Water Quality Changes Shortly After Low‐Head Dam Removal Examined With Cultural and Microbial Source Tracking Methods

Abstract

Short-term effects of low head dam removal on water quality of urbanized stream were evaluated, focusing on fecal pollution indicators. Composite river samples were analyzed for Escherichia coli concentrations, nitrates, phosphates, turbidity and human-specific marker (HF183) and antibiotic resistance marker (tetQ) before and after dam removal during dry weather conditions. The sampled Olentangy River water in summer before the dam removal showed poor water quality with mean E. coli concentration of 439 colony forming unit (CFU)/100 mL, mean turbidity of 10 NTU and mean nutrient concentrations of 0.61 and 0.41 mg/L for nitrate and phosphate, respectively. Surprisingly, even one month after the dam removal, E. coli numbers doubled and nitrate concentration tripled compared to pre-removal concentrations. Although the detected HF183 concentrations were below the quantifiable levels, they did not correlate with E. coli concentrations, suggesting E. coli from other than human fecal origin. The correlation between turbidity and E. coli during dry weather further suggests E. coli accumulation in impoundment sediments and release once dam was removed. These short-term effects of dam removal on water quality should be further evaluated, especially if recreation and other beneficial uses of water in the area are expected. *Significant correlations Figure 2. Plot of average water temperature (°C) with standard deviation (bars) at the four sampling dates (n = 8 per point); all showed significantly different water temperatures WATER QUALITY AFTER LOW-HEAD DAM REMOVAL IN AN URBAN RIVER

River dam impacts on biogeochemical cycling

“…As an example, flushing of sediments from the Guernsey Reservoir in the western USA led to a sixfold increase in downstream P concentrations 179 . In British Columbia, Canada, drawdown of water levels of the Capilano reservoir caused enhanced erosion of reservoir sediments, driving downstream ammonium concentrations to increase by two orders of magnitude 180 , and, after removal of a low-head dam on the Olentangy River (Ohio, USA), downstream nitrate concentrations were increased threefold 181 .…”

Assessment of current reservoir sedimentation rate and storage capacity loss: An Italian overview

“…Reservoir sedimentation can lead to a wide variety of problems like water quality degradation, increase the flooding risk, decrease in the reservoir capacity and power generation, negative impacts on water availability for irrigation, wildlife, and navigation, and affecting the dam's life cycle, among others (Bohrerova et al, 2017;Poff and Olden, 2017;Schmitt et al, 2018;Wisser et al, 2013). The rate of loss to the storage capacity depends on the sediment yield of the river on which a reservoir is built, the morphologic factors of the reservoir, and its operational scheme (Billi and Spalevic, 2022;Kishore et al, 2021).…”

Effect of river damming on nutrient transport and transformation and its countermeasures

“…When an aging dam remains in place, the removal efficiency of sediments and nutrients decreases over time. Therefore, weighing these risks and advantages is necessary to determine whether and how to remove a dam (Kirchherr and Charles, 2016;Bohrerova et al, 2017).…”