Soil salinity, a prevalent issue affecting arable lands across the globe, arises when soluble salts accumulate in the soil profile to levels that negatively impact post-mining rehabilitation efforts, environmental health and economic profitability. The genesis of this condition can be traced to both natural phenomena and anthropogenic activities.

This article aims to explore the root causes of soil salinity and provide insights into effective management strategies.

What Is Soil Salinity?

Soil salinity refers to the presence of high levels of soluble salts in the soil, a condition that can significantly impair the growth of plants and lead to the degradation of land. Salts commonly found in saline soils include sodium, magnesium and calcium chlorides, as well as sulphates, which can accumulate through various means such as irrigation with salt-rich water or natural processes like the evaporation of standing water, which leaves salts behind.

Techniques for Soil Salinity Mapping and Monitoring

Understanding the extent and distribution of soil salinity is crucial for its management and mitigation. Advanced techniques employed for soil salinity mapping and monitoring include proximal soil sensing and remote sensing methods.

Proximal soil sensing (PSS) involves soil property measurements taken directly within or in close proximity to the soil surface. This technique utilises sensors that measure electrical conductivity (EC) in deciSiemens per metre (dS/m) at 25°C, a key indicator of soil salinity levels, by generating electromagnetic fields that penetrate the soil. The sensors, either handheld or attached to a mobile unit like a tractor, provide immediate feedback on the salinity condition of the area being surveyed. PSS allows for detailed, site-specific assessments, enabling targeted management interventions.

Remote sensing methods, on the other hand, offer the advantage of covering extensive areas with minimal ground disturbance. These methods rely on data collected by satellites or aircraft, which capture images in various wavelengths of light to detect salinity stress in vegetation or direct soil salinity indicators. The application of geographic information system (GIS) technology in conjunction with remote sensing facilitates the mapping of saline soils over large regions, providing valuable insights into spatial patterns and trends over time.

Classification of Soil Salinity Levels

The classification of soil salinity levels is critical for determining the appropriate management strategies to mitigate salinity’s impact in post-mining rehabilitation efforts. The following ranges are recognised in categorising soil salinity:

Non-saline soil: EC less than 2 dS/m: At this level, soil salinity poses minimal to no restriction on vegetation growth, allowing for normal development and establishment of a wide range of plant species during rehabilitation.
Slightly saline soil: EC from 2 to 4 dS/m: This range begins to affect very sensitive plants but generally allows for the healthy growth of most vegetation used in reclamation projects.
Moderately saline soil: EC from 4 to 8 dS/m: Moderate salinity levels can impair the growth of sensitive and some moderately salt-tolerant plants, necessitating careful selection and management practices to ensure successful rehabilitation.
Highly saline soil: EC from 8 to 16 dS/m: At these levels, only salt-tolerant plants can grow successfully. Substantial vegetation establishment and growth reduction are common, and soil amelioration practices become increasingly necessary.
Very highly saline soil: EC greater than 16 dS/m: Salinity levels in this range severely restrict the variety of plants that can be established, often limiting rehabilitation efforts to only the most salt-tolerant species and requiring significant salinity management efforts.

Different Causes of Soil Salinisation

The origins of soil salinity are multifaceted, involving a complex interplay of natural processes and human activities that contribute to the accumulation of soluble salts in the soil.

Natural Processes

Several natural processes contribute to the development of soil salinity, significantly impacting the soil’s health and fertility. These processes include:

Weathering of rocks: The natural breakdown of rocks is a primary source of the salts found in soils. Over time, rainwater and natural acids present in soil water dissolve minerals contained in rocks. This process releases soluble salts like sodium, calcium, magnesium and potassium into the soil. These salts are then either leached away with groundwater or accumulate in the soil profile, contributing to its salinity.

Seawater intrusion: In coastal regions, the encroachment of seawater into freshwater aquifers is a significant cause of soil salinity. This intrusion can be exacerbated by over-extraction of groundwater, leading to a lowered water table and the displacement of fresh water by saltwater. The resulting saline water can alter the soil’s salinity levels, adversely affecting groundwater quality and ecosystem health.

Capillary rise: In arid and semi-arid regions, high temperatures and evaporation rates can cause groundwater to move upwards through the soil pores, a process known as capillary rise. When the water reaches the surface and evaporates, it leaves behind salts that were dissolved in it. This process can lead to the accumulation of salts on the soil surface, increasing the soil’s salinity levels and potentially harming vegetation growth and soil structure.

Human Activities

Human activities offer an opportunity to positively impact soil health, particularly in addressing the challenge of soil salinity.

Human activities can contribute to soil salinity reduction by:

Innovative irrigation practices: The adoption of advanced irrigation techniques that use water efficiently can help prevent the accumulation of salt in the soil profile. Techniques such as drip irrigation and the use of lower-salt water sources are effective in minimising the impact of salinity, particularly in areas where natural rainfall is not sufficient to support vegetation growth.
Sustainable land management: Efforts to maintain and restore vegetation cover, including reforestation and the implementation of cover vegetation, play a crucial role in preserving the natural water cycle. These practices enhance water infiltration into the soil and groundwater reservoirs, reducing the concentration of salts by diluting and washing them away.

The Influence of Salinity Levels on Mining Activities and Subsequent Rehabilitation Efforts

Elevated salinity reduces soil’s ability to hold water, making it challenging for vegetation to thrive, which can lead to operational inefficiencies and environmental degradation in mining sites.

Reduced Plant Growth and Biodiversity

High levels of soil salinity reduce a mining site’s biodiversity by inhibiting the growth of specific plant species critical for sustaining the ecosystem. With reduced vegetation, the fragile landscape is at risk of erosion and loss of habitat for wildlife.

Equipment Corrosion

The presence of soluble salts in mine water can accelerate the corrosion of equipment, leading to costly repairs or replacements.

Lower Soil Fertility

Saline soils hinder plant nutrient uptake, reducing vegetation growth and lowering overall soil fertility. This condition can result in lower productivity and increased costs for land rehabilitation efforts.

Impact of Salinity Levels on the Environment

The consequence of varying soil salinity levels extends beyond post-mining rehabilitation efforts, affecting environmental health and biodiversity. Here’s how soil salinity impacts the environment:

Change in Water Quality

Elevated soil salinity levels can significantly alter the quality of surface and groundwater. Salts from the soil can leach into water bodies, increasing their salinity and potentially making them unsuitable for human consumption and wildlife. This degradation of water quality can lead to a reduction in available freshwater resources, affecting both ecosystem health and human communities reliant on these water sources.

Increased Risk of Flood

High soil salinity can impair the soil’s ability to absorb rainfall efficiently, leading to an increased risk of flooding. Saline soils tend to have lower infiltration rates, causing water to accumulate on the surface rather than being absorbed. This not only increases the immediate risk of flooding following heavy rainfall but also contributes to long-term waterlogging issues.

Risks of Soil Erosion and Reduced Productivity

Saline soils are more susceptible to erosion due to their often deteriorated structure and reduced vegetation cover. The lack of plant roots, which help to hold soil particles together, and the decreased soil aggregate stability in saline conditions make these soils more vulnerable to wind and water erosion. Erosion further reduces soil fertility and structure, compounding the difficulties of managing saline soils and diminishing land productivity.

Possible Dust Storms

The combination of soil erosion and reduced vegetation cover on saline lands can lead to the increased likelihood of dust storms. These storms can have severe environmental and health impacts, carrying salt and other particulates over long distances. Dust storms contribute to air quality degradation and affect respiratory health, and they can deposit salt over wide areas, potentially spreading the salinity issue to new regions. The challenge of managing and mitigating the effects of soil salinity thus extends beyond the immediate vicinity, affecting regional climate and air quality.

Preventing, Ameliorating and Rehabilitating Saline and Sodic Soils

Addressing the challenges posed by saline and sodic soils is essential for successful post-mining rehabilitation and environmental health. The following sections outline some of the strategies used to prevent, ameliorate and rehabilitate these soils:

Salt Flushing and Leaching

Salt flushing and leaching are effective methods for reducing soil salinity, especially in post-mining landscapes where water supply allows for their practical application. These techniques involve the application of large volumes of water to saline soils, diluting and washing away the salts through the soil profile and beyond the root zone. For optimal results, salt flushing should be combined with adequate drainage systems to facilitate the removal of salt-laden water, minimising the potential for secondary salinisation.

Organic and Microbial Remediation

Incorporating organic matter into saline soils can improve soil structure, increase water retention and enhance microbial activity, leading to indirect remediation of soil salinity. Organic amendments, such as compost, manure or biochar, can help dilute soil salts and boost soil health, facilitating the growth of salt-tolerant microbes. These microbes play a crucial role in the biogeochemical cycles, potentially transforming salts into less harmful forms or promoting conditions favourable to vegetation growth in reclaimed mining areas.

Phytoremediation

Phytoremediation leverages the ability of certain plants, known as halophytes, to tolerate and even thrive in saline conditions. These plants can absorb salts in their biomass, effectively removing salts from the soil. Over time, harvesting these plants can gradually decrease soil salinity levels. Phytoremediation is a sustainable and eco-friendly approach, but its efficiency depends on the selection of appropriate plant species, climatic conditions and the initial soil salinity levels.

Afforestation and Reforestation

Planting trees (afforestation) in areas that were not previously forested or reforesting areas that have been disturbed due to mining activities can indirectly mitigate soil salinity. Trees can lower the water table through evapotranspiration, reducing the rise of saline groundwater to the soil surface. Additionally, tree roots can improve soil structure and aeration, encouraging the development of a healthier soil ecosystem. Afforestation and reforestation are long-term strategies that contribute to the restoration of the hydrological cycle and the stabilisation of the soil in post-mining landscapes.

How We Offer Solutions to Manage Soil Salinisation in Your Area

Our range of products is designed to address the unique needs of various landscapes, taking into account the specific characteristics, such as soil type, salinity levels and environmental conditions to alleviate the effects of soil salinisation such as erosion and loss of biodiversity.

Some of our products include:

EnviroLoc BFM: EnviroLoc Hydromulching BFM is resilient in harsh conditions, retaining water up to 20 times its weight. Our flexible fibre matrix effectively controls erosion, boosts plant growth and enhances revegetation project stability.
EnviroSoil: EnviroSoil contains active components such as thermally-refined organic fibres, high carbon, organic soil conditioners, seaweed extracts, mineral blends like basalt and microbial inoculants. These ingredients symbiotically enhance rhizosphere growing conditions.
FibreLoc: FibreLoc is an advanced dust suppression product designed to endure tough conditions where polymers won’t work. The organic wood fibres and binders create a flexible blanket that resists high salinity levels, ideal for tailing storage facilities.

Implement Long-Term Solutions to Prevent High Soil Salinity

Addressing soil salinity is not only crucial for ecological balance but also for the sustainability and profitability of Australian industries. Australia boasts a diverse range of industries from agriculture to mining, all of which stand to benefit significantly from effective soil management practices. By implementing long-term solutions to prevent and manage soil salinity, we can ensure the continued success of these industries and contribute towards a more sustainable future for all.

High soil salinity levels may cause dust storms. Learn how we can suppress it with our service.

What Causes Soil Salinity and How Can It Be Managed?