『Abstract
Reducing nitrate pollution from diffuse agricultural sources
is the major environmental challenge in the two adjacent catchments
of the Oja-Tiron(oの頭に´) and Zamaca rivers
(La Rioja and Castilla y Leon(oの頭に´), northern
Spain). For this reason, part of their territory was designated
a Nitrate Vulnerable Zone (NVM) according to the Nitrates Directive.
The Oja Alluvial Aquifer, the Tiron(oの頭に´)
Alluvial Aquifer and their associated rivers are particularly
vulnerable to nitrogen pollution due to the shallow water table,
the high permeability of alluvial deposits, interconnections between
the alluvial aquifers and surface waters and pressures from agriculture.
To this end, nine sampling campaigns, organised on a semi-annual
basis and focused on the rivers and alluvial aquifers of the two
catchments, were carried out from April 2005 to April 2009. The
main objectives of the study were: (1) to investigate the chemical
forms of nitrogen in river-alluvial aquifer systems of the Oja-Tiron(oの頭に´) and Zamaca catchments, (2) to improve
our understanding of the spatio-temporal patterns of nitrogen
distribution in the alluvial aquifers and associated rivers by
integrating hydrochemical data and hydrogeological and environmental
parameters, (3) to estimate the amount of nitrogen exported from
the rivers and alluvial aquifers to the River Ebro, and (4) to
evaluate the suitability of the current method of designating
NVZs in the area.
High groundwater flow velocities in the upper alluvial zones
favoured the advective transport of nitrate and generated a dilution
effect. In these areas, inter-annual variations in nitrate concentrations
were observed related to precipitation and N-input from agriculture.
However, low flow velocities favoured processes of accumulation
in the lower alluvial zones. Our results demonstrated hat the
entire alluvial surface was highly vulnerable, according to dynamics
of the nitrogen in the river-alluvial aquifer systems being studied.
The amount of nitrogen exported from these river-alluvial aquifer
systems to the River Ebro was estimated at 2.4±0.2 kt year-1.
Findings from this investigation highlight the need to include
the alluvial area corresponding to the Tiron(oの頭に´)
aquifer as a NVZ, particularly as the Tiron(oの頭に´)
sub-catchment provides more than half of the nitrogen exported
from the River Tiron(oの頭に´) to the River
Ebro. Based in these results, at least the entire alluvial surface
in the study area should be considered a NVZ in order to address
the recovery of water quality.
Keywords: Nitrates Directive; Nitrate Vulnerable Zone; River;
Alluvial aquifer; Catchment scale』
1. Introduction
2. Materials and methods
2.1. Study area
2.2. Sampling campaigns and water analyses
2.3. Mapping and modelling
2.4. Statistical analysis
2.5. Nitrogen export
2.6. Additional information
3. Results and discussion
3.1. Hydrogeological characterisation
3.2. Hydrochemical characterisation
3.3. Patterns of nitrogen pollution
3.4. Nitrogen exported to the River Ebro
4. NVZ designation: how and how much?
5. Conclusions
Acknowledgements
References