PhD Defence Ms Mariela Andrea Yevenes Burgos

Department of Water Resources

Title of Defence

Reactive nitrogen dynamics in streams: case study in the agricultural upper Roxo catchment, Portugal

Summary

Reactive nitrogen (N) from agricultural catchments is the major source of N load to streams and groundwater in numerous regions (EC, 2002, Balestrini et al., 2007). Concerns about nitrate impact on freshwater and the protection and improvement of water quality in agricultural areas the member states in EU are obliged to follow the Water Framework Directive and Nitrate Directive (EC, 1991; EC, 2000). Upper Roxo catchment located in Alentejo Portugal is located in an intense agricultural area within the zone of influence of the large Alqueva dam, which is classified as a vulnerable zone by the Nitrate Directive.

Nitrate can reach a large fraction of the total dissolved nitrogen in streams, but the potential for nitrate and ammonium to be available for denitrification or potentially contribute to eutrophication in streams and drinking reservoirs was not well known in Upper Roxo catchment. Transformations of reactive nitrogen along terrestrial flow paths may alter its bioavailability. Therefore, hydrology likely plays an important part in the transport of reactive nitrogen to streams. This research will improve our understanding of the processes related to the delivery of reactive nitrogen to surface water from non-point sources. Interdisciplinary approaches using stable isotopes, modelling and Landsat imagery can be used to address this biogeochemical assessment.

This thesis used chemical and modeling approaches in the analysis of reactive nitrogen dynamics in shallow streams and the receiving drinking reservoir of an agricultural catchment in Portugal. The research was driven by field measurements, chemical analysis, eco-hydrological and geochemical modelling and Landsat satellite data analysis. In order to achieve the aim, the thesis is divided in four objectives: (1) to estimate the nitrate exports by streamflow of an agricultural catchment to a receiving drinking water reservoir using SWAT model (2) a multivariate analysis using EMMA (3) stable isotopes and 1D reactive transport model (4) spectral mixing model using Landsat imagery The methods were developed for this catchment but they can be applied to other streams in agricultural catchments.

The results showed that in the catchment where denitrification naturally reduces nitrate levels in soils and streams, the largest contribution to stream nitrate originates from leached soil nitrate, re-appearing in the groundwater baseflow. In the streams, the high sediment pore water contributions to the streamflow chemical signature indicated that the water-sediment interface in the streambed zone plays an important role in the nitrate exchanges and regulation in the streamflow. The most impacted small streams and the stream sediment-water interface near to the treatment plant are important sites for nitrogen removal by processes such as denitrification. Small drainage lines and streams and by preference their water - sediment interfaces in agricultural catchments can be viewed as preferred sites for rapid nitrification - denitrification processes. Upstream was identified as an effective nitrification and denitrification zone, where residual ammonium releases from the waste water treatment plant are rapidly transformed to nitrate which is subsequently removed from the system by denitrification processes. Nitrate decreased downstream, until it almost disappeared towards the receiving waters (Roxo reservoir), hence nitrate may act as the limiting factor in the reservoir, whereas phosphate can be found in excess and associated to suspended sediments.

Biography

Mariela Andrea Yevenes Burgos was born in Concepcion, Chile. After completing studies in Marine Biology in the ‘Universidad Católica de la Santísima Concepción’, she worked in the same University as pat-time lecturer of Marine Pollution.  In 2002 she was awarded an Organization of American States scholarship (OAS) to study a Master of Science in Coastal Oceanography in ‘Universidad de Baja California, Mexico’. For her studies, she took part of an AMES-NASA sampling collection at the Guerrero Negro Salt ponds in southern Baja California Peninsula. After her Masters she worked as an environmental consultant expert in Prodigit a Natural Resources Company in water management for three years. During her stay in Mexico she was founder of Kalvucura, company related to provide consultancy in topics related to water quality and analysis. In 2007 she joined ITC to start her PhD studies in Applied Geosciences related to water issues.

Mariela is married to Rafael Bermudez, and have a son Emilio.

Yevenes, M.A., Verhoef, W. (Promotor) and Mannaerts, C.M. (assistant promotor)  (2012) Reactive nitrogen dynamics in streams : case study in the agricultural Upper Roxo catchment, Portugal. Enschede, University of Twente Faculty of Geo-Information and Earth Observation (ITC), 2012. ITC Dissertation 218, ISBN: 978-90-6164-344-9.

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