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Nitrate Retention in Riparian Ground Water at Natural and Elevated Nitrate Levels in North Central Minnesota

^a U.S. Geological Survey, Water Resources Division, 345 Middlefield Road, MS 439, Menlo Park, CA 94025
^b Dep. of Chemical Engineering and Materials Science, Univ. of California, Davis, CA 95616

View larger version (25K): [in this window] [in a new window]   Fig. 1. (a) Map of the study area consisting of the Upper Shingobee River watershed, (b) the location of well Transects 1 and 2 in relation to the relict beaver dam, and (c) a close up of the Experimental Well Array on the alluvial deposit.

View larger version (30K): [in this window] [in a new window]   Fig. 2. Contour interpolation of the piezometric water levels in the alluvial wells averaged over six dates between 1996 and 1998. Elevations are in cm measured with respect to well SHW 12.

View larger version (18K): [in this window] [in a new window]   Fig. 3. Chloride concentration in Experimental Array Wells 1 through 4 during Injection 4, September 1998.

View larger version (20K): [in this window] [in a new window]   Fig. 4. Nitrate–N/halide ratios for Experimental Array Wells 1 through 3 during (a) Injection 1, January 1998, and (b) Injection 2, January 1998. (c) Dissolved oxygen (DO) concentration during Injection 2, January 1998. Injection 1 consisted of bromide and nitrate (NO3–). Injection 2 consisted of chloride, NO3–, glucose, and acetylene.

View larger version (26K): [in this window] [in a new window]   Fig. 5. Nitrogen/chloride ratios for nitrate (NO3–), nitrite (NO2–), and nitrous oxide (N2O) in Experimental Array Wells 1 through 3 (a, b, and c, respectively) during Injection 2 in January 1998. Injection 2 consisted of chloride, NO3–, glucose, and acetylene.

View larger version (18K): [in this window] [in a new window]   Fig. 6. Bromide (Br–), nitrate (NO3–), and dissolved oxygen (DO) concentration in Experimental Array Well 1 during Injection 3 in September 1998. Injection 3 consisted of Br– and glucose.

View larger version (20K): [in this window] [in a new window]   Fig. 7. Nitrate (NO3–) predicted by chloride if NO3– was transported conservatively, and observed NO3–, nitrite (NO2–), and nitrous oxide (N2O) in Experimental Array Wells (a) 1, (b) 2, and (c) 3 in September 1998. Injection 4 consisted of chloride, NO3–, glucose, and acetylene.