We provide a critical review of the massive land drainage works, water resource degradation and a persistent eutrophication problem in agriculturally-dominated watersheds, such as the Gulf of Mexico and the Great Lakes, which have led to examination of managing agricultural drainage ditches for ecosystem benefits. Work by dissertation collaborators on alternative ditch designs has led to the two-stage ditch approach, which creates floodplain benches stabilized by vegetation and an inset channel that effectively transports water and sediment based on channel-forming discharge concepts. The goals of the approach are to create stable, well-vegetated ditches that can reduce localized flooding and bank erosion problems while maintaining drainage capacity such that frequent maintenance will be reduced or unnecessary over the life of the ditch. Evaluating seven two-stage ditches in Ohio, Indiana, and Michigan we found that 3-10 years after construction all of the ditches constructed exhibited small adjustments to the inset channel, have remained stable, and have achieved the goals for which they were designed. On-going research indicates they may ameliorate sediment and nutrient losses from agricultural watersheds.
In two separate studies, we evaluate relationships between in-stream habitat, water chemistry, spatial distribution, and geomorphic features within a predominantly agricultural watershed in Ohio using Canonical Correspondence Analysis (CCA) and variance partitioning to relate environmental variables to fish and macroinvertebrate community attributes. At 32 sites in the first study, we: (1) identify and quantify key environmental variables; and (2) evaluate the influence of those variables in structuring fish assemblage attributes. Fish communities were explained best by stream size, gradient, and substrate size and quality. Results suggest that measured geomorphology variables and consideration of spatial location of a stream reach within a watershed system should be standard data incorporated into stream monitoring programs to identify impairments that, while biologically limiting, are not fully captured using current bioassessment methods.
At 30 study sites we build on results from the first study to: (1) identify environmental factors influencing both fish and invertebrate communities; (2) evaluate the significance of naturally formed benches; and (3) compare physical structure and biotic communities of modified channels to reference streams. Geomorphically, bench sites were statistically different than trapezoidal sites in floodplain width and depth ratios indicating that bench formation provided some amount of attached floodplain and functioned more similar to how natural streams would function. Key ecological drivers for macroinvertebrate communities were stream size, gradient and connectivity to a floodplain. Key ecological drivers for fish communities were quality of in-stream habitat. Larger sites supported more aquatic biota and more diverse assemblages either as primary habitat or as conduits between higher quality upstream or downstream locations, which may be critical in highly modified agricultural watersheds. Smaller systems experienced smaller discharges and had become intermittent during dry months. We hypothesized that leaving vegetated benches in the agricultural ditch would improve local ecology, but our data do not support this. In the systems studied the proximity to a nearby “good” site might be the main driving factor rather than improved ditch condition.
|Commitee:||Martin, Jay, Williams, Lance, Witter, Jonathan|
|School:||The Ohio State University|
|Department:||Food, Agricultural and Biological Engineering|
|School Location:||United States -- Ohio|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Subjects:||Hydrologic sciences, Environmental management, Environmental Studies, Geomorphology, Water Resource Management, Environmental engineering, Aquatic sciences, Limnology|
|Keywords:||Agriculture, Drainage, Fish, Macroinvertebrates, Midwest, Two-stage ditches|
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