『Abstract
This study examines the relationship between dissolved inorganic
nitrogen (DIN: NH4+ + NO2- + NO3-)
and dissolved organic nitrogen (DON) in river water and groundwater
in an agriculturally-dominated catchment in south-east Spain,
and estimates the contribution of DON to the total dissolved nitrogen
(TDN) concentrations. The studied aquifer-dependent river system
consists of Quaternary alluvial sediments deposited by the Guadalquivir
River and its tributaries, with both river water and groundwater
in the catchment being aerobic. DON is the predominant form of
nitrogen in river water (72-97% of the TDN), whereas its proportion
to TDN varies considerably in groundwater (<1-99%). A seasonal
pattern in the concentration of dissolved nitrate in river water
was observed, whereas DON concentrations showed no significant
change during the study period. The export of DON from the Guadalquivir
River is approximately 2 kg N ha-1 year-1
and is an order of magnitude higher than the export of DON from
pristine catchments. Dissolved nitrate concentrations in groundwater
were slightly higher in winter and DON concentrations were significantly
lower (p<0.05) in summer. It is found that agricultural soils
constitute the main storage of organic nitrogen in the catchment
with a steady leaching of high DON concentrations into the alluvial
aquifer system (mean value 19.1 mg N L-1), and so indicating
that DON should not be overlooked in the nitrogen budgets of agriculturally-dominated
catchments.
Keywords: Alluvial aquifer; Dissolved organic nitrogen; Guadalquivir
river; Irrigated agriculture; Nitrate』
1. Introduction
2. Site description
3. Methods
3.1. Groundwater and surface water sampling
3.2. Laboratory analyses
4. Results and discussion
4.1. River water
4.2. Groundwater
5. Conclusions
Acknowledgements
References