Key Vocabulary: agriculture, algae, aquatic, invertebrates, biomagnification, biodiversity, point-source pollution
The Ohio River is one of the largest and most important rivers in the continental United States. Draining over 189,422 square miles (490,600 km²) from New York to Mississippi, it has been a source of food and water and has helped transport crops and people around the country for centuries. But the widespread use of fertilizer, herbicides, and pesticides in agriculture has caused chemical runoff into the Ohio River watershed, damaging local ecosystems.
What is runoff?
Pollution from farms and other industrial areas draining into local watersheds is called runoff and has caused major issues for local ecosystems in the Ohio River Basin. Much of the area surrounding the Ohio River is rural farmland. This is due to the high-quality soil, but also the river itself. Before cars and trains, the best way to sell goods in multiple markets was to use the river. If you were a corn farmer in Pennsylvania, you could put your crops on a barge to be shipped to all around the interior of the continent for sale in places as far away as Cincinnati, St. Louis, or even New Orleans.
Over the centuries, the US population grew and so did the demand for food. To increase their yields and meet this demand, farmers began using chemical fertilizers containing large amounts of nitrogen, in the form of ammonia, and phosphorus. The problem is the excess chemicals do not stay in the soil. When it rains or snows, the water picks up chemicals that have not been taken up by plants roots and drains into streams, rivers, lakes and eventually the ocean.. This is called runoff and allows pollution to spread away from its original source to damage a wide range of ecosystems.
Complicated the situation is how humans have changed the landscape. Midwestern farmland was once home to a large, dense temperate deciduous forest, which was cleared when Europeans began settling North America. With fewer trees to hold the soil back, any chemicals added to the ground are easily washed into streams and rivers when it rains.
Runoff can create a whole host of environmental problems, but perhaps the biggest is algal blooms. Algae are microscopic plants that live in every type of body of water, acting as producers in aquatic food webs. However, when excess nitrogen and phosphorus from agricultural runoff enters a watershed, it provides algae with excess nutrients, allowing their populations to grow exponentially.
“Increased algal populations in the waters of these streams and rivers can cause changes in water chemistry which can affect the fish and macroinvertebrate communities,” says Rich Cogen, executive director of the Ohio River Foundation, which does habitat restoration and education about the Ohio River’s ecosystem.
As algae populations explode during a bloom, they use up the oxygen in the water, says Cogen. Without dissolved oxygen in the water, fish and other aquatic species cannot survive. Because of these algae blooms, the Ohio River and its tributaries have lost some of their biodiversity. A study with from the Environmental Protection Agency has shown that an increase of ammonia in a local watershed leads to a lower Index for Biotic Integrity, a metric used by ecologists to measure biodiversity. And while the water quality of the Ohio River has improved since the 1950’s due to regulation on industrial pollutants and raw sewage, many areas, including several rural testing sites where farming is prevalent, still lag behind in biodiversity. However, the Clean Water Act does not define non-point source pollution such as runoff, which has made it hard for the EPA to regulate.
When the water eventually gets to the ocean, excess chemicals can wreak havoc on marine ecosystems as well. The Gulf of Mexico has a dead zone the size of New Jersey, where the runoff from the Ohio, Missouri, and Mississippi rivers have caused a huge algae bloom, making it nearly impossible for other species to survive due to the lack of dissolved oxygen.
But it’s not just large bodies of water that are at risk. The thousands of creeks and tributaries that make up the Ohio River Basin are in danger too. “Smaller creeks can be more susceptible to runoff pollution than larger rivers because of the relatively smaller volumes of stream water to runoff volumes,” says Cogen. More chemicals in a smaller volume of water increase the concentration runoff chemicals and can make algae blooms worse. Additionally, the pesticides and herbicides used to keep insects and weeds away from crops can also runoff into a local watershed. These chemicals contain many harmful substances such as formaldehyde and arsenic, which enter the food web and become concentrated at higher trophic levels. This is called biomagnification and can decimate top predator populations.
Impact on Humans
Runoff causes a lot of damage to ecosystems, but how does it affect humans? While drinking water in America is regulated and thoroughly treated, excess runoff from water sources puts pressure on local communities. “Polluted and contaminated water costs everyone money,” says Cogen “Drinking water has permitted limits for a variety of chemicals, however, the greater the concentration of potentially harmful substances in the water, the more effort and money it takes to clean and treat drinking water”.
During the summer of 2016, an algae bloom 600 miles long exploded on the Ohio River. Communities from West Virginia to Illinois had to scramble in order to make their drinking water safe. But perhaps the best-known contamination happened in 2014 when an algae bloom in western Lake Erie caused a water crisis in the city of Toledo, Ohio. Lake Erie, the main water source for northwest Ohio, had large algae bloom caused by runoff from farms, cattle feedlots, and leaky septic systems. For three days, residents could not drink or even boil their tap water. 11 million people live around Lake Erie and rely on it for their drinking water. If such a bloom were to affect the Ohio River valley, it could impact the water of up to 25 million people.
Degraded streams also impact recreational activities. Swimming, boating, and fishing can be suspended in local waterways if algae concentrations are too high, causing regions that rely on these activities to lose income. Additionally, excess runoff also causes damage to the land. Without trees and their roots to provide structure, the more soil gets washed away when it rains. This can change how a river or stream erodes the land, potentially damaging homes and other buildings as well as impacting biotic communities.
What you can do
There are many opportunities to get involved to help restore local aquatic ecosystems. The Ohio River Foundation is just one group that is involved in environmental education, stream cleanups, and water testing. Groups across the country are always looking for volunteers to help with data collection and habitat restoration.
But there’s so much more than just working within the river system, Cogen says. “Planting trees and supporting farms that use less or zero fertilizers, herbicides, and pesticides can go a long way to help reduce runoff pollution, erosion, and improve and strengthen the condition of the watershed.” Studies have shown farms which plant a wide variety of crops have less fertilizer runoff. Even using reducing or eliminating fertilizer use on your own lawn and garden can keep chemicals from getting into the local watershed.
What may be most important, however, is the mindset that how we live our lives affects the local ecosystem. Understanding that our actions have ecological consequences is critical to not only preserving our environment but helping it thrive.