Nutrients: Phosphorus, Nitrogen Sources, Impact on Water Quality - A General Overview

Water Quality/Impaired Waters #3.22 • May 2008

n the 1997 Clean Water Action Plan the U.S. Environmental Protection Agency I identified nutrients as a significant national problem contributing to water pollution. States reported that more than All lakes need half of all lakes were affected. protection from the pollution that robs Just as applying fertilizer to gardens and them of oxygen and farm fields helps crops grow, nutrients aquatic life. We can't entering lakes and rivers feed the growth of do anything about algae, bacteria, and other tiny organisms. Photo: Grace Lake, Beltrami County SWCD nutrients from natural Water bodies require some nutrients to be sources and the systems, animal feed lots, agricultural healthy, but too much can be harmful. sun’s warmth, but we fertilizers, manure, industrial waste waters, When lakes receive an overabundance of can work to prevent sanitary landfills, and garbage dumps. excessive nutrients nutrients, they can become polluted by and sediments from excessive amounts of algae. Die-off and human activity from decomposition of algae blooms can reduce Phosphorus Fuels Algae Growth getting into lakes and Phosphorus is a vital nutrient for waterways. dissolved oxygen and suffocate fish and converting sunlight into usable energy, and other aquatic life. Some forms of algae (blue-green) may produce toxins that can essential to cellular growth and be harmful if ingested by humans and reproduction. It is one of the 20 most animals. abundant elements in the solar system, and the 11th most abundant in the earth’s crust. MPCA Area Offices: Phosphorus and Nitrogen Under natural conditions phosphorus is Rochester area: typically scarce in water. In the late 1960s 507/285-7343 Phosphorus (P) and nitrogen (N) are the scientists discovered phosphorus Mankato area: primary nutrients that in excessive amounts contributed by human activity to be a 507/389-5977 pollute our lakes, streams, and wetlands. Marshall area: major cause of excessive algae growth and Nitrogen is essential to the production of 507/537-7146 degraded lake water quality. plant and animal tissue. It is used primarily Willmar area: Phosphorus occurs in dissolved organic 320/214-3786 by plants and animals to synthesize protein. and inorganic forms or attached to Detroit Lakes area: Nitrogen enters the ecosystem in several sediment particles. Phosphates, the 218/847-1519 chemical forms and also occurs in other Brainerd area: inorganic form, are preferred for plant dissolved or particulate forms, such as 218/828-2492 growth, but other forms can be used when tissues of living and dead organisms. Duluth area: phosphates are unavailable. Phosphorus 218/723-4660 Metro area: Nitrate, a compound containing nitrogen, builds up in the sediments of a lake. When 651/296-6300 can exist in the atmosphere or as a it remains in the sediments it is generally Toll-Free Number: dissolved gas in water, and at elevated not available for use by algae; however, 800/657-3864 levels can have harmful effects on humans various chemical and biological processes and animals. Nitrates in water can cause can allow sediment phosphorus to be severe illness in infants and domestic released back into the water. For example, animals. Common sources of excess nitrate reaching lakes and streams include septic wq-iw3-22

Minnesota Pollution Control Agency • 520 Lafayette Rd. N., St. Paul, MN 55155-4194 • www.pca.state.mn.us 651-296-6300 • 800-657-3864 • TTY 651-282-5332 or 800-657-3864 • Available in alternative formats Trophic State Index TSI: Higher number – greater nutrient enrichment and lower water clarity (Secchi disk transparency or SDT)

bottom-feeding rough fish such as carp can stir up such as nitrogen and phosphorus. Human activities can bottom sediments, releasing phosphorus back into the accelerate the process with urban construction, sewage water. discharges, agricultural practices, and residential development. Impact on Water Quality Poor water quality in lakes can have many unpleasant Measuring Impact of Nutrients consequences. Rough fish – such as carp and bullhead – Not all lakes are affected to the same degree. The green populations increase at the expense of game fish yuck permeates shallow lakes in the south more so than populations. Severe nuisance algal blooms yield deeper, cooler northern lakes. The MPCA uses unpleasant odor and appearance ecoregion-based total phosphorus that reduce the aesthetic appeal of guidelines in conjunction with Carlson’s lakes. This may result in declines Trophic State Index (see chart) to classify in fishing and swimming and hurt lakes in their level of quality for tourism. swimming and fishing. TSI is a numeric index of lake trophic status on a scale of 1 As algae die and decompose, the to 100, the higher the number indicating process consumes oxygen. greater nutrient enrichment. Lake nutrient Submerged plants without sunlight standards that vary according to die, decompose and consume more ecoregion and lake type have recently oxygen. Without enough dissolved been developed. These water quality oxygen in the water, fish and other Citizen volunteers use Secchi disks standards will provide a basis for organisms suffer and die because to collect data on water clarity. determining the impairment status of they can't “breathe.” This can occur Minnesota’s lakes and will be useful for protecting the locally or much farther downstream leading to degraded quality of good lakes as well. The MPCA also is estuaries, lakes and reservoirs. For example, fish and developing nutrient standards for rivers. other aquatic life can no longer survive in the so-called “dead zone” in the Gulf of Mexico. Information Sources Nutrient Sources and Pathways Water Quality Standards: www.pca.state.mn.us/water/standards/index.html The geology and land use within a lake’s watershed MPCA Lake Programs: determine the amount of nutrients that enter the lake via www.pca.state.mn.us/water/lake.html surface water runoff. Eutrophication is the slow aging Volunteer Surface Water Monitoring: process during which a lake, estuary, or bay evolves into www.pca.state.mn.us/water/volunteer-monitoring.html a bog or marsh and eventually disappears. Some of the Secchi disk transparency slide show: nutrients come from natural processes, such as www.pca.state.mn.us/water/secchi-slideshow.html decomposition of plant and animal material. During the later stages of eutrophication the water body is choked by abundant plant life due to higher levels of nutrients

Phosphorus, Nitrogen Impact on Water Quality • Water Quality/Impaired Waters #3.22 • May 2008 page 2