Weirs Control Phosphorus Transfer in Agricultural Watersheds
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Weirs Control Phosphorus Transfer in Agricultural Watersheds Danilo Rheinheimer dos Santos & Gilmar Luiz Schaefer & André Pellegrini & Jimmy Walter Rasche Alvarez & Laurent Caner & Edson Campanhola Bortoluzzi
Received: 11 May 2020 / Accepted: 20 August 2020 # Springer Nature Switzerland AG 2020
Abstract Sediments may act as a source or sink of ions from water, especially phosphorus (P). After the erosion process, the challenge is to retain suspended sediments inside the watershed area. We hypothesize that weir structures may mitigate P transfer from agricultural soils to aquatic systems. To test this, the present work aimed to evaluate P chemical fractions present in bottom sediments retained in the water reservoir of weirs built in two intensive agricultural watersheds and we discuss the sink/source behavior of these sediments. Samples of bottom sediments were collected from 12 reservoirs of weirs in two smalls Brazilian watersheds. Chemical P D. R. dos Santos : G. L. Schaefer Soil Departament, Federal University of Santa Maria, Av. Roraima, 1000, CEP, Santa Maria, RS 97105-900, Brazil A. Pellegrini Federal Technological University of Paraná, Dois Vizinhos, Estrada para Boa Esperança, Km04, CEP, Dois Vizinhos, PR 85660-000, Brazil J. W. R. Alvarez National University of Asuncion, San Lorenzo, Paraguay L. Caner University of Poitiers, UMR 7285 IC2MP-HydrASA, TSA 51106, 5 rue Albert Turpain, 86073 Poitiers Cedex 9, France E. C. Bortoluzzi (*) Laboratory of Land Use and Natural Resources, University of Passo Fundo, Campus I, BR 285, km 292, Passo Fundo, Rio Grande do Sul 99052-900, Brazil e-mail: [email protected] e-mail: [email protected]
fractionation including adsorption and desorption kinetics was performed. Total P varied from 398 to 958 mg kg−1. The easily and potentially desorbed phosphorus were correlated with the clay content and the concentrations of Fe, Mn, and Al, extracted by ammonium oxalate and dithionite-citrate-bicarbonate solutions, which are the carriers of highly reactive functional groups with phosphate. Bottom sediments have high maximum adsorption capacity under unrestricted phosphorus supply condition, while under natural condition (low anthropogenic pressure), the sediments were not saturated and therefore low desorption occurred. Only 1.34% and 7.75% of total P was in readily and potentially bioavailable P forms. The bottom sediments accumulated in reservoirs from anthropogenic areas acted as P source to water, while those from preserved areas (natural pasture or riparian forest) acted as sink of P from water. The storage of water and sediment contaminated with P in reservoir of weirs may be an efficient and temporary practice to mitigate the transfer of P to watercourses. Keywords Eutrophication . Bottom sediments . No-tillage . P fractioning . Suspended sediment
1 Introduction Agricultural lands are frequently exposed to soil erosion processes, increasing the transfer rates of sediments and pollutants to water bodies (Borrelli et al. 2017). Even common intensive agricultural prac
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