HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Related articles in JEQ Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (24) Citing Articles via Google Scholar Google Scholar Articles by Tomer, M. D. Articles by Burkart, M. R. Search for Related Content PubMed PubMed Citation Articles by Tomer, M. D. Articles by Burkart, M. R. GeoRef GeoRef Citation Agricola Articles by Tomer, M. D. Articles by Burkart, M. R. Related Collections Ground Water Quality Watershed and Landscape Processes Watershed-Scale Studies Best Management Practices Nitrogen

Long-Term Effects of Nitrogen Fertilizer Use on Ground Water Nitrate in Two Small Watersheds

National Soil Tilth Laboratory, USDA Agricultural Research Service, 2150 Pammel Drive, Ames, IA 50011

View larger version (35K): [in a new window]   Fig. 1. Maps of Watersheds 1 and 2 of the Deep Loess Research Station (DLRS), showing topography (left) and cropping boundaries (right). Topographic contours (left map) are at a 5-m interval and labeled as meters above sea level. Locations of piezometer nests and weirs are shown in both maps; the right map also identifies the nests and shows piezometer transect locations. Table 1 names the piezometer transects and gives depths of the installations at each piezometer nest.

View larger version (22K): [in a new window]   Fig. 2. Cross-sections of hydraulic heads (given as meters of elevation) along the three transects (W2, W1, and W1rip), interpolated from June 2001 water level measurements. Contour intervals are 0.5 m of head in the left and center cross-sections, and 0.25 m of head in the right cross-section. The identifier for each piezometer nest is indicated along the land surface. Stratigraphic contacts between major deposits (till, loess, and alluvium) are indicated by thick dotted lines. Refer to Fig. 1 and Table 2 for piezometer-nest and cross-section locations and identifiers.

View larger version (21K): [in a new window]   Fig. 3. Expected residual tritium activities in 2001 for water originating as local annual precipitation between 1953 and 2001. Isotopic decay based on a 12.43-yr half-life was applied to a constructed tritium record to obtain this plot. The constructed record included local data (from Lincoln, NE; Ames, IA; and on-site), a trend in the local data, and estimates for missing years based on records from St. Louis, MO and Ottawa, ON, Canada, as specified in Table 3. Precipitation data are from International Atomic Energy Agency (1992), International Atomic Energy Agency and World Meteorological Organization (2001), and Simpkins (1995).

View larger version (21K): [in a new window]   Fig. 4. Cross-sections showing variations in ground water tritium activity (TU) along three transects (W2, W1, and W1rip) during June 2001. Tritium contours are interpreted as pre-1953 in age for waters with tritium activity of <3 TU, whereas values of >12 TU show an influence of "bomb-peak" precipitation between 1963 and 1980. Intermediate values indicate recent or mixed-age waters. Piezometers not sampled for tritium are indicated by a crossed symbol. Piezometer-nest identifiers are shown along the land surface. Refer to Fig. 1 and Table 2 for piezometer-nest and cross-section locations and identifiers.

View larger version (17K): [in a new window]   Fig. 5. Plot of stable isotope data (18O versus 2H) from 33 water samples collected in Watersheds 1 and 2. A local meteoric water line (LMWL) fit to the data (solid line) has an r2 of 0.72. The global meteoric water line (GMWL; dotted line) is also plotted as a reference.

View larger version (23K): [in a new window]   Fig. 6. Cross-sections showing variations in relative isotopic enrichment or depletion, using a combined scale of 18O and 2H, in ground water along three transects (W2, W1, W1rip) in Watersheds 1 and 2. Piezometers not sampled for stable isotopes are indicated by a crossed symbol. Piezometer-nest identifiers are shown along the land surface. Refer to Fig. 1 and Table 2 for piezometer-nest and cross-section locations and identifiers.

View larger version (18K): [in a new window]   Fig. 7. (A) Nitrate N concentrations with depth in soils and deep sediments at Position 1D (Fig. 1), from core samples taken in 1996. (B) Depths of maximum NO3–N concentrations measured in 1972, 1974–1976, 1978, 1984 (Alberts and Spomer, 1985; Schuman et al., 1975), and 1996, plotted against cumulative baseflow from Watershed 1 since 1969.

View larger version (22K): [in a new window]   Fig. 8. Cross-sections showing variations in NO3–N concentrations in water from piezometers and deep lysimeters along three transects (W2, W1, W1rip) as measured in June 2001. Lysimeters are indicated by filled circles located above the water table, whereas piezometers are located below the water table. Installations not sampled for nitrate are indicated by a crossed symbol. Piezometer-nest identifiers are shown along the land surface. Refer to Fig. 1 and Table 2 for piezometer-nest and cross-section locations and identifiers.

View larger version (41K): [in a new window]   Fig. 9. Temporal changes in NO3–N concentrations in water collected from lysimeters and piezometers at D, S, T, and R positions in Watersheds 1 and 2 (see Fig. 1). Open symbols denote suction-cup lysimeters, black-filled symbols denote piezometers in loess, and gray-filled symbols denote piezometers near the till contact. Depths of monitoring (meters below surface) are noted above each plot. Nondetectable concentrations (<1 mg L-1) are plotted at zero. Symbols overlap in some plots. Some installations did not yield water samples every month (see Table 2).

View larger version (23K): [in a new window]   Fig. 10. Nitrate N concentrations in baseflow collected at the outlet weirs of Watersheds 1 and 2.