1. Chapter 12 From Global Environmental Change to Sustainability Science: Ecosystem Studies in the Yaqui Valley, Mexico © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

2. 2 Figure 12.1 Satellite image of the Yaqui Valley irrigation district (in pink), bounded to the west by the Gulf of California and to the east by the Sierra Madres, in the state of Sonora, Mexico. © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

3. 3 Figure 12.2 Expected pathways of nitrogen fertilizer transformations and losses. Most fertilizer nitrogen enters the system as urea, which is then rapidly hydrolyzed to ammonium. In the absence of plant uptake (the typical situation, given that most of the fertilizer is added before planting), ammonium (NH 4 ) is volatilized to ammonia (NH 3 ) or oxidized by nitrifying bacteria under aerobic conditions to nitrate (NO 3 ). During nitrification, some portion of nitrogen is lost in the trace gas forms of nitric oxide (NO) or nitrous oxide (N 2 O). Nitrate in the soil can be leached in soil solution to depths below the rooting zone, or can be reduced to N 2 O or to dinitrogen (N 2 ) by denitrifying bacteria. All of these processes occurred in the Yaqui Valley soils. © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

4. 4 Figure 12.3 At the landscape scale, nitrogen moved from farmers’ fields to atmosphere, water systems, oceans, and downwind terrestrial ecosystems. © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

5. 5 Figure 12.4 Irrigation water carried nitrogen from fields (a) and from other land sources to the ocean, resulting in (b) massive blooms of phytoplankton (here measured by SeaWiFS satellite imagery) that bloomed in synchrony with irrigation and fertilizer events on land. (From Beman et al. 2005.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).