STREAM QUALITY CHANGES 10 YEARS AFTER LOWHEAD DAM MODIFICATIONS, BUCK CREEK, SPRINGFIELD, OH

Recreational modifications to three lowhead dams along a 9-km reach of Buck Creek and its tributary Beaver Creek in Springfield, Ohio, effectively removed barriers to downstream sediment transport. The modifications provide an opportunity to study changes in stream habitat, surface and substrate water chemistry, and macroinvertebrates 10 years post modification. We examined three sites at each dam: a reference riffle upstream of the dam, the impacted zone in the formerly impounded area, and the recovery riffle downstream. We compared our results with data collected prior to and immediately following modification. Substrate water was extracted from a well driven into the channel bed for comparison with surface water chemistry. Dissolved oxygen (DO), biochemical oxygen demand, fecal coliform, total coliform, nitrate, temperature, and pH were measured and summarized as a Water Quality Index (WQI). Macroinvertebrates were collected using a kick-frame net, identified at the order level, and summarized as a Pollution Tolerance Index (PTI). Substrate habitat was evaluated using the substrate metric of the Qualitative Habitat Evaluation Index (QHEI).

WQI, PTI, and substrate QHEI were consistently highest in the upstream reference riffle but decreased to their lowest level in the impacted area and were intermediate in the recovery riffle. They also generally decreased downstream and over time, from pre-modification to present. For example, in the impacted reach at Snyder Park, PTI changed from 15 to 5 in the years since modification. This is consistent with decreases in DO, the most heavily-weighted factor in WQI, from 9.03 to 0.27 mg/l, and the QHEI substrate score from 19 to 7, which characterizes a change from sand and fine gravel to sand and detritus, at this same site over the same time period. Our results suggest that channel bed substrate impacts substrate water quality, in particular DO, which in turn affects the macroinvertebrates that live in the substrate. The hydraulic impact of dam modification in conjunction with the existing channel morphology in the impacted area at the time of modification allows for the throughput of sand and finer-grained materials but has slowed the transport of gravel and cobble; this should be considered in future engineering designs.