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<br />I . I
<br />
<br />February 2003
<br />
<br />ECOLOG[CALLY SUSTAINABLE WATER MANAGEMENT
<br />
<br />207
<br />
<br />and ,the services and produQts they provide beOOlne
<br />severely degraded, Watel. managers and political lead-
<br />ers are becon'ling increasingly cognizant of.these limits
<br />as th.ey are being confronted with endangered species
<br />or water quality regulations, and changing societal val..
<br />ues concerning ecological protection. During the past
<br />decadet malty exalnples 'have ,emerged from 'around the
<br />world demonstrating ways of Ineeting human needs for
<br />water while sustaining the necessary voiume and tint-
<br />ing of water flows to support affected freshwater eca..
<br />systelns. In fact, we believe that, the compatible inte...
<br />gration of human and nat1.lral ecosystem needs (iden-
<br />tified he14e as IIIJOOOl]I]illID [[](]]][[JDDOD 00[[1] 0 OJDOrn
<br />o ITJC) should be presun1ed attainable until conclusively
<br />proven otherwise. We offer this touchstone fOl~ such
<br />efforts: ·
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<br />
<br />In this paper we offer a general fian1ework for 4e-
<br />velopil1g an ecologically susta1nable water nlanage"
<br />ment program, . drawing UpGtl examples from arOund
<br />the United States and beyond to illustrate its essential
<br />elelnelltst with a focus on river systelns., Before we
<br />elaborate on the eleluents of this fralnework"weJul1her
<br />dis~US8 the' ecologlcaI degradation that we se-ek t"o ..al-
<br />leviate. - - : " . -
<br />
<br />, NATURAL va, MANAGED FLOW V AR1ABTlITY ,
<br />
<br />Ecolqgical degradation has generally been an unin-
<br />tended consequence of water manage~entJ stenl111ing
<br />from a lack of understanding.of water flows necessa.ry
<br />, to sustain freshwatel. ecosystelns. Natur~l freshwater
<br />ecosystems a.re strongly influenced by'specific facets
<br />of natural hydrologic.variability. Of particular impor-
<br />tance are seasonal high and low :flows,- and occasional
<br />floods and droughts (Stanford et al. 1996; Poff; et al.
<br />1991, Richter et at r 9970). A 'riveT~s flow regime is
<br />.now recognized as a Umaster variable'; that drives Val'''
<br />- iatiol1 in maL1Y other com-ponents of a river ecosystem,
<br />e4g.~ fish populations~ ,floodplain forest compositiont '
<br />l1utr~ent cycling, in botlJ. direct' and indirect ways
<br />(Sparks 1995~ Walker et at 1995~ Poff et at 1997;
<br />Instream Flow Council [available onlineJ6). The ex..
<br />traordinary species richness and productivity charac-
<br />teristic of freshwater ecosystenls is strongly dependent
<br />upon, and attributabh~ to, the natl'Lral variability of their
<br />hydrologic conditions~
<br />But variability runs counter to the dominant' goals,
<br />of wate~ resource management (Holling and Meffe
<br />
<br />. ~ URL: {http~lIwww.instreamflowcounci1,org)
<br />
<br />j
<br />j
<br />1996J. Traditional water Inanagement has generally
<br />sought to dampen the natural variability of rivet flows
<br />to ~ttain steady and dependable water supplies for do-
<br />mest~c and industrial usest in:igation. navigation) and
<br />hydrppoweJ.., and to madera te extreme water conditions
<br />such~ as fl00ds and droughts. Po+ instance; by storing
<br />water in reservoirs, water managers capture high flows
<br />duri~g wet years or seasons to supplement water sup~
<br />plies~ at,drier th11es, thereby maximizing the loeliability
<br />of W:ater supplies and certain economic benefits each'
<br />yea~ ,
<br />W:hen natural variability in river flows is altered too
<br />muc~, marked changes in the physical, chemical, and
<br />biolqgical cd,nditions and functions of natul'al fresh-
<br />, watdr ecosystems can be expected. When changes to
<br />natural flow l'eghnes are excessive, causing a river eco-
<br />syst~ln to degrade toward an altet.ed character, the costs'
<br />are high to .boUt biodiversity and society (Postel and
<br />Ca,l~enter 1997, IUCN 2000, .weD 2000) ,(Fig. 1). The
<br />transition to a new, altered ecosystem state can take
<br />tens l to hundreds of years as chain reactions cascade
<br />thropgh 'second- an,d third-ordel~ effects within an eco-
<br />sys~em (Petts arid Calow 1996, . IUCN 2000), thereby
<br />obsquring original causes. .',-
<br />. \Vater'mariagelnent for human use llecessarily aJters
<br />a ri~er's natural flow ~egi?te in v~rious ways4 However}
<br />ther~ is some degree and types of alteration that will
<br />nOt jeopal'diz.e the viability of native species and the
<br />abH~ty of an ecosystem to provide :val:uable products
<br />and ;services for sooietY4 Around the world, river sci..
<br />ent1sts are s,eeking better understanding of the ways
<br />and !degrees to which river ~o~s can be modified ror
<br />h~m;~n purposes while maintaining an adequate senl-
<br />b~a~ce of the composition~ structure, and functio~ of
<br />natl.\ral ecosystems' (P off et at 1997, Richter. et a(,
<br />19970, Arthington and Zalucki 1998 J' King and Louw
<br />199r, Tharme, 00 OITlIJ).
<br />
<br />: TOWARD ECOLOGICAL SUSTAl-NASrLITY
<br />
<br />.phe ultimate chaLleng~ of ecologically sustainable
<br />wat~r management is to design and unplement a water
<br />Ina4agement,.progl"sm that stotes and'diverts wa.ter for
<br />hufall purpos~s in a n1a.11ne.r that does not cause ,af-
<br />fected ecos ystems to degra.de or simpli fy, This quest
<br />for ~alance necessarily implies that there is a limit to
<br />the:a,mount of water that can be withdrawn from a river,
<br />'an~ a li.tnit in' the 4egr.e~ to which the shape of a river's
<br />nat*ral flow 'patterns can be altered~ These limits are
<br />defil]ed by the ecosystem's requirements for water4 Hu...
<br />map extraction or ma.nipulation that ~xceeds these lim-
<br />its iwill, i~ time~ cgmpromis.e th~ 'ecological ,integrity
<br />of ~he' affected ecosyst~ins~ resulting in the loss of na-
<br />tiv~ species an4 valuable ecosystem products and ser-
<br />I .'
<br />vic~s for SOcIety. .
<br />, With human uses of water and 01.1T understanding of
<br />ec~systems contil1ually evolving. the solutions for
<br />me:eting both ecosysten1 and human needs will evolve
<br />ov~t thl1e as well. Thus, ecologically sustainable wa~er
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