Phosphorus Pollution In The Mystic

Phosphorus pollution is one of the primary water quality problems in the Mystic River watershed. Since it is a nutrient, too much phosphorus can cause algae and aquatic plants to grow out of control, which in turn causes major disruptions to the ecosystem. Phosphorus pollution can have a variety of harmful impacts on a river including toxic cyanobacteria blooms, excessive growth of invasive aquatic plants, and low dissolved oxygen in the water. In some cases, decomposing algae can make dissolved oxygen levels become so low that fish no longer survive. This event is known as a “fish kill.”

Phosphorus 101

At the most basic level, phosphorus is an element. Phosphorus is one of the core building blocks of organic molecules. All life needs phosphorus, including humans, plants, and animals.

In lakes and rivers, plants and algae need phosphorus to grow. Often times, the amount of phosphorus determines how much and how fast they can grow. When there is too much phosphorus, they can grow out of control. Phosphorus is therefore called a "limiting nutrient" because it is one of the primary limiting factors controlling the growth of plants and algae. Other factors include sunlight, other nutrients (primarily nitrogen), and water temperature.

Where does Phosphorus come from?

Phosphorus is naturally found in rocks and soils, but usually in small quantities. Even in pristine forests, phosphorus can be transported from the land to nearby lakes and rivers due to natural processes like erosion.

In towns and cities, however, large quantities of phosphorus can be found on rooftops, parking lots, roadways, and fertilized lawns. When it rains, this phosphorus picked up by runoff, and carried into nearby stormwater sewers or directly into the river. Phosphorus can also come from industrial source and wastewater treatment plants that discharge treated water into receiving lakes and rivers. Agriculture and livestock are also potential contributors to phosphorus pollution.

In the Mystic River watershed, the primary source of phosphorus is from stormwater from residential and urban areas because there are no wastewater treatment plants or major agricultural areas.

Why is Phosphorus a problem?

Even though phosphorus itself is not toxic to humans, plants, or animals, too much of it can cause a variety of impacts to the natural ecosystem.

One of the primary impacts of phosphorus pollution are algae blooms. Because algae need phosphorus to grow, when there is too much of it, they can grow out of control, which causes problems to the ecosystem.

One special kind of algae known as cyanobacteria can cause additional problems. When these algae grow to excess, they can release toxic chemicals that are harmful to humans, pets, and wildlife.

Lastly, it’s not just microscopic algae that need phosphorus, larger plants do too. In the Mystic River, phosphorus pollution contributes to the growth of invasive species such as water chestnut, Eurasian milfoil, and other species. No only do these plants change the ecosystem, they also make it difficult for boaters and swimmers to navigate through the water. Each year, MyRWA enlists a team of volunteers to remove these larger plants by hand. Learn more about MyRWA’s efforts to remove invasive plants.

What are the solutions?

A large amount of phosphorus in urban areas comes from soil particles and other debris that builds up on streets and parking lots. Street sweeping is an effective way of collecting that material before it washes off into the nearest storm drain.

Lastly, portions of the Mystic River watershed have so-called combined sewers, which carry both raw sewage and stormwater in a single pipe. During large rain storms, these antiquated systems can reach their capacity due to the large volume of stormwater draining into them. When this happens, there is no choice but allow the excess stormwater-and-sewage mixture to release into the nearest waterway, which is called a combined sewer overflow (CSO). However, the EPA and MWRA are working together to improve these systems by separating stormwater and sewage pipes, and adding holding tanks and other features that will minimize and ultimately eliminate the discharge of combined sewer and stormwater.

What is MyRWA doing about it?

The first step in combating phosphorus pollution is to measure how much phosphorus is in the river. Over the past several years, the Mystic River Watershed Association has engaged in a major phosphorus study, designed to measure the amount of phosphorus entering the system and the effects it is having. The project has been executed in collaboration with US EPA, the Massachusetts Department of Environmental Protection (DEP), the United States Geologic Survey (USGS), and other stakeholders. Over the course of the study, thousands of measurements were made and compared with historical data. The results of this study are in: we need to reduce phosphorus inputs by 60%. Learn more here about the study and the importance of reducing phosphorus.

Green infrastructure is an effective way of reducing stormwater runoff, which is the primary source of phosphorus to the Mystic River. By reducing runoff, less phosphorus washes off the land surface and drains to the nearest segment of the river. There are many types of so-called best management practices (BMPs) such as rooftop gardens, rain gardens, bioswales, constructed wetlands, among others. MyRWA is leading the building of stormwater trenches—a low-cost, effective green-infrastructure that is built on our roads that helps reduce pollution in our river. Read about the building of these trenches in our watershed here.

Read about what MyRWA is doing to protect water quality—including green infrastructure.

phosphorus Tracking

During the summer we monitor for cyanobacteria blooms at popular recreational areas in the watershed, and post warnings if that level is high.

Use your smartphone to help us track cyanobacteria blooms throughout watershed using the Bloomwatch App.