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Figure 11-20. City of San Luis, Colorado in the foreground and irrigated i elds of the Culebra Creek valley behind.
Irrigation water is delivered in a common system of acequias (ditches) that are jointly operated and maintained by
all water users in the district. Blimp airphoto by S.W. Aber and J.S. Aber.
contrast with continental waters, few monitor-
ing mechanisms exist to supervise i sh catches
in the open ocean, and international i shing
policies are weakly enforced at best.
Accounting for externalities is another impor-
tant aspect of any resource valuation exercise.
Hackett (2006, p. 66) pointed out that “externali-
ties are positive or negative impacts on society
that occur as a by-product of production and
exchange…, they are not included in the factors
that underlie market supply and demand.”
Externalities may be thought of as spillover
effects, which rel ect the full cost or benei t of
any alterations to an ecosystem or resource-use
activity (Cutter and Renwick 2004). In the past,
the cost of the construction of a hydroelectric
dam rarely included the cost of habitat destroyed
or agricultural land lost, or changes to local
climate regimes. Yet, these are real ecosystem
and societal costs that are associated with the
project, but were never accounted for in the
decision to construct the dam.
The example of the oil-palm industry of Kali-
mantan used earlier illustrates this point well.
The price of oil-palm on global markets does
not rel ect the cost of carbon emissions to the
Figure 11-21. Cattle graze in acequia-irrigated wet
meadows of the Culebra Creek valley with the Sangre
de Cristo Mountains in the background. Photo by J.S.
Aber; near San Luis, south-central Colorado, United
States.
there are no guarantees that others would not
act in their own self-interest. In the event of
signii cant pressures on a particular resource,
open-access regimes may be misused to the
point of degradation. Hardin's tragedy of the
commons thesis more accurately describes these
situations. The open oceans are often used as
a classic example of open-access regimes. In
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