|Gillespie, Robert -|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: June 19, 2010
Publication Date: January 1, 2010
Citation: Smiley, P.C., Gillespie, R.B. 2010. Influence of Physical Habitat and Agricultural Contaminants on Fishes within Agricultural Drainage Ditches. In: Moore, M.T., Kroger, R., editors. Agricultural Drainage Ditches: Mitigation Wetlands for the 21st Century. Kerula, India: Research Sign Post. p. 37-73. Interpretive Summary: Agricultural drainage ditches are headwater streams that have been created or modified to drain excess water from agricultural fields. Historically, the design and management of these headwater streams has focused on drainage without considering the ecological impacts. Little is known about the ecology of these modified streams, and this ecological information is critically needed to manage these streams as multi-use systems capable of meeting both drainage and environmental goals. State and federal agencies in the midwestern United States and Canada responsible for providing drainage assistance and managing streams for water quality goals currently make management decisions without information on the ecological impacts of different drainage and conservation practices. We conducted a literature review to synthesize what is known about the ecology of fishes and the impacts of conservation practices on fishes within agricultural drainage. Our literature review documented that: 1) freshwater fishes are an integral component of agricultural drainage ditches in North America; 2) fishes in drainage ditches were most often correlated with instream habitat variables (water depth, wet width, water velocity, substrate types); 3) most research has documented the negative effects of channelization of existing streams and only limited information is available on the effects of conservation practices; and 4) the risk of fishes experiencing acute and chronic toxicity of agricultural herbicides appears to be minimal, but sublethal effects are possible. We conclude that a watershed management approach that manages agricultural drainage ditches as a multiple use system capable of providing drainage, fish habitat, and nutrient/pesticide sinks is greatly needed.
Technical Abstract: Agricultural drainage ditches are used within agricultural watersheds for the removal of excess water from agricultural fields. These headwater streams have been constructed or modified so they possess an enlarged trapezoidal cross-section, straightened channels, and riparian zones lacking woody vegetation. Additionally, many drainage ditches undergo periodic maintenance to maintain channel capacity and prevent woody vegetation colonization. Management of these modified lotic ecosystems focuses on removal of excess water without consideration of the impacts of hydrological, geomorphological, and chemical changes on the aquatic biota. Understanding the ecology of these modified systems is necessary for developing novel ways to manage these systems as multiple use systems capable of meeting drainage and environmental objectives. Our objective was to synthesize what is known about the population and community ecology of fishes within agricultural drainage ditches (i.e., channelized headwater streams). We searched online databases and journals to obtain peer review publications describing the results of field and laboratory assessments evaluating community and population responses of fishes within agricultural drainage ditches. We were particularly interested in publications that documented the responses of fishes to physical habitat modifications or exposures to agricultural contaminants (i.e., herbicides, insecticides, nutrients) found in drainage ditches. We found that freshwater fishes appear to be an integral component of agricultural drainage ditches in North America. Fishes in drainage ditches were most often correlated with instream habitat variables, which suggests the importance of these variables in determining community structure. Most research involving fishes in drainage ditches has documented the negative effects of channelization of existing streams and only limited information is available on the effects of conservation practices intended to provide ecological benefits. Overall, the risks of fishes experiencing acute and chronic toxicity appears to be minimal based on observed values of herbicides and nutrients from selected drainage ditches in Ohio and Indiana. However, more research is needed on documenting the prevalence of sublethal effects and the influence of mixtures of agricultural chemicals on fishes and other aquatic organisms. Our results suggest that a watershed approach that manages ditches as multiple use system capable of providing ecosystem services of drainage, aquatic life habitat, and nutrient/pesticide processing is much needed. Specifically, we identify four key concepts that will assist with developing novel management strategies capable of incorporating environmental considerations into the management of agricultural drainage ditches.