Fig. 1.

Location of the paired watersheds near the headwaters of the Mackinaw River watershed, Illinois (A) and locations of upstream and downstream monitoring sites in Bray Creek (treatment) and Frog Alley (reference) watersheds (B). Downstream and upstream sites were located approximately 1.6 km upstream and 4.8 km upstream, respectively, from the confluence of each stream and the Mackinaw River.

 


Fig. 2.

Discharge rating equations developed for the treatment (A) and reference (B) subwatersheds of the Mackinaw River to estimate stream discharge from water levels during water years 2000 to 2006. Log-transformed discharge estimates from cross-sectional transect surveys were regressed against respective log-transformed pressure transducer water level readings to develop discharge rating curve equations for the treatment (log treatment Q [m3 s−1] = 0.4396 + 2.5198*log treatment stage (m); R2 = 0.89; P < 0.001; n = 24) and reference (log reference Q [m3 s−1] = 0.4069 + 2.3926*log reference stage (m); R2 = 0.71; P < 0.001; n = 17) watersheds.

 


Fig. 3.

Cumulative annual implementation of agricultural best management practices within the treatment (i.e., received outreach) and reference watersheds (i.e., received no outreach) during the outreach period of 2000 to 2003. Strip-till (A), grassed waterways (B), and riparian buffers (C) increased in both watersheds during the study, although implementation rates were significantly greater in the treatment watershed.

 


Fig. 4.

(A) Results from digitized aerial photos showing the locations and relative widths of stream buffers (black) and locations of grassed waterways (gray) that were present in the treatment and reference watersheds of the Mackinaw River by 2005. Thickness of stream buffer polygons and lines indicate relative widths (m); grassed waterway lines are not indicative of waterway widths. (B) Open waterway portions of the both watersheds are shown for reference.

 


Fig. 5.

Nutrient concentrations for nitrate-nitrogen (NO3–N) (A), total phosphorus (TP) (B), and total suspended sediments (TSS) (C) from downstream monitoring sites in Bray Creek (treatment) and Frog Alley (reference) watersheds. Concentrations are based on biweekly samples collected between June 1999 and September 2006. Also shown are daily discharge (Q) values (m3 s−1) for Bray Creek and Frog Alley (D).

 


Fig. 6.

Differences between concentrations of nitrate-nitrogen (NO3–N) (A), total phosphorus (TP) (B), dissolved reactive phosphorus (DRP) (C), and total suspended sediment (TSS) (D) in water samples collected Bray Creek (treatment) and Frog Alley (reference) watersheds.

 


Fig. 7.

Differences between values for peak flow (A), low flow (B), and base flow (C) measured in Bray Creek (treatment) and Frog Alley (reference) watersheds.