Oscillation of Three Phosphorus Forms and Suspended Solids Content from 1999 to 2007 in a Spanish Agroforestry Catchment under Atlantic Climate

Abstract

Phosphorus (P) transfers may accelerate water eutrophication to waters. Increasing awareness of the role of diffuse P sources motivates land managers in different regions of Europe to undertake conservation programs that place emphasis not only on soil conservation but also on water quality and eutrophication risk. Fertilizer applications and wastes are the main sources of dissolved P in Galicia and in the Atlantic regions of Spain. The aim of this study was to assess the temporal changes in concentration of total P (TP), sedimentary P (SP), and total dissolved P (TDP) and suspended solids at the outlet of an agroforestry catchment located in northwestern Spain. The study datasets range from January 1999 to December 2007, with 992 water samples collected. The water-collection strategy was a stratified point sampling involving more frequent collections when flow was high. Phosphorus contents were assessed by inductively coupled plasma (ICP)–mass spectroscopy (MS), and suspended solids were measured by filtration. The content ranges of the different studied P forms and suspended solids were as follows: TDP between 1 and 672 mg L⁻¹, SP between 1 and 1064 mg L⁻¹, TP between 1 and 1111 mg L⁻¹, and suspended solids between 1 and 1044 mg L⁻¹. A few events of intense precipitation with peaks of TP greater than 200 mg L⁻¹ and in some cases even more than 1000 mg L⁻¹ were responsible for most of the P losses in the catchment studied. TP and SP, TP and suspended solids, and SP and suspended solids showed highly significant correlations during the entire study period, evidencing the erosive origin of P in this catchment.

Keywords:

• Agroforestry catchment
• phosphorus forms
• suspended solids
• water quality

Acknowledgments

This research was financially supported by Xunta de Galicia, Project PGIDIT 05RAG 10302PR, and Spanish Education and Science Ministry (MEC), Project AGL 2003–09284–C02–01. The authors gratefully acknowledge Carlos Carballeira Díaz for laboratory assistance.