The effect of two-stage ditch channel morphology on benthic community structure within the Blanchard River watershed

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Robert G. Verb, Colin Light, Connor Ney, Lauren Govekar and Leslie A. Riley, School of Science, Technology, and Math, Ohio Northern University, Ada, OH, Chad Carroll, Hancock County Park District, Findlay, OH, Janet L. Deardorff, Biology, Miami University, Oxford, OH

Background/Question/Methods
Two primary threats to northwest Ohio watersheds are hydrologic variation and nutrient enrichment. One such attempt to mitigate these threats is through the employment of two-stage ditches that are geomorphological modifications to existing open ditches. The two-stage ditches are designed to reduce discharge and sediment loading into primary watershed tributaries. Furthermore, these systems can be modified with filter strips and iron slag in an attempt to further reduce sedimentation and phosphorus loading. At Kurt’s Farm (Blanchard River watershed, Hardin County, Ohio), a two-stage ditch was installed with intact floodplain benches to slow current velocity and retain excess sediments, especially during flooding events. While previous studies have documented that ditches can also serve as habitat for other organisms and can make substantial contributions to diversity within watersheds, the effect of two-stage ditch morphology on benthic communities is not well known and, in at least one study, appears to not be important. Thus, the focus of this investigation was to determine if the benthic community composition in the two-stage ditch differs from neighboring traditional open ditch habitats.
Results/Conclusions
Multivariate analysis indicated that benthic communities of two stage ditch sites were significantly different from that of the traditional, open ditch sites (MRPP: T = -1.79, A = 0.07, p = 0.05). Two-stage ditch sites were characterized by low turbidity, low water temperature and a detritivore-dominant community, while the open ditch sites were characterized by higher turbidity, higher water temperature, higher dissolved oxygen, and were dominated by macroalgae and herbivorous Lymnaeid snails. Two-stage ditch sites had a closed canopy due to increased plant biomass within the ditch, leading to less light availability and possibly contributing to lower water temperatures when compared to open ditch sites. Additional data from three subsequent sampling periods will also be included to examine seasonal changes in the ditch communities.