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 Supplemental Data (63 KB) 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 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 Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Browne, B. A. Articles by Guldan, N. M. Search for Related Content PubMed PubMed Citation Articles by Browne, B. A. Articles by Guldan, N. M. GeoRef GeoRef Citation Agricola Articles by Browne, B. A. Articles by Guldan, N. M. Related Collections Watershed and Landscape Processes Surface Water Quality Nitrogen Biogeochemical Processes Watershed-Scale Studies

Understanding Long-Term Baseflow Water Quality Trends Using a Synoptic Survey of the Ground Water–Surface Water Interface, Central Wisconsin

College of Natural Resources, University of Wisconsin-Stevens Point, Stevens Point, WI 54481

View larger version (40K): [in a new window]   Fig. 1. Conceptual model of baseflow water quality estimation procedure (Eq. [1], text) using ground water seepage along a stream meander. (a) Hypothetical ground water recharge age-date distribution of ground water seepage into a stream course (inset) on three baseflow sampling dates superimposed on , the basin-wide mean annual concentration of a hypothetical chemical in ground water recharge. (b) Estimated baseflow concentrations, Cbf, for each baseflow sampling date by Eq. [1]. (c) Minipiezometer network along a stream meander intercepts ground water seepage of varying recharge age-dates and water quality characteristics. Schematic illustrates design of minipiezometers used in this study.

View larger version (41K): [in a new window]   Fig. 2. Study area and minipiezometer network. Arrows: downstream ends of Reaches F–I. Shaded area represents an approximation of the Little Plover River (LPR) ground water basin boundary provided by the Central Wisconsin Groundwater Center via MODFLOW (Harbaugh and McDonald, 1996; physical and hydrologic data used in the model are on file at the CWGC).

View larger version (35K): [in a new window]   Fig. 3. Synoptic survey data for 27 June 2000. (a) Ground water seepage (Qj, Eq. [4], solid triangle) along the stream course and comparison of cumulative seepage (Qj, solid line) to measured streamflow (open circles). Letters along x axis indicate downstream ends of Reaches A–I (Fig. 2). (b) NO3– concentrations in ground water seepage (solid triangle) and comparison of discharge-weighted mean concentration (QjCj/Qj, solid line) with measured baseflow concentration (open circles).

View larger version (34K): [in a new window]   Fig. 4. Nitrate concentrations and apparent chlorofluorocarbon (CFC) ground water recharge dates of ground water seepage measurements across all synoptic survey dates (Table 1). Hatched and solid lines: historical record of fertilizer N sales in the United States and Wisconsin (USDA, 1997), respectively.

View larger version (20K): [in a new window]   Fig. 5. Nitrate concentrations and apparent chlorofluorocarbon (CFC) recharge age-dates from the 27 June 2000 synoptic survey of ground water seepage. Best fit lines obtain by weighted (wi, Eq. [9]) linear regression were used to approximate the historical progression of the basin-wide mean annual concentration of a hypothetical chemical in ground water recharge (Eq. [1]).

View larger version (24K): [in a new window]   Fig. 6. Discharge-weighted apparent chlorofluorocarbon (CFC) age-date distribution for ground water seepage samples collected during the 27 June 2000 synoptic survey. Relative frequencies are weighted by discharge per unit length of stream (see Eq. [9] in text).

View larger version (27K): [in a new window]   Fig. 7. General procedure to estimate baseflow concentration (Cbf) from the discharge-weighted age distribution of ground water seepage. (a–c) The basin-wide mean annual concentration in ground water recharge (total NO3–) from regression line in Fig. 5a. (a) Selection of using the discharge-weighted age-date distribution (vertical point diagram) of the 27 June 2000 dataset (Fig. 6). (b) Weighting of values by the discharge-weighted relative frequency. (c) Summation of weighted concentrations to obtain Cbf.

View larger version (22K): [in a new window]   Fig. 8. Estimation of baseflow NO3– concentrations for 1960 to 2050. (a) Lines A, B, and C, projected basin-wide mean annual concentration in ground water recharge (total NO3–) scenarios, extended into the past (1920) and future (2050) sufficiently to generate baseflow concentration (Cbf) predictions between 1960 and 2050. Scenarios are described in the text. See Fig. 7a for explanation of vertical point diagram. (b) Lines A', B', C' are corresponding Cbf estimates. Shaded area in A' represents Cbf (excess N2). Cross-hair represents year 2000. (c) Cbf (±SD) values (solid circles) from the lower left quadrant (1960 to 2000) in Fig. 8b are superimposed on historical baseflow NO3– measurements (small open circles). Solid line: best fit historical data (slope = 0.152 mg L–1 yr–1). Dashed line: best fit Cbf backcasts (slope = 0.159 mg L–1 yr–1).

View larger version (64K): [in a new window]   Fig. 9. Hypothetical age intervals (ground water lag times to stream) of recharge zones in two basins: (a) similar and (b) contrasting land use and land management practices across recharge zones.