Environmental Engineering Reference
In-Depth Information
Forest cutting at Hubbard Brook and food web manipulations in Peter, Paul, and
Tuesday Lakes were potent examples of simple but large-scale manipulations used to
examine and develop core concepts in ecosystem science (nutrient cycling and the small
watershed concept in the first case, the trophic cascade in the latter). These various influ-
ences came together in thinking about dam removal. I realized I could use the removal as
a whole-ecosystem experiment to study disturbance and nutrient spiraling. My plan was
to test the nutrient retention hypothesis of
Vitousek and Reiners (1975)
—that nutrient
retention increased, then decreased over time following disturbance in forests as a func-
tion of changes in net biomass increment. This model had been successfully tested in
Sycamore Creek by Nancy Grimm (
1987
), and I wondered if it would be a robust model
that could fit a vastly different sort of disturbance.
This is where I started—all business about ecosystem concepts and experiments.
But this single motivation did not stand alone for long. I quickly learned that rather than
being a simple, elegant manipulation in a protected research setting, removing a dam
was a complicated, emotional, and very public process. It became apparent that there was
a real problem at hand—what to do with these old dams that were falling apart. The
repair-or-remove decision needed to be informed by some knowledge of what happens
following a removal, and that information simply was not available. I started getting
phone calls from managers, advocacy groups, and concerned citizens asking me about
the best course of action and what to expect if a dam was removed. It is probably not sur-
prising to report that callers were not terribly interested in nutrient spiraling. They had
much more practical questions about how the plants and animals in and around the river
would be affected, and what the river would look like after the dam was extracted
(
Figure 14.1
). At the same time, an adventurous graduate student from Purdue, Martin
Doyle, who was also interested in dam removal as a whole-ecosystem experiment (in his
case, for testing geomorphic concepts), called and asked if he could collaborate with me
on planned removals in Wisconsin.
The collaboration between fluvial geomorphology and ecosystem science was, frankly,
extremely fortuitous. The contribution of both perspectives was essential to the success
of our research. Studying dam removal from a strictly ecological perspective would have
provided an incomplete story, missing perhaps the most critical element: the fate of the
sediments trapped in the reservoir and the changes in channel form above and below
the dam. We learned that how the sediments moved not only determined the appearance
of the river, it also shaped a wide range of ecological patterns playing out in the weeks
and years after the removal. And over the long term, biotic (in particular, plant establish-
ment and growth) and geomorphic processes are inextricably linked (
Doyle et al. 2003a
)
and mutually influential. Studying only the physical changes following dam removal
would have meant that many of the broader ecological changes of interest to managers
and stakeholders would have been missed, and conversely, focusing purely on biological
variables would have severely limited our ability to understand why the changes we
observed were occurring.
While it is reasonable to say that my practice and perspective of ecosystem science
matured substantially through this research to include interactions with other disciplines
and attention to questions driven by practical needs, the basic strategy of using dam
removals as whole-ecosystem experiments proved to be successful. This management
