Farms to Faucet: The Hidden Connection

By Earth Resources Observation and Science (EROS) Center August 28, 2024

How are french fries and drinking water connected? As potato farms expand to meet growing demand, they alter landscapes and impact water sources. In Minnesota, this has led city managers to take a closer look at how land use change influences the quality of drinking water. Understanding these links is important for planning a future where land use changes affect our water sources.

Nature's Role in Clean Water

Natural landscapes, such as forests and grasslands, are important for preserving water quality and drinking water. They minimize erosion, mitigate and filter pollution, and reduce costs associated with treating water used for human consumption.

Research has shown that cities located within healthy watersheds can save on water treatment and infrastructure expenses. In many cases, it's more cost-effective for cities to protect these natural areas than to build large, expensive water treatment facilities.

While the benefits of natural landscapes are clear, watershed conditions are continuing to decline in many locations across the globe due to population growth, urban and agricultural expansion, and loss of natural lands.

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Minneapolis Water Supply

An aerial view of the Mississippi River south of downtown Minneapolis. — Aerial view of the Mississippi River south of downtown Minneapolis.

The City of Minneapolis relies on the Mississippi River for its drinking water supply. The Minneapolis Water Treatment Distribution Service pumps approximately 21 billion gallons of water from the river each year to provide drinking water to over 500,000 people in Minneapolis, seven suburban cities, and business and institutions.

The water treatment process involves several steps, such as softening, filtering, disinfecting, and testing. Water softening and filtration relies on carbon, alum, and lime to improve quality, clarity, and taste. Over the past 15 years, these treatments have increased to ensure the water remains safe and clean for the community.

The Impact of Changing Land Use

Over the past twenty years, the Mississippi Headwaters region has seen significant changes in its landscape. Using data from the National Land Cover Database (NLCD) and the USDA Cropland Data Layer (CDL), scientists have tracked a decline in natural areas as cropland, particularly potato farms, has expanded to meet the rising demand for processed potato products like french fries.

This shift from grasslands and forests to agriculture has led to more sediment and phosphorus entering the Mississippi River, especially during the early months of the growing season. As a result, Minneapolis has had to increase its use of chemicals to ensure its drinking water remains safe for the city's residents.

NLCD for the Mississippi Headwaters Subregion (HUC 0701) — Land cover from the National Land Cover Database (NLCD) for the Mississippi Headwaters (HUC 0701).

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National Land Cover Database (NLCD) Animation (2001-2021) for the Minneapolis Region in Minnesota

Field consisting of rows of potato plants

Potatoes are a leading vegetable crop in the United States

Minnesota ranks seventh nationally in terms of potato production

Minnesota farmers planted 49,000 acres of potatoes in 2022

The majority of Minnesota’s potatoes are used for processed foods

Future Projections

While NLCD and CDL have been important for understanding recent trends in land use in the Mississippi Headwaters region, future projections of change are necessary to anticipate future trends and the resulting impact on water treatment needs in Minneapolis.

To address this, the United States Environmental Protection Agency, in partnership with the City of Minneapolis, used U.S. Geological Survey (USGS) land use projections to assess: 1) potential future landscape change, 2) potential changes in raw water quality, and 3) future water treatment needs for the city.

The USGS used a multi-scenario approach to explore potential future changes in water quality. The extent and amount of change differs across the scenarios, ranging from expanded agricultural and developed lands to minimal land use change with some forest regrowth.

In scenarios where agricultural, developed, and pasture lands increase, the levels of total nitrogen and phosphorus in the Mississippi River increase. Conversely, in scenarios with less land use change, or those that include forest regrowth, showed smaller increases or even decreases in nutrient load levels.

Both current observations and future projections indicate a trend of rising nitrate levels in the Mississippi River. While these levels are currently within safe limits, ongoing land use changes may require the removal of nitrates from drinking water in the future.

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NAIP 2021 Image of the Mississippi River and Minneapolis Public Works Water Treatment and Distribution Service in Fridley, Minnesota

Policy and Management Implications

The multi-scenario approach used to model future landscape change has provided the City of Minneapolis with valuable information about land cover change and its potential impact on influent total nitrogen, total phosphorus, and sediment loadings in their water supply. This data helps water managers assess whether adjustments to water treatment processes may be necessary in the future. Additionally, it aids regional land managers in understanding the impacts of different land use decisions.

By understanding these connections, we can make informed choices about land use and conservation, helping to ensure clean water for future generations.

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