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Whole-Stream Response to Nitrate Loading in Three Streams Draining Agricultural Landscapes

^a U.S. Geological Survey, Water Resources Div., 345 Middlefield Road, MS 439, Menlo Park, CA 94025
^b U.S. Geological Survey, Portland
^c U.S. Geological Survey, La Crosse, WI
^d Univ. of Wisconsin, La Crosse, WI
^e U.S. Geological Survey, Tacoma, WA

View larger version (16K): [in this window] [in a new window]   Fig. 1. Mean denitrification (A) and nitrification (B) rates measured in sediment samples from DR2, Maple Creek, and Morgan Creek. One-way ANOVA statistics are shown in each panel. Bars with different lowercase letters indicate significant differences between mean values. Error bars indicate ±1 SE.

View larger version (38K): [in this window] [in a new window]   Fig. 2. Mean denitrification response in sediments from DR2, Maple Creek, and Morgan Creek to no amendment (Control) and amendments of 12 mg C L–1 as glucose (+C), 14 mg N L–1 as NO3– (+N), and glucose + NO3– (+C+N). One-way ANOVA statistics are shown for Maple Creek (differences among means at other sites were not significant). Bars with different lowercase letters indicate significant differences between mean values. Error bars indicate ±1 SE.

View larger version (13K): [in this window] [in a new window]   Fig. 3. Nitrate-N/bromide ratios (NO3–/Br–) in open sediment enclosures incubated in the streambed for 8 h at DR2 (n = 5), Maple Creek (n = 5), and Morgan Creek (n = 11). Error bars indicate 1 SE.

View larger version (17K): [in this window] [in a new window]   Fig. 4. (A) Ammonium (NH4+) and (B) nitrate (NO3–) concentrations in drive points at DR2, Maple Creek, and Morgan Creek.

View larger version (14K): [in this window] [in a new window]   Fig. 5. Diurnal nitrate-N/bromide ratios (NO3–/Br–) in stream water at DR2, Maple Creek, and Morgan Creek. Data were collected at three or four stations. Error bars indicate ±1 SE.

View larger version (19K): [in this window] [in a new window]   Fig. 6. Diurnal patterns of pH, dissolved oxygen (DO), and nitrate (NO3–) in stream water at Maple Creek. Data were collected at three or four stations. Error bars are smaller than the symbols.