Research

Integration of multi-isotope techniques and a water quality model for tracing and cycling nutrients along stream networks

The importance of small streams playing an important role acting as sink for nitrogen inputs has been well documented. Part of Nitrogen in the stream flow is attenuated by denitrification returned to the atmosphere and the rest exported as nitrogen loads. To understand environmental factors that control fate of nitrogen throughout the stream network at the watershed scale is a hot topic nowadays, especially if large nitrogen loads are delivered in such processes to water reservoirs for human use or in other cases to sensitive ecosystems.

My PhD research involves the identification of the major sources contributing to Nitrogen in the streams and to assess the relative importance of denitrification, in the context of seasonal changes, in a mostly agricultural and semi-arid catchment in South Portugal. This area is considered a vulnerable zone in the European Water Framework Directive.

This study will combine the use of dual isotope approach (δ ¹⁵N and δ ¹⁸O) in water samples and a development and implementation of a geochemical model (using an open source R statistical computing program). Concurrently, a hydrological model Soil and Water Assessment Tool (SWAT 2009) is used with the aim to predict long term stream nitrate export and changes in nitrate outputs under N fertilizer schemes in the catchment. Moreover, chemical (anions) and isotopic composition (δ²H and δ¹⁸O) in stream water are contemplated to assess the relative importance of hydrologic flow paths through the catchment.

With this information on the nitrogen dynamics in the stream network, we hope to understand and reveal better the coupled effects of hydrological and biogeochemical processes in the catchment.