Agricultural pollution predominantly arises from farming practices. Modern farming and agricultural operations contribute to the degradation and contamination of our environment as well as the neighboring ecosystems. Fertilizers, pesticides, herbicides, animal manure and other agro-chemicals are rich in chemical nutrients and toxic substances which are often the major sources of agricultural pollution.
The excessive use of these products can affect water quality when it rains, and the contaminated soils and water is washed into the adjacent waters or seep into ground waters. The chemicals can also be absorbed by plants which are then consumed by animals and humans, terribly harmful to animal and human health.
Agricultural pollution comes from a variety of sources because of its complexity. However, the main sources include:
- Leaching of Pesticides, Herbicides and other Agro-chemicals
Herbicides and Pesticides among other agro-chemicals are the overriding causes of agricultural pollution owing to the numbers of invasive pests, weeds, and diseases. They are highly toxic and have the potential of remaining in the environment for ages.
When it rains, water interacts with these toxic chemicals which then leach into groundwater sources or washed into the nearby waterways. Consequently, the chemicals contaminate waters and the soils, and soil microorganisms plus beneficial insects are killed. People and animals are also affected when they inhale or indirectly consume the agrochemicals.
- Excess Nutrients
However much animal manure and fertilizers are not directly toxic, they usually contain excess chemical nutrients especially phosphorus and nitrogen. They make up the main causes of nutrient pollution from agricultural sources. Excess nutrients can have tragic consequences on water quality and the survival of aquatic life.
When these nutrients are washed into the water systems e.g. rivers, lakes, streams or oceans during rainy periods, it alters the marine and freshwater nutrient cycles, and as an outcome the species composition of the respective ecosystems. The most common consequence is eutrophication which depletes the water dissolved oxygen, and in consequence can kill fish and other aquatic life.
- Organic Contaminants
Manures and Biosolids frequently contain nutrients including nitrogen, carbon, phosphorus and nitrogen. Furthermore, because they are industrially processed, they may also have within them contaminants such as personal care products (PPCPs) and pharmaceuticals. These products have been found in human and animal bodies and are believed to have negatively health impacts to wildlife, animals, and humans. Agricultural pollution becomes even harder to manage with such types of organic contaminants.
Livestock alone are substantial contributors to agricultural pollution. The feeds and unnatural diets fed to livestock are significant sources of greenhouse gases and nutrients from excretory waste. Nitrogen-based compounds such as nitrogen and ammonia are potential sources of gaseous emissions. When ammonia is deposited in large quantities in surface waters, it can harm aquatic life.
- Heavy Metals
The primary agricultural inputs including pesticides, industrial by-product wastes, some fertilizers, and specific agrochemical products contain traces of heavy metals such as arsenic, cadmium, mercury and lead. When these substances accumulate in the soil or waste dump, they can be washed into waterways or leach into ground water sources or get absorbed by plants, and are eventually consumed by animals and humans affecting their health or even causing premature deaths. Heavy metals can cause crop failure and poisons the livestock from contaminated water or food.
- Soil Erosion and Sedimentation
Intensive farming operations greatly contribute to soil erosion and sedimentation. Through the farming operations, millions of fertile soils are broken down, degraded, and eroded via storm water runoffs which end up accumulating as sediments in rivers, streams, lakes, oceans or other land regions. Thus, it affects water quality in various ways, for instance, by making it dirty or contaminating it with the agrochemical residues present in the soils.
Sedimentation may also restrict light penetration in water thereby affecting aquatic life forms, and the consequential turbidity can hamper feeding habits of the aquatic fish. Sedimentation also contributes to build up of the agricultural pollutants in waterways and other land areas.
- Invasive Pests, Weeds, and Diseases
Invasive pests, weeds, and diseases do not directly cause agricultural pollution. However, because of the persistent and growing number of pests, weeds, and diseases which can negatively impact crop yields, farmers resort to the persistent use of pesticides, herbicides, and other agro-chemicals to combat this nightmare. As a result, increased uses of these chemical products persist in destroying the soils, animals, plants, waters, and wildlife based on the agricultural pollution intricacies, and in consequence gradually alters the ecosystem.
- Farm Tillage and Oxide Emissions
Farm tillage and other operations at times involve mechanical operations such as the use of tractors and harvesters among other farm machinery that combust fossil fuel releasing greenhouse gas emissions into the atmosphere. Also, soil biochemical processes naturally emit numerous types of greenhouse gases. Additionally, irrigation is associated with accumulation of selenium (Se) which naturally occurs in the soil. Altogether, these factors result in agricultural pollution and depending on concentrations levels they can be harmful to humans, wildlife, plants, and animals.