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<br />Biological issues, comment to SWSI, August 2004
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<br />Theme: Cottonwood Crisis. Changing Channels?
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<br />In general, it appears possible that the great pulse of increased woodland vegetation and
<br />narrowing of the Plains river channels from the late 19th Century until about the 1960s has
<br />ended, and is now changing again as cottonwoods and some willows fail to regenerate and
<br />degrade, invasives and shade-tolerant species occupy the riparian understory, and sedimentary
<br />and fluvial processes change in response to land use and changes in flow regimes after decades
<br />of imposed stability. The evidence on cottonwoods in crisis is partial, but compels attention
<br />(Bratton et al. 1995, Friedman in Knopf and Samson 1997, Johnson 1994, Johnson 1997, Nadler
<br />and Schmumm 1981, Snyder and Miller 1991). At about the same time that there was massive
<br />conversion and drainage of wetlands of all sorts, there was also increase in woody habitats along
<br />mainstems, and the establishment of the wetted areas irrigated, sub-irrigated, and supplied by
<br />seepage and percolation from ditches and canals. Now, that -new. riverine habitat is changing,
<br />but there is no restoration of the long-gone wetlands areas. If current policy leads to dewatering
<br />irrigated areas and the -inefficiencies. of agricultural water use are ended, what will be left?
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<br />Wohl (2001, espec. 101-105) points out that in 1883 the whole area from La Porte to the Platte
<br />was then described as -one vast network of irrigating canals.; the Front Range hydrology had
<br />become a -vast plumbing scheme-. The flows needed for diversity were regulated away, (Richter
<br />and Richter 2000, and the geomorphic changes have been complicated by the biological.
<br />responses (see also Tockner et al. 2002).
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<br />As the policies for the Platte River endangered species, and urban supply needs are
<br />implemented, one must wonder what kind of environment will remain, in biological as well as
<br />social terms? The regional aggregation of impacts, such as -only 5% of water will be removed-,
<br />is necessarily (given fimits on analyses available and funded) uninformative, since the entire
<br />problem sets of connectivity and thresholds are aggregated out of visibility (see Fausch et al.
<br />2002 for superb explanation of this kind of problem). The right 5% might be almost meaningless,
<br />while the wrong 5% could be very consequential - we would prefer to know more before we act.
<br />And, the goal of moving some amount may require the act of moving considerably more, with
<br />considerably larger potential surprise consequences. If available partial substitutes for the
<br />dramatically impaired original environments are now undergoing natural succession along the
<br />mainstems, as cottonwoods age and are not reproduced, and the variety of unintended wetlands
<br />supported by agricultural -inefficiency" are lost, the idea of only small impacts becomes
<br />increasingly unrealistic and the imperative to consider the bigger picture becomes very strong.
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<br />Theme: Invasives
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<br />Finally, a last theme appeared in the survey: the lack of understanding of how to relate flow
<br />regimes and management choices never before available to the need for invasive vegetation
<br />management. There is a significant State commitment, for instance, on Tamarisk and Russian
<br />Olive, but the plan seems un-related to flow allocations or management choices. The literature is
<br />sparse, and that surveyed contained only some mentions of drought impacts on Russian Olive,
<br />drought tolerance of Tamarisk, and drought impacts on changing riparian vegetation in
<br />combination with hydrograph changes. Similarly, invasive grass studies may not have
<br />considered possible management manipulations related to water re-allocations (e.g. Christian
<br />and Wilson 1999). See Amlin and Rood 2002, Katz and Shafroth 2003, Knopf and Samson 1997,
<br />Nadler and Schumm 1981, Snyder and Miller 1991. We might solve a major problem- or not!
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<br />SUMMARY:
<br />We're on the verge of very serious changes on the Plains, without adequate knowledge of current
<br />conditions -.how much of the wetted environment is agricultural in origin? What is going on with
<br />mainstems right now and in the next five years? And,little attention is being directed to the
<br />critical -big picture- and the intermediate scale of research, where Fausch et at point out things
<br />actually live. SWSI, through its technical staff and the Roundtables, should consider asking the
<br />Water Conservation Board to convene at least further inquiry with CSU and agencies.
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