Rubega& Robinson:Salinization and shorebirds Water salinization and shorebirds:emerging issues MargaretA. Rubegaand Julie A. Robinson Rubega,M. A., & Robinson,J. A. 1996.Water salinization and shorebirds:Emerging issues. International Wader Studies 9: 45-54. Salinityfrom agricultural drainwater, surface flow and subsurfaceflow is a problemin at leastsome inlandwetlands in everywestern state in the UnitedStates. Water salinization is a particularly insidiousthreat to waterbirdpopulations because wetland quality ma, y not visiblydecline until the problemis advanced.In thispaper we review1) evidencethat salinizationis an important managementproblem in inlandwetlands, 2) meansavailable to shorebirdsto copewith salinity,3) mechanismsby whichthe costsof salinizationare likely to reduceshorebird reproductive success, and 4) how salinizationmodifies structure and diversityof ecosystems.Finally, 5) we discuss emergingmanagement concerns with respectto reducingor eliminatingsalinization effects on shorebirdpopulations. MargaretA. Rubega,Department of Environmental and Resource Science/186, University of Nevada, Reno, 1000Valley Rd., Reno, NV 89512,USA JulieA. Robinson,Ecology, Evolution and Conservation Biology Program/186, University of Nevada, Reno, 1000Valley Rd., Reno, NV 89512,USA •Currentaddress: Department of Biology,University of Houston, Houston, TX 77204-5513,USA Introduction seleniumand other heavy metals,concentrated throughsoil leachingand water recycling(Ohlendorf et al. 1986, 1989). Bioaccumulation of these toxicants The art and scienceof habitatmanagement revolves resultedin low hatchabilityof eggs,and dramatic around the control and enhancement of habitat malformations(Hoffman et al. 1988)and subsequent quality (cf.Reed 1995). A managementplan for death of thosechicks that did hatch (Ohlendorf et al. shorebirdsadvocates manipulating controllable 1989). In otherwords, although Kesterson received a habitatfactors in orderto providethe best habitat greatdeal of use,it was habitatof very low quality. quality possiblefor shorebirds(Helmers 1992). The Kesterson has since been filled with uncontaminated working definitionof habitatquality currently seems soilin orderto displacebreeding birds to wetlandsof to be "that which resultsin the greatestnumber of betterhabitat quality, and habitatmanagers are birds" (e.g.,Merendino et al. 1992),or, more rare135 monitoringpotential bioaccumulation through the "that which resultsin the greatestdiversity of new terrestrialfood chain (Wu et al. 1995). species"(e.g.,Boshoff & Piper1992). Although these There is an equally dangerous,potentially much may be meaningfulmanagement goals on shorttime morewidespread, mechanism of wetland water scales,for conservationpurposes only thoseaspects qualityreduction: water salinization.Water of habitatquality thathelp maintaindiverse salinizationis a particularlyinsidious threat to populationsover largetime scalesare of significance waterbirdpopulations because wetland quality may (Karr 1993;Suter 1993;Noss & Murphy 1995). not visiblydecline until the problemis advanced. Numbersof birdspresent, or evenbreeding, in a Salinizationmay resultin reducedreproduction wetland on shorttime scalesare notnecessarily throughchick mortality, while reducedvigor indicesof the contributionof habitatquality to the ci•k...... ;•,•.•lCittru ...;,t.vv lUt dehydrationmay increasemortality maintenanceof populations.For instance, because at all life stages.In this paper we review 1) evidence so muchwetland habitathas been destroyed (Frayer that salinizationis an important management et al. 1989;Dahl 1990),shorebirds may breedin large problemin inland wetlands,2) meansavailable to numbersin wetlandsof very poor quality. One very shorebirdsto copewith salinity,3) mechanismsby dramaticexample of thisphenomenon was which the costsof salinizationare likely to reduce KestersonNational Wildlife Refuge,in the San shorebirdreproductive success, and 4) how JoaquinValley of California.Kesterson was a salinizationmodifies structure and diversityof wetland suppliedwith irrigationdrainwater from ecosystems.Finally, 5) we discusspossible the WestlandsWater District. Largenumbers of managementtechniques for reducingor eliminating wading birdsbred at Kesterson,and the projectwas salinizationeffects on shorebirdpopulations. This viewed initially as a habitat-replacementsuccess. paperis notpresented as a definitivediscussion of Nonetheless,these birds failed to reproduce the cure for wetland water salinization. Our goals, successfully(Williams et al. 1989)because drainwater rather,are to identifythe problem,and generate supplyingthe wetlandwas contaminatedwith interestin the processof definingsolutions. 45 International Wader Studies 9:45-54 Why is salinization a problem in and virtually all of the Middle East(Waisel 1972; inland wetlands? Figure1). In North America,salinity from agriculturaldrainwater, surface flow and subsurface flow is a problemin at leastsome inland wetlandsin Normally, the term salinityis taken to mean the every westernstate in the U.S. (U.S. Fish and Wildlife concentration of sodium chloride. However, the ion Service1992) (Figure 2). Salinizationis particularly compositionof salty water varieswidely, and in acutein the GreatBasin, and in partsof California, inland wetlands(the focusof thispaper) salinity is Arizona,New Mexicoand Texas,where growing actuallya measureof the total concentrationof a humanpopulations and agriculturecompete for number of different ions. The exact combination of limited water, and where most wetlands are ionsand mineralsin water dependslargely on local downstreamfrom urban and agriculturalusers (E1- soilcomposition and hydrologyof surfaceand Ashry& Gibbons1988). Increasingly,solutions to groundwater. theseconflicts involve multiple use and reuseof In arid lands, where salinization is most common, water,resulting in increasedsalinity of water at soilsnaturally containvariable amountsof sodium, agriculturalsites, and subsequently, at terminal potassium,and other mineral salts,but also wetlands.Salinization is alreadya problemat many magnesium,carbonate, bicarbonate, sulfate, boron, of the world'smost important shorebird sites. Sites fluoride, arsenic, and selenium. Hence, in arid lands, declaredof hemisphericor internationalimportance wetlandsand otherbodies of water arefrequently to shorebirdsby the WesternHemisphere Shorebird naturallysalty (and significantlyalkaline) as a Reserve Network in the Great Basin include Mono functionof the processesof runoffand evaporation Lake, Great Salt Lake and Stillwater/Carson Lake over geologictime. For instance,Mono Lake in (WHSRN 1992) and all havesuffered significant California and the Great Salt Lake in Utah (two degreesof salinization(Patten et al. 1987;Woolf 1993; significantsites for shorebirds;Oring & Reed,this Lico 1992). (Unfortunately,although reserve volume) are both natural saline lakes. For the designationby theWestern Hemisphere Shorebird purposesof this discussion,we will usethe term ReserveNetwork (WHSRN) draws much-needed salinizationto meananthropogenically-caused increases in attentionto sitesof importanceto shorebirds,it watersalinity (defined very broadly as increases in providesno concretemeans of protection, conductivityofa particularwetland or bodyof water, particularlyagainst the gradual degradationof water withoutrestriction to any particular ion composition) on quality.) relativelyshort time scales, even in caseswhere some In the arid Americanwest, many factorstend to degreeof salinity was present naturally. In considering increasethe salinityof inlandwetlands. Increased largerspatial scales, we alsowill usethe term to urban use of riverine waters decreases the amount imply the decreasein relativeavailability of fresh and qualityof water availablefor terminalwetlands. water in a landscape. Effectsof suchdecreases are twofold: 1) some Globally,salinization is commoneverywhere wetlandsdry up, reducingfreshwater and the total agricultureis conductedon arid lands,e.g. north numberof wetlandsavailable in the landscape,and Africa, southern and western Asia, central Australia, 2) remainingwetlands become more shallow and Figure1. Globaldistribution of salt-affectedsoils (and hence water), and areas with thepotential for waterand soilsalinity problems(adapted from American Society of Civil Engineers1990). 46 Rubega& Robinson:Sahnlzation and shorebirds Potentialfor salinizationproblems • High • Medium • Low Figure2. Areasin the conterminousUnited States with the potentialfor waterand soilsalinity problems (adapted from AmericanSociety of Civil Engineers1990; note that coverage for NorthAmerica differs from Figure 1 becauseof differingdefinitions of risk). moresaline through evaporative concentration. For Ettinger1964). City sewagereuse can lead to example,water diversionsof easternSierra Nevada groundwatersalinization (Bagley 1967). snowmelt by the city of LosAngeles have, over the Agriculturalmultiple-use, and enforcementof last century,caused Owens Lake to disappear irrigationconservation programs, also decreases the completely,and Mono Laketo dropmore than 40 qualityof water in inlandwetlands. Federal verticalfeet while triplingin salinity(Patten et al. 1987). Bothof thesenaturally-occurring saline lakes legislationdesigned to end water disputesover the NewlandsIrrigation Project of westernNevada and wereformerly ringed with freshwaterwetlands, northeasternCalifornia (Public Law 101-618,1990), which no longerexist at Owens,and are reduced enoughat Mono to havevirtually eliminatedthe