View Full Table | Close Full ViewTable 1.

Results from digitized aerial photos taken in spring 2005 of the treatment (i.e., received outreach) and reference (i.e., received no outreach) watersheds showing total stream lengths and total counts, areas, and lengths of grassed waterways and stream buffers in each watershed. Also shown are the total lengths and numbers of grassed waterways that were <9 m and ≥9 m wide and total length of stream buffers at different width intervals. Individual length measurements may not added up exactly to total lengths due to rounding effects.

 
Treatment (Bray Creek) Reference (Frog Alley)
Stream length, km 19.8 19.6
Grassed waterways
 Total counts 108 62
 Total area, ha 54.9 52.2
 Total length, km 48.1 41.3
 <9 m width, km 9.8 6.3
 ≥9 m width, km 37.2 35.2
 No. <9 m width 47 22
 No. ≥9 m width 61 40
Stream buffers
 Total counts 24 17
 Total area, ha 100.6 49.4
 Total length, km 18.8 19.5
 <9 m width, km 0.3 8.5
 9–15 m width, km 5.1 4.8
 15–30.5 m width, km 1.9 4.8
 ≥30.5 m width, km 11.4 1.1



View Full Table | Close Full ViewTable 2.

Flow-weighted mean concentrations for nitrate-nitrogen, total phosphorus, and total suspended sediments for treatment and reference subwatersheds of the Mackinaw River, Illinois during water years 2000–2006.

 
Water year Treatment (Bray Creek) Reference (Frog Alley)
NO3–N TP† TSS‡ NO3–N TP TSS
mg L−1
2000 5.8 –§ 118.2 7.0 53.9
2001 11.9 24.6 14.5 17.6
2002 10.7 128.7 12.1 83.8
2003 9.3 193.6 10.4 36.4
2004 10.9 0.57 343.2 10.0 0.36 147.3
2005 7.8 0.18 98.3 11.5 0.29 53.0
2006 12.3 0.08 25.4 12.5 0.06 13.1
TP, total phosphorus.
TSS, total suspended sediments.
§ Total phosphorus analyses were restricted to water years 2000–2003 as indicated by dashes.



View Full Table | Close Full ViewTable 3.

Total annual export and proportion of export as stormflow for nitrate-nitrogen, total phosphorus, and total suspended sediments for treatment and reference subwatersheds of the Mackinaw River, Illinois during water years 2000–2006. Also shown is the baseflow index during individual water years for each subwatershed, defined as discharge via baseflow divided by total discharge, and mean annual discharge.

 
Water year Total export Stormflow export Baseflow index Mean annual discharge
NO3–N TP† TSS‡ NO3–N TP TSS
Mg % m3 s−1
Treatment (Bray Creek)
 2000 43 885 28.4 50.7 0.835 0.237
 2001 185 381 46.7 79.9 0.572 0.492
 2002 211 2530 51.5 88.3 0.476 0.623
 2003 63 1300 56.1 95.6 0.493 0.213
 2004 127 6.6 4003 67.0 90.2 99.0 0.323 0.369
 2005 154 3.6 1925 61.9 91.8 95.4 0.380 0.621
 2006 171 1.1 355 55.1 85.7 91.2 0.527 0.443
Mean (±1 SE) 136 (24) 3.8 (1.6) 1626 (497) 52.4 (4.7) 89.2 (1.8) 85.7 (6.3) 0.515 (0.062) 0.428 (0.063)
Reference (Frog Alley)
 2000 39 301 32.6 62.2 0.779 0.176
 2001 351 426 66.9 92.3 0.354 0.768
 2002 299 2077 46.2 87.7 0.542 0.786
 2003 131 457 50.3 75.9 0.519 0.398
 2004 153 5.5 2244 54.1 81.7 97.8 0.443 0.482
 2005 194 4.9 899 68.3 95.4 96.5 0.334 0.537
 2006 184 0.9 176 53.3 81.0 85.3 0.537 0.446
Mean (±1 SE) 193 (39) 3.8 (1.4) 940 (327) 53.1 (4.6) 86.0 (4.7) 85.4 (4.8) 0.501 (0.056) 0.513 (0.081)
TP, total phosphorus.
TSS, total suspended sediments.



View Full Table | Close Full ViewTable 4.

Annual and mean annual nutrient export per unit watershed area for nitrate-nitrogen, total phosphorus, and total suspended sediments for treatment and reference subwatersheds of the Mackinaw River, Illinois during water years 2000–2006.

 
Water year Treatment (Bray Creek) Reference (Frog Alley)
NO3–N TP† TSS‡ NO3–N TP TSS
kg ha−1 yr−1
2000 10.7 218.2 9.2 71.6
2001 45.6 94.0 83.6 101.4
2002 52.0 623.7 71.3 495.0
2003 15.5 320.5 31.3 108.9
2004 31.4 1.6 987.1 36.5 1.3 534.5
2005 37.9 0.9 474.6 46.3 1.2 214.1
2006 42.3 0.3 87.5 43.9 0.2 41.8
Mean (±1 SE) 33.6 (5.8) 0.9 (0.4) 400.8 (122.6) 46.0 (9.4) 0.9 (0.3) 223.9 (77.9)
TP, total phosphorus.
TSS, total suspended sediments.



View Full Table | Close Full ViewTable 5.

Comparison of the range of nitrate-nitrogen and total phosphorus exported among treatment (Bray Creek) and reference (Frog Alley) subwatersheds of this study (water year 2000–2006) and other tiled-drained agricultural watersheds.

 
Study site Nitrogen export Phosphorus export Reference
kg NO3- N ha−1 yr−1 kg TP† ha−1 yr−1
Treatment subwatershed (Mackinaw River, Illinois) 10.7–52.0 0.3–1.6 This study
Reference subwatershed (Mackinaw River, Illinois) 9.2–83.6 0.2–1.3 This study
Embarras River, Illinois 8.9–56.7 0.2–2.1 Royer et al., 2006
Kaskaskia River, Illinois 7.6–57.6 0.1–1.2 Royer et al., 2006
Sangamon River, Illinois 9.0–46.8 0.3–0.8 Royer et al., 2006
Walnut Creek, Iowa 10.4–43.6 Schilling, 2002
Squaw Creek, Iowa 13.0–56.3 Schilling, 2002
Total phosphorus.