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Mechanisms of basin-scale nitrogen load reductions under intensified irrigated agriculture
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Purdue University.
University of Iowa.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Irrigated agriculture can modify the cycling of nitrogen (N), due to associated water diversions, water losses, and changes in transport pathways. 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 consider 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 show that observed decreases in riverine DIN concentration near the Aral Sea outlet of ADRB primarily are due to increased recirculation and reuse of irrigation water, which extends the flow-path lengths and enhances N attenuation-retention. The observed DIN concentrations matched a developed analytical relation between concentration attenuation and recirculation ratio, showing that basin-scale attenuation - retention effects of recirculation may be considerable, which previously only have been observed in laboratory experiments and at agricultural plots. Increased recirculation can furthermore have contributed to observed increases in N attenuation in agriculturally dominated drainage basins in different parts of the world. A six-fold lower DIN export from ADRB during the period 1981-2000, compared to the period 1960-1980, is the combined result of drastic river flow reduction 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 N export as shown here for the ADRB.

Keyword [en]
Irrigation, Hydrology, Nitrogen, Attenuation, Recirculation, Semi-arid zone, Central Asia
National Category
Oceanography, Hydrology, Water Resources
URN: urn:nbn:se:su:diva-93212OAI: diva2:645534
Available from: 2013-09-04 Created: 2013-09-04 Last updated: 2013-09-17Bibliographically approved
In thesis
1. Basin-scale change in water availability and water quality under intensified irrigated agriculture
Open this publication in new window or tab >>Basin-scale change in water availability and water quality under intensified irrigated agriculture
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Changes in land use and water use can greatly impact the cycling of water and water-borne substances. Increased redistribution of river water to irrigated fields can cause enhanced evapotranspiration and decreased river discharge. Additionally, the water quality can be affected by the external input of fertilisers and pesticides, and by changed pollutant transport pathways in expansive irrigation canal systems. This thesis examines basin-scale changes in water use, river discharge, water quality and nitrogen (N) loading under conditions of intensified irrigated agriculture, using the Aral Sea drainage basin (ASDB) with its two large rivers Syr Darya and Amu Darya in Central Asia as study area. Results show that more efficient irrigation techniques could reduce outtake of river water to the cotton fields in the ASDB by about 10 km3/year, while the corresponding river water saving at the outlet would be 60% lower. The result illustrates the importance of accounting for return flows of irrigation water in basin-scale water saving assessments. Moreover, a decrease in riverine N concentrations at the outlet of the Amu Darya River Basin (ADRB) was observed during a 40-year period of increasing N fertiliser input. The decrease was identified to be primarily caused by increased recirculation of river water in the irrigation system, leading to increased flow-path lengths and enhanced N attenuation. Decreasing N loads were shown to be primarily related to reduced discharge. N export from the basin may further decrease due to projected discharge reductions related to climate change. Furthermore, nutrients and metals were occasionally found at concentrations above drinking water guideline values in surface waters in the ADRB. However, metal concentrations in groundwater in the lower ADRB were subject to orders of magnitude higher health hazards. Projected decrease in downstream surface water availability would thus imply decreased access to water suitable for drinking.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University, 2013. 34 p.
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 38
Irrigation, Hydrology, Land-use change, Basin-scale, Central Asia, Aral Sea, Semi-arid, Return flow, Water saving, Health risk, Water quality, Surface water, Groundwater, Nitrogen, Attenuation, Recirculation, Climate change
National Category
Oceanography, Hydrology, Water Resources
Research subject
Physical Geography
urn:nbn:se:su:diva-93214 (URN)978-91-7447-724-5 (ISBN)
Public defence
2013-10-18, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Manuscript.

Available from: 2013-09-26 Created: 2013-09-04 Last updated: 2013-09-25Bibliographically approved

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Törnqvist, RebeckaJarsjö, JerkerDestouni, Georgia
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