Soil is an important natural resource whose quality and management is essential to sustaining food production. Inadequate knowledge of soil ecology and its degradation is one of the greatest problems to sustaining food sufficiency and security.
In spite of the contribution of mineral mining and oil and gas production to the country’s gross domestic product (GDP), it is noted to cause environmental degradation and health implications of various degrees in the host communities.
Attempts to improve and manage the impact of mining and oil and gas activities should go beyond the technical aspect of monitoring to ensure compliance with standard requirements.
In its traditional meaning, soil is the natural medium for the growth of plants. Soil has also been defined as a natural body consisting of layers (soil horizons) that are composed of weathered mineral materials, organic material, air and water.
Soil is the end product of the combined influence of climate, topography, organisms (flora, fauna and human) on parent materials (original rocks and minerals) over time.
Soils constitute the foundation for agricultural development, essential ecosystem functions and food security. The sustainable management of soils contributes to economic growth, biodiversity and food security which in turn are key to eradicating poverty.
Soil health, therefore, is tightly linked to land use, food production as well as to the use of inputs, and to many other environmental and socioeconomic issues.
It must be highlighted that the doubling of global food production during the past decades has been accompanied by a massive increase in the use of inputs, such as synthetic nitrogen, phosphorus, pesticide applications and extensive use of irrigation and energy.
The intensification of agriculture has also led to the degradation and exhaustion of soil. Unfortunately, people have been building and expanding their cities on the most fertile soils, thereby squandering such a valuable resource.
This pattern is unlikely to change in the future. Continued urbanization will pose a further threat to agriculture production, along with the changing patterns of food consumption by the growing urban population.
Soil degradation represents a major threat to food production and environment conservation, especially in tropical and sub-tropical regions (where most of the future population growth will take place).
Soil degradation has become a very serious problem in densely inhabited agricultural regions. Soil degradation is causing a decline in crop productivity and huge economic loss, putting the food security and livelihood of farmers at risk.
In sub-Saharan Africa (SSA), soil degradation (nutrient depletion) is the primary form of soil degradation, is leading to a decline in crop productivity, and has been linked to hunger and poverty.
Soil degradation is defined as a change in the soil health status resulting in a diminished capacity of the ecosystem to provide goods and services for its beneficiaries.
Soil degradation is a human-induced phenomenon and could be described as the deterioration of soil quality: the partial or entire loss of one or more soil functions.
Soil degradation, therefore, refers to a broad spectrum of changes in soil characteristics because of natural or anthropogenic factors that alter their structure and quality, including deforestation and the removal of natural vegetation, agricultural activities, overgrazing, overexploitation of vegetation for domestic use, and industrial activities.
Two categories of human-induced soil degradation processes are distinguishable: “The first category deals with soil degradation by displacement of soil material. The two major types of soil degradation in this category are water erosion and wind erosion.
The second category of soil degradation deals with internal soil physical and chemical deterioration. In this category only on-site effects are recognized of soil that has been abandoned or is forced into less intensive usages”.
Such alterations result in reducing the soil’s capability to function and its resilience (the capacity to recover from stressor events), that is, the soil’s ability to provide actual or potential productivity or utility (to produce economic goods and services) and to perform environmental regulatory functions.
Soil degradation can occur through the following processes: physical (i.e., erosion, compaction), chemical (i.e., acidification, salinization) and biological (i.e., loss of soil organic matter, loss of biodiversity).
The factors that determine the kind of degradation are as follows: soil inherent properties (i.e., physical, chemical), climate (i.e., precipitation, temperature), the characteristics of the terrain (i.e., slope, drainage) and the vegetation (i.e., biomass, biodiversity).
Erosion is a process of soil degradation that occurs when soil is left exposed to rain or wind energy.
Poor management of agricultural land induces soil erosion that leads to reduced productivity (which must be compensated with the addition of fertilizers), or, in extreme cases, to the abandonment of the land.
Intensive conventional agriculture makes soils highly prone to water and wind erosion, which worsen when situated on a slope. Mild to severe soil erosion is affecting about 80% of global agricultural land.
Soil erosion has been estimated to reduce yields on about 16% of agricultural land, especially cropland in Africa and Central America and pasture in Africa.
Salt-affected soils occupy an estimated 950 million ha of land in arid and semi-arid regions, i.e., nearly 33% of the potentially arable land area of the world.
Soil acidity and the resultant toxicity caused by high concentrations of aluminum and manganese in the root zone are serious problems in sub-humid and humid regions. Soil compaction is a worldwide problem and can reduce crop yield by 20%–55%.
Nutrient depletion is another significant process of soil degradation, with severe economic impact on a global scale. To cover the losses more land would have to be converted to agriculture and more inputs used to replace the reduced soil fertility.
Current intensive farming practices greatly deplete soil organic matter (SOM) and soil carbon stocks.
The decrease in SOM reduces the resistance of soils to erosion agents (e.g., wind, water), lowers the water holding capacity of soils and affects overall soil health.
This in turn reduces crop productivity, resulting in the need for more fertilization and irrigation, making soils a net source of carbon dioxide emissions.
Combating Soil Degradation
A main goal of sustainable agriculture practices is to preserve soil health, enhancing SOM content and limiting soil erosion to a minimum.
Sustainable agriculture should aim at preserving the natural resource base, especially soil and water, by relying on minimum artificial inputs from outside the farm system and by offsetting the disturbances caused by cultivation and harvest, while being economically and socially viable.
The domain of sustainable agriculture includes several practices such as agro-ecology, integrated agriculture, low input, precision agriculture and organic agriculture.
The resistance of soils to erosion is closely linked to the stabilizing influence of SOM and vegetation cover. High organic matter content inhibits erosion because SOM binds soil particles together, generating an aggregate that resists erosion. Most SOM is found in the topsoil (15– 25 cm of the A-horizon) and is of key importance for soil fertility.
Practices such as no-till agriculture or minimum tillage, and organic farming can help reduce soil loss, increase SOM and restore soil fertility and biodiversity.
No-till farming can slow soil erosion and pollution runoff, benefiting aquatic ecosystems, improving agronomic productivity, and achieving food security.
No-till farming, however, may not suffice to properly protect the soil when other practices are not implemented alongside; for example, cover crops or appropriate rotation schedules, or when it is accompanied by the use of high amounts of agrochemicals.
It has also to be highlighted that low-input farming systems, such as organic agriculture, significantly increase the level of biological activity in the soil (e.g., bacteria, fungi, springtails, mites and earthworms).
Adopting agro-ecological and low input practices may allow us to preserve soil health while still increasing overall farm productivity, for example by adopting a more complex multi-cropping strategy.
The adoption of agro-ecological practices is a necessary strategy for degraded soils, in areas where farmers cannot afford to buy inputs, such as in sub-Saharan Africa.
Perennial crops are reported to be 50 times more effective than annual crops in maintaining topsoil.
Experts maintain that perennial crops, with their roots exceeding depths of two meters, can also greatly improve ecosystem functions and services, such as water conservation, nitrogen cycling and carbon sequestration (more than 50% when compared to conventional crops).
Management costs are also reduced because perennial crops do not need to be replanted every year, so they require fewer passes of farm machinery and fewer inputs of pesticides and fertilizers, thus reducing fossil-fuel use.
The abundant of solid minerals is made up of precious metals, stones and industrial minerals like coal, tin, gold, marble, limestone and others. The core of these mineral deposits scattered across the country remains a major attraction for informal and conventional mining activities.
The mining sector has been experiencing an ongoing resurgence with growing prospects as a result of the challenges posed by Nigeria‘s deeply troubled petroleum sector.
With the current dominance of petroleum industry in the economy, informal miners and small holding companies have become very active in the production of solid minerals in the absence of a clearly defined policy, better standards and reforms.
With the prevalence of artisanal and small-scale miners, recurrent hazard from thousands of abandoned mines, concentration of toxic residues and destruction of flora and fauna are some of major and widespread ecological impacts that mining communities are fraught with.
Artisanal and small-scale mining is practiced as a viable alternative source of rural livelihood however it led to devastating lead poisoning of children in addition to extensive mercury exposure and significant emissions of mercury into the air and soil.
Lead contamination continues to afflict large numbers of children and women commonly involved in the processing stage, which includes crushing, grinding, sieving, washing and panning.
The practice of mercury amalgamation at mining sites has also resulted in widespread contamination of miners and others working near the mines.
Exposure to mercury causes serious damage to the central nervous system, including respiratory failure, nausea, vomiting, diarrhea, increases in blood pressure or heart rate, skin rashes, eye irritation, and kidney damage.
For women, exposure to mercury positively correlates with an increase in malformations and miscarriages during pregnancy.
In addition to these health impacts, artisanal and small-scale mining is associated with significant environmental degradation, including toxic pollution of air, land, and water; destruction of flora and fauna; geological instability leading to landslides, flooding, erosion, and tremors; landscape degradation; and radiation hazards.
Dredging and sluicing during mining also cause severe land degradation and river siltation. The increases in suspended sediment from river siltation hinder the penetration of light into the water and greatly affect the supply of nutrients.
The suspended sediment also tends to carry high concentrations of mercury. During periods of heavy rain, the lead can leach into groundwater systems, contaminating them in the process.
Efforts to minimize the health and environmental impacts of artisanal and small-scale mining include basic practices such as moving operations outside of household areas and villages so as to reduce lead exposure for children and others, simple hygiene practice of hand and clothing washing before returning to their communities from the processing sites, the use of wet milling machines over dry machines to minimize the production of lead dust.
Oil exploration and exploitation has been on-going for several decades in the Niger Delta. It has had disastrous impacts on the environment in the region and has adversely affected people inhabiting that region.
The Niger Delta is among the ten most important wetland and marine ecosystems in the world.
The oil industry located within this region has contributed immensely to the growth and development of the country which is a fact that cannot be disputed but unsustainable oil exploration activities has rendered the Niger Delta region one of the five most severely petroleum damaged ecosystems in the world.
The Niger Delta consist of diverse ecosystems of mangrove swamps, fresh water swamps, rain forest and is the largest wetland in Africa but due to oil pollution the area is now characterized by contaminated streams and rivers, forest destruction and biodiversity loss.
This affects the livelihood of the indigenous people who depend on the ecosystem services for survival.
Oil exploration by seismic oil companies involves clearing of seismic lines, dynamiting for geological excavation, which affects the aquatic environment.
It causes mortality in fauna, turbidity in the water that blockage of gills of the filter feeders in the benthic fauna, reduction of photosynthetic activity caused by the water turbidity that reduces the amount of sunlight penetration.
Oil and gas pipeline have been installed covering 7,000km to enhance the distribution crude oil products to other parts of the country. The installation of these pipelines involved clearing large areas of habitat to make pipeline tracks.
These pipelines run across the rainforests and mangroves with incidences of leakage and rupture and accidental discharges. These discharges are caused by vandalism, failure of pipeline integrity due to aging and defects in material.
Spillages also result from the process of drilling, transportation by petroleum tanker, oil bunkering and smuggling and leakages from filling station petroleum depots.
Most incidences of the reported oil spillages have occurred in the mangrove swamp forest, which is one of the most reproductive ecosystems rich in fauna and flora.
Gas flaring is recognized as one of the main ecological problem facing the Niger Delta since 84.60% of total natural gas produced as a byproduct of oil is still being flared with 14.86% only being used locally.
There are documented cases of fire incidence that engulfed local plant and animals within the mangrove forest of the Delta resulting in a large number of human fatalities as result gas pipeline leakage.
Acid rain is another problem within the Niger Delta region caused by gas flaring which has led to loss in biodiversity, with forest and economic crops being destroyed.
The heat generated from gas flaring kills vegetation around flaring area, destroys mangrove swamps and salt marshes, suppresses the growth and flowering of some plants, induces soil degradation and diminishes agricultural productivity.
The cumulative environmental impact of these flaring activities result in contaminant build up on land, shallow ground water, greenhouse effect and general global warming and have also caused high concentration of acid rain within the region.
In terms of environmental changes occurring within the region, large areas of mangrove forest have been destroyed, oil spills spread over wide area affecting terrestrial and marine resources.
Some past spills have necessitated the complete relocation of some communities, loss of ancestral homes, pollution of fresh water, loss of forest and agricultural land, destruction of fishing grounds and reduction of fish population, which is the major source of income for the Niger Delta people and pollution exposes people also to new risk of diseases.
The development of the petroleum industry and its activities have negative consequences on the environment, some of these negative effects can be reduced or prevented basically by taking some steps in terms of prevention and monitoring.
The Federal Government has taken steps in this direction with the establishment of Niger Delta Development Commission (NDDC) and National Oil Spill Detection and Response Agency.
In conclusion, soil degradation is increasing with many great challenges of population growth, the potential effects of climate extremes and fresh water scarcity which have impact on food security. Poverty alleviation should be a priority to reduce the human pressure on the environment.
Updating and revising the laws and legislations in mining and petroleum sector by reviewing fines will go a long way in ensuring compliance, even though the government cannot systematically or frequently monitor these sites adoption of environmentally friendly technology that will minimize impacts of Mining and petroleum development on the environment should be encouraged.