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Submitted to: Review Article
Publication Type: Other Publication Acceptance Date: 12/23/2004 Publication Date: 12/23/2004 Citation: Dinnes, D.L. Assessments of practices to reduce nitrogen and phosphorus nonpoint source pollution of Iowa's surface waters. Review Article. Available at: ftp://ftp.nstl.gov/pub/NPS/NPS Nutrient Pollution Assessments of Conservation Practices.pdf Interpretive Summary: Long ago, nitrogen (N) and phosphorus (P) plant nutrients were identified as primary factors in causing water quality impairments. For compliance with the 1972 Clean Water Act, the U.S. EPA has required all states to establish N and P nutrient management strategies to reduce the amount of nonpoint source (NPS) pollution of these plant nutrients in surface waters. This extensive report was written to provide documented research evidence of various conservation practices' impacts on N and P losses from agricultural production lands, and to serve as a foundation for developing the state of Iowa's N and P nutrient management strategy. The first section of this report presents educational background information for the general public that explains the natural and human-induced factors that influence NPS nutrient water pollution. Next are water quality impact assessments of conservation practices to manage NPS N and P nutrient pollution. For each conservation practice the assessments identify mechanisms of nutrient reduction and/or removal, current documented degrees of success, applicable conditions, conditions that limit its function, and sources of its variability in performance. Finally, a summary presents a compilation of the conservation practices' estimated long-term impacts on N and P NPS pollution, plus recommendations and guidance for how the state can proceed with setting policy and action to reduce the problems. Most notable among the assessed practices are those that function to considerably reduce both N and P losses, which are cover crops, diversified cropping systems, in-field vegetative buffers, livestock exclusion from stream areas, and stream buffers. Although a number of these practices may substantially decrease NPS nutrient loss, a single practice alone may not be able to reduce nutrient losses to the extent necessary to meet water quality standards. For a field-edge conservation practice such as a stream buffer to function successfully, it is critical to implement in-field conservation practices that are designed to increase water storage and reduce sediment and nutrient losses. When determining what and where to enact changes, one must choose the applicable practices that have shown the greatest potential for achieving success. All of Iowa's citizens stand to directly benefit from this report's information and guidance if it is put into action in the state's nutrient management strategy. All others that live downstream will indirectly benefit because they will be receiving less N and P pollution in the surface waters they receive from Iowa, making it easier for them to also meet water quality standards. Technical Abstract: The quality of Iowa's water resources is an important issue to the state's citizens for many reasons and it has received much attention in recent years. Agriculture dominates land use in Iowa: over 90% of the state's land area currently is in agriculture production. It is not surprising then that agriculture is widely considered to be the dominant contributor of nutrient nitrogen (N) and phosphorus (P) nonpoint source (NPS) pollution of the state's surface waters. This document presents educational background information for the general public that explains the natural and human-induced factors that influence NPS nutrient water pollution. Next are water quality impact assessments of conservation practices to manage NPS N and P nutrient pollution. For each conservation practice, the assessments identify mechanisms of nutrient reduction and/or removal, current documented degrees of success, applicable conditions, conditions that limit its function, and sources of its variability in performance. Finally, a summary presents a compilation of the conservation practices' estimated long-term impacts on N and P NPS pollution, plus recommendations and guidance for how the state can proceed with setting policy and action to reduce the problems. Most notable among the assessed practices are those that function to considerably reduce both N and P losses, which are cover crops, diversified cropping systems, in-field vegetative buffers, livestock exclusion from stream and riparian areas, and riparian buffers. Although a number of these practices may substantially decrease NPS nutrient loss, a single practice alone may not be able to reduce nutrient losses to the extent necessary to meet water quality standards, particularly from critical source areas. Comprehensive conservation management plans may often require the adoption of both preventive and remedial treatment practices. For a remedial field-edge conservation practice to function successfully, it is critical to implement in-field conservation practices that are designed to increase soil water storage (thereby reducing runoff and leaching water volumes) and reduce N and P mass transport. It must be remembered that one cannot expect change without first performing change. When determining what and where to enact changes, one must choose the applicable practices that have shown the greatest potential for achieving success. |
