title: A framework model for investigating the export of phosphorus to surface waters in forested watersheds: Implications to management.
abstract: The present study was developed in four sub-basins of rivers Cávado and Douro, located in the North of mainland Portugal. The goal was to identify main stressors as well as driving and attenuating processes responsible for the presence of phosphorus in masses of surface water in those catchments. To accomplish the goal, the basins were selected where a quality station was present at the outlet, the forest occupation was greater than 75% and the phosphorus concentrations have repeatedly exceeded the threshold for the good ecological status in the period 2000-2006. Further, in two basins the quality station was installed in a lotic (free-flow water) environment whereas in the other two was placed in a lentic (dammed water) environment. The ArcMap GIS-based software package was used for the spatial analysis of stressors and processes. The yields of phosphorus vary widely across the studied basins, from 0.2-30 kg·ha(-1)·yr(-1). The results point to post-fire soil erosion and hardwood clear cuttings as leading factors of phosphorus exports across the watersheds, with precipitation intensity being the key variable of erosion. However, yields can be attenuated by sediment deposition along the pathway from burned or managed areas to water masses. The observed high yields and concentrations of phosphorus in surface water encompass serious implications for water resources management in the basins, amplified in the lentic cases by potential release of phosphorus from lake sediments especially during the summer season. Therefore, a number of measures were proposed as regards wildfire combat, reduction of phosphorus exports after tree cuts, attenuation of soil erosion and improvement of riparian buffers, all with the purpose of preventing phosphorus concentrations to go beyond the regulatory good ecological status.
authors.affiliation: Centre for the Research and Technology of Agro-Environment and Biological Sciences, Vila Real, Portugal.
authors.forename: R M B
authors.initials: RMB
authors.lastname: Santos
authors.affiliation: Centre for the Research and Technology of Agro-Environment and Biological Sciences, Vila Real, Portugal; Department of Engineering, University of Trás-os-Montes and Alto Douro (UTAD), Ap. 1013, 5001-801 Vila Real, Portugal.
authors.forename: L F
authors.initials: LF
authors.lastname: Sanches Fernandes
authors.affiliation: Centre for the Research and Technology of Agro-Environment and Biological Sciences, Vila Real, Portugal; Dom Luiz Institute, University of Lisbon, Campo Grande, 1749-016 Lisbon, Portugal; Department of Physics, UTAD, Portugal.
authors.forename: M G
authors.initials: MG
authors.lastname: Pereira
authors.affiliation: Centre for the Research and Technology of Agro-Environment and Biological Sciences, Vila Real, Portugal; Department of Forestry Sciences and Landscape Architecture, UTAD, Portugal.
authors.forename: R M V
authors.initials: RMV
authors.lastname: Cortes
authors.affiliation: Chemistry Research Centre, Vila Real, Portugal; Department of Geology, UTAD, Portugal. Electronic address: fpacheco@utad.pt.
authors.forename: F A L
authors.initials: FAL
authors.lastname: Pacheco
keywords: Forest management; Forested catchment; Lotic and lentic environments; Pathway length; Phosphorus; Rainfall intensity; Soil erosion and sediment transport; Wildfires