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  • Contribution to the characterization of Illinois reference/background conditions for setting nitrogen criteria for surface waters in Illinois : final report to Illinois Council on Food and Agricultural Research (C-FAR)


  • The United States Environmental Protection Agency (USEPA) National Regional Nutrient Criteria Development Program is developing regional-specific criteria for total nitrogen concentrations in surface waters. These criteria will provide the foundation for states to set total nitrogen standards to remedy impairments caused by nutrient overenrichment and to protect designated uses. Reference conditions representing minimally impacted surface waters will be developed for each ecoregion. All nutrient criteria must be based on sound scientific rationale. The first element of a nutrient criterion identified by USEPA is "... historical data and other information to provide an overall perspective on the status of the resource." The second element includes " ... a collective reference condition describing the current status." A further element requires "... attention to downstream consequences." The USEPA recognizes that nutrient concentrations in surface waters are primarily affected by the rate of weathering and erosion from watershed soils. Human activity can affect on the natural load of nutrient inputs to surface waters through, for example, vegetation disturbance of the vegetation, and addition of nutrient-containing material, such as fertilizer. At the heart of the overenrichment problem are the rates of production and decomposition of organic materials, of which nitrogen is a component. This report provides a contribution to the setting of reference/background conditions for Illinois through the evaluation of the current status of water resources against historical conditions, and some attention to downstream consequences. A particular focus of downstream consequences is hypoxia in the Gulf of Mexico, allegedly caused by the flux of excess nitrogen from the Upper Mississippi, Ohio, and Missouri River Basins. The concept of biogeochemical cycling provides an appropriate and necessary framework for understanding landscape influences on water quality throughout the Illinois River Basin. Changes in the Illinois River Valley and its system of tributary streams and lakes are well recognized, but this is the first attempt to assess in some detail how such changes have affected the aquatic carbon, oxygen, and nitrogen cycles; especially the impact of such watershed changes on the nature and quantity of aquatic nitrogen, as well as on the nitrogen cycle within the terrestrial reservoir. This is seen in the accompanying time line of the estimated nitrogen richness of the Illinois landscape. Scientists studying soils and crops from the mid-19th through mid-20th centuries documented that human activities have greatly altered the natural nitrogen cycle. Cultivation of virgin land typically depleted nitrogen and carbon stored in these reservoirs by about 50 percent in the first 60-70 years of cultivation. Some of this nitrogen was transferred to surface waters and ground waters. The depletion of nitrogen from soils in the Mississippi River Basin was so great that crop yields declined throughout the 19th and early 20th centuries. By mid-20th century, the extensive use of nitrogen fertilizer, improved plant varieties, and agronomic practices increased crop yields. Nitrogen fertilizer also began to replenish some of the large amounts of nitrogen previously removed from the soil. In the 1970s, profound changes occurred in the perception of the natural nitrogen cycle and human modification of that cycle. The nitrogen cycle, and human impacts on it came to be defined in terms of atmospheric nitrogen fixation and the return of nitrogen gases by nitrification/denitrification. The 99 percent of the nitrogen cycle which was otherwise cycled within and between the large soil, sediment, and plant reservoirs were no longer acknowledged. From this new definition of the nitrogen cycle, it was concluded that human activities, especially fossil-fuel combustion and fertilizer use, had doubled the nitrogen cycle and many lands, including much of Illinois, had become nitrogen saturated. Increasing concentrations of nitrate-nitrogen in surface waters were given as evidence of nitrogen saturation and leakage. This new limited edition of the nitrogen cycle became cast in concrete and is referred to in this report as "the new, standing nitrogen-cycle paradigm." This report uses the earlier, scientifically more complete and defensible definition of the nitrogen cycle, which includes recognition of the magnitude and importance of soil-plant reservoirs and exchanges. It uses extensive scientific documentation of major changes in ecosystems and soil nitrogen that have occurred over centuries, to place into perspective the present status of nitrogen resources -- as required by USEPA. This report examines the impact on nitrogen concentrations in surface waters in Illinois during occupation of the land by Native Americans, bison, and many other animals and birds. Theoretical impacts are complemented by written accounts of early settlers and scientific observations made under similar conditions. It is concluded that the landscape and surface waters were more nitrogen saturated at this time than today. These pre-European-settlement conditions were selected as the reference/background conditions. Just prior to and during the period of early European settlement, the populations of Native Americans and bison were eliminated and the landscape became less nitrogen saturated. Nevertheless, even in the 1820s, the Illinois River was hypertrophic, i.e. nutrient overenriched. As late as the 1850s, the amount of eroded soil transported by the Mississippi River was more than twice that transported in recent decades. Since soil erosion is reported to be the major sort of N delivery from agricultural lands, the N load in the Mississippi River was declining. The average annual concentration of total nitrogen in the Lower Illinois River in 1894-1899 was 3.68 mg N/l, and additional large amounts of nitrogen not measured were stored in plankton and luxuriant aquatic vegetation and transported downstream in copious amounts of organic debris. Allowing for the unmeasured flux of nitrogen as plankton and for low flow, the adjusted average annual concentration of total nitrogen in the Lower Illinois River in 1894-1899 is estimated to have been about 5.5 mg N/l. This report also examines the impact of European settlement and agriculture on the nitrogen cycle and water quality. Scientific data show that the average concentration of total nitrogen in the Lower Illinois River increased to about 10 mg N/l by mid-20th century and subsequently decreased to 4.8 mg N/l in the 1990s. The annual concentration of nitrate in the Lower Illinois River peaked at about 6.2 mg N/l in 1967-1971 and subsequently decreased to about 3.8 mg N/l in 1993-1998. These improvements in water quality are associated with an increasing amount of dissolved oxygen in the river. The reductions in the concentrations of all forms of nitrogen are attributable to both point- and nonpoint-source pollution control. The main conclusions of this report are that, in establishing scientifically sound reference/background conditions, it is necessary to quantify in a common unit all forms of nitrogen (in solution, as solids, and as gases; and organic and inorganic forms) and all sources, reservoirs, transformations, and fluxes of nitrogen in a common unit; and to understand interactions between nitrogen and other biogeochemical cycles of, for example, water, oxygen, carbon, and phosphorous. Criteria for setting nitrogen standards must recognize the great complexity of the nitrogen cycle and its interdependence with other variables, cycles, and anthropogenic influences.

Originally Deposited as: 999999994193

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Language(s): EN-English

Volume or Year: 2000
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Date Created: 9 24 2004
Date Last Modified: 2 14 2003

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1. A contribution to the characterization of Illinois reference/background conditions for setting nitrogen criteria for surface waters in Illinois : final report to Illinois Council on Food and Agricultural Research (C-FAR) (20060929190718_ISWSCR2000-08.pdf).
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