Temporal Oscillations of Calcium,Magnesium, Potassium,and Sodium Dissolved Contents in an Agroforestry Catchment from the Atlantic Galicia

There is an increasing awareness worldwide of the conveyance of sediment-associated nutrients across eroding soil surfaces into receiving waters. The objective of this study was to analyze the temporal oscillations of concentrations as well as the exportation of calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) at the outlet of an agroforestry catchment. These macronutrients were measured in the drainage waters of a 36.3-km² catchment located at the Valiñas River (Coruña, northwest Spain), where 560 samples were taken from 2003 to 2007. The water collection strategy was a stratified point sampling involving more frequent collections when flow was high. Element contents in the water were analyzed by inductively coupled argon plasma–mass spectrometry (ICP-MS). The dissolved content ranges were as follows: Ca between 4.47 and 20.7 mg L^–1, Mg between 2.4 and 7.3 mg L^–1, K between 1.13 and 8.6 mg L^–1, and Na between 8.9 and 27.2 mg L^–1. Significant correlations among all the analyzed elements were observed during the entire study period. Mostly, nutrient losses were related to degradation induced by soil erosion on the cultivated land portion of the catchment.