Farming's Impact: Runoff Water Pollution Explained

Agriculture is a leading cause of water pollution, with farms discharging agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. This is particularly true in the case of runoff, where rainfall and snowmelt can transport pollutants such as fertilizers, pesticides, and manure into local water sources. These pollutants can have severe environmental and health consequences, including the stimulation of algal blooms, a reduction in oxygen levels, and the contamination of drinking water supplies. The environmental and social costs of water pollution caused by agriculture are estimated to exceed billions of dollars annually in OECD countries alone.

Fertilizer and manure runoff

Fertilizers and manure are essential for farming as they provide crops with the nitrogen and phosphorus necessary for growth. However, they can also be a significant contributor to water pollution when they enter water bodies through runoff.

When nitrogen and phosphorus from fertilizers and manure are not fully utilized by growing plants, they can be washed from farm fields into nearby water bodies during rainfall or irrigation events, a process known as agricultural runoff. This excess nitrogen and phosphorus can have detrimental effects on aquatic ecosystems. For example, increased levels of nitrogen and phosphorus can stimulate algal blooms in lakes and rivers, leading to the development of hypoxic conditions, or "dead zones," where oxygen levels are too low to support marine life. This, in turn, can cause fish kills and a decrease in aquatic life.

Additionally, the decomposition of organic matter in manure contributes to increased biological oxygen demand (BOD) in water bodies, further degrading water quality. Large-scale concentrated animal feeding operations (CAFOs) often produce waste in amounts that exceed the land's capacity to absorb it, increasing the risk of runoff. The fresh manure from warm-blooded animals also contains numerous microorganisms, including bacteria, viruses, parasites, and fungi, some of which are pathogenic and can be transmitted to humans.

To minimize the impact of fertilizer and manure runoff, farmers can adopt nutrient management techniques. This includes applying nutrients (fertilizer and manure) in the right amounts, at the right time of year, and with the right placement. Storing livestock manure in lagoons, covered stockpiles, or protected upland areas can also help minimize runoff risks. Implementing conservation tillage practices, such as reducing the frequency and intensity of tilling, can improve soil health and reduce erosion, runoff, and the chance of nutrients reaching waterways.

Pesticides and herbicides

Agriculture is a major contributor to water pollution from runoff, and the use of pesticides and herbicides in farming is a significant part of this problem. Pesticides and herbicides are chemical substances used to control pests and unwanted plants, and their improper use or management can have detrimental effects on the environment, particularly water bodies.

The excessive or improper application of pesticides and herbicides on crops can result in their

Veterinary medicines

The land application of manure can contaminate soils with veterinary pharmaceuticals, which can then lead to the contamination of surface and groundwater. Studies have detected commonly used veterinary pharmaceuticals, such as amprolium, carbadox, monensin, and tylosin, in surface water near farms. These pharmaceuticals are more frequently detected during the nongrowing season when there is more surface runoff due to higher rainfall and snowmelt.

Farmers can adopt soil and water conservation practices to reduce the runoff of these and other pollutants. For example, storing livestock manure in covered stockpiles or protected upland areas minimizes runoff risks. Implementing buffer strips, such as vegetated filter strips along the margins of farms and rivers, can also effectively decrease pollutant concentrations entering waterways.

Factory farm leaks and spills

Factory farms produce an enormous amount of waste and pollution. The water used in these facilities is often polluted with animal waste, antibiotics, hormones, and bacteria. This water ends up in large open-air lagoons that are prone to leaks and spills. These leaks and spills can lead to contaminated water ending up in local water supplies, causing pollution and harm to aquatic life.

The waste in these lagoons contains high levels of "nutrients" such as phosphorus and nitrogen, which are components of synthetic fertilizer and byproducts of animal waste. When these nutrients leak or spill into waterways, they can cause an increase in algae blooms, which can deplete the oxygen levels in the water, leading to the loss of aquatic life.

Chicken manure, in particular, is high in phosphorus and nitrogen. When farmers spread chicken waste onto cropland, it often exceeds the amount that can be absorbed, and more than is legally allowed. Rainfall then washes away the excess nutrients, causing them to run off into streams, rivers, and groundwater. Chicken waste also contains high levels of ammonia, which is toxic to fish and can be converted into dangerous nitrates.

The improper storage and management of manure in factory farms can have severe environmental consequences. Manure spills and dumping in 10 states killed approximately 13 million fish between 1995 and 1998. These spills and leaks from manure lagoons contribute to the "dead zone" in the Gulf of Mexico and deplete the oxygen in waterways, causing significant harm to aquatic ecosystems.

Sediment and saline drainage

Salinization, caused by inappropriate irrigation practices, poor drainage, and excessive fertilizer use, adversely affects soil fertility, plant growth, and crop productivity. Implementing nature-based solutions (NBS) and conservation agriculture can help mitigate these issues by revitalizing ecosystem services and enhancing soil stability. NBS, such as mangrove restoration in tropical regions, can act as natural buffers against saline intrusion, enhancing agricultural resilience.

In regions with distinct geological features, such as the San Joaquin Valley, the presence of naturally saline soils and inadequate drainage due to underlying clay layers can lead to water quality issues. The Integrated On-Farm Drainage Management (IFDM) system addresses these challenges by managing irrigation water and reusing drainage water to irrigate salt-tolerant crops, ensuring compliance with regulations and enabling the production of higher-value crops.

To effectively control salinity, landowners in Western Australia are required to submit a Notice of Intent to Drain, ensuring well-designed drainage systems that minimize impacts such as waterlogging, sedimentation, and offsite effects. Groundwater drains, constructed away from the natural drainage line, play a crucial role in salinity management, with open or leveed drains offering advantages in controlling surface water inflow and reducing erosion risks.

Overall, sediment and saline drainage are essential considerations in farming to mitigate water pollution from runoff. By adopting sustainable practices, such as NBS and improved drainage systems, farmers can minimize the negative impacts of sediment and saline drainage on the environment and crop productivity.

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