A Simplified Nitrogen Assessment in Tagus River Basin: A Management Focused Review

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 (N r) load into surface waters, emission factor approaches were applied. N r 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.

Development of a groundwater contamination index based on the agricultural hazard and aquifer vulnerability: Application to Portugal

“…However, N leach was set to 0 in some regions within the limits of two NVZs located in the Western unit. Cameira et al (2019Cameira et al ( , 2021 and Cordovil et al (2018) present similar conclusions for the spatial distribution of the Tagus NVZ insofar as there was a significant reduction of the GNB in its upper section and a slow stabilization in its southern part, where livestock production is the main activity. Additionally, the expansion of intensively managed irrigated agriculture (41,962 to 48,113 ha) may have contributed to this diverging spatial tendency.…”

Nitrogen in Water-Portugal and Denmark: Two Contrasting Realities

“…However, it should be noted that the two time series are not exactly comparable because the Danish time series represents the whole country (120 monitoring stations), whereas the Valada Tejo station shows the trend at a single station, only. Also, 80% of the catchment that drains into this monitoring site is in Spain [44]. Nitrogen monitoring is clearly insufficient in Portugal, although the reason for this is unknown.…”

“…This does not provide reliable information on water (N) concentrations (Table 1 and Figure 5). Nitrogen transport from Spain to Portugal plays an important role in detremining the level of total N loading and (N) concentrations in some Portuguese rivers, such as the Tagus [44]. Total nitrogen concentrations in Portuguese rivers exhibit a pattern of generally low (N) concentrations ( Figure 5), which does not necessarily reflect reality, up to where the extent of samplings permitted estimation (i.e., ≥8 months).…”

Innovation Issues in Water, Agriculture and Food

“…At the regional scale, now focusing on water quality problems associated with the agricultural activity, Cordovil et al [22] present a simplified nitrogen (N) assessment review along the Tagus River basin, which covers a large area of Spain and Portugal in the Iberian Peninsula, mainly relative to agriculture, livestock, and urban activities. Nitrate vulnerable zones comprise approximately one-third of territories in both countries.…”