Odor and Nutrient Management Newsletter

Spring 2002

Impacts of state nutrient standards in Iowa

by Robin Pruisner, Iowa Department of Natural Resources

Iowa - a state heralded for its fertile, productive soils - may have too much of a good thing. Iowa Department of Natural Resources (IDNR) studies show that nitrate levels in the Cedar River near Cedar Rapids have tripled in the past 60 years, and nitrates in the Des Moines River near Des Moines have dou-bled. Soil test summaries confirm that phosphorus levels have increased from the 1960s through the 1980s, but have leveled off in the past 20 years, and now more than half of the soil samples analyzed in Iowa are at or above the levels needed for crop production.

Excess nitrogen and phosphorus cause eutrophication, resulting in algal blooms, low dissolved oxygen, fish kills, and depletion of desirable flora and fauna. Iowa's current list of impairments includes approximately 40 lakes with excess nutrients, and an additional 13 lakes potentially impaired by excess nutrients.

Photo: Pumping manure from concrete pits
Photo: Pumping manure from concrete pits

The U.S. Environmental Protection Agency (EPA) is requiring all states to demonstrate significant progress in developing state-specific, numeric nutrient standards for lakes, reservoirs, streams, and rivers by 2004. The standards must be based on national guidelines, further refined by ecoregional EPA work-groups. Current EPA nutrient standard criteria recommendations are listed in the table. Iowa is ultimately responsible for modifying the national and ecoregional guidance to fit Iowa's unique characteristics. EPA must approve all state-specific nutrient standards. If Iowa fails to adopt water quality standards for nutrients, or EPA finds the state standards unacceptable, the EPA will promulgate state standards. If this occurs, the EPA is expected to rely heavily on both proposed national criteria and regional criteria.

It is unreasonable to expect the EPA to approve state standards that are significantly above the current recommendations. A best-case scenario might see EPA approval of a phosphorus standard of ap-proximately 100 ppb in lakes and 200 ppb in rivers and streams. Even at this best-case scenario, more than two-thirds of Iowa's lakes and reservoirs will not meet standards, and an even greater percentage of the state's rivers and streams will not meet standards. Consequently, all the waterbodies not meeting standards would be considered impaired and be subject to the development and implementation of total daily maximum loads (TMDLs). The cost of developing and implementing these TMDLs has not been determined.

How might the standards affect Iowa? Impacts on both point sources and nonpoint sources will be significant, particularly because the cumulative impact of point and nonpoint pollution will probably cause more violations.

Point sources (municipal and industrial sources). Many point sources discharging at low-flow conditions are expected to cause violations of the nutrient standards. As part of carrying out TMDL implementation plans, additional nutrient control requirements on point sources are likely.

Nonpoint sources. Agriculture is the largest nonpoint source of nutrients to Iowa waters, and in many waterbodies it may be the only source. Research indicates traditional nutrient management best management practices will not achieve the standards. To meet the expected nutrient standards, Iowa farms may have to 1) implement additional erosion controls; 2) convert intensive row crop areas to less intensive uses; 3) establish wetlands and other water management structures; or 4) sharply restrict nutrient applications (both commercial fertilizers and manure), which may reduce yields.

How is Iowa proposing to respond? To address this issue, IDNR is proposing a four-part ap-proach as follows: 1) Establish reasonable, science-based nutrient standards for Iowa. This effort will be carried out under the established DNR water quality standards development process. As a first step, in early 2002, IDNR will submit a work plan and schedule for developing and adopting nutrient standards to the EPA. The schedule will target the adoption of the standards for the end of 2004. The EPA must ap-prove standards developed for Iowa.

2) Develop a comprehensive state nutrient budget, considering all significant sources (point and nonpoint) of nutrients to Iowa's waters. This assessment will determine the source, volume, frequency, and concentration of nutrients in the discharge. The budget will be developed on a watershed basis by using geographic information system maps and site-specific data. Some of these data exist, although not in a single location. Acquisition of data may require sample collection, analysis, review, and extrapolation with research and modeling. Data are needed on septic systems and other on-site wastewater discharges; intensively managed areas, such as golf courses and urban areas; and agricultural sources, including estimates of nutrient discharges from various agricultural activities. Iowa Department of Agriculture and Land Stewardship records, USDA Ag Statistics, and other sources may be used to estimate nutrient availability and then model nutrient discharge concentrations.

3) Assess the effectiveness of practices for reducing nutrient loadings to waterbodies. Technologies to be assessed include nutrient treatment and removal systems, source reduction, adjustment of amount of nutrients land applied, as well as land application methods. Assessment will include consideration of nutrient reduction and removal efficiency, analysis of direct and indirect costs, cost-benefit, and other impacts.

4) Develop a comprehensive strategy for managing nutrients in Iowa. This strategy will consider all sources of nutrients to Iowa's waters and identify the actions that are needed from each source to achieve compliance with the adopted state nutrient standards. A variety of actions will be considered in developing this strategy, including reductions in nutrient use and other source reduction approaches, changes in agricultural nutrient use, nutrient treatment and removal technologies, and nutrient trading programs. Input into development of this strategy will be sought from a variety of affected and interested parties, through use of advisory committees, public meetings, and other public involvement approaches.

For more information, please e-mail Robin Pruisner at robin.pruisner@dnr.state.ia.us or call

Current EPA nutrient standard criteria recommendations for most of Iowa.

LAKES Phosphorus Total Nitrogen
National EPA criteria
55 ppb 963 ppb
Draft regional criteria
35 ppb 700 ppb
National EPA criteria
118 ppb 3.26 ppm
Regional EPA criteria
expected in next 12 months

How do Iowa's waters measure up?
Based on 2000 monitoring data for 130 Iowa lakes:

  • one lake would meet the standard under a 35 ppb phosphorus standard
  • four lakes would meet the standard under a 55 ppb phosphorus standard
  • <25 percent of the state's lakes would meet the standard under a 100 ppb phosphorus standard
  • 14 lakes would meet the standard under a 963 ppb total nitrogen standard.

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