Chapter 9 Revisiting the Ecosystem Concept: Important Features That Promote Generality and Understanding © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

Figure 9.1 A simple input–output diagram for an ecosystem. © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

Figure 9.2 Major fluxes of calcium for a watershed in the Hubbard Brook Experimental Forest in New Hampshire. Fluxes were measured in 1963–1994, and estimated for 1940–1963. P is bulk precipitation input, W is weathering release, S is loss in stream water, B is net storage in biomass, and D is net release from labile soil pools (exchangeable+organically bound), which is estimated by difference. The decline in precipitation inputs (P) in the 1950s and 1960s is a result of better control of particulate air pollution from industrial sources. (Redrawn from Likens et al. 1998.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds). 3

Figure 9.3 Relationship between human population density and (a) river nitrate concentration and (b) river nitrate export for major rivers throughout the world. (Redrawn from Peierls et al. 1991.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds). 4

Figure 9.4 Relationship between water clarity (as % light transmission) and mixing depth in small (< 500 ha, closed circles) and large (> 500 ha, x’s) lakes. © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds). 5

Figure 9.5 Illustration of three hypothetical studies that include different components for resolving questions related to the net loss of organic carbon in lake ecosystems. © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds). 6