Phosphorous cycling and biogeochemistry in a Venezuelan-flooded savanna

Abstract

In 1970, a programme of land recuperation started in Venezuelan savannas, strongly affected by the seasonality of precipitation; therefore, a network of dykes has been built to alleviate the floods and retain water throughout the dry period. Under the dyked system, the environment has been altered, allowing a change in the herbaceous vegetation towards aquatic species and an increase in primary production. It is assumed that a considerable quantity of nutrients is lost from the ecosystem through the floodgates, a situation that could be worsened with the climate change. This contribution describes the atmospheric input and total output in stream run-off of phosphorous (P) in a flooded savanna. Internal pools of the biogeochemical cycle of P associated with terrestrial compartments are described. In the flooded savanna, a large amount of P is immobilised (29.6 kg ha⁻¹) in their above ground biomass by grasses, and in soil microbial biomass. The P budget was nearly balanced, as measured losses were cancelled out by the inputs in rainfall. Soils act as a sink, retaining P coming either from precipitation or from desorption/mineralisation processes. That interruption can be maximised, and losses of P and other nutrients can be minimised with an adequate management of the floodgate.

Keywords:

• redox
• P budgets
• P requirements
• biomass accretion
• sustainability

Acknowledgements

Many people had collaborated in the accomplishment of this research; particularly we are indebted to M. García, L. Yanes, M. Gúzman and M. Sosa who provided information on soils and water collection of Módulo Experimental, Mantecal. We are also indebted to Ing. Luis García, who provided data on the monitoring of the stream flow at Módulo Experimental, Mantecal. The author especially acknowledges M. Niño for her analytical assistance and F. Tovar, H. Mendoza and A. Febres for their laboratory and field assistance. We are also much indebted to Dr Megan Mc Groddy, Department of Environmental Sciences, University of Virginia and an anonymous referee for the editing and critical revision of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.

Funding

The research was sponsored jointly by CDCH (Consejo de Desarrollo Científico y Humanístico) and CONICIT (Consejo Nacional de Ciencia y Tecnología).