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TECHNICAL REPORTS

Surface Water Quality

Impact of Elevated Copper on the Rate and Gaseous Products of Denitrification in Freshwater Sediments

Dep. of Earth Sciences, Indiana Univ. Purdue Univ. Indianapolis, Indianapolis, IN 46202

^* Corresponding author (pjacinth{at}iupui.edu).

Received for publication December 26, 2007. Application of Cu-containing algicides to water reservoirs for algal control leads to sediment Cu enrichment, but the impact of Cu accumulation on the NO₃^–-attenuation capacity of these ecosystems is uncertain. With the knowledge that the reduction of N₂O to N₂ is mediated by a Cu-dependent enzyme, it is hypothesized that an inverse variation exists between Cu availability and the mole fraction of N₂O (F_N2O) in denitrification products. A study was conducted to test this hypothesis and also to assess the impact of elevated Cu on nitrification and denitrification. Sediments were collected from areas untreated (NCT) and treated (CT) with the algicide cutrine (Cu ethanolamine) in three central Indiana reservoirs, and were assayed at both in situ Cu content and after amendment with CuSO₄. Results showed that Cu addition had a depressive, but short-lived effect on the processes investigated, with nitrification being most sensitive. Past cutrine treatments did not significantly affect either denitrification or F_N2O. However, a significant difference (P < 0.04) among reservoirs was found with respect to denitrification (Eagle Creek: 3.2; Geist: 1.6 and Morse: 4.2 mg N kg^–1 h^–1) and F_N2O (0.51, 0.24, and 0.31, respectively). Negative relationships (r²: 0.30–0.64) between F_N2O and water extractable Cu were found only when the analysis was conducted separately for each reservoir, suggesting that Cu solubility is controlled by sediment properties specific to each reservoir. Overall, results of this study indicate that neither the NO₃^–-removal capacity of sediments nor the composition of denitrification N gases is affected by past treatments with cutrine.

Abbreviations: CT, cutrine-treated areas • ECR, Eagle Creek reservoir • NCT, area nontreated with cutrine • N₂O-R, nitrous oxide reductase