems should be included in a remediation strategy and plan, as appropriate for the edaphic and climatic conditions of a given marginal soil and the specific properties that make it marginal [29]. Directly or indirectly, specific approaches and technologies should synergistically act with the physical, biological, and environmental factors of degraded land to provide socioeconomic and environmental revitalization [14, 30, 31]. However, despite proposing the remediation of the properties of a particular soil, ecological and ecosystem engineering do not always

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