Abstract
Interactions among nitrogen (N) management and water resources quality are complex and enhanced in transboundary river basins. This is the case of Tagus River, which is an important river flowing from Spain to Portugal in the Iberian Peninsula. The aim was to provide a N assessment review along the Tagus River Basin regarding mostly agriculture, livestock, and urban activities. To estimate reactive nitrogen (Nr) load into surface waters, emission factor approaches were applied. Nr pressures are much higher in Spain than in Portugal (~13 times), which is mostly because of livestock intensification. Some policy and technical measures have been defined aiming at solving this problem. Main policy responses were the designation of Nitrate Vulnerable and Sensitive Zones, according to European Union (EU) directives. Nitrate Vulnerable Zone comprise approximately one third of both territories. On the contrary, Sensitive Zones are more extended in Spain, attaining 60% of the watershed, against only 30% in Portugal. Technical measures comprised advanced urban and industrial wastewater treatment that was designed to remove N compounds before discharge in the water bodies. Given this assessment, Tagus River Basin sustainability can only be guaranteed through load inputs reductions and effective transnational management processes of water flows.
Highlights
The European Nitrogen Assessment [1] estimated that around 80% of European freshwaters exceed the nitrogen threshold for high risk to biodiversity and human health
In terms of water demand, 80% of the water use is related to agricultural needs and the 20% remaining for drinking-water production, since both Madrid and Lisbon use the Tagus River Basin as the source of their water supply
The availability of these resources is disputed by the more productive irrigated agriculture in the Segura River basin that is close to the Mediterranean coastline, and which is connected to the Tagus by a water transfer channel
Summary
The European Nitrogen Assessment [1] estimated that around 80% of European freshwaters exceed the nitrogen threshold for high risk to biodiversity and human health. A more consistent delivery of minimum flows has been prescribed in the 2008 amendment of Albufeira Convention, it is doubtful if it is in accordance with ecological requirements of Tagus River Both Tagus River Basin Management Plans that were issued in 2015 did not directly address N fate at transboundary level [29]. Urban wastewater treatment directive is aiming at avoiding eutrophication processes and imposing stringent limits regarding nitrogen and phosphorus content in urban discharges, requiring the use of advanced processes for their removal Despite these top-down initiatives that are led by governmental agencies, both point and diffuse N pressures remain very significant in European watercourses, according to most recent Tagus. Gaps are identified and recommendations for a better integration of N and water resources management are indicated
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