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Evaluating Agricultural Best Management Practices in Tile‐Drained Subwatersheds of the Mackinaw River, Illinois
Author(s) -
Lemke A. M.,
Kirkham K. G.,
Lindenbaum T. T.,
Herbert M. E.,
Tear T. H.,
Perry W. L.,
Herkert J. R.
Publication year - 2011
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2010.0119
Subject(s) - tile drainage , surface runoff , environmental science , baseflow , hydrology (agriculture) , watershed , water quality , tillage , soil conservation , conservation agriculture , agriculture , streamflow , drainage basin , soil water , agronomy , ecology , geography , geology , soil science , cartography , geotechnical engineering , machine learning , computer science , biology
Best management practices (BMPs) are widely promoted in agricultural watersheds as a means of improving water quality and ameliorating altered hydrology. We used a paired watershed approach to evaluate whether focused outreach could increase BMP implementation rates and whether BMPs could induce watershed‐scale (4000 ha) changes in nutrients, suspended sediment concentrations, or hydrology in an agricultural watershed in central Illinois. Land use was >90% row crop agriculture with extensive subsurface tile drainage. Outreach successfully increased BMP implementation rates for grassed waterways, stream buffers, and strip‐tillage within the treatment watershed, which are designed to reduce surface runoff and soil erosion. No significant changes in nitrate‐nitrogen (NO 3 − –N), total phosphorus (TP), dissolved reactive phosphorus, total suspended sediment (TSS), or hydrology were observed after implementation of these BMPs over 7 yr of monitoring. Annual NO 3 − –N export (39–299 Mg) in the two watersheds was equally exported during baseflow and stormflow. Mean annual TP export was similar between the watersheds (3.8 Mg) and was greater for TSS in the treatment (1626 ± 497 Mg) than in the reference (940 ± 327 Mg) watershed. Export of TP and TSS was primarily due to stormflow (>85%). Results suggest that the BMPs established during this study were not adequate to override nutrient export from subsurface drainage tiles. Conservation planning in tile‐drained agricultural watersheds will require a combination of surface‐water BMPs and conservation practices that intercept and retain subsurface agricultural runoff. Our study emphasizes the need to measure conservation outcomes and not just implementation rates of conservation practices.