Calcium nitrate addition to control the internal load of phosphorus from sediments of a tropical eutrophic reservoir: Microcosm experiments T.M. Yamada a, *, A.P.E. Sueitt a , D.A.S. Beraldo a , C.M.R. Botta b , P.S. Fadini a , M.R.L. Nascimento c , B.M. Faria d , A.A. Mozeto a a Laborato ´rio de Biogeoquı´mica Ambiental/Nu ´ cleo de Estudos, Diagno ´sticos e Intervenc ¸o ˜es Ambientais, Departamento de Quı´mica, Universidade Federal de Sa ˜o Carlos, Caixa Postal 676, Rodovia Washington Luiz, Km 235, CEP 13565-905, Sa ˜o Carlos (SP), Brazil b Centro de Recursos Hı´dricos e Ecologia Aplicada, Universidade de Sa ˜o Paulo, Sa ˜o Carlos (SP), Brazil c Laborato ´rio de Poc ¸os de Caldas, Comissa ˜o Nacional de Energia Nuclear, Poc ¸os de Caldas (MG), Brazil d Centro de Pesquisas Leopoldo Ame ´rico Miguez de Mello/Petrobras, Rio de Janeiro (RJ), Brazil article info Article history: Received 25 March 2012 Received in revised form 31 August 2012 Accepted 9 September 2012 Available online 16 September 2012 Keywords: Sediment remediation Denitrification Eutrophication Laboratory experiments Toxicity abstract The main objective of this study was to perform laboratory experiments on calcium nitrate addition to sediments of a tropical eutrophic urban reservoir (Ibirite ´ reservoir, SE Brazil) to immobilize the reactive soluble phosphorus (RSP) and to evaluate possible geochemical changes and toxic effects caused by this treatment. Reductions of 75 and 89% in the concentration of RSP were observed in the water column and interstitial water, respec- tively, after 145 days of nitrate addition. The nitrate application increased the rate of autotrophic denitrification, causing a consumption of 98% of the added nitrate and oxidation of 99% of the acid volatile sulfide. As a consequence, there were increases in the sulfate and iron (II) concentrations in the sediment interstitial water and water column, as well as changes in the copper speciation in the sediments. Toxicity tests initially indicated that the high concentrations of nitrate and nitrite in the sediment interstitial water (up to 2300 mg L 1 and 260 mg L 1 , respectively) were the major cause of mortality of Ceriodaphnia silvestrii and Chironomus xanthus. However, at the end of the experiment, the sediment toxicity was completely removed and a reduction in the 48 h-EC50 of the water was also observed. Based on these results we can say that calcium nitrate treatment proved to be a valuable tool in remediation of eutrophic aquatic ecosystems leading to conditions that can support a great diversity of organisms after a restoration period. ª 2012 Elsevier Ltd. All rights reserved. 1. Introduction Eutrophication process is a global concern and it is a major cause of aquatic ecosystems’ deterioration which results in significant biodiversity and economic losses (Dodson et al., 2000). This process is associated with a myriad of anthropogenic activities, such as the inflow of urban and rural sewage, industrial effluents and urban and agricultural runoff pollution, which are rich in nutrients and contaminants. Anthropogenic loadings of phosphorus (P) have a key role in eutrophication. Consequently, a remediation planning for the control of P sources must be a priority (Jugnia et al., 2004). * Corresponding author. Tel./fax: þ55 16 33518212. E-mail address: thais_yamada@yahoo.com.br (T.M. Yamada). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 46 (2012) 6463 e6475 0043-1354/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2012.09.018