Original paper

Recent changes in nutrient content and accumulation in the sediments of Colgada Lake (Spain): Mineralization vs pollution effects

Rodríguez-Murillo, Juan Carlos; Álvarez-Cobelas, Miguel; Piña-Ochoa, Elisa

Abstract

Nutrient pollution effects are not always apparent in freshwater sediments, because increase of N and/or P concentrations in recent sediments is also a consequence of sediment diagenesis. In the present work, two cores of sediment have been extracted from Colgada lake (CL) (Lagunas de Ruidera Natural Park, central Spain), one of them dated using radiometric techniques, and their C, N and P contents determined at different depths. CL has experienced significant local P inputs and regional N groundwater inputs over the last 60 years. An analysis of N and organic carbon content and their accumulation rates in the cores is performed in order to ascertain the relative importance of the two processes - mineralization and pollution - in the organic C and N profiles. CL sediments were significant middle- and long-term organic N and C sinks (about 10 g C m-2 y-1 and 1 g N m-2 y-1). This sink has intensified in the last 20-25 years to about 23 g C m-2 y-1 and 3.8 g N m-2 y-1. Relatively low C/N of sediments indicated a predominantly in-lake phytoplankton source of the sedimented organic matter over the last 50 years. A diagenesis model has been applied to the organic C profile, trying to discern recent lake eutrophication from organic carbon mineralization. In spite of massive N inputs in the last 50 years, observed increases of organic C and N in sediments in these years, although parallel to the increase of lake pollution, could be satisfactorily explained with the diagenesis model, with no visible influence of lake trophic status change during that period.

Keywords

diagenesis modelsmineralizationnutrientspollutionsedimentssemiarid lake