Agriculture / Agriculture


Agriculture, accounting for approximately 27% of the Harpeth River Watershed’s land cover, degrades water quality and habitat in the Harpeth River and its tributaries. Sediments, nutrients, and bacteria are among the biggest sources of surface water quality impairment caused by agriculture. In addition, streambank erosion and riparian vegetation loss resulting from agricultural activities negatively impact stream ecosystem health. Adoption or installation of agricultural Best Management Practices (BMPs), such as exclusion fencing to keep livestock out of streams, helps reduce agricultural impacts to the rivers and creeks of the Harpeth River Watershed. Harpeth Conservancy has worked for over a decade with the Tennessee Department of Agriculture, the USDA Natural Resource Conservation Service, and local producers to encourage and facilitate agricultural BMP installations in the Headwaters region.

Agricultural Pollutants & Impacts


Nutrient Pollution

According to EPA, nutrient pollution is one of America's most widespread, costly, and challenging environmental issues. The primary sources of nutrient pollution are stormwater, households, wastewater treatment facilities, fossil fuels, and agriculture. In agriculture, animal manure, excess fertilizer, and soil erosion cause excess nitrogen and phosphorous pollution. Excessive nutrient inputs or "nitrogen pollution" can contribute nonpoint source pollution to surface waters and groundwater. When agricultural stormwater runoff laden with nutrients washes into nearby streams and ponds, natural nutrient cycles are altered, which can have dramatic effects on sensitive aquatic ecosystems. Nutrient pollution can lead to cultural eutrophication, which means the biological productivity of the water body is unnaturally increased due to human activities. Eutrophication can cause algae growth, deplete dissolved oxygen stores in the water, harm or kill aquatic life, and potentially poison the community water supplies.

Image 1, U.S. Geological Survey, Paul Terrio


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Pathogens and Pharmaceuticals

There are many sources of pathogens and pharmaceuticals that lead to water quality impairment. This section is focused on agriculture sources.

Where do pathogens and pharmaceuticals in agriculture come from?

Antibiotics and artificial growth hormones are given to livestock to help them stay healthy, fight disease, and grow big and strong. The livestock excrete varying amounts of antibiotics, artificial growth hormones, and pathogens that live inside their intestines. Pathogens are microorganisms, mostly bacteria, in human and animal waste that cause disease. Escherichia coli (E. Coli) is a type of fecal coliform bacteria and is used as an indicator to test for fecal contamination. The source of E. Coli contamination in waterways is usually sewage or animal waste pollution.

In industrial livestock farms, lagoons are used to store manure and animal waste. Before applying the animal waste as fertilizer to farm fields, the waste is processed in order to stabilize it, destroy pathogens, and reduce disease potential. After a certain period of time and favorable weather conditions, the farmer uses this manure and animal waste as fertilizer for his or her fields. This practice is called biosolid land application and must comply with EPA's 40 CFR Part 503. If applied correctly, the practice is a valuable, safe, and inexpensive way of recycling nutrients to the soil and will reduce the potential for bacteria contamination.

How do pathogens and pharmaceuticals pollute surface and ground water?

Pathogens, along with artificial growth hormones and antibiotics, can be excreted in livestock waste and water in varying amounts and use the same pathway to transport to groundwater and surface waters. The sources of pathogens and pharmaceuticals in waterways are:

  • Direct deposition from livestock, pets, wildlife into the water body. One example is cattle, who have unrestricted access to a stream, directly contaminate a stream through feces deposition.
  • Rural runoff polluted by fecal matter, urban runoff, etc.
  • Failing septic systems
  • Pipes that directly deposit sewage in the water body
  • Permitted discharges by sewage treatment plants
  • Leaching fertilizer manure during rainstorm and flooding events
  • Improper manure management practices


Pathogens and pharmaceuticals from human and animal waste sources can lead to contaminated wells and streams and contribute to water quality impairment. A major concern to human health is pathogen contamination in drinking water and recreational waterways. When ingested, these pathogens can cause gastrointestinal issues in humans. Animal growth hormones and antibiotics from agriculture operations are a major concern to fish health because in higher concentrations, they can negatively affect fish reproduction processes.

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Aerial applicator of pesticides
Aerial application of pesticides, TN Department of Agriculture


Toxic pesticides can kill soil microorganisms and poison animals eating poisoned insects, freshwater species, and people. They have the potential to disrupt species hormones and reproduction, persist generations in the environment, kill fish, and alter habitat. Even without direct application to fish, fish kills may still occur after application as oxygen depletes due to the decomposition of weeds killed. Not all pesticides harm the environment, so it is important to research the best and most environmentally friendly pesticide before purchase and application. Farmers and landowners whose land contains fish and wetland habitats, should use the least toxic pesticide, carefully follow the label's directions, and avoid using pesticides in wildlife habitats. An alternative form to conventional pesticides is biopesticide. Biopesticides have a lower toxicity, are effective in small quantities, and decompose quickly. For more information on best management practices for pesticides, click here.

The major pesticide groups include herbicides, insecticides, and fungicides:

  • Herbicides

2,4-D (Aquacide, Aqua-Cleer, Weedar, Weed-Rhap, Weedestroy, Weedtrine): A herbicide and plant growth regulator and has been used to control terrestrial and aquatic broadleaf weeds in agricultural and non-agricultural sites in the U.S. since the 1940s. Water pH is extremely important when applying this herbicide to aquatic plants. 2,4-D toxicity increases as pH decreases (more toxic in acidic waters of pH < 6). 2,4-D should not be used in water for irrigation, livestock, or domestic purposes.

  • Insecticides

Insecticides are the most toxic type of pesticide. The main types of insecticides used in agriculture are pyrethroids (PYs), organophosphates (OPs), carbamates (CBs), and biological insecticides (BIs). PYs are the most toxic type to aquatic species and should be used with caution near waterways. OPs and CBs are insecticides most commonly associated with fish kills because they are water soluble and metabolize quickly. OPs can bioconcentrate in animals. Both OPs and CBs are a threat in acute doses. BIs are hazardous because they target specific insects which can harm certain aquatic invertebrates by reducing their food supply. Insecticides that are banned in the U.S. include DDT, Aldrin, toxaphene, dieldrin, mirex, and heptachlor, which are all highly toxic to fish and wildlife species.

  • Fungicides

Fungicides are used to protect plant species, control fungal diseases, and ultimately increase crop productivity. Fungicides need to be applied multiple times before the disease occurs or at the first appearance of symptoms. In general, they have a lower toxicity to fish and aquatic species compared to other types of pesticides. Banned fungicides in the U.S. are ones containing mercury. Acute and chronic exposure to mercury can accumulate in the food chain leading to reproduction issues, as well as death.   

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Soil Erosion & Sedimentation

Sediment comes from two major sources: (1) surface erosion off land in the watershed--from construction, agricultural activities, timber cutting, etc., and (2) from stream bank and bed erosion. This occurs when high velocity water flows scour material from the streambank and bed and/or when supersaturated bank soils are structurally weakened and fall into the stream as water recedes. 

In agriculture, the amount of topsoil available has a direct effect on soil fertility therefore, its loss leads to soil fertility reduction and land degradation. Soil erosion and sedimentation is caused when farmland is ploughed or natural vegetation is cleared. This vegetation clearing causes topsoil to become exposed allowing it to be carried away by wind or washed into streams. When it rains or floods, loose topsoil, along with other soil particles, washes into streams, rivers, and other surface waters. Excessive soil particle inputs, known as "sedimentation," alters aquatic habitat and degrades water quality. Stream channels become clogged with sediments, which causes streambank erosion, channel scouring, flooding, and unnatural meandering. Habitat degradation and water quality impairment resulting from sedimentation can harm or kill aquatic life. Sediment pollution clogs fish and insect gills, smothers fish eggs, damages/abrades aquatic insect gills, and buries aquatic plants. Excessive sediments fill streambeds and reduce gravel and cobble spawning areas for fish. If a stream buffer is not present, the sedimentation problem is exacerbated. With less soil available to absorb rainwater, erosion caused by sedimentation leads to increased flooding.

A stream or riparian buffer is a natural filter and important in order to reduce soil erosion and sedimentation, improve water quality, prevent nutrient and pesticide pollutants from entering a stream, and reduce property loss. The stream buffer helps to trap and deposit sediment on the stream bank. A healthy stream buffer should be a mix of native trees, shrubs, and plants. The buffer should range between 25 to 100 feet wide on each stream side, depending on the stream channel, land use, and topography. Harpeth Conservancy has planned out and implemented several agricultural BMPs on stream margins at local farms in Eagleville. To learn more about riparian zones, click here.

Soil erosion and algae on a farm in the Harpeth Watershed in 2013


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Agricultural Best Management Practices (BMPs)

Agricultural BMPs are implemented by farm and land owners to improve crop yield, reduce erosion, enhance water quality, conserve water, save money, and protect drinking water. Some of the practices include nutrient management, elimination of pesticide application in riparian areas, control of animal waste, erosion control, streambank stablization, and improvement of soil productivity. Over the years, Harpeth Conservancy has coordinated agricultural BMPs at local farms across the watershed. In the past year, Harpeth Conservancy has worked with two farms on Headwater streams of the Harpeth River to install BMPs including livestock exclusion fencing, heavy-use protection areas, watering facilities, prescribed grazing, streambank stabilization, and riparian vegetation improvements. To learn more about practical conservation practices, funding, support resources, and agricultural BMP projects completed to date by Harpeth Conservancy, click here.


Helpful Resources:

Cover Crops Economics: This economic assessment tool will help you calculate and determine the short term and long term costs and benefits of using crop rotation for cover crops. The tool was developed by the USDA.

Water Quality Index for Agricultural Runoff (WQIag): This web-based tool was created by NRCS to help producers know the quality of water flowing off their fields. Using the tool, farmers can input field information such as slope, soil characteristics, nutrient and pest management, conservation practices, etc. Using the field information, the tool calculates a rating of your water.