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<br />sources of nitrogen is greater than the basin
<br />yield of inorganic nitrogen in these large re-
<br />gions. Given the data currently available.
<br />however. it is nearly impossible to de\'e1op a
<br />complete mass balance for nitrogen; lhat is,
<br />accurately quantify all inputs and outpuls. For
<br />this reason, some uncertainty remains about the
<br />cau~s for trends in inorganic nitrogen in
<br />stream water.
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<br />Figure 42. Median yield 01 inorganic nitrogen at U.S.
<br />Geological Survey National Stream Quality Ac-
<br />counting Network stations In relation to atmos.
<br />pheric deposihon rate 01 nitrate in precipitation
<br />lor the 18 .....ater-resources regions at the contermi.
<br />nous United States. (Source: Compiloo by A. A.
<br />Smilh and R. B. Alexander lrom U.S. Geological
<br />Survey data,)
<br />
<br />SELECTED REFERENCES
<br />
<br />Clark, E. H., Haverkamp, J. A.. and Chapman, W.,
<br />1985, Eroding ~oils- The off-farm impa\."1s of
<br />soil erosion: Wa.~hington, D.C., The Conserva-
<br />tion Foundation.
<br />
<br />.
<br />
<br />N~tional Water Summary 1934-W~ler-ouality lsl.!ues 73
<br />
<br />..
<br />
<br />Haeni, F. P., 1983, Sediment deposition in the
<br />Columbia and lower Cowlitz Ri"ers, V.'ashing.
<br />ton--Oregon, caused by the ~1ay 18, 1980, erup-
<br />tion of ."-1ount SI. Helens: U.S. Geological
<br />Survey Circular 850-t.:, 21 p.
<br />Hirsch, R. M., Slack, J. R., and Smith, R. A., 1982,
<br />T<<:hniques of !rend analysis for monthl)'
<br />Water-qua1ity data: Water Resources Re~arch,
<br />\'.18, no. l,p. 107-121.
<br />Loehr, R. c., Martin, C. S., and Rast, W., cds,
<br />1900, Phosphorous management strategies for
<br />lakes: Ann Arbor, \.1ich., Ann Arbor Science
<br />Publishers, Inc., 490 p.
<br />National R~arch Council, 1983, Acid deposi-
<br />tion-Atmospheric processes in eastern Nonh
<br />America: Washington, D,C., National Acade-
<br />my Press, 375 p.
<br />Smith, R. A., and Alexander, R. B., 1983, A statisti-
<br />cal summary of data from the U.S. Geological
<br />Survey's nalional water quality networks: U.S.
<br />Geological Suney Open-File Report 83-533,
<br />30 p.
<br />Smith, R. A., Hirsch, R. M., and Slack, J. R., 1982,
<br />A study of trends in total phosphorus measure.
<br />ments at "'~".. stations: U.S. Geological Sur-
<br />\"t'y Water-Supply Paper 2190, 34 p.
<br />U.S. Bureau of Census, 1984, Statistical abstracts of
<br />the United States 1984: Washington, D.C. U.S.
<br />Go\'ernmnet Printing Office, 1015 p.
<br />U.S. Department of Agriculture, 1983, 19f13 Hand.
<br />book of agricultural charts: Agricultural Hand.
<br />book No. 619, 96 p.
<br />_1984, National resources in\lentory-A guide
<br />for UM.:'rs of the 1982 "Rl data files: Washington,
<br />D.C., U.S. Soil Conservation Service and Iowa
<br />Slat~University, 32 p.
<br />U.S. Geological Sur\'ey, 1984. National .....ater sum-
<br />mary 1983-Hydrologic e\'ems and issues: U.S.
<br />Geological Sun'ey Wat~r-Supply Paper 2250,
<br />243 p.
<br />Williams, G. p.. and Wolman, M. G.. 1984, Down-
<br />stream effects of dam~ on a]Ju\lial ri\'ers: U.S.
<br />Geological Survey Professional Pape'r 1286,
<br />llJp.
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