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.”
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.
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.
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 is being 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–and its future implications–will be rolled out starting in 2019; so stay tuned.
MyRWA also enlists a team of volunteers to collect water samples at locations throughout the watershed each month. These samples are sent to a lab and measured for phosphorus levels and other contaminants. Read more about our Baseline Monitoring Program. During the summer we monitor for cyanobacteria blooms at popular recreational areas in the watershed. We post an warning on our cyanobacteria monitoring web page when cyanobacteria levels are too high.
Unfortunately, knowing how much phosphorus and algae are in the river is not enough to address the problem. We also need the help of towns, businesses, and residents of the watershed to take steps to prevent phosphorus from reaching the river.
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, among others. Find out more about green infrastructure and BMP from the US EPA.
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 are 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 can you do?
As a resident of the watershed, we need your help! Every parcel of land has the potential contribute phosphorus loading by allowing untreated stormwater to drain from the property into the nearest stormwater drainage system, or even directly into the river. Here are some things you can do at home to reduce or eliminate your impact. Use your smartphone to help us track cyanobacteria blooms throughout watershed using the Bloomwatch App.
Get involved and take action!
MyRWA offers a wide range of activities and events for anyone to help us make the Mystic River a better place to live, work, and play.
Come join us!