Phosphorus loading to Lake Erie

Phosphorus loading to Lake Erie from all sources

Key results

• In 2022, total estimated phosphorus loading to Lake Erie was 9 379 tonnes, with 22% (2 091 tonnes) of the total load estimated to be from Canada
• The highest total estimated phosphorus loading to Lake Erie was 13 533 tonnes in 2019 with 19% (2 588 tonnes) of the total load estimated to be from Canada
• The lowest total estimated phosphorus loading to Lake Erie was 5 672 tonnes in 2010 with 16% (903 tonnes) of the total load estimated to be from Canada
• There has not been a clear upward or downward trend over time; the 2022 results were in line with the average of the 2008 to 2022 period

Total estimated phosphorus loading to Lake Erie, 2008 to 2022

How this indicator was calculated

Note: Basin total values include loadings from runoff and tributaries in Canada and the United States, flows from Lake Huron and atmospheric sources of phosphorus. Half of the total phosphorus loadings from atmospheric sources and half of those from Lake Huron were allocated to each country.
Source: Environment and Climate Change Canada (2023).

Phosphorus loading varies year to year due mainly to climatic factors. Dry years in the region will lead to low levels of runoff from surrounding lands and less phosphorus being washed into the lake and tributaries feeding the lake.

In 2022, phosphorous loading to Lake Erie from all sources within Canada and the United States (9 379 tonnes) was relatively average compared to the last 14 years, and similar to loads in 2013 (8 634 tonnes), 2014 (9 091 tonnes) and 2020 (9 640 tonnes). Canada's contribution fluctuated over the period from a low of 903 tonnes in 2010 to a high of 2 758 tonnes in 2011. The year 2011 was marked by record high precipitation in the Lake Erie basin,^{Footnote 1}  leading to increased phosphorus loading through runoff from surrounding lands.

Lake Erie is the shallowest, warmest and most productive of the 5 Great Lakes. The lake is divided into 3 sub-basins: western (the shallowest), central (the largest) and eastern (the deepest). More than 50% of phosphorus enters the lake from either the Detroit River or the western basin tributaries. Figure 2 shows that non-point sources, such as agriculture and, to a much lesser extent, urban storm water runoff, are the largest contributors of phosphorus loads to Lake Erie, particularly in the western basin of the lake, where algae impacts are greatest.

Annual 10 year average phosphorus loading estimated in tonnes to Lake Erie, 2013 to 2022

How this indicator was calculated

Note: Point source includes municipal sewage treatment plant effluent and industrial effluent. Non-point source includes agriculture and urban storm water runoff. Atmospheric deposition refers to phosphorus being deposited directly to the lake from the air. The Huron-Erie corridor watershed includes input from Lake Huron, point and non-point sources and atmospheric deposition within the watershed.
Source: Environment and Climate Change Canada (2023).

Phosphorus loading to Lake Erie from Canadian sources

Key results

• Phosphorus loading to Lake Erie from Canada comes mainly from non-point sources such as agriculture and urban storm water runoff
• Non-point sources accounted for 77% of the phosphorus loading from Canada in 2022 compared to a high of 81% in 2014 and 2019, and a low of 47% in 2010^{Footnote 2} 

Phosphorus loading estimates to Lake Erie by source, Canada, 2008 to 2022

How this indicator was calculated

Note: The total phosphorous loadings from atmospheric sources and from Lake Huron were halved to roughly estimate the Canadian contributions. Loadings from Lake Huron are estimates generated through models. For more information, please see the Data sources and methods section.
Source: Environment and Climate Change Canada (2023).

Point sources include municipal sewage treatment plant effluent and industrial effluent. These are sources of phosphorus that can be identified as a single source such as an effluent pipe going into a water body.

Non-point sources are diffuse sources of pollution and include agriculture and urban storm water runoff. Non-point sources of phosphorus are mostly in the form of excess fertilizer and manure spread on the ground. Runoff from rainfall or snowmelt picks up and carries these pollutants, and deposits them into lakes and rivers.

Phosphorus loading from non-point sources was lowest in 2010, 2012 and 2016 which coincides with low precipitation years in the Lake Erie basin.^{Footnote 1} 

About the indicators

What the indicators measure

The Phosphorus loading to Lake Erie indicator reports on the total phosphorus loads flowing directly into Lake Erie or from its tributary rivers and includes loads from:

• atmospheric deposition
• point sources (for example, wastewater treatment plants)
• non-point sources (primarily from agriculture runoff)
• Lake Huron

In the absence of human development, natural background levels of phosphorus loading are relatively low. The indicator provides information about the amount of phosphorus flowing into Lake Erie mainly due to human activity.

Why these indicators are important

Clean freshwater is an essential resource. It protects aquatic plant and animal biodiversity. We use it for manufacturing, energy production, irrigation, swimming, boating, fishing and for domestic use (for example, drinking, washing). Degraded water quality damages the health of all freshwater ecosystems, such as rivers, lakes, reservoirs and wetlands. It can also disrupt fisheries, tourism and agriculture, and makes it more expensive to treat to meet drinking water standards. When phosphorus levels in water become too high, algal growth and certain types of bacteria associated with them, called cyanobacteria, can become excessive and harmful. Cyanobacteria can release substances that can harm, and in some cases kill animals that depend on the water. The decay of the excess algae and bacteria can also reduce the amount of oxygen available for fish and other aquatic animals. They can also affect human health, if humans are exposed to them.

Although this is not the case in Lake Erie, some lake ecosystems can have the opposite problem: too little phosphorus can result in not enough plant or algal growth to support a lake's food web, which could reduce fish populations and impact local fisheries.

Through the Canada–US Great Lakes Water Quality Agreement, Canada and the United States have agreed to reduce phosphorus loads entering the western and central basin of Lake Erie by 40% from 2008 levels in order to reduce the extent of harmful and nuisance algal blooms and zones of depleted oxygen (hypoxia), to protect water quality and ecosystem health. For Canada, this means a reduction in phosphorus loads by 212 tonnes per year. Studies are under way to support the development of a target for the eastern basin of Lake Erie. Several more years of data are necessary to detect a definite overall trend in phosphorus loading that accommodates for variations in climate from year to year.

To calculate phosphorus loads, it is important to know the volume of water and phosphorus levels in the water. Phosphorus level is the concentration of phosphorus in a given volume of water. Phosphorus loading is the total quantity of phosphorus that is being released into a water body within a certain time period such as per day, month, or year and/or by certain sources (e.g. agriculture, runoff, etc.). Increased loads from various sources can lead to increased concentrations in a water body.

This indicator is used to provide information relevant to the state of the Lake Erie basin and the Canadian environment.

Related initiatives

The indicator contributes to the Sustainable Development Goals of the 2030 Agenda for Sustainable Development. It is linked to the 2030 Agenda's Goal 6: Clean water and sanitation and Target 6.6: "By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes” and Target 6.5 "By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate."

Related indicators

The Phosphorus levels in the offshore waters of the Canadian Great Lakes, the Nutrients in Lake Winnipeg and the Nutrients in the St. Lawrence River indicators report the status of total phosphorus and total nitrogen levels.

The Water quality in Canadian rivers indicators provides a measure of the ability of river water across Canada to support plants and animals.

The Household use of chemical pesticides and fertilizers indicator reports on how many people in Canada use pesticides and fertilizers on their lawns and gardens.

Data sources and methods

Data sources

The data used in this indicator are from both Canadian and American sources, at the provincial/state and federal levels.

Methods

Data on point source discharges, atmospheric deposition and non-point sources (calculated using water flows and water quality data) are used to estimate phosphorus loading to Lake Erie.

Recent changes

Watershed areas were recalculated in 2021 using updated Canadian geographic information system (GIS) mapping, resulting in minor changes to some watersheds. Values for past years were recalculated based on these updated watershed areas.

Caveats and limitations

The indicator is based on total phosphorus concentrations only. Concentrations of total phosphorus may include differing proportions of the more bioavailable soluble reactive phosphorus which is the most impactful in terms of algae blooms and eutrophication. The indicator and data included in this report are not suitable for assessing soluble reactive phosphorus loads.

Phosphorus loadings from Lake Huron are estimates that are generated from models and then applied to all years. This approach to estimating the Lake Huron load is based on the assumption that the phosphorus loads from Lake Huron are relatively stable from year to year. Recently, studies on the Huron-Erie corridor have suggested that loadings from Lake Huron are more variable than previously assumed. The methods are under review.

Climate factors, such as precipitation or drought, greatly influence the amount of phosphorus entering a water body. Given this year-to-year variability, a longer time period is required to determine a statistically significant trend of phosphorus loading. As such, much caution is needed in making comparisons across years and estimating trends.

For the 2020 data and the 2021 data, where there were sites with low sample counts, a regression analysis approach was applied because sampling frequency at most tributaries was reduced or not completed due to the COVID-19 pandemic related restrictions.

Resources

References

Environment and Climate Change Canada and the U.S. Environmental Protection Agency (2022) State of the Great Lakes 2019 Technical Report (PDF; 19.9 MB). Retrieved on August 8, 2023.

Environment and Climate Change Canada and the U.S. National Oceanic and Atmospheric Administration (2022) 2021 Annual Climate Trends and Impacts Summary for the Great Lakes Basin. Retrieved on August 8, 2023.

Maccoux MJ, Dove A, Backus SM and Dolan DM (2016) Total and soluble reactive phosphorus loadings to Lake Erie: A detailed accounting by year, basin, country, and tributary. Journal of Great Lakes Research 42(6):1151 to 1165. Retrieved on August 8, 2023.

Related information

Canada–Ontario Agreement on Great Lakes Water Quality and Ecosystem Health

Canada–US Great Lakes Water Quality Agreement

Great Lakes protection