Runoff Pollution
Polluted runoff is one of the fastest growing and most harmful sources of pollution threatening the Chesapeake Bay and its rivers and streams.
As rainwater and snowmelt run off our streets, parking lots, lawns, and other surfaces, they pick up pet waste, pesticides, fertilizer, oil, and other contaminants. If the draining water doesn’t evaporate or soak into the ground where it can be filtered, it flushes straight into local creeks, rivers, and the Chesapeake Bay.
Polluted runoff from stormwater is one of the primary sources of pollution still on the rise in our region. Agricultural runoff from farmland is also a problem.
Runoff pollution erodes streams, kills fish, pollutes drinking water and swimming areas, floods homes, and contributes to algal blooms and dead zones.
What is runoff pollution?
Much of the pollution that impacts water quality is washed from the landscape by rain and snow.
When rain or snow hit the ground, the landscape can either act as a green filter or a gray funnel. For example, only 10 to 20 percent of rain that falls in forests, fields, and other natural areas runs off, with the rest absorbed by soil and plants, where it is filtered before reaching aquifers or local waterways. By contrast, close to 100 percent of the rain that falls on concrete and other hard surfaces produces runoff, carrying pollution and toxins into rivers and streams. One inch of rain falling on an acre of hardened surface produces 27,000 gallons of runoff.
Stormwater runoff collects an often-toxic mix of pollutants including: trash; soil and sediment; fecal bacteria, viruses, and other pathogens; nitrogen and phosphorus from fertilizers and air pollution; oil and other petroleum products; pesticides and herbicides; road salt; and toxic metals including copper, lead, and zinc. Agricultural runoff carries nutrients from fertilizers and animal manure.
Nutrients—primarily nitrogen and phosphorus—are essential for the growth of all living organisms in the Chesapeake Bay. However, excessive nitrogen and phosphorus degrade the Bay’s water quality. Each year, roughly 300 million pounds of polluting nitrogen reaches the Chesapeake Bay—about six times the amount that reached the bay in the 1600s. Water quality is so poor that the Chesapeake Bay is on the Environmental Protection Agency’s “dirty waters” list.
Both nitrogen and phosphorus feed algal blooms that block sunlight to underwater grasses and suck up life supporting oxygen when they die and decompose. These resulting “dead zones” of low or no oxygen can stress and even kill fish and shellfish. Algal blooms can also trigger spikes in pH levels, stressing fish, and create conditions that spur the growth of parasites.
Toxic algae, such as some blue-green algae (cyanobacteria), can sicken people, as well, but animals are especially susceptible. These toxins affect the animal’s liver and nervous system, and can result in death.
The majority of nitrogen and phosphorus pollution comes from sewage treatment plants, animal feed lots, and polluted runoff from crop land, urban, and suburban areas. In addition, air pollution (from vehicle exhaust) and industrial sources such as power plants contribute roughly one-third of the nitrogen pollution.
The fastest growing source of nitrogen pollution to the Bay is polluted runoff from urban and suburban areas. The amount of land covered by parking lots, roads, roofs, and driveways continues to grow. Meanwhile, forests, meadows, wetlands, and other natural filters are disappearing, and manmade filtration systems to control runoff have not compensated for the loss.
What are the effects of runoff pollution?
The effects of runoff pollution are vast and long-lasting for both wildlife and people.
Besides carrying pollutants that harm fish and other creatures, runoff also includes eroded dirt that blocks sunlight from reaching underwater grasses and smothers the aquatic homes of oysters and other life. As grasses die, fish and other creatures that rely on them are placed in jeopardy. The runoff also carries nutrients that spur algal blooms that cause low oxygen and kill fish and other species.
As land use patterns change and the watershed’s population grows, the amount of nitrogen, phosphorus, and sediment entering the Bay’s waters increases tremendously. While they are essential for the growth of all living organisms in the Bay, excessive nitrogen and phosphorus degrade water quality, contributing to algal blooms and dead zones. Runoff is a pathway for these nutrients. It also muddies drinking water sources and can carry bacteria, making the treatment and use of such water more expensive.
Virginia and Maryland caution people not to swim in waterways for 48 hours after a heavy rain, as polluted runoff carrying bacteria has resulted in serious illnesses.
Did You Know
- The brake linings of cars and trucks are often made with copper and they shed a fine dust of this toxic metal onto streets, which can then end up in our waterways. The Maryland Department of the Environment sampled runoff from the state’s major urban areas and found copper in 92 percent of the samples. Fifty-three percent of the time the levels would be acutely toxic to aquatic life. Another reason copper appears in waterways is because the metal is an ingredient in herbicides.
- Zinc from car tires, road salt, paint, and other products has also been found in runoff, as well as the toxic metals lead, chromium, and cadmium.
- Oil and other petroleum products in runoff are well known by scientists to be toxic to aquatic life, even in low concentrations.
- Researchers have detected pesticides including dieldrin and the now-banned chlordane in 97 percent of suburban and urban runoff samples nationally, and at levels high enough to harm aquatic life 83 percent of the time. For example, Lake Roland in Baltimore County is so polluted with chlordane, a termite-killing pesticide sprayed in nearby homes, that anglers are warned to limit their consumption of fish from the lake.
- Apartments with green roofs reduce pollution, lower heating and cooling costs, and are so attractive they command rents 16 percent higher on average than apartments without them. Other runoff control projects that add green to developed landscapes boost residential real estate values by two to five percent, and can lift office rental rates by seven percent.
- Rain gardens filter up to 93 percent of the oil in urban and suburban runoff, vastly reducing pollution to local streams. These gardens also filter up to 90 percent of the toxic metals, 70 percent of the sediment, 30 percent of the phosphorous, and at least 25 percent of the nitrogen pollution (some gardens are capable of removing more).
- Placed at the base of a downspout, a typical rain barrel can hold 55-75 gallons of stormwater runoff from a rooftop, reducing flooding and erosion. They can be found in garden supply centers or easily built.
- A mature leafy tree can intercept 500-1,000 gallons of precipitation a year, and a single mature evergreen can intercept 4,000 gallons a year. At the same time, a mature leafy tree like an oak can “drink up” and transpire more than 40,000 gallons of water a year. The planting of trees and gardens cools urban areas, improves the appearance of neighborhoods, absorbs carbon dioxide, and provides habitat for wildlife. Creating more open spaces, which absorb runoff, also expands recreational opportunities for local residents who want to walk, jog, and play outside.
Additional information about stormwater management can be found at the following websites:
The Center for Watershed Protection
Low Impact Development Center
Low Impact Development Urban Design Tools
How can we prevent polluted runoff?
There are many ways to reduce runoff pollution, but they all come down to a simple idea: create “green filter” landscapes that slow down and soak up runoff.
Most cities today were built to rapidly funnel runoff—and the harmful pollution it picks up—directly into rivers and streams by engineering concrete drainage ditches, stormwater drains, and sewers. Green infrastructure rethinks this model and seeks to mimic the function of the forests and fields cities replaced. It comes in many forms, from rain barrels or green roofs at a single building, to things like permeable pavement, rain gardens, and urban tree canopies that are incorporated throughout city streets and neighborhoods. The idea is to capture and clean the rain where it falls, slowing the flow of water so it can filter into the ground. It can reduce polluted runoff from cities, alleviate flooding, beautify neighborhoods, and create recreational benefits for communities.
Under the Clean Water Act, cities and urban areas must obtain permits that limit the amount of pollution they are allowed to discharge through their storm sewer systems, formally called municipal separate storm sewer systems, or “MS4s.” These are the systems of storm drains, pipes, ditches, gutters, roads, and other features that collect and channel polluted runoff from the land into local waterways. These MS4 permits are issued and administered by each state, and require city and local governments to incorporate specific measures into their strategies for reducing pollution from stormwater runoff. As part of our on-going commitment to helping communities reduce stormwater pollution, CBF provides a “Best Practices Guide for Stormwater Utilities, Fees, and Authorities,” as well as occasional webinars and other resources. CBF also advocates for strong, progressive municipal stormwater permits.
CBF advocates for strong construction and post-construction polluted runoff regulations at the state level to reduce polluted runoff from development. This includes comprehensive plans and zoning ordinances that steer development away from sensitive areas and protect forests and other open spaces that act as natural filters; effective erosion and sediment control measures at construction sites; and enforcement to ensure ordinances, construction management practices, and site design standards are followed.
CBF has helped communities across the watershed implement stormwater management projects to absorb runoff and reduce the risk of routine flooding and damage from pollution. These include projects such as planting trees and rain gardens along streams or in or around playgrounds, park areas, schools, and other public buildings.
On agricultural lands, farmers can implement regenerative agriculture practices to reduce polluted runoff. These practices include: planting forested buffers alongside streams; planting trees on land used for grazing; practicing rotational grazing, continuous no-till, and crop rotation; planting cover crops; managing fertilizer application; and using fences to keep livestock out of streams.
Implementing conservation measures on farms is one of the most cost-effective ways to reduce pollution to our local streams, rivers, and the Bay. Agricultural cost-share programs provide farmers with critical federal and state funding to install these conservation practices. CBF’s restoration staff work with farmers to install these practices.
What can I do to reduce polluted runoff?
Much of the polluted runoff impacting our water starts right in the urban and suburban neighborhoods where we live. There are many things residents can do to help.
If you are simply looking for a way to help protect or improve your watershed or you are doing a small home improvement project that creates new impervious area and you need to manage the stormwater that is generated, this guide is for you.
Planting trees, native flowers and grasses, or a rain garden can all help slow and filter rainfall, reducing pollution while also providing habitat for pollinators and wildlife. You can also practice low-impact lawn care to help restore your yard’s natural filters and minimize pollution.
Things like adding a rain barrel (or two) to your downspouts, replacing hard surfaces with pervious pavement, or making an appointment to service your septic system can limit the potential for polluted runoff from your home.
Go to a local government meeting and voice your support for effective stormwater management changes. Or, keep an eye on our events calendar for opportunities to volunteer at community tree plantings and other green infrastructure projects.
