Mechanisms of basin-scale nitrogen load reductions under intensified irrigated agriculture

Rebecka Törnqvist; Jerker Jarsjö; Josefin Thorslund; P Suresh C Rao; Nandita B Basu; Georgia Destouni

doi:10.1371/journal.pone.0120015

Mechanisms of basin-scale nitrogen load reductions under intensified irrigated agriculture

PLoS One. 2015 Mar 19;10(3):e0120015. doi: 10.1371/journal.pone.0120015. eCollection 2015.

Authors

Rebecka Törnqvist¹, Jerker Jarsjö¹, Josefin Thorslund¹, P Suresh C Rao², Nandita B Basu³, Georgia Destouni¹

Affiliations

¹ Department of Physical Geography and Quaternary Geology and the Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
² School of Civil Engineering and Department of Agronomy, Purdue University, West Lafayette, West Lafayette, Indiana, United States of America.
³ Department of Civil and Environmental Engineering and Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada.

Abstract

Irrigated agriculture can modify the cycling and transport of nitrogen (N), due to associated water diversions, water losses, and changes in transport flow-paths. We investigate dominant processes behind observed long-term changes in dissolved inorganic nitrogen (DIN) concentrations and loads of the extensive (465,000 km2) semi-arid Amu Darya River basin (ADRB) in Central Asia. We specifically considered a 40-year period (1960-2000) of large irrigation expansion, reduced river water flows, increased fertilizer application and net increase of N input into the soil-water system. Results showed that observed decreases in riverine DIN concentration near the Aral Sea outlet of ADRB primarily were due to increased recirculation of irrigation water, which extends the flow-path lengths and enhances N attenuation. The observed DIN concentrations matched a developed analytical relation between concentration attenuation and recirculation ratio, showing that a fourfold increase in basin-scale recirculation can increase DIN attenuation from 85 to 99%. Such effects have previously only been observed at small scales, in laboratory experiments and at individual agricultural plots. These results imply that increased recirculation can have contributed to observed increases in N attenuation in agriculturally dominated drainage basins in different parts of the world. Additionally, it can be important for basin scale attenuation of other pollutants, including phosphorous, metals and organic matter. A six-fold lower DIN export from ADRB during the period 1981-2000, compared to the period 1960-1980, was due to the combined result of drastic river flow reduction of almost 70%, and decreased DIN concentrations at the basin outlet. Several arid and semi-arid regions around the world are projected to undergo similar reductions in discharge as the ADRB due to climate change and agricultural intensification, and may therefore undergo comparable shifts in DIN export as shown here for the ADRB. For example, projected future increases of irrigation water withdrawals between 2005 and 2050 may decrease the DIN export from arid world regions by 40%.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Agricultural Irrigation
Agriculture*
Climate Change
Environmental Monitoring
Models, Theoretical
Nitrogen / analysis*
Rivers

Substances

Nitrogen

Grants and funding

The authors gratefully acknowledge financial support from the Swedish International Development Cooperation Agency (SIDA, www.sida.se). The work has been carried out within the Bolin Centre for Climate Research, which is supported by a Linnaeus grant from the Swedish Research Council (VR, www.vr.se) and the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas, www.formas.se). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.